We said the wave equation in air in one-dimension is

One might encounter this situation inside a long pipe. However the air in which we live is three-dimensional, so the full 3-D wave equation for air is given by

where we also include second order partial derivatives with
respect to the *y* and *z* directions.
We won't have occasion to use this complicated expression very
much in this course, but we are including it here for completeness.

Tue Feb 25 21:24:33 EST 1997