Underwater Acoustic Intensity Research Articles

The goldfish ear codes the axis of acoustic particle motion in three dimensions.

Auditory and vestibular nerve fibers of the goldfish are strongly directionally sensitive to whole-body acceleration at audio frequencies. The three-dimensional pattern of sensitivity shows that input from a receptor ensemble (hair cells) is essentially equivalent to that expected from a single hair cell having a given three-dimensional orientation of best sensitivity. Fibers from the sacculus, lagena, and utriculus differ with respect to distributions of directional orientation, but are similar in best threshold (less than 1 nanometer, root mean square, at 140 hertz). In combination with other mechanisms for detection of sound pressure, this directionality is a likely basis for directional hearing in fishes, and it could allow the determination of underwater acoustic intensity.

Instrumentation for Measuring Underwater Acoustic Intensity

Instrumentation has been developed to measure one component of underwater acoustic intensity. Acoustical intensity is defined as the rate of flow of acoustical power per unit area in a direction normal to that area. It is equal to the product of the sound pressure and particle velocity at a point averaged over a period long relative to that of the lowest frequency component present. Transducers have been developed to measure both the sound pressure and particle acceleration. The outputs of the two transducers are amplified and filtered. The voltage proportional to the particle acceleration also is integrated. Thus, two voltages proportional to the sound pressure and particle velocity whose relative phase is the same as existed between the pressure and particle velocity are multiplied and averaged to provide a measure of the intensity. This instrumentation measures the acoustical intensity in octave bands from 50 to 2000 cps. A method of calibrating the pickups in the near field of a sound projector also is described.