Absorption of Sound wave by Fabrics

Abstract

The influence of the flow resistance of fabrics on their absorption characteristics has been investigated by measuring the flow resistance and the absorption characteristics. To deal with this subject from the point of view of the design and density of fabrics, we wove 13 different kinds of cotton fabrics as samples. The results obtained are as follows:(1) The relation between flow resistance Rf of fabrics and flow speed V can be given as follows: Rf=Ai+BiV where Ai and Bi are constants fixed by the design and density of a fabric. In a range of small densities, the value of Bi is nearly zero, while Ai and Bi increase together in value as the density of a fabric increases.(2) There are two types of absorbing mechanisms, the viscosity resistance type and the resonance type depending on the kinds of fabrics. A fabric is of the viscosity resistance type if its flow resistance depends only on air viscosity in a small range of flow speeds, namely, Rf=Ai.(3) A fabric is of the viscosity resistance type if it has an air space behind it, provided the relation among frequency f0, which shows the maximum absorption coefficient, depth d of the air space, and Rf can be given as follows: f0=(c/4-aRf)d-1 where c is the speed of a sound wave and a is a constant fixed by the design of the fabric. This empirical formula means that a fabric has the maximum absorption coefficient when it is placed at a shorter distance than the place where the particle velocity is a maximum.(4) The relation between maximum absorption coefficient α∞ and of Rf fabrics woven with the same design is: α∞=a'+a“ Rf where a' and a” are constants fixed by the design of the fabrics.