An acoustic approach to double facades : a general overview and sound insulation prediction model

(eng) The past decade has seen the construction of many (high-rise) double facade (DF) buildings, for which the glazing is mounted in a pair steel or aluminium frames separated by a large cavity. In many cases, a key aspect of this system is the improved acoustic performance compared with single facades. Therefore, it has become eminent to understand the acoustic properties of DF. It also seemed that a crucial need had arisen to be able to predict the acoustic performances of DF at the tendering stage (as is already possible from a thermal point of view). In the tendering stage of a project the project managers are dealing with large amounts (typically more than 10.000 m²) of glazing to be used in the facade. The choice of a particular type of glazing has an important impact on the total cost of the building. In the years before many decisions led to over-dimensioning of the glass types due to a lack of knowledge, which obviously led to higher building costs, leaving economic optimisation out of the loop. This crucial factor led to the research on the acoustic properties of DF systems, which consist of more than two glass panes, in contrast to the usually referenced double systems, which only have two (glass) panes. The goals for this research were set: a clear and detailed picture on the acoustic behaviour of DF and the creation of an acoustic calculation model to predict the facade insulation of DF with sufficient accuracy and with limited computation time, which is crucial at the tendering stage of a building project. This model is a semi-empiric hybrid model (SEHM) which consists of existing adapted and new models based on statistical energy analysis (SEA) and semi-empiric models. The SEHM has been validated by comparison with a large amount of experimental results and reveals to be very encouraging, showing high accuracy over the investigated frequency bands and minimal computation time.