Sound Absorption Coefficient of Glass Wool

Abstract

This article presents the results of an investigation into the relation between the normal incident sound absorption coefficient and the apparent density of glass wool boards used as a sound absorbent.(1) Only one kind of glass wool boards 64kg/m3 in apparent density and 2.5cm in thickness out of 20 kinds made by 3 manufacturers has given a sound absorption characteristic belonging to the mixed type. The sound absorption characteristics of the other kinds of glass wool boards have been shown by experiment to belong to the viscosity-resistance type.(2) The relation between effective apparent density Dea (kg/m3) at which a glass wool board gives 1.00 in sound absorption coefficient and the thickness T (cm) is: Dea; =aT-b where a and b are constants fixed by the manufacturer.(3) The relation among apparent density Da (kg/m3), thickness T (cm), distance d (cm) between the center of a sample and the rigid wall, and frequency f0; at which the sample gives the maximum sound absorption coefficient is expressed by the following empirical formula: f0; =(c/4-αDβa; •T)d-1 where α and β are constants and c is the speed of sound.