On Apr 11, 11:29*pm, David Nebenzahl wrote:
On 4/11/2011 2:42 PM Evan spake thus:

On Apr 11, 1:32 pm, harry wrote:

Not he's got it right except for the fact that allr otating
electric lmachinary is AC.

I love how you can state that without any sort of qualification...

... especially when it's pure BS. But that's our Harry.

You seem to have forgotten about higher end bathroom fans
which use an inverter to operate a DC motor which is much
quieter than an AC motor...

Welll, since this is a.h.r, and since you're picking a nit, let me pick
yours. I've installed several "higher-end" vent fans (Panasonic), all of
which use AC induction motors which are very quiet. Which bath fans use
the setup you described? (Besides which, why in the world would you need
an "inverter" to run a DC motor from an AC supply? Perhaps you meant
"rectifier"?)

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Most fans are noisy due to bad fan blade design causing turbulence and/
or dynamic imbalance.
Noisy motors are defective, or if inverter run, it's a nasty cheap
inverter which does not produce a true sine wave.
Some other form of fan speed controls spoil the sine wave form too.
Resitance controls lead to slippage in induction motors which causes
noise especially in low speed settings.