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I am tring to find out any information about resistance related to matching microphones to preamps. Is the performance of the mic and pre "system" dictated by numbers or are my ears the only true judge? I was told once that lower mic and pre ohms will yield a fuller bass response (this was in regards to my EV PL20 set at 50 ohms run through an Altec 438c on bass) , true or bullshit?
Do high impedence microphones sound different than low impedence microphones when they are matched with different preamps?
Do dynamic, velocity and condenser mics have different frequency charatceristics at different ohm matches?
One more question, I have an STC 4038 original not the Coles model. I thought all the STC'c were 30 ohms, however on the back of mine there is a small badge that says 300 ohms. Were some of the STC's 300 ohms or is it possible it was modified at some point? How can I test the microphone's ohms to verify what is on the back of the microphone?
Any information would be appreciated.

Hi Champ,
a microphone's frequency response is altered by changes in it's mic preamp's input impedance.
Richard E. Werner showed that 1955 in his AES journal article "ON ELECTRICAL LOADING OF MICROPHONES". (AES Journal, vol.3, no. 5pp. 194-197, 1955). There is a summary of it in the AEA's Ribbon mic essays "Facts and Fables" , www.wesdooley.com . This is where I got my info from.

Werner measured how a mic's output impedance vs. frequency interacted with the input impedance vs. frequency of different mic preamps.

The lower impedance a mic must drive, the harder it has to work. Too low an impedance loading a mic is heard as increased distortion and decreased headroom.
Changign the turns ratio (impedance transformation) and secondary loading of a good transformer being driven by a microphone will change a mic's sound on transients from dull to open to ringing.
My Sennheiser MKH 30, 1000 ohms high impedance, tranformerless mic sounds like shit on a low impedance transformer coupled mic pre. It's overloading and distorting.
The general rule is that the load impedance a mic sees should be five or more times the mic's own source.
That would translate to 1,500 ohms for your STC 4038 300 ohm mic.
Some mic preamps have a switch to optimize the match between a mic's output impedance and the mic preamps input transformers.

Werner wrote his article in 1955 so I guess he was talking about transformer coupled pre amps only.
I hope this hepls.
Best, Max