Experimental analysis of the acoustical behaviour of Musikverein in concert and ballet configurations

Musikverein is among the best concert halls in the world. But the hall is also employed for open-to-the-public ballets. All seats in main stalls are removed, and packed under the wooden floor thanks to a large opening. Detailed acoustical measurements have been performed, with the aim of evaluating the different acoustical behavior with and without the seats. Furthermore, it was attempted to assess the contribution of the air volume under the floor, as a possible "resonant chamber", with volume and absorption significantly different when it is filled with packed seats. The results did show that the main acoustical parameters vary significantly between the "concert" setup and the "public ballet" setup, which is more reverberant, with lesser clarity and more envelopment. Regarding the hypothesis that the volume under the floor has some effect on the acoustical behaviour of the room, the experimental results excluded that this is possible. Furthermore, measurements with accelerometers and pressure/velocity probes did not reveal any difference between the behaviour of the "openable" part of the floor and the surrounding "fixed" floor. So it was concluded that the large difference in acoustical behaviour is simply caused by the removal of the seats, and by changes in fittings of the stage.