Alternator noise and induced system noise are unwanted and are a problem to diagnose in car audio setups. The more components you have the more chance you will encounter this in your system. This noise is usually caused by an incorrect installation due to lack of knowledge of the installer. This article will hopefully clear up some of the problems that can occur in car audio installs and help you counteract system noise within your car.

THE ALTERNATOR PROBLEM
The noise that can be produced by the alternator will sound like a whine or a whistle which is normally due to a faulty alternator, poor install, faulty components, or induced electrical back EMF (electro magnetic force) into adjacent wiring. The alternator produces an AC voltage, which is converted to DC by the rectifier. This DC voltage is used for all the electronics including your audio system. When the alternator is driven to its maximum power, damage can be caused that can result in a tiny amount of AC voltage entering into your system. This voltage is unwanted and with the increase of RPM the noise Frequency increases. This noise will be heard coming from your tweeters and mids but not your subs as the noise will only target high frequencies in the audio spectrum. To counteract this more powerful alternators or a capacitor could help. Note this noise will only be induced when the vehicle is running, if the noise is still there when the engine is not running the alternator is not the cause.

TEST YOUR ALTERNATOR
Use a mate’s car and hook up jumper leads. Turn your car on and turn your mate’s radio on only. Does your mate’s system have this noise now? If yes your alternator is faulty, get an auto electrician to diagnose the fault, they will usually do this for free. Alternatively, you could invest in a higher powered alternator.

WHAT ELSE CAUSES THIS NOISE

• Poor Earths/Ground Loops
• Induced Noise in the RCAs
• Incorrect Installation of the Head-unit or Components

Some electrical systems in your car use the body (metal) as an earth return (ground point). This allows a complete circuit back to the battery negative for your system to work. The further away an earth point is made the more resistance the negative return will have. This is a general rule as different metals, joins and wiring also put a resistance on the system. Your goal is to limit this resistance as much as possible to try and give every component the same voltage 12.5 volts up to 14+ when the alternator is charging. Any difference in voltage up to .5 of a volt may cause that component to have a problem with inducing noise in your system.

A magnetic field produced from this current flowing though the power wire can induce an AC voltage into any wiring harnesses or RCA wires, which will cause the audio signal to distort. You will hear this induced noise when:

• You first turn on your system (you will hear a pop noise from your speakers)
• Your amplifier requires to draw more current for your power hungry bass notes

FIXING THE PROBLEMS, DO’S & DONT’S

• Run your RCA wiring away from the power wiring (if possible run them on opposite sides of the car) for the amps and vehicle wiring harnesses to eliminate induced noise.
• If possible don’t run your power cables alongside vehicle wiring harnesses.
• Use larger gauge wiring than needed and keep earth wiring as short as possible.
• Don’t connect earths at one point.
• It is ok to link positive to positive but don’t link earths of two or more components together (for example two amplifier linking earths together).
• Get rid of paint to bare metal and connect earth using a terminal connector and a spring washer so the earth won’t wiggle loose.
• Don’t use a noise filter box unless you are certain that the noise is coming from either the head unit or an equalizer.
• Use a test battery to connect your amps (positive and remote wires to positive and negative to negative). Turn on your vehicle, if noise is gone the source of the problem is ether the amp or the wiring before or after it. You can work backwards from this point to other components and do the same thing.
• Use the correct gauge wiring to supply and earth your amplifiers. If you use less the amplifier may cause induced noise in your system.

If you correct these problems within your system and the noise problem still exists try and trace the problem down to 1 or 2 components and then subtract them one at a time in order to find the source of the noise. Time and patience will prevail.

This entry was posted on Tuesday, May 20th, 2003 at 10:34 am and is filed under Tech Articles. You can trackback from your own site.