The directivity factor (DRF) is a dimensionless characteristic value of loudspeakers and microphones, which is specified in gamma (`gamma`). It is a measure for the ratio of a certain radiation characteristic to a spherical sound radiation.
The same applies to the sound pickup of microphones. Here, the sound pickup of a microphone with a certain directional characteristic is set in relation to the sound pickup of a microphone with an omnidirectional characteristic.
As a result, the directivity is a dimensionless value and must always be >1, since all radiation patterns and directional patterns have a more bundled sound radiation or sound pickup than an omnidirectional one. The directivity is calculated from the reciprocal of the REE value(Random Energy Efficiency) and, depending on the polar pattern, is 1 for the omnidirectional pattern, 1.7 for the cardioid, 1.9 for the supercardioid, 2 for the wide cardioid and 3 for the hypercardioid.