Applications of lightweight thermoplastic sound absorptive panels

Thermoplastic panels have been developed that may be considered as collections of Helmholtz resonators. The material has a plastic layer on either side with interconnected honeycomb cells sandwiched between the two layers. The top layer has differing sized holes which act as the necks for Helmholtz resonators whereas the bottom layer is sealed. Honeycomb cell walls have been strategically removed so that Helmholtz resonators are tuned to different frequencies. The cumulative effect of the resonators produces broadband sound absorption. It is demonstrated that the panels, which are 0.9 cm thick, can be affixed inside of an enclosure and are roughly as effective as 5 cm thick acoustic fiber. The materials are then used as duct liner and similar effectiveness is observed.