Our wood stove had a fan which made a loud whoosh. I built a speed control using a triac. By reducing speed a bit it made the room noticeably quieter.
Fortunately the fan had the type of motor whose speed could be reduced by shortening the duty cycle as a triac does. Not all motors are compatible with a triac.
They are DC fans on a bench power supply, noise it seems linear with Vapplied.
And more airlfow - more heat, so I do not want to sacrifice performance if at all
possible. My noise is a fairly high pitch whine. I think the fan noise is being amped
by the sheet metal it is attached to, so thinking I will take a speaker and just set it
magnet side on sheet metal, detect freq and invert phase back to sheet metal.
Its a crap shoot but I am going to try it, make some FFT measurements to see how
complex the harmonic content is/isn't of the noise. I will use a part that can easily gen up
4 harmonics, sines, using wavetables driven by 4 DDS, all onchip, and sum them, see what
happens. Maybe use an algorithm to effect some minimalist kind of AI to autonomously
find correct amplitudes and freqs to get min noise.
Adding this to the other 5,000 projects I am working on.....
Regards, Dana.