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control you'll be running back and forth to change the volume.

If your head unit has subwoofer pre-amp outputs you'll need to test them
using a different tone. I usually test subwoofer outputs at a level
midway between the crossover points. For example, if your subwoofer
outputs are crossed over at 80Hz then you would want to use a 40Hz test
tone. Other than that the procedure for testing subwoofer pre-outputs is
the same as testing front or rear outputs.

Once you've found the clipping level of your head unit it's time to
proceed down the signal chain. If you are using an EQ, preamp, DSP, or
other processor (NOT including crossovers) test them next. Leave your EQ
set the way you usually use it. Hook up the processor and probe all the
outputs of your processors in the same method as you did your head
unit.  You should probe each of the outputs using tones that match the
bands of your EQ. For example, if you have a 9 band EQ with bands at
50/100/200/400/800/1.5k/3k/6k/12kHz you would probe your EQ 9 times,
once with a 50 Hz test tone, once with a 100 Hz test tone, and so on. If
your EQ also includes a crossover you'll need to follow the crossover
procedure.  If any of these processors are clipping you will probably
need to turn down your head unit's volume control or make any
adjustments on that unit that you can. For example, if you are testing
an EQ and you have any bands excessively boosted, try bringing down
that band first. That may be causing your clipping.

To test your crossover you need to probe each output using a test tone
that is midway between the high and low pass. For example, a channel
which is crossed over between 100 Hz and 20 KHz (like a front channel)
would be tested at 9950 Hz. Since you'll be hard pressed to find a 9975
Hz test tone on your CD use the 10Khz tone. For a rear channel crossed
over with a lowpass of 3500 Hz you would use a 1750 Hz tone. As you
again would have problems finding a 1750 Hz tone on a CD use a 2 KHz
tone. For a subwoofer channel lowpassed at 70 Hz you would use a 35 Hz
tone. This one you may find on your CD, if not use 30 Hz or 40 Hz.

Assuming your crossover has level settings you will want to turn the
level for whatever channel you're testing all the way up and probe the
output. Assuming the output is clipping, back the level down slowly
until you see a perfect wave on your scope.

Now it's time to check your amp's outputs. Hook up your amps and play
the same test tones you were using on the crossover. Disconnect the
speakers and then turn the gains all the way up. Probe the first
channel's output. Adjust the gain the same way you did your crossover.
Back the gain down slowly until your wave isn't clipping anymore.

Voila! You are done. You have just effectively eliminated clipping from
your system. If you turn your bass or treble up, or boost up a channel
on your EQ you may introduce some clipping. After major EQ work you may
want to redo this procedure, starting at the EQ.


5.19   Why are kickpanels such a popular location for mounting speakers?
       [ES]                                                        
========================================================================

There is a lot more to mounting speakers in the kick panels than just
equalizing the path length difference (PLD).  Two of which are: on-axis
response, and angling for pattern control.  On-axis response refers to
the fact that most speakers sound best when listened to on-axis, or as
close to on-axis as possible.  Second, after mounting your speakers in
the kick panels you can then angle the speakers to take advantage of
their off-axis response to use output level to overcome any PLD that is
still present. The pattern control I am mentioning is one of the ways a
horn loaded compression driver works very well, they not only use
amplitude to overcome any PLD that is still present they minimize early
reflections that can destroy imaging staging and spectral balance.

PLD can be improved more than marginally when you consider the stock
locations in a lot of vehicles, or the locations most installers choose.
Measure the PLD between tweeters when mounted high in the dash or at the
front corner at the top of the door and you will notice its probably on
the order of 24".  This mounting setup requires a lot of amplitude
adjustment to correct the problems induced by this difference.  The
nearer tweeter is out phase from the opposite side and is arriving much
sooner and with much greater amplitude due to the fact is not as far
away. When all these factors are added together, it is very difficult
for even the most flexible DSP unit to correct.  On top of that, not
many people or installers have access to the necessary tools to properly
set up time delays using a DSP - TEF, MLSSA or other very expensive
time domain measuring equipment are required to do the job properly.

There will always be trade offs involved and deciding which trade offs
to take can be very hard. A small dropout due to phase cancellation will
probably not be noticed by most people but most people will quickly
notice when a vehicle is not imaging properly, and if you can move the
problem to higher frequency where we determine localization more from
amplitude rather than phase differences, it will be much easier to deal
with.  Also, if you minimize the time/phase difference it will be much
easier to correct with amplitude.

Some people complain that kickpanel mounting gives a low sound stage.
However, keep in mind that when any stereo system is imaging properly
the point sources can no longer be localized.  When our brains can no
longer localize the point sources it will then hear things at eye level.


5.20   How can I build custom kickpanels? [MB]
==============================================

Building custom kickpanels for your car is a fairly advanced task, and
requires knowledge (and experience) in working with fiberglass.  Auto
Sound & Security published an article in the August 1996 issue that
covered the basics of working with fiberglass.

This is kick panels in a nutshell.  It takes about 2 days to do this
right, although it is possible to do overnight (a LONG night) in one
vehicle.

Step 1:  Cover base area with plastic & duct tape.

Step 2: Lay fiberglass over the entire area.  Don't worry about getting
the pieces cut to the exact size and shape, you will trim them later.

Step 3:  Build the baffles for your speakers.

Step 4: After the fiberglass has cured, set the baffles (with the
speakers properly mounted into the panels and use a backstrap to secure
the baffle to the panels.  Now, spend some time listening to the car and
aim the baffles until you get the best image and stage in the car.
Note: Take your time aiming the speakers - once you fix the baffles,
you won't be able to readjust the speakers.  You may want to spend a few
days listening to different positions to determine what sounds best.

Step 5: Remove the speakers from the baffle and fill from behind with
self-expanding insulation foam.  This will allow you to mold the baffle
into the rest of the car.

Step 6: After the foam has hardened, sand it to the shape you want the
panel to have.

Step 7: Lay fiberglass over the foam to form the top panel of the kick
panel.

Step 8: After the fiberglass has hardened, sand the surface smooth.
This may require the use of a little bondo to get things perfect.

Step 9: Remove the foam by grinding it out from the inside of the
kickpanel.

Step 10: Cover the panels with carpet, vinyl, leather, fleckstone or
other substance of your choice.

Step 11: Install the kick panels in the car.

Step 12: Install the speakers in the panels.

Step 13: Make speaker baffles from Plexiglas, and grilles.

Step 14: Enjoy.


5.21   What's worse for a speaker, too much or too little power? [IDB]
======================================================================

Problems occur (in everyday operation) when distortion is fed to a
speaker.  This occurs MUCH more often when you are dealing with an
underpowered system - typically the owner will turn up the volume too
much or set the amplifier gains too high to try and get more volume
from the system.  These introduce distortion to the signal - this will
destroy *any* speaker. ((see Section 5.22).)

When a speaker is overpowered, however, it is not nearly as common to
have these kind of problems, so speakers aren't blown as much.  Of
course, it is certainly possible to destroy a speaker (thermally) by
overpowering it, but you'll have a pretty hard time doing this on your
own, especially with standard car audio amplifiers.


5.22   Why is distortion harmful to my speakers? [RK]
=====================================================

Distortion is hard on speakers for two reasons.

Reason 1: Distortion causes the power spectrum to shift upwards in
frequency.  A bass note, when distorted, will have lots of high
frequency energy.  This will cause mid-ranges and tweeters to fry, if
the amplifier is operating full range.  It doesn't harm woofers,
necessarily.

Reason 2: Distortion causes the average power to be much higher.
Typically, a music signal that never clips has an average power level of
1/4 the peak power level for even the most compressed speed metal or
pop.  More dynamic music will be 1/8 the peak level or less on average.
When you clip the amp hard, the average output moves up to the
full-rated output of the amp or more.  The peak to average ratio can be
less than 2 to 1, with the peaks being at double the rated power of the
amp, and the average being at the rated power of the amp or higher.

Thermally, the speaker can handle the average power being 1/4 the rated
power of the amp (little to no clipping), but it will have a much harder
time with the average power being the amp's rated power or more (massive
clipping).  As you might expect, this is pretty hard on the amp, too.

For transients, most speakers can handle a ton of power.  But for long
term signals, the power handling is much less.


5.23   What tools do I need to cut Plexiglas? [PS]
==================================================

A good quality Carbide Tipped Triple Chip saw blade is preferred when
cutting Plexiglas.  This reduces the amount of chipout on the opposite
side of the material and produces a smooth edge.

A Router can be used to cut Plexiglas as well.  The Router should be at
least 1.5 HP or better and with changeable collets for a 0.5" Shank
quality 2 flute Carbide bit.  This reduces the vibration and chattering
when cutting and will produce a more smooth edge.

Since Plexiglas is an acrylic plastic (polymer), heat generated by the
saw blade or router bit when cutting will melt the material and create a
glazed imperfection viewed from the face if you do not maintain a steady
rate of cut.  It is best that when cutting you do a rough cut first,
then do the finished size cut to reduce stress on the cutting blade and
equipment.


5.24   Are there any other special requirements for working with Plexiglas?
       [PS]                                                        
===========================================================================

Check the protective paper covering for any rips, tears or folding at
the time of purchase.  In most cases if visual inspection is not done
at the place of purchase, it's very difficult to prove product defects
or damage done by the seller.

Inspect all surfaces that will come into contact to reduce tearing and
scratching of the protective paper covering and the Plexiglas finish.
Make sure that the protective paper covering remains in place until all
machining and milling tasks are finished.




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