[Peter Larsen]

Knack wrote:

However, I can definitely hear two distinctly different noises
coming out of this ceiling fan: a low rumbling sound and a higher
pitched sound. Presumably, the former is due to air turbulence
and the latter is from the electric motor.

Appears reasonable.

Unfortunately the higher pitch sound component is the more
objectionable of the two that I wish to attenuate.

Appears reasonable.

Surely, someone with a flush mounting 52" (132 cm) ceiling fan
of their own,

Not just A fan, same make model and possibly batch.

and a microphone, and an oscilloscope

No, a microphone and a computer with a sound application that can do
freuquency content analysis, just one example: a demo of audition will
do nicely.

A typical bedroom is not a huge space. And remember that the
design need only satisfy a maximum of 2 sleepers who's ears
will always be located at approximately the same places whenever
noise control is needed.

ANR's possibiblities are defined by the likelihood of a phase-match, ie.
by the wavelength. It seems probable that the high pitched noise is
caused by some sort of gears or bearings. My guess is that it is in the
kHz range, just a guess and I could be wrong, but I have seen high
pitched noise from powerdrills appear in the 10 kHz band of octave
analysis.

A major problem with implementing the idea is .... that there
will be no available electronic schematic diagram for any ANC
headphone with which to build the system around.

Attenuating high pitched noise at the source is relatively simple, but
there may be cooling necessities that prevent so doing without voiding
the fire safety of the fan.

Stop looking for a complex solution, look for a simple one.


Kind regards

Peter Larsen