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Cancelling Out CPU Fan Noise

Posted by timothy on from the need-one-for-car-alarms dept.

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."

72 of 507 comments (clear)

  1. I should have patented it... by zeux · · Score: 3, Interesting

    I though about it a long time ago because I know we are using the same kind of technology in the airports.

    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.

    --
    Iraq: war to save the U
    1. Re:I should have patented it... by Anonymous Coward · · Score: 5, Informative

      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.

    2. Re:I should have patented it... by Martin+Blank · · Score: 4, Interesting

      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.
    3. Re:I should have patented it... by zeux · · Score: 5, Funny

      Of course he is much smarter than I am, otherwise I wouldn't be posting on slashdot.

      And I'm French, remember ;)

      --
      Iraq: war to save the U
    4. Re:I should have patented it... by fireweaver · · Score: 5, Informative

      Not to worry, the cancellation -can be- that complete. In practice, there will be some residual noise, but it will be very quiet.

    5. Re:I should have patented it... by Reverberant · · Score: 4, Informative
      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 canceled by itself.

      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).

    6. Re:I should have patented it... by bcrowell · · Score: 5, Informative

      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.
    7. Re:I should have patented it... by Cosmic_Hippo · · Score: 5, Interesting

      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.

    8. Re:I should have patented it... by bcrowell · · Score: 5, Interesting
      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.

      --
      Find free books.
    9. Re:I should have patented it... by Cosmic_Hippo · · Score: 4, Interesting

      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.

    10. Re:I should have patented it... by sjames · · Score: 3, Informative

      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.

      Your bloodline is safe :-) I'm guessing the energy is dissipated as heat in the speakers and voicecoils themselves. The cone will travel further than normal since it will be 'flowing with' the incoming pressure waves rather than working against the air as normal.

      As you say, there's only a small amount of power in the small zone where the sound is deadened, so not all that much extra heat in the speakers.

    11. Re:I should have patented it... by FallLine · · Score: 3, Interesting

      Well I'm no PhD in physics, but I (did stay at the holiday inn express last night^H^H^H^H^H^H^H^H^H) do own a QuietComfort2 headphone set. I would agree that there is no discernible noise coming from outside the earphones. I suspect the explanation though is relatively very simple (or perhaps I'm just naive). The earphone cup is already quite muffled. The noise cancelling circuity only needs to "cancel out" a tiny amount of noise, that which would reach your ear by leaking through the insulation. Whatever noise is created by the cancellation speaker is quiet relative to outside background noise and will be further muffled by the headset before someone sitting next to you can hear it. In other words, whatever background noise you'd hear without the headphones is almost certainly (in real world applications) going to be orders of magnitude louder to a neighbooring passenger than the noise coming through your earphones.

    12. Re:I should have patented it... by xtal · · Score: 3, Interesting

      You'd get the Nobel Prize if you found a violation of conservation of energy.

      Not mine, but.. compelling.

      Casimir Effect

      --
      ..don't panic
    13. Re:I should have patented it... by tiger99 · · Score: 3, Interesting
      No, the cancellation can only be partial and in certain positions. The problem is simply a matter of time delay, the speed of sound is not very high so for practical dimensions there is substantial phase shift. By using a lot of speakers and very complicated processing, you can make it better, but it is still in the form of an interference pattern, and will always show peaks in certain places. You would need to make the summation of the speakers look like the original source, but in antiphase, to everyone around, to get cancellation. The wavelength of sound at 1KHz is about a foot, if you use one speaker you need to get the difference in disatnce between everyone and the speaker very much less than 1 foot so they all see cancellation. The idea is to put the maxima where they do least harm. These systems only work on regular frequencies, you can't predict random noise, and so can't cancel it unless maybe the speakers are all very much nearer people than the original source so there is time to do the computation.

      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.

  2. Wow by michaelhood · · Score: 3, Interesting

    Active Noise Cancellation stuff is a really cool technology. I wonder if this could be applied to cars and other "larger louder" things in the future.

    1. Re:Wow by crackshoe · · Score: 5, Informative

      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.
    2. Re:Wow by Martin+Blank · · Score: 4, Funny

      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.
    3. Re:Wow by SEWilco · · Score: 3, Funny

      Excuse me, what did you say?

    4. Re:Wow by krosk · · Score: 5, Interesting

      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.

    5. Re:Wow by Cornelius+the+Great · · Score: 3, Interesting

      "Active Noise Cancellation stuff is a really cool technology. I wonder if this could be applied to cars and other "larger louder" things in the future."

      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.

      --
      Sigs are for losers
    6. Re:Wow by Genda · · Score: 4, Insightful

      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.

    7. Re:Wow by RabidOverYou · · Score: 5, Funny

      If you reverse the wires, it sounds like a V20.

  3. Negating Sound? Its like new cars.... by RobertTaylor · · Score: 5, Informative

    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!!

    1. Re:Negating Sound? Its like new cars.... by electrichamster · · Score: 5, Funny

      "I have heard of something like that for cars ages ago, basically replays the engine sound over the car sound to negate it."

      Alternatively instead of wasting all that money on a sound cancelling system you could just install hugeass speakers, sub and an enormous exhaust pipe, that way no-one will be able to even *hear* the engine noise over all that deafening dance music you'll be playing.
      If you feel like it add undercar neons and go-faster stripes for extra style - they're guaranteed to bring the hot chicks from miles around.

  4. now for the hard drives by xobes · · Score: 4, Insightful

    The noisest part of all my computers i the hard drive, not the CPU fan.

    --
    - AZ
    1. Re:now for the hard drives by Martin+Blank · · Score: 4, Informative

      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.
    2. Re:now for the hard drives by darkwiz · · Score: 4, Informative

      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.

  5. Same tech as noise reducing headphones by CormacJ · · Score: 4, Informative

    I think this is how noise cancelling headphone do it - they just feed the external noise back into the earpieces after inverting it.

  6. This would be a lot more useful... by Trolling4Dollars · · Score: 3, Funny

    ...if it were applied to noise reduction of one's ass after a good bean based dinner. ;p

    --
    Un-news
  7. Huh. by dupper · · Score: 5, Funny

    When my CPU fan starts to make noise, I just whack my case until it stops.

  8. Re:Noise and Heat by thebes · · Score: 3, Insightful

    The amount of heat that a small microphone and speaker generate would be small enough that it would likely be transmitted through whatever the mounting system was made of, into the heatsink itself, and thereby take care of itselt. The heat increase would be negligible.

  9. Re:No need to worry. by hampton · · Score: 5, Interesting

    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.

  10. Keep everything quiet by nmoog · · Score: 4, Funny

    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.

    1. Re:Keep everything quiet by electrichamster · · Score: 5, Funny

      I wonder what would happen if you placed some huge speakers in a room connected to mic's and some noise cancelling gubbins....would everything just fall silent no matter how loud you shouted?

      Could be a useful mute tool for the girlfriend when she goes on too long:

      GOD, you're so inconsiderate, you never take my feelings into acco
      *click*..........

    2. Re:Keep everything quiet by afidel · · Score: 4, Informative

      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.
  11. Alternatives to Noice Cancellation by breakinbearx · · Score: 4, Informative

    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
  12. It never ends though by irokitt · · Score: 5, Funny

    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...

    --
    If my answers frighten you, stop asking scary questions.
    1. Re:It never ends though by dlevitan · · Score: 3, Funny

      No, that's not how it ends. I actually did this. I bought a very quiet hard drive (Seagate Barracuda IV), and a quiet power supply (Antec Trupower 330). But then the video card fan made too much noise, so I bought a replacement. But then the power supply was two loud, so out went the standard "loud" fan and in went a super-quiet pc power & cooling fan. Then the CPU fan and the case fans became too loud, so I replaced them all with the same fans as the power supply. But then the PS fan was still too loud, so I put in rubber spacers and undervolted the thing. But then the case fans were too loud and I undervolted them. But then the PS fan was too loud, and I undervolted it. Except that then my PS started overheating from the heat rising from my CPU. So I built a duct from the CPU directly to the outside of the case (which works fairly well). It's still too loud, and I don't really know what else to do except possibly undervolting the fan on my cpu. But if I start with that again, I'll probably never stop.

    2. Re:It never ends though by shadowbearer · · Score: 3, Interesting

      Damn funny post, irokitt.

      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

      --
      It's old. The more humans I meet, the more I like my cats. At least they are honest.
  13. I could use this by crass751 · · Score: 3, Interesting

    My laptop is so loud that if the fan(s) isn't/aren't running my roommate asks me if I turned it off. This thing generally has two fans running at times, and when it's really working hard, a third kicks in. My four year old desktop machine is much quieter than this thing.

    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.

  14. Absorbing technique instead by fembots · · Score: 5, Interesting

    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.
    1. Re:Absorbing technique instead by reidbold · · Score: 4, Funny

      Yeah man, damn plants and cubicles never shut the hell up.

      --
      -Reid
  15. Comment removed by account_deleted · · Score: 3, Funny

    Comment removed based on user account deletion

  16. Re:Why go through all this trouble? by irokitt · · Score: 4, Funny

    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.
  17. Your solutions are crap by Chuck+Chunder · · Score: 3, Insightful

    Quiet fans tend to get noiser with age.

    A box is not going to be good for heat dissipation or size constraints.

    Water cooling is certainly not going to be cheaper or less complex.

    If an active sound nullifier that will automatically adapt to the changing noisyness of a fan as it ages can be made for as little as $20 it is surely a more credible solution than your suggestions...

    --
    Boffoonery - downloadable Comedy Benefit for Bletchley Park
  18. Prior art? 'rev' by janbjurstrom · · Score: 3, Funny

    $ echo 'I CANT HEAR YOU' | rev
    UOY RAEH TNAC I

    Ah, the silence :)

    --
    668.5
  19. Wrong direction by Anonymous Coward · · Score: 5, Insightful

    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.

  20. Wow, imagine... by serutan · · Score: 4, Funny

    A Beowulf cluster of those, attached to Rush Limbaugh.

  21. Analog Devices app note for this four years ago by dlleigh · · Score: 4, Informative
    Analog Devices published an app note for this exact application four years ago.

    "Adaptively Cancelling Server Fan Noise" can be found here. They were able to lower the whine by 30dB and the broadband noise by 20dB.

  22. Power Supply by jmichaelg · · Score: 3, Insightful

    I installed an 80 mm Panaflow on top of a $30 all-copper heatsink to cut the noise from my computer but it didn't do much. As soon as the cpu fan noise was gone, the power supply noise was that much more noticeable. I ended up installing a new power supply. It was the best $80 I ever spent. The combination of a quiet cpu fan and quiet power supply result in a reasonably quiet computer. Not dead silent but at least it's no longer objectionable.

  23. diy? by frankmu · · Score: 3, Interesting

    can you take apart the cheap "noise cancelling" headsets and do it yourself? i would imagine all the parts and circuitry are there. lets see if my wife will miss her airplane headset....

    --
    Supreme executive power derives from a mandate from the masses, not from some farcical aquatic ceremony.
  24. I must be retarded by macemoneta · · Score: 3, Funny

    I probably should have built a noise canceling tower or some similar nonsense, so I could get published.

    Instead of all the research and electronics, I put a drop of oil on the axle and removed the dust from the blades with a q-tip. It's been silent ever since.

    Silly me.

    --

    Can You Say Linux? I Knew That You Could.

  25. Or, instead by lingqi · · Score: 4, Insightful

    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!

    --

    My life in the land of the rising sun.

  26. Whinny noise? by 6Yankee · · Score: 4, Funny

    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?

  27. I've got more sounds... by lpangelrob2 · · Score: 5, Funny
    it only nixes the whine, not the whoosh
    That's good and all, but what about my "braaagh"? I've also got a "whizzz!" and a "fhwhhhh" that still need to be dealt with...
    --
    -Rob
    Marriage doesn't have to suck!
  28. Re:Like the noise cancelling headphones? by Reverberant · · Score: 4, Interesting
    I thought the noise cancelling headphones worked because they were right against your ears.

    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.

  29. Nope by Sycraft-fu · · Score: 4, Insightful

    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.

    1. Re:Nope by Ralph+Wiggam · · Score: 3, Interesting

      Seperating audiophiles and thier money is like shooting fish in a barrel. I think there is a lot of placebo effect in high end audio. You just paid 800 bucks for a few meters of cable. It was a multi-thousand dollar system before the new cables. Do you think it could sound bad now?

      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

  30. woosh would be hard to cancel by nomel · · Score: 3, Insightful

    cause it varies depending on listenning angle, where the whine is pretty constant.

    probably why he's having trouble.

  31. Silent PC Review by PoisonousPhat · · Score: 5, Informative

    No Slashdot post about computer noise is complete without a link to Silent PC Review.

    --
    Losers choose to abuse the use of "loose".
  32. SPCR by Anonymous Coward · · Score: 4, Informative

    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."

  33. the best way to cancel pc noise... by mgoodman · · Score: 5, Informative

    ...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
  34. Re:Me too! by gosh_d · · Score: 3, Interesting

    You're forgetting that sound, being simply a pressure wave, travels a _lot_ slower than an electrical signal (6 orders of magnitude). If the mic is placed closer to the fan than the speakers, the speakers can have plenty of time to invert the signal and replay it. The distance is precisely chosen such that the speakers produce their noise simultaneously with the passing noise of the fan, even though it originated farther away. Delay's not a problem--no predicting needed.

    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.

  35. Not a new concept ... by scdeimos · · Score: 3, Interesting

    ... just a new application.

    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. ;)

  36. Re:hard drive whine by BCW2 · · Score: 3, Informative

    Try Maxtor's fluid bearing drives. In an old AT box the only way I knew the drive was being acessed was the case fan slowing down. I now have 2 in my current box, along with Panaflo Low case fans (80mm and 92mm) and AMD's own heatsink and fan on a 2000+. Very quiet for the performance. Also check out the Volcano 10 heatsink and fan, thats quieter than AMD.

    --
    Professional Politicians are not the solution, they ARE the problem.
  37. why bother ... by cwg_at_opc · · Score: 3, Informative
    when zalman have a fanless case: THG sez you can still hear(barely) the HDD and optical, but if you're a noise weenie, do like the govt and replace everything with solid state(HDD and use CF for transportable media)
    The case is stupid expensive at $1400US and the adventurous could probably build one for less by cannibalizing heat pipes from VGA coolers and stripping heatsinks from dead hifi amps, but there are ways of reducing PC noise without killing yourself or your bank account:

    case - antec sonata or slk3700bqe

    PSU - antec's yet-to-be-released phantom 350W PSU, or check this list:

    using vibration absorbing grommets for everything that vibrates(HDD, Optical, fans, etc.)

    quieter fans:


    OR, get longer cables and put the machine in an airconditioned closet; with a long USB2 cable and a powered hub, you might never hear your machine again. it'd just be you, your KB, monitor and a 7-in-1 media reader.
    --
    "...that's as white as it gets; all the bits are on..."
  38. I have a better and cheaper solution... by Scratch-O-Matic · · Score: 4, Funny

    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.

    --


    Evil is the money of root.
  39. Ears are sensitive indeed! by chadjg · · Score: 4, Interesting

    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.
    1. Re:Ears are sensitive indeed! by ziggy_zero · · Score: 4, Informative

      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.
    2. Re:Ears are sensitive indeed! by TwistedGreen · · Score: 3, Funny

      The logical next step, then, is to evolve quieter blood!

  40. Noise Cancellation in Powermac G5 by amsr · · Score: 5, Informative

    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.

  41. A Cheaper Way by Kombat · · Score: 4, Interesting

    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.

    --
    Like woodworking? Build your own picture frames.