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Methods for sound cancellation in a room

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Full Member level 1
Jan 7, 2002
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Dear All,

I just wander that we can make sound cancellation. What I means is to cancel the sound or/and noise from outside the room (target room), so that the room is quite enough. I need to make the quite room with "active" way, not with the "passive" way, such as using sound damper in my wall.

I know in physics we just have to create the waveform with exact amplitude, but in anti-phase. So just use the microphone for the input device and speaker for the output anti-phase.

In real world (technically) can not be that easy. Can we do this by using the powerfull DSP chips to create the anti-phase? Is it possible?

Anyone has try this? Any comment?



Sound Cancellation

yes you must use DSP and generate anti-phase sound. i heard about it .

Re: Sound Cancellation

Hello hr_razaee,

Have you seen somebody has implement it with the real DSP circuit?
I just wander where to put the transducers (microphone and laudspeaker) in the room. I think we also have to give the close loop control for this. Is there any clue?


Re: Sound Cancellation

Sound cancelling headphones work. Some work very well.

I don't think canceling sound in a whole room is practical. You may be able to cancel the sound at one spot in the room but at other places in the room the sound and the anti-sound will not be at the right phase relative to each other.

Sound in air travels is about 340m/s
At 1Khz 17cm difference in the path of the two sound waves gives a 180deg phase shift and the sound is twice as loud instead of being canceled. How far apart are your ears?

There is also the problem of reflections and reverberation.

Sound Cancellation

i heared about headphones noise cancelation.

Re: Sound Cancellation

Dear All,

I know may be I am asking to much to cacel the sound in whole room, but I have heard that this technology has been used on :
1. Air plant, to minimized the noisy jet engine sound.
2. Some high class car to minimize the sound/noise frm the engine.

Ok, I will reduce to only some spot on the room. This spot will be use for baby's bed for instand.

For the room aplication we should take care of the acoustic effect (like Throwaway18 says). I also aware that we should cancel the complex wave (because of acustic effect). This complex wave are mixed of several frequencies, that means several wavelength too. Every wavelength has it's own antiphase, that also means each frequency has it's own "distance" between the laudspeaker & microphone. (Correct me if I am wrong!)
How can we solve this problem?


Re: Sound Cancellation

In today’s hectic and noisy world, we are all searching for a little peace and quiet. Well, you might not be able to slip off to a tranquil forest for an hour or two, but you can block out background noise with the Noise-Canceling Headphones. The theory behind this project is that by picking up ambient sound with a microphone and reproducing it out of phase, we can actively cancel or "null" out background noise. In fact, several commercially available devices perform the same function. However, by building your own headset, you can add features not otherwise available and have fun while doing it!
Quoted from:
**broken link removed**

Whether you can adopt this, or similar, idea to your design it is really difficult to judge ..


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