Vibro-acoustic analysis of the stage floor of a concert hall – A case study

Due to the continuous and intensive use the building of the Academy of Music Ferenc Liszt in Budapest, Hungary, is considerably aged by now and therefore it will undergo a total reconstruction. One of the critical elements of the reconstruction is the totally worn wooden stage floor construction, which should preserve its favourable acoustic properties while ensuring increased amount of storage place hereunder, to be used for new logistic purposes. The aim of the investigations reported herein is to determine, which parts of the structure should be rebuilt in unvarying form and where may the system be modified to meet the new requirements. In order to determine the characteristic vibro-acoustic properties of the existing stage structure, an extended measurement series on a selected part of the stage was performed and evaluated. Due to the nonlinearities and inhomogeneities of the system the measurement results are difficult to interpret, but some general conclusions could be drawn. In order to extend the data set generated by experimental means, an approximate modal model of the structure was developed and the vibro-acoustic interaction of the stage and the sound field above was investigated by numerical methods. Eventually, based on the obtained results the architect, the structural engineer and the acoustician have decided to rebuild the stage floor in its original form but to replace the supporting wooden structure by simple reinforced concrete studs. The paper summarizes the means, methods and most important results of the experiments, discusses the applied vibro-acoustic model, the used model reduction techniques and the obtained results on the behaviour of the coupled vibro-acoustic system at issue, and presents some predicted characteristics of the final design too.