In this paper, we are going to look at some of the common causes of noise in
your system, and how to track down and eliminate their sources. Some of the
things this page will cover include:
- external interference
- batteries
- alternator whine
- isolator whine
- grounds
- trouble shooting step by step ...time to
get dirty
Common Causes
The Environment. Sometimes the environment can play a role in the noise your system is making. Around hospitals, high voltage power lines, and radio stations (not the public listening type either), you pick up alot of interference. Also, extremely HIGH humidity can cause problems. A cold start on foggy morning can lead to some alternator whine thanks to moisture. For the same reason, corrosion builds up on your electrical connections, causing increased resistance. And the most obvious, you are at a show and keeping your battery topped off with a charger! AC power lines are very dirty, and you should disconnect all sources of external power during judging anyhow.
A poor battery. Check the voltage on your battery with the engine off. IME a good battery will be somewhere around 12.7 volts, plus or minus 0.2 volts. If you're right at 12, or even under, then try charging your battery. Constant low voltage is a sure indication you need a new battery, OR have a charging system problem. Check this link if you suspect your charging system. If you have a dual battery setup, then it is likely you have more complicated problems. Differing voltage in a system can be cause for minute annoying little buzzes. Proper power systems should keep a constant voltage (although this is next to impossible, it's what you want to work towards. If you have one battery that's keeping a different voltage, the unbalance between equipment using that voltage can cause interface problems with equipment not using that source.
Bad grounds. A bad ground is probably the most common cause of noise. If one of your audio componants is poorly grounded, it's not getting as much voltage as other componants are. For more on proper grounding, check the appropriate tech paper.
Isolator whine. Before proceeding to the next culprit, it is VITAL that you bypass your isolator and make sure it is not the problem. This is simple to do, and is just as mandatory as checking a fuse when nothing works at all. To bypass the isolator, unhook all of the wires from it, there should be four wires. hook the 3 wires from the alternator, battery 1 and battery 2 together (easiest way to do this is with a bolt and nut) BE SURE and tape the assembly off so that an accidental grounding does not occur. You could also test the system with the alternator unplugged, (engine off of course)
Only after you have eliminated the above possibilities should you begin to tear apart your system and start checking components (unless of course you just changed amps or something and have good reason to believe it is the system). In the end use your head, think about it logically. MOST important of all, write down EVERYTHING you find out no matter how insignificant it may sound, if in the end you cannot isolate the problem, and have to drop it off at the store your notes may reveal to a skilled installer exactly what the problem is saving you A LOT of $$. As you're reading through this, the idea is to eliminate as much of the electronics as you can between you signal source, and your speakers. Then, read each componant till you're done.
- You may find throughout this procedure your noise may change in pitch and volume. This is due to various levels of processing. To counter act this Set all of your processors, eq curves, bass levels, treble etc to the middle or zero setting, depending on equipment... working upline to a component that amplifies or alters a bad signal, may cause a false assumption. (its amplified or altered now and is misinterpreted as the source, while it is merely amplifying or distorting the source noise.), .........even though in theory it cant amplify a bad component that isn't hooked up (further upline), still good to keep this in mind
- Gather supplies: If you don't already have one go to radio shack and find a cord that turns the headphone output on your walkman or home stereo into an RCA cable. Use this cable for all source signals during the testing. Also buy about 4 female-female RCA y splitters...(to be used in steps 5 and 7), also have handy an extra RCA cable, at least 10 feet long, or long enough to bridge any two components.
- Now your ready for the fun part, what's
behind door #1? Unhook the RCA's from each of your amps or the suspect
amp, feed it the clean signal from the home stereo... do you have noise?
- NO I don't have any more noise: then your in good shape this means the amp(s) AND the speakers are OK, hook the RCA's back up to each amp, move to the end of these RCA's (your not at the next piece yet, its time to check the RCA's themselves leading to the amps. move on to step 4
- YES I still have noise: check for the
following, since you have noise you can assume for now that the problem
is in your amp, speakers, or speaker wire routing.
- Power supply problem, if you went through the beginning of this paper and did not find anything wrong, then it is safe to rule this possibility out, though be sure and make a note of it.: TAKE NOTES
- Possibly poor speaker mounting/wire
routing: Unhook the speakers from the amp and test them from an
external source, do you still have noise?
- NO: Good then you know your speakers are OK, this means that your amp is a likely suspect. read on.... and TAKE NOTES.
- YES: either your speakers or the crossovers (if you have components) are bad, you can test each driver individually in this case in order to rule out the speakers, leaving the crossover as the culprit
- Bad amp: if none of the above criteria solve your problem then your amplifier is probably bad, or the power supply to it, you can test the power supply with another amp you know is good, or you can just "fiddle", checking the grounds and wire routing.
- Check the RCA's: Again feed a clean
signal from the end of the RCA's to each amp. This may require a
female-female connector from radio shack, our king-of-connects.
Y-splitters work very well and serve a dual purpose for later on when you
test out the crossovers. Do you have noise?
- NO: Good then your RCA's are not damaged fried or poorly routed* (*keep in mind that the other RCA's and wires don't all have power and signals at this point. TAKE A NOTE OF THIS. proceed to step 5
- YES: Check the routing of your RCA's for help on this refer to the tech paper on "wire routing", also, check to make sure that none of your RCA cables are physically damaged. Damage on the outside may be a sure indication that the inside of the cable is also damaged. Have a spare RCA, a cheap-o will do fine. Use this cable and test again for noise. If you still have noise then re-check your amplifier in step three. This is rather bizarre, I would not expect anyone to have such luck, if so mail tech@mmxpress.com
- This step will be repeated for each set
of signal processors, in-between each step refer back to step 4, and check
each set of RCA's. AS you move up the line, hook your signal processor up
to the RCA's leading down to the amps, remember we already know that every
thing in this particular setup is good, so if there is noise, then the
processor is causing it. Do you have noise?
- NO: If you don't have any noise then your first processor or crossover is in good shape, proceed to check the RCA's leading up to the next level. (step 4)
- YES: If you have noise then your
crossover/processor, is the problem, likely causes for this may be:
- Poor ground on the crossover, see the tech paper on grounds. Damage due to insecure mounting, (internal breakage) is the crossover spliced into the amps power supply? that's a NO NO, as I read in another paper once....what happens in the shower when you flush the toilet?
- NOTE: If you're looking for the source of turnoff - pop, and you now have turn off pop, it is because your processor is cutting of the signal before the amp shuts down, remedy? you need to create a circuit with a diode, and capacitor to keep the EQ on longer. (mine stays on for 30 seconds after shut down) a good explanation of this can be found in the RAC-FAQ, look for turn off pop. It will explain how to wire up the diode.
- At this point refer back to step 4, and
then 5, and then 4, and then 5, etc until your at the head unit. Each
time testing the system with an external source. TAKE NOTES ! ! If you
make it up to the head unit with no noise, after having completed step 4
once again... remove the head unit, your problem may be:
- Bad Ground: check the ground on your head unit. tech paper on grounds
- Poorly mounted, is your head-unit in an other-than-stock location? If so, is there a heat vent blowing on it 24-7?
- Mechanically bad mount, does your head-unit dance around inside the dash every time you hit a bump, when you hit a bump do you look at your HU and sigh relief that it still works? If so, FIX IT.
- The dash contains a lot of vents, and such, it may be that your head-unit is just dirty, you may try blowing it off gently with an air compressor.
- Bad Head-Unit: Get it fixed or purchase a new one.
- Once you have found your faulty component, by-pass it and make sure the system works well without it, this is where the RCA Y-splitters come in handy, mainly if a crossover is your problem.
