## 3 A Taxonomy of Surveys, and Some Unresolved Instances
Moreover, the Ferrara charter states a minimum amount of drapes in the fly tower--about 400 m\({}^{2}\) in case of mid-sized opera house--in order to have a 'acoustic' scene comparable to the opera performance. Indeed, when the amount of drapes increases, the sound energy in the main hall decreases and the opposite one. Some scholars tried to measure the fly tower and the main hall when they are separated by the firedoor, some others measure the audience by closing the scene curtains [96]. The second unresolved point concerns the measure of spaciousness. Indeed, the result of spatial measurement depends on the technologies used in the measurements: different microphones can \begin{table}
\begin{tabular}{l c c l} \hline \hline Theatre(s) & Year & Size & Measurement & Repository \\ \hline [PERSON], Benevento & 1862 & small & TC [44; 127] \\ [PERSON], Spoleto & 1864 & mid & TC [93] \\ [PERSON], Cesenatico & 1865 & small & TCGS [20; 129] \\ [PERSON], Pisa & 1867 & mid & T [44; 140] \\ [PERSON], Cerignola & 1868 & mid & TCGS [83] \\ [PERSON], Busesto & 1868 & small & T [114] \\ [PERSON], Treviso & 1869 & mid & TCS [44; 84; 94] \\ [PERSON], Salerno & 1872 & mid & [44; 75; 145] \\ [PERSON], Barletta & 1872 & small & TCGS [83] \\ Paisiello, Lecce & 1872 & small & TCGS [44; 83; 142] \\ R. Margherita, Caltanissetta & 1875 & small & TC [127] \\ Rossetti, Trieste & 1878 & mid & TC [127] \\ Comunale, Russi & 1887 & small & TCGS [20; 129] \\ Bellini, Catania & 1890 & large & TC [86; 127] \\ Van Vesterhout, Mola & 1896 & small & TCGS [83] \\ Massimo, Palermo & 1897 & large & TC [127] \\ Sociale, Rovigo & 1904 & mid & TCS [44; 84] \\ Comunale,Nardo & 1908 & small & TCGS [83] \\ Civico, Schio & 1909 & small & TC [44; 84] \\ Opera, Roma & (1928) & large & TCG [44; 85] \\ Comunale, Adria & 1935 & mid & TCS [44; 84] \\ Duse, Bologna & (1943) & mid & TCC [146] \\ TEA, Bologna & 1975 & large & TCGS [73] \\ [PERSON], Genova & (1991) & large & TC [44] \\ Lirico, Cagliari & 1993 & large & TCG [44; 109] \\ Arcimboldi, Milano & 2001 & large & TCGS [44; 110] \\ La Fenice, Venezia & (2003) & mid & TCS [44; 84; 133] \\ Garibaldi, Bisceglie & (2003) & mid & TCGS [83] \\ [PERSON], Brindisis & (2006) & large & TCGS [83] \\ Comunale, Gradisca d’Isonzo & (2009) & mid & TC [44; 148] \\ Petruzzelli, Bari & (2009) & large & TC [105] \\ Maggio Musicale Fiorentino & 2011 & large & TC [111] \\ Eschilo, Gela & (2013) & small & TC [149] \\ Civico, Schio & (2014) & small & TC [90] \\ Galli, Rimini & (2018) & mid & TC [107; 108] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Surveyed Italian-style opera houses built in the unitarian Italy (1861–2020). Rebuildings are indicated by brackets. The “measurement” column specify which kind of measurements were performed: \(T\) means reverberation time, early decay time, and more; \(C\) means, e.g., early-to-energy ratio, sound clarity, definition; \(G\) means Sound Strength, \(G_{E}\), \(G_{L}\) using a calibrated sound source; \(S\) means spaciousness criteria, such as \(IACC\), \(LFC80\), and more. provide different results [153]. Moreover, the spaciousness varies considerably if it measured in the center of the stalls, or near the side walls; if the receiver is in the boxes, it may vary if it is placed close to the edge or inside the box. Spatial measurements [154; 155] could become a helpful tool to resolve this ambiguity [156]. The third point concerns the sound strength. This criterion was still rarely measured, according to Tables 2 and 3. Moreover, a theoretical model for sound energy distribution in an opera house is needed. It must take into account the size of aperture, the coupling effect between the two sub-rooms [146; 167; 168; 169; 170]--the fly tower and the main hall--and the sound source position [129]. Furthermore, due to the subjective relevance of the balance and listener envelopment, the SISO (single-input-single-output) model of sound strength could be extended. An attempt of MIMO (multiple-input-multiple-output) measurements were done in Comunale Theatre in Bologna.