[Top] [All Lists]

Re: Edmund Parabolic Reflectors

Subject: Re: Edmund Parabolic Reflectors
From: "Dave J" <>
Date: Wed, 04 Aug 2004 19:39:41 -0000
--- Mike Feldman <> wrote:
> Gregory Kunkel wrote:
> > The math of parabolas states that the width of 
> > a parabola at the level of the focal point is 
> > 4 times the focal point. So each of the parabolic
> > dishes have a depth equal to its focal length.
> That's true given the assumption that the design 
> happens make the depth of the dish equal to focal 
> length, but there's nothing mathematical forcing 
> the manufacturer to this constraint.

y = kx^2
y'= 2kx
y' = 1 = 2kx at focus
x = 1/(2k)
y = k(1/2k)^2
y = k/4

Is that right? It's been too long...

> > So the 18" has a depth of 4.5" and the 24 inch 
> > has a depth of 6".
> 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...


<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU