Disconnecting each in turn and they run perfectly normally with no change of sound. I may dig out a strobe if i can remember where it is and see if the blade speed does vary in the double active case.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Beat oscillation. Basically, the normal fan physical noise pitch of the two fans are _almost_ the same. What you're hearing is the difference between the two. (it may be less than 1Hz, because the fans will probably be quite closely matched in noise and speed).
It doesn't cause any harm other than you getting fed up with the noise and smashing it to bits.
To "fix" the problem, you could try to physically isolate the two fans from each other (or the common chassis) by using some sponge or rubber or some such, to help prevent fan vibration getting into the chassis or other fan (if you have them physically stuck together).
-- Linux Registered User # 302622
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I should have said these are 3inch, 12V dc fans rather than shaded pole motors so unlikely to match speed that closely. Both are mounted rigidly, no grommets, to steel chassis and separated by 1.2 inch , the nearest parts of the heatsink fins are only 3/8 inch from the fan surrounds. Placing a piece of card between the 2 fans seems to stop the interference but not desirable in the case of failure of one fan perhaps.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
"AJ" wrote in news:hPydnaYmtMZwlGXbnZ2dnUVZ snipped-for-privacy@comcast.com:
sounds like a case of the heterodyning fans!
-- Jim Yanik jyanik at kua.net
Cor a googlewhack , can I claim the prize.
Both fans are 1/2 inch apart, 3/8 inch from the nearest part of the heatsink but heatsink channels an inch deep. Trying a piece of card divider in that 3/8 ins made no difference but the airflows could still mix in those channels.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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