## 3 Methodology
### In Situ Measurement  
Measurements in the church were carried out in situ without an audience to characterize its behaviour [27]. The measurement chain was used to obtain impulse responses (IR) from which all the acoustic parameters that define the sound field can be obtained. At each point where a receiver was located, the IR was obtained from sweeps of sinusoidal wave signals, with frequency increasing exponentially with time [28]. Both the frequency range and the duration of each sweep were adjusted to suit the environmental conditions in order to have impulse responses of adequate quality, so that the signal-to-noise ratio exceeded 45 dB in all the octave bands analysed, 125 to 4000 Hz. WinMLS2004 software with a Roland Edirol UA 101 sound card was used to generate the signal, recordIRs, and analyse results. The signal generated by the laptop was fed to a Behringer Eurolive B1800 DProas amplifier connected to an AVM D012 01 dB omni-directional source. IRs were recorded using an Audio-Technica AT4050 multi-pattern microphone with omnidirectional configuration connected to the Soundfield polarization source (SMP 200). A Head Acoustic HMS III torso simulator pointed towards the sound source was used, together with the OPUS 01 dB signal conditioner, to obtain the cross-correlation coefficients. The background noise spectrum is measured with a Bruel & Kjaer B&K 4165 microphone connected to a Svantek SVAN 958 noise analyser. In the acoustic measurement of the church, the sources were placed in four positions. Positions S1 (main altar), S2 (dome) and S3 (choir) corresponded to the positions described in Figure 3, used in the study of the different hypotheses. Source S4, on a side altar, was considered only as an in situ measurement. The positions for the receivers located in the audience area coincided with those in Figure 3, numbered from 1 to 9. The sources and receivers were placed at heights of 1.50 m and 1.20 m, respectively. With respect to the interior material used (Table 3), the plaster of the walls and dome accounts for more than half of the surfaces, while the marble of the flooring and decorative elements also has a great impact. The wooden altarpieces also occupy a large surface area, with other materials such as glass or ceramic flooring found, albeit to a lesser extent, on the upper floor. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Materials** & **Location** & **Surface Area (m\({}^{2}\))** & **Surface Area. (\%)** \\ \hline \hline \multirow{2}{*}{Plaster} & Walls and dome & 1527.80 & 58.62 \\ \cline{2-4}  & Ground and choir floor. & 577.34 & 23.15 \\ \cline{2-4}  & Solomonic and choir columns. & 283.70 & 10.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Materials, location, surface area, and percentage. Table 4 shows the results for the acoustic parameters of the ISO 3382-1 standard, obtained for the position of the source on the main altar (S1), the source position considered for the validation of the computer model. Based on the measurement results evaluated by [PERSON] et al. (2019), it can be stated that _\"the analysis showed negligible differences in the reverberation time for all sources, as also confirmed by conventional criteria proposed by standards to evaluate the curvature of decays. Nevertheless, for EDT values, the differences in early energy growth gave rise to a different behaviour as a function of the position of the source clearly appeared. Bayesian analysis showed that several double slopes appeared in decay curves, spanning different frequencies, particularly when the source was under the dome or close to a lateral altar. The most affected octave band frequencies were 2 kHz and 4 kHz. Although not particularly evident, the double slope phenomenon could be associated to an uneven distribution of sound energy due to acoustic coupling between different sub-volumes\"_.