On Thu, 10 Aug 2017 15:32:44 +0100, "Brian Gaff"
wrote:

Sometimes I wish I'd never asked.
OK then, I was under the impression that directivity was due to phase of
the wavefronts on both sides of a diaphragm. In the case of the ear, there
is only one clear side though. Also ears are log, and most amps are linear,
so I'd always assumed that it was the loudness ratio that caused the effect
in the ear and using headphones etc makes the ears perform differently.
Brian

Nope - none of that. Sorry. It is about phase, but also amplitude. The
velocity response of a mic - the figure 8 aspect - has a positive
phase for air approaching from the front, and obviously a negative
phase for sound from the back. It has an amplitude response that is
the Cos of the approach angle. Take the vector sum of the pressure
response, which is unity and constant phase all the way round, and the
velocity response which is as I just described, and you get a
cardioid. From the rear the pressure response and velocity response
are the same amplitude and opposite phase so they cancel.

And that is pretty much it.

d

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