Abstract:

In Principles of Underwater Sound (1946), edited and largely written by Carl Eckart, he showed what acoustic pressure levels in dynes per square centimeter (rms) meant in decibels (air and water) compared with one another and also in watts per square centimeter. In Principles of Underwater Sound by Bob Urick, 3rd ed. (1983), Sec. 1.6 deals very clear with absolute units of intensity with respect to the new standard pressure reference level of 1 ((mu)Pa)=10[sup -5] dyn/cm[sup 2] (rms) for both air and underwater acoustics; see ``Preferred Reference Quantities for Acoustic Levels,'' ANSI S1.8-1969(R1974). In physical units this intensity amounts to 0.67x10[sup -22] W/cm[sup 2]. A few examples will be given of difficulties encountered by not including absolute units, most recently with respect to whales and sound sources radiating only 250 W. The inclusion of absolute units would facilitate understanding of acoustics to the scientific, technical, and public communities.