Improved Pressure‐Gradient Noise‐Canceling Microphone

A miniature pressure‐gradient microphone exhibits improved noise discrimination and extended crossover frequency. Ability of a cosine pressure‐gradient microphone to discriminate against the pickup of unwanted noise is known to be limited by the acoustical pathlength between the two sound entrance points in front and back of the diaphragm. Noise discrimination is further limited by unwanted phase shifts occurring in the acoustical treatment surrounding the diaphragm. A miniature, efficient magnetic transducer actuated by a slender drive pin connected to a pressure‐gradient diaphragm permits a reduction of diaphragm size with corresponding decrease of front‐to‐back distance. Added symmetrical acoustical networks avoid differential phase shifts. Further enhancement of noise discrimination stems from a mechanically balanced system that diminishes sensitivity to mechanical vibration. Prototypes exhibit noise discrimination of 40 dB at 200 cps and a crossover frequency above 5 kc/sec. [This work was supported ...