pressure gradient receiver
A pressure gradient receiver is a principle of microphones in which the pressure difference in front of and behind the microphone causes the diaphragm deflection. The housing of the pressure gradient receiver is open at the rear, allowing sound to strike the diaphragm from the front and from behind.
Sound hitting the diaphragm from the front causes a higher diaphragm deflection than sound hitting the diaphragm from the side. The same applies to sound striking the diaphragm from behind, which is exposed to sound from both sides. The diaphragm displacement is proportional to the sound velocity. For this reason, such microphones are also called high-speed microphones.
In an ideal pressure gradient receiver, the directional characteristic is octagonal, since the sound pressure produces the same, but opposite, effect on both sides of the diaphragm.
By constructive measures, other, kidney-shaped directional characteristics can be generated from the figure-of-eight characteristic by means of delay elements. In addition to the principle of the pressure gradient receiver, there is also that of the pressure transducer. Condenser microphones, moving coil microphones and ribbon microphones can be used in both techniques.