# Acoustic Shell Optimization in Opera Houses for Concert Halls
## 4 Comparison of Results and Discussion
#### Musicians' Opinion  
A total of 64 musicians were interviewed to gather their opinions about their preferred configuration of the acoustic shell on stage. A simple questionnaire was used, which asked two questions. The first one asked musicians to choose their favourite layout between the two analyzed (the big shell and the small shell). The second one asked musicians to indicate their choice of why, between acoustic and comfort reasons, while adding some personal motivations.  
90% reported that they preferred to play in the hall, justifying staying as close to the audience as possible, considering acoustic quality improvements by the acoustic shell of secondary importance. When asked whether their position corresponded to the optimization of sound distribution for the orchestra and in the hall, the answer was negative.  
The musicians reiterated that, although a big, deep acoustic shell improves the sound field quality both for the players and the audience, it was more important for them to feel visually and physically closer to the audience by playing a symphonic piece, as in a concert hall. In concert halls, in fact, the stage is usually lower than that in a theatre and the first row is much nearer, as it is not constrained by the orchestra pit gap or by the pit itself used to create the extension of the stage.  
Furthermore, musicians highlighted that they do not appreciate being positioned at the back, too far from the proscenium. For these reasons, they considered the small acoustic shell (layout 2) to be the best compromise.  
For most of the musicians, the proscenium represents a separation line beyond which one is no longer part of the hall; that is, one becomes part of a show in which musicians have the psychological experience of not being part of the same space of the audience, even if the acoustic quality is improved.  
Musicians instead confirmed the importance of isolating the stage space from the hall through a back wall, placed not so far from the proscenium, to avoid dispersing the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Configurations** & \multicolumn{3}{c}{**Symbolonic Music**} \\ \hline  & C80 [dB] & G [dB] & T30 [s] \\ Optimal Range & \(-3<\) C80 \(<\) +3 & \(\geq\)\(-4\) & \(1.8<\) T30 \(<\) 2.2 \\ OAC2 & 0 & 3.4 & 2 \\ OAC3 & 0 & 4.2 & 1.9 \\ OAC5 & 1.2 & 2.5 & 1.85 \\ \hline \hline \end{tabular}
\end{table}
Table 16: Main acoustic parameters’ average values.  
Figure 18: Average G comparison for the three main configurations, OAC2, OAC3, and OAC5.  
sound behind them. For all these reasons, the reduced acoustic shell on the stage (OAC5) was chosen by the musicians as the best layout to satisfy both their psychological and acoustic necessities. They also argued that, in many visited theatres, big acoustic shells lay abandoned in the backstage of the fly tower.  
Some practical discussions about new, modern, lighter construction technologies to hang the shell panels (such as aluminum and fibre-reinforced plastic polymers, which are entering the market [54, 55, 56]) were also taken into consideration, to give them the possibility of adjusting the panels' position after the main layout has been fixed.