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Re: Re: Parabolic, Stereo and Mono

Subject: Re: Re: Parabolic, Stereo and Mono
From: Klas Strandberg <>
Date: Mon, 10 Mar 2003 14:30:57 +0100
>>>>A second thought about the stereo parabolic.  You folks have me 
>>>>confused about using a barrier in the dish, is the barrier in 
>>>Lang's 
>>>>most recent photos acting as a PZM?  Is the barrier simply 
>>>>reflecting the wave to a new path and the mic diaphragm is large 
>>>>enough to gather all the semi focused wave?  
>
When I tried two omnis without a barrier I got some kind of stereo of what
was happening far away and no stereo of ambience. I didn't like it. It
sounded really strange when replayed in loudspeakers. 
I tried to figure out what such a recording could be used for and found that
a researcher perhaps could use it to make it easier to separate several
birds singin in a flock. I have been into that problem myself, when it was
nearly impossible to determine wheather it was one or two birds singing a
certain phrase. In such a case such "distant stereo" could be helpful.
Otherwise, the sound picture resembles nothing of what is present in real life.
I will do more such tests, though. Could be useful on a cheap stereo model,
having 2 small electret omnis. 

Klas.

>It's acting like a boundary mic, but not a very efficient one. The 
>diaphragm is too large, most of it is too far from the boundary to make 
>much difference.
>
>If you wish to do proper boundary mic in this sort of setup put the mics 
>perpendicular to the barrier, either spaced closely from it or through 
>it with the diaphragms even with the barrier surface on each side. When 
>I get some time I'm going to machine up such a setup to test using 
>MKH-20's. I've a few more complexities to it as well.
>
>>>>relying on the efficiency of the mic to offset any loss of gain, 
>>>>since the mic is not at the focus point.  How far from the focal 
>>>>point can you move the mic elements?  
>
>No more than a inch or so either way. Unless you are recording close 
>subjects, then you can go a bit more out. At least that's my experience 
>with the regular Telinga mic elements.
>
>Walt
>
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Phone & fax int + 295 310 01
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