Slashdot Mirror
Cancelling Out CPU Fan Noise
Percy_Blakeney writes "After realizing how noisy his computer was, a professor at BYU has created a new CPU fan that uses small microphones and speakers to cancel out its own noise. It isn't perfected yet -- it only nixes the whine, not the whoosh -- but it looks like it could be promising, especially given the professor's background: making jet engines quieter."
I have heard of something like that for cars ages ago, basically replays the engine sound over the car sound to negate it.
There were various addons with such a system so you could add a roar of a 911 or rattle of a clapped out sad wanker boy racer in the car.
Jonty! Neil! Work!!
I think this is how noise cancelling headphone do it - they just feed the external noise back into the earpieces after inverting it.
Its actually used on some heavy earthmovers and tractors simply because its actually cheaper than making a decent muffler.
Don't worry - its just stigmata. Pass me a napkin and don't you dare tell my mother.
What you describe is not that same thing which is mentioned in that article. You describe passive cancellation (i.e. simply reflecting and hoping it will cancel the original noise), whereas the article describes active cancellation (i.e. recording the noise, computing the negating and sending it off) of noise.
Pick up some of the new fluid-drive-bearing units most companies are producing these days. I can hear my 60GB drives when they access, but the 250GB drive is completely without any detectable noise.
Of course, I do need one of the prof's nifty new toys for other parts of my system...
You can never go home again... but I guess you can shop there.
Although, it would be very very cool to get this technology to work on big loud things, and is very cost effective, for quite pc's, the Voodoo F:50 does a very good job at keeping noise at a minimum, using no fans, only convective heat pipes, and using the entire case as a heatsink. Voodoo claims that their system operates at below 20 dBs, and cannot be measured in a room with regular ambient noise.
Skill is successfully walking a tightrope over Niagara Falls. Intelligence is not trying. -- Anonymous
Not to worry, the cancellation -can be- that complete. In practice, there will be some residual noise, but it will be very quiet.
I think you're referring to a "blast fence." Those have nothing to do with active sound cancellation, they're strictly passive noise control devices that block the path between the noise source and the receiver (just like highway noise barriers). See here or here for examples (the latter is a run-up enclosure, but it's the same principle).
If you can't hear it, it's not hurting you (assuming that it's a frequency that you could normally hear). Typically what will happen with a scheme like this is that the cancellation will only work in one direction. In other directions, it will reinforce rather than cancelling. For instance, you can buy noise-cancelling headphones, but the cancellation only works for your own ears, which gets the sound in just right right phase; to the people around you, there will be a perceptible noise coming from your headphones! Conservation of energy says you can't just destroy the energy of those sound waves. Most likely you're just sending extra-strength sounds waves somewhere else. Theoretically the extra energy could be converted into heat, or electrical energy, but I doubt that's really practical.
Find free books.
"Adaptively Cancelling Server Fan Noise" can be found here. They were able to lower the whine by 30dB and the broadband noise by 20dB.
Bose noise cancelling headphones suck, they aren't even the best active noise cancelling headphones available. Sennheiser has better models for around the same price. Far better than either though is the Etymotic ER-4P, these in ear canal headphone provide over 24dB of isolation, with some nice jazz playing you won't hear anything outside, headphone.com has them for only $219, about the same as the Bose units.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
No Slashdot post about computer noise is complete without a link to Silent PC Review.
Losers choose to abuse the use of "loose".
The noisest part of all my computers i the hard drive, not the CPU fan.
How to reduce drive noise:
1. Take your hard drive off the mounts.
2. Find a 3.5" drive mounting kit and a piece of foam (styrofoam, or packing foam).
3. Mount drive on mounting kit, place on top of foam in the bottom of your case.
4. For completeness, ground the mounting kit to your case.
This will knock out a very large portion of your drive noise that is getting transmitted to the body of your case. It is a little Rube Goldberg, but it is very effective.
Someone send this guy a link to
http://www.silentpcreview.com
Implementing noise cancellation for poor quality whining fans seems ridiculous in comparison to replacing the fans with better quality ones.
Quote from SPCR -
" What is a good inexpensive & quiet general purpose fan?
The 80mm Panaflo FBA08A12L with "HydroWave bearing" is widely used and recommended for its combination of low noise (21 dBA), good airflow (24 cfm), wide availability (but not in Canada where I type this) and low cost. At 7V, it is almost inaudible in most applications. At 5V, it is inaudible but still provides some airflow. We think of it as a workhorse, suitable for use as a case fan, CPU heatsink fan, or PSU fan replacement."
...is to buy Zalman components ( http://www.zalman.co.kr/english/intro.htm )
I built my last PC with their components. When I powered up for the first time I freaked out because I saw the power light go on, but that was it. Then the BIOS came up, thank god. No noise at all...seriously. I mean, I expected quiet, but not noiseless...
I was extremely let down by my hard drive though. Considering Seagate had a great reputation for quiet hard drives, I figured I'd get a Seagate SATA hard drive...well their SATA drives are loud as heck when writing...
01100111 01100101 01110100 00100000 01101111 01110101 01110100 00100000 01101101 01101111 01110010 01100101 00101110
The fan controller in the Power Mac G5 is aware of the noise amplifying and canceling effects of running different fans at different speeds in different combinations. It actively uses this information and uses it in decisions on how to cool the G5 in the quietest manner using the 9 strategically placed fans.
It should be noted that the flow of blood, chewing, other internal sounds, etc. would be a LOT louder if we didn't have the middle ear. One of its (theoretical) functions is to reduce the transmission of bone-conducted sound to the cochlea.
/trying to see if I can actually interject something I learned in my music psychology class into a conversation....
I belong to the ______ generation.