looking for ultrasonic source

[Joe Pompei <pompei@xxxxxxxxxxxxxxxxxxx>]

        As some of you know, I am wanting to take high frequency HRTF
measurements, and have settled on the Knowles microphone, which is pretty flat
up to 80-100kHz.
        Now I'm looking for a good ultrasonic source, something that can create
frequencies in the 30-100kHz range (or as close as I can get).  B&K mics go the
distance, but aren't very powerful.  Radio Shack (yes, rs) has a tweeter that
goes to 40kHz.

        Does anyone know of any others that might go higher?  Narrowband is ok,
too...

Thanks,

Joe Pompei
Northwestern University

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