Computation of Spherical Harmonics Based Sound Source Directivity Models from Sparse Measurement Data

Jens Ahrens, Stefan Bilbao

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Models of sound source directivity that are based on spherical harmonics have been applied in diverse scenarios including wave-based room acoustic simulation, spatial audio, and urban sound propagation. The measurement of directivities of real-world sound sources that are not electroacoustic transducers exhibits fundamental limitations in terms of the accuracy and spatial resolution than can be achieved. Particularly if the directivity is measured only in a plane or over a limited solid angle range, a classical spherical harmonic representation cannot be computed. In many cases it is also such that angle-dependent directivity data are available only at a sparse set of frequencies. We demonstrate in this paper that complete spherical-harmonics-based directivity models can be obtained from such sparse measurement data by interpolating the available data over both the angle and the frequency and then imposing the result onto a spherical wave. We present results based on publicly available directivity data for the human voice as well as for directivity data in the Common Loudspeaker Format. The presented directivity models are available for download.
Original languageEnglish
Title of host publicationForum Acusticum
Place of PublicationLyon, France
Number of pages8
Publication statusPublished - 27 May 2021


  • directivity
  • spherical harmonics
  • room simulation
  • FDTD


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