Recent research has revealed that granular material, in addition to its sound absorption
properties, also exhibits unexpectedly high sound insulation that surpasses theoretical
predictions based on the mass law. Promising preliminary results call for further systematic experimental investigations. The findings of these studies will contribute to the development of the theoretical framework for a new physical model of sound insulation in granular materials.
In the final project, we determined the frequency dependence of the absorption coefficient
and sound insulation with respect to granule size. Within the scope of the project, we
prepared various samples of granular material through sieving, which were placed in 3D printed test tubes for measurements in a flat sound field. The first test tube had a highly porous termination on one side, while the second one was sealed with PVC film on both sides. In addition to sieved sand, we also examined the acoustic properties of polystyrene and polymer granules. Measurements were conducted using the impulse response method.
Experimental results were evaluated and analyzed using basic statistical methods. The
project's conclusion, based on the results, confirms the hypothesis that fine-grained granular material exhibits unexpectedly high sound insulation, which is independent of the absorption coefficient. This allows for the arbitrary adjustment of absorption or sound insulation, and partially their combination, in acoustic elements based on granular material.
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