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theperfectmuse t1_j2dpc7w wrote

Reply to comment by jswansong in Eli5 How exactly does Noise cancellation work? That too in such small airbuds by Professional-Ad3441

I can't wrap my head around the idea of "opposite sound".

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quietcore t1_j2dvfkl wrote

Sound is made up of waves. If you create the opposite wave, the low point of the wave happening at exactly the same time as the high point of the original wave and visa versa then the two waves will cancel each other out.

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PokebannedGo t1_j2e4wan wrote

That's because the "opposite sound" doesn't make sense.

If a cat makes a happy meow, the noise canceling headphones does not make a sad meow noise.

The happy meow makes a sound wave

Think of these waves like waves in the ocean

If you were to send the exact same wave from the beach towards the ocean waves, imagine what's going to happen.

Both waves hit together at their peaks and you'll notice that after that point, the waves that would reach dry sand will be much lower in height.

So it's the same wave just coming at the opposite direction

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ShouldBeeStudying t1_j2f49sz wrote

If I blare huge sound at my ears it will ruin them. Like gunshots, jet engine or concert speakers. If I blare huge opposite sound at the same time are my ears fine?

Let's ignore the practicality of this please

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DragonFireCK t1_j2f6nlx wrote

If you managed a perfect inverse of the wave, the two waves will cancel enough other out and there will be no sound at all. This means that, with perfect noise cancelation, you could be sitting right on top of a jet engine and would hear nothing and have no damage occur.

Practically, getting a perfect inverse is impossible. You'd need a speaker perfectly aligned between the source of the sound and your ears, and the source will actually be a bunch of different points inside the engine, meaning you need roughly an infinite number of infinitely small speakers and microphones.

I did find a video that shows how the phasing works. Its worth noting that the antiphase (opposite) sound will sound the same as the original if heard on its own.

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UXyes t1_j2dz486 wrote

Sound waves or vibrations are very small and air is very thin and mostly invisible. It’s easier to understand/imagine using something you can see, like big slow (compared to sound) waves in water.

Next time you’re in a pool or bath or whatever, put your hand flat on top of the water and start moving it up and down in a rhythm to make some sustained waves. Once you’ve got that going, start changing your rhythm and you’ll see that some changes make the waves bigger by amplifying the existing motion or energy in the water, and some changes make the waves smaller by going against the existing wave.

Now think about how there’s a perfect adjustment to that rhythm that will cancel out the existing wave entirely. That’s what’s going on with sound in the air that gets canceled by an “opposite” sound. It’s an opposing wave calibrated just right to cancel the other one.

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femboy_artist t1_j2eprhc wrote

Me either: I get the waves effect, personally, visually it makes sense and by the numbers it makes sense, but I really want to see it in action with sounds because it still doesn’t make sense from a “that’s how it works” perspective.

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friendlyfredditor t1_j2f8lf4 wrote

You can do it by playing low noises from two speakers set far apart and walking around between them.

The noise will be louder in some spots and quieter in others.

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bibdrums t1_j2dviqg wrote

Sound travels in waves. The waves travel toward your ears and vibrate your ear drums. Noise cancelling headphones send a wave of the exact shape and speed toward the wave coming at your ear and they crash into each other and the energy from both dissipates.

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brazeau t1_j2e3xei wrote

A speaker moves in and out to make pressure waves picked up by your eardrums. You can make a speaker that basically catches the incoming pressure waves.

If one speaker moved outwards, the opposite one would move inward.

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