Archive-name: car-audio/part2
Rec-audio-car-archive-name: FAQ/part2
Version: 3.1
Last-modified: 5 September 95

      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,DK]

	Usually, yes.  Using separates allows you to position the
	drivers independently and more carefully, which will give you
	greater control over your imaging.  For best results, try to
	keep the mid and tweeter as close together as possible -- this
	will make the two drivers act more like a single point source
	(which is ideal).

	For rear fill applications, however, coaxial speakers will perform 
	fine, as imaging is not a primary concern.  However, it is very
	common to use a low pass crossover with the rear speakers (at
	2500 Hz) since rear-fill is intended to produce "ambiance," and
	high frequencies (> 2500 Hz) can confuse the soundstage, making
	it appear that music is originating behind you.

    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 an 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
	off of ONE pair of the amp's channels.  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.

	However, for this to work, the amplifier must actually use both
	input channels in bridged mode.  Many amplifiers, when placed
	in bridged mode, will simply "copy" and invert either the left
	or the right channel.  This practice ensures high output to the
	mono speaker, but eliminates the possibility of mixed mono
	since you lose one channel.

    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, IDB]

	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.  

	Generally, "good" amplifiers tend to cost more (in money/watt) 
	than "bad" amplifiers.  So when you see an amp advertising 300W
	for only $100, and are comparing an amp with 50W for $300, you
	will usually find that the 50W/$300 amp will be of much higher
	quality than the 300W/$100 amp.

   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 collections of purely passive (unpowered)
	devices - mainly capacitors and inductors and sometimes
	resistors.  There are also active crossovers which are powered
	electrical devices.  Passive crossovers are typically placed
	between the amplifier and the speakers, while active crossovers
	are typically placed between the head unit and the amplifier.
	There are a few passive crossovers on the market which are
	intended for pre-amp use (between the head unit and the
	amplifier), but the cutoff frequencies (also known as the
	"crossover point", defined below) of these devices are not
	typically well-defined since they depend on the input impedance
	of the amplifier, which varies from amplifier to amplifier.

	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.

	It should be noted that the slope (rolloff) of a crossover, as
	defined above, is only an approximation.  This issue will be
	clarified in future revisions of this document.

	The expected impedance of a passive 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,JR]

	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, since the
	losses can effectively be negated by adjusting the amplifier
	gain.  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 -18dB/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.  Furthermore, since an active crossover is by definition
	a powered device, the use of one will raise a system's noise
	floor, while passive crossovers do not insert any additional
	noise into a system.

	Many people find it advantageous to use both active and passive
	crossovers.  Often, a separate amp is dedicated to the subwoofers, 
	to give them as much power as possible.  The other amplifier is 
	used to power the mids and tweeters.  In this scheme, an active
	crossover is used to send only the sub-bass frequencies to the 
	sub amp, and the other frequencies to the other amp.  The passive 
	crossovers are used to send the correct frequencies to the 
	individual speakers (e.g., mids and tweeters).

	Thus, if you have extra money to spend on an active crossover
	and separate amplifiers, and are willing to deal with the
	slightly more complex installation and possible noise problems,
	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 design my own passive crossovers? [JSC,JR]

	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 roles can be reversed
	under certain circumstances: a capacitor in parallel with a
	driver will act as a low pass filter, while an inductor in
	parallel with a driver will act as a high pass filter.
	However, a parallel device should not be the first element in a
	set; for example, using only a capacitor in parallel to a
	driver will cause the amplifier to see a short circuit above
	the cutoff frequency.  Thus, a series device should always be
	the first element in a crossover.

	When like combinations are used, the order increases: a
	crossover in series 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 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 simply reversing the
	polarity of one of the drivers, since they would otherwise be
	180 degrees out of phase with respect to each other.  In any
	case with any crossover, though, you should always experiment
	with the polarity of the drivers to achieve the best total
	system response.

	One other thing to consider when designing passive crossovers is
	the fact that most passive crossovers are designed based on the
	speakers' nominal impedance.  This value is NOT constant, as it
	varies with frequency.  Therefore, the crossover will not work 
	as it has been designed.  To combat this problem, a Zobel circuit 
	(also known as "Impedance Stabilization Network") should be used.
	This consists of a capacitor and resistor in series with one
	another, in parallel with the speaker, e.g.,

			  ________                __
	  	 +  o----|        |----o-----o + |  | /
	   INPUT         |  Xover |    R1        |  |/
			 |        |    C1        |  |\
                 -  o----|________|----o-----o - |__| \

	To calculate these values, R1 = Re (in ohms) x 1.25, and C1 =
	(Lces {in henries} / Re^2) * 10^6.  See 4.1 for definitions of
	Re and Lces.  R1 will be in ohms, and C1 will be in uF (micro-
	farads).  As an example, an Orion XTR10 single voice coil woofer 
	has Re = 3.67 ohms and Lces = 0.78 mH.  So, R1 = 3.67 * 1.25 
	= 4.6 ohms.  C1 = ( 7.8E-4 / 3.67^2 ) * 10^6 = 57.9 uF  (be
	careful with units -- 0.78 mH = 7.8E-4 H)

	As with the definition of crossover slopes, the above
	definition of the phase shift associated with a crossover is
	also an approximation.  This will be addressed in future
	revisions of this document.

	For tips on building the crossover, please see section 3.30.

   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 typically have the adjustments
	for anywhere from five to eleven (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? [HK]

	Generally, companies that produce 1/3 octave (30 band) and 2/3 
	octave (15 band) equalizers are good.  These include AudioControl, 
	USD, Rane, Phoenix Gold.  Most people try to stay away from
	equalizers that contain a "booster;"  these are made by Kraco,
	Urban Audio Works and others.

   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? [IDB]

	It is getting difficult to find pullout CD players any more,
	since detachable faceplates are much more convenient to carry
	around.  However, there is the obvious trade off -- it is still
	possible to steal the chassis for the detachable face unit, when
	that is not possible with a pullout.  Although some companies
	will advertise that it is very difficult to get replacement
	faces without the original receipt, theives can still get the
	faceplates.

	Some companies, such as Eclipse, are starting to offer
	alternative methods for preventing theft.  Some Eclipse decks
	now offer ESN (Eclipse Security Network), where the owner
	chooses a "key" CD that must be inserted to "revive" the deck
	should it lose power.  The entire deck stays in the dash, with
	nothing to carry around;  this expands on the trend towards
	convenience while offering the owner peace of mind.


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

	Generally, Alpine, Clarion, Eclipse, McIntosh, Phillips and 
	Pioneer are considered to produce good quality CD head units.
	They all have their problems, but these brands seem to be
	common and relatively problem-free.

	Bad brands include Kraco, Radio Shack, Rockwood and other
	"bargain" brands.

   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]

	MiniDisc (MD) seems to have a better future than Digital Audio
	Tape (DAT) or Digital Compact Cassette (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 CDs 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 CDs.

   3.25 Are those FM modulator CD changers any good? What are my other
	options? [PW,JGr]

	Almost all manufacturers offer an FM modulator for their
	changers.  As with all equipment, some are good and some are not. A 
	person thinking about using an FM modulator must take into 
	consideration that the sound quality will only be as good as the 
	tuner in your head unit.  Also, FM is limited in its frequency 
	response.  There is usually a noticable loss of the high 
	frequencies, due to the nature of transmitting via FM. 

	If you do not want to use an FM Modulated CD changer, some
	manufacturers make controllers for changers that feature
	line-level (RCA) outputs.   This allows you to connect the 
	changer directly to an amplifier, bypassing the stock system
	altogether.  Some models offer line-level inputs, allowing you
	to connect the stock system to the changer (so you can continue
	to use your radio/tape).  Clarion, Sony, and Kenwood make such
	units.

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

	You will find that those companies who make high-quality in-dash
	CD players will also make good CD changers.  Refer to 3.20 for
	a list.

   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? [DK]

	Sound field processors (also known as DSPs) are fun toys to play
	with, and can have some use, but it is generally good to keep
	the KISS principle in mind:  Keep It Simple, Stupid.

	The fewer signal processors (this includes equalizers, and active
	crossovers) that are in your system, the less chance there will
	be for noise to enter your system.  You'll also save money, have
	a lower noise floor.  Surround sound processors and bass
	regenerators are nothing more than bells and whistles and are
	totally superflous in a properly designed system.

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

	If you do decide to buy a signal processor, try to stick with 
	reputable brands like:  AudioControl, Clark, Crystal-Line,
	Phoenix Gold, Rane or Clarion.  Try to stay away from brands
	such as Petras, Urban Audio Works and Kraco.

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

        This section assumes that you have a basic understanding of how
	to solder, so the actual assembly of the crossover is not
	discussed.  Rather, tips on choosing the proper types of
	capacitors and inductors are given here.

        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.

--
Ian D. Bjorhovde                  UofA Div. of Neural Systems, Memory & Aging
ianbjor@NSMA.Arizona.EDU                           UNIX Systems Administrator
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Pager/VoxMail:  520/571-4347       WWW:  http://www.nsma.arizona.edu/~ianbjor