Acoustics: Sound Fields, Transducers and Vibration, 2nd Edition

5.9. Dual-diaphragm combination of pressure and pressure-gradient microphones

A versatile microphone that is popular in recording studios and for recording ensembles on location is the dual-diaphragm variable-pattern capacitor microphone, the schematic of which is shown in Fig. 5.31. It has two diaphragms: one mounted in front (F) of and the other mounted at the back (B) of a common central plate (P). An array of holes in the central plate provides a mixture of resistance and reactance. When the slider of the potentiometer is at position “k,” the polarizing voltages on both diaphragms are equal so that they behave like a pair of back-to-back pressure microphones. Hence the resulting directivity pattern is omnidirectional. The low compliance ...