Measurements of acoustic attenuation and velocity in sand

Although there is a considerable amount of published work on the velocity of sound in granular materials such as sand, little has been published on the acoustic absorption in such media. Experiments show that, whilst little difficulty is experienced in estimating velocity using quite small samples, the measurement of absorption is generally difficult and is best carried out in bulk media. In the author's laboratory an attempt has been made to measure sound absorption in small samples of granular materials under controlled conditions. The work has shown that there is a lower limit to the size of the sample for which reliable attenuation measurements can be obtained. In the case of sand the upper frequency limit of 73 kc/s has been set by attenuation whilst the lower 7 kc/s limit was due to the size of the sample. No velocity dispersion or variation of loss factor was found over the frequency range investigated.