Transducer transmitting sensitivity measurements in restricted environments

Transducer transmitting sensitivity is normally measured under free-field conditions. In laboratory tanks, this is often achieved by using time gating to isolate the direct signal from the reflected signals. However for high-Q, low-frequency projectors, the free-time availability in laboratory tanks may be too short. A measurement technique has been developed to perform these calibration measurements in the presence of a reverberant field. The measurements have been performed at ultrasonic frequencies so that the free-field sensitivity can be determined in order to assess the accuracy of this new technique. The technique involves extracting the direct field from the combination of the direct and reverberant fields by plotting the variation of pressure squared against the reciprocal of separation squared. The gradient of this graph is proportional to the acoustic power radiated into the tank, and from this, the direct field pressure and projector sensitivity can be calculated. This paper investigates this technique and looks at the influences of tank size and construction, as well as the effect of averaging over different bandwidths.