Chapter nine

 CHAPTER 9

WHAT CAN I DO NOW?

It's about 6 o'clock (three days later) and Fred's car is

finally done. Needless to say he got more than he deserves but

in the interest of the book we'll let him live. Now keep in mind


that when he gets here he will do the exact same thing that every

other person has done in the heat of excitement and blurt out the

following annoying statement: "So what could I do to make it even


better?" Slap! Whoops. Hey Fred, get up... sorry about that.

Yea it's my trick elbow or something, it does something trick

every time someone like you says something stupid. Oh Fred


doesn't mean any harm, but the truth is it will take him weeks if

not months to fully appreciate the fidelity of his new stereo,

and perhaps he never will, so after 15 minutes of listening to it


on one song over and over hardly qualifies him to ask such a

question. I told him the best part is that you don't have to do

anything to make it better because it will keep getting better by

itself while it burns in! (Gave him a buzzword to fantasize


about for awhile)

 

You know it really does blow my mind how every single person

does this though. One time I did a car for a guy who wanted the

same ultimate stereo of his wet dreams for nothing, and really


thought after he heard his car, the question would never be

asked. I thought this because I used a professional grade

McCulley 18" sub woofer with a reference efficiency of 104dB and

put it where his back seat used to be. His truck had to be lined


with cement to take the force of the 6 or 7 hundred watt

amplifier I drove it with. The thing would reach over 137 dB

without the engine running and the VERY first thing he asked

after hearing it was if it could get any louder than that. I


just moved my lips so he would think he was already deaf.

 

For those who have good car audio systems and would like to

improve the over all quality and or performance the remainder of


this book may give you some insights. And yes there is always

something you can do to make your stereo sound better. No matter

how good it is it can always be better (or at least different).

 


So you want to make your stereo louder? Do you want it to

be louder when the car is setting still, or while you drive?

There are two ways to make your system louder. One is to replace


your amplifier(s) with twice the power. That will give you a 3

decibel increase in volume which is just enough to notice a

slight difference. The second way is to make your car quieter by

installing sound deadening everywhere. When properly done, this


can reduce the noise floor by as much as 3 decibels. That would

be the same thing as doubling your power. Sound deadening

(Dynamat) will, however, have little if any effect when your car

is parked.

 


The recommended way to make your stereo louder if you feel

it has gotten quieter over time is to take the main fuse out and

place it in your glove box for about a week. By the end of the


week, your ears will no longer be desensitized and your stereo

will sound fresh and new again.

 

What if you wanted to make your stereo twice as loud as it

is now? I would say rather than put your fuse in the glove box


for a week, make it two. Or you could double your power 4 times.

It takes approximately a 10 dB increase to make the sound seem

twice as loud. If you had Fred's system which consisted of about


200 watts on a stock charging system, the following would be

required to make it twice as loud:

 

*3200 watts

*a second battery


*a new voltage regulator

*a dual battery isolator

*1 gauge power cable

*a pair of 1 farad stiffening capacitors

*a high output alternator capable of 200 amps (hot)


*more and or better speakers to handle all the

power

*ear plugs

*healthy pocket book with about 6,000.00 in it.

 

 


For those who are more interested in sound quality there are

a few additional things that can be purchased to improve the

sound of you're system. These things fall into the category of


signal processing equipment and range from the simple to the

exotic. DSP, or Digital Signal Processing equipment can give you

the ability to control delays and echoes to make your stereo

sound more natural (that is assuming you adjust it right).

 


In the case of Fred's stereo I would replace his amplifiers,

run high performance patch cords, add a stiffening cap, and

install a digital processor designed for spatial restoration, add


some rear speakers for fill, and sound deadening material to the

entire vehicle.

 

One of the final things you can do to improve your stereo is

probably one of the most important things also. Select


recordings that are well done. Even with CD's, you will find

that on a high fidelity system (home or car) the recording

quality of the songs on your CD's (or tapes) will vary greatly.

This didn't used to be the case on your stock car stereo because


it's lack of performance and speed acted like a filter making

everything sound about the same. With a good high quality system

you will find that good recordings sound great, and poor

recordings sound terrible. The reason for this is simply that on


a high fidelity system you are listening to the recording instead

of the stereo equipment itself. That is, was, and always will be

the goal of high fidelity systems.

THE END.

 

 

Tovább »

Chapter eight

CHAPTER 8
DESIGNING A SUB WOOFER

In this chapter we are going to build a perfect box for

Fred's sub woofers, and install it in his car. We are at

somewhat of a disadvantage here, because one of the variables to


good design have been fixed. I am referring to the woofers that

we already have as that handicap. Understand that no two brands

or types of woofer will have identical results in the same

enclosure. Fred's woofer's are a pair of 10" Orgasmis brand subs


with the word "POWER" written on the dust caps to well uhm,

obviously make them more powerful! The woofers came with no

specification sheet since they were already in a box when Fred


bought them, so I had the factory fax me a sheet.

 

Fred's woofers have the following specs:

 

NOMINAL IMPEDANCE 4 ohms

POWER HANDLING RMS 100 watts MAX 150 watts


FS 25 Hz

VAS 2.56 ft^3

QTS 0.295

 

For those who are thinking "hey just plug these figures into

the computer box program and throw together a box the size it


says and you've got it", at least you're willing to attempt to

put them in the right enclosure. Once you get past thinking that

to get bass - you put a speaker in a box, you're making progress!


We will in fact be using a program on the computer to design

Fred's box, but probably not the specs listed above. It has been

my experience that the Thiel and Small Parameters listed for any


particular speaker are usually in error by as much as 20 percent.

 

The first thing to do is to measure the Thiel and Small

Parameters on these woofers, the two sit actually sitting here


that we are going to use. To test the woofers we will need a

sine wave generator, an AC voltmeter and a couple of resistors.

Starting at the top of the list we begin with IMPEDANCE.

 

To measure the impedance we will take a 10 ohm precision


resistor and connect it at points x and y in Fig. 11. Nothing is

happening. Oh yea, it helps to turn on the Frequency Generator

before proceeding. There, I now have everything hooked up like


the diagram in Fig. 11, but have my 10 ohm resistor in place of

the speaker. The purpose for this is to calibrate our equipment.

FIG. 13

 

Setting the generator at a frequency of 100 cycles or so, adjust

the output to read approximately 10 units on the voltmeter. I

have set the voltmeter to use the 1 volt scale, so the reading


should be 0.1 volt or 100 milivolts. Adjust the output of the

frequency generator to 100 milivolts. Now that the frequency

generator is set at the correct and calibrated amplitude, we will

replace the resistor we used to calibrate with one of Fred's


speakers.

 

Even though the voltmeter is set to read voltage rather than

resistance, we are going to read the scale as if it were

resistance. For example, if the voltage reads 0.1 volts, that


will be 10 ohms, if it reads 0.2 volts that would be 20 ohms and

so on. Now we can plot the impedance curve by varying the

frequencies and recording the readings on our voltmeter.

Starting at 10 Hz increment the frequency by 10 Hz until you


reach 100 Hz, then change the increment to 100 Hz until your

reach 1000 Hz. Once you reach 1000 Hz you can stop since this

application only requires frequency reproduction up to around 200

Hz.

 


Be sure that the speaker you hook up is either hanging from

a rope, or being held out in the open air when you measure its

impedance. In Fig. 12 I have plotted both of Fred's woofers.


As you can see, they are slightly different.

 

FIG. 14

 

One of the primary reasons we want to find out the impedance

at several frequencies is to find the natural resonance of the

woofer. This value will become the FREE AIR RESONANCE or Fs of


the woofer being tested. While the woofer is still in mid-air,

angle to woofer to match the angle it will take when mounted in

the enclosure. If it's is on a vertical baffle, hold the woofer


with the cone in the normal vertical position. If it is going to

be mounted at a 30 degree angle, then hold the woofer at that

same angle. Vary the frequency from the frequency generator

until you find the low frequency that produces the greatest rise


in impedance. Record this frequency as Fs.

 

Next we need to find the "Q" of the woofer. To do this

let's calibrate our ohm-meter with a 10 ohm precision restore.


Now measure the DC resistance of the voice coil. Record this

value as Re. Set the frequency generator to the frequency we

determined to be Fs. Read the impedance value and record it as

Zmax. Calculate the value of Ro from the following formula:

 


ZMax

Ro = ---------------

Re

 

Record this value. Find the square root of Ro and record its

value. Now calculate the value of reduced impedance (Z) by the


following formula:

 

Z = * Ro x Re

 

Find the frequencies below and above the Fs where the impedance

equals Z. Record these frequencies as f1 & f2. You can check

the accuracy by using this formula:

 


Fs = *f1 x f2

 

The solution to this formula should be accurate within about 1 Hz

or 2%, whichever is GREATER.

 

To find the woofer's mechanical Q (Qms) use this formula:

 


Fs*Ro

Qms = -------------------

f1 - f2

 

To find the woofer's electrical Q (Qes) use this formula:

 

Qms

Qes = -------------------


Ro - 1

 

And finally to find the total Q (Qts) you may use this

formula:

 

Qes x Qms

Qts = -----------------------

Qes + Qms

 

 

 


The final measurement we will take from Fred's woofers will

be the Vas or the Volume of air equivalent to the suspension of

the woofer. This value is measured in cubic feet, as well as


liters. We will use cubic feet. To help you better understand

how to relate the static compliance of the woofer cone to air,

picture this:

 

 

Create a large square tube in your mind, making it several


feet long, and exactly 1 foot square. If your tube is 6

feet long, you have inside it exactly 6 cubic feet of air.

Now place a baffle on one end and install the woofer into

the baffle. In the other end of the tube place a baffle that


slips just inside the tube. Slowly move the baffle towards

the woofer end of the tube. When the woofer cone begins to

compress, stop and measure the distance from the woofer cone

to the baffle you were moving. Lets say you moved the


baffle to within 24" of the woofer when the woofer cone

started to compress. That would mean that the stiffness of

the 2 cubic feet of air matched the stiffness of the

woofer's suspension.

 


I just think of Vas as the long block of air spring needed

to match the compliance of the speaker. Of course in the real

world that never works, so we have to hold the woofer over the


cut-out in our standard box. (Plans for building a standard

reference box for testing Vas are illustrated in Fig. 13). Apply

enough pressure to make a good seal. Measure the frequency of

resonance on the box. Record this frequency as Fct. Now you can


find Vas by:

 

Fct

Vas = 1.15 x [(-----------)^2-1] x Vb

Fs

 

 

We now have the essential Thiel & Small parameters needed to

model our box on the computer. Gee, there seems to be a slight


discrepancy between our measurements and the ones listed here on

our fax from the manufacture.

 

FIG. 15

 

The Thiel Small Parameters listed by the manufacturer for

Fred's woofer are listed on the left. The actual values are

listed in the right column.

 


Fs....................... 25Hz Fs...................... 27Hz

Qts...................... 0.29 Qts..................... 0.32

Vas...................... 3.95 Vas..................... 3.70

 


As you can see, there is a significant enough difference here to

justify the extra process of measuring the woofer. If we used

the values on the left, we would be designing a box that is about


20% off, resulting in lost performance. What has just happened

here is fairly typical. Paper cones are particularly notorious

for variance because of the added weight of moisture which

changes with the weather. Don't run out and buy plastic, or


polypropylene woofers because of this. Moisture may account for

only 5% of the problem, the rest is a problem with the

manufacturing process. Most woofers are not tested for

tolerances in their design specifications because of costs. In


fact many manufactures do not have methods for measuring dynamic

compliance, and will relay on static compliance tests. This is

not a slam on manufactures because the added accuracy is not

demanded by the market for which these woofers are manufactured.

 


In choosing a design for Fred's car, we must first determine

a few objectives or goals we want to accomplish though our

design. My objectives are to give wide band performance with low


distortion. With that we have a choice. Either build a

conventional 4th order box with two woofers, or the same

approximate size box but couple the woofers into one isobaric

driver. Before we can decide which is the best option, we need


to model both types on the computer and compare the results.

 

Using the Thiel & Small values that we measured, lets find

out what the "perfect" size box is for these woofers. Fig. 16


contains the results of our computer model.

 

 

 

FIG.16

 

If we consider a box to hold two tens that fits nicely into

Fred's trunk, we have about 3/4 of a cubic foot per side to work


with. In Fig. 14, Trace 1, I have modeled Fred's woofers in a

box just that size. The box is divided, and acoustic suspension

(sealed). If we look at the point where the response is -3dB


down, we can see that the frequency is rather high at 80 Hz. We

have usable base (-10 dB) down to 50 Hz. In all honesty, this

box would sound pretty good to about 75% of the people who might

own it. It's weak points are in efficiency and low bass


extension. I generally like to shoot for a strong output at 32

Hz. Although the cabin gain would make the sealed box measure

flat down to probably 40 Hz, everyone seems to want the ability

to greatly exaggerate the low bass response without distortion.

 


If we look at Trace 2, we have modeled a perfect box for

Fred's woofers. A perfect box in so much as it gives the maximum

flat response that the woofer can deliver. If you examine the -3


dB point of this box, you can see that we have dramatically

improved low bass extension. Out cutoff has moved from 80 Hz

down to about 39 Hz with usable bass down to 29 Hz. The box was

made larger and ported to accomplish this. Now there is only one


problem; how to fit a 4 1/2 cubic foot box in Fred's trunk! It

is just too impractical. Physically possible yes, but the box

would have to be made into a strange shape and there would be no


more trunk space left.

 

What if we ported a smaller box, like the first one we did.

If you look at Trace 3 in Fig. 14 you can see that porting the

.75 cubic foot box (each side) appears to improve the performance


over that of it's sealed counter part in Trace 1. While it is

still no where near the large "perfect" box in Trace 2, it could

be a reasonable compromise. The cutoff point is down around 50


Hz with usable bass down to 35 Hz. The response is peaked

slightly at 75 Hz which will tend to add a little boominess, but

there IS still a hidden problem here. Since the port frequency

to achieve all this ends up being 45 Hz, there will be a serious


power handling problem whenever Fred plays music a half octave

lower than that frequency (about 35 Hz). At 35 Hz and below the

port will begin to work backwards. This in turn will completely


unload the woofer, and reduce it's 100 watt power handling down

to about 15 watts at that frequency. Well, since Fred has just

purchased an in dash CD player, and one of the new CDs laying on


his front seat is BASS ZONE, do you think it would be reasonable

to ask him not to play it? Next idea.

 

The last box I modeled is represented on Trace 4 of Fig. 14.

In this box, I have selected a true isobaric alignment using both


of Fred's woofers in the same box. This allows us to obtain the

results of the "perfect size" box in less than half the space.

The total box volume is only 1.2 cubic feet. This size will work


perfectly in Fred's trunk. The Port Frequency is 31 Hz, which

means we are safe with good power handling down to 20 Hz. The

advantage of isobaric vs. a more standard alignment is two fold:

 


A) Power handling is Doubled.

B) Distortion is halved.

 

This is the box we will go with for Fred's system. The woofers

will be wired in series bringing the nominal impedance of the box


up to around 8 ohms. We will be bridging Fred's amplifier

channels to create a monaural signal. Since each rail of the

amplifier sees 1/2 of that impedance, the load will be considered

4 ohms.

 


Fig. 17 illustrates the isobaric box going in Fred's car.

Note the way the woofers are coupled together. It is important

to know that this is the only TRUE isobaric alignment. Putting


two woofers face to face (clamshell) will have the same results

with one exception. The box size would have to be twice as large

to obtain the same results. The reason for this is the absence


of capacitance between the two woofer cones. Clamshell

alignments simply super charge a woofer by making the cone twice

as stiff. Isobaric alignments create a two stage box with the

air space between the woofer cones acting as a buffer to lower


resonance.

 

Fred's new sub box is sized to fit under the rear package

tray of the car's trunk. It sits about 5 inches away from the

seat back, and the woofer and ports are facing the rear of the


car. The box is of course centered leaving an air space of about

12 inches on both the right and left sides.

Iso box

FIG. 17

 

One of the secrets to good sounding bass in a car is the amount

of air left in the car when your done shoe horning a box into it.

The less air space the box takes up the higher the quality factor


gets. Of course taken to the extreme, too small a box probably

won't have any low bass extension so it becomes a delicate art of

balance.

 

Another secret to great bass in a car, is how you locate the


box in the car. Proper location will effect how a sub woofer

performs, but not nearly to the degree it would in a house. The

biggest benefit in a car gained from proper location is correct

PHASE ALIGNMENT with the rest of your speakers. In the case of


Fred's car it is extremely important since his speakers are in

the front of the car. Before we started this install, one of the

obvious flaws in the stereo was that the bass lagged behind and


sounded inebriated. By this I mean that each time the bass notes

hit, they sounded like they came from behind and were always

late. The objective is to make it sound the bass is coming from

the front of the car.

 


It is possible to move or relocate a sub woofer enclosure

without actually moving it. Now I sound inebriated right? Well

it's true (no not that I am inebriated) and you better be doing


it when you experiment with box placement or you may never get it

right. Also every time you move your box you're placing it in

two different places at once... depending on the polarity. Yes


folks that's right, just by switching the speaker leads from

minus to plus and plus to minus you too can hear your box move up

to 20 feet away. By reversing the leads you can shift the output


by 180 degrees. 180 degrees represents 1/2 of a sine wave. Since

the distance between each wave crest at lower frequencies can be

40 feet, changing the phase (polarity) of the sub woofer will in


effect move the crest either closer or farther away from the

listener by as much as half the distance of that frequency.

 

Polarity is considered a course adjustment. Once you have

determined the best sounding polarity for your sub woofer,


changing its position and the way that it passes into the cars

interior can act as fine adjustments to perfectly align the phase

of your sub woofer with the main speakers in front. Doing so

will create a perfectly transparent sub woofer, one that you


cannot detect. When people sit in your car, they should be

wondering how those door speakers have that much bass rather than

what is making all that bass in the trunk. That is the illusion

we strive for anyway.

 


And now for the burning question... why did we face the

woofer towards the rear of the car instead of pointing it at the

seat back? ...Because it works better. Yes another secret is


about to be unraveled. It is one of the MOST common

misconceptions I have seen. It's kind of along the lines of

bigger is better, so closer must be too. Let me just say simply

that a low bass note (one again) creates sound waves in excess of


20 and 30 feet apart. How long is your car? Since you car is

not even long enough for one cycle of a 40 Hz frequency, that

wave must travel to the front of the car and reflect back to the

back and then back to the front until the distances total that


frequency. Getting farther away from the sub woofer will let you

hear the lower bass that otherwise goes around you. Pointing

Fred's box to the back gives us about a 9 feet of additional


distance by the time the wave reflects off the back of the trunk

and passes around the sub box and on through the rear seat/deck.

 

I guess that answers the question about the air space on


either side of the box and the fact that the box was not shoved

up against the seat back doesn't it! Breath baby breath!

 

A few notes on Fred's box would be in order before we let


him come and get his car. Now that we have it installed, and

properly phased you can only imagine how it sounds. No

comparison. The box sounds particularly good you imagine...

besides the designed benefits of 50% less distortion there are


some additional reasons why Fred's box sounds particularly tight

and clean.

 

MATERIAL

 

We used 3/4 inch Medium Density Fiberboard rather than 5/8

or 1/2 inch particle board. The joinery (cuts) is perfect, and


the box was double wrapped making the total wall thickness 1.5

inches. Generally speaking, the thicker the walls the better the

sound. The box we took out of Fred's car if you remember was not


made like this.

 

PORTS

 

Rather than using those whiz-bang plastic ports you see in

almost EVERY commercial carpeted enclosure we used thick

cardboard tube similar to that found inside carpet rolls. This


makes the port wall thickness the minimum 1/4 inch we need to

round the edges. Those plastic ports are thin plastic with sharp

edges usually pressed into the box, and stapled together. This

is why I called them whiz banger's because they make a whizzing


noise and bang around in the hole. In fact I have seen several

fall out completely. The port must be as securely fastened to

the box as the woofer because it in effect does the same thing,

create a piston of resonating air.

 


COUPLING TUBE

 

Rather than using a square chamber to couple the two woofers

together we used a round tube the exact diameter of the woofer.

This allows us to achieve the minimum amount possible of cubic


air between the two divers for stiffer coupling. It also

requires less space inside the box making the over all box

smaller. The round tube also is symmetrical which theory would

suggest improves the balance of force over the woofer cone


allowing greater alignment control at high power levels.

 

BRACING

 

Most commercial boxes lack any kind of bracing which when

combined with thin walls of 5/8" or less yields high levels of


distortion between 140 cycles and 450 cycles or so. A box like

this creates instant ear fatigue at high volumes. If you

eliminate the resonance's of the box, and body panels you could

listen to your stereo at loud levels for hours without feeling


ear fatigue. In Fred's box we put bracing where the box wanted

to be braced. It told us where when we knocked on it several

hundred times. The ideal way to do this would be to set your box


on the left and a cement block on the right. Knock on each

several times. Add bracing to the box and repeat. When they

sound the same your box would be .... well a container full of

bracing,... but the idea is SOLID. The bracing was also used in


Fred's box to break up the back waves of the woofer and offset

the parallel surfaces so that we don't suffer any of the side

effect common to square shaped boxes. Although Fred's box is a


square, it performs like a wedge because of the angles we set the

braces at.

 

Always use as much bracing as you can justify. Don't forget

to calculate the cubic inches in each brace and deduct it from


your box volume. Yea, it usually means that you have to figure

the total volume of the braces during the design phase.

 

INSULATION

 

We sprayed the inside of Fred's box with adhesive and then


applied a 1.5" layer of fiberglass insulation to dampen the

enclosure. This helps absorb higher frequencies and smoothes the

response some. Adding too much can have the same effect as

increasing you box size slightly so don't get carried away.

 


INSURANCE

 

To insure that Fred's box continues to perform as it does

now, the inside and outside has been sprayed with a good sanding

sealer. This makes the box moisture resistant (you know like a


watch) and most sub boxes do come in contact with moisture at

some point... it's Murphy's Law.

 

Tovább »

Chapter seven

CHAPTER 7
RE-INSTALLING FRED'S STEREO
Fred returns with his car as planned, and leaves it with the key. After Fred has gone, I finish sweeping the shop and turn the stereo on at a low volume. It's Sunday and one of the local public radio stations play some real good jazz. I move the 55 gallon Rubber-Maid full of junk we pulled out of Fred's car before he left and backed the car in. I then opened all the doors and windows, trunk and hood. Yea, the car is sitting in the center of a large room with lots of space to work, excellent lighting, and the tools and materials to do anything that pops into my head. I remove the fuse serving the dome lights so that the battery won't run down and then step back to the bench and stare at the car for a period of time. After a moment I decide that everything feels right, I am in the mood to it and have everything I need. There are the first three secrets to a successful install. I don't know what, but something good is going to happen, let the tweaking begin. First thing I do is sit in the car and turn on the stereo, without adjusting any of the controls. That way I get an initial idea of how Fred listens to it. As before, the loudness is on, and the bass is turned up. The overwhelming impression that hits you first is that the Subs sound like shit. As SOON as you turn up the volume there is distortion. My technique for correcting this type of dilemma is not to get sucked into why it sounds bad, but rather just un-hook everything and start over. That has proven for me to take less time. Well lets see what we have again so we know what we have to work with. Two door speakers in the front doors, sub woofer in the trunk, two amps and a crossover. On the seat we have a CD player, and a noise filter, and two new CD's. Lets see, Rap Babies, and Metalica. Now I know what type of box we need, something stiff with a "Q" of about 1.0. What? An enclosure designed NOT to sound sloppy and distorted, with a slight rise in response at around 75 hz. We are going to re-install this system so that Fred does not have to use the tone controls to achieve the sound he wants. Since Fred's bass is very week now, we will want to design a replacement for his sub woofer that basically plays louder with less power. Either that or make Fred buy an amplifier about 3 times as big as the one he is currently using. Walking around the trunk lets get this box out. There seem to be no screws holding it down judging by the way it slides all over the place when I push on it. There are the wires going into it. Oh-boy, look at this. The wires are stripped back about an inch longer than necessary. See Fig. 7 and see if you can locate any potential bombs! That's the cool thing about doing one of these jobs, you find lots of little land mines any one of which could take out the entire stereo!

 

 

FIG. 8

 

Any time wires touch together between the speaker and the

amplifier, it becomes a short circuit and usually blows up the

amplifier. In the case of Fred's amp, it would defiantly blow

up. I clip the wires and pull the box from the trunk. It is

about 3 feet wide with carpet all over it, and a Plexiglas

window in the center. The ten inch woofers are visible behind

the window. The box feels damp on the bottom, looks like Fred's

trunk leaks, or he has just spilled something in there. I set

the box on the bench, and examine it. The plexi glass window is

1/4" thick, and getting hairline cracks around each screw hole.

The window is actually how you gain access to the subwoofers.

 

After getting the window off, and the ten inch woofers out, it

was easy to inspect the box from the inside. The material is 5/8

inch pine particle board. There are no braces. The ports on

each end are those plastic flanged inserts that you cut to

length. They are stapled to the box from the inside. They move

when you wiggle them. The edges of the port tube inside the box,

are sharp, which creates wind noise when the box is turned up.

Inside the box the seams are clearly visible and you can see how

the glue is spread missing parts of the seam completely. The

lower right corner of the box is dark with mildew, and the wood

looks swollen. Flipping the box over and pealing the carpet

back, we can see the corner joint has opened up and is leaking

air. The woofers have paper cones too, and they feel soft.

 

I took the woofers and placed them in front of the heating

vent so the warm air would dry out the paper speaker cones, and

returned to the trunk. The amplifier was screwed to the carpet

on the floor of the trunk, but not to the floor. It was easy to

remove. The wire connections were not much better than they were

on the speaker box. The ground wire for the amplifier ran over

to the back rear tale light and was wrapped around one of the

studs holding in the tale light. Whoever installed this

amplifier doesn't realize the importance of good connections.

You might wonder how good do connections have to be. The answer

on a scale of 1 to 10, would be unless it is a 10 it's a terrible

connection. The ground wire for an amplifier is every bit as

important as the power wire, and must be securely grounded to the

steel body or chassis of the car.

 

Lets see what effect this one connection has on the

performance of Fred's stereo. Taking a digital volt/ohm meter I

hook one end to a good ground, and the other to the clipped end

of the ground wire where it was connected to the amp. The

resistance should be zero, but here it is reading 11.6 ohms. I

jiggle the wire a bit and the reading jumps from 4.3 ohms to 35

ohms. This was not good. Lets check the power wire going to the

battery. It has a place back here in the trunk where the

insulation has been stripped off and another wire twisted around

it with some electrical tape. The other wire goes to the small

amp that Fred uses to run his door speakers.

 

Following the cable through the car we end up at the battery

where again, the connections are less than desirable.

 

The amplifier that was serviced by these two wires, is fused

with a 20 amp fuse. The connections and smaller than ideal wire

size make questionable whether or not these wires can deliver a

full 20 amps. Returning to the bench, I get my tester and hook

it in place of the amplifier. The tester displays voltage and

current. On the right side is a dial that adjusts the load from

zero to 100 amps. I set the dial to 5 amps, and the voltage is

an unstable 11.8 Volts. In trying to determine the maximum

current the cables will deliver the 30 amp fuse at the battery

blew. The funny thing is, I never got past 15 amps at the

tester. This tells us that Fred's amplifier was fed with 15 amps

of current at 11.8 volts, or put another way 25% under powered.

 

I bring Fred's amp over to the bench and hook it up to the

analyzer. I set the voltage for 12 volts, and the available

current to 20 amps. I then measure the output of the amplifier

and find that it delivers 105 watts total. Into a 4 ohm load

like Fred had it, the power increased to 134 watts at the point

where distortion began. I then reduced the voltage to 11.8 volts

as it was measured in Fred's circuit, and set the available

current to 15 amps. Fred's amplifier was now putting out pure

distortion. I turned the input single down until the distortion

stopped, and the measured power was now only 44 watts! So this

is what Fred had going on in his car, I guess it's no wonder

there was no bass.

 

The first order of business is to install a properly

connected power feed, and ground for Fred's amplifier. Remember,

that while properly connected the SIZE wire Fred has is adequate,

but since it is spliced in the trunk and has a large scrape in it

where it passes through the un-grommeted fire wall, I am going to

replace it. When removing the power cable, I discovered that the

installer also ran the RCA cables in the same spot. Both the

power cable and the low level RCA single cable (path cord) were

running side by side the entire length of the car. Since the

power wire creates a large magnetic field, the patch cord gets

saturated with stray voltages creating classic engine noise. In

Fig. 8 we have the most important ingredient for high fidelity,

the power supply.

 

FIG. 9

 

The power supply starts with your car's battery which is

supplemented by your car's alternator. Around 12" away from the


battery there is a fuse holder containing a fuse ranging from 30

to 60 amps. This fuse is NOT here to protect your amplifiers.

If your amplifiers are not individually fused, you must install


fuses for each amplifier AT each amplifier. The fuse by the

battery is to protect your CAR from fire when or if your power

line is somehow shorted. A common place for shorts is where your

power wire passes through the fire wall. The most popular time


for a short to occur is when you get into an accident.

 

Standing here looking at how Fred has connected his power

wire to the battery post I can't stress enough how important it


is to make good connections. Make sure each connection is clean

and shinny. In the case of the battery post, remove the positive

and negative cables and clean both the inside of each cable and

the battery posts themselves. Adding a car stereo will add


stress to your car's battery and charging system. Most cars have

somewhere between 40 and 100 amp alternators. These alternators

were designed by the car manufacture to serve the needs of the


car's electrical system and one 20 amp accessory via an optional

cigarette lighter. An average car stereo system will use between

20 and 80 amps of the alternators output. The left over output


from the alternator (if there is any) charges the battery. When

the stereo is on and drawing say 40 amps, and you are driving at

night with the headlights on, heat on, and windshield wipers

running, you're alternator can't deliver the power, so it comes


from your battery. This is not a good situation because instead

of charging while you drive, your battery is draining. This

condition also becomes conducive to a drop in voltage which

starves your amplifiers until they eventually cook. Nothing like


walking home knowing your stranded car and blown stereo are just

waiting to be vandalized before you return.

 

OK, I have finished hooking the new power cable to the

battery and have installed the fuse block at the end of the cable


which is about 12 inches long. This is when we shift to the

inside and find a good location in the fire wall to stick the

power cable through. It is important to choose a place where

nothing press against or rubs on the surface of the cable. The


hole should be larger than the cable diameter so that you can fit

a rubber grommet around the cable. Choosing not to do so will

allow the steel edge of the hole to slowly cut through the cable


sheath until it contacts the copper wire inside and shorts the

battery to that spot. Of course, as I mentioned earlier, this

fuse is to protect the car, not the amplifiers. All amplifiers,

and other electronics at the other end of this cable must be


individually fused. Naturally, installing the fuse holder does

not guarantee you're car won't burn up. You also have to install

the proper fuse. Failing to do so, and improvising with a piece


of wire or tinfoil is like not having a fuse.

 

Now I have the grommet in the hole I drilled, and the power

wire ran to the location of the fuse holder by the battery. I

will be running the cable under the carpet, rather than the mud


guard under the door. It's just too easy to run screws through

the cable when re-installing the mud guards. One time I had an

install where a guy ran his 4 gauge power wire UNDER the car! He


was driving down town and ran over someone's muffler. The power

wire caught the muffler (or the other way around) and pulled his

amplifier through the back seat! It gets better... He solved


the problem by running conduit from his battery to his trunk and

ran the power cable through that. (Grin) That was going great

for several weeks, until at a coupling in the middle, the

vibration from driving created a fracture and pinched the power


cable. The power cable welded itself to the conduit in a shower

of sparks as the poor guy screamed over to the shoulder. He

popped the hood and fanned the smoke away while the battery and

conduit continued to melt. He didn't bother to fuse it claiming


that the conduit would protect it. To come to the point, his car

started on fire.

 

Now that I have completed the power wire and the amplifier,

we need to choose a spot for the ground wire. I like to keep it


within a foot or so of the amplifier. I have chosen to locate

the amplifier upside down under the rear package tray where the

6x9's are located. This way the amplifier and wire is up out of


the way, protected from moisture, and less prone to get covered

up with junk. About 8 inches to the left of the amplifier I take

some 80 grit sand paper and sand off all the paint in a little

circle. This is where I will be hooking the ground wire.


Biggest mistake everyone makes here is drilling a hole for the

ground screw. The screw always comes loose after about 4 days.

The reason is that the steel here where we're working is only


about 1/64th of an inch thick. That means it can only support

one thread of the screw. The proper way is to take a punch that

is 1/2 the diameter of the screw, a hammer, and punch a hole in

the steel. This method does not remove metal like drilling, but


flanges it up around the screw to support several threads.

 

The next step is to solder the ring connector to the end of

the ground wire and using a screw and washer attach it to the


steel package tray where we have punched the hole. Take care not

to over tighten the screw. If you strip the threads, you will

have to start over. After the ground is in place, We need to

cover it with a silicone cement. The cement absorbs vibrations


and keeps the screw from eventually coming loose and prevents

oxygen from the connection. Oxidation causes dark coloration in

connections and reduces performance.

 

Fred only has a pair of door speakers in the front of this


car, but I would like to take a moment to mention that if there

were 6x9's back here, we would have to figure out a way to make

them compatible with the sub woofer. If you have speakers in


your rear deck (package tray) and a sub woofer in your trunk, bad

things are happening you may not even know about. First off, the

sub woofer(s) are going to move several times more air than the


speakers in the rear deck. Since there is no hole between the

trunk and the interior of the car, the air pressure generated by

the sub woofer will inevitably locate on the cones of the rear

speakers. Think of it like two things having a pushing contest.


The rear speakers always loose. In some cases they can even rip

apart. In all cases they sound bad compared to how they could

sound without this ailment. Another side effect is that the sub


woofer is not in exact phase with the rear speakers and their

frequencies overlap causing cancellation resulting in less bass.

The cure for this situation is to enclose the rear of the

speakers in the rear deck so that they essentially are operating


in their own sealed boxes. This way they become isolated from

the sub woofer in the trunk and can once again deliver tight

clean sound. The second requirement to sealing the backs of the

6x9's with a STIFF material, is to make sure the bass in the


trunk has an easy way to penetrate the interior. This

penetration occurs through the back seat, but Fred's car has a

thick piece of cardboard covering the entire back seat. Behind

this there is a 1/2 inch layer of felt with a rubber backing.


Some cars have a solid steel wall behind the back seat. I'm

removing the cardboard and felt "sound deadening" from the back

seat so we can cut a hole in the center of both. Make the hole


about the size of a book, and pinch off some of the foam from the

back of the back seat where the hole will be. Don't remove too

much, just a little bit. Now we take some flat black spray paint


and spray the area we just nibbled out. After re-installing the

cardboard we removed, it is a good time to touch up the inside of

the trunk and edges of the hole you cut in the cardboard. Making


a job look good can have a phyco-acoustic effect of improving the

sound.

 

With the now clean trunk waiting for a box, I run the low

level patch cord(s) down the passenger's side of the car from the

 


trunk to the in-dash CD player. I will be using a heavy duty 20

foot RCA patch cable with an accessory wire running down the

center. Note, the power cable runs down the left side of the


car, looking at it from the trunk, and the single wire is run

down the right side... far away from the magnetic fields

surrounding the power cable. The trigger wire, or turn on wire

as it is called, can run down either side. Generally it does not


carry enough current to create large magnetic fields.

 

Now it's time to move back inside to the front seat and

install the CD player. Since Fred has an after market cassette


deck installed already, the new CD player will fit exactly where

the cassette deck was without modification. After removing the

cassette deck I take the liberty to re-install the adapter kit

because I can make it move when I giggle it. A couple added


screws, and some glue stiffened it up very nicely. A CD player

that vibrates as you go down the road from a loose kit may not

skip, but it is over-sampling which reduces fidelity. Since I

see one type of speaker wire here, and a different one down by


the speakers in the door, I am going to pull fresh new speaker

wire from the CD player to each door.

 

Remember Fred had his door speakers running on a small cheap

amplifier that distorted from lack of power. We are going to run


his door speakers off of his new high power CD player because

given the two options, the CD player's amplifier is of higher

quality than the external amp Fred had. Installing speaker wire


to the doors requires a little extra effort to drill holes and

properly grommet and seal everything. Removing Fred's door

speakers we see an average quality coaxial door speaker which has

been screwed to a crudely cut opening in the door panel. The


problem here is that the door panel is made from cardboard, they

all are. The steel behind this panel is full of different

indentations making it difficult to get a good seal.

 

Another secret to exceptional car audio, is not to skimp on


the installation of the door speakers if you have speakers in

your doors. Once the speaker has been removed, and the door

panel removed I like to cut some oak strips and using liquid

nails glue them to the inside of the door. Then I like to take a


slightly larger one and screw it into the door panel side. This

makes a substantial difference by STIFFENING the door panels.

After the oak cleats are installed, I spray the inside of the

door with rubberized undercoating. Fig. 9 illustrates a cross-


sectional view of the door cleating.

 

FIG. 10

 

Now the door is prepped and ready for the speaker. Before

we install the inside door panel we will need to fix the hole cut


by the last installer when the door speakers were originally

installed. Since this car did not come originally with door

speakers, the inside surface of the door is not perfectly flat.

This means that after you have cut a hole the speaker will not


seat properly in the door. There will be gaps, and sometime only

places for a few screws. To correct this situation we will take

an old scrap speaker of the same size and butter it up with

Vaseline and install it into the door. Next we take some auto


body filler (bondo) and spread a thick layer around the speaker

using the outside ring of the speaker as a guide. Once this has

dried, we remove the speaker and we have a perfect recessed

baffle approximately 1/2 inch thick. The solid air tight fit


will greatly improve mid bass response. In fact it is common to

expect frequency response to extend to about 40 Hz after making

these modifications to your door.

 

Before re-installing the door speakers, we must do one more


thing. Taking a scissors cut some 2 inch wide strips of box

carpet making each strip about 6 inches long. Take each strip

and lay it out on some newspaper, you will need 4 strips. Take

some spray adhesive and spray the strips (one side only). Next


take the door speakers and carefully apply the strips to the

speaker basket so that you cover the holes. Now spray a few

light coats of acrylic clear coat to the carpet. This process

keeps the noises inside your door from the back of the speaker,


and acts as a moisture barrier. Last but certainly important,

we need to solder the speaker wires to the speakers. Doing so

eliminates possible loose connections in a place you won't want


to go looking. Since we will be using the in-dash CD player to

power the door speakers we will need to install a passive

crossover on each speaker. The component consists of a capacitor

(100 uf) simply connected to the positive speaker lead in series


with the amplifier.

 

Since the location of Fred's door speakers (or any door

speaker) are less than ideal, we are going to add an in-expensive

pair of tweeters to the circuit. Although the door speakers are


coaxial, and have a tweeter, it points into your legs making the

high frequencies hard to hear. We are going to put a pair of

tweeters in the factory locations for Fred's original dash

speakers. By removing the factory dash speakers we have plenty


of room to install a pair of tweeters. We will be wiring these

in parallel with the door speakers. The tweeters I have chosen

are small 1/2 drive dome tweeters made by Audax, a popular

speaker used in the home speaker industry. They cost about 15.00


each and are high in efficiency. To keep the sound quality high

in Fred's car we need to be able to turn the CD player up fairly

loud without any distortion.

 

In Fred's case we have limited power available to run the


front speakers. This means we cannot waist any of it with sloppy

circuits. Originally, the way the door speakers were installed,

with gaps and loose screws, the impedance rose sharply and fell


sharply at 4 different frequencies. This can waist up to 50% of

the power available from the amplifier. By modifying the doors

and re-installing the speakers we have dramatically improved the

impedance curve. We have lowered the resonant frequency, and


removed the peaks and dips. In Fig. 10 you can see how it

measured before and after our re-installation.

FIG. 11

 

Installing the tweeters in the dash could easily ruin our

nice impedance curve at the higher frequencies because there is


already a tweeter in the door speaker. Solution, clip the wires

on the tweeter located in the door speaker. Disable it. The new

tweeters located in the dash will more than make up for it

believe me. Believe it or not, the location or positioning of


the tweeters is more important than any other speaker. This is

because high frequencies travel in narrow beams. Placement of

these frequencies will determine the success or failure of your

stereo's ability to image and create a life like sound stage. By


removing the tweeters down in the door speakers we've eliminated

phasing and time alignment problems with respect to the sound

stage. It will be easier to maintain a clearly focused image


without the lower pair of tweeters.

 

To install the new tweeters requires a good quality mylar

crossover network. I selected a 12db network for a frequency of

6500 cycles. This was above the point at which the door speakers


roll off in response. Blending these two speakers at this

frequency maintains our nice smooth impedance curve. Since the

CD player is now installed and everything is hooked up, it's time


to turn it on and listen to it. First we place both tweeters

face down on the dash and use some jumper leads to hook them up.

We will leave one lead unhooked on each tweeter so that you can't


hear them and listen to just the door speakers. If the door

speakers are wired right they will sound warm and rich. If one

is wired backwards, the sound will be tinny and shift from side

to side as you move your head. With that, we sit in the center


of the car and hook up one tweeter. Just lay it on the dash so

that it points up into the glass and listen for second. Now

reverse the leads on the tweeter and listen again. The second

way throws the sound back and seems to make the windshield and


door disappear. This is referred to as depth of reproduction.

People who insist on following directions will fail at this point

because it is in fact wiring the tweeter backwards throwing it


180 degrees out of phase with the door speaker. That's exactly

what I want it to do, that creates depth by creating a time

alignment between the two drivers where the tweeter output is

delayed 1/2 cycle. Since the tweeter is closer to your head by


half the distance of the door speaker, what I have actually done

is put the system back in proper phase.

 

The next step is to hook up the other side in the same

fashion and flip it over so we can't hear it right now. Now we


have the opportunity to experiment with different angles.

Holding the tweeter so that the sound hits the glass, slowly

rotate the angle from left to right and front to back. There

will be one spot that is best. We will have to use some hot glue


to temporarily hold it here, and do the same to the other

tweeter. This is considered a rough in. Sitting in the driver's

seat and occasionally leaning towards the middle of the car,

listen for proper placement of instruments in the recording.


Make adjustments, listen to the same thing and repeat. This can

take several hours or a few minutes depending on the variables

involved.

 

FIG. 12

 

 

I used some soft flexible thick wire to fashion a bracket for the

tweeter so that it points the same way I had it when it sounded


best. Before screwing the tweeter in the original 4x6 opening,

we are going to pack the cavity below it with foam. This will

insure that all we hear from this location is a tweeter, and not

noises inside your dash and glove box. Do the same thing to the


other side, install the tweeters and replace the factory grills.

 

If you've noticed that the grill just compromised the sound,

you can cut the center out of the factory grill, and wrap it with


black grill cloth, and re-install it. Now the tweeters and front

doors are complete. BTW, the grill cloth will make an audible

improvement over the plastic factory grill by absorbing the sound


that refracts back from the glass into the tweeter. The

subjective effect this has is a smoother top end.

 

Now that the mids and highs are completed, the next secret

is to listen to it while we finish the install. Think I'm


kidding again right? Let me tell you about polypropylene

capacitors, in fact any type capacitor. A new capacitor out of

the box will sound terrible for the first several hours while the

dielectric forms itself to the circuit. The BURN IN, as we call


it, is a cycle of playing and resting the system. Five hours on,

five hours off, five times. At first the speakers or electronics

with the new capacitors will sound real bright, and even harsh.


Then the system will sound dull as if there is a film over the

music. Then it will start to go from one to the other, each time

getting a little better. At the end of the burn in, and what

determines that it is the end, is what we call the big bloom.


You'll be listening and all of a sudden the sound will blossom

into focus and that big 3D sound stage will finally be there. If

you follow the 5 by 5 method of burn in, the system will bloom


within 25 hours, usually. If you don't specifically burn the

system in, you'll notice it bloom after around 50 hours. Is it

necessary to burn in your car stereo? Hell no! The secret is


that I want old Fred and anyone else who listens to this car to

be amazed. That first impression is the one that talks. Since

we have to build Fred's sub woofer box, the system will be about


burned in when he picks it up tomorrow.

 

Tovább »

Chapter six

Chapter 5

A sample system

For several years I have worked sales floors specializing in car audio equipment. About half of my customers during that time were starting from scratch, didn't have a ton of money, and wanted ten times more than they could afford.

One of the first things I would do is point out that people who come in and buy a complete full blown stereo for their cars usually have poorer end results than those who build their systems in stages over time. A simple reason for this is that if you build your stereo slowly, and listen to each thing you add, you are in a position to know exactly what you need based on the sound you have. The other person who buys it all at once can only guess.

Lets assume that we have a sedan with a 4 speakers factory stereo cassette and everything works. You would like to replace all this with state of the art gear. The first thing to do is NOT to buy a new head unit and new speakers for the front and rear. That's right, don't do it, not yet. If you spend your first 500 bucks on that you will only improve the quality of what you have. It won't get much louder, and the bottom line is that there still wont be any BASS. The idea is to get as much audible difference as possible as soon as possible, which means from the first purchase. This first decision is the corner stone of your system design, and therefor the most important.

In order to maximize your first purchase, we need to augment what you already have. And everything we buy must have a place in the finished system. By that I mean never buy something because of price and plan on replacing it with something better down the road. Since bass is what separates a high performance car stereo from an average one and the factory stereo has none, this is the place to focus. We will be adding bass to the factory system as stage one - the first purchase. To make this chapter hit home a little better let us bring in a couple new characters; Jane and Bill. Jane will be my customer who owns the sedan with a 4 speaker factory stereo cassette. Bill has an identical car, and Bill has just purchased an In-Dash High Power CD Player and 4 new speakers with his 500 bucks. Lets assume Bill and Jane both work at the same place and bump into each other in the lunch room almost daily.

See, Bill started it, that's why Jane came into the store. Jane really has her eye on that new CD player... like Bills. Any sales person will tell you that I could have sold Jane that CD player and 4 new speakers, had her 500 bucks and had her out the door in about 15 minutes, or less. So why didn't I you ask? Because the sales business was pretty boring when you weren't waiting on someone, and since Jane and Bill are friends, somewhat competitive too I would guess, I knew that what I was about to do would, besides being the honest thing, create a domino effect of pure entertainment over the next several months as Bills superior male intellect goes up in flames trying to keep up with Jane.

Back to Jane's car stereo. You know she tried to buy the in-dash CD player and 4 new speakers. I spent some time with Jane. Jane decided to augment her existing system by adding a sub woofer in the trunk, and a couple of other things. We decided that the place to start would be in selecting the amplifier to run the sub woofer. Compromise in Quality is out of the question, yet the BEST sub woofer amplifier cost almost 500 bucks so obviously that was out of the question for now. We selected a good high quality amplifier that gave a clean 100 (real) watts. It would be ideal for running a sub woofer at a volume that would serve to augment the factory stereo and later on be used as a mid and high frequency amp. That was 200 bucks. Then we built a no compromise sub woofer enclosure specially engineered for her car. That was 150 bucks. We selected an EFFICIENT 10" woofer with a lower power rating instead of an INEFFICIENT by comparison 10" woofer with a very large power rating. This was 60 bucks. Then we selected a pair of tweeters from the separates display. They were 50 bucks. The rest went for an amp install kit, and a line-level adapter to convert the rear speaker signal into an RCA type adapter that could feed the amplifier.

We installed the 10" woofer into a band pass enclosure which we designed for Jane's needs. Jane's 10" woofer would be joined by another 10" woofer at some future point making her box become isobaric. This meant the enclosure had to be designed to work both ways and it does. We then installed the amplifier and augmented the front dash speakers by adding some tweeters. Later we will replace the dash speakers with a mid-range and eventually add the midbass drivers to the front doors. When we wired Jane's car, we installed passive crossover components on her front and rear factory speakers. We used 99uf 200 volt capacitors on the dash speakers and 200uf caps on the rear speakers. The lower value blocks more bass so we choose this value for the fronts since they are small 4" speakers. The back speakers are 6.5" which will play lower, so we didn't need as large a capacitor. By installing these passive crossover parts, we have effectively removed the low bass from her speakers, and as a result increased their power handling, and reduced their distortion.

In an effort to give the most audible difference for the buck, we removed the rear speakers from Jane's factory stereo, and hooked them to the new amplifier. We then bridged the sub woofer across both channels and used an additional passive crossover component called an inductor (coil) to remove the mid and high frequencies from the sub woofer. Sub woofers should only play bass, you should never hear voices from your subs. In doing this, we have effectively raised the SPL (sound pressure level) in Jane's car by a very noticeable 18 dB!

By removing the rear speakers from the factory head unit, we decreased the amount of work it must do, and increased it's performance slightly. By installing tweeters on the front dash speakers and adding crossovers, we increased the sound quality and performance by leaps and bounds. By using a quality amplifier turned down slightly, we improved the performance of the rear factory speakers by at least 100%! In fact, if you sat in Jane's car right now and listened to the radio, and than sat in Bill's car and did the same, you would be shocked to hear very little difference. Except that Jane's car gets louder and has a more solid sound coming from the rear. Last but not least, by installing the perfect sub woofer design in Jane's car the sound is now full, deep, rich, and powerful. Jane is very pleased.

A few days later in the lunch room, Bill and Jane get together and he asks if she got her CD player yet? She informs him that she decided to wait on the CD player, and bought a sub woofer and some other little things instead for right now. Bill jump in and says yea, he is going to get one of those next, soon as he saves up the money. Bill and Jane go out into the parking lot and Jane invites Bill to take a listen. Bill was in a bad mood for the entire remainder of the day. A week or so pass, and by now every employee at work has asked Bill if he has heard Jane's system.

Bill can't take this anymore, so long before originally planned, bill arrives at the stereo store. "I want a sub woofer, and make it a damn big one!", Bill exclaims. Bill and the salesperson haggle around for an hour or so, and Bill finds himself in somewhat of a compromised position. What he wants and what he can afford are no where close. Bill draws the line somewhere down the middle and buys a sub woofer and amplifier to run it. Bill has a box with 2 12" subs off the floor and the same size amplifier as Jane. Bill would have agreed to get a custom box built, but he didn't want to wait. Another week of humiliation would be too much to stand. Bill spent another 500 bucks.

Bill's sub woofers are installed, and a passive crossover between the amplifier and the subs. Since bill used the full power from the amplifier to drive his subs, and the 10 watts or so per channel from his CD player to drive everything else, guess what? Bill's car is all bass. Every time Bill turns it up the bass overwhelms the rest of the music, and you can't even tell what songs are playing. But Bill has more bass than Jane, so he receives his vindication.

About a month or so pass and the general consensus at work is that Jane's stereo still sounds better than Bill's. Even Bill admits that it does. Then Bill makes his next move... Bill adds a second amplifier to run the mids and highs, because his CD player doesn't have enough power. Bill buys a small 4 channel amplifier of good quality, with a built in crossover, and has it installed on his 4 new speakers. Now Bill his smiling big time! His stereo really sounds bitchen now. The amp only set bill back another 179 bucks. Lets see now, that makes 1179 bucks for old Bill. While bill's system is a little louder than Jane's, and a little more sparkly, and a little more dynamic, you still can't sit in both cars and say one is better or worse than the other. Jane's system is a little smoother, a little better balanced, and the bass is tight and accurate, making Jane's system actually more musical, which is what Jane wants. Several more months pass and the issue fades away until Jane makes her second purchase, the in-dash CD player she has been patiently saving for. It was easy for her to wait, because her car stereo already sounds good. Jane buys a CD player. She even choose a better model than the one she originally looked at because of the sale! Yes, a slightly nicer one than Bills, unfortunately.

We install Jane's CD player, and her system simply came alive. Everything it did well before it does better. Because we have taken car to keep Jane's system balanced, and put separate tweeters in a different location on her dash, Jane is now hearing the music presented in a large dimensional stage with precise imaging and depth. Bill, with his new dash speakers cannot achieve this performance because of the location. The most amazing thing that happened in Jane's car was the BASS improved dramatically. Jane's bass is now as loud as Bill's was and sounds much better. Funny thing is, she is only using one 10" woofer! Since the new CD player we sold Jane is a high power model similar to Bill's, we gained a large increase in performance from the factory dash speakers due to the increased power and lower distortion of her CD player. Since the front speakers got louder, we turned up the volume on the rear amplifier a little to maintain balance. This also increased the bass proportionately.

Yea, Jane and Bill, by now all the salespeople are aware of the situation between Jane and Bill, and anxiously huddle around to hear the latest each time one of them leave. Jane's stereo is audibly superior to Bill's, and so far has cost less money. Jane's stereo has been audible superior to Bill's since day one.

I don't need to tell you that Bill is in a bad way trying to figure out what he can do to improve his stereo without spending more money. What can Bill do? Gee, Bill bought 4 new speakers, and amplifier to run them, a sub woofer, an amplifier to run that, and a in-dash CD player. Bill is done. There is nothing fundamental that bill can do to improve his stereo without getting rid of something he already has. Unless bill want's to spend big bucks on digital processing accessories to act like a Band-Aid to smooth over some of the rough spots, Bill is done.

Well, Bill's not done. Bill is now highly motivated. And you thought Fred had it rough. Bill rearranges his priorities and sells some non stereo related things that he owned. Bill buys a bigger sub woofer amplifier. Bill sells his original sub amplifier at a huge loss. Bill now has more bass. Bill cannot use all of the power his new amplifier has because his box starts to make the woofers flop around. The box is a generic design, and does not maximize the acoustics of the car like Jane's box. Also, the mids and highs start to get lost again when Bill turns the bass up too loud. Never the less Bill has something new again, and lives with it for awhile. Bill buys a BASS ZONE CD to really push his system, and blows a woofer. That's OK, Bill didn't like those woofers anyway, the flop around when you turn it up. Bill buys 2 new woofers that are a stiffer compliance. Bill didn't realize that the new woofers have a different quality factor than his original woofers that came in his box. The new woofers require a different size box, and need a different size port to go with it. The new woofers which are in the wrong box, play higher bass notes much louder than the old ones, and play lower notes much quieter than the old ones. Bill's new bass is loud and high, with no deep bass extension. This made bills bass CD sound differently than it used to. Some songs sounded better, and some sounded worse. One track in particular was Bill's favorite, it had a pounding thump that made your hair vibrate.

After work one day, Bill and Jane ran into each other in the parking lot and started to chat. Eventually Bill decided he would like to hear his Bass Disk in Jane's car. They hopped inside, and Jane started the car. She popped the CD in the player and turned it to Bill's favorite track. The loud pounding thump Bill was used to hearing was now a tight clean kick drum, which until now Bill always thought it to be... well... not sure. Then Bill's eyes lit up, and looked at Jane. The console and the rear view mirror were starting to shake. Not buzz, but shake! There was a super low synthesizer playing behind the kick drum, generating some 28 cycles tones. The bass actually squeezed you a little. Bill was flabbergasted. Bill got back in his car and did the worst thing he could ever have done in regard to his stereo. He played the CD. There was no synthesizer at all. Bill's head sinks down to the steering wheel and suddenly the total that he'd spent to date popped into his head, 1800 bucks, and he lost it.

To wrap up a long story, Jane having had so much positive attention as the result of her stereo's performance, decided to Finnish the system. We sold her the high quality midrange speakers for her dash, and some 5.25 inch midbass drivers and installed them in her door panels. We then replaced the rear speakers with a pair of 5.25 inch midbass drivers, and installed a pair of tweeters on the rear deck next to the midbass speakers. Now Jane has eliminated all of her factory speakers. Next we took the amplifier that was running her sub and moved it to the front and rear speakers. We then replaced the sub amplifier with a larger one, and added a good active crossover. The sub woofer cabinet was re-fitted and re-tuned to accommodate the second 10" woofer making Jane's Box isobaric. Jane's bass now goes down to 20 Hz. Before it was hitting just below 30 Hz. Jane's stereo is now of competition quality in both sound, and appearance. Bill is screwed, because he buried himself in his system and can't sell it until it's paid for.

This has been one of the most common scenarios I've seen as a sales person. It is in fact the motivating factor behind writing this book. Remember it's not how much money you spend, but how you spend your money. And, if left alone to purchase your first system without the knowledge of experience, you will fail and find yourself in Bill's shoes. Jane's stereo has been a constant source of pleasure since day one. Bill's stereo has been a source of pleasure and an even bigger source of stress, ending up solely as the later.

In the next chapter we will be looking at various system layouts which yield a balanced high quality output. You may use this as a guide for your future reference.
 

Tovább »

Chapter five

Chapter 5

A sample system

For several years I have worked sales floors specializing in car audio equipment.  About half of my customers during that time were starting from scratch, didn't have a ton of money, and wanted ten times more than they could afford. 

One of the first things I would do is point out that people who come in and buy a complete full blown stereo for their cars usually have poorer end results than those who build their systems in stages over time. A simple reason for this is that if you build your stereo slowly, and listen to each thing you add, you are in a position to know exactly what you need based on the sound you have.  The other person who buys it all at once can only guess.        

Lets assume that we have a sedan with a 4 speakers factory stereo cassette and everything works.  You would like to replace all this with state of the art gear.  The first thing to do is NOT to buy a new head unit and new speakers for the front and rear.  That's right, don't do it, not yet.  If you spend your first 500 bucks on that you will only improve the quality of what you have.  It won't get much louder, and the bottom line is that there still wont be any BASS.  The idea is to get as much audible difference as possible as soon as possible, which  means from the first purchase.  This first decision is the corner stone of your system design, and therefor the most important.        

In order to maximize your first purchase, we need to augment what you already have.  And everything we buy  must have a place in the finished system.  By that I mean never buy something because of price and plan on replacing it with something better down the road.  Since bass is what separates a high performance car stereo from an average one and the factory stereo has none, this is the place to focus.  We will be adding bass to the factory system as stage one - the first purchase.  To make this chapter hit home a little better let us bring in a couple new characters; Jane and Bill.  Jane will be my customer who owns the sedan with a 4 speaker factory stereo cassette.  Bill has an identical car, and Bill has just purchased an In-Dash High Power CD Player and 4 new speakers with his 500 bucks.  Lets assume Bill and Jane both work at the same place and bump into each other in the lunch room almost daily.        

See, Bill started it, that's why Jane came into the store. Jane really has her eye on that new CD player... like Bills.  Any sales person will tell you that I could have sold Jane that CD player and 4 new  speakers, had her 500 bucks and had her out the door in about 15 minutes, or less.  So why didn't I you ask? Because the sales business was pretty boring when you weren't waiting on someone, and since Jane and Bill are friends, somewhat competitive too I would guess, I knew that what I was about to do would, besides being the honest thing, create a domino effect of pure entertainment over the next several months as Bills superior male intellect goes up in flames trying to keep up with Jane.        

Back to Jane's car stereo.  You know she tried to buy the in-dash CD player and 4 new speakers.  I spent some time with Jane.  Jane decided to augment her existing system by adding a sub woofer in the trunk, and a couple of other things.  We decided that the place to start would be in selecting the amplifier to run the sub woofer.  Compromise in Quality is out of the question, yet the BEST sub woofer amplifier cost almost 500 bucks so obviously that was out of the question for now.  We selected a good high quality amplifier that gave a clean 100 (real) watts.  It would be ideal for running a sub woofer at a volume that would serve to augment the factory stereo and later on be used as a mid and high frequency amp.  That was 200 bucks. Then we built a no compromise sub woofer enclosure specially engineered for her car.  That was 150 bucks.  We selected an EFFICIENT 10" woofer with a lower power rating instead of an INEFFICIENT by comparison 10" woofer with a very large power rating.  This was 60 bucks.  Then we selected a pair of tweeters from the separates display.  They were 50 bucks.  The rest went for an amp install kit, and a line-level adapter to convert the rear speaker signal into an RCA type adapter that could feed the amplifier.        

We installed the 10" woofer into a band pass enclosure which we designed for Jane's needs.  Jane's 10" woofer would be joined by another 10" woofer at some future point making her box become isobaric.  This meant the enclosure had to be designed to work both ways and it does.  We then installed the amplifier and augmented the front dash speakers by adding some tweeters.  Later we will replace the dash speakers with a mid-range and eventually add the midbass drivers to the front doors. When we wired Jane's car, we installed passive crossover components on her front and rear factory speakers.  We used 99uf 200 volt capacitors on the dash speakers and 200uf caps on the rear speakers.  The lower value blocks more bass so we choose this value for the fronts since they are small 4" speakers.  The back speakers are 6.5" which will play lower, so we didn't need as large a capacitor.  By installing these passive crossover parts, we have effectively removed the low bass from her speakers, and as a result increased their power handling, and reduced their distortion.        

In an effort to give the most audible difference for the buck, we removed the rear speakers from Jane's factory stereo, and hooked them to the new amplifier.  We then bridged the sub woofer across both channels and used an additional passive crossover component called an inductor (coil) to remove the mid and high frequencies from the sub woofer.  Sub woofers should only play bass, you should never hear voices from your subs.  In doing this, we have effectively raised the SPL (sound pressure level) in Jane's car by a very noticeable 18 dB!        

By removing the rear speakers from the factory head unit, we decreased the amount of work it must do, and increased it's performance slightly.  By installing tweeters on the front dash speakers and adding crossovers, we increased the sound quality and performance by leaps and bounds.  By using a quality amplifier turned down slightly, we improved the performance of the rear factory speakers by at least 100%!  In fact, if you sat in Jane's car right now and listened to the radio, and than sat in Bill's car and did the same, you would be shocked to hear very little difference.  Except that Jane's car gets louder and has a more solid sound coming from the rear.  Last but not least, by installing the perfect sub woofer design in Jane's car the sound is now full, deep, rich, and powerful.  Jane is very pleased.        

A few days later in the lunch room, Bill and Jane get together and he asks if she got her CD player yet?  She informs him that she decided to wait on the CD player, and bought a sub woofer and some other little things instead for right now.  Bill jump in and says yea, he is going to get one of those next, soon as he saves up the money.  Bill and Jane go out into the parking lot and Jane invites Bill to take a listen.  Bill was in a bad mood for the entire remainder of the day.  A week or so pass, and by now every employee at work has asked Bill if he has heard Jane's system.        

Bill can't take this anymore, so long before originally planned, bill arrives at the stereo store.  "I want a sub woofer, and make it a damn big one!", Bill exclaims.  Bill and the salesperson haggle around for an hour or so, and Bill finds himself in somewhat of a compromised position.  What he wants and what he can afford are no where close.  Bill draws the line somewhere down the middle and buys a sub woofer and amplifier to run it.  Bill has a box with 2 12" subs off the floor and the same size amplifier as Jane.  Bill would have agreed to get a custom box built, but he didn't want to wait.  Another week of humiliation would be too much to stand.  Bill spent another 500 bucks.        

Bill's sub woofers are installed, and a passive crossover between the amplifier and the subs.  Since bill used the full power from the amplifier to drive his subs, and the 10 watts or so per channel from his CD player to drive everything else, guess what?  Bill's car is all bass.  Every time Bill turns it up the bass overwhelms the rest of the music, and you can't even tell what songs are playing.  But Bill has more bass than Jane, so he receives his vindication.        

About a month or so pass and the general consensus at work is that Jane's stereo still sounds better than Bill's.  Even Bill admits that it does.  Then Bill makes his next move... Bill adds a second amplifier to run the mids and highs, because his CD player doesn't have enough power.  Bill buys a small 4 channel amplifier of good quality, with a built in crossover, and has it installed on his 4 new speakers.  Now Bill his smiling big time! His stereo really sounds bitchen now.  The amp only set bill back another 179 bucks.  Lets see now, that makes 1179 bucks for old Bill.  While bill's system is a little louder than Jane's, and a little more sparkly, and a little more dynamic, you still can't sit in both cars and say one is better or worse than the other. Jane's system is a little smoother, a little better balanced, and the bass is tight and accurate, making Jane's system actually more musical, which is what Jane wants.  Several more months pass and the issue fades away until Jane makes her second purchase, the in-dash CD player she has been patiently saving for.  It was easy for her to wait, because her car stereo already sounds good. Jane buys a CD player.  She even choose a better model than the one she originally looked at because of the sale!  Yes, a slightly nicer one than Bills, unfortunately.          

We install Jane's CD player, and her system simply came  alive.  Everything it did well before it does better.  Because we have taken car to keep Jane's system balanced, and put separate  tweeters in a different location on her dash, Jane is now hearing the music presented in a large dimensional stage with precise  imaging and depth.   Bill, with his new dash speakers cannot achieve this performance because of the location.  The most amazing thing that happened in Jane's car was the BASS improved dramatically.  Jane's bass is now as loud as Bill's was and sounds much better.  Funny thing is, she is only using one 10" woofer!  Since the new CD player we sold Jane is a high power model similar to Bill's, we gained a large increase in performance from the factory dash speakers due to the increased power and lower distortion of her CD player. Since the front speakers got louder, we turned up the volume on the rear amplifier a little to maintain balance.  This also increased the bass proportionately.        

Yea, Jane and Bill, by now all the salespeople are aware of the situation between Jane and Bill, and anxiously huddle around to hear the latest each time one of them leave.  Jane's stereo is audibly superior to Bill's, and so far has cost less money. Jane's stereo has been audible superior to Bill's since day one.        

I don't need to tell you that Bill is in a bad way trying to figure out what he can do to improve his stereo without spending more money.  What can Bill do?  Gee, Bill bought 4 new speakers, and amplifier to run them, a sub woofer, an amplifier to run that, and a in-dash CD player.  Bill is done.  There is nothing fundamental that bill can do to improve his stereo without getting rid of something he already has.  Unless bill want's to spend big bucks on digital processing accessories to act like a Band-Aid to smooth over some of the rough spots, Bill is done.        

Well, Bill's not done.  Bill is now highly motivated.  And you thought Fred had it rough.  Bill rearranges his priorities and sells some non stereo related things that he owned.  Bill buys a bigger sub woofer amplifier.  Bill sells his original sub amplifier at a huge loss.  Bill now has more bass.  Bill cannot use all of the power his new amplifier has because his box starts to make the woofers flop around.  The box is a generic design, and does not maximize the acoustics of the car like Jane's box. Also, the mids and highs start to get lost again when Bill turns the bass up too loud.  Never the less Bill has something new again, and lives with it for awhile. Bill buys a BASS ZONE CD to really push his system, and blows a woofer.  That's OK, Bill didn't like those woofers anyway, the flop around when you turn it up.  Bill buys 2 new woofers that are a stiffer compliance. Bill didn't realize that the new woofers have a different quality factor than his original woofers that came in his box.  The new woofers require a different size box, and need a different size port to go with it.  The new woofers which are in the wrong box, play higher bass notes much louder than the old ones, and play lower notes much quieter than the old ones.  Bill's new bass is loud and high, with no deep bass extension.  This made bills bass CD sound differently than it used to.  Some songs sounded better, and some sounded worse.  One track in particular was Bill's favorite, it had a pounding thump that made your hair vibrate.        

After work one day, Bill and Jane ran into each other in the parking lot and started to chat.  Eventually Bill decided he would like to hear his Bass Disk in Jane's car.  They hopped inside, and Jane started the car.  She popped the CD in the player and turned it to Bill's favorite track.  The loud pounding thump Bill was used to hearing was now a tight clean kick drum, which until now Bill always thought it to be... well... not sure. Then Bill's eyes lit up, and looked at Jane.  The console and the rear view mirror were starting to shake.  Not buzz, but shake! There was a super low synthesizer playing behind the kick drum, generating some 28 cycles tones.  The bass actually squeezed you a little.  Bill was flabbergasted.  Bill got back in his car and did the worst thing he could ever have done in regard to his stereo.  He played the CD.  There was no synthesizer at all. Bill's head sinks down to the steering wheel and suddenly the total that he'd spent to date popped into his head, 1800 bucks, and he lost it.        

To wrap up a long story, Jane having had so much positive attention as the result of her stereo's performance, decided to Finnish the system.  We sold her the high quality  midrange speakers for her dash, and some 5.25 inch midbass drivers and installed them in her door panels.  We then replaced the rear speakers with a pair of 5.25 inch midbass drivers, and installed a pair of tweeters on the rear deck next to the midbass speakers. Now Jane has eliminated all of her factory speakers.  Next we took the amplifier that was running her sub and moved it to the front and rear speakers.  We then replaced the sub amplifier with a larger one, and added a good active crossover.  The sub woofer cabinet was re-fitted and re-tuned to accommodate the second 10" woofer making Jane's Box isobaric.  Jane's bass now goes down to 20 Hz.  Before it was hitting just below 30 Hz.  Jane's stereo is now of competition quality in both sound, and appearance.  Bill is screwed, because he buried himself in his system and can't sell it until it's paid for.        

This has been one of the most common scenarios I've seen as a sales person.  It is in fact the motivating factor behind writing this book.  Remember it's not how much money you spend, but how you spend your money.  And, if left alone to purchase your first system without the knowledge of experience, you will fail and find yourself in Bill's shoes.  Jane's stereo has been a constant source of pleasure since day one.  Bill's stereo has been a source of pleasure and an even bigger source of stress, ending up solely as the later.        

In the next chapter we will be looking at various system layouts which yield a balanced high quality output.  You may use this as a guide for your future reference.

Tovább »

Chapter four

Chapter 4

Dispelling the myhts

In this chapter you will find out the truths about car audio components, and their ratings.  You will find out what you do and don't need.  In the car audio industry there are a wide variety of manufactures, hence a large selection of similar products. How do you know which one to buy when there are 6 variations of the same thing?  By the end of this chapter you should know.

AMPS        

We will start with amplifiers since they are the most common ingredient found in after market car stereos.  Amplifiers for cars all share the following similarities:  They all run on 12 volts DC and they all amplify a single and send it to your speakers.  90% of all car amplifiers will put out more power and or less distortion when the car is running.  The reason for this is because your car's alternator raises the voltage from 12 VDC to 13.8 VDC. This concludes the similarities between car amplifiers.  Amplifiers range in size from 12 watts per channel to around 200 watts.  Smaller amplifiers are often called "Power Boosters", some even have equalizers built in. Larger amplifiers are often referred to as "Big Amps", although you probably could have got that one.

Amplifiers can be divided into two main groups and they are Group 1 - DECENT and Group 2 - CRAPPIE.  What is it that decides which is which?  Is it size? No.  Is it price? No.  Is it how much power it claims to have? No. Ahhh, is it the color?  ...No. In fact it can be difficult if not impossible to tell if you don't know ahead of time.  The answer is: How it is marketed.

WATTS        

Amplifiers that are mass marketed through large electronics supermarkets, and mail order catalogues are designed to make their manufactures and dealers money, not to necessarily sound good.  In this market price is what sells product, and the reason for that is simple enough.  If your product sits on a shelf in a mass merchants store next to 4 or 5 other products just like it, what is going to make the customer choose yours?  What you print on the box. Since there are no qualified salespeople to help you choose the right one, you are left to read each box carefully and decide.  The combination of what you read and the asking price are the determining factors.  A crappy amp and a decent amp are rarely sold in the same place and here is an example of why.  A crappy amp and a decent amp both sit on a shelf side by side. Both amps are the same physical size.  The crappy amp has the following specs printed on the box:        

200WATTS X 200WATTS MAX POWER  Frequency Response 20-20K Not more than .7% total harmonic distortion @ 1 watt both channels driven.  
REGULAR EVERYDAY LOW PRICE 9.00 
NOW .95 with 90 day warranty.

 

The decent amp has the following specs printed on the box:

        40WATTS X 40WATTS  RMS From 20 - 20K @ .07% THD.  9.00

Now judging from this information you would choose the crappy amp.  It has more power (way more power) and cost less, plus it's on sale.  FRED fell into this trap too, and so do about 500 people every day just in this city.  The truth is that the bottom amp, the decent one, is FAR better than the crappy amp.  It has FAR more power, and the difference in sound quality cannot even be compared.  How can this be you wonder?  Both manufactures have listed specifications for their amplifiers that are within the boundaries of the law.  One has stretched it to the limits of the law, and one has slightly under rated theirs.  This is the difference between the two types of amplifiers.  It is easy to see why the better of the two products are not sold in mass merchandise marts, and why the others are not sold in specialty shops. 

A simple guideline to remember is the "DOLLAR PER WATT" theory.  A decent amplifier should cost MORE than one dollar per watt.  If you find an amplifier like the one in the sample above, that is less than a dollar per watt, don't buy it.  The sample above calculates out to 25 cents per watt.  The irony of this is that the second amp is actually LESS money per watt than the first.  If you take the REAL watts that each puts out the figures are like this:  First amp total REAL watts is 50.  That's .00 per watt.  The second amp total REAL watts is 160.  That's a

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.55 per watt.

RATINGS        

For those of you who demand more of an explanation on why ratings vary so much, the law does not require enough information to be printed on the products rating.  And what information the law does require most people don't understand anyway.  The first of the two amplifiers was rated under NON-REAL conditions in a test lab connected to a "dummy load" rather than a real speaker. In the lab, under ideal conditions, the amplifier was tested to have 50 watts.  Then they found if they use a tone rather than music the power doubled,  easy to understand since the amp is only playing one note instead of combinations of 20,000 notes. Then they discovered that if they raise the voltage to 15 or 16 volts the power doubled again.  Then they discovered that if you let the amp sit with no signal going to it, and than burst it with one note for a millisecond, the peak (MAX) measured higher still!  Now the power supply and most of the other parts in the amplifier are getting so hot that the amp is starting to smell, so they found out that if you spray freon on the amplifier and keep it cold, the voltage could be increased to 19 volts before smoke rolls out of it.  So that's what they so, and however high the power meter says just before the amp smokes is what they print on the box.  The second of the two amplifiers was rated under simulated worst case conditions with low voltage (12 VDC) across the entire musical spectrum with no distortion.  A rating that will be accurate for the life of the amplifier even if it is never shut off.  That's the difference.

FANCY WIRE        

So does all this fancy 1.00 per foot speaker wire make a difference?  Yes and No.  Yes it makes a difference, and No, you probably won't hear it.  On a audiophile grade system you can hear a difference and the investment in premium wire is usually worth it.  In a car, however, the noise floor will mask any of the additional detail gained from the use of fancy wire.  And, most car stereos, unless someone like myself does it, aren't up to par enough to benefit from it.        

You can think of fancy wire like buying fancy high performance spark plugs for your car.  Only your car has worn valves which leak oil down onto the plugs and keep them about half fouled out.  You car runs exactly the same as it did with the stock plugs.  Point being, if your just throwing together an inexpensive car stereo you wont hear any difference from that 5 foot piece of monster size wire you hooked to your sub woofer.        

Why is there so many sizes and types of wire available? Because people are buying it.  Basic speaker wire consists of between 12 and 16 gauge stranded copper.  It is always "Polarized" or labeled for plus and minus.  The next step up from this would be oxygen free copper wire, with more strands.  When an amplifier is hooked to a speaker via a piece of speaker wire, the speaker AND the wire become the load.  Long lengths of thin wire can actually add resistance to a speaker and increase the load to the amplifier.  This is not good.  The longer the distance between the amplifier and speaker, the bigger the wire.        

Usually it is hard to get a speaker very far away from an amplifier in a car, which is why 12 gauge wire is acceptable for any car stereo system.  High performance speaker cable will have more strands than basic speaker wire, which means it will have less resistance.  If you use a high performance speaker wire, it is acceptable to use 14 gauge throughout.  14 gauge wire is smaller than 12 gauge.  The numbering system is backwards.        

In a high end stereo system, high performance cable sounds better for a couple reasons.  The increased number of strands in the wire decrease the resistance and allow more current to hit the speaker.  The audible difference is a tighter, stronger bass. The insulation that is found in most high performance cable is also different.  A typical material used is Teflon.  When you place an insulator directly on a conductor, such as wire, the magnetic fields created as the voltages change create capacitance.  The capacitance or interaction between the conductor and insulator will have a audible effect found in the higher frequencies.  The audible effect is said to add harshness to the music.  High performance speaker wire and cable minimize this effect.        

The same principle applies to patch cords (RCA CABLES) as well.  Primarily due to the added shielding, premium patch cords are almost always an audible improvement in a car stereo system. The higher quality means better connectors, and stronger thicker jackets.  I recommend that no one uses the very cheapest patch cords available.  One pull and the wire inside stretches where you can't see it and you're stereo will intermittently sound bad from that point on.  The difference between a 6' generic patch cable at 5.00, and a high performance cable at 25.00 is money well spent.

FANCY SPEAKERS        

When purchasing car speakers i.e. 6x9's, door and dash speakers, there are two options.  One is to use speakers designed to replace the original factory speakers in the factory locations.  The second is to use separates, and have them custom installed in your doors, dash, or where ever needed.  The later will not necessarily sound better, because it relies completely on who does the custom install, and how they do it.        

The most common difference between a factory car speaker and an after market one is that the after market speaker will usually have a separate tweeter.  This is referred to as a two-way speaker.  There are 3 and even 4 way speakers available also, but whether they sound better than a two way depends on your ears, and personal taste.  Just remember that MORE is not BETTER in audio, its just more complicated.  I personally lean towards a two way speaker because I like the sound better.        

The point I want to make about fancy speakers is that while they are great and everything they do not automatically improve the sound quality.  The way they are installed, particularly in a custom job, is in my opinion responsible for 75% of the sound quality that they will produce.  A PROPERLY INSTALLED FACTORY OR INEXPENSIVE SPEAKER will ALWAYS sound better, distort less, and get louder than an IMPROPERLY INSTALLED 200.00 after market model.  That is the real secret to good sound, so place your emphasis on getting a speaker that fits properly and have it installed properly.  Later on when we reinstall Fred's stereo, I will show you in detail how to properly install one. SUB WOOFERS        

At this time, lets apply the same general gist of what I said about fancy speakers, and add that BIGGER IS NOT USUALLY BETTER.  I consistently get MORE bass IN THE CAR with one ten inch (properly installed) sub woofer than the car came in with when it had two fifteen's in a huge box.  Implementation accounts for 95% of the bass a woofer delivers, not the woofer itself. In a later chapter we will discuss how real good sub woofers are built, and the many differences between good boxes and bad boxes.

HEAD UNITS        

A head unit is the industry nick name for a AM/FM Stereo cassette deck or CD player.  It is possible to obtain reasonable to very good sound from the FM section of most head units. Typical Frequency Response on FM is 30Hz to 16KHz or so.  What makes a head unit start costing money is the cassette deck portion of it.  There are only a few ways to make an FM tuner, but there are dozens of gadgets and features in cassette deck mechanisms.  The most crucial to the sound quality is the cassette head.  This is commonly the most expensive part of any cassette deck mechanism.  In addition to sound quality, a cassette head is also responsible for the frequency response when you listen to taps.  The inexpensive decks only go down to 50 Hz, so there is NO deep bass at all.  Mid priced cassette head units will usually go down to 30Hz which is adequate for good bass response in a car.  Some high priced cassette decks go down to 20 Hz.  Most store bought cassette tapes do not have the fidelity to take advantage of the high priced decks.  If, however, you properly record CD or LP's onto high quality metal cassette tapes, you probably will be pleased to know your tape deck sounds like a CD player.        

The best value sonically and in every other aspect is the in-dash CD player.  Even an inexpensive model which cost less than a mid priced cassette deck, will sound superior.  It's almost hard to get real carried away on a sub woofer design unless you have a CD player.  In general a CD player will have LOWER and TIGHTER bass than a cassette deck. That's what you want.  It has always been easier for me to get great performance from a sub woofer when the source is a CD player.

CROSSOVERS        

Generally a confusing topic that complicates the buying experience, but a requirement in all good car stereo systems.  No matter what you will have a crossover network as part of your stereo, the question will be what kind, and where will it be. Starting with what kind, there are two main types, active and passive.  Finishing with where they go, depends on what type. Active crossovers may be found in the circuit between the head unit and the amplifier, and is sometimes located in the amplifier itself.  Passive crossovers may be found in the circuit between the amplifier and the speakers.  Passive crossovers must be made from large heavy duty parts to accommodate the power that goes through them.  For this reason they can be expensive (if properly designed) and since they add resistance to the speaker at selected frequencies, heat is generated, and some power is lost. Active crossovers are the opposite in that respect, as they consist of a few circuit chips, and create no heat.        

If you intend to design you car stereo using only one two channel amplifier to run everything (sub woofer included), you will have to use passive crossovers.        

If you use a multi-channel amplifier with built in crossover(s), you will not need any passive crossovers.        

If you intend to run two or more amplifiers, you will have the option of running either active or passive crossovers or both.        

To keep life simple, I recommend when given the choice, use an active crossover, and buy the one with more adjustments/features.

In Fig. 4 there are two sample crossovers.  They are active or sometimes called electronic crossovers.  The smaller one on the left is the basic minimally equipped model.  The two switches are for make coarse adjustments in crossover frequencies (points). The model on the right has some very important features which are:        

A) Variable level controls to adjust the volume (gain) going to each amplifier.  This is a major asset to properly balancing a system.  Even though each amplifier has an input level (gain) control on it, the additional controls on the crossovers allow for proper impedance matching.  Proper impedance matching has the audible effect of making the sound warm and rich, or lean and cold.  Personal taste, type of equipment, and acoustics of the car determine what impedance sounds the best.        

B) Infinitely adjustable crossover frequency.  Allows you to adjust the crossover points with exactness, and lets you create a gap between the high and low frequencies to counter act the cabin gain at peaks that fall in that area.        

C) Phase Switch for the low out.  Creates the same effect as switching the speaker wires plus for minus on the sub-woofer. This is not essential, but it can save several hours of your time.                

In the next chapter we are going to design a high quality sound system in incremental steps for people on a budget. Consider it a simple guideline for making your first car stereo purchases.  Be aware that there are dozens of ways to do the same basic things in car audio, therefor the following system is only an example of something that will work well.

Tovább »

Chapter three

Chapter 3

Three men digging

The largest misconception that I run into regarding bass is that free-air sub woofers do not need any enclosures.  If we start there we should be at the heart of the matter.      

If you take a "free-air" sub woofer hanging from a string in free air and play it there will be NO bass.  The industry term  "Free-Air" is obviously... misleading.  To understand exactly why this is let's take a deeper look at how speakers generate bass.  In Fig. 2 we show you representation of a sound wave as seen on an oscilloscope.

 

Sound waves (or any type of radiation) consist of 2 main parts.   A positive section and a negative section.  When a woofer cone moves OUT the POSITIVE part of the sound wave is made.  When a woofer moves IN the NEGATIVE section of the sound wave is made.  These two steps complete the cycle, and the process is repeated.  If for example the cycle repeats 60 times in one second, you will hear a high bass note.  If the process is slowed down, and the cycle repeats itself only 25 times in one second, you will hear a very low bass note.  This process is often referred to as "cycles per second" or "Hz" which stands for "Hertz" which is the same thing.  Remember the human ear can detect sounds as low as 20 Hz,  and as high as 20 KHz (Kilo Hertz).           

In Fig. 3 we have shown how the process of cycles are related to a speaker.  The front of the woofer creates a positive wave front and the back side of the woofer creates a negative  wave front.  BASS only happens when these two wave fronts are kept apart.  If the two wave fronts are allowed to collide, there will be no bass.  This is called CANCELLATION.

To help you better understand cancellation, let me compare  the cycle process to digging holes.  Lets get Fred to dig the holes!   We are going to compare the lowest bass note we can hear, 20 cycles, to hole digging.  We have assigned Fred the task of digging 20 holes.  Each hole is to be dug in a straight line some 40 feet apart.  Fred begins to dig.  Are you digging yet Fred? He responds; Uh-huh...  Are you positive?  Yes I am positive!  Yes, you are!  And we will be negative.  So Fred is  digging holes which represent the wave fronts coming off the front of the speaker, the positive half.  If Fred gets all 20 holes dug he gets to hear a great big bass note! 

Fred finishes the first hole and looks at us funny.  "Aren't you going to do anything?" he exclaims.  "Yea, Fred, we also have to dig 20 holes, but we can't start until you finish!"  That's the way the cycle works.  "Go down there and get by the spot where you're going to dig the second hole... you can start digging again as soon as we're finished!"  Fred takes off walking... Quick, help me start shoveling this pile of dirt back into Fred's hole!  Hurry up, he's almost there.  With great finesse we managed to fill the hole Fred just dug clear back up to the top.  You can't even tell there was a hole!  This is great isn't it?  Fred stops and yells back to us that he is ready so we walk over to meet  him.  Stopping a few feet away, there is a pause and Fred starts digging his second hole. 

By this point it's getting hard not to crack a smile, but somehow we manage.  Fred finishes the second hole, and leaves to start the third one.  We fill the hole again while he is not looking.  About an hour later Fred completes his last hole, and sits down on the grass.  "Well, let me hear the bass note you promised!" demanded Fred. Sorry Fred, it only works when you have 20 holes straight in a line, and I only see one hole here. "What?", he shouts!  Yea, take a look!  We filled in all of the holes one at a time right after you dug them!   That's because we're Negative today, and what you've just experienced is called CANCELLATION!          

Fred didn't get off on our little joke very much. Bound and determined to hear that giant bass note we promised him, and wanting to even the score a little, Fred returned with a large wooden box.  Fred put us in the box, and sealed it up real good!  He then began digging 20 new holes.  When he finished he was over joyed to look back and see 20 holes in a straight line.  He shouted from the other end "Well where is the note?"  Come back here and let us out Fred, then I'll tell you...  "You won't try to fill in my holes will you?" he asked.  No Fred, just open the door please.  Fred unlocks the door, and we exit.  Anxiously Fred asks about the note.  Come on Fred, it was just an illustration! Poor Fred.        

The technical explanation for cancellation may be phrased like: "Your woofers are 180 degrees out of phase!"  That means we were 180 degrees out of phase with Fred.  You see, I didn't mention that we were required to move the exact amount of dirt as red, and each time the same distance apart.  If we had only filled each hole 1/2 way with dirt, and shoveled the rest onto the grass, we would have been only 90 degrees out of phase with  Fred.  Fred could have heard his bass note half as loud, since all his holes are half full. 

By putting us in a box, Fred was able to TRAP us a keep us from canceling his holes.  Therefor the purpose for a box is to eliminate cancellation and thereby permit low frequency information (bass) to exist.  The moral of this story is that for a speaker to have bass, it must be in a box, or in some kind of baffle that is large enough to delay the back- wave so as not to be out of phase with the front wave.  "Boxless"  woofers do not exist. The term Free-air & Boxless was meant to mean you can mount woofers in a baffle board located against the  back seat inside your trunk rather than in a box placed in your trunk.  If done correctly, your trunk becomes the box and traps the back waves of the woofers, while the front waves come through your back seat.        

The difference between a "Free-Air" woofer and any other kind is a rather gray area.  In general a Free-air woofer will be lower compliance than usual which means it is stiffer.  Since it will not have a tightly sealed box to push against, the suspension system which controls how the cone moves in and out, must be tighter.  If it were not, the speaker would do something not unlike a fish out of water every time you turned it up loud.        

7 out of 10 "Free-Air" installations that I have seen are done incorrectly. These installs use a board with two holes in it and screw it to the back seat from the trunk.  All around the  board are gapping holes from which cancellation can occur.  These installs perform about like Fred's holes when they're 1/2 full of  dirt.

Tovább »

Chapter two

Chapter 2

Knowledge is power

You know, in chapter one we see a hypothetical but also very typical circumstance.  The first car stereo purchase by a person of average intelligence and equipped with average knowledge about car stereo.  I know the story to be accurate because I was that person once, and remember my first experiences.  I have since that time also been the other person, the salesman.  I specialized in car audio sales for several years and watched thousands of people go though the same experience.

I am still learning new things about audio almost every week, and I own a loudspeaker company where we design and manufacture high end home speakers and high performance sub woofer enclosures for car audio.  If after all these years of experience I can admit that there's more to learn, you should feel more comfortable doing the same

First of all, to finish our story in chapter one, a sequence of events takes place which is all too common for the average car audio consumer.  Lets call our character in chapter one Fred. After about 3 weeks, Fred becomes somewhat displacement about his stereo.  He has taken several critical listens to everyone else's stereos, and while better than 2 he heard, his system just doesn't measure up.  The biggest problem is the bass and distortion.  Not enough of one and too much of the other.  Had Fred purchased his stereo from the stereo store he went to instead of Wally World (or whatever), it is probable that he would have received a better system for around the same money. However probable is not to say always, it could have been the same and in some instances worse.  It really depends on the credibility of the store you deal with and the expertise and experience of their staff.

Trust me, it is better to pay more money for something if it comes with a knowledgeable human to help you use it, and to fix it if it breaks.  Saving 15 or 20 dollars on a car stereo component is usually the same thing as spending twice that if it means being on you own vs. having a store with people you can depend on to help you.  If money is a concern but not a serious deal, than my advise would be to find a small to medium size specialty shop that carries a good reputation with custom work. If they don't do custom work, find another shop.  Find a sales person you are comfortable with and give him a very GENERAL idea of what you want, let him know you trust him, and tell him to do whatever he wants.  Give him a reasonable spending limit, between 1500 and 5000 dollars, and have them call you when they are done. In a specialty shop with a competent reputation, their personal pride will guarantee you get more than your moneys worth, and the system will sound good.

For some of us however, it's the hands on that makes car audio so exciting.  There is a great feeling in listening to a system that you've worked on and as a result of, increased your education in audio by leaps and bounds.  For others it's just being in charge of deciding what goes in and where it goes.  This book will explain some fundamental truths about audio and cars, truths which are not always parallel with everything you read and see in the stereo shops.  Marketing and its necessity for "Buzzwords" does not always display information in an accurate light.

Back to Fred.  Fred's problem is that the bass only sounds good at low levels.  When he turns up the volume everything sounds crappie.  Since Fred likes to party, Fred on several occasions has elected to ignore the fact that it sounds crappie and play it as loud as he could.  Fred simply wants to enjoy his stereo.  The last time Fred did this, one of his speakers blew up.  Fred can't understand how a speaker rated at 150 watts could get blown up by an amp that only puts out 100 watts!  Fred knows he can probably get the speaker replaced but is so frustrated that he now has the urge to go back to the stereo shop and complain about his situation.  Unfortunately the sales people at the stereo shop couldn't find much sympathy for Fred since he took an hour of their time and than bought his stereo somewhere else.

"Fred" was my stereotype customer who was sent over hearing that I was sort of a Maverick in the local audio industry.  I spent hundreds of hours talking to hundreds of Fred's.  In each case it took a crash course in car audio, an injection of knowledge before I could really help them.  Sometimes the injections were too big and I lost a few, and sometimes the injections had no effect at all.  But for those with a strong common sense, the reward was great, they got their stereo sounding great and did it without being sucked into the marketing hype and spending more money than they should have.

Lets just bring Fred over and see what we can do for him. There is a knock on the door.  Guess who it is?  Yup, its Fred. "Hello, are you Steve?" he asks.  We walk out to his car.  It's a 1979 Chevy Nova with a little rust on the drivers door.  The first thing I do is ask him to open the trunk.  He wants me to listen to it first.  I tell him to turn it on and proceed to listen to it.  The first thing I do is turn all of the adjustments on the cassette deck to flat.  Set the balance to the center position, and do the same with the Fader.  I felt sorry for him right away.  The sound was thin, there were no highs, bass was barely there and when you turned it up the sub woofer got muddy.  Fred exclaims that you have to turn the bass up to make it sound bad.  Knowing full well what he meant I asked him why he would want to make it sound bad!  He returns with a dumfounded look and says "Yea but there is no bass."  OK, go ahead and show me I said as he turned the bass up and demonstrated the distortion.  Fred also mentions that this is a lot better than it was before because some guy put the dash speakers on their own amplifier.  Before he did that they were hooked up to the cassette deck and distorted real bad when you turned the bass up.

I asked Fred what kind of amp did he buy for the dash speakers, and he took me back to the now open trunk and showed me.  It was a little tiny thing that used a 5 AMP fuse.  On the case was written 40 x 2 max. power.  He boasted "Yea, and it was only 39.00!"  Fred's system consists of the following: Cassette deck - valued at 219.00 with RCA outputs for rear out. 5.25 Coaxial Door speakers located in the doors.   Value 79.00. A band pass box using 2 10" woofers, value 179.00. An amplifier claiming 200 x 2 max. power, value 179.00. An amplifier claiming 40 x 2 max. power, value  29.00. A 2-way electronic crossover, value  59.00.

Fred, I said, come in here for a minute and sit down.  We need to talk... Fred followed me inside and sat down.  He made himself comfortable and we proceeded to talk.

First of all you don't have anywhere near enough bass, right?  His eyes lit up, and he nods his head while scooting to the edge of his seat.  Amazing how bass effects people isn't it? Your system is letting you down.  Think of it like a car that only goes 56 miles an hour.  Everyone wants to pass it on the highway, and since you have to floor it to go 56 miles an hour your car is always breaking.  I'll bet you've blown a speaker haven't you.  Fred sits up and admits that its happened twice. He continued that someone told him he needed a crossover so that the dash speakers wouldn't pop and crackle with every bass note. He then added that he also had to buy a little amp which he did. So you bought an active crossover and a second little amp to run your dash speakers right?  He nodded.

Fred stops me and insists "What is wrong with it anyway?" Well, I said, your sub woofer is a little under powered, your power cable running from the battery to the amp is barely big enough to service the sub amp.  Adding the second amplifier increased this problem.  The second amplifier isn't any good at all.  The door speakers are crossed over a little high, and could be reinstalled to sound twice as good in the same door.  The frequency response on the tape head in your cassette deck only goes down to 50 cycles. Your box is tuned at 40 Hz and in an effort to hear base you're increasing the gain at 80hz with the bass control which makes the 50hz notes play half as loud which means you really can barely hear them. The small amplifier has poorer specs than the amplifier in your cassette deck, and about the same power.  The gain control on the small amp is set too high, and the gain on the sub amp is also set too high.  The efficiency of the front speakers are 91db at 1 watt, and the sub woofer has an efficiency of 87db (typical in cheaper sub woofer packages).  That means to play at the same loudness the sub woofer needs over twice the power.  The smaller amp has a total of about 30 watts clean, and the bigger amp is only about 90 watts clean.  So you see they play at the same volume.  What you want is for the sub woofer to play at a level 3 to 9 dB louder than the front speakers.  To do that you could double the power of your sub amp 3 times, or get a better sub woofer.  I recommend the later.

The simplified secret to good audio is balance.  You want to hear each note in the music without coloration.  If your system exhibits real peaky frequency response that is coloration.  In Fig. 1 we show a graph of each frequency our ears can hear. The lowest note is 20 cycles per second.  If take the speed of sound and do the math you will see that the sound wave travels over 40 feet before the next wave follows it.  So a 20 cycle note would be 20 waves spaced around 40 feet apart in one second.  The highest note we can hear is 20,000 cycles.  Most music does not exceed 16,000 cycles.  Some people can't hear past 12,000 cycles, and if for example you were to continue to listen to your car stereo when it is distorting for another year your will be one of them.  Fred has now taken the poise of a tree stump, motionless on the couch and in some sort of a daze.   The bomb has been dropped.  Poor Fred, all he ever did is try to buy a car stereo.

If you examine fig 1 again, you see a solid line and a dashed line. At the far left the graph represents 20 cycles. At the far right the graph represents 20,000 cycles.  The solid line lays fairly flat.  That means all the notes will play at the same volume.  This way you can hear all of the notes.  If you look at the dashed line you will see it is very peaky.  The peaks represent notes that are way too loud.  The dips are notes that are way to soft.  When dips and peaks are close together you cannot hear any of the notes in the dips.  In Fred's case, his bass response sounds like it only goes down to about 75 cycles, in other words no bass, when in fact it can reproduce 50 cycles. Fred created a large peak at 80 cycles with his bass control, and than another one at 120 cycles.  The dashed line is an accurate representation of the average frequency response found in cars. Cars have very different acoustics than houses.

Cars are different than living rooms in two ways where stereo is concerned.  The first is that the noise floor (noise around you) is bass heavy and fairly high, around 80db.  A living room can reach a noise floor as low as 40 dB in the evenings. This means car stereos must have more power than home stereos just to sound like home stereos.  The second is that rooms effect dramatically how the frequency response will balance out.  A car is so small that we're not sure if we should treat it like a room or another box.  When you put a box inside of another larger box, an interesting thing happens.  The low bass is amplified. This is referred to as "cabin gain".  So it should be easier to get bass in a car than in a living room you ask?  If you consider only the two different types of rooms, yes.  To make a long story short Fred, what you need to do is leave me your car, and come back outside so I can show you some things about your sub woofer box.

Fred, now carrying the weight of the world on his shoulders slumps a little and than pops up to his feet.  He follows as we go back outside.  At the trunk, we look at his box.  It is about 4 feet wide and 13" tall.  It is crammed as close to the back seat as possible.  The trunk is full of rattles, and the box itself is so thin that it too is creating a very annoying peak at around 400 cycles.  Fred given your two options of doubling your amplifier power 3 times or getting a new sub woofer, I would recommend getting a new sub woofer.  Fred thinks for a minute and asks how much power would that be.  I pointed out that at a rating of 200 x 2 max. power he should get one that is 3200 watts. Fred hits his head on the trunk lid and starts to turn a little white.  Then he realizes they don't make an amplifier that big. If they did, and if Fred could afford it, the cheap sub woofer wouldn't handle the power anyway.

I think its time to let Fred off the hook, before he melts. But not until we bring him back up with a little tease.  I unhook his box and take it into the shop.  In there I have 20 or so different sub woofers on a switcher for demonstration and testing reasons.  I hooked up his box to switch one.  His box has two tens, with an efficiency of 87db.  I demonstrated his box on a good flat CD source on an amplifier similar to his own.  His eyes got big when for the first time he heard 50 cycle notes from his box.  He starts to speak... I hold up my hand and tell him to hold on, and let me finish.  This I said is what your box should sound like.  This is as good as your box can sound.  If you buy an indash CD player you can achieve this sound, if you only listen to your box in this show room.  Fred, your box is a little large for your trunk.  In fact it is so large that it obstructs the air flow in your trunk and does not breath properly.  Fred is amazed.  I then hook up a properly and professionally built box, also a band pass, about 1/2 the size using only one 10 inch woofer.  I let Fred hold the button and tell him to wait till the music plays and then flip the switch.  I explained that what will happen is that the smaller sub woofer will start playing instead of his, all without changing the signal going to the box.  Fred lets the music play for a bit.  I choose Mariah Carey, because there is a rich harmonic bass line centered around 35 Hz. Fred's box begins to roll off at 45hz, and at 35hz is playing only half as loud.  The smaller sub woofer has a reference efficiency of 91db and is ported to achieve 12 dB of gain centered at 38hz.  That makes it well over twice as loud as Fred's box on 35hz frequencies.  Fred flips the switch, and a bass note straight from hell rips through our pant legs.  Fred almost knocked over a speaker setting on the bench just behind him.  Fred was flabbergasted.  It took about 15 minutes for Fred to wind back down and he realized the story about his grandma's bird bath which he was somehow in the middle of telling...  oh well.  Twice as loud with half as much.  This is the difference between a good box and a bad box.  What makes a good box good is design and craftsmanship, and the proper materials.

Just for kicks, and since he asked, I decided to let Fred hear the 28 cubic foot folded horn over in the corner.  He walked over to it and stood directly in front of the horn throat.  I suggested he get over here across the room with me where its safe.  He laughed, and then realized I might actually not be kidding and came over.  "OK," I said, "Now your going to hear all the notes we've been talking about for the past hour."  I reached around behind me and flipped on my vacuum tube frequency generator and let it warm up.  I switched the signal back to Fred's box, and adjusted the dial for 100 cycles.  I turned it up until the box started to hack, and backed it off a little.  "This is 100 cycles," I said.  I then slowly rolled the dial down until the bass reached 45 cycles.  The box was starting to get quieter fast.  I continued to turn the dial until I reached 30 cycles. Now the box was just making a soft puffing sound.  I continued to turn the dial until I reached 20 cycles and either of us heard anything at all. 

A short discussion followed, and then without adjusting the volume, I returned the dial to 100 cycles.  I pointed to the switch and Fred knew what to do.  Pow!  On came the Imperial which was using one 12" woofer at the time.  It was about 15 dB louder than Fred's box.  We had to turn it down. Arriving at the same level that we heard on Fred's box, I continued.  As I turned the dial down the bass kept increasing until at 50 cycles we had to turn it down again. Finally I finished at 12 cycles and you could feel the concrete floor resonate, and when we talked our voices went up and down.  It was a unique twist on the Doppler effect. 

The folded horn had a sweet spot at 28.5 cycles in this particular room so I turned the volume down and adjusted the dial to that frequency.  I then turned to Fred to see if he was ready.  Grinning with anticipation, I turned the volume up to one quarter.  The bass was so deep and so strong that the cabinet doors on the wall started to open.  I increased the volume to one half and the experience started resembling an elephant sitting on your chest 28 times a second.  I held it there until a multitude of things started falling off the shelves, and then backed it off, and shut it down.  Fred was no longer carrying the weight of the world on his shoulders.  If bass were like drugs, and it is, Fred just  about had an overdose!

On the way back out to his car Fred asked me if I could make him a box, and he would sell the one he has.  I told him to sell the small amplifier as well, and come back with two tweeters, and some better power wire.  An hour latter Fred returned with two tweeters and some of the fat red power wire, and a noise filter.        

Pretty soon we are going to take Fred's car stereo and re- install it but before we do that, we need to go over some of the basic facts about car stereo components.  One of the most miss- understood things is BASS and how to achieve it efficiently.  The next chapter will clue you in on how bass works and the most common problem found in car stereo systems, cancellation.  If BASS is Superman, than Cancellation is Kryptonite

Tovább »

Chapter One

Chapter One

A trip to the stereo store

You find yourself at that point when you realize it's a done deal, you have decided to buy a car stereo.  You're feeling pretty good right about now and the best part still awaits....  spending some money!  What a great rush it is to know that you are going to go to the stereo store and buy some brand new stuff!          

You arrive at the front door.  You can see inside and the place looks like it's packed with stuff.  There are three or four sales people running around, a guy standing at the counter and half a dozen people scattered throughout the various rooms.  You walk inside and one of the sales people (who has been watching you from the time you pulled up in the parking lot) comes darting around from behind the sub woofer display and greets you with a great big smile.  "What can I help you find today?" he exclaims!  You reply, "Oh... just looking, thanks" as you shift your look to anywhere else but at him, at least until he leaves.  He smiles  and tells you to take your time, and hopes you will feel free to ask for him if you have any questions.   A programmed greeting followed by a programmed response. Now if the rest of this  buying experience could only be so easy.         

You begin to look around you and notice some BIG woofers over to your left.  Yea, there we go... BIG woofers, lots of 'em too.  You think to yourself, "I'll surely need some of those, 'cause everyone has those!"  You arrive at the display, and square off with it. 

There they are, woofers.  Woofers in a display that seems to tower over your head.  The boxes stacked on top just grazing the ceiling.  Damn, there are a lot of speakers here.  Lets see now, there are 18" woofers on the bottom, 15"  woofers above those, 12" woofers above those, 10" woofers above those, 8" woofers above those, 6" woofers above those, 5-1/4" woofers above those!  Over here we have some 4" woofers, some 3- 1/2" woofers next to them and just above there are a bunch of little ones. I guess they're tweeters, too many different ones to think about right now. 

You turn around and see another display almost as big with just as many speakers in it, only they're all blue instead of black.  To your right, in stacks on the floor are  boxes of more woofers.  They are gray ones.  A little overwhelmed, you draw the conclusion that at least there are  plenty of them, and with some help you'll be able to figure out which ones you want, and maybe even the inside scoop on which color sounds better.          

OK, you browse over to your left and walk around the corner.   Hey what's this?  Stacked up to cover an entire wall, and most of the floor in front of it, are boxes.  I've never seen so many  boxes.  There are boxes of every shape and size, and speakers in the boxes.  Some black ones, some green ones, some red ones, and some blue ones.  You step back a little to take in the whole view, and crash! "Shit, I knocked something over."  Some kind of round tube... hmmm... is there a speaker in here?  What in the world are these?  Bass Cannons!  At least that's what the sign  says. Over here, another sign with a picture of some weird thing shaped like a teardrop with holes in it and fire coming out of the holes!  You stop for a minute, you spin around slowly and realize all of these boxes have holes in them.  You back away, slowly, and find yourself standing kind of out in the middle of nowhere.          

You quickly realize that the dazed look on your face in this open area makes you a prime target for another programmed encounter with the sales person and you haven't finished looking at everything yet.  You spot a little room on the other side of the counter, and make your way into it's safe haven.  Here you see a wall completely filled with radio's and cassette decks, amplifiers ranging in size from about that of a cigarette pack to  a large box of Cheerios.  Behind you a wall of speakers, 6x9's,  4x10's, 6-1/2's, more 5-1/4's, every size imaginable all a little  differently shaped.  Some are full-range, some are 2-ways, some are 3-ways.  You wonder which size fits in your doors, and narrow it down to possibly... twenty.         

Over to the right are three displays with the word "SEPARATES" above them.  Yep, there they are, filled with lots of separate individual little speakers.  The small ones at eye level are playing some new age jazz or something, but there is bass coming out of them.  Crap, they are making the whole room shake!   Well, these are obviously going to be contenders for my car!  You make a mental note to ask the sales person how those little speakers can have so much bass and suddenly what are these down  here?  You kneel down and see a cluster of neat little flat  things with fancy little lights on each knob.  Wow, equalizers!    "Probably if I have some extra money one of these would be the thing to get, you think?", you say to yourself.  You're sure that would be like icing on the cake... you think...          

Soon you stand back up and some shinny stuff catches your eye from the other corner.  You go over there and see coils and coils of speaker wire and red power wire.  Perhaps if I get some of those BIG woofers I saw, I should use this fat red POWER wire to hook them up so I can get more power.  You ponder about wire for a moment realizing that you obviously will need some wire to hook every thing up.  You see more stuff in the distance, wire stuff.  Another wall of "Accessories" awaits your inspection with over 300 separate individual little things like oh lets see...  here's some noise filters, 6 different kinds too.  Hey, your  buddy's car buzzes when the engine runs so he always has to listen to it in his driveway.  In fact, he always runs his battery down too.  If he would have bought one of these, and maybe some of that POWER wire, he wouldn't have these problems.          

Well, now you feel like your getting somewhere.  You have a plan.  So far it includes a noise filter, some of those BIG woofers and some wire.  You know your stereo will be better than your buddy's right off because you're going to have a noise filter to eliminate engine noise, and your going to buy the BIG woofers which are bigger than his.  With that thought, you wonder how much this is all going to cost, so you decide to pick out a hypothetical system and tally it up. That way when the sales person comes back you'll know ahead of time approximately what you want to spend.  You go back to the woofers, then the cassette  decks.  Hey, you wonder if you should get a CD player instead.  You know they sound better but you have a bunch of tapes already.  You see that there is a cassette player that offers a CD CHANGER as an option. It's more expensive than the some of the in-dash CD players, but oh well, let see.          

At this time the sales person feels he has let you flounder around long enough, and the nice couple he was waiting on have left.  He arrives, and you now take the poise of a person who knows what he likes, and wants what he needs...  or something like that.  You ask him how much is this cassette deck, and those BIG woofers across the way and what kind of amp you should get to run everything.  He starts asking you questions regarding what you already have, and finishes 25 minutes later with what type of crossover do you want.  That's one of those things that crosses  every thing over to the car, or no, makes bass come out of the BIG speakers, or ugh no the amp does that.  Frankly you got lost somewhere between "active" and "passive", and too confused to think anymore.          

You thank him, Joe, for his time. You know his name is Joe because it's the last thing you heard as you were walking out the front door.  Eight hundred and fifty bucks, you think as you walk out to your car, holy crap.  Suddenly a mild stress head ache begins to grip you as you pull out of the parking lot and realize that car stereo has become an ultra complicated and potentially super expensive proposition.  The guy (Joe) said he has people spend five grand on systems all the time and those really sound good!        

It takes about a week of asking all your friends what they have before you understand they don't know any more than you do. All seven have different things and different ideas about what is the best, but all agree that theirs are the best.  You begin to realize that it seems as equally important to have certain BRANDS as it does to have good sound.  As a matter of fact, most of your friend's systems didn't actually sound all that wonderful.  Certainly nothing like Dad's old tube stereo on those black speakers in the living room.  Oh sure there's more bass, but  nothing else sounds better.          

You pick up a mail order catalogue and find page after page of the same or similar stuff but with better prices than those you saw at the stereo store.  You spend the next evening circling things in the catalogue, and try to decide if you should order everything.  Problem is, who will install it when it gets here and do we want to wait that long... not me, and hell no!  By now you are about half tempted to forget the whole thing but all this activity in your brain about car stereos is about ready to make you burst!  If you don't spend some money soon on something related to stereo the whole concept could just fade away, so you head to Everything World to get a cassette tape.        

While in Everything World looking for a tape, you observe that they have a Car Audio Department so you wonder over there.  Right in the archway sits a display containing a tape deck, separates (which you know are better since you saw they cost more at the stereo shop) and a sub woofer box complete with amplifier.  A whole system for six hundred bucks!  You turn it on and it actually played!  It doesn't sound too bad either!  Wonder what happens when you turn it up...  Oh look, two sales people are running towards you!  Sounded really bad when you did that.  The  first salesperson to arrive exclaims that someone turned the bass all the way up and that's what made it distort so badly.  The second sales person adds that it only sounds good inside my car, since after all my car is much smaller than the inside of this store.        

At the check out counter you modestly hoist up this giant box full of your complete car stereo system.  That's right, you bought it.  If the other place would have made it this simple you wouldn't be here! The girl hands you a receipt not unlike the kind you get at McDonnalds and tells you to drive around back and set an appointment with the installation department.  Your friendly installation department exclaims that they could get you in tomorrow if you had only a cassette deck but since you want an ENTIRE system installed, it will have to be in 9 days at 2:30  P.M.  And lets see, you'll need one of these amp install kits,  and a GM kit for your dashboard to accommodate the new cassette deck.  That's another 40 bucks, and the labor to install all this will be a mere 178 bucks.  Boy, you never even thought about this.  The good news is that you only have to pay half now.  The rest is due when they put your stuff in.        

Well, minus the minor unplanned financial upset at the install department, you didn't do too bad.  You drive home with your giant box in the back seat signifying your triumphant decision making abilities, a genuine celebration of your independence and your ability to provide... kinda like Daniel Boon after a 3 day hunt walking back home with the big black bear over his shoulder.  Actually you never saw him do that, but why spoil the moment!  You pull in the driveway and drag your kill into the house where you allow it to set in the middle of the floor.  You take a rest and from the safety of your couch, you study it trying to determine the best procedure for skinning it.   Eventually you can't stand the suspense any more, and unpack EVERYTHING. This is the best part of spending money on stuff isn't it?          

After attempting to install various parts of the ominous system in your car, you pull into the installation department for your scheduled install.  The installer takes your keys and grumbles because you just HAD to open EVERYTHING making his job even more joyful than it already is, and your ride takes you away.  You decide to stop for something to eat with your ride to help kill time, and end up telling the waitress all about your awesome stereo being installed at this very moment.  She smiles and pats you on the back asking again what you would like to eat.  Suddenly you hear, no feel, a small bass note coming from the parking lot.  Yes, it is, someone else has a car stereo.  You just smile.        

Six o'clock rolls around and your car is finished.  You anxiously drive back to the install department, and you see your car sitting in the lot behind the install bay.  You go in and ask how everything went?  The installer smiles and says just fine, minus a few missing screws, but he had some more so he just added them to the bill.  You pay the man and almost run out to your car.  You hop in and turn it on.  WOW, not bad!  You find the bass knob on the cassette deck, and crank it up.  Hey there is a loudness button too, to you engage it.  Thank God, bass!  For a  second you weren't sure if there was any or not.  You now begin to rotate the volume control to max.  Approximately half way there, everything begins to sound just like it did in the store when the two sales guys came running.  You quickly turn it down,  and decided to listen to it at a normal level for now.  You can wonder about the rest later, and drive away listening to the radio because you forgot to buy the cassette tape you originally went to Everything World for.

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dual amp installation

Dual Amplifier Car Audio Installation Guide

by:

prowebservices

Having recently connected my dual-amp system, I'd like to document a simple guide for less knowledgable car audio enthusiast's. I see that many people have viewed this guide, and I have reviewed it myself and I have came to the conclusion that this guide needs to be edited to help other users better understand the process. The initial guide that I wrote was not very clear and a little hard to understand, I guess thats why I only have received about 15 or so votes out of almost 1800 views, at the time of this update. I have also noticed that this guide receives about 25 views per day, and I would like all of the future readers to be able to understand this guide better.

 

For this particular sound system, I am using 2 Pioneer GM-5300T's. These particular amps are a very good bargain, around the price range of 0.00 at your nearest wally world, so I'm sure you can find them even cheaper on eBay.

I personally recommend a power capacitor for each amplifier. This will significantly reduce the load on your vehicles battery, although it will not reduce the load on your alternator, infact it will increase the load on your alternator. The capacitors are generally like having another battery on the electrical system, making sure the amps always have the power they are requesting. This helps overall performance of your audio system, but your alternator will have to work overtime to keep not only the vehicle battery charged, but also the two capacitors charged. I must inform you, stock alternators are generally very lousy performance based equiptment, I highly recommend investing in a high-performance alternator, if not, you are likely to be replacing your alternator fairly often. If your headlights dim, or inside lights dim during loud play, you are overtaxing your alternator, and it is only a matter of time before the components inside those cheap, stock alternators fail.

A good CD player is also highly recommended, some players are really crappy, and the quality of your head unit will play a major roll in how your audio is going to sound. My installation included a Sony Xplod Head Unit, with a rated output of 52w X 4-channels. A Dual-Amp Wiring Kit will also be necessary, unless you already have a generous supply of 5 - 8 gauge insulated wire. There are different kinds of Dual-Amp wiring kits available, and depending on the total amount of power you are going to be moving, you should select a kit that best fit's into your wattage range. If both amplifiers have 1000w peak power handling capacities, then be sure to pick up a wiring kit that is rated to handle at LEAST 2000w. The wiring kit will include many different components required for sucessfully installing a dual-amp configuration, such as the proper cables, connectors, RCA jacks, distribution block, fuses and probably some speaker wire.

First Step.

You will need a large power cable if using two amp's, I personally recommend using the biggest wiring available for wiring your entire system. This will improve the complete systems efficiency, not needed, but recommended. Included in the Scoshe Dual-Amp Wiring Kit (1440w kit), is a nice sized 5 gauge power cable. This power cable should include an inline fuse, open the cap and remove the fuse from the holder. This will allow you to connect your entire system up without worrying about damaging components, or draining your battery. Connect the cable to the positive (red) terminal of the battery and run the wire around any components under the hood, ensuring the cable wont be touching anything that gets to hot. This power cable should be the largest cable in the entire system, and any exposed wire that is under your hood should be wrapped with a heat-barrier, also usually included with the wiring kit. Drill a hole through the firewall somewhere around the area where the steering column is, be sure the other side of your drilling plane is free from any important component or wire. Run the cable through the hole, taking up any slack left under the hood. Secure the cable in it's route underneath the hood using wiring ties. Run the power cable to the location of the amplifiers under your own discretion, my wiring is under the carpet and attached together with wiring ties.

From here, you will need to supply power to 2 different components. So at the end of your main power cable you will need to connect a distribution block. One end of the block attaches to the 5 gauge wire connected to the battery, and the other end of the distribution block contains 2 connectors, so you have have a seperate, dedicated power wire for each component that you are connecting. Connect the distribtion block to the 5 gauge wire. Run 2 wires, 8 guage, from the other end of the distribution block directly to the positive terminals of the 2 capacitors.

Grounding.

A good chassis ground is needed, just make sure the ground is good and the connection is tight, a good ground is imperative. Run each wire and connect them firmly to the negative post on the capacitors. Run an 8 gauge from the ground terminals of the amplifiers to the ground.

Speakers.

Make sure to maintain polarity while wiring your speakers! The positive wire is usually red, or has a discolored line running the entire length of it, while the other wire (negative) will be a solid color. Make sure you dont connect several speakers in parallel with each other. Different speakers use different ohms. Other research is required for better understanding of ohms, but for example, if you wire 2 four ohm subwoofers on the same bridged channel of an amplifier, you would actually be creating a 2 ohm load on the amp, which will damage your amp and speakers.

Final Configurations.

Try to resist the urge to tamper with on-board amplifier settings, unless you really know what your doing. Increasing the Gain or bass boost on your amps will make your system hit hard, but will likely damage your system and speakers. Usually factory settings such as the preset gain setting on my amps provide sufficient bass, and increasing an amps Gain past the rated output of your cd player, only adds distortion and adds only very little extra power to the speakers. Try to tweak the CD player settings to achieve optimal listening performance. If you use your system responsibly, you will enjoy alot of great sounding music!

You also may want to verify that the inline fuse on the main power cable is large enough. Check out the fuse ratings for your amp's, if both amps have 30w fuses, then you need to make sure that the main inline fuse is at least a 60w.

 

Thanks for reading my guide, and please vote for it if you find it useful in any way.

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CD players, digital sampling

Digital Sampling

In the audio industry, nothing has revolutionized the way we listen to recorded music like the compact disc (CD). Commercial availability of compact discs and players is a little more than a decade old, and over this time, CDs have slowly replaced the Long Playing (LP) record to the point that music stores (except for the specialty market) carry only CDs and cassette tapes. LPs represent the last vestige of analog music reproduction, where the musical sound wave is recorded continuously.

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Cables

Cables

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Power supply

Power Supply

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Amplifiers and electricity

Transistor Amplifiers

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Speakers

Speaker Sound Coloration

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