Abstract:

There are two well-known methods for the evaluation of absorption of a material. One is the acoustic tube method (normal incidence) and the other is the reverberation room method (random incidence). In a real situation, however, oblique-incidence absorption coefficients are required. For example, it is necessary to have knowledge of absorption coefficients for various angles in order to evaluate the effect of the road surface on traffic noise. In the previous paper [H. Suzuki et al., ASA-ASJ Third Joint Meeting, Honolulu, Hawaii, J. Acoust. Soc. Am. 100, 2588(A) (1996)], a method of using the sound intensity technique was proposed. An absorbing material was placed on the floor of a semi-anechoic room. A line source with 16 loudspeakers with 100 mm diameter was used in order to try to generate a uniform sound field in the direction normal to the incidence-reflection plane. Measured results showed some irregular changes as a function of frequency. One possible reason for this irregularity was that the multi-loudspeaker source had a more complex directivity near the main axis than a single loudspeaker source. Results obtained by use of the single loudspeaker source are presented in this paper.