Inter-laboratory comparisons of low-frequency sound transmission: I. Conventional and intensity measurements

Abstract

Sound transmission through nominally identical steel plates was measured in two laboratories; NRC, Canada and PTB, Braunschweig in Germany. The two laboratories differ markedly in construction; one has rooms with volumes 65 and 250 m3 and the other volumes of 54 and 69 m3. The specimens measured 1.5×1.25 m and were mounted in window test frames that satisfied the recommendations of ISO 140. The measurement frequency range was extended to 50 Hz in each laboratory. As well as conventional 1/3-octave band measurements, sound reduction index was measured using sound intensity techniques. Measurements were made in both directions, that is, each room served in turn as the source room and then the receiving room. Similar behavior was seen in each laboratory; conventional measurements into the smaller room tended to give higher values of sound reduction index. When the mean values of sound reduction index for each laboratory for both directions of measurement are compared, agreement is good but there are still differences at low frequencies that need explanation. This paper presents the measured data. Possible reasons for the differences are discussed in the companion paper.