On Thu, 2006-07-20 at 13:51 -0400, K4IA@aol.com wrote:
> Is it fair to suggest that the mic element is omni but because of the way it
> is mounted - in a case with an opening on one side and with sound absorbing
> material behind it - that it effectively functions as a uni?
> Craig "Buck"
> Fredericksburg, Virginia USA
A true unidirectional microphone takes a lot of acoustics to get a
decent front to back and front to side that involves getting acoustic
pressure to the back of the diaphragm to counteract that which arrives
from the sides and rear on the front of the diaphragm. Good
unidirectional microphones have always cost 5 times or more the price of
a workable more or less omni directional. And more or less
omnidirectional is what you get with a single electret element in a
case. Not perfect omni, but not very directional either.
I think, in microphone parlance, the omni microphone is one without any
acoustical treatment. Just a plain diaphragm on or near the front of the
case. Its not truly omni, just nothing has been done to make it uni.
I suppose with the cost of electrets so low, one might mount a few in
the case in various directions with a bit of acoustics in front of each
to increase directionality, and then use an OP amp summer to enhance the
front and cancel the signals from the sides and back. Probably is what
makes a helicopter noise canceling microphone work and so expensive.
if its broadcast quality you want including freedom from fan noise and
room echoes, then you need to make the room have fewer echoes (drapes on
the walls or acoustical tile) and move the fans to other rooms and
operate the ran equipped radio by remote control (as well as thee
computer) or else keep the microphone gain low and SPEAK UP. Turn off
the compression in the audio and ALC.
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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