Full scale field study of sound transmission across plenum windows

A full scale field measurement of the acoustical insertion loss of plenum windows was carried out in the present investigation. Two identical mock-up test rooms with dimensions the same as those commonly adopted for Hong Kong public housing were built side-by-side next to a busy trunk road. One of them was equipped with plenum windows, while the other with the conventional side-hung casement windows. Four internal room settings were included in this study. Results show that both the room modes and the acoustic modes within the plenum window cavities were affecting significantly the low frequency sound transmission. After correcting for the indoor reverberation/absorption effect, the acoustical benefit achieved by replacing side-hung casement windows with the plenum windows tested in the present study was between 7.1 and 9.5 dBA. By comparing the average equivalent sound pressure levels inside the two test rooms with the traffic noise weighted acoustical benefit, it was found that the changes of receiver room reverberation and acoustic modal effects due to such replacement would result in a reduction of plenum window sound insulation performance by 0.2-1.5 dBA. The insulation is stronger for larger room size with stronger indoor sound absorption.