## 3 Methodology
### Model Validation  
Once the data of the model of the current state with the empty church had been entered in CATT-Acoustic, it was validated to adjust it to the results obtained in the in situ measurement, so that its acoustic behaviour was similar to the current one (Figure 5). To achieve this objective, the absorption and scattering coefficients of the materials, especially those which present greater uncertainty, must be modified. This adjustment was applied to the reverberation time (\(T_{30}\)) so that the values obtained in the calculation were similar to those measured in situ for the different octave bands. As a validation criterion (29), it was estimated that the coincidence was adequate if they differed less than the perceptible threshold Just Noticeable Difference (JND), that is, 1 JND for \(T_{30}\) (less than 5% of the values measured for each octave band). The rest of the parameters were considered adequate below 2 JND, according to consensus (30). In contrast, as indicated by [PERSON] (31) in his study for the value of JND in \(C_{g0}\) and Ts for three churches, the value of 1 JND for clarity and sharpness in widely reverberant spaces can be modified in relation to the regulations in place, considering 1.5 dB for \(C_{80}\). In the case studied, although \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **125 Hz** & **250 Hz** & **500 Hz** & **1 kHz** & **2 kHz** & **4 kHz** & **Single Number** \\ \hline \(T_{30}\) (s) & 3.59 & 3.72 & 3.72 & 3.39 & 2.81 & 2.16 & 3.55 \\ EDT (s) & 3.030 & 3.09 & 3.03 & 2.75 & 2.20 & 1.71 & 2.89 \\ G (dB) & 15.07 & 15.63 & 14.28 & 10.97 & 10.37 & 9.42 & 12.62 \\ \(C_{80}\) (dB) & \(-\)0.42 & \(-\)1.18 & \(-\)1.80 & \(-\)0.61 & 0.41 & 1.52 & \(-\)1.20 \\ \(D_{50}\) (-) & 0.38 & 0.32 & 0.27 & 0.35 & 0.40 & 0.45 & 0.31 \\ \(I_{\rm{LE}}\) (-) & 0.13 & 0.27 & 0.40 & 0.35 & 0.31 & 0.28 & 0.28 \\ \(I_{\rm{ACC_{E}}}\) (-) & 0.96 & 0.84 & 0.58 & 0.57 & 0.40 & 0.34 & 0.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Acoustic parameter values in frequency octave band and single number frequency averaging (27). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **Location** & **Surface Area (m2)** & **Surface Area. (\%)** \\ \hline Glass & Dome and choir windows & 82.80 & 3.20 \\ \hline Hole & Communication gap with the & 43.70 & 1.70 \\  & Noviiate & 38.26 & 1.50 \\ \hline Organ & Choir organ & 23.50 & 0.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(Cont.\)a faithful adjustment of the reverberation times was achieved, the validation criterion could not be met in almost any of the parameters. EDT values, corresponding to the early decay time, are more closely related to the subjective perception of reverberation, given its dependence on the energy associated with the early reflections obtained in the in situ measurement. Major variations in EDT were observed based on the position of the sound source and in its behaviour in relation to the source-receiver distance. This highlights the presence of double slopes in the energy decay curves, showing that the dome behaves as a coupled space. For this reason, EDT was chosen as the adjustment parameter, allowing improved behaviour of most of the acoustic parameters which determine the sound characteristics of the church. The model was validated with the source located at the main altar (S1) and the receivers in the positions used in the in situ measurement. Table 5 shows the absorption and scattering coefficients of the different materials found inside the room used for the validation of the model. The composition of the plaster walls, which account for more than 50% of the total interior surface, is not known exactly. Therefore, in the interactive process of fitting the model, the initial absorption coefficient values were modified to ensure that the space simulated presents the same acoustic behaviour as the real room. Another aspect to consider in the model is that the room is not independent from the novitiate building, as the church and novitiate are connected by spaces with no door.