To produce the in-between polar patterns one could consider the omnidirectional
microphone where the diaphragm is open on one side only, and the figure-of-eight
microphone where the diaphragm is completely open on both sides.
Allowing partial access only to one side of the diaphragm would therefore seem
to be a viable means of producing the in-between patterns, and indeed it is.
A cardioid or hypercardioid mic therefore provides access to the rear of the
diaphragm through a carefully designed acoustic labyrinth.
Unfortunately the effect of the acoustic labyrinth is difficult to equalize
for all frequencies, therefore one would expect the polar response of cardioid
and hypercardioid microphones to be inferior to that of omnidirectional and