Oops, my mailer sent a reply before I had written it.
I found a link on the CVX rig:
http://www.pamodelforest.sk.ca/pubs/PAMF2800.pdf
I'm always open to new ideas but I can't see how this rig would give a clean
sound. It is a type of horn (not a "reverse horn" as described) but there is
still going to be a resonance across the device horn terminal as it is about
a wavelength wide at 1KHz. Put another way, it is in effect a "closed
housing" between the distributed horn mouth and the focal centre.
The theory that sounds will travel bidirectionally ignores the effect of a
sudden change in acoustic impedance at the distributed horn mouth.
The article made no attempt at describing the frequency response or vertical
polar response and while there would be a small acoustic gain from the horn
loading, this would only have the effect of reducing the effective mic noise
at high frequencies after a gain adjustment. The three dimensional pickup
solid area would be reduced at high frequencies, countering the horn gain.
The horn mouth vertical dimension is about 30mm, roughly a wavelength at
10KHz, so I would expect any vertical directional response to be near omni
at lower frequencies.
What the article does not include is any indication of the vertical polar
response and the vertical frequency responses of the rig which I would have
thought would be a starting point. The least would have been a direct
comparison with an open omni mic.
If this rig is still in existence, it would be interesting to hear some
comparative recordings against a simple omni.
David Brinicombe
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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