Locally reactivity analysis of multi chambers acoustic mufflers with microperforated tubes
Fernando Henrique Nardelli1; Arcanjo Lenzi2
1 Federal University of Santa Catarina; 2 Federal Univesity of Santa Catarina
doi:10.20906/CPS/COB-2015-2232
Resumo
Dah-You Maa (1975) proposed a model of panel absorber, where perforations reduce to submillimeter range and perforations ratio about 1%. This model includes satisfactory acoustic resistance, sufficiently low acoustic mass reactance, and substantial sound absorption. A muffler based on this theory consists of a microperforated tube backed by a number of cavities. A simplified Finite Element Method (FEM) model could be used, e.g. modeling microperforations and cavities with combined impedance, considering locally reactive cavities. If this assumption is not valid more comprehensive FEM models are required. These models incorporate the main duct and the cavities, i.e. transfer admittance matrixes are introduced to couple the main duct and the cavities. This paper aims to study the width of muffler cavities, to understand the behavior of local reactivity, and to establish a relation between the length of the cavity and the wavelength corresponding to the highest frequency of interest. The developed algorithm will be validated with the Cremer optimum impedance theory, e.g. with an example of an optimum locally reactive filter.
Palavras-chave: Microperforated muffler; Transmission Loss