This is a 5 bladed fan so 5 times 1.8 rps is about 9 blades per second. I saw the sidebands on my measurements at just about 9 hz spacing.
Hmmm... Reflections per second and not reflecting surface velocity? Why spaced bands? Hmmm...
I cannot speak for the King of Audio's apparent disinterest in your observations.
Hopefully he's diligently searching for a scholarly paper that discusses the scenario.
30 spins in 35 seconds = 30/35*60 = 51.43 rpm x 5 blades = 257.1 blades per minute = 4.3 blades per second
I see 4.3Hz spacing on the bands around 1000, 1500, and 2000hz tones.
Ok, so it looks like it's related to reflections per second and not blade velocity, so it's not primarily a Doppler effect (unless the numbers magically align for that too, somehow).
Increasing the volume makes more bands come out of the noise floor. I exposed 7 or 8 or 9 bands at 90dB and 1500hz.
I would have been happier (even if wrong) if it had stopped at 5 bands for 5 blades.
I can't explain "number of bands".
I don't see any bands around 100Hz. My guess is the wavelength is too big to interact with the blades.
Too many bands to count around 10kHz.
Hmm...