Characterization of acoustic materials at arbitrary incidence angle using sound field synthesis

Abstract

Standardized methods for measuring sound absorption such as the impedance tube and reverberation chamber methods are limited to normal or diffuse incidence, respectively. Two research axes have been generally followed in the literature to develop alternative techniques, the first one focusing on the measurement part, that is from the two-microphone technique to the use of microphone arrays or pressure-velocity sensors. The second axis focuses on the excitation part with for instance the use of sound field synthesis techniques. Since acoustic impedance and sound absorption coefficient of materials are classically defined under normal and oblique plane wave excitation, synthesizing an “ideal” plane wave using a loudspeaker array would allow measuring these acoustics quantities using a simple microphone pair. In this article, the effect of the different parameters of a loudspeaker array on acoustic plane waves reproduction on a material’s surface is first numerically studied. Then, numerical and experimental results for the estimation of both impedance and absorption coefficients are reported. These results show that sound field synthesis allows to characterize a material for arbitrary incidence angles over a wide frequency range, thus offering an alternative method to standard techniques and an improvement over existing works.

Estimation of acoustical materials sound absorption coefficient under oblique incidence plane wave and diffuse field via Allard model inversion

“…2. Once the complex effective density and the complex wave number are obtained, it is possible to estimate the acoustic absorption coefficient for any angle of incidence for a plane wave, or under diffuse field by summation over the elevation angles (in the case of isotropic materials) and to even vary the maximum incidence angle in the computation of α ω d ( ) , as in Dupont et al 48 3. The low frequency limitations for this method are pushed back to a frequency as low as 100 Hz, and even if the identification of the two complex parameters is sometimes imperfect, the estimation of the sound absorption coefficient is relatively unaffected by these imprecisions (especially for the diffuse acoustic field case).…”

“…45,46 A single loudspeaker was moved at discrete positions above the material to define a virtual array at a post-processing step in Robin et al, 45,46 and the sound absorption coefficient was estimated under a synthesized diffuse acoustic field (the sound field is virtually achieved at a post-processing step, whence the term synthesized). Dupont et al 47,48 extended previous works, by using a 64-loudspeaker array to estimate the surface impedance and the sound absorption under plane waves with variable incidence angle, 47 and the diffuse field sound absorption coefficient was derived following Paris formula using angle-dependent sound absorption coefficients. 48 In Dupont et al, 47,48 the sound field was reproduced using a physical loudspeaker array.…”

Vibroacoustic analysis of multi-layered micro-perforated plates coupled to an acoustic enclosure

“…Although MPPs perform well as sound absorbers, they are inadequate for STL. When compared to a plate of the same thickness, the STL of an MPP is lower as shown by Chen 26 and Dupont et al 27…”

“…Although MPPs perform well as sound absorbers, they are inadequate for STL. When compared to a plate of the same thickness, the STL of an MPP is lower as shown by Chen 26 and Dupont et al 27 Currently, researchers are now considering MPP and sandwich panel combinations for STL and SAC. Perforated sandwich panel face plates can absorb sound, while back plates can function as noise barriers.…”

“…Perforated sandwich panel face plates can absorb sound, while back plates can function as noise barriers. The acoustic performance of an MPP-air cavity-plate coupled system was initially analyzed analytically and experimentally by Dupont et al 27 It was discovered that the STL could be increased with a good SAC. Honeycomb structures were inserted into the air cavity of the system by Toyoda and Takahashi 28 to enhance the STL at medium frequencies.…”