Equivalence in diffraction-reducing efficiency between T-profile and thick barrier against road traffic noise

Abstract

Diffraction-reducing efficiency of a T-profile noise barrier is discussed using boundary element analyses considering a point source against an infinitely long barrier. The efficiency against a fixed point source includes both an increased thickness effect due to the T-profile cap and an interference effect due to phase difference between propagation paths around cranked edges of the cap. The latter interference effect depends on the relationship between wavelength and geometries; the effect disappears for incoherent point sources moving parallel to the barrier. For incoherent line sources such as road traffic noise, the efficiency of the T-profile barrier is almost equivalent to that of a thick barrier, and difference between them is almost less than 1 dB when the T-cap depth is equal to or less than 1 m. As a result, reduction in road traffic noise by a T-profile barrier is approximately calculated using a kind of engineering prediction models based on geometrical acoustics.