Study of sound absorption using acoustic impedance tube

Abstract

This report presents an experimental study on sound absorption coefficient of micro-perforated plate by using the acoustic impedance tube. The large tube setup for the impedance tube was used in the experiment with a test frequency range of 50 Hz to 1.6 kHz. In this experiment, the effects of different perforation shape, the effects of different plate material, the effects of plate thickness and the effects of air cavity thickness were examined on how they would affect the sound absorption coefficient. A detailed study of micro-perforated plate absorber theory based on the principle of Helmholtz resonator was reviewed and formulae from a published journal were used in the theoretical calculation of sound absorption coefficient. The experimental results were used in comparison with the theoretical calculation. The plotted graphs showed reasonably good agreement between them. It was found that the thicker micro-perforated plates resulted in a lower value of sound absorption coefficient. It was also found that a micro-perforated plate backed by a larger air cavity makes it a better sound absorber than one without any air cavity backing. Discussions of the theoretical and experimental results, experimental setups and procedures, detailed drawings of the specimens are presented in this report.