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Posted by Richard Crowley on 01/27/06 02:25
"Bailey The Dog" wrote ...
> Actually the sound detected by a shotgun along its length is
> used only for noise canceling, thus rejecting the side noise.
> This characteristic is exactly what we desire in a parabolic
> situation as the result is a highly focused sound source with
> excellent side rejection.
Actually ALL the sound is collected along the length of a
"shotgun" microphone. Many (most?) shotgun microphones
have no opening at all in the end that points at the source.
Many have a fake grill there to prevent disorienting users who
don't understand how line-gradient microphones work.
They work by keeping the sound in-phase which enters along
the length of the tube, while mixing out-of-phase (thus cancelling)
sound that arrives from other angles. Of course this is possible
only down to a few hundred Hz, below that they are designed
to behave as conventional cardioid (or hyper-cardioid) micro-
phones. There is an interesting discussion of shotgun micro-
phones currently running over on news:rec.audio.pro, and they
are discussed quite regularly over on
news:rec.arts.movies.production.sound
I started experimenting with parabolic reflectors for light and
sound as a child and learned early on that the sound/light is
concentrated at the focal point. If you are making a parabolic
microphone, you want a small omnidirectional microphone at
the focal point. Take a look at any modern satellite antenna to
see how the principles still apply today.
Putting the end of a shotgun microphone at the focal point of a
parabolic reflector will theoretically yield no sound at all, but in
the real world, you will hear some sound, but it will be very
poor quality compared to using an omni at the same point.
> Please reference the following article
>
> http://www.nrgresearch.com/microphonestutorial.htm
Interesting article, but doesn't actually mention how a line-
gradient ("shotgun") microphone works.
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