Several things come to mind after looking at this device:
1. Has the fan blade shape and number been optimized for minimum noise?
That would make installation simpler. Take a look at the previous
generation of nuclear sub propeller blades (the current generation is
classified).
http://americanhistory.si.edu/subs/a...s/taming6.html
2. The motor appears to me to be an AC induction motor of ~1/2 HP. I'd
guess it takes ~1/8HP to spin that fan at 800RPM. Would a smaller
motor, maybe brushless DC or hysteresis, be quieter?
3. There were attempts in the past to use LF sound as a weapon. Pick a
frequency that nauseates a soldier/target. One could increase the
diameter and RPM of the fan and replace the voice coil blade pitch
control with a mechanical coupling of fixed frequency and put the
result in the throat of a big horn. Gutblaster!
Tim
John Atkinson wrote:
Arny Krueger wrote:
If the pictures I've seen are any indication, the motor might
develop 1/2 hp if it spun at 1725 rpm, which it doesn't. I
seem to recall that its actual speed is 800 rpm, so it might
be rated at 1/4 hp.
I meant to include this in my previous response. You're
probably correct, Mr. Krueger. As long as the fan motor
has enough motive force/torque to keep spinning at a
constant rpm when the blades change their angle of
attack, that is sufficient.
As I understand it, the subwoofer's dynamic range is
ultimately limited by the fan blades stalling at
extreme angles.
John Atkinson
Editor, Stereophile