Complexities of tank acoustics warrant direct, careful measurement of particle motion and pressure for bioacoustic studies

Abstract

Tank-based bioacoustic experiments are useful for recording organisms’ produced sounds and responses to sounds in a controlled environment, but care must be taken to accurately measure and thoroughly report in-tank acoustic fields. For studies involving particle-motion sensitive fish or invertebrates, particle motion should be directly measured since it cannot be accurately calculated from sound pressure without use of complex propagation models for enclosed spaces. We present a high-spatial resolution, empirical dataset of pile driving sounds played in a seawater tank utilized for experiments on squid behavioral responses to these sounds. Pressure and particle acceleration were recorded with a hydrophone and accelerometer, respectively, in 10 cm increments throughout a 1.1 m diameter, 0.5 m deep cylindrical tank. Sound pressure and particle motion were not proportional to each other, and had variable patterns with distance from the speaker. Resonant frequencies and reverberation influenced propagation and spectrotemporal structure of received pile driving sounds. We further discuss how phase must be carefully tracked to produce accurate particle motion vector fields in tanks. These data reinforce the importance of direct measurement of particle motion in tanks, and that tank-based bioacoustic studies must carefully consider and report influences of resonant frequencies and reverberation on recorded signals.