Unidirectional Microphone Utilizing a Variable Distance between the Front and Back of the Diaphragm

A unidirectional pressure‐gradient microphone is described which utilizes a front‐to‐back distance which varies approximately inversely as the frequency. The varying front‐to‐back relationship is achieved by utilizing two sound entrances with frequency discriminating parameters. One entrance is situated at a large distance from the front surface of the generating element while the other entrance is placed directly behind the sound responsive element. With this microphone desirable characteristics can be obtained which would not be possible in the conventional cardioid type having a fixed front to back distance. The principle of its operation is described and compared with that of the conventional fixed distance cardioid microphone.