# Acoustic Shell Optimization in Opera Houses for Concert Halls
## 5 Conclusions  
The acoustic shell size in a baroque theatre, as a function of proscenium and stage dimensions, confirms that its installation significantly influences the sound field of the baroque theatre itself, by transforming the acoustics' quality to that of a concert hall. In a baroque theatre, the reverberation time is affected by both the shape and dimensions of the acoustic shell and the number of musicians on stage. In the presented case study, the RT decreases for each frequency, both as the number of musicians on stage increases and as the size of the acoustic shell decreases. As the number of musicians on stage increases, for the same acoustic shell dimensions, the RT is slightly reduced and the uniformity of the parameter distribution in the hall increases. The C80 parameter, referred to a large acoustic shell, is very similar in the two configurations (with and without the choir), has significantly higher values relative to the small acoustic shell, with an approximate change of 1 JND at all frequencies. The C80 is more sensitive to a reduction in acoustic shell volume and less sensitive to changes in the number of musicians than the T30. In the big acoustic shell configuration with choir, the C80 values in the boxes are higher than those in the stalls, also with a larger standard deviation. In the small shell configuration, the standard deviation in the stalls does not differ significantly from the boxes, even if the mean value in the stalls is higher than that in the boxes. The G parameter is also very similar in the two configurations, referring to a large acoustic shell, not reaching 1 JND by introducing the choir on stage, while it exceeds 2 JND in the small acoustic shell configuration compared with both previous configurations. The G parameter is affected more by the decrease in acoustic shell volume compared to the other two parameters. From the presented acoustic analysis, the configuration that optimizes the acoustic field for symphonic music is the one with the big acoustic shell, for which the mean parameter values are in the middle of the optimal range, as suggested by the literature. This configuration was recognized by the musicians to be the one with the best acoustics for concerts. Nevertheless, for psychological reasons, such as the need to feel as close as possible to the audience, interviewed musicians mostly preferred the reduced acoustic shell configuration, confirming the importance of isolating the stage space from the hall through a back wall, placed not far from the proscenium, to avoid dispersing the sound behind them, optimizing orchestra distribution on stage. This paper would like to underline the rules regarding the musicians' opinions during the acoustic design and/or analysis process, to better focalize the applied acoustics activities. For this case study, in the case of the acoustic shell configuration made of reflecting wood panels, it was found that, even if a large volume better satisfies the acoustic con ditions for concerts, a small shell represents dimensional optimization according to the musicians' requests. Collecting musicians' opinions in a preliminary phase could be very useful to find easier solutions able to converge both acoustic quality and musicians' wishes. In further research, the acoustic shell dimensions optimization could be standardized according to the theatre dimensions, seating capacity and orchestra composition (number of musicians with or without choir), recommending a modular structure for easier adjustments on site, avoiding that big acoustic shells lay abandoned in the backstage of the fly tower. Given the widespread use of shells in other historic theatres and churches, the methodology adopted here could be investigated to enlarge the standards applications to those building typologies, also verifying whether similar objective-subjective divergences occur elsewhere. Conceptualization, A.T. and U.D. ; methodology, S.S. and U.D. ; software, U.D. ; validation, A.T. and U.D. ; formal analysis, U.D. ; investigation, U.D.