Which fans growl & don't growl with a PWM is almost a black art:
o It will vary between speed specs, between makes & sizes
o It will vary between bearing types
o It will vary with PWM frequency used
Most of all, mix fans on the PWM rail, and some will growl and
some will not - finding a balance when all don't can be impossible.
You can't extrapolate from 1 fan to another even next to it in
the range with regard to noise on VoltageReg or PWM control.
There are too many discontinuities - very frustratingly :-)
So if a PWM is bought...
1) test it with your fans, don't assume it will or will not be silent
2) try to get one with variable frequency if you can't do "1)"
PWM is chopping voltage up into bits, and relying on the very
mechanical aspects of the fan to keep turning AND the very
individual IC motor drive circuitry to not add other noise when
it essentially has a non-DC power applied to it (not designed).
Amusingly (or not) it's quite common to find a companies own
PWM solution utterly unusable with fans it cites as usable. For
example the PAPST PCM001 is *unusable* with 6212NM fans,
as it gets to ~60% running it growls louder than full-rpm noise.
So you can't assume anything about an entire fan range, or a fan.
Have fun :-)
--
Dorothy Bradbury
http://homepage.ntlworld.com/dorothy...ry/panaflo.htm (Direct)