Sound Fields within Aquaria

Abstract

Small aquaria are generally convenient for bioacoustic experiments. Sound introduced into such tanks is often measured with pressure-sensitive hydrophones. Unfortunately, sound in a small tank never propagates in a plane wave, and therefore pressure measurements can be highly misleading. The sound field also fails to resemble the natural acoustic environemnt of the organisms. We have obtained further measurements of the effective wall impedance and, hence, estimates of the wave impedance within such tanks, using the technique described at the Second Symposium on Marine Bio-Acoustics (1966). The fields within the tanks are similar whether the sound source is located in the water or in the air nearby. Particle velocities in the water (and hence displacements) are orders of magnitude greater than has been sometimes assumed from uncritical use of pressure hydrophones. This suggests that animal behavior may be due to lateral-line response rather than to auditory system response. [Hudson Lab. of Columbia Univ. Informal Documentation No. 148. This work was supported by the U. S. Office of Naval Research.]