Hi Ric, > What did you think of the sound? I never received a wav file. I haven't heard it. No matter, though. I trust that the 500 Hz component is audible. I no longer have the test equipment necessary to figure out anything more than that. <<Thanks Don, but damnet, can't I get two stand alone supersonic audio generators?>> <<On another tack, how do they make supersonic dog whistles? Is it that hard to get two that are 300 or 400 or 600 apart and blow them together and listen for audible resultants??? That would prove it once and for all, above all the mumbo~jumbo theoretical-if-ands-or-butts; or perhaps sirens as described in Helmholtz. ---ricrm>> Most audio generators are capable of ultrasonics. If you're interested in pursuing this, try two audio generators feeding into two power amplifiers, driving two piezo tweeters. Don't use two channels of a stereo amp, since voltage sag can cross channels, depending on the design. (That is, if both channels are pushing current in the same direction, the power demands on one channel can affect the power output on the other channel -- and thus we have a small degree of amplitude modulation.) The dog whistle approach would be fine too. I'm sure no two dog whistles have exactly the same frequency, even from the same production run. Go to your local pet store and start blowing dog whistles in pairs. (They'll love you! <grin>) See if any pair creates an audible resultant. This would only work, by the way, if the whistles are loud enough to tap into nonlinearities in sound propagation through air -- about 125 dB SPL. They would probably be that loud over a very short distance, but perhaps not over a long enough distance for nonlinearities to do their tricky stuff. Peace, Sarah
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