For flat frequency responce moving coil microphones must have the diaphragm vibrating at constant velocity as frequency rises.
For flat frequency responce condencer, crystal and carbon microphones must have the amplitude of the diaphragm constant as frequency rises.
This is because moving coil microphones operate on the principle of magnetic induction, voltage is proportional to the rate of change of magnetic lines cut by a moving conductor.
Constant velocity means that as frequency rises the displacement of the diaphragm must be arranged to be progressively smaller.
So the reasonant frequency of the diaphragm on ribbon and cardioid moving coil microphones is placed at a low frequency. As we ride on the right of the curve of this reasonant frequency diaphragm excursion is reduced.
The reasonant frequency on pressure (omnidirectional) moving coil microphones is placed at mid band and it is damped.
The reasonant frequency on true directional condencer microphones is placed at mid band and it is
damped.
The reasonant frequency on pressure condencer and crystal microphones is placed at a high frequency.
Reference:
Microphones - Bore, Peus - Neumann - free PDF
Microphones - Borwick - Focal Press
Microphone Manual - Huber - Focal Press
Microphones - Lou Burroughs - Electro-Voice
Sound Recording Handbook - Woram - Sams.
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