The_quest_for_wisdom t1_j2e3wkw wrote
Reply to comment by GanondalfTheWhite in Eli5 How exactly does Noise cancellation work? That too in such small airbuds by Professional-Ad3441
We assume the speed of sound is much faster than it is. Locally it seems almost instantaneous, when it is not.
If you have a large bell like the kind used in a church steeple you can see this disconnect with your own eyes.
If you get more than about an eighth of a mile away you will see the ringing bell move quite a bit out of sync from the sound of the bell ringing that you hear.
It gets even wielder when you consider that the image of the bell being rung is also arriving in your eye AFTER the bell is actually being rung, due to the speed of light. It's just a much shorter delay.
It might be tempting to just hand wave that away and say that the light travels effectively instantaneously, but that thinking with sound is exactly how we ended up here in the first place.
GanondalfTheWhite t1_j2elevv wrote
> thinking with sound is exactly how we ended up here
While everything you said is true, the speed of sound, which, yes, is much slower than light, is still pretty damn fast when we're talking about how much time there is to process something in the time between a soundwave passing from one side of your earbud to the other. Right? Cuz that's what we're talking about. Not how long the sound of something vs. the light of something takes to hit your brain.
Ultimately what we're talking about is that the earbud needs to be able to detect the soundwave, compute its opposite waveform, and emit the counter wave all in the same time that it takes for the soundwave to pass the earbud so that the original wave and the counterwave hit the eardrum at the same time. Right?
So if we assume the earbud is maybe half an inch thick, means it has to do all of that in about 1/27,000th of a second. 0.04 milliseconds.
Even knowing how fast sound travels, that ability to process seems unintuitively quick. That's all I'm saying, it's unintuitive and pretty darn cool.
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