Having great respect for Randy, and having the full "proud owner
bias" from knowing that the dish I use did take into full
consideration his work as well as his words. Not to mention being
biased in favor of the sound from this described configuration. I
comment.
I can take my 32" dish with its focus just outside of the rim and cut
the outside edge section off to make a 10" dish. The dish will still
be a parabolic, will still have the same focus distance, and will be
less deep. It would then be a design option to use an external baffle
to reduce the side heard sound which is always an option anyway. I
don't because I use the side sound in the stereo image.
So depth, diameter, and focal point are all inter-related yet each
variable.
Rich Peet
--- In Gregory Kunkel
<> wrote:
> Here is a quote from a paper previously mentioned in this forum:
>
> ACOUSTIC PROPERTIES OF PARABOLIC REFLECTORS
> 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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~->
> >
> >
> > "Microphones are not ears,
> > Loudspeakers are not birds,
> > A listening room is not nature."
> > Klas Strandberg
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> >
> >
> >
> >
> >
> >
>
>
>
>
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