Average Speech Directivity

Document Type

Voice and Speech Directivity

Publication Date



The directivity function of human speech describes the angular dependence of acoustic radiation from and diffraction about a talker and a talker’s chair (if seated). It is an essential physical aspect of communication that affects sounds and signals in acoustical environments, audio, and telecommunication systems. Because high-resolution, spherically comprehensive measurements of live, phonetically balanced speech have been unavailable in the past, the authors have undertaken research to produce and share such data for simulations of acoustical environments, optimizations of microphone placements, speech studies, and other applications. The presented data were acquired from and averaged across three male and three female talkers who repeated phonetically balanced passages in an anechoic chamber. Each was seated on a chair connected to a subject-rotation system, with his or her mouth at the circular center of a 1.22 m-radius, semi-circular array of 37 microphones having Δ𝜃 = 5° polar-angle increments. The mouth axis was aligned toward 𝜃 = 90° in the polar angle (0° elevation) and ϕ = 0° in the azimuthal angle. Azimuthal rotations progressed in Δϕ = 5° increments, meaning data were acquired at 2,522 unique positions over the measurement sphere. They were likewise acquired at three positions within the rotating reference frame for subsequent signal processing. Several steps mitigated the effects of repeated speech variations. The directivities derived from transfer functions and other measurement calculations. The results are available under Additional Files, which may be updated periodically.


While higher resolutions also derive from the raw measurement data, the files presented here are in third-octave bands from 100 Hz to 10 kHz and based on degree-10 spherical harmonic expansions. The coefficients were derived using a least-squares approximation. The directivities have been symmetrized about the median plane in the spherical-harmonics domain, effectively doubling the number of subject averages. The continuous expansions were resampled, such that the mouth axis falls at 𝜃 = 0° and ϕ = 0° angles in the files. The poles were thus rotated by 90° so that the original zenith falls at (𝜃, ϕ) = (90°, 0°) and the original nadir falls at (𝜃, ϕ) = (90°, 180°). The CSV file provides results in generic format, organized by third-octave bands. Columns represent the 37 polar sampling angles, while rows represent the 72 azimuthal sampling angles, all with 5-degree increments. The GLL file may be opened using the AFMG EASE GLL Viewer, currently available at The MP4 file is an animation of the directivity balloons rotating 360 degrees for each third-octave band within the original coordinate system. As indicated earlier, these data should be useful for many applications and are presented here for general usage. The authors request that the work be cited as suggested under Recommended Citation.

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