Variability of low frequency sound transmission measurements

In this paper we discuss the characterization of low frequency sound transmission between two rooms via a flexible panel. A fully-coupled modal model is used to investigate the individual effect of the source room and the receiving room on the measured sound reduction index, and the results are compared with the ideal case of having a free field on both sides of the panel. The effect of the source room on the measured sound reduction index at low frequencies can be reduced by using a number of suitable-driven loudspeakers close to the panel to simulate a diffuse incident field. However, the effect of the receiving room was found not to be reduced by calculating the transmitted acoustic power from a dense array of acoustic intensity measurements, instead of an array of microphones in the receiving room. (C) 2004 Acoustical Society of America.