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

The sound intensity method is usually recommended instead of the pressure m ethod in the presence of strong flanking transmission. Especially when smal l 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 r eduction indices obtained by the intensity method, R-I,R-max, and by the pr essure method, R-max. In addition, the influence of adding room absorption to the receiving room was studied. The experiments were carried out in an o rdinary two-room test laboratory. The exact value of R-l,R-max, was estimat ed by applying a fitting equation to the measured data points. The fitting equation involved the dependence of the pressure-intensity indicator on mea sured acoustical parameters. In an empty receiving room, reverberation time was reduced from 3.5 to 0.6 s, the values of R-l,R-max increased by 2-10 d B compared to the results in the empty room. Thus, it is possible to measur e wall structures having 9-22 dB better sound reduction index using the int ensity method than with the pressure method. This facilitates the measureme nts 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 bet ween the rooms. (C) 2001 Acousticral Society of America.