How do active noise canceling headphones work?

Almost every pair of the best wireless headphones and earbuds you can buy these days come with active noise cancellation (ANC). It makes sense: wherever you use these headphones or earphones – at home, in the office, in the city, on public transport – your listening experience will be better if less external sound comes into your head.

The ANC helps accomplish this. With the push of a button, the ANC earbuds attenuate incoming noise, letting you enjoy more of the sounds you’re actually trying to listen to. When it’s effective, it’s amazing; reducing the noise around you like adjusting your media volume is an amazing experience. But the way it works is perhaps even wilder.


What is sound?

This probably sounds like a weird question, but before we get into how chickpea-sized headphones like Sony’s LinkBuds S can drown out the roar of jet engines, here’s some background. What many of us perceive as sound is the product of changes in atmospheric pressure.

Our eardrums are thin membranes inside our ears that sense waves of changing air pressure, causing them to vibrate. These vibrations then travel through certain delicate bones in our head to finally reach a part of the brain called the auditory cortex, which interprets them as what we perceive to be sound. (Bone conduction headphones cut off all moving air business, instead of sending vibrations straight through your skull.) These pressure changes are also why we can To feel particularly loud or low-pitched sounds, such as fireworks or music from a concert. Loud sounds move a lot of air in a short time – sometimes enough to feel the reverberations in parts of your body other than your ears.

Illustration of a waveform.

You may have seen sound waves illustrated as waveforms. The y-axis on these undulating graphs represents a sound wave amplitude. In this context, it can be thought of as a measure of the amount of air moved. More air moved means louder sound – and higher waves on the chart. X axis is sound wave length. High-pitched sounds have short wavelengths; low sounds have long sounds.

How does the ANC counterattack it?

Noise-canceling headphones use built-in microphones to listen to sound from your surroundings. A processor (or two, in the case of Sony’s new WH-1000XM5s) inside the headphones then analyzes this incoming sound and creates what is known as anti noise which is played to neutralize the noise, so you don’t hear it.

It sounds like science fiction, but consider the sound waveform again. The Y axis, amplitude, technically plots the compression and decompression of air molecules – above the X axis is compressed, below is decompressed.

The ANC, in a nutshell.

The anti-noise has the same wavelength as its target sound wave, but the phase of its amplitude is reversed – their waveforms are like mirror images of each other. This means that when the sound wave from noise causes negative air pressure, the sound wave from noise canceling causes positive air pressure (and vice versa), resulting, ideally, in blissful silence for the wearer of the ANC headphones.

There are, however, limits to what the ANC can do. If you’ve used ANC earbuds or headphones yourself, you’ve probably noticed that while they’re great at drowning out the kinds of low, constant noise you might hear on an airplane, they usually struggle with other people’s music or the clinking of a coffee. While deep, consistent sound is relatively easy to predict and counter with proper noise canceling, it is much more difficult to react in real time to irregular organic background sound.

Behind the curtain of the ANC

We hope this helped demystify ANC headphones for you! For more explanation on the technical stuff, we’ve covered the complexity of pixel grouping in mobile photography and some exciting details about the upcoming Matter smart home standard.

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