[BC] Mic impedance question...

[mark at shander.com]

On Feb 7, 2012, at 8:32 AM, RichardBJohnson at comcast.net wrote:

> Many microphones, all the dynamic ones including ribbon microphones, and capacitor microphones as well have a basic frequency response that rises 6 dB per octave. This is because the voltage output of these devices depends upon the rate-of-change of the input audio. Since the rate-of-change of a 2 kHz signal is twice that of a 1 kHz signal, the output of the active element will be twice that of 1 kHz when a 2 kHz signal is received.
> 
> To compensate for this, there is normally an inductance placed between the microphone element and its load. This will produce a compensating 6 dB per octave reduction in frequency response. The inductance is normally the leakage inductance of the microphone's built in transformer. When the microphone is loaded with its designed load impedance, the two frequency-response deltas cancel and one has a reasonable flat frequency response within a specified range.
> 
> Capacitor microphones also have an increase in output with frequency. However, they normally have a built-in preamplifier with the required compensating frequency response. Such microphones may operate into any reasonable impedance although the impedance specified in its data-sheet will usually produce the best overall results.

And don't lift ground and try to stay with balanced cables.

I would argue that tonal characteristics of certain mics, and the actual sound it produces, is more important than the technical architecture.  The reason I say this is that there are may mics that are not optimized regarding technical design that sound competitive with those that are. 

That being said, I was able to tweak a $60 dynamic RS mic in the 80's and, using processing, make it competitive in terms of "fat sound" with a Shure SM-7.  In fact, you can occasionally find  transformer-less (modded) 55's that compare to SM7's....