Chris Hornbeck wrote:

Is there any factor-of-two difference in the two arguments,
or have I just been watching too many French movies lately?

Not a difference. You get it either way.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

In article ,
says...
The fact that
sound approaching the PZM at any angle other than
perpindicular reaches the opening at the center of the
capsule with a variety of delays only implies combing at the
highest frequencies. The cantilever itself introduces
diffraction and angular variations that reach lower.

Absolutely no benefit from this configuration is apparent to
me in theory.

Forgive my ignorance, but isn't the point of it being that
very little direct sound enters the capsule at all? Isn't that
why it's inside that arm? All the sound it hears is a reflection
from the boundary, correct? I know some small amount will actually
come in, but it should be miniscule compared to the reflected sound.
I have two of them that I've modified back-to-back on a sheet of
plexiglass; I use them for drum overheads, and they are clean and
detailed. A check with my software reveals a bit of top-octave
rise, but not a lot, and it's pretty smooth (about 4dB by the top
of its range, around 20KHz).
---Michael (of APP)...

Bob Cain wrote:

BTW, a member of the micbuilders yahoo newsgroup posted links to some
recent research showing that all the PZM mode does is screw up the
frequency response compared to a surface mounted small omni without a
baffle or gap. Directional performance is the same, a hemisphere.

Here's more information on that:


The Acoustical Behavior of Pressure-Responding microphones
Positioned on Rigid Boundaries - a Review and Critique

Stanley P. Lip****z and John Vanderkooy

AES Preprint 1796 (1981 May)

Abstract
Pressure-responding microphones have occasionally been
placed on rigid boundaries for recording purposes, and
indeed there is merit in this idea. A new type of
microphone, called the "pressure zone microphone", has
recently been introduced for this purpose. This microphone
obscures the diaphragm from receiving any direct sound by
pointing it towards the rigid boundary, in the mistaken
belief that, were it pointing forwards, it would display the
on-axis high-frequency rise characteristic of such
microphones when used free-field. It is shown that this is
not true, and that, for a given capsule size, the frequency
and polar responses are significantly degraded by obscuring
the diaphragm. Conversely, for a given frequency and polar
response tolerance, a larger diaphragm, giving lower
self-noise, could be used for a non-occluded design. We
present both experimental data and a theoretical model to
verify our contentions.

Conclusion:
A small (less than 0.5 in diameter) pressure-calibrated
microphone mounted flush with a large rigid boundary
exhibits almost perfect frequency and polar responses over
the entire audio band. Placing an obstruction between its
diaphragm and the incident sound degrades both aspects of
performance. In order to regain acceptable performance, such
an obscured microphone must resort to a substantially
smaller diaphragm size with the attendant deterioration in
its self-noise.

--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

"Bob Cain" wrote in message
...


Bob Cain wrote:

BTW, a member of the micbuilders yahoo newsgroup posted links to
some
recent research showing that all the PZM mode does is screw up the
frequency response compared to a surface mounted small omni
without a
baffle or gap. Directional performance is the same, a hemisphere.

Here's more information on that:


The Acoustical Behavior of Pressure-Responding microphones
Positioned on Rigid Boundaries - a Review and Critique

Stanley P. Lip****z and John Vanderkooy

AES Preprint 1796 (1981 May)

Abstract
Pressure-responding microphones have occasionally been
placed on rigid boundaries for recording purposes, and
indeed there is merit in this idea. A new type of
microphone, called the "pressure zone microphone", has
recently been introduced for this purpose. This microphone
obscures the diaphragm from receiving any direct sound by
pointing it towards the rigid boundary, in the mistaken
belief that, were it pointing forwards, it would display the
on-axis high-frequency rise characteristic of such
microphones when used free-field. It is shown that this is
not true, and that, for a given capsule size, the frequency
and polar responses are significantly degraded by obscuring
the diaphragm. Conversely, for a given frequency and polar
response tolerance, a larger diaphragm, giving lower
self-noise, could be used for a non-occluded design. We
present both experimental data and a theoretical model to
verify our contentions.

Conclusion:
A small (less than 0.5 in diameter) pressure-calibrated
microphone mounted flush with a large rigid boundary
exhibits almost perfect frequency and polar responses over
the entire audio band. Placing an obstruction between its
diaphragm and the incident sound degrades both aspects of
performance. In order to regain acceptable performance, such
an obscured microphone must resort to a substantially
smaller diaphragm size with the attendant deterioration in
its self-noise.

All of this is true. The diameter of an RS PZM is closer to 1/4",
and the self noise is indeed higher. But much of the increased self
noise is reduced by the 6db increase in sensitivity due to the
pressure zone.

Norm Strong

normanstrong wrote:

All of this is true. The diameter of an RS PZM is closer to 1/4",
and the self noise is indeed higher. But much of the increased self
noise is reduced by the 6db increase in sensitivity due to the
pressure zone.

Norm, that is due to being at the boundry rather than being
"pressure zone". A surface mounted omni will give the same
sensitivity increase without interfering with the response
or directivity.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Bob Cain wrote:

I can't see how the PZM configuration offers anything positive
compared to a single omni at that position.

I'll give you 3 reasons :

1) They are hemispherical, not omni, which may be the desired pattern.

2) They are low profile. You can place them on a conference table and
they won't be in the sight of anyone.

3) The timber (color of the sound, tone, whatever you want to call it)
of the sound is constant whatever the distance of the source.

I frequently use PZMs on the lip of the stage when videotaping theater
performances. The mics are invisible from the public perpective and
will provide a perfect balance between on-stage and audience sound. The
fact the sound is constant (in timber, not volume!) whether the
comedians are close or far from the mics is an outstanding and desirable
characteristic for this application. You just need to ride the faders
and/or use an AGC or compressor.

PS : I kinda work at the bottom of the chain, quality-wise, so YMMV!

PS2 : Placing them on a soft but thin material is usefull to isolate
them from the surface they are on, to avoid floor noise.

Regards,
--
Eric (Dero) Desrochers
http://homepage.mac.com/dero72

Hiroshima 45, Tchernobyl 86, Windows 95

"alan" .@. wrote in message news

-snip-

wow that mic is a POS! not even worth doing tests on. i took it back to RS.
i would have liked to do more with it but got busy with less important
things hey thanks everyone for your expert input *bow-grovel-grovel*
-OP alan