A Third-Order Pressure Gradient Microphone

A microphone has been constructed which exhibits the characteristics of a third-order pressure gradient microphone when tested objectively and subjectively. That is to say, the voltage output of the microphone is proportional to the third derivative of sound pressure incident upon the microphone with respect to the distance from the sound source. When used in high ambient noise levels it clearly exhibits more intelligible speech output than first-order gradient microphones. However, its noise discrimination at low frequencies is limited by noise conducted through the structure of the microphone. The microphone is of the magnetic armature type and employs a single diaphragm fed from an array of pressure pickup points. Considerable improvement in the signal-to-noise ratio may be obtained by talking into a selected position in this array instead of along the axis of the array.