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Hi is it possible to make audio cancellation inside a bus/train cabin? I am thinking of gathering background noise and predict some delay playback the negative of the noise clip wave and try to cancel it.

But I know the sound wave is all different everywhere. is the idea feasible?

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    You mean like noise-cancelling headphones do? You mean for 'in the room' loud-speakers so the whole carriage goes quiet… nope. – Tetsujin Nov 13 at 17:06
  • in room, open air, sorry about not specifying clear enough – c2h2 Nov 14 at 1:16
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No. Nope. Not possible. Cannot be done. At all. Ever.

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Yes, to an extent. But this has to be done during the design of the vehicle. You can build in sensors that measure vibrations in the bodyshell, actuators that try to counter these vibrations, and noise reduction schemes to get rid of noise sources that can't be handled by ANC. This could work for engine noise, for instance: a localized and predictable source. Tire noise would be more difficult due to its random nature.

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With traditional noise cancellation, the noise you are cancelling has to come from one direction while your "quiet zone" is in a the opposite direction. It is all about racing electrons against air particles. The type of cancellation that you want to do could only be possible to the extent that the noise consists of tones which last long enough for your waveform to be generated and sent back (music, for instance). Even then, the cancellation would only happen in a limited space where your waveform is out of phase with the incoming waveform. In other areas, your waveform may even increase the volume. Try wiring one speaker on a stereo with reverse polarity and see how much that reduces the volume in the room. That's the level of noise cancellation that you are talking about.

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