A new diffractor to reduce traffic noiseDespite the use of noise barriers and silent roads, traffic noise has become one of the major causes of annoyance. In this respect, it is fortunate that also, so-called, noise diffractors have now been accepted in the Dutch legislation as a legal means to mitigate traffic noise. Diffractors bend noise upwards, creating a shadow zone behind the diffractor. Diffraction can be accomplished by quarter-wavelength resonators, placed either within the ground but also mounted on top of a (low height) noise barrier.In this paper, we describe a numerical model for a diffractor mounted on a noise barrier. The model is used to calculate the scattered noise in the proximity of the diffractor allowing for noise sources also at larger distances from the diffractor. The acoustic pressure and particle velocity on the outer boundary of the computational domain are subsequently used in the Kirchhoff-Helmholtz integral to evaluate the pressures in the far field. We discuss the quarter-wavelength diffractor but also introduce a new, reflection-type, diffractor. The advantages of such a diffractor is the simpler design and the more direct response to the incoming sound waves.Y.H. Wijnant4Silence B.V.University of Twente