"what kind of amp should I use?" or "how will these speakers sound?".
I've done a little searching and I've decided to compile a little FAQ (frequently asked questions) list on I.C.E. (In Car Entertainment)
Where should I buy the components I want?
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.
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What mail-order companies are out there?
Crutchfield -- 800/955-3000
1 Crutchfield Park, Charlottesville, VA 22906 USA
Advantages:
Great customer service
Generally knowledgeable sales and tech support personnel
Custom mounting kits, wiring harnesses, etc. free of charge.
Disadvantages:
limited product line generally higher prices than local shops
J.C. Whitney -- 312/431-6102
1917-19 Archer Avenue, P.O. Box 8410, Chicago, IL 60680 USA
Advantages:
Lots of "miscellaneous" items 10kW amps for $19.99
Disadvantages:
10kW amps that really only put out 1mW and break after first 10 minutes of use.
Parts Express -- 800/338-0531
340 E. First St., Dayton, OH 45402 USA
Advantages:
Large selection of electronics supplies at respectable prices.
Showroom prices said to be better than catalog prices.
Disadvantages:
Also carries some of the same quality-level components as J.C. Whitney.
Classic Research/Z-Box -- 520/571-0171
5070 E. 22nd St., Tucson, AZ 85711 USA
Advantages:
Creates custom door panels with car audio in mind.
Disadvantages:
Only services expensive sports and luxury cars.
MCM Electronics -- 800/543-4330
650 Congress Park Drive, Centerville, OH 45459-4072 USA
Advantages:
Sells lots of decently priced trinkets (fuses, fuse holders, wire, etc.)
Has excellent service and available technical support.
Disadvantages:
?
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There are many other mail-order houses that can be found in the back of magazines, such as S.B.H. Enterprises, Speed and Sound and Smile Electronics, but people seem to have mixed feelings about these companies. The prices are very low, often due to the fact that these companies are not factory authorized -- this means that there could be problems getting the unit serviced by the manufacturer should it break. To get around this, these mail order houses will often provide their own service departments, to repair defective units. Generally, it is advised to be careful when dealing with any mail order companies, to protect yourself.
There are also a number advertisements for mail order houses (such as Apex Audio & Electronics or Insider's Audio) that offer special deals or free equipment if you buy their expensive catalog or pay a membership fee. While these ads may be enticing, keep in mind that they are often too good to be true! Usually you have to buy a large amount of equipment before you qualify for the "bonus" or the prices are very high for most equipment.
What tools should I have in order to do a good installation?
Electrical tape
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
The specific sizes you need will depend 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
Soldering Iron
Makes excellent connections, but can be messy if not careful.
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.
In addition to the fuses for your stereo system, check your car's fusebox to find the various sizes you'll need. Also, you can use needle-nosed pliers to pull 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
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What is "rear fill", and how do I effectively use it?
Rear fill refers to the presence of depth and ambiance 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 ambiance. 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.
How do I set the gains on my amp?
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.
Disconnect all signal inputs to the amp
Turn all sensitivity adjustments as low as possible
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
Plug in one channel's input to the amp
Slowly turn that channel's gain up until you just start to notice distortion on the output
Turn it down just a wee little bit
Disconnect current input
Repeat steps 4-7 with each input on your amp
Turn off head unit
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.
How do I select proper crossover points and slopes?
Basically, this requires a degree of patience. The subwoofer should be started off at about 100Hz and adjusted until you are happy with the sound. Keep in mind that the higher the crossover point, the more power the driver on the high-pass will be able to handle but raising excessively may cause the low-pass driver to sound raspy or unnatural. The idea here is to first make rough selections to protect the drivers and then to fine tune crossover point selections to achieve optimum fidelity. It's all a matter of what sounds good to you after that, but remember that even minute changes in crossover frequency can make dramatic differences in the way your system sounds and images.
As a rule, subs should be crossed over no higher than 120Hz, a 6 1/2 mid should be able to handle about 90 Hz, a 5 1/4" should be okay with about 100Hz, a 4" -- about 500Hz, and tweeters vary from about 3500-5000Hz. These points all assume the use of a 12dB/octave crossover ... if you have a steeper roll-off a lower crossover point may be chosen. Remember, these are not hard and fast rules but rather a rule of thumb to help you get started (and so you don't blow up all your speakers when you are setting your gains!).
How do I flatten my system's frequency response curve?
First, you'll need a good quality equalizer - either a 2/3 octave (15-band) or 1/3 ocatve (30 band) equalizer or a quasi- parametric equalizer such as PPI's PAR 224 that allows you to choose the center frequency and bandwidth (Q) of each knob on the EQ. This will allow adjustments to very specific frequency ranges. Next, you'll need to get a hold of an RTA (Real Time Analyzer), which is an expensive piece of equipment that good shops will usually have. The shops can then equalize the system by making a measurement with the RTA, and varying the levels on the equalizer in order to make the overall response curve flat.
Unfortunately, most shops will not do this for free, since proper equalization can take anywhere from a half hour to many many hours.
Another method involves buying an SPL meter (available from Radio Shack for between $32 and $60) and a test disc (Autosound 2000 makes one that runs about $25) that plays discreet frequency ranges - in 1/3 octave groups. Then, moving through the range of frequencies, SPL measurements can be taken at each range, and you can plot out a "response" curve. You'll be able to see what frequency ranges need to be boosted and which need to be cut. This process will be time consuming (more so than an RTA, which can analyze the entire frequency spectrum simultaneously), but should be much less expensive than having it professionally done.
One last note: While a smooth curve will get the most points at an auto sound competition, you must NOT rely only on the RTA to tell you what sounds good. Use the RTA to get a good start, and then use your (better, use someone experienced in tuning systems) ears to do the fine-tuning.
How do I wire speakers "in series" and "in parallel?"
Wiring speakers in series involves connecting at least two speakers so that the first speaker's positive lead is connected to the amplifier's positive terminal, and the negative lead is connected to the positive lead of the second speaker. If there is a third speaker, its positive lead will be connected to the second speaker's negative lead ... and so on. The last speaker in the chain will have its negative lead connected to the amplifier's negative terminal.
Speakers that are wired in parallel are all connected to the positive and negative terminals of the amplifier. So, when two speakers are wired in parallel, you'll connect each speaker's positive lead to the amplifier's positive terminal, and you'll connect each speaker's negative lead to the amplifier's negative terminal.
Be careful when wiring multiple speakers in parallel or series so that you do not exceed your amplifier's rating. To calculate the effective impedance of a number of speakers, use the following formulas:
Series Connections: Z(t) = Z(1) + Z(2) + Z(3) + ... + Z(n)
That is, add up all of the impedances for each speaker to
get the total impedance. For example, with 3 4-ohm speaker
in series, the total impedance is 4 + 4 + 4 = 12 ohms.
Parallel Connections: 1/Z(t) = 1/Z(1) + 1/Z(2) + 1/Z(3) + ... + 1/Z(n)
That is, add up the inverse of the impedance of each
speaker and invert the sum to get the total impedance. For
example, with 3 4-ohm speakers in parallel, the total
impedance is 1 / ( 1/4 + 1/4 + 1/4) = 1 / (3/4) = 1.33 ohms.
Are there any alternatives for Dynamat? It's too expensive!
In this question, "Dynamat" refers to all commercial products that are marketed expressly for reducing ambient noise in the car. Dynamat, Stinger RoadKill, et al. all have similar pricing, so this question is intended to give non-standard options.
There is a material known as "Ice Guard," which is used by roofing contractors. It is similar to Dynamat, both in thickness and density. It is self-adhesive on one side, and seems to work very well. Unfortunately, it is sold only in large quantities (225 ft^2 rolls), and runs about $70 for this much. Perhaps a few people could get together for a roll, or it might be possible to get scraps from a roofing contractor.
How many devices can I attach to my remote turn-on lead?
The remote turn-on lead that most head units will not provide very much current (usually 250-300mA), so there is a limit to the number of components you can activate with it. Generally, it is safe to hook up two devices to the lead without having to worry about problems. However, if you'll be activating more components, then you should probably use a relay.
How do I wire a relay in my system?
There are two types of relays that are commonly used in 12-volt automotive applications: Single-pole Double Throw (SPDT) relays, which have 5 pins, and Single Pole, Single Throw (SPST) relays, which have 4 pins. Depending on the application, you can use either of these; for remote turn-on leads See section 5.11 How many devices can I attach to my remote turn-on lead? , an SPST relay is fine, SPDT relays are often used in alarm installations. Make sure that you get a 12-volt relay -- this specifies the voltage required to make the relay "switch."
Pins 85 and 86 connect to the coil which causes the relay to switch. On both relays, pins 30 and 87 are normally disconnected. When the relay is activated (switched) pin 30 and 87 are then in contact. The difference with the SPDT relay is that in the "normal" state, pins 30 and 87a are in contact.
To hook up a relay (either kind) for a remote turn on, make the following connections:
Pin 30
+12 Volts (Battery +)
Pin 87
Amplifiers' remote turn-on terminal
Pin 86
Head unit remote turn-on lead
Pin 85
Ground
Pin 87a
No connection (SPDT only)
How do I turn a stereo signal into a mono signal?
Creating a mono signal is often necessary when you are powering a subwoofer by bridging the amplifier. Many people do not realize that bridging an amplifier does not always provide a mono signal -- many amplifiers will simply use only one input channel, which means that the subwoofer won't be receiving the full signal.
Some amplifiers have a switch that will allow you to combine the left and right channels into a mono signal. Some signal processors and head units provide a subwoofer-out channel that can be switched between stereo and mono.
If you don't have this feature on any of your equipment, you will need to provide a mono signal to the amplifier. The common thought is to use a Y-adapter to "combine" the left and right channels. However, by using a Y-adapter, you are actually summing the line voltages and directly shorting the left and right channels at the head unit, which could cause problems.
The correct way to create a mono signal is to cut off the ends of the RCA cables, combine the signal grounds (the outer shield), and then use a 1 kOhm (1/4 watt, 5% tolerance) resistor to each of the center conductors. Solder and insulate the resistors so that you don't short them prematurely, and then connect the two resistors together. Connect the summed signal ground to the shield of the new RCA plug, and the summed center conductor to the center pin of the RCA plug.
How do I determine a speaker's polarity?
If you have a speaker and the terminals are no longer marked, you can do a simple test to determine which terminal is positive (+) and which is negative (-). This test is useful for midrange/midbass/subwoofers, but not for tweeters.
Use a 1.5V battery (AA, C, D) and connect the (+) terminal on the battery to one terminal of the speaker, and connect the (-) terminal to the other terminal of the speaker.
If the cone moves OUT, then the battery is connected "properly," i. e., the (+) terminal of the battery is connected to the (+) terminal of the speaker, and the (-) terminal of the battery is connected to the (-) terminal of the speaker.
If, however, the cone moves IN, the battery has been connected "backwards," i. e., the (+) terminal of the battery is connected to the (-) terminal of the speaker, and the (-) terminal of the battery is connected to the (+) terminal of the speaker.
Why are kickpanels such a popular location for mounting speakers?
There is a lot more to mounting speakers in the kick panels than just equalizing the path length difference (PLD). Two of which are: on-axis response, and angling for pattern control. On-axis response refers to the fact that most speakers sound best when listened to on-axis, or as close to on-axis as possible. Second, after mounting your speakers in the kick panels you can then angle the speakers to take advantage of their off-axis response to use output level to overcome any PLD that is still present. The pattern control I am mentioning is one of the ways a horn loaded compression driver works very well, they not only use amplitude to overcome any PLD that is still present they minimize early reflections that can destroy imaging staging and spectral balance.
PLD can be improved more than marginally when you consider the stock locations in a lot of vehicles, or the locations most installers choose. Measure the PLD between tweeters when mounted high in the dash or at the front corner at the top of the door and you will notice its probably on the order of 24". This mounting setup requires a lot of amplitude adjustment to correct the problems induced by this difference. The nearer tweeter is out phase from the opposite side and is arriving much sooner and with much greater amplitude due to the fact is not as far away. When all these factors are added together, it is very difficult for even the most flexible DSP unit to correct. On top of that, not many people or installers have access to the necessary tools to properly set up time delays using a DSP -- TEF, MLSSA or other very expensive time domain measuring equipment are required to do the job properly.
There will always be trade offs involved and deciding which trade offs to take can be very hard. A small dropout due to phase cancellation will probably not be noticed by most people but most people will quickly notice when a vehicle is not imaging properly, and if you can move the problem to higher frequency where we determine localization more from amplitude rather than phase differences, it will be much easier to deal with. Also, if you minimize the time/phase difference it will be much easier to correct with amplitude.
Some people complain that kickpanel mounting gives a low sound stage. However, keep in mind that when any stereo system is imaging properly the point sources can no longer be localized. When our brains can no longer localize the point sources it will then hear things at eye level.
What's worse for a speaker, too much or too little power?
Problems occur (in everyday operation) when distortion is fed to a speaker. This occurs MUCH more often when you are dealing with an underpowered system -- typically the owner will turn up the volume too much or set the amplifier gains too high to try and get more volume from the system. These introduce distortion to the signal -- this will destroy *any* speaker.
When a speaker is overpowered, however, it is not nearly as common to have these kind of problems, so speakers aren't blown as much. Of course, it is certainly possible to destroy a speaker (thermally) by overpowering it, but you'll have a pretty hard time doing this on your own, especially with standard car audio amplifiers.
Why is distortion harmful to my speakers?
Distortion is hard on speakers for two reasons.
Reason 1: Distortion causes the power spectrum to shift upwards in frequency. A bass note, when distorted, will have lots of high frequency energy. This will cause mid-ranges and tweeters to fry, if the amplifier is operating full range. It doesn't harm woofers, necessarily.
Reason 2: Distortion causes the average power to be much higher. Typically, a music signal that never clips has an average power level of 1/4 the peak power level for even the most compressed speed metal or pop. More dynamic music will be 1/8 the peak level or less on average. When you clip the amp hard, the average output moves up to the full-rated output of the amp or more. The peak to average ratio can be less than 2 to 1, with the peaks being at double the rated power of the amp, and the average being at the rated power of the amp or higher.
Thermally, the speaker can handle the average power being 1/4 the rated power of the amp (little to no clipping), but it will have a much harder time with the average power being the amp's rated power or more (massive clipping). As you might expect, this is pretty hard on the amp, too.
For transients, most speakers can handle a ton of power. But for long term signals, the power handling is much less.
What do all of those acronyms mean?
`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 have a potential difference of slightly higher than 12V, and the charging system can produce upwards of 14.5V when the engine is running.
`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 average 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.
An 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.
What is meant by "frequency response?"
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.
What is a "soundstage?" What is an "image?"
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.
What is meant by "anechoic?"
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).
The info in this section was obtained from Autosound 2000 by David Navone.
My speakers make this high-pitched whine which matches the engine's RPMs. What is it, and how can I get rid of it?
1. Check out the Amplifier(s)
After you have determined that there is noise in the system, determine if the amplifier is causing the noise. To do this, mute the signal at the inputs to the amp by using shorting plugs. If there is no noise, then the amp is fine, and you can proceed to level 2. However, if there is noise, then use a test speaker at the amp's output. If this stops the noise, then the problem is originating in the speaker wiring, or the passive crossovers. Check to make sure that none of these are shorting with the body of the car, and start again at level 1. If noise is still present when using the test speaker, then there may be a problem with the power supply on the amp. Try connecting an isolated power supply - if this does not get rid of the noise, then there is something seriously wrong with the amp, and it should be replaced. If the noise goes away, then there may be a problem with power supply filtering or isolation. This can be fixed by changing the amp's ground point or b adding external supply filtering.
2. Reduce the System
The amps have been determined to be noise free. If you have any processors between the head unit and the amps, disconnect them and connect the head unit directly to the amp. If this gets rid of the noise, then one (or more) of the processors must be at fault, so proceed to level 5. Otherwise, try running the signal cables over a number of different routes. If you are able to find one that does not produce any noise, permanently route the cables in the same manner, and proceed to level 5. If not, then you must isolate the head unit from the car's chassis (except for its ground!) -- don't forget to disconnect the antenna, since it is also grounded to the car. If isolating the head unit does not solve the problem, the move the grounding point of the head unit. Hopefully the noise will be gone, and you can install the head unit with a quiet ground and proceed to level 5, otherwise go on to level 3.
3. Move the Head Unit
The amplifiers are fine, but moving both the ground for the head unit and the signal cables does not solve the noise problem. Take the unit completely out of the dash, and put it on either the seat or carpet, and run new signal cables to the input of the amp. If this solves the problem, re-install the head unit, one step at a time and skip to level 5. But if the noise persists, then move the head unit as close to the amp as possible and use the shortest possible signal cables. This will verify that the original signal cables are not causing the problem -- assuming the noise is gone, reinstall the head unit one step at a time and go to level 5. Otherwise, there may be a problem with the power filtering for the head unit. As with the amps, power the head unit with an isolated power supply (again making sure that the head unit isn't touching the car's chassis at all). If the noise goes away, you can add power supply filtering or an isolated power supply; go to level 2. But if the isolated power supply does not solve the problem, then you can either replace the head unit and go to level 2, or check the car's electrical system in level 4.
4. Testing the Car
There does not seem to be a problem with either the head unit or the amplifier, and the car's charging system is suspect. To see if this is the case, we can use a system in a car that is already known to be "quiet." Bring both cars together as if you were going to jump one, and use jumper cables to connect the two batteries. Start the engine of the car with the noise problem, and listen to the "quiet" car's system. If the noise does not go away, there is a SERIOUS problem with your car's electrical system (possibly a bad alternator). Have a qualified mechanic check the charging system out. If there is no noise in the "quiet" car, then the "noisy" car's charging system is definitely quiet, so continue with level 5.
5. Adding Signal Processors
We have proven that the amplifiers are good, the head unit is good, and the car's electrical system is good. Now we need to reconnect each signal processor. Repeat this level for each signal processor used in your system; if you have added all of your signal processors, and there is no longer any noise, CONGRATULATIONS! You've removed the noise from your system! Connect the signal processor. If there isn't any noise, then go on to the next signal processor. Otherwise, try re-routing the signal cables. If this cures the problem, the route them permanently over the quiet path, and install the next processor. If not, then isolate the processor from the car's chassis except for a single grounding point. If this works, then permanently isolate the processor, and move on to the next processor. If isolation does not help, then advance to level 6.
6. Processor Isolation Tests
Now, noise enters the system when one particular processor is installed, but regrounding it does not help. Move the processor very close to the amp, and check for noise again. If there isn't any, then re-install the processor, carefully routing the cables to ensure no noise, and continue at level 5 with the next processor. Otherwise, use an isolated power supply to power the processor, making sure that no part of the processor is touching the car's chassis. If this solves the problem, the consider permanently installing an isolated power supply or possibly a 1:1 transformer, and go to level 5 with the next processor. Otherwise, separate the processor and isolated power supply from the car by many feet and re- test. If there is still noise, then there is a serious problem with the processor's design. Get a different processor, and continue at level 5 with it. If separating the power supply and processor from the car does solve the noise problem, then either the processor is damaged, or your tests were inaccurate. Repeat level 5.
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