Progress in sound reflection measurements on noise barriers in situ

In situ measuring sound reflection from noise barriers is a very difficult task; it is addressed in the European technical specification CEN/TS 1793-5, but some open problems still remain. In the frame of the EU funded QUIESST project, working package 3, several new improvements have been introduced to get a better and more robust measurement method. They include: using a square 9-microphone array not rigidly connected to the loudspeaker, multichannel acquisition, optimized alignment of free-field and global impulse responses including fractional step shifts and least squares estimation of the best relative position, corrections for geometrical divergence and sound source directivity. Overall, these improvements led to a new definition of the reflection index. In this paper the essential of these improvements is presented and some exemplary results are shown.