Measuring oblique incidence sound absorption using a local plane wave assumption

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In this paper a method for the measurement of the oblique incidence sound absorption coefficient is presented. It is based on a local field assumption, in which the acoustic field is locally approximated by one incident- and one specularly reflected plane wave. The amplitudes of these waves can be determined with an unidirectional sound intensity probe. The local active- and incident acoustic intensity are straightforwardly obtained. The area-averaged sound absorption coefficient is calculated after spatial integration of these quantities over the surface area of interest. Alternatively, one may use a three-dimensional intensity probe. In that case, the determination of the amplitudes of the plane waves can be formulated as a least-squares problem. Measurements performed for a sound absorbing foam demonstrate that accurate results can be obtained, even under non-ideal acoustic conditions. Measurements carried out for a periodic absorber show that the method is accurate below the cut-on frequency of scattering as long as the amplitude of the evanescent surface waves is significantly smaller than that of the specularly reflected wave.
Original languageEnglish
Pages (from-to)205-214
JournalAcustica united with Acta Acustica
Publication statusPublished - 2014


  • IR-94383
  • METIS-297481


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