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I'm hearing impaired. I'd like to dampen all the sounds around me filtering out all the stuff I deem unworthy of reaching my ears like the sound of my cars engine, computers fan or the rattling of dishes in the kitchen or any other ambient noise. Is it possible to create a system of noise canceling like bose headphones without say the headphones but isntead wearable speakers or strategically placed speakers?

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2 Answers 2

Is it possible to create a system of noise canceling like bose headphones without say the headphones but instead wearable speakers or strategically placed speakers?

No, not really. The sound from an interfering noise source may have a particular repetitive waveform shape at distance X but at distance X +/- 1 metre the waveform shape can look (using a microphone and oscilloscope) a lot different.

Consider a 1kHz sinewave - it has a wavelength in air of \$\dfrac{340m/s}{1000 Hz}\$ = 0.34m.

If you had a microphone at X and a 2nd microphone at X +/- 0.17m, the 2nd microphone waveform, displayed on an o-scope, would be 90 degrees shifted: -

enter image description here

The green image is the original microphone output at X and the red image is X +/- 0.17m.

What about wall reflections? They are going to disrupt things even more - there will be positions, in a typical room, where complete cancellation of the pure tone will occur in one ear but not the other.

What about complex sounds containing many, many individual sinewaves? I'm going to have to say "forget it". Headphones work (reasonably) because the measurement point of the noise, the ear and the re-injection of the cancelling signal are all fairly close and their relative distances don't change much at all.

Say you managed to position wearable speakers around you that kind of worked, what sort of sound would the person stood next to you hear? As sure as I can be, the person stood next to you would hear the original interfering sound and the sound from your speakers. They won't cancel out for someone in a different position.

Does it get better at higher frequencies? No it gets worse because the wavelength is smaller and the positional accuracy needs to be tighter.

What about the interaction between your left ears noise cancellation system and the right ear cancellation - there is no segregation between left and right without fairly decent headphones.

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Noise canceling headphones work on two premises. First is the acoustic isolation. I.E. the headphone part creating a partial or complete seal against your head. With the right material, this cuts a significant amount of noise. The second is active canceling. Noise is recorded/sampled with an external microphone, then processed and acoustically inverted/phase-shifted then injected into what you are listening to, so that it cancels out the noise that does get through.

Both parts are needed for proper noise canceling. A strategically placed speaker or two might work, but unlike headphones, where the noise source and the canceling is done fairly close to your ears. If the microphone and speakers are at different locations, the noise you hear at point A, and the noise the microphone picks up at point B, and the speakers at point C, are not in sync.

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so several mics and speakers in the car could phase invert the sound of the engine? –  caseyr547 Mar 24 at 1:59
    
@caseyr547 yea, in theory. There is all the acoustics to worry about, but it should be plausible. In fact, Bose does design noise canceling tech for cars: businesswire.com/news/home/20131217005237/en/… –  Passerby Mar 24 at 2:12
    
The trick with noise canceling head phones is that they rely on repetition of the noise. They're really good at canceling hum or engine noise (predictable), but they're terrible at random (unpredictable) incidental noise (like plates in the kitchen). –  jippie Mar 24 at 7:33

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