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The way noise cancelling headphones work is by listening to sound, and created the inverted sound to 'cancel it out'. Doesn't this mean that the headphones create double the amount of noise, but our ears just can't pick it up due to the noise being 'equalized'?

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This question blends over into the realm of Physics:

Yes, noise-cancelling headphones create what is known as 'anti-sound', which is (virtually) the same sound (and equally loud) as can be heard in the environment, but with an inverted phase. This inverted sound wave indeed cancels out the original sound wave from the environment, resulting in (virtually) no air displacement at your ears: i.e. no sound, no noise.

The actual anti-sound created by real-world noise-cancelling headphones is not exactly the inverse sound as your surroundings, but a (close) approximation. The quality of this approximation limited by the quality and latency of the microphones, chip, software and speakers in the headphones. This means that they will only reduce and not perfectly cancel all noise.

It also means that if you have a noise that only lasts a very short time, the headphones might actually be too slow to cancel the noise. In this case, your ears will first hear the original sound (at full volume) and then the anti-sound (also at full volume). In this case you could say that the headphones have created a lot of additional noise (which in that case will be heard).


To summarize: Yes, noise-cancelling headphones are constantly making noise themselves. The net effect of this is however that the amount of noise that reaches your ears is greatly reduced.

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  • $\begingroup$ Thank you! Is this 'anti-noise' a concern in terms of hearing damage? It's using a noise cancelling headset worse than a regular headset? $\endgroup$ – Titulum Aug 14 at 18:16
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    $\begingroup$ Although this looks like a good answer, it doesn't meet site requirements. We require answers to provide supporting references for assertions of fact. $\endgroup$ – Carey Gregory Aug 14 at 18:23
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    $\begingroup$ @Titulum A sound is a pressure wave. If you produce an "anti-sound" the result (at the ear) is not two waves of opposite sign, there is only one "space" so only one wave, in this case a mostly flat line equal to silence. $\endgroup$ – Bryan Krause Aug 14 at 19:14
  • $\begingroup$ Electronics work at nearly the speed of light, so I can't imagine there's much latency relative to the speed of sound. And there's no such thing as inverted sound. $\endgroup$ – BillDOe Aug 14 at 19:31
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    $\begingroup$ When the noise-cancelling headphones kill the sound by producing a wave of opposity polarity (i.e., when they do what they should do), they should decrease the risk of hearing loss (due to loud sounds) considerably. Anything that sounds silent, is silent! $\endgroup$ – Erik Sep 2 at 7:59

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