Randy,
Does this explain why some members of the list write that it is
theoretically impossible to record very low frequency sounds with a
parabolic reflector whereas others say that they manage to do it?
Jeremy
At 10:33 21/02/04 -0500, you wrote:
>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
>-----
>Randolph S. Little <>
>111 Berkeley Circle, Basking Ridge, NJ 07920-2009
>Phone: (908)221-9173 Fax: (908)630-0871
>
>[Non-text portions of this message have been removed]
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
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