Posted by: "D Secomb"
>
> Thanks for your thoughts Walt and Paul for the information placed on file=
.
> Walt. I can see what you are saying by having a deeper dish so the
> focal point within the dish. This statment " And more or less removes
> this "advantage" of a cardioid.", are implying that both types of mics
> are now equal.
>
> When looking at the graph that Paul posted,( were the focal point is
> near the edge of the dish) its the cardioid has the edge. A clue how
> mics behave in a deeper dish (were the mic is placed inside the dish)
> is on the Telinga site on picture gallery 4. Although this is a test it
> does indict below 5 000 Hz the omni has the edge and the cardioid has
> the edge above it. Maybe Klas can give his thoughts on that.
You might want to read "The Parabolic Reflector as an Acoustical
Amplifier" a paper by Sten Wahlstrom. It gives much more detail on the
acoustical behavior of a parabolic dish. I'm not sure if anyone has it
up on their site right now, I posted it several times in the past. I've
found it to be about the most accurate description of what's going on.
Note that the Telinga stereo mic I use is a boundary mic with multiple
capsules, so not omni or cardioid mics. There are other mic choices. And
I'd somewhat question the polar patterns of omnis or cardioids being
purely that in the field of a parabola. You are dealing more with the
characteristics of the reflector than the mic.
Walt
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