It is not uncommon for a that noise free gain to be reflected in the noise
specs of a boundary mic.
For instance, specifications for the omnidirectional Shure capsule R183B show
20.5 dB when configured as lavalier mic MX183, and 14.5 dB when configured as
boundary mic MX391/O.
WL-183 specs show 22.5 dB which I am guessing is different than the MX183
because the noise specs include a different intended powering device - the
wireless bodypack transmitter for the wl-183, and the inline preamp for the
MX18.
WL183:
http://www.shure.com/idc/groups/public/documents/webcontent/us_pro_wl183_wl184_wl185_ug.pdf
MX183:
http://www.shure.com/idc/groups/public/documents/webcontent/us_pro_mx183_mx184_mx185_ug.pdf
MX391:
http://www.shure.com/idc/groups/public/documents/webcontent/us_pro_mx391_ug.pdf
John Hartog
--- In 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
>
>
|