Enhancing maximum measurable sound reduction index using sound intensity method and strong receiving room absorption

Abstract

The sound intensity method is usually recommended instead of the pressure method in the presence of strong flanking transmission. Especially when small and/or heavy specimens are tested, the flanking often causes problems in laboratories practicing only the pressure method. The purpose of this study was to determine experimentally the difference between the maximum sound reduction indices obtained by the intensity method, RI,max, and by the pressure method, Rmax. In addition, the influence of adding room absorption to the receiving room was studied. The experiments were carried out in an ordinary two-room test laboratory. The exact value of RI,max was estimated by applying a fitting equation to the measured data points. The fitting equation involved the dependence of the pressure-intensity indicator on measured acoustical parameters. In an empty receiving room, the difference between RI,max and Rmax was 4-15 dB, depending on frequency. When the average reverberation time was reduced from 3.5 to 0.6 s, the values of RI,max increased by 2-10 dB compared to the results in the empty room. Thus, it is possible to measure wall structures having 9-22 dB better sound reduction index using the intensity method than with the pressure method. This facilitates the measurements of small and/or heavy specimens in the presence of flanking. Moreover, when new laboratories are designed, the intensity method is an alternative to the pressure method which presupposes expensive isolation structures between the rooms.

Transmission of Sound Through Finite Multiple-Panel Partition

“…1.22 presents more details for the clamped case. The transmission loss measurements are performed by utilizing a pressure method [58,59]. Two condenser microphones (Knowles: FG-23742-150, diameter d D 2.59 mm) are located on the incident side and the radiated side, respectively, with the same distance 20 cm from the corresponding panel at the centerline of the structure.…”

The summary of techniques on the airborne sound insulation measurement

“…Jonasson pointed out that the sound intensity method has two advantages: It would suppress flanking transmission and has a higher maximum measurable sound insulation. V.Hongisto did follow-up researches [30] . KuoTsai Chen measured the sound leakage of some apertures and proved the validity of measuring sound leakage with sound intensity method [39] .…”

“…However, if the back wall of the receiving room is a reflected one and is parallel with the measuring surface, the experiment results would be imprecise. This effect increases with the sound insulation become higher, and it can be decreased by disposing some sound absorptive materials on the back wall [30] (3) Determining the sound leakage path by drafting the contour of the sound intensity levels, the bigger sound intensity level indicates the possibility of sound leakage. This method is useful to determine sound leakage in the in-situ sound insulation measurement (4) Measuring sound insulation of different building elements in the same space.…”

Effect of resilient joints on the airborne sound insulation of single-leaf heavyweight constructions

“…They influence the modal coupling between the source and receiving room and lead to major interlaboratory variations [10,11]. Furthermore, when heavyweight constructions are tested in laboratory, flanking sound transmission can be strong and reduces the highest measurable SRI [14]. Flanking transmission is a serious problem for the pressure method, especially, for heavyweight constructions at low frequencies.…”