Final Thesis

Directional Sound Field Decay in Reverberation Rooms

Master Thesis of Kersten, Simon

According to the international standard ISO 345, the random-incidence sound absorption coefficient is measured in a reverberation room by determining the reverberation times with and without the absorber. The sound field in the room is assumed to be diffuse, the corresponding energy decay curves are single-exponential. However, measured curves often exhibit a multi-exponential nature and indicate the existence of different decay processes. In the modal theory of the sound field this is assigned to the existence of groups of modes which decay according to their similar damping. In this thesis, the use of a multiple-input multiple-output system allows to obtain directional energy decay curves, which enable a directional, time-dependent analysis, while varying the source directivity. Groups of differently decaying modes are identified qualitatively and quantitatively. They are discussed in terms of their reverberation times and with respect to the resulting isotropy of the sound field in the room, which is a fundamental property of a diffuse field. Furthermore, by optimizing the source directivity with respect to a single-exponential decay and a maximum isotropy, its ability in weighting the groups of modes and its impact on the sound field decay is shown.