On Thu, 30 Dec 2004 17:20:23 -0600, Don Foreman wrote:
On Thu, 30 Dec 2004 16:02:14 -0600, "Rex B"
wrote:


I scrounged a DirecTV satellite dish and was builiding a whistle

So what would that have been like? Use the parabolic reflector to focus the
incoming sound, or the outgoing?

It would focus the ultrasound from a whistle into a focussed beam,
resulting in much higher sound pressure level at a distant point.
The wavelength of 22 KHz sound is about 0.6 inches while Ku band
satellite signals have a wavelength of about 1 inch -- so this dish
would be highly directional with ultrasound. The beamwidth would
(theoretically) be about one degree, making a "spot" of about 21"
dia at 100 feet.

It might be a little tricky finding the focal point of a dish, though.
A simple horn would probably work just fine and it'd be easy to make.

Right, that's why I suggested starting with a parabolic microphone.
You already would have the mounting hardware pointing the element to
the right spot, just replace the mic with your driver.