Are you sure it's the speed controller that's causing the problem.
I wonder if you ran it at full speed without the blades and the
'whoosh' they cause you might still hear the buzz/hum.

Perhaps as an experiment power it off a resistor for a couple of
seconds.

On 7/16/2011 6:27 AM, klem kedidelhopper wrote:
We have a ceiling fan in our bedroom that we sometimes like to run at
very slow speed at night. The fan was purchased as new surplus many
years ago and never came with a speed control. So I have been using a
generic solid state speed controller. With this unit we are able to
take the unit down to complete "crawl" however there has always been a
slight rhythmic buzzing noise whose loudness and duty cycle are both
directly proportional to the motor speed. I know it's related to the
pulse type of control I'm using but short of just using a variac or a
rheostat for that matter, does anyone know of a method to achieve a
very slow speed without the noise?

Also this motor has no brushes and so even though its not labeled as
such I wonder if it could be a "Universal" type of motor that could
run on DC? It wouldn't take much to put a bridge and perhaps even a
filter in the electrical box ahead of the motor. I'm thinking that DC
operation could possibly be quieter. Thanks, Lenny