3. Appendices

• The table 2 (page 10) helps to avoid confusion between the fundamental laws of propagation most often expressed in terms of the plane wave equation (left-hand column) and those sometimes abusively extrapolated to spherical waves (right-hand column). It's important to understand that the equations for spherical waves reflect a difference in behavior between near and far fields. The essential difference lies in the phase difference between pressure and velocity.

The relations characteristic of plane waves can also be considered as the limit, when v ® 0, of the relations characteristic of spherical waves.

The middle column of this table 2 gives the relationships translating the physical principles...