Bruce Thigpen, the inventor of the Thigpen Rotary Woofer, forwarded me this article.
I am posting here, for your edification: Machine Design Article on the Rotary Woofer
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August 30, 2007
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Hi
You seem to be suffering from unwanted high frequency fan noise which demands intervening damping manifolds.
I am at a loss to understand why you have no smoothing of the turbulent airpath around the tips of your rotary subwoofer “fan” blades.
It would seem so obvious that noise would be generated by having the blades drawing air through a relatively thin, square-edged hole in a flat board.
A cowl (shaped rather like flared reflex ports on both sides of the fan aperture board) might help.
Or even something shaped like an old-fashioned ship’s lifesaver ring around the fan aperture on both sides of the board would help to guide the air smoothly through the aperture with much lower turbulence.
There are very few axial fans which don’t use a cowl of some sort. Maximum turbulence is at the tip of any wing or fan blade.
Perhaps my suggestion is too simple and you have already tried it without obvious advantage?
Regards
Chris.B
Comment by Chrisbee — April 4, 2008 @ 1:46 am