I have been wondering about this for a bit. I wonder if it would be possible to use sound nullification technologies/concepts to negate a relatively constant sound, such as a case fan. While I see the inherent doubts as to the effectiveness/practicalness for a standard desktop, I think it could be quite useful for a server or other box you don't want heard. Anybody ever done anything with this?

Noise canceling headphones will do this. If you are talking about negating sound for an entire room with a speaker or something, I am not sure that would work, because of the varying acoustics depending on your location in the room. A headphone can do it because it analyzes the sound right next to your ear.

Couldn't you do it at the source though? If all you were worried about was getting rid of the noise from the fan (as opposed to the noise in the room) then that seems like something that would be possible.

Yeah, i'm pretty sure it would be impossible to do it for a whole room. Think back to phys 23, you could calculate the distance a second speaker would have to be from you to completely cancel the sound from another speaker, but it was only effective when you were at that exact location. Once you changed the proximity to either, the cancellation effect went away. I suppose you could possibly do it for your desk chair, but not really for a whole room. Even then it would be quite difficult.

I was thinking along the lines of putting speakers on the computer case itself. I figured the closer to the source of noise you could get them, the better cancellation effect it would get. I realize that it probably would not eliminate all noise, but I think it might be an interesting project to try to cancel a good portion of the noise anyways.

http://svc.com/silent-damp.html

Not active silencing like a speaker, but probably easier.

Thanks for the thought, but I am wanting to do active silencing. I am just at the beginning point, doing some research on it, wondered if anybody else had tried it at all.

Well, I think in theory it would mostly work if you had a speaker next to each fan pointed in the same directions (and radiating sound the same way as the fans) doing the inverse of the noise. Keep in mind though if you get your phases off a bit that you'll have moments of silence, then moments when it is twice as loud (I think anyway, I don't really remember physics that well)

I have been reading about some different systems of sound transmission, and found an interesting one, albeit expensive. Its a system that uses a couple central projectors that project some finely-tuned electromagnetic waves [the article wasn't specific, but I know it would have to be ultrasonic, but unlikely that it would broach microwave wavelength, so probably a higher-frequency FM radio band or something]. These waves intersect at a certain point [namely, where they are aimed, usually at a previously-configured point as to achieve optimal surround sound or similar effect], and cancel most of each other out. The remaining wave [if done correctly] will produce an audible sound, from the spot they intersect

I thought this a rather neat idea, as it gives the illusion of having speakers in places where none can be seen, and functions completely without wiring.

But I digress. The point is that this could be of use for sound cancelling technology. The speed of sound in air is 343 m/s, and despite the drawbacks, if projected from inside a computer case [or any other object that would require sound cancellation, such as an engine], this comes to an approximate maximum of about 0.00058 seconds of delay [plus whatever processing time said projector requires], which I believe would be sufficient [for now] of a delay. While I do not doubt that this would be an audibly noticeably delay, it will shorten with time [and as the distance from projector to target decreases] as the processing becomes faster.

I find these thoughts intriguing, and though I have no practical experience [and no doubt my theoretical experience is also lacking], I think it could be a legitimate study in a few years.

Thoughts?

naw i think itll just cause some phase distortion and freak your ears out... i dunno it might even just do a partial cancellation but more than likely enough if the levels are set right youd never notice. if you ran from a mic to something like an lm386 (if i remember right its a little 1/2W 8-pin DIP 'power' amplifier) with a small speaker... i dunno it should be interesting. if you get it going keep an update here.