Characteristics and functioning of membrane absorbers covered with micro-perforated panels
Rapport, 2007

The use of sound absorbers is a standard treatment in noise control engineering. Absorbers are available in a variety of basic configurations, e.g. membrane absorbers, porous absorbers, and micro perforated panels. There are also configurations that combine two or more of these basic configurations to achieve more efficient absorbers. This study focuses on the fundamental behaviour of an absorber configuration that is mounted in the sub-frame under the engine in a passenger car. This configuration consists of a plastic material forming closed volumes with a flexible membrane directed toward the incident sound field. These membrane absorbers are partly covered with a micro perforated plate that also covers regions without any membrane absorbers. Therefore, three different cases were analysed: the membrane absorber alone, the micro perforated panel alone, and the combination of both. Absorption coefficients were measured with the Kundt’s tube for a variety of conditions. The absorber configurations were studied with theoretical models and results from measurements and theory were compared giving good agreement. A parameter study was made to determine the most important parameters when optimizing the absorber configurations. Hence, calculations were done to study the influence of the characterising parameters such as size of the cubes, size of the micro holes of the perforated plate or the distance between them. In addition, since absorbers are commonly used in diffuse-like fields, the absorption coefficients for oblique incidence and diffuse fields were calculated.

Kundt's tube

coupled absorbers

micro-perforated panel

absorption coefficient

membrane absorber

vehicle acoustics

numerical models of absorbers


Franziska Möbius

Chalmers, Bygg- och miljöteknik, Teknisk akustik


Annan materialteknik

Strömningsmekanik och akustik

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