Combined Pressure and Velocity Microphone

Figure 17. Illustrating the principles of operation of the Cardioid microphone. (Courtesy Western Electric Co.)

For the velocity microphone, however, sound waves from one direction cause a motion of the ribbon in one direction, and corresponding sound impulses from the opposite direction cause a motion in the opposite direction. The pressure or diaphragm-type microphone and the velocity or ribbon-type microphone can be used together to produce a highly directional sound pickup combination, as will now be explained.²²

If the coil of wire attached to the diaphragm shown in Fig. 17 is properly connected in series with the ribbon of this same illustration, then, for sound approaching from the front, the voltage outputs of

the two generating elements will add, but, for sound coming from the back, the two generated voltages will subtract. The result is a directional sensitivity pattern that is heart shaped.