Nice work again, Martin.
When I was doing loudspeaker measurements as a hobby, I noted that there could be repeatable environmentally induced harmonics within the measurements. Sometimes these were related to the size of the speaker (size of the fan perhaps in this instance) and its relation to the mounting baffle (perhaps similar here, who knows). In this case, if we decide that we see repeated artifacts, then we should try to assess any patterns.
I see peaks at 100-200hz, and especially ~400hz (and possibly at 1200-1400hz as a 3rd harmonic of 400-500). The fans don't always excite these modes, but they seem to do so several times throughout their RPM range. Just for reference, 400hz corresponds to a wavelength of about 86cm.
This seems true for some fans more so than for others.
I'll have to watch all the videos more closely when I'm in the mood to take notes (or maybe you've already done that for us). But it's also worth noting that we'll all have to contend with our own noise artifacts within our setups.
Of interest is that you can make a powerful ultra low frequency subwoofer out of a (large) servo-controlled fan-like device. To control the movement of airflow is to control the sound produced.
Thanks for the new data
Edit: yes, you seem to be fully aware of everything I've said. Nvm... heh... I need to L2Read.
Bookmarks