# Statistical guideline factor

The statistical directivity factor st (gamma) (also called directivity deviation factor or statistical directional factor ) is one of the variables used in acoustics to describe the directional characteristic of a sound source . It is defined as the ratio of the effective value of the sound pressure in a certain direction of radiation and distance to the effective value of the sound pressure averaged over all radiation directions at the same distance: ${\ displaystyle \ Gamma}$${\ displaystyle (\ varphi, \ theta)}$

${\ displaystyle \ Gamma _ {st} = {\ frac {{\ tilde {p}} (\ varphi, \ theta)} {\ sqrt {\ frac {} {{\ tilde {p}} ^ {2} ( \ varphi, \ theta)}}}}}$.

The statistical directivity factor is therefore dependent on the direction of radiation, values> 1 stand for preferred radiation directions.

In an analogous manner, receivers for sound such. B. microphones , specify a statistical directivity factor.

The degree of directivity is the square of the statistical directivity factor, the directivity or directivity is the corresponding dimension with the auxiliary unit of measurement decibel :

${\ displaystyle G = 20 \ lg \ Gamma _ {st} \; \ mathrm {dB}.}$