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Re: Edmund Parabolic Reflectors

Subject: Re: Edmund Parabolic Reflectors
From: Gregory Kunkel <>
Date: Wed, 4 Aug 2004 15:08:41 -0700 (PDT)
Here is a quote from a paper previously mentioned in this forum:

Randolph Scott Little
Laboratory of Ornithology
Cornell University
Ithaca, New York*

"In order to avoid deep cavity resonances, as indicated by the 200 Hz
peak, the microphone should lie outside the plane of the edge of the
reflector.  On the other hand, in order to suppress sounds coming
from directions behind the reflector, the microphone should be well
inside the rim.  A suitable compromise is to place the microphone at
the plane of the rim.  This means that the focal length must be
one-quarter of the diameter in order to satisfy the formula for a
parabolic curve."

            Greg Kunkel
--- Dave J <> wrote:

> > 
> > That being said, the Edmund dishes are in fact as 
> > deep as their focal length, and my 24" diameter 
> > dish measures 6" deep.  It seems to me that there
> > was some discussion here or on a related list
> > about the Telinga dishes being deeper than their 
> > focal length, and that's important for sound 
> > reflectors more so than for optical reflectors.
> > 
> > -- Mike
> I do wonder if the edge of the dish would be a source 
> of wind noise, and if the mic might be wind-shielded if 
> lower, but I would think that gain might be optimized
> if the mic was higher -- but then I guess this would 
> depend on the shape of the mic element and its pattern...
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