Optimization of an Acoustic Resonator for Noise Barrier Top Elements

Noise barriers are a common tool to mitigate roadway and railway noise. Noise barriers are characterized by intrinsic parameters, i.e., the sound reflection index as defined in the standard EN 1793-5, the sound insulation index as defined in EN 1793-6, and the sound diffraction index (DI), and by extrinsic parameters, e.g., the insertion loss. The DI is defined in the EN 1793-4 for road traffic noise and in the EN 16272-4 for railway noise and depends mainly on the shape and on the acoustic properties of a noise barriers top element, e.g., on its width and acoustic surface impedance.In this study, a noise barrier top element consisting of acoustic resonators was optimized in terms of achieving a maximum DI with respect to the standardized railway noise spectrum (EN 16272-3-1). In the optimization process, the quasi-periodic boundary element method was used, where the sound field for a setup based on the EN 16272-4 was simulated and the DI was calculated up to 5 kHz for top elements with various resonator lengths and shapes. The best performing top-element designs were built and measured according to EN 16272-4.