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Captain Terrific

Phase Cancellation

14 posts in this topic

okies... here's a strange one

lets say i have 2 identical fridges, running at the exact same specs sitting next to each other...

OR

can i record the sound of a fridge running, play it back 180° out of phase, will it cancel out the sound of the running fridge?

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You can get a plug-in called X-noise which will remove the noise once you tell it what it is. But for a free alternative I'm not too sure. :- Is your first choice some kind of wierd vocal booth made out of fridges? ;D I guess a bit of phase would be removed that way.

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;D You're 180degree thing would work to a point. You'd need to trigger playback as the compressor comes on... but don't forget the compressor will change pitch through it's cycle.

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maybe you could set up a noise cancellation headphone kinda thing

maybe chuck a small mic (pzm or something small) down the back of the fridge and then phase invert it and have it come out a small speaker live rather than recorded.

But would you point the speaker at the fridge or the people in the kitchen?

I think you'd be trying to have it as close to the sound sorce as possible (your buzzing fridge  ;D) and point it back to the listeners right?

You'd have a tight sounding fridge then

maybe get you robotic voice triggered by the door opening to "the hands you are using, are too fat" etc hehe

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But would you point the speaker at the fridge or the people in the kitchen?

See, it's not such a stupid question!! - there be some valid points in these replies...

and lol @ vocal booth made out of fridges :)

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not so strange really, i believe this is partly how new cars minimise interior noise. and how noise-cancelling headphones work also.

you should patent it and license it to fridge manufacturers :)

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Excellent practical question, CT!

Couple of questions:

- Where are you going to mount the speaker?

- And the microphone?

Something tells me the microphone and speaker need to be mounted right beside the ear canal, or right against the fridge's compressor

Anything else and inverted phase will be thrown out due to:

- the sound needing to travel a different distance from the speaker-to-ear versus fridge-compressor-to-ear.

- the reverberant sound bouncing of the walls being unique to the location of each sound source.

Of course, I've never tried this for myself, but I'm open to other people's experiences. :)

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not so strange really, i believe this is partly how new cars minimise interior noise. and how noise-cancelling headphones work also.

you should patent it and license it to fridge manufacturers :)

I'd say an important aspect to the success of cancellation working in cars and headphones is that, as Spectrum suggests, the out of phase speaker is essentially pointing at the ear. In the case of cars, a person is sitting still in a confined space, and headphones are permanently placed over the ear.

So in the case of the fridge, I can imagine it working if the listener was in a nodal spot between the fridge and the speaker and the speaker pointing straight back at the fridge.

Also the effective noise cancellation in cars and cans is around 300Hz worth of low-mid, steady-state, narrow-band noise. It's what gets rid of the low but largely unchanging 'whoosh' of air rushing past cars and planes and air-con fans. Fridges emit a range of oscillations, buzzes and rattles with mid-range emphasis. Much harder to cancel completely.

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i remember watching a science show about this when i was a kid and some brit scientist demonstrated how to make a silent muffler with this technique...

not sure why it wasnt implemented from then on?

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I'd say an important aspect to the success of cancellation working in cars and headphones is that, as Spectrum suggests, the out of phase speaker is essentially pointing at the ear. In the case of cars, a person is sitting still in a confined space, and headphones are permanently placed over the ear.

So in the case of the fridge, I can imagine it working if the listener was in a nodal spot between the fridge and the speaker and the speaker pointing straight back at the fridge.

Also the effective noise cancellation in cars and cans is around 300Hz worth of low-mid, steady-state, narrow-band noise. It's what gets rid of the low but largely unchanging 'whoosh' of air rushing past cars and planes and air-con fans. Fridges emit a range of oscillations, buzzes and rattles with mid-range emphasis. Much harder to cancel completely.

well just add in one of those tinnitus-relief boxes, put your favourite armchair in the (not)listening possy, and try not to move around too much :)

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