The modeling of sound absorption by flexible micro-perforated panels

Taewook Yoo, Purdue University

Abstract

In the work described in this thesis, the absorption performance of flexible micro-perforated panels with finite-depth air backing spaces has been studied experimentally and analytically. Perforated materials are relatively stiff and robust compared to fibrous materials from a structural point-of-view and can perform as well as fibrous materials in certain frequency ranges when combined with a finite-depth air backing. To predict the acoustical performance of perforated panels, several models were developed. The modeling effort was divided into two types, based on the assumed size of sample: finite or infinite. For the finite model, it is also divided into two parts: normal incidence in a duct, and arbitrary incidence angles in free space with an infinite array of finite-size, flexible micro-perforated panel with segmented and unsegmented backing spaces. For the infinite size sample, the Maa model, which is a well known theory for the impedance of rigid micro-perforated panels, was studied. Though the Maa model works reasonably well, the panel is assumed to be rigid in his model which can cause differences between measurements and predictions, especially for lightweight materials. In the experiments, the absorption coefficient and transmission loss of various samples were measured in an impedance tube. A model was developed for the finite-sized samples by making use of two frequency-dependent properties: the end correction and flow resistance. According to the results, the absorption performance of finite-size, perforated membranes can be tuned to a certain frequency range by adjusting hole size, number of holes per unit area, hole depth, mass per unit area of the material, flexural stiffness and size of the panel. The air backing depth is another important parameter determining the location of the absorption peak. As the backing space increases, the low frequency absorption increases. In the arbitrary incidence angle model, segmented and unsegmented backing spaces were studied and it was found that a segmented backing space generated a locally reacting field that causes higher absorption at lower frequencies. From the comparison between measurement and prediction, it was found that the predictions and measurements showed reasonable agreement.

Degree

Ph.D.

Advisors

Bolton, Purdue University.

Subject Area

Mechanical engineering

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