## 7 Data Analysis and Results  
Graphs in Figure 12 show the results of the simulations related to all the different scenarios, considered to be the average values of all the receivers inserted in the model. The virtual sound source in the digital model has been installed in the center of the stage, where most of the time the action takes place and simulates the actor singing other than to reproduce the location of the sound source placed during the acoustic survey. The characteristics of the sound source has been simulated to be provided of 1W at 1m, equal to a sound pressure level of 110 dBA. Graph (a) in Figure 12 indicates that no difference was obtained between the scenery of the three different acts, except for 2 kHz and 4 kHz, where EDT values related to Acts I and II are slightly higher than values related to Act I [20]. However, by considering only Act I, the values obtained by simulating the presence of the audience at 50% and 100% occupancy are lowered by up to 0.1 s at low frequencies, while no difference has been found at high octaves [21]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{**Area (m2)**} & \multicolumn{6}{c}{**Absorption Coefficients—Octave Frequency Bands (Hz)**} & \multirow{2}{*}{**Scattering**} \\ \cline{3-3} \cline{5-8}  & & **125** & **250** & **500** & **1 k** & **2 k** & **4 k** \\ \hline \multirow{3}{*}{Heavy cloth—Actors} & 33 (Act I) & & & & & & & \\  & 6 (Act II) & 0.80 & 0.80 & 0.80 & 0.80 & 0.80 & 0.80 & 0.05 \\ \cline{1-1} \cline{3-3} \cline{5-8}  & 51 (50\% capacity) & & & & & & & \\  & 102 (100\% capacity) & 0.60 & 0.60 & 0.60 & 0.60 & 0.60 & 0.60 & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Surface, absorption and scattering coefficients of the additional materials considered during the acoustic simulations. Figure 12: Simulated results of the main acoustic parameters: early decay time (**a**), reverberation time (**b**), clarity index (**c**), and definition (**d**). In terms of reverberation time, the difference of the T\({}_{20}\) values among all the five scenarios, as shown in graph (b), is very minimal such that it can be considered negligible. However, the T\({}_{20}\) value at 500 Hz equal to 0.9 s is considered optimal for an Opera theater with this volume size [22]. Graph of Figure 12c indicates that the speech clarity index is within the optimal values at low frequencies, because it is between 0 and +2 dB [23], and is up to 4 dB above the upper range limit. In addition, the C\({}_{50}\) values related to all the acts have similar trends; however, graph (c) shows an upward shift of 0.3 dB between values of Act II and III, and a further upward shift of 0.4 dB between values of Act III and I. The simulations carried out with the presence of the audience, although no variance has been found between 50% and 100% occupancy, shift upward the curve of similar trend, to be 0.3 dB above the values related to Act I [24]. The values of definition (D\({}_{50}\)), as shown in graph (d) of Figure 12 have been found to be fluctuating between 0.5-0.6 at low frequencies and 0.75-0.85 at high-frequency bands, meaning that the speech definition is considerably good inside the National Theater of Zagreb, considered very suitable for Opera [25]. An alternative way of representation has been carried out in terms of spatial distribution. This is another output data that can be obtained with Ramsete software and it consists of the contour levels describing the variation of the acoustic parameters across the audience areas. The setup options allow the determination of the selected octave frequency band to be analyzed other than the range limits of the values. On this basis, Figure 13 indicates two examples of spatial distribution related to two acoustic parameters: the reverberation time (T\({}_{20}\)) and the speech clarity index (C\({}_{50}\)), considered at 500 Hz and related to the scenery of Act I without any audience.