# Simplified Fly Tower Modeling for Preliminary Acoustic Predictions in Opera Houses
## 5 Conclusions  
The new digital Baroque scenography representations are characterized by an empty stage, in which projection screens are hung and furniture is minimized. Because most screens are transparent to sound, the new digital Baroque scenography can be considered as an empty fly tower condition for acoustic analysis, the same configuration that is used for the ballet. As digital sonography is gaining more and more ground nowadays, and because of its similarities with the ballet set, the empty stage configuration is also becoming the most common real stage condition for an opera piece. For this reason, firstly, the paper focuses on the definition of a possible standardized empty fly tower volume, describing the most common real stage acoustic configuration to be included in the acoustic simulation process in a preliminary prediction analysis for opera houses, reducing the uncertainty linked to the fly tower model construction. According to the identified fly tower configuration, in which the upper part of the fly tower is used as storage space full of opera sets, an acoustic active volume definition is found. The volume height is suggested to be equal to the distance from the stage floor to 1.5 m above the proscenium, the Depth must be equal to 2/3 of the stage dimension, and the length is considered to be equal to the proscenium dimension plus 2 m ca. According to possible real situations, the surface properties are as follows: the ceiling is considered highly absorptive, the stage surface is a wooden floor on studs, the back wall is a heavy plastic screen for spotlights (not for projections), and the cyclorama is now included in the fixed stage absorption area. This absorption distribution guarantees that the average absorption coefficient will exceed 0.5 at central frequencies of 500 Hz and 1 kHz, to reduce the variable effects of the traditional scenography elements, as suggested by the literature, justifying their absence in the simplified fly tower modeling. The utility of the suggested volume definition was confirmed by the comparison between the empty space configuration and the Semiramide set. Considering the three most important acoustic parameters, T30, C80, and G, only the first one increased significantly in the Semiramide configuration, in accordance with the expectations suggested by the literature, confirming the possibility to preliminarily estimate it, without simulating a traditional set. Considering the Semiramide compared to the empty stage configuration, there is not only a variation in the absorption properties, which decrease because of the presence of many reflecting surfaces, but there is also a shape and position difference of these reflecting surfaces. The back wall and the lateral walls are, in fact, hidden by the scenography that creates an earlier reflection in comparison to the back surface of the empty stage, being nearer to the source. This justifies the different energy distribution during the time in the hall and a different ratio between early and late reflections used to calculate the C80 values. In the literature, it was found that variable stage elements have a significant influence on Reverberation Times in halls, only for low absorption of the walls and ceiling of the fly tower, and that the absorption coefficients of the walls and ceiling over 0.5 avoid the RT from decreasing over 10% for variable absorption of stage elements [11]. In the Semiramide, this is only partially confirmed, with the lateral perimetral walls being partially hidden by reflecting surfaces, supporting the RT increase that can be approximated to 2 JND (10%) compared to that of the empty stage. Also, the preliminary considerations for which the installation of stage sets could increase the Reverberation Time by about 0.1 s, and that the RT can vary from 1.5 to 1.7 s, are confirmed in this case study.