The radiation impedance concept is employed to establish relations between the near-field sound pressure of a piston in a large wall, the radiated power, and the far-field sound pressure. Attention is drawn to the fact that at long wavelengths the relative pressure distribution across the piston tends to be constant, but not uniform. A recapitulation is given of a simple theory of the mutual radiation impedance for two interacting pistons in a large wall, and expressions for the total radiated active and reactive power are derived. The interaction is strongly dependent on the phase difference between the piston velocities. The influence of the mutual radiation impedance on the function of a vented loudspeaker cabinet has been investigated in detail, and is shown to be decisive below the port resonance frequency. The variations are large but unimportant, as they occur outside the active range of the radiator in question. The findings do not call for changes in design methods.
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