Reflection index measurement on noise barriers with the Adrienne method: source directivity investigation and microphone grid implementation

In this work the sound source directivity influence on the Reflection Index measurement has been investigated. Two different sound sources and two different noise barrier surfaces (absorptive and reflective) were used. The measurements have been performed following the CEN/TS 1793-5 European standard (“Adrienne” method) using a 3 x 3 microphone grid instead of the single microphone required by the standard. The loudspeaker has been rotated on the horizontal axis for both the “free field” and “on barrier” measurements, covering an angle of 180 degrees in steps of 10 degrees. The results clearly show that the source directivity has limited influence on the final measurement results and that the average of the measurement values on the grid is more accurate and reliable than the single microphone measurement. It is also shown that the signal subtraction can reliably be done without a rigid connection source-microphone(s).