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Noisy Papst Fan

Discussion in 'Desktop & Laptop Computers Forum' started by feet14, Nov 20, 2002.

  1. feet14

    feet14
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    I recently swapped the bottom 92mm fan in my Enermax PSU with a Papst 3412NGL which has a claimed noise level of 23dB, only slightly more than the 19dB of the 80mm fan many people seem to be pleased with.

    As the fan runs faster, a clicking/buzzing sound emmited by the fan becomes increasingly noticeable. I've taken the PSU outside of the case resting on a mouse mat so it's not vibrations being amplified by metal surfaces.

    A possibility is that the fan is suffering from turbulence caused by reflected air. The fan blows onto a heatsink and electronic circuitry above it (clearance varies from a few mm to about 3cm) and the air is meant to exhaust out of one side. Another possibility is that I have received a faulty fan.

    Any ideas as to an explanation/possible solution?

    [Edited for typo]
     
  2. nutcase_1uk

    nutcase_1uk
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    A couple of thoughts:

    1) A faulty fan. Papst are among the best, if not the best, but noones perfect :)
    2) There is some debris of some kind rubbing against the blades/hub.

    Try teh fan on its own outsied the case, and if it still makes the noise you probably have a duff fan. If not then it's either the way it has been fitted, or something in the air path vibrating or similar.
     
  3. Garrett

    Garrett
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    Just a passing observation but does not the sound level double per each db i.e. 20db is twice as loud as 19db.
    So rather than being about a quarter louder as the old fan it will be quite a lot louder.
     
  4. Dubbing Mixer

    Dubbing Mixer
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    Not quite. Perceived loudness doubles every three dB (power) or every 6dB (voltage). Remember, dB are only a ratio measurement of relative quantities. LEQ is a better measurement of loudness.
     
  5. Dubbing Mixer

    Dubbing Mixer
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    PS an increase of 3dB (power) requires double the watts......
     
  6. Dubbing Mixer

    Dubbing Mixer
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    Sorry folks! last two posts probably not 100% accurate (alcohol) I'll look it up in the morning and get it right.
     
  7. nutcase_1uk

    nutcase_1uk
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    lol dubbing mixer :) I was going to mention the sound pressure increase, but noticed the clicking/buzzing bit and thought that the fan really ougth not to be doing that - making it def an overcomable problem :)
     
  8. feet14

    feet14
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    I've checked and there's nothing obstructing the blades and also I have a 60mm Papst on my heatsink which is rated at 27dB but doesn't make this noise. As suggested, I'm going to remove the fan and run it in free space. If it's ok there then it's probably turbulence and I will need to buy an 80mm fan to fit on the rear as there is nothing bar the fan grille to block the airflow out of the fan.
     
  9. Dubbing Mixer

    Dubbing Mixer
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    Hi Nutcase,

    Actually I wasn't so far out. To double perceived loudness you need a really big increase in power. E.g. to double the (undistorted) loudness of a 10 watt amp requires approximately a 100 watt amp, assuming the rest of the system remains the same. To double the loudness of a 100 watt amp would need a 1000 watt amp and so on. This of course makes a mockery of one upmanship based simply on specs such as, 'my amp is 120 watts, yours is only 100'. The real world is, as usual, more complex, because of the instantaneous current requirements of fast transients. In other words a 100 watt amp may well be capable of delivering 1000 watts for a very short period without distortion. I have an old Sansui amp which is only rated at 25 watts per which sounds subjectively louder than a 100 watt amp with inferior power supplies. (less storage capacitance)

    Back to the fan problem. I reckon you may be right. Turbulence could be the answer. However, I wouldn't discount the possibility that the fan is a 'rogue' duff one. I'm using a number of the Papst 80mm 19 dB fans which really are quiet. (They don't move a lot of air but enough for the application.)
     
  10. Dubbing Mixer

    Dubbing Mixer
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    By the by, a 1dB variation in level is generally regarded as the smallest change perceivable by humans on average programme material. On single sine wave tones 0.5dB is probably more realistic.
     
  11. nutcase_1uk

    nutcase_1uk
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    Heh heh, I certainyl wasn't disagreeing with your theory, dubbing, more a case of "darned if I know" - been a few years since I looked at anything to do with acoustics etc. It 'sounded' right :p :D

    Mines more a practical side of things. I think I've specced about 40 differing fans in the last year or so. Mostly it was for maximum airflow but a few applications needed to keep noise to a minimum, but still having the max possible airflow. Whilst I didn't use exclusively papst, they were by far the most common as they're so good! All good fun :)
     
  12. Dubbing Mixer

    Dubbing Mixer
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    I have tried a Panasonic fan or two. They do a half thickness 80mm one which is about as quiet as the Papst '19dB' model. Depending on application it can be subjectively quieter.(model FBA08T12L for interests sake) Truth is, the subjective noise level is probably just as dependent on the enclosure, the way it is pointing and the room. But every little helps!
     
  13. feet14

    feet14
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    I've now taken the Papst out of the PSU and running it off a motherboard header. Held in the air the clicking sound dissappears, just a whoosing sound (this is at full speed). As soon as I plonk the fan directly above where it would normally be inside the PSU, I hear the clicking sound.

    Thus, it appears the PSU case is resonating. To counter this, instead of plonking the fan on top of the PSU, I've used squash balls cut in half to isolate the fan from the casing. I tried Blue-Tak but it didn't isolate it much.

    This solution is slightly impractical - would I be able to use a Zalman fan bracket to place the fan underneath the cpu in the case? (the fan would be at right angles to how a cpu fan would be on the bracket)
     

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