<<Well, it's actually about thirty feet deep at the bottom end...>>
Sure, but that's just a fraction of the entire audible range. Dan,
when you say there's no such thing as a pressure zone, I'm assuming
you mean for all possible frequencies, right? However, if we limit our
concern to everything below, say, 16kHz or 18kHz, then certainly we
can say a pressure zone devoid of audible comb filtering exists within
that band. Further, I would suggest that a perfectly flat frequency
response at the very top limit of our hearing, the half octave above
maybe 12kHz is just not absolutely critical to a well defined overall
sense of a balanced spectrum.
When PZM's first became available, late 1970's I recall it was, my
studio partner & I got one . We recorded everything with it; piano,
double bass, violin, acoustic guitar, vocals, woodwinds. Then after a
month or two of infatuation we went back to using our U87's & KM84's
for all the things they excel at, & more or less put away the PZM for
good. I believe we suffered from the "New Girlfriend Syndrome".
Critical examination of the results revealed that what is in fact a
hearing aid capsule simply doesn't compete, resolution-wise, with the
1/2" to 1" diaphragms in the various Neumanns & Sennheisers we had on
hand.
The results that Paul obtained, showing significant cancellation in
the high end, is indicative of the fact that placing a mic body on the
boundary with the capsule perpendicular to the boundary doesn't locate
the diaphragm sufficiently within the pressure zone for those
frequencies. Obviously part of the diaphragm is in & part of the
diaphragm is out of the zone. The Schoeps boundary mic places the
diaphragm flush with the boundary, & thus is truly reflection free at
all frequencies.
Scott Fraser
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