Directivity Factor

directivity factor

[də‚rek′tiv·əd·ə ‚fak·tər]
(engineering acoustics)
The ratio of radiated sound intensity at a remote point on the principal axis of a loudspeaker or other transducer, to the average intensity of the sound transmitted through a sphere passing through the remote point and concentric with the transducer; the frequency must be stated.
The ratio of the square of the voltage produced by sound waves arriving parallel to the principal axis of a microphone or other receiving transducer, to the mean square of the voltage that would be produced if sound waves having the same frequency and mean-square pressure were arriving simultaneously from all directions with random phase; the frequency must be stated.

Directivity Factor


(1) For a transmitting antenna, a number indicating the factor by which the radiated power would have to be increased if the antenna were replaced by an isotropic radiator (assuming the same field intensity for the antenna and the isotropic radiator).

(2) For a receiving antenna, a number indicating the factor by which the input power of the receiver for the direction of maximum reception exceeds the mean power obtained by averaging the power received from all directions of reception (if the field intensity at the antenna location is equal for any direction of wave incidence).

The directivity factor is a quantitative characterization of the capacity of a transmitting antenna to concentrate the radiated energy in a given direction or the capacity of a receiving antenna to select signals incident from a given direction.


References in periodicals archive ?
i] = Surface area for the ith plenum wall Q = Directivity factor which is equals 2, 4, or 8 depending on whether the opening is at the center of the wall, a bihedral corner, or a trihedral corner respectively d = Slant distance between the inlet and exit [alpha] = Average sound absorption coefficient for the walls [[alpha]S.
Uncertainties of the measurement results obtained for each one-third-octave frequency band of measurement with the NIST system are shown for the directivity factor in Table 3, and for the directivity index in Table 4.
Directional response data used to determine the directivity factor and the directivity index are acquired with a standardized sampling method (15) that utilizes sound source locations distributed in a forty eight point semi-aligned zone array on an imaginary spherical surface surrounding the manikin.
Results obtained with the NIST system were compared with the reference values of the comparison by calculating normalized deviations for all 119 values of the directivity factor measured (seven directional response patterns as a function of seventeen frequency bands).

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