A non-directional microphone

A moving coil microphone is described which responds uniformly over a wide frequency range to sound arriving from any direction. A study of diffraction, the main factor causing directivity of microphones of the pressure type, leads to the conclusion that a small spherical shape is the most desirable for a non-directional microphone. But even fulfilling this requirement in the design of the housing leaves a large directional effect. Hence an acoustic screen has been developed which diminishes diffraction to an extent necessary to make the change in response due to angle of sound incidence imperceptible to the ear. The non-directional microphone is of simple and rugged construction. Adequate precautions have been taken to prevent atmospheric changes from affecting the stability. The small size and unusual shape of the microphone contribute much to its attractive appearance.