# Historically Based Room Acoustic Analysis and Auralization of a Church in the 1470s
## 4 Room Acoustic Analysis
### Acoustics within the Choir and Gallery  
The acoustic simulation results within the gallery (source and receiver both near point P1 in Figure 9, reflecting the experiences of the nuns), and within the chair (source and receiver near point P2, reflecting the experience of the monks) are presented in Figure 10. In these graphs, room acoustical parameters \(T_{20}\), EDT, \(C_{80}\), and G are shown in octave band resolution. The gallery data are shown together with lines denoting \(\pm\)1 JND, such that when the chair data falls within these lines there is no perceivable difference between the two locations. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Gallery**} & \multicolumn{3}{c}{**Choir**} & \multicolumn{3}{c}{**Nave**} \\  & **Empty** & **Sext** & **Full** & **Empty** & **Sext** & **Full** & **Empty** & **Sext** & **Full** \\ \hline \(T_{20}\) (s) & 5.17 & 4.90 & 4.00 & 4.06 & 3.89 & 3.26 & 5.37 & 5.19 & 4.36 \\ EDT (s) & 1.21 & 1.10 & 0.62 & 2.41 & 2.33 & 2.21 & 5.47 & 5.29 & 4.55 \\ \(C_{80}\) (dB) & 8 & 8 & 10 & 1 & 1 & 1 & \(-\)10 & \(-\)10 & \(-\)10 \\ G (dB) & 16 & 16 & 15 & 15 & 15 & 15 & 6 & 6 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Room acoustic parameters in various configurations of the reconstructed abbey. The values have been averaged according to ISO 3382-1:2009 [52]. The reverberation time is significantly lower in the choir compared to the gallery. A review of the full results in Table 1 shows that the results in the gallery and the results in the rest of the church only differ by \(\pm\)1-2 JND, whereas the discrepancy with the choir is larger. The second reverberation parameter, EDT, shows a different pattern. The EDT is much smaller than \(T_{20}\) for both positions, and the EDT in the gallery is significantly lower than that in the choir. The large discrepancy between the EDT and the \(T_{20}\) may indicate that the decay curves in these spaces follow a multi-slope decay pattern, which would be consistent with these spaces acting as acoustically distinct subspaces. The energy decay curves are more closely investigated in Figure 11.  
Figure 10: Graphs showing (**a**) \(T_{20}\), (**b**) early decay time (EDT), (**c**) \(C_{80}\), and (**d**) G in octave band resolution in the reconstructed obey choir and gallery. The results for the gallery (red) are shown with dotted lines corresponding to \(\pm\)1 JND. When the results for the choir (blue) falls within these lines, there is no perceivable difference between the two data sets. Reviewing the energy decay curves in Figure 11 shows a distinctly curved decay pattern in both gallery and choir. As expected from the results in Figure 10, the acoustic energy in the gallery decreases rapidly in the early parts of the decay, and then flattens out to a much slower decay rate. This is consistent with the formation of an acoustic subspace within the gallery, coupled to the larger, more reverberant space in the naive. As the acoustic energy within the subspace decreases, the reverberance of the naive becomes more dominant. The transition seems to occur after about 100 ms. The energy decay curve in the choir seems more complex, and is likely influenced by the three close, hard walls on three of four sides as well as the more distant vaulted ceiling. It is possible that these decay curves are formed by more than two distinct decay patterns. It can, however, be seen that the decay process after about 750 ms is more smooth. This transition time is later than in the gallery. Returning to the results in Figure 10, it is seen that \(C_{80}\) is also significantly different between the gallery and the choir across all octave bands. Clarity is much better in the gallery compared to the choir, which is in turn much better than what is found in the rest of the church (Table 1). The reason for these differences can be explained by the physical configuration and particularly the effects of the ceiling vaults.