Hacker News Reader

Comment by literalAardvark | Hacker News Reader

We do know: ANC doesn't reduce sound pressure, thus it doesn't protect hearing.

ANC uses destructive interference to quite literally cancel the sound waves coming from the outside. It reduces sound pressure by definition.

Piggybacking on this top comment to retract the parent post.

ANC has a many dodgy edge cases that can go wrong, but I've done some more reading on it and if acoustics PhDs say it's very safe I'll just have to take it at face value until more data exists.

Would you mind explaining this further? Since sound is literally pressure waves, I don't understand how reducing sound can still leave "sound pressure".

ANC works by detecting the outside noise, deriving how these noises reach you ear and then play the antiwave so that in cancels out. The issue is that the canceling out part only works on the receiving end so there is still pressure on the eardrum even if you don't hear it.

I still think that ANC is good for the ears by reducing the needed volume in every day situations. And it also helps that most ANC headphones are designed in a way that also passively isolates the outside world to reduce the burden on the ANC and as a side effect also on your ears.

> pressure on the eardrum even if you don't hear it

Hearing is literally "pressure [changes] on the eardrum". Unless it's outside the frequency range of our hearing, if there's waves hitting your eardrum, you hear them.

So either you're not expressing yourself clearly enough our you've seriously misunderstood how sound works.

https://youtu.be/VIi04uD8LtY

Constant elevated pressure created by ANC working to destructively interfere with an external sound waves is not perceived as sound.

But it is extra pressure on the eardrum.

But why would there be elevated pressure? Headphones can't pump air into your ear, they can only make it wiggle back and forth. ANC headphones use the same speaker that normally plays your music and just mix the noise-cancelling sound into your music, nothing else. When you aren't playing any music, outside noise makes the air wiggle back and forth and the membrane of the speaker makes the air wiggle back and forth in the opposite phase. These movements destructively interfere, resulting in the air staying still.

BTW where in the video do they mention elevated pressure?

I see this is downvoted and people are asking for an explanation, and I don't have any backing for this either, but I'll share my experience. I have an "issue" with my left ear that makes it feel muffled, and distorted, and painful at loud noises. I have been to a few doctors but they weren't able to diagnose it, need to get it checked at a better doctor I guess.

I can definitely feel my issue get exacerbated with ANC even when I am not playing any music or playing music at low volume (have tried several devices including airpods where my issue is the worst, probably because their ANC is the best). So there is definitely something going on with ANC such that even when I have it on with extremely low volume music, it triggers my issue. -- Even when at the same "perceived volume" of non-ANC sounds the issue doesn't get triggered.

So much so that I do not use ANC. The issue gets triggered within seconds of when I start using it. So instead I just play music on very very low sound on my wireless earphones.

I don't why it happens with ANC, would love to know.

I don't believe this is true, it doesn't make sense from a physics perspective. Could you explain what you mean?

Reply on news.ycombinator.com