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Combatting Oscillation with randomness for cooling fans and harddisks.

Discussion in 'Nvidia' started by Skybuck Flying, Jul 19, 2013.

  1. Hello,

    I just cleaned my PC today and I just noticed the fans started humming in
    sync. They were all running at the same speed. Perhaps the humming is cause
    by some dust which is on the fan blades, I am not sure, ultimately this
    build up probably leads to them oscillating in sync. Like soldiers walking
    across a bridge and causing the bridge to collapse (resonance).

    But I did manage to get rid of the humming by using the following trick:

    Since I have the antec 1200 case I can adjust the speed of each intake fan
    individually with each fan's speed knub. So I put the fans at slightly
    different speed and low and behold it got rid of the humming ! Perhaps some
    of the humming is also amplified by cables pressing against the case doors.
    Some cables are now loose since the sticky tape let go.

    Right now 100% of the humming is gone ! Quite marvelous.

    So this has given me an idea which could be applied in practice, it might be
    a bit risky since it takes away control/precision from the user but it's
    worth considering if not done already:

    Harddisks produced by for example hitachi/ibm could spin around a slightly
    random rounds per minute.

    So instead of having an entire rack full of harddisks spinning at exactly
    5000 RPM some might be spinning at 4999 or 4998 or 5001 ot 5010, I am not
    sure what the speeds need to be to prevent osillation but probably very
    little variation is already enough to stop the oscillation.

    This might protect harddisk from resonance... tiny little oscilliations from
    harddisk racks could make the head from the disk hit the platter. How real
    this danger is I dont know...

    Perhaps bumps against the table or pickup of case is main cause of bad

    At least the randomness could be introduced to cooling fans.

    The randomness could be static/fixed... so each fan runs at slightly
    different speeds...

    Or even better it could be dynamic... if it's dynamic then buyers don't have
    to be afraid that they accidently bought fans or harddisk running at exact
    same randomness.

    So dynamic randomness seems to be the better idea.

    This entire idea is quite interesting... it's one of the first ideas I have
    seen so far where "exact" is bad, and "slightly off" is good ;)

    Skybuck Flying, Jul 19, 2013
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  2. Hard disks must always be in a solid and dampening enclosure. The cheap
    ones that vibrate will cause rapid failure regardless of the speed of
    other drives.

    Some new variable speed fans have slightly uneven blade spacing that's
    supposed to reduce resonation.

    There's also the perfect synchronization fix:
    NTSC television had the vertical sweep phase locked to AC power so that
    magnetic fields from power wires would not cause throbbing effects in
    the CRT. If you had a CRT TV during the DTV transition, you probably
    saw the wiggle and throbbing on some stations that got rid of the phase
    Kevin McMurtrie, Jul 21, 2013
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  3. Skybuck Flying

    bruce56 Guest

    Fans on large hydraulic machines have had blades with unequal angles for
    decades. I am astonished that this has only recently appeared in
    computer fans. It is more of a psychological effect - the noise
    is less annoying although the sound power is the same.
    bruce56, Aug 26, 2013
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