Propagation of sound through a series of contraction micro-tubes

Abstract

Ordinary fibrous material is mainly quantified by its density and the acoustic resistance is tightly coupled with other parameters, a feature which is not always desirable for every sound absorption task. This study investigates the acoustic property of a structure consisting of unit cells made by simple contraction tubes. Wave element method is used to simulate the property of a unit cell, and the equivalent fluid model is employed to calculate the performance of an absorber of finite thickness. The acoustic mass and resistance are controlled by the contraction ratio and the diameter of small tubes, respectively. In terms of the spectra of sound absorption, it is shown that the contraction ratio mainly controls the peak frequency of the absorption curve while the tube diameter influences the bandwidth of absorption. The performance of the finite absorber is compared with the usual layer of porous material, and the structure parameters are conveniently optimized for specified sound absorption tasks. A mul...