Measurement of Absorption Coefficient of Road Surfaces Using Impedance Tube Method

Abstract

The absorption coefficient of dense and porous road surfaces has been measured using core samples with 4 and 6-inch diameter impedance tubes. The 6-inch tube allows the absorption of a large core sample surface to be determined, but only up to a frequency of about 1250 Hz. The 4-inch tube allows the absorption coefficient to be determined up to a frequency of about 1950 Hz. The two different diameter impedance tubes were also mounted vertically on road surfaces of the same pavement types and the absorption coefficient of these surfaces was measured in situ. The peak sound absorption coefficient of the fine and coarse mix aggregate porous surfaces shows that is it only slightly different for the two types of porous surface. The fine mix aggregate porous surface is smoother and its acoustical performance is also preferable. It is also preferable since its use also results in less tire tread impact noise and thus lower overall tire-road noise than a coarse aggregate surface.