[John Atkinson]

Arny Krueger wrote:
I would expect this woofer to generate more spurious noises
given as a percentage, when operating at low levels. IOW,
the largest source of spurious responses would be turbulence
generated by the fan blades, which is always spinning.

This is correct. As I wrote in my blog, the fan fires into a
foam-lined box about 5' on a side, which you can see in
my photograph. This then communicates with the room
in which the sound is being experienced via a 2'x2' hole
in the wall. The is arrangement does effectively filter the
fan turbulence noise, as no sound could be heard at all
with the blades feathered and no intermodulation or
other noise modulation effects could be heard with pure
tones.

The fan _was_ noisy in the room in which it was operating,
but that is irrelevant given that that is not the room in
which it producing useful sound.

I found it very impressive, but its requirements really
restrict its possible market to industrial set-ups,
like special LF effects at a theater or amusement park.

John Atkinson
Editor, Stereophile