Abstract
It has known that ballast for tracks has disposition of acoustic absorption, but absorption of granular material like ballast has not been estimated enough. This paper describes properties of acoustic absorption for granular structures. Selected measuring materials were bearing steal ball (φ3.0mm), plastic bullet (φ6.0mm), pachinko ball (φ11.0mm) and marble (φ15.7mm), in order to exclude heterogeneity of shape. The 2 microphone method was used to measure acoustic absorption coefficient. Influence of grain diameter, thickness of acoustic absorber and air layer were estimated. The result obtained that sound absorption coefficient is higher according as diameter of grains is smaller.
