Issues associated with sound exposure experiments in tanks

Abstract

For practical reasons it is often necessary to carry out sound exposure experiments on marine animals in tanks or pools that may have dimensions ranging from less than one meter to a few tens of meters. The boundaries of such tanks are almost invariably highly reflective to underwater sound, resulting in a sound field that can vary spatially in unexpected ways, and in which the relationship between pressure and particle velocity is quite different from that in an animal's natural environment. In this paper a numerical simulation based on the finite difference method is used to illustrate these effects. The results show that, at frequencies below the tank's lowest resonant frequency, the particle velocity and pressure fields vary smoothly in space and with changes in frequency, but that both the ratio of the particle velocity to the pressure and the way in which their amplitudes vary with distance from the source are different than in a freefield situation. At frequencies above the lowest resonant frequency the particle velocity and pressure fields, and their ratio, vary rapidly both spatially and with changes in frequency. Experimental measurements of pressure and particle velocity in a tank agree qualitatively with these results. © 2016 Acoustical Society of America.