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Q & A: noise-cancelling headphones

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Most recent answer: 06/11/2015
Q:
If there is destructive interference of two sound waves (e.g. in noise-cancelling-headphones) - where does the energy go? I read the answer about two light waves, telling that there is constructive interference someplace else - does it mean there is a louder noise, somewhere around the headphones?Thank you!
- Tim (age 17)
Heidelberg, Baden-Wuerttemberg, Germany
A:

Yes, that's typically what it would mean. Think of low-frequency sound, say at the moment that the pressure is up near the ear. The headphone diaphragm would have to pull back away from the ear to cancel that. That same motion would increase the pressure just outside the diaphragm.

There are, however, other places that energy can go, such as heating up parts of the electronics, so the conservation of sound energy doesn't have to be exact.

Mike W.

p.s. Here's some old discussion of the issue: .


(published on 06/11/2015)

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