Properties of transparent sound-absorbing panels for use in noise barriers

Sound absorption and optical transparency are among the most useful properties of noise barriers.While the latter is required to reduce visual impact and for aesthetical reasons, the former is requiredwhenever conditions of multiple reflections and presence of close, high receivers occur. Thetechnical feasibility of a transparent, sound-absorbing panel for outdoor antinoise devices isinvestigated in this paper. An analysis of acoustical performance of multiple perforated plates isperformed employing an existing theory for microperforated absorbers under normal incidence anddiffused sound field. An optimization of the geometrical parameters is carried out on the basis of theEuropean classification criteria of noise barriers for roadways. An optimized three-layerconfiguration can achieve sound-absorption properties similar to nontransparent products with onlya limited loss of visual transparency and appropriate mechanical strength. Experimental dataobtained with an impedance tube on small test samples made of transparent polycarbonate and in areverberation room on full-scale prototypes are reported, showing a rather good agreement with thetheoretical predictions. The optical performance of a multilayered configuration is evaluated also.