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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.
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The noisest part of all my computers i the hard drive, not the CPU fan.
- AZ
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.
When my CPU fan starts to make noise, I just whack my case until it stops.
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.
Maybe on the inside. On the outside, they're already quiet enough that I miss when they're coming up behind me.
Damned cars always trying to stalk and eat me.
You can never go home again... but I guess you can shop there.
Installing a Zalman HSF is exactly what I did. Highly recommended. Or (and), you can just buy a fan controller for the money (or both) to really quiet down your system.
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.
Thats really cool. Its like those amazing bose noise cancelling headphones.
I have wondered if it was possible to do this in my house. Where I live there is a lot of people who like to scream at each other alot, and it rather gets on the nerves. It would be cool if you could record your neighbourhood noises, and instantly replay them out of phase into your living room. Presto. The beautiful sounds of silence.
I have a question about active cancellation, as I've heard of it being used in other places. Does the cancellation of a noise of a given frequency have any potentially harmful effects that become less obvious through cancellation? For example, does a high-pitch tone that could cause hearing loss over time become more dangerous now that there are two high-pitch tones (albeit directly off-phase) now sounding, or is the cancellation that complete?
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.
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Once you silence my CPU, you'll hear my hard drive. After you silence my hard drive, contend with my video card cooler. Quiet my video card cooler, and hear all 4 of my case fans instead. Quiet those, and hear the active cooler on my northbridge. Shut that up, and I'll go mad with all the silence...
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Of course he is much smarter than I am, otherwise I wouldn't be posting on slashdot.
;)
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In most offices, they don't use noise generators (ie Gossip Support Group) to cancel out talking noises, instead they put in a lot of plants, cubicles, which act to absorb most of the noises.
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).
Rock that crushes, Paper & Scissors that don't matter.
I have honestly seen computers put in freezers. Keeps it cool and eliminates noise at the same time. Leaves less room for the ice cream though.
If my answers frighten you, stop asking scary questions.
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).
Most car noise these days is not from the engine running. Technology these days allows new cars to run incredibly quiet. Probably 99% of the noise you hear while traveling down the highway is road noise. Noise produced from your rubber tires against pavement. I saw a news flash a couple years ago about a new type of pavement that dramatically reduces that noise, but it's too expensive to be widely used.
All this does is allow PC makers to get away with making hotter and noisier systems. We should be pressuring the industry to be cooler and more efficient.
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.
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A Beowulf cluster of those, attached to Rush Limbaugh.
"Adaptively Cancelling Server Fan Noise" can be found here. They were able to lower the whine by 30dB and the broadband noise by 20dB.
Design quieter cooling technologies.
I mean it's not like it's not possible.
Case in point #1: NEC (in japan) has a water cooled computer now on sale to the teeming millions. water runs over the CPU and goes into a radiator to the back of the case. the radiator sits just outside of the power supply fan, which turns at an incredibly low speed (kinda like the apple G5 fans). Damn quiet.
Case in point #2: Mitsubishi, after not building any planes since WWII (zero fighter was by them, after all), entered the business-jet arena. The first thing they did was to design a new shape of turbine intake blades using computer simulation that cuts something like 10dB off the engine noise compared to traditioal strait blade intakes.
So, instead of brute forcing one's way around the noise problem, there are more elegant ways!
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Sommerfeldt set about to find a way to drown out the whinny noise from built-in fans that cool computers and other electronic devices.
Did he try a fan with less horsepower?
-Rob
Marriage doesn't have to suck!
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.
Sound is a wave, specifically a compression wave. It is fluctations of air pressure, which your ear interprets. You can see this in how speakers work. They vibrate back and forth to produce compression and expansion waves. Well, as with all wave dynamics, if you hit a wave with it's opposite, it cancels. Quite simple to think of why with sound. You have a high pressure peak and an equal low pressure peak that collide. The net effect is zero pressure (in relation to ambient atmospheric pressure).
Now if you screw it up and don't time it right, yes, you could increase the sound. However provided your system is indeed doing it's job and producing opposite waves in correct time alignment, it cancels out.
Try it yourself some time. Take two identicle speakers and feed them both the same sound (as in one mono sound to both channels, not a single stereo source). Reverse the polairty on one speaker (plug the black plug into the red and vice versa). If you have them setup normally and listen to the sound far away, it'll simply sound defocused, as though it has no apparent centre or source. This is a good way to focus your speakers, the more defocused an out of phase sound is, the more in focus an in phase sound is. However now take them, get them right next to each other, and point them at eachother. You'll hear almost nothing. PRetty much all you hear is the sound that radiates from the cabinets.
I use this trick when I'm burning in speakers. New speakers come from the factory with everything a little tight, as everything does new. Over the first month of playing they slightly change their sound as they get to their normal "burned in" point. It reach it quicker, you can just pump some white noise through your speakers. Well loud white noise is likely to piss off the neighbours, so I invert one speaker and have them face each other. Reduces it to a pretty minimal level and gives the speakers the desired workout.
No Slashdot post about computer noise is complete without a link to Silent PC Review.
Losers choose to abuse the use of "loose".
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.
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.
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.
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Actually it has been used in a variety of applications for some time. Back in the 70s a huge diesel generator had mikes place on it, then further out was surrounded by large speakers. The mikes picked up the motors full spectrum and the speakers played it back at the motor. There were two marked effect;
1. The generation room went from deafening to almost whisper quiet...
2. The motor efficiency jump markedly. It seems that one of the significant causes of mechanical inefficiency, is the increased friction due to vibration (both resonant and nonresonant) in the motor. By canceling out that vibration, the motor operated more smoothly, wore out more slowly, ran cooler, and used less fuel.
Of course, at the time, this only made economic sense with huge motors who's cost of maintenance, operation, and replacement justified spending megabucks in improving performance and endurance.
With the new technologies available to produce sound, or damp it in a given space... this technology could be used to improve efficiency and eliminate noise pollution from automotive engines, turbines, and a whole host of noisy machines including the fans in our computers.
I mean, if Bose can do it with your headphones, why shouldn't we do it with our environment...
Genda
- Why are there so few Zen performers? Because it's no fun making a curtain call to the sound of so many people clapping with one hand.
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
Heh, I hope I wasn't implying that conservation of energy was being violated. I just though that destruction of energy and cancellation of the signal were different in this case. I think I worded it wrong. No testicles need to be wagered :-)
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.
If you reverse the wires, it sounds like a V20.
I've constructed a simple device that cancels almost all noise from my fan. A common #2 pencil inserted into the fan blades does the trick quite nicely. I've used this system sucessfully on three different computers, and I can tell you that the noise reduction is dramatic. Oddly, all three of them stopped working within minutes due to unrelated problems.
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My acoustics book said that if you put a person with normal hearing into a sound isolated anechoic chamber, and give them awhile to adjust, they will actually hear the blood flowing in their ear.
Point being is that it would be completely pointless for them to be any more sensitive. Quite amazing really.
Why do I have this? I don't smoke.
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.
My acoustics book said that if you put a person with normal hearing into a sound isolated anechoic chamber, and give them awhile to adjust, they will actually hear the blood flowing in their ear.
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.
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