How do noise cancelling headphones actually work?
In: Engineering
There’s two types of noise cancelling in headphones;
– Passive Noise Cancelling
– Active Noise Cancelling (ANC)
I’ll go over passive first. You ever put a pillow over your head? That’s passive noise cancelling. It tries to create as best seal it can with your skin, and then as much noise insulation that can realistically fit in the desired form factor. This is why they’re often associated with feeling sweaty, because they’re also stopping the air inside from escaping. That’s the simple one.
Active is a little harder to explain, but I’ll try to do my best.
So it works based on all the sounds we hear (or most) having an opposite noise, that will cancel them out, at least we won’t perceive them. So they’re always listening on the outside, and playing the anti-noise version of that on the inside.
It’s a little hard to visualise, since it’s not visual (duh), so I’ll try to make a visual equivalent. You remember when you learnt how to mix paints in school, and you mixed yellow and blue to make green? red and blue to make purple? yellow and red to make orange? What happens if you add the 3rd color to those paints? Technically you’re supposed to get black, but in the real world you always got brown, that’s kind of what we’re doing with ANC.
They will also often have “Transparency mode”, or something similar. This is just them swapping from playing the anti-sound, to replaying the normal sound that the microphone is picking up on the other side, kind of like how VR headsets like the new Apple one you may have seen, can flip between showing you a view of the world from it’s cameras, or just not showing you anything at all. Some of the more advanced ones, will also apply “noise cancelling” techniques to the microphones input when in Transparency mode, to help pickup voices, or road noises, depending on the situation they’re in, to give you a better idea of what it thinks you’re trying to pay attention to.
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