The measurement and prediction of radiation efficiency is important in many areas of acoustics. It has recently become an even more important topic, because the radiation efficiency needs to be known in order to predict the flanking sound transmission using EN12354 when the frequency is below the critical frequency of one or more of the walls involved in the flanking sound transmission path. This prediction is more difficult for lightweight walls because they usually consist of a complex construction. This paper uses Maidanik's and Leppington's approximate formulae to predict the resonant radiation efficiency of a finite size panel and Davy's approximate formulae to predict the forced radiation efficiency when a finite size panel is excited by a diffuse sound field. The radiation efficiency of an infinite size panel excited by a point or line force is predicted using Heckl's approximate formulae. The damping loss factor of the panel is needed in order to calculate the magnitude of the resonant vibration of the panel relative to the point or line near field vibration of the panel or relative to the vibration of the panel forced by an incident diffuse sound field on one side of the panel. The theories used in this paper assume that the finite size panel is mounted in an infinite baffle and the predictions are for the power radiated on one side of the panel. This paper compares the theoretical predictions of radiation efficiency with experimental measurements made in sound insulation laboratories. The surface velocities of the panels were measured with a laser velocimeter or accelerometers. The sound power radiated on one side of the panel was determined using sound intensity measurements or reverberation room measurements of sound power that utilised sound pressure measurements and reverberation time measurements.
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