The effect of consolidation on the acoustic properties of loose rubber granulates

Acoustic measurements performed on non-spherical granular mixtures with different states of consolidation suggest that their acoustic performance can be related to that measured in loose granular mixes. It was found that the non-acoustic parameters of the pore size distribution, porosity, tortuosity and flow resistivity are highly sensitive to the median grain size in the mix, the compaction ratio and the binder content. The effects of these parameters on the acoustic properties have been investigated for a number of loose and consolidated samples with different grain sizes. Several established models for the acoustic properties of rigid-frame porous media have been tested. It is shown that some models can fail to predict accurately the acoustic properties of these materials and can require considerable adjustment of the input parameters. In this respect, the experimental results are of importance in the development of a scientific methodology for the design of granular absorbers with good acoustic efficiency and sound mechanical properties.