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Old 09-09-2003, 04:09 PM
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68fury 68fury is offline
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Default Fixing common car audio problems

Apologies if some/all of this is in "British English" technical terms... Might be of some use to some of you guys.

One of the most common and annoying faults with installs is the presence of noise being amplified through the speakers. This noise is caused by the car’s ignition system being picked up by the stereo system. Taking a methodical approach we can often cure these faults quite easily though.

This is what works for me…

Always start at the front. Is the noise present on radio and CD or radio only? A damaged or badly earthed aerial can pick up noise, or a chaffed or damaged aerial cable. Also be aware that faults with the ignition system can cause interference being picked up through the aerial. Check for damaged HT leads, arcing coil, cracked distributor cap, etc. If the noise is present when the CD is played too then on to step two.

Disconnect the RCA leads from the back of the head unit. If there are more than one pair of RCAs then disconnect all of them and repeat this test on each in turn. Get a portable music source (I use a walkman - you can get adaptors to turn the headphones socket into RCAs from Maplins and other such places). Play the portable source down the RCAs. If the noise is no longer present then the problem is with the head unit. Check it is correctly earthed. Most times they are earthed through the cars wiring loom via the ISO block. If you have head unit generated noise then it is best to earth the head unit to the car body directly and bypass the loom. I usually find there is a suitable earthing point behind the dash where the eater bolts to the front bulkhead. If this doesn’t cure the noise then run a separate power lead to the head unit direct from the battery (remember to fuse this wire somewhere near the battery terminal end).

If the fault isn’t on the head unit (i.e. the noise stays when you did the test above) then lets go open the boot. Disconnect the RCAs from the first point they enter the boot. This could be Y-Leads, an amp, a crossover, whatever. Play the walkman down the Y-leads or into the amp directly using a known-good RCA lead. If the noise stops now its because the main RCA lead(s) down the car are damaged. Replace them with new ones to cure this. Don’t forget to test the Y-leads or any male-female adaptors you have too.

If the noise persists on the test above then repeat for every device in-line until you reach the amp itself. This is when you realise simple installs are the best ones! Which ever electronic device is actually causing the noise the fix is the same. Check the main power feed is cleanly connected (this is just good practice rather than an attempt to fix the noise problem) and check the earth point that the earth lead goes to. If you have multiple amps or other devices (EQs, bass cube, etc.) in the boot you should always aim to have them earthed at the same point. Ideally if the battery is in the boot you should run the earth for the system back to the negative terminal on the battery. Use a distribution block for this so that you only have one lead at the terminal itself.

Earth points in the car should be cleaned up with 400 grade sand paper so that they are smooth and shiny, then screw the earth to it nice and tight, then apply a blob of Vaseline or axle grease over the bare metal/connector to prevent corrosion.

If your install has more that one set of RCA leads down the car then you will have to repeat the above tests for each set of RCAs until you have been through the whole system and isolated all the noise.

NOTE: If re-earthing etc. the device causing the problem does not fix the fault it is likely faulty. Try swapping in a similar device from a mate’s install to see. Some devices are very prone to introducing noise in systems – these are usually cheapo brand active crossovers (Pro-Sound, Tornado, etc.) or some real cheapo amps can do
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Old 09-09-2003, 04:10 PM
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Default

This is not an exhaustive list of faults and not intended to list every possible cause, just those I have found to be most common. Any other suggestions welcomed.

AMP DOES NOT POWER ON: Usually the remote lead has become detached. Use a crimp on connecter (the flat sort with a hole through the middle rather than the “fork” type) to prevent this happening again.

BASS GETS TOO QUIET WHEN SPEAKERS ARE BALANCED (USUALLY FRONT/REAR): The RCA output on your head unit is not set non-fading. On head units without a dedicated sub-out the RCA outs can be set fading or non-fading. For a sub you want them non-fading. Consult your head unit’s instruction manual to see how to set this up.

FRONT SPEAKERS DO NOT BALANCE CORRECTLY (LEFT/RIGHT): Usually you find unexpected changes in volume when fading left to right. In this case one of your speakers is wired out of phase. Simply disconnect the speaker wire and reverse the wiring of one of them (easiest done on the amp if you are using one). Even if you KNOW your speakers are wired up right its worth trying this as some systems sound a lot better when wired out of phase.

SYSTEM “POPS” WHEN TURNED OFF: (usually through subs) This is usually only a problem in systems with extra boxes such as EQs or active crossovers as most decent amps these days have “soft turn off circuitry” fitted as standard. Basically one of your devices is emitting a pulse down the RCA when it is turned off, this is then amplified by the amplifier as a sound. What you want to do is arrange things so that this device turns off AFTER the amp has done so that there is nothing to amplify the pop. I have seen “turn off delay” boxes for same. Basically these are just small capacitors wired in the remote line to the device so that it stays on a few milliseconds longer – long enough for the amp to have shut down. You can make your own with a few bits from Maplins for less. I can’t recall the value of the cap to use – anyone else know?

SUB SOUNDS TO BE “CHUFFING” (Ported enclosure) – port size is wrong for the sub/enclosure. In which case get a box designed by someone who knows how to use Bass Box Pro or similar. Box leaks can also cause bad sound in ported boxes. Check it is sealed properly around all joints. Use a thick glue like Liquid Nails for this rather than silicon sealer which gives of a vapour when it dries which can damage the sub.

SUB SOUNDS MUFFLED / LACKS PUNCH – most usual cause is sub not sealed properly against box. Ensure sub is screwed in tight, box face is flat etc. You can use a MDF ring, sealing tape, etc. to ensure a good seal. Also if the box is leaking this will affect bass. Fix as above.

SUB IS OUT OF TIME WITH MUSIC: Either the sub is out of phase (reverse the wiring if the sub to the amp) or the box design is wrong for the sub (usually too big). Try padding the box out with something solid like MDF off-cuts to reduce its internal volume or try a smaller box. If it’s a ported box check the design is correct for the sub with suitable software.

FRONT SPEAKERS LACK MIDBASS/ DEPTH – check high pass is not set too high. Check speaker is screwed in to mounting correctly. If there is any air gap between the speaker frame and the surface it mounts to then bass response will be reduced (just as in the sub example). Use draft excluder, rubber, thin MDF spacer, or even mastic etc. to ensure an airtight seal.

FRONT SPEAKER BUZZES (same pitch all the time) – speaker or grill is loose. Possibly speaker cable is vibrating against part of the dash/door/whatever. Remove speaker, tidy up wires and tape up as necessary, screw speaker/grill in nice and tight.

FRONT SPEAKER DISTORTS ON LOW NOTES: Speaker is being asked to produce bass lower than it can handle. Check the high pass filter is on at the amp and adjust up until distortion stops. If you are running the speaker off the head unit check if there is a high pass filter option on the internal amp. If not then a bass-blocker can be used (these cost about a tenner from Halfords and similar places).

FRONT SPEAKERS DISTORT FULL RANGE (usually noticeable on high notes) – amp is clipping. Check gain setting on amp is set right (usually should never be over three quarters mark). If running speaker off head unit – what volume are you using? If more than 75% of maximum volume then you really need more power – get an amp to drive the front speakers, set it up right and the fault should go away.

NEW SPEAKERS/SUB SOUND BAD – speakers, especially subs, need to be broken in for a while before they give their best. Play gently at low volumes for a few hours before spanking the system to prevent damage to new drivers and to ensure you get the best sound out of them.

SPEAKERS IN REAR SHELF DISTORT BADLY (installs with sub) – bass sound pressure from the sub is causing the cones of the speakers to be pushed about and often even pushing them out of shape. The better your sub/amp the worse this will be. I practically blew a set of Infinities out of the back shelf with a Kicker sub on one car I had some years ago! Remove the rear shelf speakers. Fit grilles over the holes. You will get better bass in the cabin this way and less rattles from the shelf area. If you really must have rear speakers, these should be mounted in the rear doors/side panels not in the shelf.

SUB MAKES LOW RASPING NOISE – I think you’ve blown it up mate!

and if the store names are British ones, apologies again. I wrote this for a UK forum but thou
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