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Thread: Are noisy appliances a fault of design or Nature?

  1. #1
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    Are noisy appliances a fault of design or Nature?

    Is the noisy nature of appliances (like computers, toaster ovens, microwave ovens) due to the fact that engineers don't go to any trouble to design how these machines sound? Or is there no practical (including inexpensive) way to make them quieter?

    Sound is hard to "block". The fact that it is detectable through massive objects always amazes me. I don't think it is reasonable to expect the case of a machine to block the sound of the machinery inside. However, could there be designs that don't hum and buzz?

    The fans and motors in equipment like a desktop computer aren't very powerful, but the equipment is operating at roughly constant frequency so resonances develop. If you have good hearing, you detect that most desktop computer cases hum. The really irritating ones develop a rattle or buzzing sound. Some toaster ovens buzz because their heating elements vibrate.

    In designing antennas it is important how the physical length of the antenna compares to the wavelength of the signal. In examining and modifying the cases of computers, altering the physical dimensions of the surfaces of the case don't seem to have much effect on keeping them from resonating. Why this disparity between the two situations?

    Perhaps it's an illusion of judgement. Perhaps to make a case that resonated really well, we would have to design them very precisely and they would hum a hundred times louder than the average case.

    Perhaps it's something to do with the wavelengths involved or with the fact that the problem is in 2 or 3 dimensions instead of 1-dimension.

    I have a table saw blade that is a "vari-tooth" design. The teeth aren't spaced evenly apart around the blade. This is supposed to make the blade operate more smoothly. I suppose the idea is to alter the way that the blade "rings". Would running a fan or motor at an irregular rate would make equipment cases resonate less?

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    I wouldn't say it's all due to resonance, but rather vibration. Moving parts will vibrate and displace air. The human ear can sense ridiculously small vibrations. Either you can spend a lot of money trying to damp these sounds, or accept a certain level of noise. To reduce existing noise, you can stiffen the structure to raise the frequency or add mass to vibrating parts in order to damp the noise. As you know, that costs miney that most people don't want to spend.

    Then you have companies like Ford that engineer their engine intakes to specifically make noise.

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    Quote Originally Posted by ShinAce View Post
    Either you can spend a lot of money trying to damp these sounds, or accept a certain level of noise.
    This is the problem. I have a huge issue with background noise of a computer, other people don't seem to mind it. The majority will decide that the expense of quietening computer fans is just not worth it. I used to have to contain my computer in a concrete box, though today the noise level of my desktop is almost acceptable.

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    Quote Originally Posted by Perikles View Post
    This is the problem. I have a huge issue with background noise of a computer, other people don't seem to mind it. The majority will decide that the expense of quietening computer fans is just not worth it. I used to have to contain my computer in a concrete box, though today the noise level of my desktop is almost acceptable.
    Why not just look into passive cooling if you're resorting to concrete? Get some big old heatsinks. They even have fanless power supplies. I just replace the fans with ones I like and clean them out twice a year.

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    Quote Originally Posted by ShinAce View Post
    I wouldn't say it's all due to resonance, but rather vibration. Moving parts will vibrate and displace air. The human ear can sense ridiculously small vibrations. Either you can spend a lot of money trying to damp these sounds, or accept a certain level of noise. To reduce existing noise, you can stiffen the structure to raise the frequency or add mass to vibrating parts in order to damp the noise. As you know, that costs miney that most people don't want to spend.

    Then you have companies like Ford that engineer their engine intakes to specifically make noise.
    Got it in one

    We can make things really quiet, by stiffening, sound insulation, using low speed fans and low air flow velocities, designing for natural convection, or using such techniques as liquid cooling and heat pipes.

    It's the money. Mostly, computers produce more-or-less white noise, which most people can filter out of their perceptions fairly easily. It can be reduced, but this costs money. Most people would rather get a larger hard drive than pay a similar amount for a quieter computer.

    Kitchen appliances are a different matter, in that most makers do pay attention to keeping them quiet, because low noise is seen as very important by most consumers. For evidence of this, just look at the advertising for dishwashers.
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    Now that we have discussed this topic, engineers will make appliences quiteter.
    There is some additional cost. The next generation won't be smaller as the sound insulation takes space: Won't be more efficent as quieting envolves some functionality compromises. Neil

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    I'm a big time audio enthusiast. The most important thing I learned about sound is not the source of the sound, but the environment the sound exists in. You can buy the best speakers in the world and the quietest appliances available, but if your room is 70% glass, it will sound like ***.

    In my bedroom, I have sound panels(basically fiberglass with a frame) on the wall. Much like you would do in a recording studio. It actually reduces noise from outside, reduces echos in the room(which can 'fatigue' the ears) and helps with fan noise.

    The problem is our sensitivity to it and all these radiating surfaces that the noises are linked to. Take a tuning fork, ring it, then set it down on a wooden table. Same sound, same energy, but now the table is amplifying it.

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    Quote Originally Posted by tashirosgt View Post
    The fans and motors in equipment like a desktop computer aren't very powerful, but the equipment is operating at roughly constant frequency so resonances develop. If you have good hearing, you detect that most desktop computer cases hum. The really irritating ones develop a rattle or buzzing sound. Some toaster ovens buzz because their heating elements vibrate.
    Mostly it just costs more to design a product that makes less noise. For computers you typically have 5 different sources of noise.
    1) The power supply, mostly the PS fan. There are lower noise power supplies available, but they cost more.
    2) The graphics card. High end graphics processors are truly massive chips, and they typically come pre-packaged with a fan that blows out the back of your case to keep them cool. They will vary from noticeable to very noisy, but the fan does slow down when you are not doing something graphics intensive. You have to either forgo high end graphics or do something very customized to get rid of this.
    3) Case fan. This gets rid of the warm air the CPU and other components generate from inside your case. You can get something fairly quite by going to a large low RPM fan.
    4) CPU fan. Modern CPU’s can draw 50+ Amps and pump out more heat than a 100W light bulb. It takes a big heat sink and fan to keep them cool. A larger heat sink equipped with a large low RPM fan will make less noise, and a water-cooling system will make almost none.
    5) The hard disk. These spin very fast internally and this causes vibration and noise. You can mitigate this somewhat by cases equipped with sound buffering and rubber grommets. It also helps to have sufficient memory so the HDD isn’t in use as much. Lower speed disks generally make less noise, and solid state drives make almost none.
    If you build your own PC rather than buying one you can get a low noise case/PS put in water cooling and a solid state drive and it will be pretty quite. If you want high end graphics capabilities for games etc, you probably won’t be able to get rid of video card noise.

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    You can get water cooling for the high-end graphics cards too.
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    Quote Originally Posted by tashirosgt View Post
    I have a table saw blade that is a "vari-tooth" design. The teeth aren't spaced evenly apart around the blade. This is supposed to make the blade operate more smoothly. I suppose the idea is to alter the way that the blade "rings". Would running a fan or motor at an irregular rate would make equipment cases resonate less?
    Sure, although it would be easier to use unevenly spaced blades. Most cars -- at least most cars from US manufacturers -- have unevenly-spaced blades on their engine cooling fans for just that reason. There has also been some work for higher performance fans (iirc, for HVAC air handlers) with unevenly spaced blades to move the harmonics to higher frequencies, where they're easier to blanket.
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    Quote Originally Posted by HenrikOlsen View Post
    You can get water cooling for the high-end graphics cards too.
    Yeah but that's typically a lot more customized than water-cooling for the CPU.

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    For computers you can use heat pipes and avoid fans but your computer looks like a flower pot with flowers. That's not so bad perhaps. For moving things like pumps noise reduction can be difficult beyond a certain point but slower flows are good. Turbulent flow is noisy and laminar flow is quiet. Gearboxes have improved hugely with modern manufacturing techniques, finishes and accuracy. The biggest problem remaining is neighbours!

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    Sometimes its best to have some noise. In the same way the best sensor a NASCAR driver has is his..seat, you can tell how something runs by any change in noise. Maybe toasters should have something similar to this:
    http://www.greencarreports.com/news/...ew-alert-sound

    Or a microwave--shades of Terry Gilliam

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    Quote Originally Posted by publiusr View Post
    In the same way the best sensor a NASCAR driver has is his..seat
    For a pilot on the other hand, the seat of the pants tends to lie to you. Ask JFK, Jr. Except you can't, because he apparently trusted the seat of his pants instead of his instruments and spiraled into the sea.

    We have a "library quiet" room air conditioner. At least that's how it's advertised. I'm not sure I'd want it in a library.

    I think the chevrons on the latest jet engine exhausts work by avoiding a single frequency of sound.
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    "If sound doesn't travel in a vacuum, why are vacuum cleaners so noisy?"


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    Not to mention one could use active noise cancellation technologies.
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    Quote Originally Posted by Ara Pacis View Post
    Not to mention one could use active noise cancellation technologies.
    Not really. Even if you isolate the problematic frequencies, cancellation depends on where the observer is standing, or sitting, or facing, or moving.
    Active noise cancellation should have the word 'personal' in front of it, since it really only works with headphones.

    I'm just happy that TVs don't have that annoying whine anymore. Dimmer switches, old TVs, and such. Basically old school switching electronics had the worst high pitched screech. I used to walk out of the living room when the TV started acting up. The days of ultrasonic torture are likely over.

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    Quote Originally Posted by ShinAce View Post
    I'm just happy that TVs don't have that annoying whine anymore. Dimmer switches, old TVs, and such. Basically old school switching electronics had the worst high pitched screech. I used to walk out of the living room when the TV started acting up. The days of ultrasonic torture are likely over.
    I'm not sure if the dimmer switches no longer have that whine or my ears no longer detect that whine.
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    "Come hear the whine, come taste the band . . . "

    I think that Liza had that wrong.

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    Or if you have a rig like mine, you have water cooled CPU unit that has a radiator with a fan on the case...LOL and it's not quiet. Once you start getting into the 6 to 16 cores on a chip CPU's you pretty much are going to have to live with the fan noise.

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    Bah. Just drop the whole PC in a vat of mineral oil. Done!

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