Abstract
This paper demonstrates that the logo of the New Zealand Acoustical Society has a sound physical basis. The logo shows concentric circles with a discontinuity between the right and left hemispheres. If the logo were a sound field, these discontinuities would represent amplitude inversions. This behaviour occurs in sound fields containing focused sources, where circular wavefronts converge on a focal point from one hemisphere and then diverge into the other hemisphere. At certain times during the propagation of the wavefronts, the quadrature part of the sound field is maximum, and this demonstrates concentric wavefronts with a phase discontinuity between the two hemispheres and a null along the line separating the two.