It is seen from Fig. 4.13 that for kR   <   0.3, that is, when the diameter is less than one-tenth the wavelength, the impedance load on the surface of the sphere is that of a mass reactance because the resistive component is negligible compared with the reactive component.

At all frequencies, the loading shown in Fig. 4.13 may be represented by the equivalent circuits of Fig. 4.33. The element sizes for the mechanical and acoustic admittances and impedances are given with the circuits.