Acoustic Absorption in Sand and Soil

The acoustic absorption properties of sand and soil with varying amounts of water, ranging from dry to saturated, have been investigated. In most of the work the frequency range was 10–30 kc, although data were obtained at as high as 150 kc. Two methods were used. In one, the source and a number of equally spaced probe microphones were imbedded in the medium. In the other method the source and receiver were in air and the transmission loss was determined for samples of varying thickness. The unsaturated media were found to have attenuation coefficients ranging from 2 db per cm for nodulous, loose soils to greater than 25 db per cm for finely divided soils and sand, the value for any particular sample depending in an important way on its flow resistance. In water‐saturated media the attentuation was found to depend markedly on the amount of gas present in the mixture. Air‐free mixtures prepared in an evacuated chamber had attenuation coefficients which were too small to be measurable—probably less than 2 db per cm. On the other hand, for mixtures prepared in the presence of air the attenuation coefficients immediately after mixing were extremely large. For one sample it ranged from 26 db per cm at 10 kc to 64 db per cm at 30 kc. When such a mixture is then left undisturbed the intensity level increases strikingly—as much as 50 db at 30 kc over a period of 100 hours.