The Edge Absorber as a "Modal Brake"

Nowadays, knowledge about the acoustical influence of edge absorbers on a sound field is mainly based on empirical experience. Unfortunately, there is no computational model, which describes the acoustical effect of an edge absorber in a room. To eliminate this insufficiency, this contribution investigates the absorption behaviour of edge absorbers systematically and proposes a computational model for those in cuboid rooms. For the investigations a modular edge absorber was developed and constructed. In the course of the development, measurements in the impedance tube were performed. Optimal parameters for perforation ratio of the absorber housing as well as flow resistivity and layer thickness of the incorporated porous material were determined. Due to the modular principle of the edge absorber flexible assembly, regarding arbitrary room geometries, is possible. Absorption coefficient and equivalent are of absorption of different absorber configurations, concerning room layout and absorption layers, were measured in the reverberation chamber. Furthermore, the acoustical behaviour of the edge absorber was determined in four lecture halls. Absorption efficiency and lower frequency limit of the edge absorber are highly dependent on the assembly depth and the respective edge of assembly. Moreover, the effective bandwidth of absorption is dependent on the proportion of the room?s edge, which is covered by the absorber. The modular edge absorber was deployed in a room acoustical redevelopment of a lecture hall. For a pre-post comparison, room acoustical measurements were performed and the vast effect of the edge absorber could be confirmed. For perceptual evaluation, binaural pre-post recordings are available. Furthermore, based on the modal structure of the sound field at low frequency excitation and the assumption of simple room geometries, a computational model for the use of the edge absorber as a "modal brake"was developed and implemented.