This study measured and assessed the performance of sound insulation of composite walls in the closed university classrooms in terms of the Apparent Sound Reduction Index (R') values. The level difference (LD) between a source and a receiving room was also measured to assess the sound leaks from doors and windows in the composite walls. The measurements were carried out in 12 classrooms located in 7 different buildings in the university campus.
The present results show that the measured mean R'(avg) value averaged over the measured data in the 12 classrooms was 26 dB (s.d.=3.9 dB). This value is about 6 dB higher than that of the measured mean LD(avg) value, which is 20 dB (s.d.=4.0 dB). The difference between the worst and best composite walls in terms of the performance of sound insulation in the 12 classrooms is 13 dB and 12 dB for the two measures, R', and LD, respectively. Only one composite wall met the requirement for a minimum SPC values of 30.
The most important architectural parameter influencing the LD value is the presence of openings, such as doors, and windows, in the composite walls between the source and receiving room. The LD value decreased by 4.5 dB to 4.9 dB with presence of entrance doors without door seals in the composite walls. Therefore, if the doors in the composite wall is replaced by highly insulated doors, the adequate STC value of the classrooms can be achieved.