The Surprising Science Behind Noise Cancelling Headphones | The Secret Genius of Modern Life – BBC

There is something that is called active noise cancelling and it’s a very very clever thing so okay I’m going to play a tone through one of these speakers I mean not particularly Pleasant to the ear and now what I’m going to do is I’m going to plug in the

Second speaker and see if you can notice what happens to the sound as I do logic might make you think that adding a speaker will make it louder okay it’s going in now did you hear that let me just unplug it and plug it in again can you hear

That you’ve got double the number of speakers playing exactly the same sound and yet instead of it getting louder it actually gets quieter so what is going on well when I hooked up that second speaker I switched around its wires at the back meaning it’s wired up

In the opposite way to speaker one so I’m essentially putting in the inverse the exact opposite what’s coming out here do you see that the tone sounds the same and it’s the same volume but the sound wave has been flipped upside down this is the shape that the wave is

Making that’s like the sound wave wobbling the air now okay if I put in another speaker of course this wave is going to get bigger right it’s just going to get louder but because I have wired in a speaker the wrong way around the second speaker ends up making that same wave

But flipped upside down so this one up here ends up being cancelled out by this one down here and so what you end up with in ideal circumstances is a complete Flatline through the middle no noise at all the noise is cancelled by playing the same sound just

Flipped this is how all active noise cancelling headphones work microphones pick up unwanted sounds which get flipped and played back to cancel out the original noise all the coming through your earbuds is what you are choosing to listen to

So it makes sense, but it also doesn’t 😅 #SecretGenius #iPlayer
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Hannah Fry uncovers the secrets behind the miraculous technologies of the modern world, revealing the mind-blowing stories behind their invention.
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