Dolphin Audition and Echolocation Capacities
C. Scott Johnson Naval Ocean Systems Center, San Diego
We know considerable information about audition and echolocation in several delphinid species, but have the most complete data on Tursiops truncatus. Therefore, my discussion will concentrate on audition and echolocation in T. truncatus.
A few basic physical concepts will assist the reader. The pressure (p, in dynes/cm2) of a plane sound wave is related to particle velocity (u, in cm/sec) by (cf. Urick, 1967, p. 12.):
p = ρcu (1)
where ρ is the density of the fluid (in gm/cm3) and c is the velocity of sound in the fluid (in cm/sec). The product pc is called the specific acoustic impedance of the fluid. Particle displacement (y, in cm) is related to pressure, acoustic impedance, and frequency (f. in Hz) by (cf. Heuter & Bolt, 1955, p. 52):. (2)
Sound intensity (i, in watts/cm2) in a plane wave is related to instantaneous pressure by:. (3)
When sound in one medium havng an acoustic impedance of ρ1c1 is transmitted into a second medium of a differing acoustic impedance of ρ2c2, part of the incident wave's intensity is reflected back into the first medium. Assuming a