Collection of Internet/Collection of Internet.iso/faq/rec/car_audi/part1

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From: [e-mail] (Jeffrey S. Curtis)
Newsgroups: rec.audio.car,rec.answers,news.answers
Subject: rec.audio.car FAQ (part 1/3)
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Followup-To: rec.audio.car
Date: 6 Apr 1994 05:47:14 GMT
Organization: University of Illinois at Urbana
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Summary: This article describes the answers to the frequently
     asked questions on the rec.audio.car newsgroup.  This
     article is posted once per month.
Originator: [e-mail]
Xref: bloom-beacon.mit.edu rec.audio.car:14903 rec.answers:4772 news.answers:17720

Archive-name: car-audio/part1
Rec-audio-car-archive-name: FAQ/part1
Version: 2.1
Last-modified:  5 Apr 94


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+ Frequently Asked Questions with answers for rec.audio.car +
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      0 Introduction and Table of Contents

    This is the FAQ list for the Usenet newsgroup rec.audio.car,
    maintained by Jeffrey S. Curtis ([e-mail]), with
    contributions from many other people (see the credits
    section).  This document may be freely distributed and
    reproduced as long as it remains wholly unaltered and includes
    this notice.  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.  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,JW]

    Again, there is much debate over the benefit of the various
    schemes that are being used by different manufacturers.  In
    general, however, you will probably want to upgrade your
    speaker wire from the factory ~20 gauge to something bigger
    when you upgrade your amplifiers and speakers.  In most cases,
    16 or 18 gauge should be sufficient, with the possible
    exception of high-power subwoofers.  According to an example by
    Jerry Williamson, using 18 gauge instead of 12 gauge would only
    result in a power loss of 0.1dB, which is essentially
    undetectable by humans.  Thus, other factors play more
    important roles in the selection of speaker wire.  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 other areas with an
    abundance of sharp metal.

    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 - [e-mail] <> "You say these days are made of rust:
Network Coordinator - UI Housing Div <> ``Counted out! Counted out in loss!''
   Proton    <  Dodge  >   Pioneer   <> I've got plans to prove them wrong.."
Phase Linear < Stealth > StreetWires <> -- INXS _Full Moon Dirty Hearts_ 1993