Yacoubou Salissou | Searcharxiv

arXiv2010

Evaluation of the acoustic and non-acoustic properties of sound absorbing materials using a three-microphone impedance tube

This paper presents a straightforward application of an indirect method based on a three-microphone impedance tube setup to determine the non-acoustic properties of a sound absorbing porous material. First, a three-microphone impedance tube technique is used to measure some acoustic properties of the material (i.e., sound absorption coefficient, sound transmission loss, effective density and effective bulk modulus) regarded here as an equivalent fluid. Second, an indirect characterization allows one to extract its non-acoustic properties (i.e., static airflow resistivity, tortuosity, viscous and thermal characteristic lengths) from the measured effective properties and the material open porosity. The procedure is applied to four different sound absorbing materials and results of the characterization are compared with existing direct and inverse methods. Predictions of the acoustic behavior using an equivalent fluid model and the found non-acoustic properties are in good agreement with impedance tube measurements.

physics.class-ph↗

arXiv2006

Comparison of Methods for Characterizing Sound Absorbing Materials

Sound absorbing materials are usually defined by five parameters: open porosity, static airflow resistivity, tortuosity, and two characteristic lengths. In recent decades, different methods have been developed in order to characterize these parameters. These methods may be divided following three approaches: i) inverse, ii) indirect and iii) direct. The inverse approach is based on an optimisation problem where the material parameters are adjusted in the acoustic model to reproduce acoustical measurements. The indirect approach is based on the acoustical model from which analytical expressions linking the material parameters to acoustical measurements are derived. Contrary to the previous two approaches, the direct approach is not based on acoustical measurements. It is based on the physical and mathematical definition of the parameters and requires dedicated equipments. In this study, the five parameters have been measured for different porous materials using some direct, indirect and inverse methods. A comparison of the different results is carried out, and shows that the different methods may yield large variability in the found parameters. A discussion is given to explain the observed variability and the limitations of the methods.

physics.class-ph↗