The accuracy of some models to predict the acoustical properties of granular media

There is a general lack of understanding on the accuracy of theoretical and empirical models which can be used to predict the acoustical properties of unsaturated granular media. It is also unclear how well these models are suited for parameter inversion in application to these media. In this work three popular prediction models available in commercial software packages, e.g. COMSOL Multiphysics, are used to invert key non-acoustical parameters of two types of glass beads and two fractions of silica sand for which acoustical data are obtained with a standard acoustic impedance tube setup. These results are compared against predictions made with four established non-acoustical analytical models which relate these characteristics to the effective particle size and other pore characteristics. A discrepancy between the two model classes (acoustical and non-acoustical models) and measured data is quantified. This work also quantifies the accuracy of acoustical characterisation methods used to estimate key pore characteristics of granular media with a relatively inexpensive laboratory setup and rapid inversion method based on optimisation.