Noise suppression guide
Diagnosing and treating noise problems in your car audio system
In the 1950's, I'd take the family television's vacuum tubes down to Willow Grove Radio and TV Repair, check them with the giant tester machine, buy new replacement tubes, and reassemble the repaired television, so my mom and dad could enjoy their precious, respectively, Dean Martin and Red Skelton shows. In the 1960's, I studied radio and electronics at the Franklin Institute in Philadelphia. After college, in the early 70's, I joined a rock 'n roll band as the soundman, learning how to operate the electronics that make music sound good. Then, I worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems and components for recording studios, nightclubs, and touring bands. I moved back to Charlottesville permanently in 1984 and opened a little demo recording studio. I also attempted to put to practical use the creative writing degree I had picked up along the way. In 2006, I finally came to my senses and got this job at Crutchfield where they actually pay me to ramble on, rant, and explain the things I love about music, electronics, and getting good sound.
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This guide will help you diagnose and treat problems with extraneous noise in your car audio system.
Dealing with noise
You've installed a new receiver or amplifier in your car, and now you have a noise problem. What can you do? The trick is to determine what the source of the noise is. Noise can be introduced into your system from a number of sources. This is especially true if you have an amplifier. The type of noise you're hearing can help determine the cause.
Read over this article for some hints and explanations of what can cause noise in your system. Use it as a checklist, eliminating possibilities until you find the culprit. You can also use this diagnostic flowchart as a guide to walk you through the troubleshooting process.
And don’t forget – if you purchased your gear from Crutchfield, or purchased tech support separately, don't hesitate to call on our tech support team (have your Crutchfield invoice handy).
Noise and your new receiver
If you’ve just installed a new receiver, here are two quick and easy starting points:
Noise in your receiver is often due to a poor ground wire connection or a poorly grounded antenna.
Is your receiver securely grounded?
Improper ground is one of the biggest causes for introducing noise into your audio system. Is the ground wire located near a noise source (like a heater, air conditioner, or computer)? Is the ground wire actually connected to the vehicle's ground? Since the antenna lead can act as a ground (thereby enabling a new receiver to operate without its ground wire properly connected), the antenna lead is frequently the source of noise problems.
Check to see if you're getting noise on all sources — CD, auxiliary/USB, AM, and FM
If the noise is present only on the radio, then it's most likely coming through your antenna lead.
Unplug the antenna. If the noise goes away, try an antenna noise suppressor (like American International's AS100). This filter plugs in-line between your receiver and your antenna, breaking the ground path between them, thus preventing noise from entering your system.
An antenna filter, installed between the vehicle's antenna and the receiver, can minimize noise entering your system from a poorly grounded antenna.
If the noise isn’t coming in through the antenna, try pulling the receiver from the dash while a CD is playing. If the noise goes away, it's being radiated into your system due to the receiver's proximity to a noise producer (like a heater motor or car computer). This is often referred to as “sideway noise.”
If the noise-causing accessory has a motor, a source noise filter can be installed on the accessory's power lead to minimize radiated noise. If the car computer (or other motor-less accessory) is causing the problem, move your receiver's wiring away from that accessory to minimize the radiated noise.
Try using magnetic shielding foil (also called Mu-metal) to shield the back of the receiver or wrap the wire or component that's radiating the noise into your system.
Noise introduced through the power and ground wires connected to your receiver is called engine noise (sometimes referred to as “backway noise”). If engine noise is your culprit, you may hear a whining or clicking sound. Its pitch will usually vary with engine speed.
If this is the case, you can install an alternator noise filter on the power line between the battery and the alternator to minimize the problem. You can also install a noise filter on the receiver's power lead to cut down on signal pollution (American International's S15A (15-amp, 250-watt) or S25A (25-amp, 350-watt) filters, for example). Most often, however, backway noise comes from a loose or intermittent ground connection. See the section below about noise in the electrical system.
An alternator noise suppressor connects inline between the alternator and battery, and can reduce high-pitched whining noise that modulates according to engine RPMs.
Noise and your new amplifier
An amplifier can introduce noise into your system through a bad ground or through a poor mounting. Rubber grommets or feet can help isolate the amplifier from the chassis of the vehicle, a potential source of noise. If all else fails, install a noise suppressor. The tricky part is figuring out which step or steps to take. Please read the rest of this section and try some of the simple tests.
Where is the amp mounted?
Is it near something that could be radiating noise, like a rear-mounted tuner or computer? If so, unbolt it and move it away to see if the noise stops. Remove your patch cables. If you still hear noise, check to see if your amp is isolated from the vehicle's chassis. Any contact between your amp's metal casing and your vehicle's body could cause noise problems.
Check your ground wire
Is it securely attached to the vehicle's chassis with a good contact to clean metal? Your ground wire should ideally be 18" long at most — a longer ground wire can cause noise problems. Improper grounding causes most system noise problems.
Check your gain structure
If you have an external amplifier in your system, the first thing to do is to quiet any system noise, which sounds like a constant, low hiss. First, check for system noise with the engine off. Insert a CD and put your CD player on pause. Listen to the system with the volume way down, then way up. Put on music. If you hear hiss in either instance, reduce the gain on your amplifier.
Pass more signal from the receiver to the amp by leaving the receiver's volume higher before you set the amp's gain. Experiment until you eliminate the hiss or reduce it as much as possible. A tiny bit of hiss is okay — you won't hear it while driving.
Noise in the patch cables
Noise can be picked up by the RCA patch cables connecting your components. To test this, detach the cables from your amp. Insert one side (left or right) of a spare patch cable into the amp's left and right input jacks (see illustration below). Turn on your system and engine.
If the noise is gone, reconnect the cables to the amp, and disconnect them from your receiver. If you hear the noise, your patch cables are definitely picking it up. Try re-routing them. Separate them from your power cable by at least 18 inches. You could try a better brand of patch cables. The inexpensive RCA cables many people use to connect their components don't have the insulation or conductivity necessary to deflect noise in a metallic, highly conductive automobile.
How much noise your cable receives depends largely on the size of its “loop area;” the larger the loop area, the more vulnerable your cable is to induced interference. A cable's loop area is equal to the distance between its center conductor and outer shield times the length of one complete twist in a twisted pair configuration, or the entire length of the cable in a coaxial type. Consider trading your old cable for one with a twisted pair design. You'll get a smaller loop area and less noise.
Patch cables with a "twisted pair" design help reject noise
As a last resort, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and your amp to minimize this problem.
Noise picked up by the power or ground cables
We discussed ground cables above, because that’s the cause of noise more often than not. If the noise wasn’t due to a poor ground or through the stereo’s antenna cable, it may be coming in through the amplifier's main power cable. Noise can be created by cable of insufficient gauge, so you might try thicker cable.
If you cannot find the faulty ground in your multi-amp system, a ground loop isolator can help minimize the problem.
Multiple amplifiers can also create ground loop problems, which can usually be solved by grounding each amplifier with its own separate wire. If you are unable to locate the cause, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and the amplifiers to minimize this problem.
Noise in speaker wiring
Noise can also come in through the speaker wires. To test them, turn the system off and disconnect the speaker wires from the amps. Now start the car. If the noise is still there, then it's being radiated into the speaker wires. Reposition them, or, as a last resort, shield them by wrapping them with Mu-metal foil.
Noise from electrical system
If you've tried all of the noise-fighting tips above and you still hear the noise, the problem might be with your vehicle. You might simply need to fill your battery with fluid. If that doesn't help, have a mechanic check your alternator and battery.
If your car is older and hasn't been tuned up recently, you may have ignition noise. It's a ticking noise that varies in speed as you accelerate. You may need a tune-up involving resistor-type spark plugs, shielded carbon-core spark plug wires, distributor cap, and coil.
If the noise doesn't disappear, then your ignition system may not be grounded well enough and is broadcasting ticks to other items such as your air cleaner, hood, exhaust system, etc. Chances are, grounding one of the under-hood components will eliminate the noise. With your sound system on and the car running, try grounding each of these different components of the car. It's possible that grounding one of your car's components will eliminate the noise. If so, make the ground permanent with a braided ground strap.
A very effective fix for electrical system noise is called "The Big Three" upgrade. This is where your vehicle's battery charging wire and chassis ground wires are augmented by adding large gauge wires (1/0- or 4-ga.) to those connecting the alternator to the battery's positive pole, the battery's negative pole to the chassis, and the chassis to the engine block. This establishes better current flow and more consistent voltage, which improves your system's signal to noise ratio. It also ensures against loose or restrictive ground connections, which, as said before, are common sources of noise. Read our article about The Big Three for more information.
Noise and your nervous system
Noise problems can be very frustrating, especially when you can't wait to hear your new equipment. It helps to remember that you've just placed a very sophisticated piece of electronic gear (a new receiver or amplifier) in the middle of an extremely complex system — your vehicle's electrical wiring. Noise is just nature's way of telling you that something's out of whack. Just run down the list, eliminating possible noise sources until you find the problem.
Crutchfield Tech Support
If you bought your gear from Crutchfield, you could call Tech Support for free help troubleshooting your system. The toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support — 90 days-worth for only $30.