NEAR-AND FARFIELDS IN A MARINE ENVIRONMENT

A particle velocity sound unit is introduced, the microvar, which equals 1/μc cm sec. Approximate formulas for the nearfield and farfield are derived which indicate that in the farfield, velocity in microvars and pressure in microbars are equal; in the nearfield, the pressure velocity ratio falls off at 6 dB per distance octave as the source is approached; and the crossover point between near and farfields on the major vibration axis is distant from the source n⋔, 2π, where n = 1 for a monopole, 2 for a dipole, and 3 for a quadrupole source. Off the major axis the crossover point moves farther away from the source. The approximate formulas are shown to be in reasonable agreement with theoretical values. It is concluded that the stimulus is present to permit a velocity displacement sensitive organism to detect sound at any distance from a source of sufficient intensity. © 1969, Acoustical Society of America. All rights reserved.