Doughnut-Shaped Directional Pattern Microphone

This paper shows that a microphone with a doughnut-shaped directional pattern, omni-directional in the horizontal plane and bidirectional in the vertical plane, can be made by combining two bidirectional microphones via 90-degree phase difference networks. In this paper, deviations from the doughnut-shaped directional pattern caused by incorrectness in sensitivities, directivities, directions of the principal axes, and positions of the two microphones, and the angle of the phase-difference networks are discussed.

Experimental microphones are constructed of two ribbon microphones. This type of microphone has no sensitivity in the upward and downward directions, so that it does not collect reflected sound from the ceiling, paper noise on the table, and ventilation noise. Moreover, the microphone collects voices of all the participants in a discussion equally, and so is suitable for picking up sounds during group discussions.