## 3 A Taxonomy of Surveys, and Some Unresolved Instances
A loudspeaker orchestra was adapted for the pit layout, taking into account the loudspeaker directivity and the sound power level of each source [171]. Virtual acoustics can be a useful tool for improving the knowledge of opera houses [172]. Simulated impulse responses allow us to extend the virtual experience of an opera house, including the occupation and other variables, such as the scene configuration. Virtual acoustics allows also to enjoy a no-longer existing space [91; 173]. While scale model were widely used in the design and analysis of opera houses until recent years [110; 166; 174; 175], numerical simulation of sound field was introduced, in the context of Italian opera houses, during the 1990s [148; 176; 177]. However, many models have been developed for acoustic consultancies and they are not available on a repository. As a consequence, there is a limited literature on the materials and acoustic peculiarities of Italian opera houses. Instead of this, the data sharing could provide many benefits. [PERSON] et al. [178] shared measurements, made by a 32-element spherical microphone array, and both omnidirectional and \begin{table}
\begin{tabular}{l l l l} \hline \hline Ref. & Theatre(s) & Year & Country \\ \hline
[18] & Bayreuth Markgrafliches & 1750 & Germany \\
[18] & L’Opera Royal Versailles & 1770 & France \\
[157] & Grand Theatre, Bordeaux & 1780 & France \\
[158] & S. Carlos, Lisbon & 1793 & Portugal \\
[159] & Palace Theatre, Archangelskoje & 1818 & Russia \\
[160] & Bolshoi, Moscow & 1825 & Russia \\
[161] & Teatro Principal, Valencia & 1832 & Spain \\
[162] & Opera House, Wroclaw & 1841 & Poland \\
[158] & Donna Maria II, Lisbon & 1846 & Portugal \\
[160] & Maríinsky, St. Petersburg & 1860 & Russia \\
[160] & Opera House, Saratov & 1860 & Russia \\
[158] & Trindade, Lisbon & 1867 & Portugal \\
[160] & Opera House, Voronezh & 1870 & Russia \\
[158] & Sa de Miranda, Viana do Castelo & 1879 & Portugal \\
[68] & Hungarian State Opera House & 1884 & Hungary \\
[158] & Coliseu dos Recreios, Lisbon & 1890 & Portugal \\
[158] & Garcia Resende, Evora & 1892 & Portugal \\
[158] & S. Luiz, Lisbon & 1894 & Portugal \\
[158] & Viriato, Viseu & 19 th Century & Portugal \\
[59; 68] & Colon, Buenos Aires & 1908 & Argentina \\
[163] & Grand Theatre, Poznan & 1910 & Poland \\
[160] & Opera House, Ekaterinburg & 1912 & Russia \\
[164] & Municipal Theatre, Lima & 1920 & Peru \\
[158] & S. Joao, Oporto & 1920 & Portugal \\
[160] & Music Hall, St. Petersburg & 1928 & Russia \\
[160] & Maliy, St. Petersburg & 1944 & Russia \\
[165] & Teatro Argentino, La Plata & 1999 & Argentina \\
[166] & Opera House, Astana & 2013 & Kazakhstan \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Surveyed Italian-style opera houses built outside Italy. a directional sound source, of American and European concert halls. Concerning the opera houses, as of today there are few examples of free-available data. [PERSON] et al. [PERSON] et al. (2015) shared their work on Italian court theatres, including measured and simulated impulse responses. More models were provided by the author's workgroup for Bayreuther Festspielhaus (2019), Alighieri Theatre in Ravenna (2019), Comunale of Bologna (2019). In the author's hope, this approach could be shared by the scholars' community, in order to increase the knowledge on this complex topic.