Influence of ground reflections and loudspeaker directivity on easurements of in-situ sound absorption

Sound absorption is a relevant property for the acoustic quality of noise barriers. The Adrienne method is the most used in-situ measurement method in Europe for testing the acoustic performance of noise reducing devices in real life conditions. This method was introduced in 2003 with the technical specification CEN/TS 1793-5 [1] and the development of this method is now one of the main objectives of the European project QUIESST. In the frame of this project AIT Mobility has performed a first measurement campaign in order to investigate the influence of ground reflections and the role of the sound source for measurements of sound absorption in the near field. Two different sound sources and different microphone heights have been used for analyzing the influence of the source directivity and the role of ground reflections. The study shows that particular attention should be paid to the source directivity and to the microphone position, while the ground reflection does not seems to represent a problem for the method at all. 1 Introduction The present paper describes the first investigations carried out by AIT in the frame of the WP3 of the EU project QUIESST. During this measurement campaign the influence of ground reflection and the influence of loudspeaker directivity have been investigated with a modified version of the Adrienne method. The primary goal of the presented measurements was to analyze if ground reflections are still present in the reflected impulse response function (IRF) after subtraction and windowing in the time domain was applied to the function. The investigations were performed using two different sound sources and different microphone heights, in order to investigate also the influence of the source directivity on the results.