Sound reflection and sound insulation measurements on a sonic crystal noise barrier according to the new European methodology

Noise barriers based on sonic crystals are very promising, being light-weighting and permitting light and airflow passage. On the other hand, they have unusual sound insulation and sound reflection properties, dominated by multiple scattering phenomena. Theoretical literature predicts sound transmission spectra exhibiting stop-band regions, while very few considerations have been published on the sound reflection spectra. The main aim of this work is to show the applicability of the European standards EN 1793-5 and EN 1793-6 (originated from the QUIESST project) to these kind of structures. Measurements were done on a sample made of hollow PVC - outer diameter 160 mm - arranged in a square lattice with a height of 3 m and an overall width of 3 m. Its depth varied from 1 to 5 rows of cylinders. FEM simulations were performed in order to control and address the experimental campaign. Regarding sound insulation, a good matching between simulations and measurements was found in the first Bragg band gap, occurring in the 800 Hz one-third octave band. Increasing the number of rows, sound insulation increases as expected. Regarding sound reflections, the study confirms the existence of a strongly interferential sound field, as for reflecting non-flat noise barriers.