On the low-frequency acoustic center.

Acousticians typically consider the acoustic center of a source to be the point from which sound waves appear to diverge spherically. Many applications require the center's accurate determination, but its deeper significance and means of assessment have often remained ambiguous. This work revisits the acoustic center and shows how a low-frequency sound radiator with omnidirectional far-field directivity has a center defined by its dipole-to-monopole moment ratio. This definition yields conclusive results for several theoretical sources and highlights the limitations of characterizing the acoustic center only in terms of an equivalent point source.