- © TU Berlin / Casa Acustica
The effectiveness of edge absorbers, i.e., compact broadband absorbers encased in the edges of a room, was evaluated in a seminar room at TU Berlin. For this purpose, the acoustic properties of the seminar room H 3001 were measured before and after an acoustic treatment, with the aim to optimize speech intelligibility and acoustic comfort during lectures, conversations, as well as music ensemble uses.
Prior to the hardware installations, which were conducted in February 2019, H 3001 showed low frequency droning as a result of strong excitation of the room's eigenfrequencies ('modes'). Speech intelligibility was poor due to low frequency reverberation and a booming noise as a result of modes excited at the eigenfrequencies of the room, which users found particularly annoying in the rear part of the room.
H 3001 measures 310 m3, with a height of 5.4 meters and 4 large glass windows to the exterior of the building. The room was treated with encased compact broadband absorbers in the 4 horizontal and 2 vertical edges of the room. These slim, visibly and spatially unobtrusive (see image top right) measures proved to introduce the missing absorption and flatten the reverberation characteristic below 0.8 s when the room is occupied by 20 users (see diagram below). A substantial improvement of the room acoustics was subjectively confirmed by members of the department as well as members of a choir group who regularly rehearse in the room.
In addition to reverberation time measurements, binaural room impulse responses of H 3001 were obtained for the before and after states of the room using the Artificial Head-Torso-Simulator FABIAN . With this data, auralizations were generated for the condition before and after the treatment using an anechoic voice recording. The audio examples have been optimized for playback over headphones and can be heard by clicking the links below.
The seminar room H 3001 is accessible for demonstrations of the effect of low frequency absorption on speech intelligibility and acoustic comfort, in comparison with neighbouring, untreated rooms. The investigation was supported by the foundation Casa Acustica .
 Fuchs, H. V. (2017). Raum-Akustik und Lärm-Minderung. Konzepte mit innovativen Schallabsorbern und -dämpfern. Springer Vieweg Verlag.
 Lindau, A., Weinzierl, S. (2007). FABIAN - Schnelle Erfassung binauraler Raumimpulsantworten in mehreren Freiheitsgraden, Fortschritte der Akustik – DAGA Stuttgart, 633–634.