Klaus you wrote:" In cardioid, a small amount of rear side voltage is added out of phase, in an attempt to mitigate the perceived shortcomings of the relatively wide acoustic cardioid pattern of the K49 capsule."
It is the opposite. The pattern of the K49 when only used on one side is a cardioid with a tendency to super-cardioid in the higher regions, and to make the narrow pattern more wide, a positive charge is put on the backside of the capsule.
SFN
I quote Mr. Martin Schneider from Neumann:
The standard K47/49, just like the M7 is an in-between capsule. Cardioid somewhere below 1kHz, super/hypercardioid the higher you go. That's the way the capsule came out of the design process in 1935. And that's why the manual for U47fet said 'supercardioid'.
Thus, the M147 has the polar pattern of a U47 or U47fet, tendency towards super/hypercardioid, as there's no polarisation voltage on the rear half.
In the M149, when set to cardioid, we put some volts on the rear half, so the setting 'cardioid' does mean 'best possible cardioid for this capsule', and does NOT mean 'zero volts on the rear'.
For 'zero volts on the rear' in the M149 you have to select the intermediate setting between cardioid and hypercardioid.
Note: The M49 had a potentiometer. There, 'cardioid' meant 'zero volts'. Interestingly, to my knowledge, the M49s were mostly used not at 'zero volts' but at 'best cardioid' setting. Some users even made marks on the potentiometer at 'best cardioid' setting. That's why we chose the above approach with M149.
Best regards, Martin Schneider Neumann Mic. Development