Acoustic characteristics and objective evaluation of acoustic quality in historical Italian theaters

In order to determine an objective range of acoustic parameters for historical Italian theaters and to recommend ideal values for the primary acoustic parameters reverberation time (\textit{$T_{20}$}, \textit{$T_{30}$}), early decay time (\textit{EDT}), sound strength (\textit{G}), clarity index (\textit{$C_{80}$} and \textit{$C_{50}$}), definition (\textit{$D_{50}$}) and interaural cross correlation coefficients (\textit{IACC}), an acoustic survey of 24 historical Italian theaters spread over 8 regions of Italy was conducted. In the survey, two distinct acoustic measurements were used: 1. Conventional monaural and binaural measurements under unoccupied conditions. 2. Sound field visualization utilizing a 360{\textdegree } camera and an em32/64 Eigenmike\tsup{\textregistered}. The geographic distribution features of the 24 theaters, correlations among parameters, performance of each parameter across various frequencies, and dispersion characteristics were analyzed and quantified through computational methods. The acoustic quality of the theaters was ranked according to the statistical results, giving a range of desirable values for each acoustic parameter. It has been discovered that: 1. Correlation analysis indicates that at 1000 Hz, all parameters exhibit the strongest correlations, with a notably strong negative correlation between reverberation time and both clarity index and definition, and a strong positive correlation between clarity index and definition. These results suggest that data at 1000 Hz may be most suitable for machine learning predictions of parameters affected by measurement distance. 2. Boxplot analysis indicates that \textit{G} is the only parameter without outliers, with variations in other parameters attributed to differences in geographical location, temperature, humidity, theater size, and interior decoration, highlighting the need to consider performance-specific acoustic requirements in evaluations. 3. Objective assessments reveal that most theaters perform best in clarity index values, with Italian historical theaters exhibiting significantly higher \textit{G}-values, possibly due to factors such as reflective surfaces, stage structure, and architectural design features. 4. Theaters such as Teatro Amintore Galli (Rimini), Teatro dell'Opera (Rome), and Teatro Minimo (Atri) demonstrated notable acoustic performance based on the evaluated parameters.