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Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!spool.mu.edu!sdd.hp.com!vixen.cso.uiuc.edu!uxa.cso.uiuc.edu!jsc52962 From: stealth@uiuc.edu (Jeffrey S. Curtis) Newsgroups: rec.audio.car,rec.answers,news.answers Subject: rec.audio.car FAQ (part 1/1) Followup-To: rec.audio.car Date: 6 Aug 1993 14:35:55 GMT Organization: University of Illinois at Urbana Lines: 1415 Approved: news-answers-request@mit.edu Distribution: world Message-ID: <rac-faq-143637Aug61993@uxa.cso.uiuc.edu> Reply-To: stealth@uiuc.edu (Jeffrey S. Curtis) NNTP-Posting-Host: uxa.cso.uiuc.edu Summary: This article describes the answers to the frequently asked questions on the rec.audio.car newsgroup. This article is posted approximately once per month. Originator: jsc52962@uxa.cso.uiuc.edu Xref: senator-bedfellow.mit.edu rec.audio.car:13228 rec.answers:1746 news.answers:11086 Archive-name: car-audio/part1 Version: 1.5 Last-modified: 05 Aug 93 *+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+*+* + 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. 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). 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 "sound stage"? What is an "image"? [JSC] When you attend any sort of music concert, the various performers tend to be spread across the stage - bassist on the right, drums in the rear, lead vocalist front and center, lead guitarist on the left, etc. One goal of a car audio system is to reproduce the music as though it were live. Accordingly, the "sound stage" should sound live: if you close your eyes and listen, you should be able to hear the bassist on the right, the drums in the rear, the vocalist in the front and center, and so on. An image is where a sound "looks" like it is coming from: in the above example, the lead guitarist's image is on the left side of the sound stage. A system which exhibits good staging will produce the guitarist's image on the left; a system with good imaging will "lock" his image into a fixed place instead of letting it "drift" across the stage to the right, or from front to back. 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? 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. 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! Your wire's insulation may very well become weak and brittle with age, and could 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. 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] 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. 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. 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, 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, 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(25) = 5V. 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 +). 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? 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? [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 absorbtion 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 resistave 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 propogation 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) _______________________ _______________________ | | | _____| | / | / / | / | / / | || | || || | || | || || | \ | \ \ | \ | \____\ |_______________________| |_______________________| Third Order Third Order Third 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? 4.6 What is an "aperiodic membrane"? 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] Crutchfield 800/955-3000 ? ? 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? 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 ? ? Advantages: large selection of electronics supplies at respectable prices. Disadvantages: also carries some of the same quality-level components as J.C. Whitney. Z-Box 602/571-0171 ? ? Advantages: creates custom door panels with car audio in mind. Disadvantages: only services expensive sports and luxury cars. 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] 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. 6.4 Should I compete? 6.5 What class am I in? [HK,JSC] 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. Within each class, there are categories based on total system power calculated from the amplifier ratings into a four ohm load. The novice and amateur classes have breakdowns for 1-50W, 51-100W, 101-250W, 251-500W, 501-1000W, and 1001+W. The pro class is the same, except for combining the 1-50W and 51-100W classes into a single 1-100W class. 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] Loudspeaker Design Cookbook by Vance Dickason Published by Audio Amateur ISBN ? $??.?? Designing Speaker Enclosures by David Weems Published by ? ISBN ? $??.?? 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) -- 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_