Granular materials have been conventionally used for acoustic treatment due to their sound absorptive
and sound insulating properties. An emerging field is the study of the acoustical properties of
multiscale porous materials. An example of these is a granular material in which the particles are
porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical
properties of these materials are introduced. Image processing techniques have been employed to
estimate characteristic dimensions of the materials. The model predictions are compared with measurements
on expanded perlite and activated carbon showing satisfactory agreement. It is concluded
that a double porosity granular material exhibits greater low-frequency sound absorption at reduced
weight compared to a solid-grain granular material with similar mesoscopic characteristics