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Zone36's avatar

How do noise cancelling headphones work and to what extent?

Asked by Zone36 (416points) January 18th, 2010

I just saw this video of these guys yelling at their friend who had the headphones on. I’m 99.99% certain they don’t work that well.

But what exactly do they do? I’m guessing they can block out ambient noises like hums and such, but what are they doing exactly?

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12 Answers

cbloom8's avatar

There are technically two types of “noise canceling” headphones. The first are pretty normal, simply insulating your ear to the point of isolation. The second type is more advanced; they put out ambient and white noise to counteract noise around you.

I didn’t see the video but I would expect that with a high enough volume of the music, both types would have blocked out the yelling pretty well, especially the second type. You might be able to faintly hear the yelling from the first, but I think there is a good chance that you couldn’t hear a thing with the second type.

Vincentt's avatar

I don’t know how they work, but I’ve tried someone’s noise cancelling headphones and, when turned on, they worked great. I don’t believe it cancelled out all other noise, but I did all of a sudden hear next to no environment noise – and that was without it playing music. I guess if you do play music you’ll hear zilch apart from the music.

Zone36's avatar

Well it was just a joke video. They eventually start bouncing a ball on the guy’s head and he pretends it’s not happening. But they are literally screaming at him.

jrpowell's avatar

They have a microphone in them that analyzes outside sounds and does some magic on what you hear.

Tenpinmaster's avatar

cbloom is very correct about the technology. I think they work great at screening out a lot of ambient background noise. Though the BOSE are very expensive, I would gladly pay the price for peace and quiet.

filmfann's avatar

Sounds around you are cancelled out by the headphones producing the same sounds out of phase, which is kind of like adding negative numbers to similar positive numbers.
So you are actually hearing two sounds cancelling each other out. The result is you don’t hear anything.
That’s how it works on paper, anyway.

Harp's avatar

Here’s a decent explanation of the accoustic theory behind noise cancellation. If you have a very simple, continuous sound, like an electronically-generated sine wave tone, another tone can be generated that has a waveform whose peaks and valleys are exactly opposite those of the original tone (though if you were to listen to this new tone by itself, it would sound exactly like the original tone; it’s the timing of the two waveforms that causes the cancellation).

So the headphones just take the incoming sound and reproduce it, but time the reproduction in such a way that the peaks of the new wave overlap the valleys of the original waves.

This gets much more difficult when the sounds becaome more complex (and most sound is incredibly complex).

IchtheosaurusRex's avatar

I have a pair and they work very well. I use them on aircraft. Mine are the on-the-ear variety. You’d get the best noise cancellation out of over-the-ear models, and the least out of in-the-ear or earbuds.

jaytkay's avatar

I have a Sennheiser PXC 250 headphones and they work very well. You still hear ambient sounds but they are muffled, like wearing ear plugs.

The active electronics work a lot better than the passive ear buds which are sold as “noise reducing”.

I bought them when I traveled a lot, and they probably reduced aircraft engine noise and constant whooshing air noise 80%. I would still hear the “ding” when the ‘Fasten Seat Belts’ sign would change. People talking would be muted, I would take them off to converse.

The headphones are great if you want to listen to music or podcasts, but for noise reduction foam ear plugs from the pharmacy work just as well for a very small price.

life_after_2012's avatar

the kind i have work great on air planes – i also mix music and there not that great for engineering – but the dr. dre ” beats ” headphones are good for mixing – there just expenxive

gasman's avatar

They have a built-in microphone that picks up ambient noise, inverts the waveform, and adds it back in to the signal, thus canceling the noise. This technique works best for low frequencies, where it’s easy to generate a 180-degree out-of-phase signal. For high frequencies it’s unlikely to correctly generate a phase-reversed signal.

So noise such as the low rumble of aircraft engines is effectively cancelled. But that crying baby in the seat behind you isn’t canceled nearly as effectively, and random high-frequency noise heard as ‘hiss’ can’t be effectively canceled at all.

dabbler's avatar

I have some Sennheisers too and they work well on airplanes. I have also used them at work in a cubical farm environment with dopes having loud “discussions” and using their speaker phones.

They do not cancel out everything, making silence, but they can definitely mute a lot of it.

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