John and friends:
I've thought about this a lot as well (though with less expertise than
others, I'm sure)
I use a parabola with an omni microphone near its focus (Telinga,
actually) and think there are several advantages to having the focus
inside the rim --- especially reduction of wind noise and the
elimination of extraneous sounds.
My only good recording of a "pitpitpit" vocalization of an Acadian
Flycatcher has a park district lawn mower in the background. The
recording is 100% useable, but if made with an un-protected omni or even
a cardioid, would be consumed by the sounds of the machinery.
So I suspect that in the kinds of recording I do, at least, theoretical
acoustic considerations are overruled by the contingencies of the
settings in which I record: Highly directional is necessary.
I look forward to everyone else's opinions. I haven't yet solved the
wave propagation problem in a paraboloid!
SP
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