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Re: Idea's for recording kit

Subject: Re: Idea's for recording kit
From: "Walter Knapp" waltknapp
Date: Thu Aug 17, 2006 10:04 am (PDT)
Posted by: "Rich Peet"

> I will put this on this list as non-pay test project 34.
> I have a hard time understanding how the gain would be the same in
> this test.  I would expect something more of a gain drop, and it
> having a frequency component to the loss in gain.  Thinking 11db drop
> on my dish.
> 
> The more important issue I need to test and understand is the behavior
> of the physical space of an certain frequency amplified wave by a
> parabolic.  I am hearing that people don't think that a barrier will
> allow a dish to see only half a dish and I will look into that.

Since I seem to have precipitated this again, a few things:

My comments applied to only one design, the Lang Elliott design with the 
Telinga dish as I modified it. That used for a barrier 1/8" plastic high 
density foam sheet. The sheet behaves like solid plastic but is lighter, 
don't know for sure what variety plastic, behaves kind of like pvc. The 
barrier was between the mics centered on the diaphragm, both mics with 
their sides against the barrier. The barrier did not completely divide 
the dish, but was approximately 6" X 8" in a sort of oval, long end 
pointing out of the dish. Inside end extended out in a tab to slot into 
the support block for the mics.

I only spent about a hour with this dish before packing it up and 
shipping it out, so could easily have missed something that longer use 
may find.

Note that half the sound intensity is only a few dB difference, picking 
that out of a natural stereo field is not going to be that easy to 
prove. I listened to the mic only with natural sounds in my home woods 
and fields. I've found that natural sound is a far better predictor of 
mic performance in the field than lab tests.

Yes, since gain is frequency dependent any change in gain could also be 
frequency dependent.

Please note this is the Telinga dish, extrapolating any other dish to it 
will probably contain more than enough error to loose small differences.

I've not heard back from the recordist I made it for except for initial 
positive impressions before the trip started. So don't know how or if 
it's still being used.

Walt





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