Allen Dick asks if there is an upper limit to the accoustic spectrum.

Last week I interviewed a man who had spent his life doing sonar research.
Using piezo transducers he used frequencies up to 2Mhz for detecting fish!
I repeat 2 megahertz.

In some of his work he used scale models.  In a 6 foot long tank he used a
stickleback as a model for a cod!

My suggested definition for sound is, 'pressure waves that are detectable by
the human ear'.  One might add, 'or that of a sheepdog'.  Beyond this it
becomes ultrasonics

Rex Boys