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Author Topic: How do noise-cancelling headphones cut in-ear noise?  (Read 2741 times)

Mark Severn

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Mark Severn  asked the Naked Scientists:
   
Hi
I would like to Ask a question that came up as a result of the show the 9th Jan 2011.

The process described is similar to the technology of Active noise cancelling Headphones.

I have a pair of these and they have a very interesting effect. We all know the effect of putting a shell to your ear to hear the sound of the ocean. When you put the headphone over your ears you can hear this effect. When you turn on the headphones the sound  disappears.

I would have thought that once you block your ears the heard sound would stop but this isn't the case.

So what are you hearing when you cover your ears and why do the noise cancelling head phones remove it?
 
Love the show, listen to it via the podcasts as it is too early in the morning for me live.
 
Keep up the good work.
 
Cheers
 
Mark Severn
Melbourne, Australia.

What do you think?
« Last Edit: 06/02/2011 16:30:04 by _system »


 

Offline yor_on

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How do noise-cancelling headphones cut in-ear noise?
« Reply #1 on: 06/02/2011 18:19:32 »
The vibration from sounds hit the tympanic membrane (ear drum), which in turns causes the ossicles (malleus, incus, and stapes) to amplify and send the signals to the cochlear (inner ear). The cochlear processes the sounds and sends the information through the Vestibulocochlear nerve to the brain. and even without sound they might vibrate. In some types of tinnitus the ringing sound that you hear comes from the random electrical impulses that the damaged auditory hairs in the cochlea transmit, which the brain interprets as sound. A seashell also have chambers conducting and amplifying the sound from your body. Your headphones acts like a cylindrical reflector of that noise, as a guess :)
 

Offline graham.d

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How do noise-cancelling headphones cut in-ear noise?
« Reply #2 on: 06/02/2011 18:28:51 »
Noise cancelling works by a small microphone listening to the ambient received sound and actively subtracting this sound from that being actively sent from the wanted sound source.
 

Offline yor_on

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How do noise-cancelling headphones cut in-ear noise?
« Reply #3 on: 06/02/2011 18:35:29 »
heh. :)

what more can we say?
 

Offline Mark Severn

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How do noise-cancelling headphones cut in-ear noise?
« Reply #4 on: 14/02/2011 08:51:39 »
Thanks for your responses.

I do understand how the noise cancelling feature of the headphones work and as Graham.D indicated they use microphones on the outside of the cans to cancel out ambient sound. The noise you hear "the sea" is coming from inside the the cans so how can it cut out this noise if the microphones cant "hear" that sound?

Cheers

Mark 7
« Last Edit: 14/02/2011 09:00:22 by Mark Severn »
 

Offline CZARCAR

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How do noise-cancelling headphones cut in-ear noise?
« Reply #5 on: 14/02/2011 11:51:25 »
years ago, i saw a show where someone had experimented with noise cancellation & predicted that a car muffler could be replaced with noise cancellation & results would be 5% better gas mileage? Only headfones since, what happened?
 

Offline graham.d

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How do noise-cancelling headphones cut in-ear noise?
« Reply #6 on: 14/02/2011 13:00:15 »
Mark, when I put headphones on I don't hear any "sea" at all. I notice that I do get this when I lift a part of the headphone up so that it doesn't seal very well around my ear though. I suspect that it maybe that you are still hearing ambient noise getting around the headphone seal. I don't think you ever get this effect from earpieces as the good ones make a decent fit in your ear - a notable improvement over older designs. It tends to be the mid to higher frequency ranges that make up this sea-sound. The lower frequencies often can be heard despite the cans but these are eliminated rather well be noise cancelling.
 

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How do noise-cancelling headphones cut in-ear noise?
« Reply #6 on: 14/02/2011 13:00:15 »

 

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