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Re: DIY Parabolic Dishes.

Subject: Re: DIY Parabolic Dishes.
From: "Rich Peet" richpeet
Date: Sun Oct 1, 2006 8:21 am (PDT)
Well, we do have issues with standing waves to be honest.
My simple response was "do not worry so about them".
It becomes very complex very fast from there.

Some of the effect you get with a parabolic you will like and some you
wont.  If a very flat freq response is the goal then a parabolic is
not the way to record. Some day when I have the time and a fresh snow
I will post the freq plot of my dish

If you are going to use a smaller dish I do recommend that you run
some eq to curve the high freqs down some.


--- In  "John Hartog"
<> wrote:
> Thanks Rich,
> Hearing you have not had any noticeable issues with standing waves
> with your dish is encouraging.
> John Hartog
> --- In  "Rich Peet" <richpeet@> wrote:
> >
> > As you may recall I use a 32" dish with the focal point being close to
> > the rim.
> >
> > Do not worry so much about standing waves.
> > If cavity resonance is noticable to you than you can easily dampen
> > that.  My windscreens dampen it well.
> >
> > Ideal in my eyes is setting the focus at the rim or just outside.
> > On occation I do use a mic above the dish as a noise cancellation
> > device and if standing waves were a large problem with my dish I would
> > hear it.
> >
> > More often I use two close mics without a barrier. One is on target
> > and one is off. I am not a fan of ever having the target partly out of
> > the focus. Because I am recording with two mics and hearing one that
> > is always out of focus I understand focus fairly well. Using my two
> > mic setup a Song Sparrow can appear to be moving as it gives its song
> > when the ideal focus is between the two mics yet closer to one.
> >
> > The focal length a dish is designed for does change the flavor of the
> > recorded sound. Randy Little who did the math on that, I recall, also
> > ended up recommending a 1:1 ratio of focus to depth.  Klas does not
> > agree and that is simply another flavor.
> >
> > Rich Peet
> >
> > --- In  "John Hartog"
> > <hartogj_1999@> wrote:
> > >
> > > I must be nuts to bring this up again, but I still have some
> > > unanswered questions -so here is one.
> > >
> > > Regarding the focal point (and I know it is not really a point),
> > > is the ideal distance inside the rim.  I am hearing different
> opinions.
> > > One from a Cornell page suggests if the mic is positioned inside
> > > dish there would be a distortion from cavity resonance (or
> > > like that) off the sides of the dish.
> > > Conversely, a few of this group suggest a standing wave at the rim
> > > opening would cause distortion, so the mic is best put inside the
> dish
> > > somewhere below the level of the rim.
> > > Is the standing wave only exactly at the rim level or does it
> > > somewhat into and out-of the dish?  If so how far each way?  Would
> the
> > > optimal position of of the focus be at a certain ratio of the dish
> > > depth?
> > >
> > > If anyone can bring a little more light to this problem or steer
> me in
> > > the right direction, I will be sincerely grateful.
> > >
> > > John Hartog
> > >
> >

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