In article , Don Pearce
wrote:
On Sat, 23 Mar 2013 12:08:26 +0000 (GMT), Jim Lesurf
wrote:

In article , Dave Plowman (News)
wrote:

I think what you are describing in the first part is the "distance
cancelling" microphone. It responds to the pressure difference between
two capsules, hence responds strongly to close sources, and very little
to more distant ones.

That's a different effect to the one I (and Olsen, etc) was referring to.
he goes on to use this to explain the construction of highly directional
end-fire mic arrays. I was just pointing out you can do this, but getting
it right isn't easy.

The point is there is a time delay required for a sound wave to propagate
from one sensor element to the other. That leads to a pressure difference
given a finite wavelength, even for a plane wave which has the same peak
amplitude in both locations.

In effect, it is just like using a phased array in RF to sculpt a required
pattern of directionality.

Slainte,

Jim

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