[Roy W. Rising[_2_]]

(Scott Dorsey) wrote:
Nick Brown wrote:
Interesting point. So when the two are combined the result would be...
comb filtering?

Well, that always happens when you put two mikes together unless they are
in precisely the same place in space.

I'm not clear what you mean by "condensers and dynamics (pressure)" -
taken literally it would seem to imply that all condenser mics are
pressure operated, even the hypercardioid Schoeps under discussion here,
even the single-diaphram figure-8 condensers (Schoeps MK8, Sennheiser
MKH30). That can't be right, can it?

An omnidirectional microphone is sensitive to air pressure. A figure-8
microphone is sensitive to air velocity. Cardioids, hypercardioids, and
supercardioids are sensitive to both in varying degrees.

If combining air pressure and velocity information is inherently flawed,
wouldn't that flaw be manifest in every cardioid mic ever? I thought
that was how the cardioid pattern was formed.

Cardioid microphones are inherently flawed and will always have frequency
response that changes with direction. In general, the closer you get to
the edges of the spectrum (omni and figure-8), the better the off-axis
response will be.

Consequently if you compare the Schoeps cardioid and hypercardioid
capsules, you'll find the hypercardioid is actually cleaner off-axis than
the regular cardioid.

There are various tricks you can play to regularize the off-axis response
and some of them work better than others. Most microphone vendors use
a few of them.
--scott

I think this oversimplifies the pressure vs. velocity subject. I've just
reviewed Howard M. Tremaine's discussion of mics in his Audio Cyclopedia.
In *every* case he refers to ribbon-velocity mics as contrasted to pressure
responding condenser and dynamic types. However, he acknowledges there
certainly are bi-directional condenser mics ... without explanation.
Generally, directional patterns are accomplished by controlling the phase
of sound pressure reaching the back of the diaphragm. The Altec 639 summed
the outputs of forward facing dynamic and ribbon elements in one of the
very few attempts to use the 90 degree phase difference between pressure
and velocity.

On another note, the EV RE15 and RE20 are examples of directional mics with
*very* little frequency response change with respect to direction.

--
~
~ Roy
"If you notice the sound, it's wrong!"