h a l f b a k e r yGuitar Hero: 4'33"
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The industrial age has created a background level of noise from machines that is almost impossible to escape. Why not counter this with noise cancellation ?
The problem: we have noise cancellation in headphones, but this only works to a limited degree. The ideal would be to actively cancel noises
at their source, by emitting an inverse wave of sound at the noise. After studying the problem, I discovered that the major problem was that one's head is constantly moving, creating a phase difference by changing the position of the ears.
So anyone wanting noise cancellation would still need to wear a pendant or something like that, which would be a wireless device. From the pendant, the "system" could infer the position of the wearer's ears. Now the system would adjust the anti-noise signal based upon where the listener is positioned.
A further level of complication arises in that a group of people in the house would need different cancellation signals. These would have to be coordinated, so Joe's cancellation signal would have to include a cancellation of Mary's cancellation signal. Finally, the "system's" feedback loop would obviously have to employ a medium faster than sound, to sample sounds for correction.
Whispering Windows
http://www.washguy.com/_wwg/00000006.htm
Obscure technology for sound propagation [undata, Sep 11 2006]
[link]
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To account for phase differences between two listeners (or two ears on one listener) you would need two spacially separated speakers. It's a matter of degrees of freedom. To get good noise cancellation you would also have to model the propagation paths of both the noise and the cancellation signals, which would need some fiendish computation. |
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You can get a feel for this by playing a tone and its inverse through a pair of speakers and positioning one ear (block the other one, as the zone of good cancellation is narrow) at a point eqally distant from the two speakers. The effect is noticable but slight; a large proportion of the sound travels by an indirect path, and is therefore not cancelled. |
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I like the thinking behind this, but I suspect that the effect would be small at best. Also, noise cancellation at the source has been discussed before. |
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Welcome to the halfbakery. |
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I'll vote for it, mainly because undata is one of the few people here who realized that noise cancellation is not that easy. |
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Determining exact position from a pendant though, is a piece of cake. |
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<practices making advanced noises> |
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One of my first paying jobs was working at builders warehose. I remember going between piles of insulation batts and my workmate was 2 metres away across the other end of the insulation alley. I talked very loud to my workmate and he could not hear me!
I would think insulation and double glazing makes a difference in not hearing things like traffic noises.
Making noise to combat other noise is not the aanswer. Like being in a pub, people like to talk but the restaurant staff cranks up the music volume, and people need to talk even louder. |
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I believe the technology has to evolve. There exist today specialized industrialized applications. Pellepeloton is correct, you do have to add noise. But if the added noise is added at the source, then the increased noise level does not have to be significant. But the real story is not decibels. The constant hum of a refrigerator or air conditioner plays on the nerves, and have been shown to be a health hazard over time. That sound I hear of a barking dog is not deafening loud, just annoying. On the other hand, I can fall asleep to the louder sound of crickets and katydids. I can sleep like a baby near the click-clack of railroad train tracks. |
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Following your argument, wouldn't it make more sense for the noise-cancelling sound generators to be implanted directly inside the ear canal, so that there is only one path from the sound to where you hear it, and it would be independent of head movement? |
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I know they made passive noise cancelling devices that fit in the ear canal made out of wax or foam a while ago... they used no energy during operation, fit most individuals, and were even reusable but were cheap enough to be disposable... |
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Foam earplugs are one of the best inventions in recent memory. However, because we don protective gear, does that make it fine to slog around in a toxic environment? "Improvements" like the segway are stupid. The people that market them live on estates with long driveways, far from noisy roads, or in the uppermost penthouses, above the noise and confusion. |
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