Abstract
This paper proposes a method for estimating the angle-dependent sound absorption coefficient of a large material sample using a compact microphone array. The method relies on the description of the pressure field as a pair of in-going and out-going waves or using an image source model and stands as a generalization of the classical two-microphone method. The array includes an irregular spacing normal to the surface to avoid spatial aliasing. Furthermore, the benefit of additional microphones parallel to the sample is investigated, while keeping the array compact. The approach is validated against the transfer matrix method as well as against locally and non-locally reactive surface models and compared to the two-microphone method. The sensitivity of the estimation to uncertainties in the microphone positions is evaluated by means of a Monte Carlo approach. Measurements above melamine foam and gravel samples are presented and illustrate the reduced uncertainty in the sound absorption estimation. In particular, the proposed method exhibits improved robustness compared to the two-microphone method, especially at low frequencies.
Highlights
This paper proposes a method for estimating the angle-dependent sound absorption coefficient of a large material sample using a compact microphone array
The method relies on a wave splitting (WS) technique where the acoustic field is modeled as a superposition of incident and reflected plane waves above an infinite plane and assuming specular reflection
The method is suitable for the in situ acoustic characterization of sufficiently large planar surfaces for which sample size effects occur at frequencies below the range of interest
Summary
B) at: DMMS core lab, Flanders Make, Gaston Geenslaan 8, 3001 Heverlee, Belgium. 8% (ISO, 2014). With direct application to in situ acoustic characterization of porous asphalt, Bezemer-Krijnen et al (2014) presented a measurement technique to obtain the oblique-incidence sound absorption coefficient based on the local specular plane wave assumption. The method is suitable for the in situ acoustic characterization of sufficiently large planar surfaces for which sample size effects occur at frequencies below the range of interest In this paper, this effect is not accounted for in the sound absorption estimation. II introduces the analytical pressure field models used as the target for the validation of the proposed method
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