I bought this replacement Sanyo Denki fan for my air purifier. The sound out of that fan is louder than the other two pre-installed fans. The original fans mfg is out of business, and replacement parts are not offered, so I wanted to fix the mechanism myself.
It does not make a smooth noise, as there is an oscillation to the sound that I think comes from the pulsing of rotors & stators in the fan motor. When I read that pdf spec, I see that the dB output is correlated with certain operating params.
I'm wondering if the fan would run more smoothly and quietly if the power regular was different. Or, if based on the oscillating sound, the issue will not principally change with better controls, and only get slightly less noisy. I am worried that down-speed'ing the fan will result in the same 'oscillation' noise. I assume this from the square waveform of I/O on pg3 & 4.
I've read this Q&A on fan noise, which leads me to believe that my question is a duplicate, or is a XY Question on the same.
I understand 'no noise' is not physically possible, and that making thee noise uniform is the first important step toward reducing thee perception of any dB level of noise.
((At this point, I assume the $150-200 for a new filter unit is less imposing than the effort to determine the above, cracking open the thing again (not a fast tear-down), taking some measures of the power supply output, and maybe calculating new electronics to re-balance the circuit))