Investigations on the Influence of Source Directivity for measurements of in-situ Sound Absorption

The European project QUIESST is dealing with the development of an improved method for measuring the in-situ sound absorption of noise barriers. In the frame of the activities carried out in work package 3, the Austrian Institute of Technology has performed several measurements in order to investigate the influence of the source directivity on this method. During a first investigation a directional sound source and an omnidirectional one have been experimentally compared by using different microphone positions and different setups. After a second measurement campaign the use of an additional free field measurement in a distance of 1.75 m has been proposed in order to overcome the main issues related to the source directivity. The present paper explains the assumptions based on the proposed method and shows the first experimental results comparing different post-processing options.