A laboratory method for measuring out-of-plane scattering coefficients of wall surfaces in two-dimensional sound field

Hyojin Lee, Tsuyoshi Seike, Tetsuya Sakuma
2016 Acoustical Science and Technology  
Introduction In architectural spaces, a variety of diffusers are frequently applied to wall surfaces for reducing echoes and promoting spaciousness. As one of the indices to evaluate scattering characteristics of surfaces, the scattering coefficient, which is defined as the ratio of non-specularly reflected energy to totally reflected energy [1,2], was proposed, and a reverberation room method was standardized in ISO 17497-1 [3] on account of its powerful process for direct determination of
more » ... e-dimensional random-incidence coefficients. In order to enhance the accuracy of geometric room acoustics simulation, the random-incidence coefficients are currently incorporated into some commercial software programs. However, in practical room acoustics design, one-dimensional rough surfaces such as ribbed or corrugated walls are often used, which have strong dependence of incidence angle on scattering coefficient. Recently, the authors proposed a laboratory method for measuring normal-incidence scattering coefficients in a rectangular room, where a quasi-one-dimensional sound field is generated between the floor and ceiling by installing highly absorptive sidewalls [4]. The normal-incidence coefficients of a test sample mounted on the entire floor are estimated by measuring the changes of reverberation time with and without the sample. Through scale model measurements, the validity of the method was confirmed in comparison with theoretical and numerical results. In this paper, as an extension of the above method for normal-incidence coefficients, a new laboratory method is proposed for measuring a scattering property of surfaces in a quasi-two-dimensional sound field, which is named out-ofplane scattering coefficient. It should be noted that the new index is equivalent to the ratio of scattered energy out of the two-dimensional field to totally reflected energy, and not in accordance with the original definition of scattering coefficient. Considering that ordinary rooms with absorptive floor and ceiling have quasi-two-dimensional sound fields, the index will be useful to evaluate the scattering performance of wall surfaces in such cases, and is also required for theoretical
doi:10.1250/ast.37.42 fatcat:djxk2kp34ng3fjku43tx4dyoeu