The extinction of sound in a viscous atmosphere by small obstacles of cylindrical and spherical form

Abstract

Abstract The results obtained in this paper are only valid when the dimensions of the obstacles are small compared with the wave-length of the incident sound. For cylinders and spheres whose radius is not less than 10-3 cm. it is found that the ratio of the lost energy to that incident upon the obstacle is at most of order 10-2; this is a very much larger proportion than is obtained in the case of a non-viscous air. The results obtained for a single obstacle are extended without difficulty to the case of a large number of obstacles. This extension is valid only when the space occupied by the obstacles is small compared with the total volume. It appears in the case of spherical obstacles, that, if each small obstacle has radius 10-3 cm., and there are 106 of them per cubic centimetre, then sound of wave-length 50 cm. will have its intensity diminished in the ratio 1: e after passing through a thickness of less than 12 cm. of such a medium.