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Headsets such as the Lynx Micro System are modelled on ear defenders and physically attenuate the noisy cockpit environment by clamping hard onto your noggin. Most modern GA headsets (e.g. Bose A20) seem to be built with far less attenuation, don't clamp on as hard, and tend to rely on ANR features rather than isolating the ear.

Naively, it seems that this would pump more audio power into the ear. Granted, it will be in opposition to the original noise, but it seems it would be very tricky to get the cancellation exactly in phase. So, is there a risk that using ANR and less attenuation would not be as effective in preventing ear damage as passive attenuation?

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    $\begingroup$ I'm voting to close this question as off-topic because this is purely an audio signals or physics related question. $\endgroup$ – mins Jan 21 '17 at 16:24
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    $\begingroup$ I'm not sure I can make this question any more on-topic without changing the scope of the question. It's a question asked by a qualified pilot about cancelling noise in a noisy cockpit environment related to aviation. It seems to fall between the permitted or prohibited topics in aviation.stackexchange.com/help/on-topic Granted, it is as much about audio or physics as aviation, but will they accept it at physics.stackexchange.com? $\endgroup$ – Mat Jan 21 '17 at 20:56
  • $\begingroup$ I doubt it'll be accepted on Physics, which is pretty selective, and not oriented day-to-day physics. But a Google is rather generous on this topic. Sample. $\endgroup$ – mins Jan 21 '17 at 21:03
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    $\begingroup$ Headsets and the use thereof is very much an aviation topic. This question may also fit on other exchanges, but a headset is very much an integral part of the aviation experience. Many (most?) headsets are TSO'd aircraft equipment. I see this question as being on-topic just as much as other questions regarding aviation physiological factors or the function of aircraft parts and equipment. $\endgroup$ – J Walters Jan 21 '17 at 22:45
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    $\begingroup$ We already have a question on how to choose a headset, surely a question specifically about the safety a subset of headsets is on topic. $\endgroup$ – fooot Jan 22 '17 at 0:34
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Naively, it seems that this would pump more audio power into the ear. Granted, it will be in opposition to the original noise, but it seems it would be very tricky to get the cancellation exactly in phase.

If the headphones succeed in reducing the noise you hear, then they will also have succeeded in reducing the power delivered to your eardrum (at the relevant frequencies) -- because those are one and the same.

It is conceptually and mathematically convenient to imagine that the original noise and the canceling noise both reach your eardrums and interfere there -- but if you actually work out how energy moves in the combined situation, what actually happens is that the cancellation speaker sets things up such that much of the sound energy will get reflected away from your ear canal instead of entering it.

The core mathematical point is that the air displacements and minute pressure differences that make up the sound do indeed (to a good approximation) behave linearly -- so you can take a description of the noise and a description of the cancelling noise separately and simply add the displacements at the location of your eardrum. But power goes as the square as the displacement, so it does not add linearly. You can't take the power transport of one sound along and add it to the power of another sound to get the power of the combination (except averaged over time if the sounds are not coherent in frequency, which is specifically not the case for noise-cancelling headphones).

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Yes, they are safe for your hearing.

I've used them for about a decade, and the noise level is clearly lower with ANR than without. I've never seen any evidence that the energy they put out can damage one's hearing; by every account, rather, they do a good job protecting your hearing from the damaging effects of hours in a noisy environment.

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  • $\begingroup$ I also have used ANR headsets for over a decade and still have excellent hearing, something I particularly note with the high frequency range (17-20+khz). $\endgroup$ – J Walters Jan 22 '17 at 14:43

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