Archive-name: car-audio/part1
Version: 1.9
Last-modified: 05 Nov 93


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+ Frequently Asked Questions with answers for rec.audio.car +
*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*

      0 Introduction and Table of Contents

 This is the FAQ list for rec.audio.car, maintained by Jeffrey
 S. Curtis (stealth@uiuc.edu), with contributions from many
 other people (see the credits section).  This document may be
 freely distributed so long as it remains wholly unaltered.  If
 you have suggestions for improvements to this document, or if
 you fail to understand any part of it, please feel free to send
 a note to the FAQ maintainer or to the author of the relevant
 section.  If you find this document useful, the FAQ maintainer
 would greatly appreciate a note saying what you read and how it
 helped you (it's nice to know what you're doing right as well
 as what you're doing wrong!).  The initials of the author(s) of
 each section can be found in brackets following each question.

 This document is posted once per month to the Usenet newsgroups
 rec.audio.car, rec.answers, and news.answers, and is available
 via anonymous FTP from rtfm.mit.edu in the directory
 "/pub/usenet/rec.audio.car".

 Table of Contents
 ===== == ========

 1 Definitions
    1.1 What do all of those acronyms mean (A, V, DC, AC, W, Hz,
        dB, SPL, THD, ohm)?
    1.2 What is meant by "frequency response"?
    1.3 What is a "sound stage"? What is an "image"?
    1.4 What is meant by "anechoic"?
 2 Electrical
    2.1 My speakers make this high-pitched whine which matches the
        engine's RPMs.  What is it, and how can I get rid of it?
    2.2 What is the best power wire to use?
    2.3 What is the best speaker wire to use?
    2.4 I heard that I should run my power wire directly to my
        car's battery.  Why should I bother, and how do I do it?
    2.5 Should I do the same thing with my ground wire, then?
    2.6 Sometimes when I step out of my car, I get a really bad
        shock.  What is wrong with my system?
    2.7 When my car is running and I have the music turned up
        loud, my headlights dim with the music.  Do I need a new
        battery or a new alternator?
    2.8 What is a "stiffening capacitor", and how does it work?
    2.9 Should I install one in my car? If so, how big should it
        be, and where do I get one?
 3 Components
    3.1 What do all of those specifications on speakers mean?
    3.2 Are component/separates any better than fullrange or
        coaxials?
    3.3 What are some good (and bad) brands of speakers?
    3.4 What do all of those specifications on amplifiers mean?
    3.5 What is "bridging"? Can my amp do it?
    3.6 What is "mixed-mono"? Can my amp do it?
    3.7 What does "two ohm stable" mean? What is a "high-current"
        amplifier?
    3.8 Should I buy a two or four (or more) channel amplifier?
    3.9 What are some good (and bad) brands of amplifiers?
   3.10 What is a crossover? Why would I need one?
   3.11 Should I get an active or a passive crossover?
   3.12 How do I build my own passive crossovers?
   3.13 Should I buy an equalizer?
   3.14 What are some good (and bad) brands of equalizers?
   3.15 What do all of those specifications on tape deck head
        units mean?
   3.16 What are features to look for in a tape deck?
   3.17 What are some good (and bad) brands of tape decks?
   3.18 What are features to look for in a CD head unit?
   3.19 Should I buy a detachable faceplate or pullout CD player?
   3.20 What are some good (and bad) brands of CD head units?
   3.21 Can I use my portable CD player in my car? Won't it skip
        a lot?
   3.22 What's that weird motor noise I get with my portable CD
        player?
   3.23 What are some good (and bad) brands of portable CD
        players?
   3.24 What's in store for car audio with respect to MD, DAT and
        DCC?
   3.25 Are those FM modulator CD changers any good? What are my
        other options?
   3.26 What are some good (and bad) brands of CD changers?
   3.27 Why do I need a center channel in my car, and how do I do
        it?
   3.28 Should I buy a sound field processor?
   3.29 What are some good (and bad) brands of signal processors?
 4 Subwoofers
    4.1 What are "Thiele/Small parameters"?
    4.2 What are the enclosure types available, and which one is
        right for me?
    4.3 How do I build an enclosure?
    4.4 What driver should I use?
    4.5 Is there any computer software available to help me choose
        an enclosure and a driver?
    4.6 What is an "aperiodic membrane"?
 5 Installation
    5.1 Where should I buy the components I want?
    5.2 What mail-order companies are out there?
    5.3 What tools should I have in order to do a good
        installation?
    5.4 Where should I mount my speakers?
    5.5 What is "rear fill", and how do I effectively use it?
    5.6 How do I set the gains on my amp?
    5.7 How do I select proper crossover points and slopes?
    5.8 How do I flatten my system's frequency response curve?
 6 Competition
    6.1 What is IASCA, and how do I get involved?
    6.2 What is USCA, and how do I get involved?
    6.3 What are the competitions like?
    6.4 Should I compete?
    6.5 What class am I in?
 7 Literature
    7.1 What magazines are good for car audio enthusiasts?
    7.2 Are there any newsletters I can read?
    7.3 What books can I read?
 8 Credits


      1 Definitions

 This section contains background information which defines some
 of the acronyms and terminology commonly used in the car audio
 world.  Understanding these definitions is important in order
 to understand the other sections of this document.

    1.1 What do all of those acronyms mean (A, V, DC, AC, W, Hz, dB,
 SPL, THD, ohm)? [JSC]

 "A" is for "amperes", which is a measurement of current equal
 to one coulomb of charge per second.  You usually speak of
 positive current - current which flows from the more positive
 potential to the more negative potential, with respect to some
 reference point (usually ground, which is designated as zero
 potential).  The electrons in a circuit flow in the opposite
 direction as the current itself.  Ampere is commonly
 abbreviated as "amp", not to be confused with amplifiers, of
 course, which are also commonly abbreviated "amp".  In
 computation, the abbreviation for amps is commonly "I".

 "V" is for "volts", which is a measurement of electric
 potential.  Voltages don't "go" or "move", they simply exist as
 a measurement (like saying that there is one mile between you
 and some other point).

 "DC" is for "direct current", which is a type of circuit.  In a
 DC circuit, all of the current always flows in one direction,
 and so it is important to understand which points are at a high
 potential and which points are at a low potential.  For
 example, cars are typically 12VDC (twelve volts direct current)
 systems, and it is important to keep track of which wires in a
 circuit are attached to the +12V (positive twelve volts) lead
 of the battery, and which wires are attached to the ground (or
 "negative") lead of the battery.  In reality, car batteries
 tend to be about 13-14VDC.

 "AC" is for "alternating current", which is a type of circuit
 in which the voltage potential fluctuates so that current can
 flow in either direction through the circuit.  In an AC
 circuit, it is typically not as important to keep track of
 which lead is which, which is why you can plug household
 appliances into an outlet the "wrong way" and still have a
 functioning device.  The speaker portions of an audio system
 comprise an AC circuit.  In certain situations, it is indeed
 important to understand which lead is "positive" and which lead
 is "negative" (although these are just reference terms and not
 technically correct).  See below for examples.  The voltage of
 an AC circuit is usually given as the RMS (root mean square)
 voltage, which, for sinusoidal waves, is simply the peak
 voltage divided by the square root of two.

 "W" is for "watts", a measurement of electrical power.  One
 watt is equal to one volt times one amp, or one joule of energy
 per second.  In a DC circuit, the power is calculated as the
 voltage times the current (P=V x I).  In an AC circuit, the RMS
 power is calculated as the RMS voltage times the RMS current
 (Prms=Vrms x Irms).

 "Hz" is for "hertz", a measurement of frequency.  One hertz is
 equal to one inverse second (1/s); that is, one cycle per
 second, where a cycle is the duration between similar portions
 of a wave (between two peaks, for instance).  Frequency can
 describe both electrical circuits and sound waves, and
 sometimes both.  For example, if an electrical signal in a
 speaker circuit is going through one thousand cycles per second
 (1000Hz, or 1kHz), the speaker will resonate at 1kHz, producing
 a 1kHz sound wave.  The standard range of human hearing is
 "twenty to twenty", or 20Hz-20kHz, which is three decades
 (three tenfold changes in frequency) or a little under ten
 octaves (ten twofold changes in frequency).

 "dB" is for "decibel", and is a measurement for power ratios.
 To measure dB, you must always measure with respect to
 something else.  The formula for determining these ratios is
 P=10^(dB/10), which can be rewritten as dB=10log(P).  For
 example, to gain 3dB of output compared to your current output,
 you must change your current power by a factor of 10^(3/10) =
 10^0.3 = 2.00 (that is, double your power).  The other way
 around, if you triple your power (say, from 20W to 60W) and
 want to know the corresponding change in dB, it is
 dB=10log(60/20)=4.77 (that is, an increase of 4.77dB).  If you
 know your logarithms, you know that a negative number simply
 inverts your answer, so that 3dB corresponding to double power
 is the same as -3dB corresponding to half power.  There are
 several other dB formulas; for instance, the voltage
 measurement is dB=20log(V).  For example, a doubling of voltage
 produces 20log2 = 6.0dB more output, which makes sense since
 power is proportional to the square of voltage, so a doubling
 in voltage produces a quadrupling in power.

 "SPL" is for "sound pressure level" and is similar to dB.  SPL
 measurements are also ratios, but are always measured relative
 to a constant.  This constant is 0dB which is defined as the
 smallest level of sound pressure that the human ear can
 detect.  0dB is equal to 10^-12 (ten to the negative twelfth
 power) W/m^2 (watts per square meter).  As such, when a speaker
 is rated to produce 92dB at 1m when given 1W (92dB/Wm), you
 know that they mean that it is 92dB louder than 10^-12W/m^2.
 You also know than if you double the power (from 1W to 2W), you
 add 3dB, so it will produce 95dB at 1m with 2W, 98dB at 1m with
 4W, 101dB at 1m with 8W, etc.

 "THD" is for "total harmonic distortion", and is a measure of
 the how much a certain device may distort a signal.  These
 figures are usually given as percentages.  It is believed that
 THD figures below approximately 0.1% are inaudible.  However,
 it should be realized that distortion adds, so that if a head
 unit, equalizer, signal processor, crossover, amplifier and
 speaker are all rated at "no greater than 0.1%THD", together,
 they could produce 0.6%THD, which could be noticeable in the
 output.

 "ohm" is a measure of resistance and impedance, which tells you
 how much a device will resist the flow of current in a
 circuit.  For example, if the same signal at the same voltage
 is sent into two speakers - one of which is nominally rated at
 4 ohms of impedance, the other at 8 ohms impedance - twice as
 much current will flow through the 4 ohm speaker as the 8 ohm
 speaker, which requires twice as much power, since power is
 proportional to current.

    1.2 What is meant by "frequency response"? [JSC]

 The frequency response of a device is the range of frequencies
 over which that device can perform in some fashion.  The action
 is specific to the device in question.  For example, the
 frequency response of the human ear is around 20Hz-20kHz, which
 is the range of frequencies which can be resolved by the
 eardrum.  The frequency response of an amplifier may be
 50Hz-40kHz, and that of a certain speaker may be 120Hz-17kHz.
 In the car audio world, frequency responses should usually be
 given with a power ratio range as well, such as (in the case of
 the speaker) 120Hz-17kHz +/-3dB.  What this means is that given
 an input signal anywhere from 120Hz to 17kHz, the output signal
 is guaranteed to be within an "envelope" that is 6dB tall.
 Typically the extreme ends of the frequency range are the
 hardest to reproduce, so in this example, the 120Hz and 17kHz
 points may be referred to as the "-3dB points" of the
 amplifier.  When no dB range is given with a frequency response
 specification, it can sometimes be assumed to be +/-3dB.

    1.3 What is a "soundstage"? What is an "image"? [CD]

 The "soundstage" is the position (front/back and high/low)
 that the music appears to be coming from, as well as the depth
 of the stage.  A car with speakers only in the front will
 likely have a forward soundstage, but may not have enough
 rear fill to make the music seem live.  A car with both front
 and rear speakers may have anything from a forward to a rear
 soundstage, with an accompanying fill from the softer drivers
 depending on the relative power levels and the frequencies
 reproduced.  The high/low position of the soundstage is
 generally only obvious in a car with a forward soundstage.  The
 music may seem to be originating in the footwells, the dash, or
 out on the hood, depending on how the drivers interact with the
 environment.

 The "stereo image" is the width and definition of the
 "soundstage".  Instruments should appear to be coming from
 their correct positions, relative to the recording.  The
 position of the instruments should be solid and easily
 identifiable, not changing with varying frequencies.  A car can
 image perfectly with only a center-mounted mono speaker, but
 the stereo placement of the music will be absent.

    1.4 What is meant by "anechoic"? [JSC]

 Anechoic means "not echoing".  It usually refers to a style of
 measuring a speaker's output which attempts to eliminate echoes
 (or "reflections") of the speaker's output back to the
 measurement area, which could alter the measurement (positively
 or negatively).

      2 Electrical

 This section describes various problems and concepts which are
 closely related to electronics.

    2.1 My speakers make this high-pitched whine which matches the
 engine's RPMs.  What is it, and how can I get rid of it?

 This is perhaps the single most frequently asked question on
 rec.audio.car, and is coincidentally enough the most difficult
 to answer.  But there will indeed be a lengthy answer soon -
 stay tuned.

    2.2 What is the best power wire to use? [JSC]

 There is much debate over the benefit of certain wiring schemes
 (oxygen-free, multistranded, braided, twisted, air core, you
 name it).  However, most people do agree that the most
 important factor in selecting power wire is to use the proper
 size.  Wire is generally rated in size by American Wire Gauge,
 abbreviated AWG, or commonly just "gauge".  To determine the
 correct wire size for your application, you should first
 determine the maximum current flow through the cable (looking
 at the amplifier's fuse is a relatively simple and conservative
 way to do this).  Then determine the length of the cable that
 your will use, and consult the following chart, taken from the
 IASCA handbook (see 6.1):

                           Length of run (in feet)
 Current     0-4  4-7 7-10  10-13  13-16  16-19  19-22  22-28

      0-20A     14   12   12     10     10      8      8      8
    20-35A     12   10    8      8      6      6      6      4
    35-50A     10    8    8      6      6      4      4      4
    50-65A      8    8    6      4      4      4      4      2
    65-85A      6    6    4      4      2      2      2      0
   85-105A      6    6    4      2      2      2      2      0
 105-125A      4    4    4      2      2      0      0      0
 125-150A      2    2    2      2      0      0      0     00

 If aluminum wire is used instead of copper wire, the next
 larger size (smaller number) should be used.  You should also
 consider the installation demands: will you need to run the
 wire around corners or through doors or into the engine
 compartment? These sorts of problems in the car audio
 application require some special care in cable selection.  You
 will want to have cable that is flexible; it should have thick
 insulation as well, and not melt at low temperatures.  You
 don't want to install wire that is rigid and prone to cracks
 and cuts, or else the results could literally be explosive.

    2.3 What is the best speaker wire to use? [JSC]

 Again, there is much debate over the benefit of the various
 schemes that are being used by various manufacturers.  In
 general, however, you will probably want to upgrade your
 speaker wire from the factory ~18 gauge to something bigger
 when you upgrade your amplifiers and speakers.  In most cases,
 14 gauge should be sufficient, with the possible exception of
 high-power subwoofers.  One issue is that different wires will
 have different line capacitances, which could cause the wire to
 act as a low pass filter.  Generally, however, the capacitances
 involved are so small that this is not a significant problem.
 Be sure to heed the warnings above regarding cable flexibility
 and insulation, especially when running wire into doors and the
 like.

    2.4 I heard that I should run my power wire directly to my car's
 battery.  Why should I bother, and how do I do it? [JSC]

 For some components, like head units and equalizers, it's
 acceptable to use the stock wiring for power.  However,
 amplifiers generally require large amounts of power, and
 accordingly will draw large amounts of current.  The factory
 wiring in most cars is not designed to handle large amounts of
 current, and most wires have 10-20A fuses on them.  Thus, you
 will almost always want to run the power line for your
 amplifier directly to the positive terminal of the battery.
 This could require drilling a hole through the car's firewall,
 or at least spending time hunting for an existing hole (the
 steering column is a good place to start looking).  Always
 remember to place a fuse on your wire as near to the battery as
 possible! For various reasons, such as an accident or simple
 wear and tear, your wire's insulation may eventually crack,
 which could allow the conducting wire to make contact with the
 chassis of the car and short the battery through this wire,
 which could lead to a serious fire.  The closer you place a
 fuse to the battery, the more protected you are.  Also, when
 running wire through areas with sharp metal corners, it is a
 good idea to use rubber grommets to provide extra protection
 against tearing through your wire's insulation.

    2.5 Should I do the same thing with my ground wire, then? [JSC]

 No.  In almost every case, the best thing to do is to ground
 your amplifier to a point that is attached to the chassis of
 the car and is as close to the amplifier as possible.  The
 ground wire should not need to be more than about eighteen
 inches long, and should be at least as large as the power
 wire.  The point to which you make your ground connection
 should be an unpainted piece of bare metal.

    2.6 Sometimes when I step out of my car, I get a really bad shock.
 What is wrong with my system? [JSC]

 Probably nothing.  This is usually caused by static buildup by
 rubbing against the seats, floormats, etc., just like walking
 across a carpet in a home.  Shocks which can be felt are
 usually in the kilovolt range, so touching a 12VDC wire isn't
 going to do much to you.

    2.7 When my car is running and I have the music turned up loud, my
 headlights dim with the music.  Do I need a new battery or a
 new alternator? [CD,MO]

 The headlights will dim because of a momentary drop in the
 voltage level that is available to power the vehicle's
 accessories, including the headlights, amplifiers, the engine,
 etc.  This voltage drop can be caused by a very large current
 demand by an accessory, such as an amplifier trying to
 reproduce a loud bass note.

 The first thing to do is to get your battery and alternator
 checked for proper functioning.  A failing battery can place
 undesirable loads on the alternator, leaving less power for
 your system.

 If the power system appears to be working correctly, an
 improved alternator may be required for the large current
 demands of the audio system.  When upgrading an alternator,
 be careful in your purchase, for there are some potential
 problems.  An alternator which advertises a certain output
 level may only achieve that output at very high engine RPM
 ranges, for instance.  Also, the new alternator must be
 adjusted to provide an output voltage within a reasonable
 range in terms of the voltage regulator.

 If you find your car will not start after playing the stereo
 for long periods of time with the engine off, and the present
 battery is in good working order, then another, paralleled
 battery could prevent this embarrassing problem.

    2.8 What is a "stiffening capacitor", and how does it work? [JSC]

 "Stiffening Capacitor" (note capitals) is a trademark of
 Autosound 2000 (see 7.2).  However, "stiffening capacitor"
 (note lowercase), as a generic term, refers to a large
 capacitor (several thousand microfarads or greater) placed in
 parallel with an amplifier.  The purpose of doing so is to
 provide a sort of reserve power source from which the amplifier
 can rapidly draw power when it needs it (such as during a deep
 bass note).  The electrical theory is that when the amplifier
 attempts to draw a large amount of current, not only will the
 battery be relatively slow to respond, but the voltage at the
 amplifier will be a little lower than the voltage at the
 battery itself (this is called "line drop").  A capacitor at
 the amplifier which is charged to the battery voltage will try
 to stabilize the voltage level at the amplifier, dumping
 current into the amplifier.  Another way to think about it is
 that a capacitor in parallel with a load acts as a low pass
 filter (see 3.10), and the voltage level dropping at the
 amplifier will appear as an AC waveform superimposed upon a DC
 "wave".  The capacitor, then, will try to filter out this AC
 wave, leaving the pure DC which the amplifier requires.

    2.9 Should I install one in my car? If so, how big should it be,
 and where do I get one? [JSC]

 If you have a problem with dimming headlights when you have
 your music turned up and the bass starts to hit and the engine
 is running and you don't want to upgrade your alternator, or if
 the transient response of your amplifier is unacceptable to
 you, a stiffening capacitor could help you out.  The commonly
 accepted "formula" for determining the proper size capacitor to
 use is 1F/kW (one farad per kilowatt).  For example, a system
 running at 300W would need a 0.3F (or 300,000uF) capacitor.  To
 install the capacitor, you should not simply attach it to your
 power and ground wires near your amplifier, as it will draw
 very large amounts of current from your battery and could blow
 fuses (or overcharge).  Instead, you should insert a
 small-value power resistor (perhaps one ohm) or a 12VDC test
 lamp in between the power lead and the capacitor, and then
 charge it.  If you use a lamp in series with the cap, when the
 lamp goes out, the capacitor is done charging.  When it is done
 charging, carefully remove the capacitor's leads from the
 charging circuit, being certain not to touch the two leads
 together.  You may then permanently install the capacitor by
 wiring it in parallel with your amplifier (be careful not to
 short the leads!).  Large caps are currently available from
 some audio dealers, such as Phoenix Gold.  You could also try
 electronics shops or mail-order houses.

-- 
Jeffrey S. Curtis - stealth@uiuc.edu <> "Resplendent  in  full  regalia, they
Network Technician - UoI Housing Div <> revel in their role as self-appointed
Proton - Phase Linear - Polk - Sanyo <> critics  of   the   establishment..."
StreetWires - Jensen - Sony - Sennet <> -- INXS _Welcome to Wherever You Are_



******************************************************************************



From Packet: CHANNEL1
Message # 51048                                  Area : 1446  answers
From : Stealth@uiuc.edu                          11-06-93  01:31
To   : All                      
Subj : rec.audio.car FAQ (part 2
------------------------------------------------------------------------------
ÿ@SUBJECT:rec.audio.car FAQ (part 2/3)                                 
Message-ID: <rac-faq-p2-063122Nov61993@uxa.cso.uiuc.edu>
Newsgroup: rec.audio.car,rec.answers,news.answers
Organization: University of Illinois at Urbana

Archive-name: car-audio/part2
Version: 1.9
Last-modified: 05 Nov 93


      3 Components

 This section describes various components that you can have in
 a car audio system, along with common specifications, desirable
 features, some of the best and worst brands, and so on.

 Be aware that there is no standardized testing mechanism in
 place for rating car audio products.  As such, manufacturers
 are open to exaggerating, "fudging", or just plain lying when
 it comes to rating their own products.

    3.1 What do all of those specifications on speakers mean? [JSC,CD]

 "Input sensitivity" is the SPL the driver will produce given
 one watt of power as measured from one meter away given some
 input frequency (usually 1kHz unless otherwise noted on the
 speaker).  Typical sensitivities for car audio speakers are
 around 90dB/Wm.  Some subwoofers and piezo horns claim over
 100dB/Wm.  However, some manufacturers do not use true 1W
 tests, especially on low impedance subwoofers.  Rather, they
 use a constant voltage test which produces more impressive
 sensitivity ratings.

 "Frequency response" in a speaker refers to the range of
 frequencies which the speaker can reproduce within a certain
 power range, usually +/-3dB.

 "Impedance" is the impedance of the driver (see 1.1), typically
 4 ohms, although some subwoofers are 8 ohms, some stock Delco
 speakers are 10 ohms, and some stock Japanese imports are 6
 ohms.

 "Nominal power handling" is the continuous power handling of
 the driver.  This figure tells you how much power you can put
 into the driver for very long periods of time without having to
 worry about breaking the suspension, overheating the voice
 coil, or other nasty things.

 "Peak power handling" is the maximum power handling of the
 driver.  This figure tells you how much power you can put into
 the driver for very brief periods of time without having to
 worry about destroying it.

    3.2 Are component/separates any better than fullrange or coaxials? [JSC]

 Usually, yes.  Using separates allows you to position the
 drivers independently and more carefully, which will give you
 greater control over your imaging.  For rear fill applications,
 however, coaxial speakers will perform fine, as imaging is not
 a primary concern.

    3.3 What are some good (and bad) brands of speakers? [JSC]

 People will emotionally defend their particular brand of
 speakers, so asking what the "best" is is not a good idea.
 Besides, the best speaker is the one which suits the
 application the best.  In general, however, various people have
 claimed excellent experiences with such brands as Boston
 Acoustics, MB Quart, a/d/s/, and Polk.  Also, most people agree
 that you should avoid brands like Sparkomatic and Kraco at all
 costs.

    3.4 What do all of those specifications on amplifiers mean? [JSC,BG]

 "Frequency response" refers to the range of frequencies which
 the amplifier can reproduce within a certain power range,
 usually +/-3dB.

 "Continuous power output" is the power output of the amplifier
 into one channel into a certain load (usually four ohms) below
 a certain distortion level (usually at most 1%THD) at a certain
 frequency (usually 1kHz).  A complete power specification
 should include all of this information, e.g. "20W/ch into 4
 ohms at < 0.03%THD at 1kHz" although this can also be stated as
 (and be assumed equivalent to) "20W/ch at < 0.03%THD".  The
 amplifier should also be able to sustain this power level for
 long periods of time without difficulties such as overheating.

 "Peak power output" is the power output of the amplifier into
 one channel into a certain load (usually four ohms) below a
 certain distortion level (usually much higher than the
 continuous rating level) at a certain frequency (usually
 1kHz).  A complete power specification should include all of
 this information, e.g.  "35W/ch into 4 ohms at < 10.0%THD at
 1kHz" although this can also be stated as (and be assumed
 equivalent to) "35Wch at < 10.0%THD".  Consumer warning: some
 manufacturers will state the "peak power output" rating by
 including the amount of power which can be drawn from
 "headroom", which means power supply capacitors.  They usually
 will not tell you this in the specification, however; indeed,
 they tend to prominently display the figure in big, bold
 letters on the front of the box, such as "MAXIMUM 200W PER
 CHANNEL!!!" when the continuous rating is 15W/ch and the unit
 has a 5A fuse.

 "Damping factor" represents the ratio of the load being driven
 (that is, the speaker - usually four ohms) to the output
 impedance of the amplifier (that is, the output impedance of
 the transistors which drive the speakers).  The lower the
 output impedance, the higher the damping factor.  Higher
 damping factors indicate a greater ability to help control the
 motion of the cone of the speaker which is being driven.  When
 this motion is tightly controlled, a greater transient response
 is evident in the system, which most people refer to as a
 "tight" or "crisp" sound.  Damping factors above 100 are
 generally regarded as good.

 "Signal to Noise" or "S/N" is the ratio, usually expressed in
 decibels, of the amount of true amplified output of the
 amplifier to the amount of extraneous noise injected into the
 signal.  S/N ratios above 90 to 95dB are generally regarded as
 good.

    3.5 What is "bridging"? Can my amp do it? [JSC]

 Bridging refers to taking two channels of an amplifier and
 combining them to turn the amplifier into a one channel
 amplifier.  In normal operation, one wire which goes to a
 speaker from the amplifier is "neutral", that is, the potential
 never changes (with respect to another fixed point, like
 ground).  The other wire is "hot", that is, it carries the
 fluctuating AC speaker signal.  The speaker "sees" a potential
 between these two leads, and so there is a voltage applied to
 the speaker.  When an amplifier is bridged, both leads are
 "hot".  However, one signal must be inverted, or else the
 speaker will never see a potential, as both wires are carrying
 roughly the same signal.  With one signal inverted, the speaker
 will see a signal that is twice as great as one signal alone.
 Thus, if your amplifier does not have a switch or button of
 some sort which inverts one channel, you cannot bridge your
 amplifier (unless you build an external inverter).  With
 respect to power, the commonly accepted definition is that when
 you bridge and amplifier, you add all of the characteristics of
 the bridged channels together.  Thus, if you bridge an
 amplifier that is 50W/ch into 4 ohms at < 0.05%THD, your
 bridged channel is 100W/ch into 8 ohms at < 0.10%THD.
 Therefore, an amplifier which is 2 ohm stable in stereo mode is
 only 4 ohm stable in bridged mono mode, and an amp which is 4
 ohm stable in stereo is only 8 ohm stable in bridged mono.

    3.6 What is "mixed-mono"? Can my amp do it? [JSC]

 Some amplifiers which are both bridgeable and able to drive low
 impedance loads also allow you to use "mixed-mono" mode.  This
 involves driving a pair of speakers in stereo mode as well as
 simultaneously driving a single speaker in bridged mono mode.
 What happens is that you put your amp in bridged mode, which
 inverts one output signal.  You then connect the mono speaker
 as you normally would in bridged mode.  To the channel which is
 not inverted, you connect your stereo speaker as you normally
 would.  To the channel which is inverted, you connect the other
 stereo speaker with its leads reversed (+ to - and - to +)
 since the signal is inverted.

    3.7 What does "two ohm stable" mean? What is a "high-current"
 amplifier? [JSC]

 An x ohm stable amplifier is an amp which is able to
 continuously power loads of x ohms per channel without
 encountering difficulties such as overheating.  Almost all car
 amplifiers are at least four ohm stable.  Some are two ohm
 stable, which means that you could run a pair of four ohm
 speakers in parallel on each channel of the amplifier, and each
 channel of the amp would "see" two ohms.  Some amps are
 referred to as "high-current", which is a buzzword which
 indicates that the amp is able to deliver very large
 (relatively) amounts of current, which usually means that it is
 stable at very low load impedances, such as 1/4 or 1/2 of an
 ohm.  Note that the minimum load rating (such as "two ohm
 stable") is a stereo (per channel) rating.  In bridged mode,
 the total stability is the sum of the individual channels'
 stability (see 3.5).

    3.8 Should I buy a two or four (or more) channel amplifier? [JSC]

 If you only have one line-level set of outputs available, and
 wish to power two sets of speakers from a single amplifier, you
 may be able to save money by purchasing a two channel amplifier
 which is stable to two ohms rather than spending the extra
 money for a four channel amp.  If you do this, however, you
 will be unable to fade between the two sets of speakers
 (without additional hardware), and the damping factor of the
 amplifier will effectively be cut in half.  Also, the amp may
 run hot and require fans to prevent overheating.  If you have
 the money, a four channel amp would be a better choice.  You
 would need to add a dual-amp balancer in order to maintain
 fader capability, however, but it is more efficient than
 building a fader for a two channel amp.  If you wish to power a
 subwoofer or additional speakers as well, you may want to
 purchase a five or six channel amp.

    3.9 What are some good (and bad) brands of amplifiers? [JSC]

 As with speakers, people emotionally defend their amplifier, so
 choosing the best is difficult.  However, some brands stand out
 as being consistently good while others are consistently bad.
 Among the good are HiFonics, Phoenix Gold, a/d/s/, and
 Precision Power.

   3.10 What is a crossover? Why would I need one? [JSC]

 A crossover is a device which filters signals based on
 frequency.  A "high pass" crossover is a filter which allows
 frequencies above a certain point to pass unfiltered; those
 below that same point still get through, but are attenuated
 according to the crossover slope.  A "low pass" crossover is
 just the opposite:  the lows pass through, but the highs are
 attenuated.  A "band pass" crossover is a filter that allows a
 certain range of frequencies to pass through while attenuating
 those above and below that range.  There are passive
 crossovers, which are generally collections of capacitors and
 inductors and sometimes resistors, which are placed in between
 the amplifier and the speakers.  There are also active
 crossovers which are powered electrical devices which are
 placed between the head unit and the amplifiers.

 There are many reasons for using crossovers.  One is to filter
 out deep bass from relatively small drivers.  Another is to
 split the signal in a multi-driver speaker so that the woofer
 gets the bass, the midrange gets the mids, and the tweeter gets
 the highs.

 Crossovers are categorized by their "order" and their
 "crossover point".  The order of the crossover indicates how
 steep the attenuation slope is.  A first order crossover "rolls
 off" the signal at -6dB/octave (that is, quarter power per
 doubling or halving in frequency).  A second order crossover
 has a slope of -12dB/octave; third order is -18dB/octave; etc.
 The crossover point is generally the frequency at which the
 -3dB point of the attenuation slope occurs.  Thus, a first
 order high pass crossover at 200Hz is -3dB down at 200Hz, -9dB
 down at 100Hz, -15dB down at 50Hz, etc.

 The expected impedance of a crossover is important as well.  A
 crossover which is designed as -6dB/octave at 200Hz high pass
 with a 4 ohm driver will not have the same crossover frequency
 with a driver which is not 4 ohms.  With crossovers of order
 higher than one, using the wrong impedance driver will wreak
 havoc with the frequency response.  Don't do it.

   3.11 Should I get an active or a passive crossover? [JSC]

 Active crossovers are more efficient than passive crossovers.
 A typical "insertion loss" (power loss due to use) of a passive
 crossover is around 0.5dB.  Active crossovers have much lower
 insertion losses, if they have any loss at all.  Also, with
 some active crossovers, you can continuously vary not only the
 crossover point, but also the slope.  Thus, if you wanted to,
 with some active crossovers you could create a high pass filter
 at 112.3Hz at -37.2dB/octave, or other such things.

 However, active crossovers have their disadvantages as well.
 An active crossover may very well cost more than an equivalent
 number of passive crossovers.  Also, since the active crossover
 has separate outputs for each frequency band that you desire,
 you will need to have separate amplifiers for each frequency
 range.

 Thus, if you have extra money to spend on an active crossover
 and separate amplifiers, an active crossover is probably the
 way to go.  However, if you are on a budget and can find a
 passive crossover with the characteristics you desire, go with
 a passive.

   3.12 How do I build my own passive crossovers? [JSC]

 A first order high pass crossover is simply a capacitor placed
 inline with the driver.  A first order low pass crossover is an
 inductor inline with the driver.  These can also be reversed: a
 capacitor in parallel with the driver is a low pass filter; an
 inductor in parallel with the driver is a high pass filter.
 When like combinations are used, the order increases: a
 crossover in series (inline) followed by an inductor in
 parallel is a second order high pass crossover.  An inductor in
 series followed by a capacitor in parallel is a second order
 low pass crossover.

 To calculate the correct values of capacitors and inductors to
 use, you need to know the nominal impedance (Z) of the circuit
 in ohms and the desired crossover point (f) in hertz.  The
 needed capacitance in farads is then 1/(2 x pi x f x Z).  The
 needed inductance in henries is Z/(2 x pi x f).  For example,
 if the desired crossover point is 200Hz for a 4 ohm driver, you
 need a 198.9 x 10^-6 F (or 199uF) capacitor for a high pass
 first order filter, or a 3.18 x 10^-3 H (or 3.18mH) inductor
 for a low pass first order filter.

 To obtain low insertion losses, the inductors should have very
 low resistance, perhaps as low as 0.1 to 0.2 ohms.

 Also, be sure to select capacitors with proper voltage
 ratings.  The maximum voltage in the circuit will be less than
 the square root of the product of the maximum power in the
 circuit and the nominal impedance of the driver.  For example,
 a 4 ohm woofer being given 100W peak will see a maximum voltage
 of sqrt(100*4) = sqrt(400) = 20V.  Make sure that the
 capacitors are bipolar, too, since speaker signals are AC
 signals.  If you cannot find bipolar capacitors, you can use
 two polar capacitors in parallel and in opposite polarity (+ to
 - and - to +).  However, there are some possible problems with
 this approach: the forward voltage rating will probably not be
 equal to the reverse voltage rating, and there could be a
 reverse capacitance as well.  Both problems could adversely
 affect your circuit if you decide to use opposite polarity
 capacitors in parallel.

 To build a second order passive crossover, calculate the same
 initial values for the capacitance and inductance, and then
 decide whether you want a Linkwitz-Riley, Butterworth, or
 Bessel filter.  An L-R filter matches the attenuation slopes so
 that both -3dB points are at the same frequency, so that the
 system response is flat at the crossover frequency.  A
 Butterworth filter matches the slopes so that there is a peak
 at the crossover frequency, and a Bessel filter is in between
 the two.  For an L-R filter, halve the capacitance and double
 the inductance.  For a Butterworth filter, multiply the
 capacitance by 1/sqrt(2) and the inductance by sqrt(2).  For a
 Bessel filter, multiply the capacitance by 1/sqrt(3) and the
 inductance by sqrt(3).

 You should realize, too, that crossovers induce a phase shift
 in the signal of 90 degrees per order.  In a second order
 filter, then, this can be corrected by reversing the polarity
 of one of the drivers.  In any case with any crossover, though,
 you should always experiment with the polarity of the drivers
 to achieve the best total system response.

   3.13 Should I buy an equalizer? [JSC]

 Equalizers are normally used to fine-tune a system, and should
 be treated as such.  Equalizers should not be purchased to
 boost one band 12dB and to cut another band 12dB and so on -
 excessive equalization is indicative of more serious system
 problems that should not simply be masked with an EQ.  However,
 if you need to do some minor tweaking, an EQ can be a valuable
 tool.  Additionally, some EQs have spectrum analyzers built in,
 which makes for some extra flash in a system.  There are two
 main kinds of EQs available today: dash and trunk.  Dash EQs
 are designed to be installed in the passenger compartment of a
 car, near the head unit.  They have the adjustments for
 anywhere from five to eleven (and sometimes more) bands on the
 front panel.  Trunk EQs are designed to be adjusted once and
 then stashed away.  These types of EQs usually have many bands
 (sometimes as many as thirty).  Both types sometimes also have
 crossovers built in.

   3.14 What are some good (and bad) brands of equalizers?

   3.15 What do all of those specifications on tape deck head units mean?

   3.16 What are features to look for in a tape deck?

   3.17 What are some good (and bad) brands of tape decks?

   3.18 What are features to look for in a CD head unit?

   3.19 Should I buy a detachable faceplate or pullout CD player?

   3.20 What are some good (and bad) brands of CD head units?

   3.21 Can I use my portable CD player in my car? Won't it skip a lot? [JSC]

 You can use any portable CD player in a car provided that you
 have either an amplifier with line level inputs (preferred) or
 a tape deck.  If you have the former, you can simply buy a 1/8"
 headphone jack to RCA jack adapter and plug your CD player
 directly into your amplifier.  If you have the latter, you can
 purchase a 1/8" headphone jack to cassette adapter and play CDs
 through your tape deck.  The cassette adapters tend to be far
 more convenient; however, there is a significant tradeoff: by
 using cassette adapters, you limit your sound to the frequency
 response of the tape head, which is sometimes as much as an
 entire order of magnitude worse than the raw digital material
 encoded onto the CD itself.

 Portable CD players which were not designed for automotive use
 will tend to skip frequently when used in a car (relatively).
 CD players that are specially designed for automotive use, such
 as the Sony Car Discman, tend to include extra dampening to
 allow the laser to "float" across the bumps and jolts of a
 road.  Some people have indicated success with using regular
 portable CD players in a car when they place the CD player on a
 cushion, such as a thick shirt or even on their thighs.

   3.22 What's that weird motor noise I get with my portable CD player? [JSC]

 Many people report problems while playing CDs from a portable
 CD player into their car audio systems.  The problem, stated
 very simply, has to do with the stepping of the motor requiring
 a varying amount of current and non-isolated power and audio
 signal grounds.  Using a liberal application of capacitors and
 inductors, this voltage variance can be restricted to a window
 of 8.990 to 9.005V for a 9V CD player, yet even the swing
 between these two levels is enough to cause annoyingly loud
 noise on the outputs.  It has been reported that this entire
 problem can be solved by using a true DC-DC inverter at the
 power input to the CD player.

   3.23 What are some good (and bad) brands of portable CD players?

   3.24 What's in store for car audio with respect to MD, DAT and DCC? [HK]

 MD seems to have a better future than DAT or DCC which don't
 seem to have appeal to the public.  Ease of use seems to be an
 important factor and the CD formats allows direct access to
 musical tracks at an instant.  Although MD doesn't match the
 sound quality of the standard CD's it will probably be popular
 since the players have a buffer to eliminate skipping.  DAT
 will remain as a media for ProAudio for recording purposes
 before pressing CD's.

   3.25 Are those FM modulator CD changers any good? What are my other
 options?

   3.26 What are some good (and bad) brands of CD changers?

   3.27 Why do I need a center channel in my car, and how do I do it? [HK,
 JSC]

 If a proper center image isn't achievable via a two channel
 configuration, installation of a center channel can help.
 Since the majority of recordings are done in two channel, a two
 channel system designed correctly should be able to reproduce a
 center image which was captured during recording.  A center
 channel is not simply a summation of the left and right
 channels, like bridging an amplifier; rather, it is an
 extraction of common signals from the left and right channels.
 This usually means the lead vocals, and perhaps one or two
 instruments.  These signals will then be localized to the
 center of the stage, instead of perhaps drifting between the
 left center and right center of the stage.  A signal processor
 is usually required in order to properly create a center
 channel image.  The image should then be sent to a driver in
 the physical center of the front of the car, at an
 amplification level somewhat lower than the rest of the
 speakers.  The correct frequency range and power levels will
 depend on the particular installation, though a good starting
 point is perhaps a pass band of 250-3000Hz at an amplification
 level of half the power of the main speakers (3dB down).

   3.28 Should I buy a sound field processor?

   3.29 What are some good (and bad) brands of signal processors?


      4 Subwoofers

 This section describes some elements necessary for
 understanding subwoofers - how they operate, how to build
 proper enclosures, how to pick the right driver for you, and
 how to have a computer do some of the work for you.

    4.1 What are "Thiele/Small parameters"? [CD,RDP]

 These are a group of parameters outlined by A.N. Thiele, and
 later R.H. Small, which can completely describe the electrical
 and mechanical characteristics of a mid and low frequency
 driver operating in its pistonic region.  These parameters are
 crucial for designing a quality subwoofer enclosure, be it for
 reference quality reproduction or for booming.

 Fs    Driver free air resonance, in Hz.  This is the point at 
  which driver impedance is maximum.
 Fc    System resonance (usually for sealed box systems), in Hz
 Fb    Enclosure resonance (usually for reflex systems), in Hz
 F3    -3 dB cutoff frequency, in Hz
 
 Vas   "Equivalent volume of compliance", this is a volume of 
  air whose compliance is the same as a driver's 
  acoustical compliance Cms (q.v.), in cubic meters
 
 D     Effective diameter of driver, in meters
 Sd    Effective piston radiating area of driver in square meters
 Xmax  Maximum peak linear excursion of driver, in meters
 Vd    Maximum linear volume of displacement of the driver 
  (product of Sd times Xmax), in cubic meters.
 
 Re    Driver DC resistance (voice coil, mainly), in ohms
 Rg    Amplifier source resistance (includes leads, crossover, 
  etc.), in ohms
 
 Qms   The driver's Q at resonance (Fs), due to mechanical 
  losses; dimensionless
 Qes   The driver's Q at resonance (Fs), due to electrical 
  losses; dimensionless
 Qts   The driver's Q at resonance (Fs), due to all losses;
   dimensionless
 Qmc   The system's Q at resonance (Fc), due to mechanical 
  losses; dimensionless
 Qec   The system's Q at resonance (Fc), due to electrical 
  losses; dimensionless
 Qtc   The system's Q at resonance (Fc), due to all losses; 
  dimensionless
 Ql    The system's Q at Fb, due to leakage losses;
  dimensionless
 Qa    The system's Q at Fb, due to absorption losses;
        dimensionless
 Qp    The system's Q at Fb, due to port losses (turbulence,
        viscousity, etc.); dimensionless
 
 n0    The reference efficiency of the system (eta sub 0) 
  dimensionless, usually expressed as %
 
 Cms   The driver's mechanical compliance (reciprocal of 
  stiffness), in m/N
 Mms   The driver's effective mechanical mass (including air 
  load), in kg
 Rms   The driver's mechanical losses, in kg/s
 
 Cas   Acoustical equivalent of Cms
 Mas   Acoustical equivalent of Mms
 Ras   Acoustical equivalent of Rms
 
 Cmes  The electrical capacitive equivalent of Mms, in farads
 Lces  The electrical inductive equivalent of Cms, in henries
 Res   The electrical resistive equivalent of Rms, in ohms
 
 B     Magnetic flux density in gap, in Tesla
 l     length of wire immersed in magnetic field, in meters
 Bl    Electro-magnetic force factor, can be expressed in 
  Tesla-meters or, preferably, in meters/Newton
 
 Pa    Acoustical power
 Pe    Electrical power
 
 c     propagation velocity of sound at STP, approx. 342 m/s
 p     (rho) density of air at STP 1.18 kg/m^3

    4.2 What are the enclosure types available, and which one is right
 for me? [JLD]

 Only the order of the enclosure         First Order
 itself is shown here.  The addition     Infinite-Baffle or Free-Air
 of a crossover network increases
 the order of the system by the                  |
 order of the crossover.                         |
 Example:  If a First-Order, 6dB/Oct.           /
 crossover (single inductor in series          /
 with the speaker) is used with a            ||
 Fourth Order enclosure, the total           ||
 system is a fifth order.                      \
 Note:  Air volumes and ratios shown            \
 here may not be to scale.  This is              |
 designed to provide order information           |
 only.


 Second Order                        Second Order
 Acoustic- or Air-Suspension         Isobaric* Acoustic-Suspension
 or Sealed                           (Compound Loaded)
  _______________________             _______________________
 |                       |           |                  _____|
 |                      /            |                 /    /
 |                     /             |                /    /
 |                   ||              |              ||   ||
 |                   ||              |              ||   ||
 |                     \             |                \    \
 |                      \            |                 \____\
 |_______________________|           |_______________________|


 Fourth Order            Fourth Order            Fourth Order
 Bass-Reflex or          Passive Radiator        Isobaric*
 Vented or Ported        Bass-Reflex             Bass-Reflex
  _______________         _______________         _______________
 |               |       |               |       |          ____ |
 |              /        |              /        |         /    /
 |             /         |             /         |        /    /
 |           ||          |           ||          |      ||   ||
 |           ||          |           ||          |      ||   ||
 |             \         |             \         |        \    \
 |              \        |              \        |         \____\
 |               |       |               |       |               |
 |               |       |              /        |               |
 |               |       |             /         |               |
 |           ____|       |            |          |           ____|
 |                       |            |          |
 |           ____        |             \         |           ____
 |               |       |              \        |               |
 |_______________|       |_______________|       |_______________|


 Fourth Order                    Fourth Order
 Single-Reflex Bandpass          Isobaric* Single-Reflex Bandpass
  _________________    ____      _______________________    ____
 |         |       |  |    |    |               |       |  |    |
 |        /        |  |    |    |              / \      |  |    |
 |       /                 |    |             /   \             |
 |     ||                  |    |           ||     ||           |
 |     ||                  |    |           ||     ||           |
 |       \                 |    |             \   /             |
 |        \                |    |              \ /              |
 |_________|_______________|    |_______________|_______________|


 Fourth Order                      Fourth Order
 Three Chamber                     Three Chamber Isobaric*
 Single-Reflex Bandpass            Single-Reflex Bandpass
  ____________   ____________      ______________   ______________
 |      |     | |     |      |    |       |      | |      |       |
 |     /      | |      \     |    |      / \     | |     / \      |
 |    /                 \    |    |     /   \           /   \     |
 |  ||                   ||  |    |   ||     ||       ||     ||   |
 |  ||                   ||  |    |   ||     ||       ||     ||   |
 |    \                 /    |    |     \   /           \   /     |
 |     \               /     |    |      \ /             \ /      |
 |______|_____________|______|    |_______|_______________|_______|


 Fifth Order = Fourth Order Enclosure + First Order Crossover
             = Third Order Enclosure + Second Order Crossover, etc.


 Sixth Order                        Sixth Order
 Dual-Reflex Bandpass               Isobaric* Dual-Reflex Bandpass
  ____    _____________    ____      ____    ____________    ____
 |    |  |       |     |  |    |    |    |  |      |     |  |    |
 |    |  |      /      |  |    |    |    |  |     / \    |  |    |
 |    |  |     /               |    |    |  |    /   \           |
 |           ||                |    |          ||     ||         |
 |           ||                |    |          ||     ||         |
 |             \               |    |            \   /           |
 |              \              |    |             \ /            |
 |_______________|_____________|    |______________|_____________|
 
 Sixth Order
 Three Chamber                        Quasi-Sixth Order
 Dual-Reflex Bandpass                 Series-Tuned Bandpass
  _    _________   _________    _      _________________    ____
 | |  |   |     | |     |   |  | |    |           |     |  |    |
 | |  |  /      | |      \  |  | |    |          /      |  |    |
 |      /                 \      |    |         /               |
 |    ||                   ||    |    |       ||                |
 |    ||                   ||    |    |       ||                |
 |      \                 /      |    |         \               |
 |       \               /       |    |          \              |
 |________|_____________|________|    |       ____|             |
                                      |                         |
                                      |       ____              |
                                      |           |             |
                                      |___________|_____________|


 Seventh Order = Sixth Order Enclosure + First Order Crossover, etc.


 * Isobaric or Coupled Pair (Iso-group) Variations:

 A variety of configurations may be used in the isobaric loading
 of any order enclosure. Physical and acoustic restrictions may
 make one loading configuration preferable to another in a
 particular enclosure.

 Composite or Push-Pull                  Compound or Piggy-Back
 or Face-to-Face Loading                 or Tunnel Loading
  _________________                 ___________________________
 |                 |               |                       ____|
 |                / \              |                      /   /
 |               /   \             |                     /   /
 |         >>> ||     || >>>       |               >>> ||  || >>>
 |         >>> ||     || >>>       |               >>> ||  || >>>
 |               \   /             |                     \   \
 |                \ /              |                      \___\
 |_________________|               |___________________________|

 Back-to-Back Loading                    Planar Loading
  _________________________         ___________________________
 |                _________|       |                        |  |
 |                \       /        |                       /   |
 |                 \     /         |                      /    |
 |              >>> || || >>>      |                    || >>> |
 |              >>> || || >>>      |                    || >>> |
 |                 /     \         |                      \    |
 |                /_______\        |                       \   |
 |_________________________|       |________________________|  |
                                                            |  |
                                                           /   |
                                                          /    |
                                                        || <<< |
                                                        || <<< |
                                                          \    |
 >>> indicates direction of                                \   |
 >>> simultaneous cone movement.                            |__|

    4.3 How do I build an enclosure?

    4.4 What driver should I use?

    4.5 Is there any computer software available to help me choose an
 enclosure and a driver? [MH]

 Various enclosure design software is available via ftp from
 csd4.csd.uwm.edu in the directory "/pub/high-audio/Software".
 The most popular program there is Perfect Box, which is in the
 file "perf.uu" (or "perf.zip").

    4.6 What is an "aperiodic membrane"? [CD]

 An aperiodic membrane is one part of a type of subwoofer
 enclosure.  It is an air-permeable sheet which has
 frequency-dependent acoustical resistance properties.  The
 original design goes back to Naim, for use in home systems, but
 has been applied by several individuals and companies in car
 audio.

 The completed system will be aperiodic, which means it will
 prove to be over-damped with a Q below 0.7.  In contrast, most
 car audio systems range from sort of to grossly underdamped,
 with Q's > 0.8 and higher.  These high-Q systems have poor
 transient response, nasty peaks in frequency response, and high
 rates of roll-off.  Aperiodic systems will feature excellent
 transient response, smooth frequency response, and extended
 very-low frequency reproduction.

 Another benefit of the system is that you can pretty much
 choose whichever driver you'd like to use, as long as they are
 big.  The Thiele/Small parameters (which would normally
 determine what kind of box would be used) are taken into
 consideration by the membrane designers so that the response is
 extended and overdamped, regardless of the characteristics of
 the driver.

 Physically, the aperiodic membrane isn't for every car.  It
 requires sealing the trunk from the passenger compartment in an
 air-tight manner, as well as sealing the trunk from the outside
 for best results.  The drivers are then mounted into the baffle
 between the passenger compartment and the trunk, as would be
 standard in an infinite-baffle/free-air set-up.  The aperiodic
 membrane is then placed either in front of the driver or behind
 the driver, depending on the type.  When mounting behind the
 driver, the membrane is used as the rear-wall of a very small
 box which the driver sits in (as in Richard Clark's infamous
 Buick Grand National).  So, in short, it's not suitable for
 trucks, jeeps, R/V's, or hatchbacks.

 You should probably only get an aperiodic membrane if you've
 got money to burn, lots of amplifier power, some big subs, a
 sedan, a desire for trunk space, and no wish to boom.  If your
 tastes lean towards bass-heavy booming, as opposed to
 well-recorded acoustic instruments, you're not going to be
 pleased with the result.

-- 
Jeffrey S. Curtis - stealth@uiuc.edu <> "Resplendent  in  full  regalia, they
Network Technician - UoI Housing Div <> revel in their role as self-appointed
 A typical "insertion loss" (power loss due to use) of a passive
 crossover is around 0.5dB.  Active crossovers have much lower
 insertion losses, if they have any loss at all.  Also, with
 some active crossovers, you can continuously vary not only the
 crossover point, but also the slope.  Thus, if you wanted to,
 with some active crossovers you could create a high pass filter
 at 112.3Hz at -37.2dB/octave, or other such things.

 However, active crossovers have their disadvantages as well.
 An active crossover may very well cost more than an equivalent
 number of passive crossovers.  Also, since the active crossover
 has separate outputs for each frequency band that you desire,
 you will need to have separate amplifiers for each frequency
 range.

 Thus, if you have extra money to spend on an active crossover
 and separate amplifiers, an active crossover is probably the
 way to go.  However, if you are on a budget and can find a
 passive crossover with the characteristics you desire, go with
 a passive.

   3.12 How do I build my own passive crossovers? [JSC]

 A first order high pass crossover is simply a capacitor placed
 inline with the driver.  A first order low pass crossover is an
 inductor inline with the driver.  These can also be reversed: a
 capacitor in parallel with the driver is a low pass filter; an
 inductor in parallel with the driver is a high pass filter.
 When like combinations are used, the order increases: a
 crossover in series (inline) followed by an inductor in
 parallel is a second order high pass crossover.  An inductor in
 series followed by a capacitor in parallel is a second order
 low pass crossover.

 To calculate the correct values of capacitors and inductors to
 use, you need to know the nominal impedance (Z) of the circuit
 in ohms and the desired crossover point (f) in hertz.  The
 needed capacitance in farads is then 1/(2 x pi x f x Z).  The
 needed inductance in henries is Z/(2 x pi x f).  For example,
 if the desired crossover point is 200Hz for a 4 ohm driver, you
 need a 198.9 x 10^-6 F (or 199uF) capacitor for a high pass
 first order filter, or a 3.18 x 10^-3 H (or 3.18mH) inductor
 for a low pass first order filter.

 To obtain low insertion losses, the inductors should have very
 low resistance, perhaps as low as 0.1 to 0.2 ohms.

 Also, be sure to select capacitors with proper voltage
 ratings.  The maximum voltage in the circuit will be less than
 the square root of the product of the maximum power in the
 circuit and the nominal impedance of the driver.  For example,
 a 4 ohm woofer being given 100W peak will see a maximum voltage
 of sqrt(100*4) = sqrt(400) = 20V.  Make sure that the
 capacitors are bipolar, too, since speaker signals are AC
 signals.  If you cannot find bipolar capacitors, you can use
 two polar capacitors in parallel and in opposite polarity (+ to
 - and - to +).  However, there are some possible problems with
 this approach: the forward voltage rating will probably not be
 equal to the reverse voltage rating, and there could be a
 reverse capacitance as well.  Both problems could adversely
 affect your circuit if you decide to use opposite polarity
 capacitors in parallel.

 To build a second order passive crossover, calculate the same
 initial values for the capacitance and inductance, and then
 decide whether you want a Linkwitz-Riley, Butterworth, or
 Bessel filter.  An L-R filter matches the attenuation slopes so
 that both -3dB points are at the same frequency, so that the
 system response is flat at the crossover frequency.  A
 Butterworth filter matches the slopes so that there is a peak
 at the crossover frequency, and a Bessel filter is in between
 the two.  For an L-R filter, halve the capacitance and double
 the inductance.  For a Butterworth filter, multiply the
 capacitance by 1/sqrt(2) and the inductance by sqrt(2).  For a
 Bessel filter, multiply the capacitance by 1/sqrt(3) and the
 inductance by sqrt(3).

 You should realize, too, that crossovers induce a phase shift
 in the signal of 90 degrees per order.  In a second order
 filter, then, this can be corrected by reversing the polarity
 of one of the drivers.  In any case with any crossover, though,
 you should always experiment with the polarity of the drivers
 to achieve the best total system response.

   3.13 Should I buy an equalizer? [JSC]

 Equalizers are normally used to fine-tune a system, and should
 be treated as such.  Equalizers should not be purchased to
 boost one band 12dB and to cut another band 12dB and so on -
 excessive equalization is indicative of more serious system
 problems that should not simply be masked with an EQ.  However,
 if you need to do some minor tweaking, an EQ can be a valuable
 tool.  Additionally, some EQs have spectrum analyzers built in,
 which makes for some extra flash in a system.  There are two
 main kinds of EQs available today: dash and trunk.  Dash EQs
 are designed to be installed in the passenger compartment of a
 car, near the head unit.  They have the adjustments for
 anywhere from five to eleven (and sometimes more) bands on the
 front panel.  Trunk EQs are designed to be adjusted once and
 then stashed away.  These types of EQs usually have many bands
 (sometimes as many as thirty).  Both types sometimes also have
 crossovers built in.

   3.14 What are some good (and bad) brands of equalizers?

   3.15 What do all of those specifications on tape deck head units mean?

   3.16 What are features to look for in a tape deck?

   3.17 What are some good (and bad) brands of tape decks?

   3.18 What are features to look for in a CD head unit?

   3.19 Should I buy a detachable faceplate or pullout CD player?

   3.20 What are some good (and bad) brands of CD head units?

   3.21 Can I use my portable CD player in my car? Won't it skip a lot? [JSC]

 You can use any portable CD player in a car provided that you
 have either an amplifier with line level inputs (preferred) or
 a tape deck.  If you have the former, you can simply buy a 1/8"
 headphone jack to RCA jack adapter and plug your CD player
 directly into your amplifier.  If you have the latter, you can
 purchase a 1/8" headphone jack to cassette adapter and play CDs
 through your tape deck.  The cassette adapters tend to be far
 more convenient; however, there is a significant tradeoff: by
 using cassette adapters, you limit your sound to the frequency
 response of the tape head, which is sometimes as much as an
 entire order of magnitude worse than the raw digital material
 encoded onto the CD itself.

 Portable CD players which were not designed for automotive use
 will tend to skip frequently when used in a car (relatively).
 CD players that are specially designed for automotive use, such
 as the Sony Car Discman, tend to include extra dampening to
 allow the laser to "float" across the bumps and jolts of a
 road.  Some people have indicated success with using regular
 portable CD players in a car when they place the CD player on a
 cushion, such as a thick shirt or even on their thighs.

   3.22 What's that weird motor noise I get with my portable CD player? [JSC]

 Many people report problems while playing CDs from a portable
 CD player into their car audio systems.  The problem, stated
 very simply, has to do with the stepping of the motor requiring
 a varying amount of current and non-isolated power and audio
 signal grounds.  Using a liberal application of capacitors and
 inductors, this voltage variance can be restricted to a window
 of 8.990 to 9.005V for a 9V CD player, yet even the swing
 between these two levels is enough to cause annoyingly loud
 noise on the outputs.  It has been reported that this entire
 problem can be solved by using a true DC-DC inverter at the
 power input to the CD player.

   3.23 What are some good (and bad) brands of portable CD players?

   3.24 What's in store for car audio with respect to MD, DAT and DCC? [HK]

 MD seems to have a better future than DAT or DCC which don't
 seem to have appeal to the public.  Ease of use seems to be an
 important factor and the CD formats allows direct access to
 musical tracks at an instant.  Although MD doesn't match the
 sound quality of the standard CD's it will probably be popular
 since the players have a buffer to eliminate skipping.  DAT
 will remain as a media for ProAudio for recording purposes
 before pressing CD's.

   3.25 Are those FM modulator CD changers any good? What are my other
 options?

   3.26 What are some good (and bad) brands of CD changers?

   3.27 Why do I need a center channel in my car, and how do I do it? [HK,
 JSC]

 If a proper center image isn't achievable via a two channel
 configuration, installation of a center channel can help.
 Since the majority of recordings are done in two channel, a two
 channel system designed correctly should be able to reproduce a
 center image which was captured during recording.  A center
 channel is not simply a summation of the left and right
 channels, like bridging an amplifier; rather, it is an
 extraction of common signals from the left and right channels.
 This usually means the lead vocals, and perhaps one or two
 instruments.  These signals will then be localized to the
 center of the stage, instead of perhaps drifting between the
 left center and right center of the stage.  A signal processor
 is usually required in order to properly create a center
 channel image.  The image should then be sent to a driver in
 the physical center of the front of the car, at an
 amplification level somewhat lower than the rest of the
 speakers.  The correct frequency range and power levels will
 depend on the particular installation, though a good starting
 point is perhaps a pass band of 250-3000Hz at an amplification
 level of half the power of the main speakers (3dB down).

   3.28 Should I buy a sound field processor?

   3.29 What are some good (and bad) brands of signal processors?


      4 Subwoofers

 This section describes some elements necessary for
 understanding subwoofers - how they operate, how to build
 proper enclosures, how to pick the right driver for you, and
 how to have a computer do some of the work for you.

    4.1 What are "Thiele/Small parameters"? [CD,RDP]

 These are a group of parameters outlined by A.N. Thiele, and
 later R.H. Small, which can completely describe the electrical
 and mechanical characteristics of a mid and low frequency
 driver operating in its pistonic region.  These parameters are
 crucial for designing a quality subwoofer enclosure, be it for
 reference quality reproduction or for booming.

 Fs    Driver free air resonance, in Hz.  This is the point at 
  which driver impedance is maximum.
 Fc    System resonance (usually for sealed box systems), in Hz
 Fb    Enclosure resonance (usually for reflex systems), in Hz
 F3    -3 dB cutoff frequency, in Hz
 
 Vas   "Equivalent volume of compliance", this is a volume of 
  air whose compliance is the same as a driver's 
  acoustical compliance Cms (q.v.), in cubic meters
 
 D     Effective diameter of driver, in meters
 Sd    Effective piston radiating area of driver in square meters
 Xmax  Maximum peak linear excursion of driver, in meters
 Vd    Maximum linear volume of displacement of the driver 
  (product of Sd times Xmax), in cubic meters.
 
 Re    Driver DC resistance (voice coil, mainly), in ohms
 Rg    Amplifier source resistance (includes leads, crossover, 
  etc.), in ohms
 
 Qms   The driver's Q at resonance (Fs), due to mechanical 
  losses; dimensionless
 Qes   The driver's Q at resonance (Fs), due to electrical 
  losses; dimensionless
 Qts   The driver's Q at resonance (Fs), due to all losses;
   dimensionless
 Qmc   The system's Q at resonance (Fc), due to mechanical 
  losses; dimensionless
 Qec   The system's Q at resonance (Fc), due to electrical 
  losses; dimensionless
 Qtc   The system's Q at resonance (Fc), due to all losses; 
  dimensionless
 Ql    The system's Q at Fb, due to leakage losses;
  dimensionless
 Qa    The system's Q at Fb, due to absorption losses;
        dimensionless
 Qp    The system's Q at Fb, due to port losses (turbulence,
        viscousity, etc.); dimensionless
 
 n0    The reference efficiency of the system (eta sub 0) 
  dimensionless, usually expressed as %
 
 Cms   The driver's mechanical compliance (reciprocal of 
  stiffness), in m/N
 Mms   The driver's effective mechanical mass (including air 
  load), in kg
 Rms   The driver's mechanical losses, in kg/s
 
 Cas   Acoustical equivalent of Cms
 Mas   Acoustical equivalent of Mms
 Ras   Acoustical equivalent of Rms
 
 Cmes  The electrical capacitive equivalent of Mms, in farads
 Lces  The electrical inductive equivalent of Cms, in henries
 Res   The electrical resistive equivalent of Rms, in ohms
 
 B     Magnetic flux density in gap, in Tesla
 l     length of wire immersed in magnetic field, in meters
 Bl    Electro-magnetic force factor, can be expressed in 
  Tesla-meters or, preferably, in meters/Newton
 
 Pa    Acoustical power
 Pe    Electrical power
 
 c     propagation velocity of sound at STP, approx. 342 m/s
 p     (rho) density of air at STP 1.18 kg/m^3

    4.2 What are the enclosure types available, and which one is right
 for me? [JLD]

 Only the order of the enclosure         First Order
 itself is shown here.  The addition     Infinite-Baffle or Free-Air
 of a crossover network increases
 the order of the system by the                  |
 order of the crossover.                         |
 Example:  If a First-Order, 6dB/Oct.           /
 crossover (single inductor in series          /
 with the speaker) is used with a            ||
 Fourth Order enclosure, the total           ||
 system is a fifth order.                      \
 Note:  Air volumes and ratios shown            \
 here may not be to scale.  This is              |
 designed to provide order information           |
 only.


 Second Order                        Second Order
 Acoustic- or Air-Suspension         Isobaric* Acoustic-Suspension
 or Sealed                           (Compound Loaded)
  _______________________             _______________________
 |                       |           |                  _____|
 |                      /            |                 /    /
 |                     /             |                /    /
 |                   ||              |              ||   ||
 |                   ||              |              ||   ||
 |                     \             |                \    \
 |                      \            |                 \____\
 |_______________________|           |_______________________|


 Fourth Order            Fourth Order            Fourth Order
 Bass-Reflex or          Passive Radiator        Isobaric*
 Vented or Ported        Bass-Reflex             Bass-Reflex
  _______________         _______________         _______________
 |               |       |               |       |          ____ |
 |              /        |              /        |         /    /
 |             /         |             /         |        /    /
 |           ||          |           ||          |      ||   ||
 |           ||          |           ||          |      ||   ||
 |             \         |             \         |        \    \
 |              \        |              \        |         \____\
 |               |       |               |       |               |
 |               |       |              /        |               |
 |               |       |             /         |               |
 |           ____|       |            |          |           ____|
 |                       |            |          |
 |           ____        |             \         |           ____
 |               |       |              \        |               |
 |_______________|       |_______________|       |_______________|


 Fourth Order                    Fourth Order
 Single-Reflex Bandpass          Isobaric* Single-Reflex Bandpass
  _________________    ____      _______________________    ____
 |         |       |  |    |    |               |       |  |    |
 |        /        |  |    |    |              / \      |  |    |
 |       /                 |    |             /   \             |
 |     ||                  |    |           ||     ||           |
 |     ||                  |    |           ||     ||           |
 |       \                 |    |             \   /             |
 |        \                |    |              \ /              |
 |_________|_______________|    |_______________|_______________|


 Fourth Order                      Fourth Order
 Three Chamber                     Three Chamber Isobaric*
 Single-Reflex Bandpass            Single-Reflex Bandpass
  ____________   ____________      ______________   ______________
 |      |     | |     |      |    |       |      | |      |       |
 |     /      | |      \     |    |      / \     | |     / \      |
 |    /                 \    |    |     /   \           /   \     |
 |  ||                   ||  |    |   ||     ||       ||     ||   |
 |  ||                   ||  |    |   ||     ||       ||     ||   |
 |    \                 /    |    |     \   /           \   /     |
 |     \               /     |    |      \ /             \ /      |
 |______|_____________|______|    |_______|_______________|_______|


 Fifth Order = Fourth Order Enclosure + First Order Crossover
             = Third Order Enclosure + Second Order Crossover, etc.


 Sixth Order                        Sixth Order
 Dual-Reflex Bandpass               Isobaric* Dual-Reflex Bandpass
  ____    _____________    ____      ____    ____________    ____
 |    |  |       |     |  |    |    |    |  |      |     |  |    |
 |    |  |      /      |  |    |    |    |  |     / \    |  |    |
 |    |  |     /               |    |    |  |    /   \           |
 |           ||                |    |          ||     ||         |
 |           ||                |    |          ||     ||         |
 |             \               |    |            \   /           |
 |              \              |    |             \ /            |
 |_______________|_____________|    |______________|_____________|
 
 Sixth Order
 Three Chamber                        Quasi-Sixth Order
 Dual-Reflex Bandpass                 Series-Tuned Bandpass
  _    _________   _________    _      _________________    ____
 | |  |   |     | |     |   |  | |    |           |     |  |    |
 | |  |  /      | |      \  |  | |    |          /      |  |    |
 |      /                 \      |    |         /               |
 |    ||                   ||    |    |       ||                |
 |    ||                   ||    |    |       ||                |
 |      \                 /      |    |         \               |
 |       \               /       |    |          \              |
 |________|_____________|________|    |       ____|             |
                                      |                         |
                                      |       ____              |
                                      |           |             |
                                      |___________|_____________|


 Seventh Order = Sixth Order Enclosure + First Order Crossover, etc.


 * Isobaric or Coupled Pair (Iso-group) Variations:

 A variety of configurations may be used in the isobaric loading
 of any order enclosure. Physical and acoustic restrictions may
 make one loading configuration preferable to another in a
 particular enclosure.

 Composite or Push-Pull                  Compound or Piggy-Back
 or Face-to-Face Loading                 or Tunnel Loading
  _________________                 ___________________________
 |                 |               |                       ____|
 |                / \              |                      /   /
 |               /   \             |                     /   /
 |         >>> ||     || >>>       |               >>> ||  || >>>
 |         >>> ||     || >>>       |               >>> ||  || >>>
 |               \   /             |                     \   \
 |                \ /              |                      \___\
 |_________________|               |___________________________|

 Back-to-Back Loading                    Planar Loading
  _________________________         ___________________________
 |                _________|       |                        |  |
 |                \       /        |                       /   |
 |                 \     /         |                      /    |
 |              >>> || || >>>      |                    || >>> |
 |              >>> || || >>>      |                    || >>> |
 |                 /     \         |                      \    |
 |                /_______\        |                       \   |
 |_________________________|       |________________________|  |
                                                            |  |
                                                           /   |
                                                          /    |
                                                        || <<< |
                                                        || <<< |
                                                          \    |
 >>> indicates direction of                                \   |
 >>> simultaneous cone movement.                            |__|

    4.3 How do I build an enclosure?

    4.4 What driver should I use?

    4.5 Is there any computer software available to help me choose an
 enclosure and a driver? [MH]

 Various enclosure design software is available via ftp from
 csd4.csd.uwm.edu in the directory "/pub/high-audio/Software".
 The most popular program there is Perfect Box, which is in the
 file "perf.uu" (or "perf.zip").

    4.6 What is an "aperiodic membrane"? [CD]

 An aperiodic membrane is one part of a type of subwoofer
 enclosure.  It is an air-permeable sheet which has
 frequency-dependent acoustical resistance properties.  The
 original design goes back to Naim, for use in home systems, but
 has been applied by several individuals and companies in car
 audio.

 The completed system will be aperiodic, which means it will
 prove to be over-damped with a Q below 0.7.  In contrast, most
 car audio systems range from sort of to grossly underdamped,
 with Q's > 0.8 and higher.  These high-Q systems have poor
 transient response, nasty peaks in frequency response, and high
 rates of roll-off.  Aperiodic systems will feature excellent
 transient response, smooth frequency response, and extended
 very-low frequency reproduction.

 Another benefit of the system is that you can pretty much
 choose whichever driver you'd like to use, as long as they are
 big.  The Thiele/Small parameters (which would normally
 determine what kind of box would be used) are taken into
 consideration by the membrane designers so that the response is
 extended and overdamped, regardless of the characteristics of
 the driver.

 Physically, the aperiodic membrane isn't for every car.  It
 requires sealing the trunk from the passenger compartment in an
 air-tight manner, as well as sealing the trunk from the outside
 for best results.  The drivers are then mounted into the baffle
 between the passenger compartment and the trunk, as would be
 standard in an infinite-baffle/free-air set-up.  The aperiodic
 membrane is then placed either in front of the driver or behind
 the driver, depending on the type.  When mounting behind the
 driver, the membrane is used as the rear-wall of a very small
 box which the driver sits in (as in Richard Clark's infamous
 Buick Grand National).  So, in short, it's not suitable for
 trucks, jeeps, R/V's, or hatchbacks.

 You should probably only get an aperiodic membrane if you've
 got money to burn, lots of amplifier power, some big subs, a
 sedan, a desire for trunk space, and no wish to boom.  If your
 tastes lean towards bass-heavy booming, as opposed to
 well-recorded acoustic instruments, you're not going to be
 pleased with the result.

-- 
Jeffrey S. Curtis - stealth@uiuc.edu <> "Resplendent  in  full  regalia, they
Network Technician - UoI Housing Div <> revel in their role as self-appointed
Proton - Phase Linear - Polk - Sanyo <> critics  of   the   establishment..."
StreetWires - Jensen - Sony - Sennet <> -- INXS _Welcome to Wherever You Are_



******************************************************************************



From Packet: CHANNEL1
Message # 51052                                  Area : 1446  answers
From : Stealth@uiuc.edu                          11-06-93  01:31
To   : All                      
Subj : rec.audio.car FAQ (part 3
------------------------------------------------------------------------------
ÿ@SUBJECT:rec.audio.car FAQ (part 3/3)                                 
Message-ID: <rac-faq-p3-063122Nov61993@uxa.cso.uiuc.edu>
Newsgroup: rec.audio.car,rec.answers,news.answers
Organization: University of Illinois at Urbana

Archive-name: car-audio/part3
Version: 1.9
Last-modified: 05 Nov 93


      5 Installation

 This section describes how to do what you want once you know
 what it is you want to do.

    5.1 Where should I buy the components I want? [JSC]

 Most of the time, you will either buy from a local dealer, or
 from a mail-order house.  Buying from a local dealer can be
 good because you get to deal directly with a person: you can
 show them your car, ask specific questions, haggle prices, get
 quick service when there are problems, get deals on
 installation, etc.  But there can also be advantages to buying
 mail-order: generally cheaper prices, sometimes better service,
 etc.  In either case, you should always check prices before you
 buy, inquire about warranty service, and ask about trial
 periods.

    5.2 What mail-order companies are out there? [JSC,JM,MM]

 Crutchfield             800/955-3000
 1 Crutchfield Park
 Charlottesville, VA 22906 USA

 Advantages: great customer service; generally knowledgeable
      sales and tech support personnel; custom mounting
      kits, wiring harnesses, etc. free of charge.

 Disadvantages: limited product line; generally higher prices
         than local shops.


 J.C. Whitney            312/???-????
 ?
 Chicago, IL 6060? USA

 Advantages: 10kW amps for $19.99

 Disadvantages: 10kW amps that really only put out 1mW and break
         after first 10 minutes of use.


 Parts Express           800/338-0531
 340 E. First St.
 Dayton, OH 45402 USA

 Advantages: large selection of electronics supplies at
      respectable prices.  Showroom prices said to be
      better than catalog prices.

 Disadvantages: also carries some of the same quality-level
         components as J.C. Whitney.


 Classic Research/Z-Box 602/571-0171
 5070 E. 22nd St.
 Tucson, AZ  85711

 Advantages: creates custom door panels with car audio in mind.

 Disadvantages: only services expensive sports and luxury cars.


 MCM Electronics         800/543-4330
 650 Congress Park Drive
 Centerville, OH 45459-4072

 Advantages: sells lots of decently priced trinkets (fuses, fuse
             holders, wire, etc.) and has excellent service and
             available technical support.

 Disadvantages: ?

    5.3 What tools should I have in order to do a good installation? [JSC]

 Electrical tape - lots of it.  Make sure you get some that can
 withstand extreme temperature ranges.

 Wire cutters/strippers and crimpers.  Get a big pair with
 stripper holes precut for individual wire sizes.

 Angled screwdrivers.  Makes taking dash and rear deck speakers
 out a lot easier.

 Multiple size screwdrivers, both flathead and Phillips.
 Magnetic screwdrivers can be a big help when trying to get
 screws into (or out of) tight spaces.

 Various wrenches, pliers, and socket sets, depending on your
 vehicle.

 Metal drill and saw.  You'll need these if you need to modify
 your vehicle for new speaker cutouts or to accommodate a new
 head unit.

 Hot glue gun.  Good for putting carpeting or door panel trim
 back in place after modifications.

 Razor knife.  Helps for detailed modifications of door panels
 or carpeting, especially when installing new speakers.

 Wire.

 Shrink wrap or flex tubing.  Good for protecting wire,
 especially in the engine compartment.

 Multimeter.  Helps to diagnose installations.

 Extra hardware (screws, nuts, bolts, connectors, etc.).

 Fuse puller and extra fuses.

 Wire ties.  Helps to tuck wire away in otherwise exposed
 areas.

 Small light source.  A flashlight will do - you just want
 something that you can poke around the innards of your car
 with.

 Tape measure.

    5.4 Where should I mount my speakers?

    5.5 What is "rear fill", and how do I effectively use it? [HK,JSC]

 Rear fill refers to the presence of depth and ambience in
 music.  A properly designed system using two channels will
 reproduce original rear fill on the source without rear high
 frequency drivers.  Since recordings are made in two channels,
 that is all you will need to reproduce it.  What is captured at
 the recording session (coincident pair mics, Blumlein mic
 patterns, etc.) by a two channel mic array will capture the so
 called "rear fill" or ambience.  Many of the winning IASCA
 vehicles have no rear high frequency drivers.  Also a lot of
 this has to do with system tuning.  If rear high frequency
 drivers are added, however, the power level of the rear fill
 speakers should be lower than that of the front speakers, or
 else you will lose your front-primary staging, which is not
 what you want (when was the last time you went to a concert and
 stood backwards?).  The proper amount of amplification for rear
 fill speakers is the point where you can just barely detect
 their presence while sitting in the front seat.  Separates are
 not a requirement for rear fill; in fact, you may be better of
 with a pair of coaxial speakers, as separates may throw off
 your staging.

    5.6 How do I set the gains on my amp? [JSC]

 The best way to do this is with a test tone and an
 oscilloscope.  Since most people have neither item, the
 following will work approximately as well.

   1) Disconnect all signal inputs to the amp
   2) Turn all sensitivity adjustments as low as possible
  3) Turn head unit on to around 90% volume (not 100% or else
     you'll have head unit distortion in there - unless you've
     got a good head unit) with some music with which you're
     familiar, and with EQ controls set to normal listening
     positions
   4) Plug in one channel's input to the amp
   5) Slowly turn that channel's gain up until you just start
     to notice distortion on the output
   6) Turn it down just a wee little bit
   7) Disconnect current input
   8) Repeat steps 4-7 with each input on your amp
   9) Turn off head unit
 10) Plug in all amp inputs, and you're done

 If by some chance you do have an oscilloscope (and preferably a
 test disc), you do essentially the same thing as above, except
 that you stop turning the gains up when you see clipping on the
 outputs of the amplifier.

 Note that if you are paralleling multiple speakers on a single
 amp output, you need to set the gains with all of the speakers
 in place, since they will be affecting the power and distortion
 characteristics of the channel as a whole.

    5.7 How do I select proper crossover points and slopes?

    5.8 How do I flatten my system's frequency response curve?


      6 Competition

 This section describes the competition branch of the car audio
 world - what it is, and how to get involved.

    6.1 What is IASCA, and how do I get involved? [JSC,HK]

 IASCA is the International Auto Sound Challenge Association, a
 sanctioning body for car audio competitions held throughout the
 world.  Competitors earn points at each competition, and those
 that perform the best each year can advance to the finals.
 Prizes (trophies, ribbons, and sometimes cash) are usually
 given out to the top competitors in each class at every
 competition.

 There are registration forms for IASCA in every issue of Auto
 Sound and Security (see 7.1).

    6.2 What is USAC, and how do I get involved? [HK]

 USAC is another sanctioning body, similar to IASCA.  However,
 USAC places greater emphasis on SPL measurements than IASCA.

    6.3 What are the competitions like? [HK,CD]

 [HK writes:]

 They are much like loud car shows: a lot of cars parked with
 their hoods/doors/trunks open showing their audio systems.
 There are two types of judging styles: 1) drive through - where
 competitors drive their own vehicles to judging stations to be
 judged, and 2) walk-arounds - where the teams of judges will
 walk around the event site and judge vehicles that fit within
 their judging assignments.  Typically SPL is done first with
 the mic stand in the driver's seat and the competitor in the
 passenger side adjusting only the volume.  Hearing protection
 must be worn.  After SPL measurements are completed, RTA
 measurements are performed by playing pink noise.  When the
 volume level is within the specified "window" around
 90db-110db, the RTA judge will signal you out, and at that
 point you must exit the vehicle for the actual scoring
 measurements.  The next area for judging should be sound
 quality where two judges will sit in your car and judge the
 sound quality based on IASCA's reference CD/tape.  The next
 area is installation judging where the competitor has 5 minutes
 to explain and show the installation of his/her vehicle.  It is
 very useful to have a picture book/album of photos of the
 installation that may not be visible to prove that items not
 visible do exist.  When that is completed, the competitor can
 park the vehicle and show spectators the vehicle.  These
 procedures may differ from show to show, and at the
 regional/final levels they are very strict in what can and
 can't be done, e.g. a judge will make sure no adjustments are
 made after SPL until after sound quality judging is over, ear
 protection, etc.

 [CD writes:]

 Most involve a lot of waiting around.  Thus, they are perfect
 for meeting other people interested in car audio, and seeing
 some installations which may give you some ideas.  They're also
 perfect for listening to some cars that sound a lot better and
 a lot worse than your own.  In IASCA competition, the cars are
 judged on:

   Sound Pressure Level (30pts)
   Frequency Response (40pts)
   Staging (40pts)
   Stereo Image (40pts)
   Frequency Separation/Clarity (40pts)
   Sound Linearity (20pts)
   Absence of Noise (40pts)
   Ergonomics (20pts)
   Wiring/Electrical System Cosmetics and Integrity (35pts)
   Cosmetic Integration Consistency (40pts)
   Component Installation Integrity (55pts)
   General Creativity (20pts)
   Attention to Detail (15pts)

    6.4 Should I compete? [CD]

 You should compete if:

 a) You have an ok sounding stereo
 b) You have an ok installation (i.e. no amps/changers sliding
    around in the trunk)
        c) You'd like some pros to comment on your system
 d) Your feelings won't get hurt if you don't get first
 e) You've been to a contest and talked to competitors about it
 f) You've read the IASCA rulebook
 g) You've listened to the IASCA Test Disc in your car, and
    understand what the sound quality judges are listening for

 You can compete even if you don't do all of the above, but the
 recommendations will help you understand and gain the most from
 competing.

    6.5 What class am I in? [HK,JSC]

 [HK,JSC write:]

 There are three classes: novice, amateur, and pro.  The novice
 class is intended to be an unintimidating level where beginners
 can start out; however, a competitor may only be in the novice
 class for one year, at which time he is automatically moved to
 the amateur class.  Most competitors stay in the amateur class
 indefinitely, unless they become affiliated with a car audio
 shop or manufacturer, at which point they are moved into the
 pro class.

 [CD writes:]

 Are you or were you employed by a car audio manufacturer or
 dealer?
   Yes:  You compete in pro
    No:  Is this your first year of competing?
           Yes:  You compete in novice for the first year
            No:  You compete in amateur

 Note that modifying your amplifiers, buying your equipment
 below retail, or being sponsored by a manufacturer or dealer
 will get you kicked into pro.

 Also note that any home built active gear in the signal path
 (e.g. custom built equalizers, crossovers, or noise gates) will
 get you kicked out of novice.

 Once you know what group you are, you next need to know what
 power category you are in.  Add up the 4-ohm non-bridged rating
 of all your amplifiers, including your head unit if your head
 unit is powering speakers (rather than exclusively feeding
 amplifiers).  Then, find the category you fit into:

 Novice:  1-50  51-100  101-250  251-500  501+
 Amateur: 1-50  51-100  101-250  251-500  501-1000 1000+
 Pro:        1-100      101-250  251-500  501-1000 1001+

 Thus, if you had a Rockford Punch 40 (20Wx2) and a Punch 60
 (30Wx2), with a head unit that put out 6Wx2 (powering, perhaps,
 a center channel) you're in the 101-250 class.  It does not
 matter if your amps are bridged down to .002 ohms; it's only
 the 4ohm rating that counts.  If you no longer used your head
 unit to power speakers, you would be in the 51-100 class (or
 the 1-100 class if you were a pro).

 Competition is usually most viscious in the 101-250 and 250-500
 categories at typical contests.


      7 Literature

 This section describes various literature which you can read to
 brush up on your car audio skills, or to keep current, or to
 see other people's installations, or whatever else you'd like.

    7.1 What magazines are good for car audio enthusiasts? [JSC,MI]

 Car Audio and Electronics   $21.95/year
 P.O. Box 50267              (12 issues)
 Boulder, CO 80321-0267      800/759-9557

 Car Stereo Review           $17.94/year
 P.O. Box 57316              (6 issues)
 Boulder, CO 80323-7316      303/447-9330

 Auto Sound and Security     $28.95/year
 P.O. Box 70015              (12 issues)
 Anaheim, CA 92825-0015      714/572-2255

    7.2 Are there any newsletters I can read? [MO,HK]

 Autosound 2000 Tech Briefs  $35.00/year
 2563 Eric Lane, Ste D       (6 issues)
 Burlington, NC 27215        800/795-1830

    7.3 What books can I read? [JSC,JW,TT]

 Loudspeaker Design Cookbook
 by Vance Dickason
 Published by Audio Amateur
 ISBN ?
 $??.??

 Designing Speaker Enclosures
 by David Weems
 Published by ?
 ISBN ?
 $??.??

 Killer Car Stereo on a Budget
 by Daniel L. Ferguson
 Published by Audio Amateur Press
 ISBN 0-9624191-0-9
 $19.95


      8 Credits

 [JSC] Jeffrey S. Curtis (stealth@uiuc.edu)
 [JLD] Jason Lee Davis   (jdavis@wizard.etsu.edu)
 [MI]  Matt Ion          (matt@ship.net)
 [JW]  Jerry Williamson  (jerry.williamson@amd.com)
 [CD]  Cal Demaine       (demaine@ee.ualberta.ca)
 [MO]  Mark Obsniuk      (Mark_Obsniuk@sfu.ca)
 [HK]  Harry Kimura      (harry@alsys.com)
 [RDP] Dick Pierce       (DPierce@world.std.com)
 [BG]  Brian Gentry      (brian@eel.ufl.edu)
 [JM]  Jeff Meyers       (meyers@tellabs.com)
 [MH]  Marvin Herbold    (11mherbold@gallua.gallaudet.edu)
 [TT]  Trevor Tompkins (tt17+@andrew.cmu.edu)
 [MM]  Matthew E. Meiser (meiserme@nextwork.rose-hulman.edu)

--
Jeffrey S. Curtis - stealth@uiuc.edu <> "Resplendent  in  full  regalia, they
Network Technician - UoI Housing Div <> revel in their role as self-appointed
Proton - Phase Linear - Polk - Sanyo <> critics  of   the   establishment..."
StreetWires - Jensen - Sony - Sennet <> -- INXS _Welcome to Wherever You Are_