"Scott Dorsey" wrote in message
...
coffelt2 wrote:

D-104C had a "ceramic" crystal element which was far
more tolerant of
moisture, shock, etc.
I can't remember just now what the frequency response was
(compared to the
original) but when
I used one, I was looked down upon as a traitor to
tradition.

You can no longer get either the original crystal element
or the ceramic
element, but Astatic will sell you a dynamic replacement.

The dynamic is a whole lot smoother and less brittle
sounding, but maybe
that's a bad thing in a pileup.

What was good about the D-104 types, was that you
didn't have to speak
directly into it. One
could just walk around the shack, and in some instances,
around the house
with little loss of
readability.

They were very, very omnidirectional compared other
communications mikes
back then. The good part of this was the effect you note.
The bad part
is that noise sources like fans and people yelling in the
background were
also very readable on the air.

I am currently using an old Turner microphone and like the
way it sounds.
Also I am a fan of some of the older EV desk microphones,
which still turn
up cheaply at hamfests. If you find a low-Z mike that
you like, there is
no reason you can't just stick a step-up transformer in
the base to drive
the Viking.
--scott

There aren't many polar patterns published for cheaper
mics but the directional properties of mics like the D-104
are mostly due to the diffraction around the body. At low
frequencies they are almost perfectly omnidirectional but at
some frequency begin to have some directionality which
increases with frequency. The same diffraction effect causes
a rise in the frequency response unless its compensated in
some way. At a frequency where the path around the body
approximates a half wave length the microphone can approach
a super-carioide pattern, i.e., unidirectional with one or
more lobes toward the back. The shape is important, a flat
pancake shape like the D-104 will have a somewhat different
pattern than a bullet-shaped mic. The ultimate was the
Western Electric 630A "Eight-Ball". The spherical shape made
it quite omnidirectional to rather high frequencies but the
pattern was made even more uniform by the partial baffle
mounted in front of the diaphragm. Metro-Goldwyn-Mayer made
some microphones using probably standard Western Electric
condenser elements mounted in a spherical case to reduce the
diffraction rise typical of the older mics. I don't remember
whether these had baffles on them but the elements were
mounted in a way that also tended to reduce the cavity
resonance typical of both this and other large condenser
type elements. In some respects the rise was useful in
dialogue recording although it could also make some voices
sound harsh. All sorts of mechanical filters and baffles
were tried to aleviate this effect, mostly with limited
success. Electrical filters, which would have been a better
solution, while known in the telephone industry, were not
very well known outside of it. Much of the early theory of
electrical wave filters was developed by George A. Campbell,
of Bell Labs, in the mid 'teens. This was cosidered very
advanced stuff at the time.
I am not surprized that no one makes crystal or ceramic
elements any more. For the most part microphones to fill
similar applications now are electrets.



--
Richard Knoppow
Los Angeles
WB6KBL