Getting back to those interested:
I tested a Sony PCM-M10 mounted a Telinga parabolic dish (the M10 mounted a=
s shown in the photos below)at 20 feet and 70 feet using a small speaker pl=
aying radio static noise and by shaking dried beans in a paper bag (David's=
"peanut" test) while moving across the direction of focus.
This resulted in a audible split focus with a hole in the center. A slight =
change in direction of the parabolic dish a few degrees to either side from=
center relative to a fixed subject shifted the amplified focus to one caps=
ule or the other. When played back in stereo on speakers a drop in the cen=
ter was quite apparent. However, when mixed to mono the center seemed to su=
m (?) in a way providing sufficient lift between the dual focuses so any dr=
op from crossing the center was no longer apparent. While the amplificatio=
n at these, slightly off parabolic focus, dual focuses is certainly less th=
an what could be expected at the true parabolic focus, it seems there still=
sufficient gain (maybe 6 to 8 dB) to still consider the arrangement a high=
ly directional microphone.
This photo should give an idea how the M10 was mounted.
http://rockscallop.org/test/20120103_m10-mount.jpg
Here is a photo of the whole setup on tripod stand.
http://rockscallop.org/test/20120103_dish-stand.jpg
John Hartog
rockscallop.org
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