Utilization of microperforated panel parallel baffle silencers for noise reduction in ducts

Parallel baffle silencers made of glass fiber are a common means for attenuating building noise. Microperforated panel (MPP) baffles are similar to their glass fiber counterparts consisting of two parallel microperforated (MPP) panels with a honeycomb structure between the panels. In this study, the metric used to assess the MPP parallel baffle performance is insertion loss which is defined as the difference in outlet sound power without and with the MPP baffle in place. The insertion loss measurements demonstrate that the combination of the MPP and the honeycomb is preferable to similar configurations. It is demonstrated experimentally that the insertion loss exceeds 20 dB above 1000 Hz using three baffles in a 40.6 cm by 30.5 cm cross-section duct. A finite element model of the MPP parallel baffle is developed and predictions correlate reasonably well with insertion loss measurements. The model is then used to investigate the effect of varying baffle thickness and spacing between baffles. The finite element study reveals that increasing baffle thickness lowers the frequency of maximum insertion loss while reducing the spacing between baffles increases the insertion loss.