NatureRecordists,
Sorry for being slow to respond to Rich Peet's invitation to join this thread,
but I have been rather pre-occupied with publication of my new book on the
history of the Cornell Laboratory of Ornithology, For The Birds, (URL:
http://RSL.HOME.ATT.NET) and am about to head to Florida for a week.
Rich refers to my "Acoustic Properties of Parabolic Reflectors" thesis at
Cornell's School of Electrical Engineering. Unfortunately, it is even harder
to get than Sten's paper (Sten cites it), so perhaps I could be coerced into
transcribing it and posting it on my website some day. In the meantime let me
offer one all-important point about all of these theoretical analyses, at least
all that I know of to date. And this I have discussed with Sten who also
agrees.
Key point:
Whereas the mathematical analyses attempt to predict the acoustic pressure
at the focal POINT, the actual microphones that we use to transduce this
acoustic pressure into an electrical signal are sensing the mean acoustic
pressure over some finite area approximating that of the diaphragm.
Thus, the net acoustic pressure over a certain focal area (I have previously
called this "focal volume") is what counts, and this does NOT increase
monotonically with frequency. In fact, it levels off for wavelengths shorter
than the diameter of the microphone.
So, if there are any hot-shot mathematicians among you who would deign to
include finite microphone size in the theoretical analysis, Sten and I would
both welcome your contribution.
Good recording,
Randy
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Randolph S. Little <>
111 Berkeley Circle, Basking Ridge, NJ 07920-2009
Phone: (908)221-9173 Fax: (908)630-0871
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