"David Satz" wrote in message
oups.com...
Bob, I don't have specific mike recommendations, but just wanted to
clear something up. For distant miking with omnis, air absorption
("adiabatic loss") really isn't the primary concern--it's the fact that
you're in a diffuse sound field, and most of the sound has already
bounced off of various room surfaces a number of times before it
reaches your microphones. The high frequency energy is absorbed to a
considerable extent by the materials that have reflected the sound
waves, more than it is by the air.

Thanks for that clarification. My concern is sparked by users' notes that
various mikes sounded "dark", or had an extreme droop at 20 kHz (Rode NT-5).
I figured that for distance miking, this would be undesirable.

Especially with more distant recording, it's hard to get an optimal
signal-to-noise ratio from a very small (say, 1/4" diameter) pressure
transducer. But larger ones (1/2" and up) aren't omnidirectional for
short wavelengths--at high frequencies the response is always stronger
on-axis than off-axis. People still want the microphones to have
basically flat response overall, but when the main sound energy is
arriving from all angles at once, to get flat average (integrated)
response people generally choose omnis that are "diffuse-field
equalized", i.e. that have ~6 dB or so of on-axis lift at high
frequencies.

Their printed on-axis response curves may look as if they'd sound
harsh--and they can indeed sound harsh when used very close up and/or
in an overly "dry" acoustic. But when they're used at the distances
where they're designed to be used, they should sound natural despite
the way the on-axis curves look.

--best regards

Dave,
First class post! This is a saver, thanks. I am aware of the issues from
the physics perspective, but it takes someone like you to make it practical.
It seems that all the Chinese mikes are copies of the Neumann 180 series,
which appears to have a 20mm diaphram. These mikes get out to 20 khz, but
the low end manufacturers, perhaps because of the lack of sophistication of
the market, don't label the curves as on-axis/diffuse, and they tend to
exaggerate the qualities in the curves (at least the inexpensive ones, not
Neumann et al), so it's very difficult to get a true picture. Ironically,
the Rode NT-5, which uses a somewhat smaller 1/2" diaphram, is reputed to be
darker than most of the 20mm mikes. Perhaps they had to roll it off to save
the s/n.

As the diaphram shrinks, s/n decreases, while physical perfection of the
response has at least the potential to increase. I am curious what
proportion of a mike's self-noise is due to Brownian motion of molecules
hitting the diaphram, as opposed to the 1st stage of the mike's electronics.

Do you have an opinion on whether the Jecklin disk can be used with 20mm
cardioids? The originator claimed a requirement of omnis.

Best regards,
Bob Morein