Hi Paul,
It is best to locate the focal point by ear. It seems to me the
equation being discussed will not give the depth of the focal point,
because the equation gives the the diameter of the dish at the focal
point and if the edge of the dish is not on the same plane as the
focal point,well then how do you know where to measure the diameter.
That equation will come in very handy when you decide to build your
own parabolic dish, but for now I'll tell you the focal point of the
Telinga lies about a half-inch or so below the edge of the dish. Fine
tune it with the radio-between-channels method. Open your car door
with the static playing, walk back fifty feet or so, and adjust the
mic so it sounds the loudest.
John Hartog
--- In Paul Jacobson <> wrote:
>
> Thanks for all the replies. I'll work out where the focal point on
> the dish and start from there.
> I'm assuming that the idea is align the diaphragm with the focal
> point rather than the nose of capsule?
>
> cheers
> Paul
>
>
> On 03/04/2008, at 8:33 AM, John Tudor wrote:
> > Oops. My Bad!!!
> >
> > Bill is quite correct. 16 NOT 4 is used in the focual point equation
> >
> > So focus is
> >
> > (Dia squared) / (16 X depth)
> >
> > Sorry for the confusion.
> >
> >
> > ------------------------------------
> >
> > "While a picture is worth a thousand words, a
> > sound is worth a thousand pictures." R. Murray Schafer via Bernie
> > Krause
> > Yahoo! Groups Links
> >
> >
> >
>
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