In article , Don Pearce
wrote:
On Sat, 23 Mar 2013 12:57:16 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:
[snip]


Ah, OK, I see what you are talikng about. Sennheiser use a tube in front
of the mic with a slot down the side. The tube is lightly damped so it
doesn't resonate. Anyway, the idea is that sound coming from boresight
enters the tube all the way down the slot in phase (travelling, but in
phase) and reinforces at the capsule. Any other angle and there is
sufficient length of tube for cancelling wavefronts to enter, and reduce
the level at the capsule. they manage a pretty good shotgun this way,.

Yes, that's a practical example of the kind of system people make based on
the approach. Here each section of the gap acts as a small hole as a sensor
collector.

You could make something nominally similar with an array of actual pressure
mics with delays on their outputs before adding them.

Its similar to an end-fire RF array of elements.

If you use a pair of actual pressure sensors you can then *subtract* their
electronic outputs, leading to what I described earlier if the sensors are
far enough apart to make the acoustic propagation time large enough between
them. The behaviour is analogous to something like a ribbon that senses the
difference in pressure between its sides.

Slainte,

Jim

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