 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 windshielded 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...
________________________________________________________________________
________________________________________________________________________
