Use of Nonwovens of Variable Porosity as Noise Control Elements

Abstract

The optimal design of multilayer combinations of nonwoven fiberwebs is of prime importance in their applications as noise control elements. Such combinations can be simulated as a single layer with variable characteristics along the propagation of the sound wave. The paper examines the effect of variation of porosity on the sound absorption coefficients of three webs made of cotton, acrylic fibers and polyester. The numerical procedure is based upon our generalization of the C. Zwikker and C.W. Kosten theory on sound transfer through porous media reported elsewhere. We have considered four functional forms of the porosity: linear, quadratic, exponential and logarithmic. Our results clearly indicate that for all materials considered the logarithmic form yields the highest noise absorption coefficients for f=1000 Hz.