sorry to have two threads going at the same time,i'm at the age where if i dont sort things as the come into my head, i tend to forgrt about them till the time comes to use them.
i 'm wondering if anyone has ever tried noise cancellation.
the reason i ask, is i have a prop that emits a jet of air,it works well,
the only snag is, (theres always a snag) its a powerfull motor and impellor,see pic, dont laugh, and naturally makes a lot of noise, ive killed most of the motor noise etc (the more observant might guess how ive done it)
unfortunately at the" jet" end theres the typical whine/whistle that i suppose is to be expected, usually its in a disco/party environment so its not that noticable, this isnt always the case, so im wondering if noise cancellation might work.and if so where do i start.

regards
tibbles

 

I had a set of Bose noise-cancelling headphones several years ago, and they did work. They have been improved since then.

As I understand the problem of cancelling noise over a larger area, say a room, are all the reflections and multipaths that give phase shifts, so a simple anti-noise sound won't work.

John

 

how about a muffler?

 

thanks guys
alfacliff,
i did briefly and crudely put a 3" diameter plastic bottle halfway along the tube, i didnt give it much of a chance, so i might give it another go, is that what you had in mind ?
regards
doug

 

like a real muffler, baffles inside, possalby some pot scrubber material stuffng. just an empty bottle wont do much.

 

An automobile muffler.

 

There are active noise canceling auto muffler systems.

https://www.google.com/url?sa=t&sou...aEeZ3NS5O53MyjK1g&sig2=S_9jPHhqKaAZ2hrBCHRM1w
https://www.google.com/url?sa=t&sou...Y5vPz2XLtz-MObfpg&sig2=VwNCF76YwDEe1n1hjCDzJg

https://www.google.com/url?sa=t&sou...8wlC9IcroTp-5ZPFQ&sig2=PJpjguOstJ_eRXRfoO2Zzg


I think the key is you have to sample the sound (microphone) and apply the cancelling signal (speaker) all within an enclosed, acoustically consistent environment, like the solid cylinder of an exhaust pipe, not out in open space. Anything done from the outside is hopeless, but you might be able to add a length of straight pvc in the middle of your air path with the appropriate hardware in it and make something happen. My first impression is that it's tricky and expensive, but if you're looking for a fun challenge, this could be it!

 

Go to a good hobby store that carries RC airplanes. They should have a muffler for you.

Alternatively, pack a soda bottle with steel wool (or one of those brass scrubbing pads or even ScotchBrite scrubbing pad. Then make 6 vertical slices down the length of the bottle (make them about 1 mm wide). The goal is to decrease the velocity of the air exiting the bottle - and the only way to do that effectively is to increase the area of the flow-path.