SPECTRAL VARIATION OF SOUND TRANSMISSION LOSS ACROSS PLENUM WINDOWS WITH NON-PARALLEL GLASS PANES

摘要

It has been reported in a previous scale model study that the overall traffic noise transmission loss across a plenum window can be enhanced by making the two glass panes of the window inclined relative to each other. The improvement, by tilting the internal glass pane varies with the elevation angle of the window outer opening relative to the source, and ranges between 0 to 4 dBA. There are two elevation angles, 8 and 19 deg, where no improvement is found. This study is made in an attempt to explain the observations. It is found that these elevation angles are those at which the sound transmission loss in the 800 Hz 1/3 octave band of the parallel pane cases are relatively high. The opposite is observed for the case of the largest improvement, which occurs at an elevation angle of 13 deg. The separation between the two glass panes in the parallel case is 400 mm, which is approximately the wavelength of a 857 Hz sound. There are many resonance cases but the excitation of this transverse gap mode (the second cut-off) appears dominating in the overall A-weighted traffic noise reduction.