i remember reading a while back about a college professor working on a system that would actively cancel a great deal of noise generated by computer components and do so cheaply. recently i discovered a company called silentium which offers active noise canceling products specifically designed for pc's. however there system is a few thousand dollars which is way too expensive for my liking. is there another company or at least news of a company releasing a cost effective method of actively reducing noise in computers?

"a few thousand dollars"

Active Noise Cancellation is commonly used in Headphones which sell for under $US100. It should be cheap'n'easy to do this for a PC as it already has a microphone input and a speaker output.

This topic pops up from time to time. Summary: Easy to do on headphones, not feasible to do on a PC. Nothing new here...

"not feasible to do on a PC"

What if you were sitting inside a surround sound speaker setup?

The addition of a microphone at the PC operators location and sound cancelling software could nullify a significant percentage of noises. By listening to the ambient noise from the microphone location and then transmitting the noise at 180' phase change at each speaker in a test sequence a room characteristics signature could be developed. Some of the ambient room noise, whatever the source, could be cancelled.

http://www.silentpcreview.com/forums/vi ... hp?t=55271

Or you can just wear noise cancelling headphones when sitting at your desk...
Or you can build a quiet computer...

Why?
We already have it, its called SPCR.

-slow fans, big heatsinks, undervolting, pico psu's, drive suspension/ssd, insulation/vibration dampening- are all cost effective ways of actively reducing noise inside computers.

You would have to know exactly where every speaker was, where your ears would be, the type and intensity of any reflections, and have a pretty good idea of the "shape" of the output noise. Since the distance from the computer to your head is not >> the size of the computer, where the sound leaves the computer is important... The idea of adding sound which will result in perfect wave cancellation is ... complicated.
Then consider that based on system response, active cancellation is mostly only useful for low frequencies (maybe your fans), but your hard drives will still be clicking away, and any whining components will whine away.

The thing about headphones is that you can use materials for high frequency cutoff, and active cancellation for lower frequency cutoff. Since the low frequency waves have longer wavelengths, pinpointing exactly where your ear canal is and how waves move through it is less important. (Because the distances involved are << wavelength, phase changes in the medium can be ignored)

In summary: go buy some headphones, don't wait for magical room-wide active cancellation.

I have bose active noise cancellation on my car stereo, so its certainly feasible for a PC. However, it isn't as effective as it is on the headphones and only mildly reduces the low frequency noises - it doesn't completely cancel them.

Interesting.

In terms of 50Hz, which has a wavelength about 22.5ft, or 6.9m, the distance between the heads of passengers would be on the order of 1/4 wavelength. I am unfamiliar with the nature of road noise, but it would be very difficult to use a few point sources to actively dampen a wide frequency range when interference patterns come into play.

Is this an after market device? To calibrate I would think you would need to place a mic roughly where each passenger's head will be and build a table of phase offsets for the output of each speaker. Otherwise I very much doubt it is doing much, unless I am overlooking something.

Have you tested turning it on and off? What kind of noises does it work on? Is is more in the 20Hz range, or does it go higher?

Anyway, I guess if you know roughly where any ears are going to be (within ~1/16 wavelength or better), have a sufficiently complex output system (1 point speaker per point of interest or more), and have a fairly acoustically static room (no moving a speaker, large furniture, etc), you could set up a working system... But it would be pretty time intensive to set the microphone in the correct area and get phase offsets for all frequencies of interest... Oh, and if you are talking about 5 people in the room, and 50Hz sound you may end up needing 5 subs depending on how close they are sitting. You might be able to arrange your seating to minimize speaker requirements though :)

Anyone know if I am overlooking something? Assuming point sources and individual points of interest I just don't see how you get a generalized method for the interference without an equal number of speakers and points of interest, and proper calibration. Are there approximations/simplifications that can be made?

The car is still a static environment that they can engineer the system to work in. To work with a PC you would have to engineer the system for each individual room and the positioning of the PC and person.

It really doesn't matter if you can do it or not though. It's clear that it's much easier and cheaper to build a quiet PC, or even a completely passive silent PC.

The above post makes the precise point I was going to make.

Maybe SPCR should build some silent computers from stock stuff, but toss some old faux speaker grills and mic pickups on the case, and sell them as expensive fancy pants "active noise canceling super high-tech silent computers"

"Or you can build a quiet computer..."

Yes, but:

=> the last step from quiet to silent can be more than some pocketbooks can manage
=> why not use our brains to develop a cool way to manipulate our environment
=> how about doing active noise cancelling inside the PC case
=> Yes, SPCR is about silent/quiet computing and some Gamers like their PC to be reasonably quiet and non-annoying at idle.

I'm not sure if you understand how noise cancelation works..

You can't just put a little box in the bottom of your PC case and expect it to effectively cancel out all sound being produced within the case.

Noise canceling headphones work so well for two reasons:

A) they "know" where your ears are. In other words, your ears don't change position relative to the speakers, so sound waves can be generated that will reach your ear almost exactly when the environments sound does.

B) They work in conjunction with a natural sound dampening device: headphones! By design, headphones physically block external sound waves from reaching the ear drum, at least undistrubed. this has quieting effect that is completely independant of noise cancelation...like less effective ear plugs

As others have said, the best way to solve this problem the cheapest, is to select computer components that don't generate audible noise to begin with! Furthermore, don't say that it is out of people's budget, becasue building a computer in the first place saves you hundreds, if not thousands over pre-built products from Dell, HP and Apple. Its more of a matter of priority rather than budget.

A) the reason they work relatively well is because close to the ear, it becomes much easier to generate a point source of counter-phase sound to cancel the noise.
Instead of having to put a lot of speakers very close by the noise generating sources (for each source one noise cancelling speaker), just use one single noise cancelling speaker close to the ears. Even then, the result is not that great.
It's relatively easy to reduce surrounding noise of 65 dB(A), it's very very hard to reduce surrounding noise of 30 dB(A) or even less.

B) Most headphones are "open" instead of "closed". Ear covering headphones don't necessarily block sound, most of them don't. Usually, you will get a weird sensation just because of the blocking, and some people complain about sweaty ears or pressure to them.
I'm wearing a Sennheiser PC-150 and still hear my clock as loud as without them.

Noise cancellation for an already relatively quiet PC is near impossible.

Or pay me $500 and I'll silence your entire computer for you.