--- Walter Knapp <> wrote:
> If one can tolerate a extremely messed up polar pattern and
> directionality is all one wants, then maybe a flat plate could be
> useful. Though a shotgun might be a better way for just
> directionality.
I thought you liked the SASS design, is that not a flat reflector?
> However, I strongly doubt the gain. And really wonder just what
> parabolic he was testing. As we have seen it's very important to know
> the particulars of the parabolic people are talking about. There is a
> wide range in how well they work, as there is for any microphone
> type.
>
> Walt
>
Dr. Swenson did not test a parabolic mic, he used computation to
predict the characteristics of reflector mics, using "boundary element
method to compute the solution to the Helmholz integral equation, which
represents the pressure field everywhere and thus accounts for all
diffraction effects." The diffraction effects are not a part of
Wahlstrom's computations.
bret
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>From Tue Mar 8 18:27:02 2005
Message: 25
Date: Thu, 26 Feb 2004 15:48:12 -0800 (PST)
From: Bret <>
Subject: Re: the nature of parabolic reflectors
--- Walter Knapp <> wrote:>
> Remember, sound is working with particles with real mass. Radio and
> light work with essentially massless particles. Much easier to
> diffract
> those.
I have compared rf parabolic reflectors understandings to relate to
parabolic mics on this list. More than one person has said this is not
valid.
I asked Dr. George Swenson, author of the USACERL reflector mic study,
and specialist in rf telescopes whether my comparing these 2 was wrong.
He replied:
'The argument that electromagnetic and acoustical diffraction must be
different because "acoustical particles have mass while electric fields
do not" is nonsense. Both phenomena are represented by the same wave
equation and have the same general solutions. The boundary conditions
are different though even there analogies can be identified. The
practical difference is that electromagnetic fields are vectors while
sound pressure fields are scalars, and the vector components must be
computed separately so that problem is somewhat more involved.'
Regarding computational methods for parabolics for electromagnetic and
sound waves he told me:
'Although such computations apparently have not been published
previously they were performed by widely used boundary-element methods.
That particular figure can certainly be relied upon as it is consistent
with experience in acoustics, optics, antennas, and astronomical
telescopes (both optical and radio; the latter is my principal
specialty).'
bret
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"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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>From Tue Mar 8 18:27:02 2005
Message: 24
Date: Thu, 26 Feb 2004 16:45:05 -0700
From: "Jim Morgan" <>
Subject: Re: King Rail vs. Virginia Rail
Rich - The VIRA has a large variety of vocalizations many are on your copy
of the Reference Library.
Jim
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