ABSTRACT
There are many approaches one can take to describe the wave motion or vibratory characteristics of sound. For example, it is easy to relate a plane sound field in appearance to expanding water waves resulting from disturbing a quiet pond. Another conceptual picture which is both popular and useful is to draw rays or arrows to illustrate the direction of propagating wave fronts. For industrial noise control, however, describing sound as the vibratory motion of displaced molecules in an elastic medium provides an easy and simplifying initial approach. When particles of the medium move perpendicular to the direction of wave propagation, the waves are called transverse. As a matter of interest, the classic example of a transverse wave is the circular diverging surface waves created when a stone is tossed into a calm pond. The transverse action is easily seen here by noting that the motion of a bobbin or leaf is perpendicular to the passing waves.
