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How Does Noise Cancellation Work?

I’ve Always Wanted To Know:

How does noise cancellation work?


Noise cancellation headphones have become increasingly popular over the last decade but how do they work? What is the difference between noise reduction and noise cancellation? Which is better for what situation?

Let’s start by going over what noise cancellation is. Noise canceling is the process where a speaker produces a sound which cancels out the background sound in an environment. This is done via microphones and sound processing chips and requires power (batteries usually) to perform the noise cancellation.

But how does noise cancellation work? Sound transmits through the air and into your ears via sound waves much like a wave moves through the ocean. If you accurately measure the incoming sound and create a sound wave that is out of phase (the opposite of it) the sound waves will combine and produce a flat wave. If a wave is flat you hear nothing, thus the cancellation has worked. Look at the graphic below and notice wherever there is a peak in the sound wave of the background sound there is a valley in the out of phase sound generated to cancel it.

What is the difference between noise cancellation and noise reduction? Noise cancellation uses an active signal to cancel out the sound waves coming in from the background where noise reduction just seeks to absorb the sound so you don’t hear it. Various materials can be used for this purpose. From large heavy foam and plastic canisters to fit over the ear to silicone form fitting ear buds to block or absorb the sound.

Which is better for what situation? The answer comes down to if you have regular background noise of random spikes in noise. Noise cancellation handles regular consistent background noise very well due to the ability to cancel out a sound wave. This technology is used in many aviation headsets to cancel the sounds of engines and in industrial applications to cancel the hum of fans or machinery.

Noise reduction is better for situations which have random inconsistent sound because the noise cancellation circuitry needs a short period to adapt to the recorded sound to cancel it and can not react fast enough to random sounds. Noise reduction equipment is often used at gun ranges to lower the sound level of firearms and in industries like metal stamping or blacksmithing.

You can tell the difference between the two technologies by the packing and phrases used to describe the functionality of the device. If the device says active or powered noise cancellation or requires batteries, then it is most likely noise cancellation. If the device says sound absorbing, noise reducing or sound insulating, then it is most likely noise reduction.


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