At 7:53 AM -0700 7/15/10, Scott Fraser wrote:
>
>
><< i would expect a six db improvement in self noise when a capsule is
>used in the boundary layer.
>
><Wouldn't the self-noise percentage in the mic's signal be raised
>along with the increased output from the boundary effect?>
>
><no. the gain is noisefree. and first time you hear it, very
>impressive. (i have
>built many varients on the boundary layer principle.)
>umashankar>>
>
>Note that the 'gain' is actually an increase in the acoustic volume at
>the surface of the boundary, hence the name Pressure Zone Microphone
>of the original commercial implementation of this principal. So the
>microphone simply has a louder acoustic signal presented when the
>diaphragm is in the pressure zone. Thus less preamp gain is required,
>& less gain means lower noise in the resulting recording, even though
>the self noise of the system stays the same. I seem to recall that the
>pressure zone is about a quarter inch deep in the audible band.
>
>Scott Fraser
Hi Folks--
Here's a blind comparison movie for downloading to add some
specificity to this interesting discussion:
http://tinyurl.com/28aqxkw
Which is the boundary mic arrangement and which is open air? Is
there a significant difference in self-noise performance? Is there
"awful comb filtering" in one sample that is not in the other?
The two clips were recording at the same time with the two, same
model mics less than 5" apart. I used a 1" set-back to emulate the
popular setting for Olson-like Parallel Boundary rigs. 4" X 5"
boundary. The clock is head-on, the crows are through a closed
window above the clock. Rob D.
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