[LAU] Audio over WIFI

Gene Heskett gheskett at wdtv.com
Sun Jan 18 08:56:08 UTC 2015

On Saturday 17 January 2015 22:12:20 Ralf Mardorf did opine
And Gene did reply:
> On Sat, 17 Jan 2015 22:02:58 -0500, Gene Heskett wrote:
> > Biggest problem with the electret was the 2nd harmonic distortion
> > when driven to higher levels.
> Pff, are you serious? Or you just talking about one special capacitor
> microphone?

Any of them unless they are built with matching but reversed biased from 
side to side stationary plates.  The capacitance between 2 objects has a 
square-law relationship when the distance is varied.  Since its a 
difficult problem trying to drive the central plate, the diaphragm, the 
movable by air pressure plate when its in close proximity to a stationary 
plate on both sides, they are are built only with a stationary back plate.  
As long as the spacing variation is a small fraction of the overall 
spacing, its not too bad, and has even been compensated for by using a FET 
preamp with the correct bias etc to introduce a compensating 2nd harmonic 
of the opposite polarity.

The electret condenser type has a huge advantage in this case because they 
contain their own permanent charge, and its a quite high voltage, so the 
spacing can get sloppily large (= cheap to make) and still have adequate 
output to drive the FET buffer in it at quite low distortion.  Radio Shack 
used to sell, for a tenner, a pencil mike that ran the FET on a pair of 
AAA cells, and it was pretty darned good for a 10 dollar mic.  Way the 
heck and gone better than the $60 Shure clones they had at the same time.

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Cheers, Gene Heskett
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US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

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