Cancelling Out CPU Fan Noise 507
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 should have patented it... (Score:3, Interesting)
Near the landing strips you can sometimes find some "sound reflectors" which just reflect the sound wave they receive from the planes. The sound is then cancelled by itself.
I saw it once in an airport in France and it works really well and costs next to nothing. AFAIK there's no sound wave modification in that system but I'm not sure (maybe the surface of the reflectors is made in a certain shape to change the sound wave a little).
But in this case it's different because the "box" must produce the counter sound wave. It's not just reflection, there is sound generation here. It means that the microphone and the speakers must be very precise or you just end up with more sound.
But if this guy can do it with 20 bucks it means that it's much easier than I though.
Wow (Score:3, Interesting)
Re:No need to worry. (Score:5, Interesting)
Where this would be really useful is for the whine of hard drives. It would be far better than the current system of enclosing it in some casing thus making it run even hotter.
Mods... (Score:3, Interesting)
Re:now for the hard drives (Score:2, Interesting)
Re:I should have patented it... (Score:5, Interesting)
I could use this (Score:3, Interesting)
Stupid HP. Had to go sticking a desktop chip in a laptop. Oh well, it still runs circles around my roommate's silent Centrino-based machine.
Absorbing technique instead (Score:5, Interesting)
If the noise is pointing at your directly, then you probably need a cancelling method. If it is a general-direction noise, it should be absorbed rather than trying to cancel it (where you need to find it in the first place).
Re:Wow (Score:5, Interesting)
Re:No need to worry. (Score:1, Interesting)
Re:Keep everything quiet (Score:3, Interesting)
When you first put those headphones on it freaks you out a bit, because its like being in an anechoic chamber - the noises you use to judge distances (the rooms natural reverb) are cancelled. Its wierd.
diy? (Score:4, Interesting)
Specific noise cancellation.. bad. (Score:1, Interesting)
Re:Wow (Score:3, Interesting)
Re:Negating Sound? Its like new cars.... (Score:2, Interesting)
It's a great feature - I find myself messing with the volume control a LOT less. It also doesn't require the technology and expense of sound-cancellation.
--RJ
Re:Like the noise cancelling headphones? (Score:5, Interesting)
Well yes and no. Noise cancelling headsets are particularly effective because the ANC speaker and microphone are right next to your ears. This helps insure that the signal that arrives at your year can be sampled and inverted so that the sum cancels at the ear. It would be much harder to accomplish this with speakers and/or mics located away from the ear.
However, remote mics/speakers may work if the noise source is highly directional, like a waveguide (I suspect that's happening here). If you can effectively cancel the sound at the orifice, you'll probably achieve a significant reduction in transmitted sound, no matter the location of the receiver.
Re:Wow (Score:3, Interesting)
The 2003 Dodge Viper SRT/10 has side exhaust with active noise cancellation. It can be switched on/off to allow for "stealth mode" or a throaty sound- though I can't imagine why... I love the sound of a V-10.
I've used the headphones that do this... (Score:3, Interesting)
One really important use of these will be in ultra-quiet studio computers. Of course, its not to make sure the fan noise doesn't get recorded as its not a real recording studio if there isn't a separate recording booth/room (the studio I use in london from time to time is two rooms built within one large one, resting on a buttload of industrial springs, but I digress.
When you are listening to playback, making sure the singer was in tune, mixing the track, or whatever, you don't want ANY extraneous noise from fans. There is already a market for ultra ultra quiet pc's for this kind of application and advances like this can only help further the art.
Re:I should have patented it... (Score:5, Interesting)
I own a set of noise cancelling headphones and there is no perceptible noise being emmitted from them to the outside world. The noise cancellation circuitry takes the incoming signal and inverts it to cancel out the original incoming sound wave. Conservation of energy doesn't really apply. You aren't really destroying the energy of the sound waves, just cancelling it. Energy is spent on both the positive and negative signal. Although I just minored in acoustics so I'm probably missing something. Any professional opinion is appreciated.
Re:I should have patented it... (Score:5, Interesting)
Well, I do have a PhD in physics, but I should bow to your actual experience with the device
My guess is that the sound coming into your ears is only a tiny amount of power, so reradiating that power in all directions doesn't make any amount of sound that would be perceptible to someone a significant distance away. Your eardrums only have a surface area of a few square mm, the the amount of energy impinging on them is normally only a gazillionth of a watt. Your ears are amazingly sensitive devices.
Conservation of energy doesn't really apply.
I was obviously wrong in my prediction about an audible noise for people not wearing the headphones, but I'll bet both my testicles that it's not because conservation of energy is violated. You'd get the Nobel Prize if you found a violation of conservation of energy.
Re:now for the hard drives (Score:3, Interesting)
I have one of the new design Alienware towers, and by far the most noise comes from the case fans. I have 2 seagate hard drives, and I can hear them somewhat, but the case fans are much louder. Although the fans themselves don't make that much noise, but the amount of air that they throw around does. If it is quite in the room, the whoosing sound can be quite loud.
Re:now for the hard drives (Score:3, Interesting)
The graphics fan is the noisiest component in my case. Those Gigacube Radeon 9600 XT Extremes are damn loud.
I also have a 30-35dBA fan which doesn't help with the noise. To help, I have an Sonata case, and when the case is on, the only thing I can hear is the clicks from the hard drive, and only when it's being used (during loading. Get more RAM if you are using swap!)
Normal operation is silent, or at least silent with respect to the other, louder computers that are not in Sonata cases. :-)
And of course right now the damn thing is quieter than it's ever been while parts are back for repairs. :-(
Re:Keep everything quiet (Score:3, Interesting)
Re:It never ends though (Score:4, Interesting)
One day a fan on your computer fails, and you never noticed, because you couldn't hear the squealing of the tortured bearings...
The interesting thing is with modern mobos (which control fan speed based on how hard the cpu is working/generating heat) you can actually tell to a point what's going on. I can set a compile going, go sit on the couch and read a book, and tell when it finishes (the cpu fan noise goes down and the hard drive noise goes up briefly - I run Gentoo where it writes the files at the end of the compile/emerge).
SB
Re:I should have patented it... (Score:4, Interesting)
The experience I've had with the equipment in class showed that the noise cancellation circuitry recorded the original sound wave, inverted it and fed it back into the speaker. The combination of positive and negative voltage basically told the speaker to output zero signal for that particular frequency. Nothing is destroyed, it's more like an electronic tug-of-war. It makes listening to music a lot more enjoyable, however it works.
Thanks for the reply.
Re:Me too! (Score:3, Interesting)
I had an interesting idea based on this (I don't know if it's actually used). Fixing the distance and delay may not be accurate enough to match the signals completely, so you could have a second mic which listens _after_ the cancellation for beats. Superposition of the two similar waves produces the "beats" that musicians use to tune an instrument. By observing the frequency of the beats, the microprocessor could adjust the delay to more perfectly cancel the noise.
Not a new concept ... (Score:3, Interesting)
Before CPU's came along, this sort of thing used to be done with BBD (Bucket Bridge Delay) circuits, replaying the sampled sound 180 degrees out of phase. Of course, this only worked with single-frequency tones and the BBD had to be clocked at just the right correct frequency. Cancelling white noise (ie: fan whoosh) is a somewhat more difficult problem.
A number of "professional" aircraft pilot communications headsets have had active-cancelling (as in the article) built into earpieces (as opposed to the microphones) for several years, so as to reduce engine noise and pilot stress.
Car buffs here might even remember that VW had a Concept Car in the nineties which had an (I think) Bose-powered active-cancelling system in the cabin, the purpose being to cancel road noise and engine bay noise so you could replace it with sound samples of your favourite sports cars: Ferrari's, Porsche's, etc. Not sure it ever took off, though.
Re:Nope (Score:2, Interesting)
Re:now for the hard drives (Score:2, Interesting)
You can't touch anything else with the reliability and stability of that system without spending four figures today.
And Pentium Pro systems are cool. A good PPro server is like a diesel truck. I can't afford to collect diesel trucks but I can afford to keep around some nice hardware, and even use it.
Re:now for the hard drives (Score:3, Interesting)
Re:I should have patented it... (Score:4, Interesting)
Make fans with predictable noise? (Score:2, Interesting)
Re:Me too! (Score:2, Interesting)
Mod up! (Score:3, Interesting)
From what little of the results I've looked at, it's pretty clear that tire noise is dominant during cruise.
Re:Nope (Score:3, Interesting)
You will get a lot more bang for your buck with a good set of monitors while only taking fraction of the space. Check out the Event TR [event1.com] series or M-Audio [m-audio.com]'s line. Most decent music equipment stores like Guitar Center should have some demos.
Re:Nope (Score:2, Interesting)
This is one reason why I love Slashdot... you pick up all sorts of neat science project ideas for the kids. Thanks!
Rod!
Ears are sensitive indeed! (Score:5, Interesting)
Point being is that it would be completely pointless for them to be any more sensitive. Quite amazing really.
Re:Nope (Score:4, Interesting)
I'm lucky. I have very good hearing, but I'm pretty tone deaf. The medium priced stuff at Best Buy sounds just as good to me as the high end stuff at the specialty stores. There's no point for me to shell out the cash.
-B
Re:I should have patented it... (Score:4, Interesting)
Not mine, but.. compelling.
Casimir Effect [wikipedia.org]
Re:It never ends though (Score:3, Interesting)
A Cheaper Way (Score:5, Interesting)
An even cheaper demonstration is to simply plug your ears. It works better in an area that's already quiet, but if you simply plug your ears with your fingers, you'll hear the blood flowing in your veins and arteries. That's what that low, rumbling noise is that you'll hear.
Been There, Almost Done That (Score:2, Interesting)
Re:I should have patented it... (Score:3, Interesting)
If anyone can remember the name of the story or even the Author, I'd be very grateful...
Re:I should have patented it... (Score:4, Interesting)
A very greatly hyped and over-rated technology, which in some specific circumstances will provide a useful reduction (10dB?) in low-frequency noise, for example in the Dash8-Q400 aircraft, where propeller blade fundamental frequency noise is at 85Hz in the cruise (6 blades at 850 rpm, which is lower than most), and where people tend to sit in predictable places, it does quite well, although a fair part of the reduction is by trimming the relative phases of the two propellers (which should run in synchronism in steady flight, although this is not a safety-related function and might not always work, as it is not provided with any backup system), how that compares to the contribution from the speakers I don't know. The active noise suppression system can command the propeller controls to adjust the phasing, and indeed select which blades to synchronise, as they might be slightly unequal, of course it has only extremely limited control authority to avoid it becoming safety-critical, so it can only trim the relative angles very slowly. That is basically adjusting two noise sources so they make the least overall noise, inside the aircraft. I always had the suspicion that at certain precise positions outside (as presumaly happens with all twin-engined aircraft), the noise would be doubled, but it passed certification so it must have been acceptable. Probably much quieter than the average jet, Avro 146 excluded, anyway.
At 85Hz, the wavelength is about 12 feet, so the problem is somewhat simpler, but still very complex....
I am not a noise expert, but I can clain very intimate knowledge of the propeller sync system, called "syncrophase" in this case, being one of its main hardware designers. The propellers are synchronised at the desired angle, within about quarter of a degree, which is not bad considering there is no mechanical connection, the engine power is several thousand horsepower, and only a little pulse as each blade passes a sensor gets sent from the master controller to the slave. Oh! sorry, I forgot, can't use these words any more..... Back to the drawing board. Ground the aircraft in the interests of political correctness. Now, did it have any IDE drives on board?
On a jet, by comparison, the fundamental frequency is much greater, and the engines can't be synchronised anyway, so these systems are not worth bothering with.