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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