What Is A Car Audio Noise Filter: how do they work?

Do you hear interference noise when you turn on your radio? Usually, this noise sounds like a whine in the background of your speakers and the pitch of the noise gets higher the faster your engine revs. This noise can be so annoying even on short journeys. In this helpful article, I will explain why and where these sounds come from. So…..what is a car audio noise filter?

What is a car audio noise filter?

A car audio noise filter is also known as a ground loop isolator. This device blocks high-frequency current coming from your car electrics into your car audio system. The removal of this high-frequency interference will stop all unwanted whining sounds and interference.

An audio noise filter is simply a circular piece of soft ferrite (magnetic inductor) circle core with a single piece of wire coiled around it. The ferrite absorbs the high-frequency noise from the coil of wire (your audio power wire) thereby fixing the noise issues. I have used an audio noise filter to remove many ground loop sound/ alternator whine problems.

The ground loop can also be referred to as the earth of your car’s electrical circuit. All the electrics on your car are earthed to this point (the body of the car). This is what your stereo equipment should be earthed to.

Some cars have an audio noise filter pre-installed in the stereo, others may need an external filter.

Why should I think about getting a noise filter? 

You should think about getting an audio noise filter if you can hear interference from your car audio equipment.

There are two possible reasons for unwanted noises in your car audio equipment.

One is from ground loop noise sometimes referred to as alternator whine. I would fix this by adding an audio noise filter (ferrite core) to the power wire of the audio device. The device could be a car stereo or a power wire to an ungrounded device such as a playlist from my mobile phone

The problem here is that your phone is not earthed to the car and is causing an ungrounded loop. This ungrounded loop can cause interference. You should add an audio noise filter to the power wire for this ungrounded device (your phone)

The second way noise can affect your audio equipment is through electromagnetic interference through your RCA cables.

How to troubleshoot an audio noise problem

The way to check if you have a ground loop problem or electromagnetic RCA problem is the following:

1. Start your car engine and disconnect the RCA cables from the back of your stereo.

2. If the noise stops then you should wire an audio noise filter (ferrite core) to the power wire of your audio headunit or other input source (phone, iPad, iPod)

3. If the noise continues then you have electromagnetic interference from a nearby wire traveling along your RCA cables to your amplifier. The amplifier is then amplifying this noise.

4. To fix this issue you should install an RCA line filter connected before the amp.

Are audio noise filters expensive?

Audio noise filters are not expensive at all. They are simple circuits available at affordable prices. I buy mine on Amazon or eBay for around $15. Some are even cheaper than this, but beware of buying dirt.

If you are not comfortable buying online, go to your nearest car audio shop. When buying an audio noise filter do not forget to check its power rating (in amps) with your car’s receiver or amplifier. Your audio noise filter should be at least as many amps as your system’s requirements.

Where do you install a car audio noise filter?

There are a few ways to install an audio noise filter in your car. Audio noise filters or ground loop isolators are wired into the ignition power wire before the stereo or mobile device. Sometimes I would add another to the battery power (constant live) wire to the head unit also. The main focus is to remove the high-frequency interference which can travel along the power wire into your audio system.

How do you wire a car audio noise filter?

Connect the power wire either from the battery or ignition to one side of the audio noise filter device and then connect the output wire from the audio noise filter to the power supply (either ignition +ve or constant +ve or both) on the stereo or other input device

What if the noise filter does not stop the interference?

As i discussed above, if the audio noise filter does not stop the noise then you should add an RCA line filter also.

Which noise filter would I recommend?

car audio equipment

Once you have identified the problem and have decided to fix it by using an audio noise filter or an RCA line filter, you should take a look at which is best for your system.

There are many noise filters available, I have compiled a list of some of the best below, with links to check prices.

Filter NameUseCable Diameter
Smof Ground Loop Noise IsolatorCar Audio, external phone connector (Eliminate the buzzing noise)3.5mm Audio Cable
Pipemans 10 amp Audio Noise Filter Audio Noise filter, 10 Amp Power wire connection
PAC SNI -1 Line FilterRCA Line Filter RCA Jacks
Vosarea RCA Line Filter RCA Line FilterRCA Jacks
ZIOCOM Ground Loop Noise Isolator  Car Audio, external input, mobile phone, iPod, iPad3.5mm Aux Audio Cable
Pienoy EMI RFI Noise Filter Cable Ring/Noise Filter Suppressor Cable Clip   Audio Noise Filter3mm/ 5mm/ 7mm/ 9mm/ 13mm Diameter/Video Cable Power Cord

Conclusion

Although there can be many places where you can get interference in your audio system. The trouble shooting I have listed above and armed with a better understanding of where these noises come from. You should be well on your way to solving all your audio noise issues from now on. However, If you are still having difficulty, feel free to send me a message if you are unsure of anything- Good luck!- David

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