The capsule behaves as a variable capacitor, changing its capacitance in response to changes in air pressure (i.e. sound). In order to generate a signal, the capsule needs to be polarised by some voltage, creating a difference in potential between the diaphragm and the back plate. This is the first decision that needs to be made - should the polarising voltage be applied to the diaphragm or the capsule backplate?
An example of this arrangement may be seen in the Neumann Gefell M582.
In some cases the grid resistor may be omitted. In the circuit below, which appeared in an article in Tape Op magazine by Dave Royer, the capsule diaphragm is grounded by grid leakage rather than a 'real' resistor. It works perfectly.
This simple arrangement is not possible when the capsule backplate is mechanically (and electrically) connected to the body of the microphone. In this case the diaphragm must be polarised directly.
An example of this method of connection is the Neumann-Gefell CMV563, which is designed to be used with bayonette style capsules such as the M7, M8 and M9.
Sometimes it is the membrane which is connected directly to the body, such as in this Teladi K120. The approach is the same as the circuit above.
In my next post I'll consider how to connect mic capsules with two membranes, and how to combine them to generate different polar patterns.