Sound absorption measurements of some porous loose granular materials

This work deals with the study of the basic acoustic properties of five expanded loose granular materials (cork , perlite, clay, vermiculite and glass) as a function of granular size distributions and thickness.Direct measurements of the normal incidence sound absorption coefficient were conducted in the impedance tube based on the transfer method.In addition numerical inverse estimation of the main quantities involved in most outstanding acoustic models of porous materials (b. e. flow resistivity, tortuosity and porosity) was performed using constrained global algorithms such as Differential Evolution, Nelder Mead and Simulated Annealing. For a given grains size, results show that the expanded perlite and glass exhibit the best absorption performances.