I bought a Shure Model 55 multi-impedance Unidyne microphone on Ebay
recently, intending to use it with my vintage ham radio equipment. The mic
is working, but the frequency response is clearly not what it should be.
There is little or no lower midrange/bass response. I have examined the mic
cartridge and it appears to be undamaged and the voice-coil moves freely.
My preamp does provide the proper impedance matching for the high output
impedance setting of the 55.

A friend of mine bought the same model a year ago and had exactly the same
problem with it. Is this typical of the Model 55, or are we both just
unlucky?

Plus, if anyone has any insights into how the cardioid pattern of this mic's
cartridge is obtained, I'd be very interested in hearing about it.
Visually, I don't see any of the trappings I associate with the usual
phasing approach to achieving a cardioid pattern with a moving-coil dynamic
element.

Any help or info will be much appreciated.

Thanks, Bruce AB7YD