Reciprocity and the Prediction of the Apparent Sound Reduction Index for Lightweight Structures According to EN12354
In the derivation of the equation for the flanking sound reduction index for EN12354-1, reciprocity was used to remove the radiation efficiencies of the elements from the calculations. The exclusion of the radiation efficiencies was beneficial since they are often not known. However, the assumption of reciprocity may only be applicable to the heavy monolithic constructions for which EN12354-1 was intended. If EN12354-1 is applied to lightweight constructions which may exhibit direction dependent sound transmission, the assumption of reciprocity may contribute to an over prediction of the apparent sound reduction. A correction factor is proposed to correct for the over prediction due to the assumption of reciprocity. However, due to the inclusion of the radiation efficiencies in the correction factor, its use is limited. Alternatively, the correction factor may be used to estimate the error due to the assumption of reciprocity so that the accuracy of the EN12354-1 predictions can be assessed for lightweight constructions.