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Re: HC selectivity ...

Hi Kevin,

It's not really a question of dynamic vs. condenser (or electret), it's a
question of velocity vs. pressure microphones. Ribbon microphones (as an
example) fall into the category of dynamic microphones, and their output is
proportional to the velocity of the pressure wave, as you were implying.
However, "normal" dynamic microphones (i.e. those with a diaphragm, enclosed
on one side) produce voltages proportional to the pressure itself, at least
over the design frequency range. Thus they're essentially the same as
condenser/electret microphones (it's just that condenser microphones work
over a more extended frequency range and have a better phase response).

Also, if you do get DC out of a condenser microphone, it's only because it's
broken! In fact, most condenser microphones require a decoupling capacitor
in the audio path to get rid of the DC bias applied to the "plates" of the
capacitor. This limits the low-frequency response, quite apart from any
other factors.

Steve Beet

" -----Original Message-----
" From: AUDITORY - Research in Auditory Perception 
" [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Kevin Austin
" Sent: 05 October 2007 10:04
" To: AUDITORY@xxxxxxxxxxxxxxx
" Subject: Re: HC selectivity ...
" Hi
" If I understand microphones, it may be necessary to revise the 
" statement below to read "dynamic microphones", as I believe the 
" statement is not correct regarding condenser (capacitor) mics, which 
" can output DC, and are 90 degrees out of phase with dynamic mics.
" Best
" Kevin
" Martin Braun <nombraun@xxxxxxxxx> wrote:
" >Microphones are pressure sensors, not displacement sensors.