I tend to think that just as pure red and pure violet light appears
out of focus to the eye so would sound have a different focal
distances based on the size of the reflector and distance from the
ideal focused center frequency with a small dish being similar to a
high f stop in a lense. But as you move away from the exact center
sideways away from the perfect focus, also like light, the image is
still in focus but the focused image is moved over to a differnt
origin point to the side and reverse orientated. And this is why I
am able to get a stereo sound image using separated mics without a
barrier and yet the sound received by each mic is very similar to the
sound as received at the exact center. And maybe why I hear a
preferred sound from a larger dish where the high frequencies are
going to be more out of focus than a smaller dish.
Rich
--- In Bret <> wrote:
>
> --- Walter Knapp <> wrote:
> > From: "Rich Peet" <>
> > >
> > > The things that I am fighting myself with here are:
> > > 1. Is it agreed that the size of the focal globe changes with
> > > frequency?
> >
> > I'm not so sure but what the focal globe idea is not misleading
or at
> >
> > least misused. In my visualization of things, if it exists as a
> > useful
> > concept, then it's size is not frequency dependent. It's
dependent
> > primarily on how well the dish conforms to a ideal parabola, and
how
> > far
> > off axis we are including in the 'globe'.
>
> I may be wrong, but I think the size of the globe must be frequency
> dependent. I believe this is true especially if you have an ideal
> parabolic reflector.=20
>
> As you move a given distance from the absolute point of focus, this
> distance is a larger phase difference for shorter wavelengths than
it
> is for longer wavelengths. This phase difference at the off focus
> position is one mechanism that would give rise to interference or
> cancelation rather than the addition of pressure as occurs at the
> absolute focus (because the arrival at focus is in phase from all
dish
> reflecting points).=20
> bret
>
>
> __________________________________
> Do you Yahoo!?
> Yahoo! Mail SpamGuard - Read only the mail you want.
> http://antispam.yahoo.com/tools
________________________________________________________________________
________________________________________________________________________
|