3. Microphone fundamentals 3.1 Pressure transducers Only the front face of a pressure transducer is exposed to the sound field. The diaphragm responds equally to all sound pressure fluctuations occurring at its surface, regardless of the direction from which the sound waves emanate. Pressure transducers thus have no directional characteristic, and are by nature “omnidirectional”. 3.2 Pressure gradient transducers These microphones have a figure-8 directional pattern along the longitudinal axis. They respond to the momentary sound pressure difference occurring between two points A and B, which are a slight distance apart in the sound field. In the arrangement shown in Fig. 1, sound waves from 0° and 180° produce the largest difference in sound pressure and are received most strongly. By contrast, the sound arriving from 90° is received simultaneously and at the same strength at A and B, and thus produces no pressure difference. The field transmission factor TF or sensitivity of such microphones conforms to the rule: TF = TFo · cos
TFo = field transmission factor (sensitivity) with sound arriving perpendicularly to the diaphragm. = angle between the perpendicular to the diaphragm and the direction of sound incidence.
Fig. 1 Figure-8 characteristic
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