The relationship between the in situ flanking sound reduction index and the laboratory measured flanking normalized level difference

From Gerretsen’s 1979 Applied Acoustics paper through four series of standards including ISO 12354 and ISO 10848, a significant amount of effort has gone into creating a standardized prediction method that uses standardized laboratory measured values to predict the apparent sound reduction index to demonstrate compliance with regulations. The terms and equations in the prediction method have evolved over time as researchers have evaluated the results of the prediction method, especially in the case of lightweight constructions for which statistical energy analysis is not well suited. To reflect the changes to other equations in the prediction method over the past 40 years, this paper suggests an update to the relationship in ISO 12354-1 between the in situ flanking sound reduction index and the laboratory measured flanking normalized level difference. The suggested changes are of importance for Type B elements such as timber and steel framed walls and floors for which the prediction of flanking transmission according to ISO 12354 requires the measurement of the level difference in laboratory flanking facilities.