| Summary: | The acoustical insertion losses of plenum windows installed on a building facade in the presence
of a non-parallel line source are studied by using a 1:4 scaled down model in a semi-anechoic
chamber in the present investigation. Two types of insertion losses, weighted by the normalized
traffic noise spectrum (from the 100 Hz to 5000 Hz one-third octave bands), are defined with
different references. The first one is for the case where the orientation of the building facade
relative to the line source is fixed. The reference case is the opened window having the same
orientation angle as the plenum window. The maximum and minimum insertion losses under this
condition across the orientations tested are found to be around 14 dB and 5 dB, respectively. The
other is the opposite situation where such orientation is allowed to change because of practical
purposes and the reference for this condition is the opened window with its width span parallel
to the line source. The corresponding maximum and minimum insertion losses are found to be
around 18 dB and 8 dB, respectively. There are evidences showing that the lower order plenum
acoustic modes are responsible for the relatively high low frequency insertion loss.
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