Foliar Sound Absorption Capacities of Tree Leaves by Impedance Tube Method

Abstract

 The sound absorption coefficients of substances are measured using a variety of methods. Sound absorption coefficients are often tested with expensive tools and absorption coefficients are calculated. The current study uses an impedance tube, function generator, standard audio amplifier, omnidirectional microphone, and oscilloscope to calculate sound absorption ratios of leaves from several tree species. In a closed system, a sound absorption ratio was developed to evaluate sound absorption on a relative scale. Sabine's formula was used to compute the sound absorption ratio, and the absorption ratio was calculated. When the sound absorption ratio approaches unity, it implies that the sound absorption capacity is poor. The sound absorption ratio of different tree species' leaves was investigated for different frequencies. Observations were done using an oscilloscope connected to a long impedance tube and a speaker. A range of 500Hz–1000Hz was chosen as the operating frequency for reverberation testing and sound absorption testing when constructing the tube.  The leaves of several plant species showed varying absorption at different frequencies. It was observed that leaves of  Barringtonia acutangula Goerb, Eucalyptus globulus Labill, Ficus benghalensis L, Ficus glomerata Roxb, Ficus religiosa L, Mangifera indica L, Polyatlhia longifolia Thev, Sterculia urens L and Thespesia populnea Soland are good at sound absorption. The method is relatively inexpensive and easy to use to measure sound absorption of foliar surfaces.