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Re: Placing Mics in a Parabola

Subject: Re: Placing Mics in a Parabola
From: Walter Knapp <>
Date: Sat, 07 Aug 2004 10:54:09 -0400
From: "Rich Peet" <>

> Two different techniques with two results on 2 pzm's vs 2 separated 
> stereo mics.
> Klas prefers the 2 pzm's and I prefer the 2 seperated.
> Play with them and decide which you like.
> pzm
> On target subject is mono off and off target subjects are stereo.
> advantage is that the target gets front and center image just like 
> the rock and roll bands on radio.  Disadvantage is that each channel 
> only sees 1/2 the dish and that translates to gain and sound 
> charecter changes.  Advantage is that there is no "hole in the 
> middle".

The PZM technique normally gives a extra 6dB or so gain as well. And in 
the case of the telinga it's several capsules in each channel. Making it 
low self noise and more gain.

I don't see any gain problem from the 1/2 dish worry. The telinga has a 
lot of gain for it's size. It's not a sound quality problem either. I 
have both the dual science and DAT Stereo mics for the Telinga, and 
don't see a lot of difference in sound quality. Except stereo is better.

The target subject is not mono, even in the center. It's evenly in both 
channels, as it should be for it's stereo location. As you move the 
target subject off center, there is no sudden jump from mono to stereo. 
It's location in the stereo field moves off center as it should. It's a 
error to call all that mono.

The big advantage of the PZM approach on top of that is that the mics 
can be very close to on axis, where the sound quality is most predictable.

> seperated omni mics
> each mic is using the whole dish and picking up a different 
> direction.  Spaced correctly you get full gain with different distant 
> and narrow angle targets brought in to a duet.  By using the whole 
> dish for each image the quality of the sound is held as high as 
> possible. but, the disadvantages are that the image of heard sounds 
> on the sides without gain are image fliped and if there is only one 
> target it will never be up front and in the center. And there is a 
> hole in the middle of the image who's size changes with pitch of 
> sound and spacing of the mics.

I would suggest, before moving mics very far off center to read Sten 
Whalstrom's paper paying particular attention to the changes in gain 
that occur as you move off axis. Any off axis compromises the sound 
quality, but it's fairly minimal if you don't move too far off axis. You 
will have to move some just to put two regular mics in. At least the way 
it's usually done.

> Klas's papers need updating and revisions for other techniques.

I think his papers are more for explaining his mics and do that well 
without being too technical. And, of course one does not revise a 
published paper. The info needed is available elsewhere.



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