[ynneb]

Does any one know about how to make a noise cancellation circuit.
The type of circuit that hears the ambient noises and generates a negative sound to cancel out the noise or reduce it.

[cbass]

I don't know much about circuit design but I do know the principle behind this application. I think you want your speakers to be out of phase with the ambient sound. If you've ever hooked up speakers for your home system out of phase, you've experienced this first hand... Obviously it has to be in real time. You could run it through a computer but I guess a dedicated circuit would be much more streamiline.

Is your project aimed at keeping the neighbours asleep at night?

A side note: Volkswagen was experimenting with this a few years back to reduce the appearant sound of road and engine noise inside their vehichles.


Sorry I couldn't help more...

Good luck!

[H500]

The sophisticated ones uses a DSP. Even then, they work best if the noise is periodic.

[ViperTX]

Essentially you have to sample your noise, you invert the sample and feed it back to a transducer (your speakers). DSPs are used....are you trying to build one...or looking to buy one....most everyone has noise cancellation headphones available....what are you trying to do?

It is most effective on noise that is continuous...basically you need some time to collect the sample, invert it and reproduce it. It was first used in work areas where a worker was in one location.....kinda like being close to the generators in a power plant....

[ynneb]

Yes Viper, the noise I want to cancel is the router. So it will be a consistant noise and I dont think the time taken to do the cancellation processing will matter, because whatever it recieves it can feed or the next sound wave.
I want to aim speakers at the router so as to cancel ambient room noise. I am worried about the neighbours and not necessarily my self ( I can just wear ear muffs)

Yes I wish to build it myself if someone has a circuit design that I can copy.

[Al_The_Man]

Benny, Have you investigated the sound curtain material used for these applications? I have seen them used effectively in hydraulic & vacuum pump applications, it is just a heavy absorbant curtain the encloses the motor, It does not come in contact sufficiently to affect the cooling of the motor however.
Al

[ynneb]

Al, the sound curtain is probably the best option. I was just worried about if it would restrict the air flow / cooling. You think it wont? I will look into it and see what I can find out. The only thing with this option is that it isnt very hi tech

[H500]

I don't think it would be that easy to build a sound cancellation circuit like you decribed, or rather, it would be extremely difficult to make one that works. The noise source is quite complex and radiates in all direction with varying intensity and phase. A speaker would not be able to produce a sound that is perfectly out of phase in all directions. I played with systems that only need to cancel sound at a single location. Even then, it is difficult to tune.

[ViperTX]

ynneb,
Noise cancellation is very localized, it won't work like you want. I guess you could always seal the shop and draw out a few atmospheres....I understand that sound does not travel in a vaccum.

Anacheoic...I believe that is the spelling....basically you use material that is cone shaped to absorb the noise, a sound deading material helps like what Al describes. You could also create a room within a room with an air gap between.