[ProAudio] Microphones question

[Scott Dorsey]

Oh, we can measure the microphones and plenty of folks do.  But if you
do that, you'll find a huge range of values.  

If I were wanting to give a number on the datasheet, I'd want to do it
with a 50 ohm source impedance or maybe even a 22 ohm source impedance
because that is a reasonable reflection of a typical modern condenser
microphone.  Since most of the cases where people are dealing with low
volume sound sources are using condenser microphones, that would seem 
appropriate.

On the other hand, you could make the argument that your reference 
source impedance should be about 3k ohms, because that's about the 
impedance of an RCA ribbon microphone.  Since ribbon microphones have
very low output, most of the cases where the primary noise source is
the mike preamp are cases involving ribbon microphones.  So that would
also seem appropriate.

Seeing that these are both perfectly appropriate ways to measure noise
because they both apply well in the cases where noise is a problem, I
think it might be best to split the difference and pick something around
150 ohms or so to model both cases somewhat.
--scott