Sound transmission across plenum windows with non-parallel glass panes

Plenum windows, which take the form of a partially opened double glazing window, have attracted the attention of both government officials and researchers in the past several years because of their high sound insulation loss and their allowance for reasonable level of natural ventilation. However, it is very difficult to improve their sound insulation capacity as the gaps between the window panes are always restricted because of the building facade thickness. Application of sound absorption is basically not practical unless the material is transparent and thin. In this study, an attempt is made to examine how a small inclination of the indoor side window pane can affect the overall sound insulation of the plenum window. It is found that there is a 2dB sound insulation increase when the window panes are non-parallel and the source is relatively close to the window. The improvement becomes less obvious as the source distance increases, but improvement can still be observed by an appropriate revision of the window pane inclination.