Report of Committee on Sound-Absorption Measurements

Abstract

The Acoustical Society Committee on Sound Absorption presents a report for the information of the members of the Society. After preliminary experiments on a variety of materials, using different methods, a plan was evolved by which each of the various laboratories would be furnished a sample of the same material, with the expectation that the results obtained would be more strictly comparable than the data for different samples. The Celotex Company volunteered to make up a special run of BBB Celotex and furnish it gratis to the laboratories. The results of this experiment are shown (lantern slides) and exhibit a wide variation in the values of the coefficients. The reverberation method was used in all the tests, but there was considerable difference in the electrical instruments used. One chief reason for the variation in results was found in effect of area of material used; for instance for the frequency of 500 cycles per second, 12 sq. ft. of material gave a coefficient of 1.55, where 192 sq. ft. gave 0.44. No standard method is approved at the present time, but certain recommendations have been adopted for guidance in absorption tests. In the meantime, several different methods are being investigated, with the expectation that a solution of the present difficulties will be found.