# Historically Based Room Acoustic Analysis and Auralization of a Church in the 1470s
## 4 Room Acoustic Analysis
### Acoustics in the Nave
In Figure 13e, the standard deviation of the EDT is shown for each source position together with the global JND. The standard deviation for a source in the gallery is smaller than the others, and falls below 1 JND for low frequencies. The typical variations for the sources in the naive and in the choir exceed 1 JND. This shows that the perceived reverberance of sources in those two locations varies significantly depending on the listener's position. It also indicates that the small difference in average EDT between sources in the choir and elsewhere (seen in Figure 13e) may be too small to be relevant, compared to the variations between receiver positions. G in the naive is shown in Figure 13e, in octave band resolution for each of the three source positions under consideration. The gray area delimits values within 1 JND of the global average. In this case, there are significant differences between the average results for the three positions. Sound emitted from the source by the high altar is on average heard louder, and sound from sources in the choir are on average heard more quietly. Part of the explanation for this fact may be that there are more receivers with a direct line-of-sight to the sound source in the naive than for the sources in the gallery and the choir. The contribution of the direct sound has a significant impact on the overall sound pressure level, and thus on G.  
The standard deviations of G is also shown, in Figure 13f. Again, these are shown together with the corresponding JND. This graph shows that for sources located in the choir or by the high altar, the spatial variations of G are of a very similar magnitude, and significantly larger than when the source is located in the gallery. This can partially be explained by the position of the gallery in the middle of the church. G is affected by the distance between the source and the receiver, and the gallery's position ensures that the distance between source and receiver varies minimally. C\({}_{80}\) simulation results are shown in octave band resolution in Figure 14. As \(C_{80}\) is not expected to be uniform in a space, all measurement points are shown, together with a line indicating the spatial average. The average C\({}_{80}\) for sources in the choir and gallery fall in the region of \(-15\) dB to \(-5\) dB, significantly below what would be characterized as \"good\" for a concert hall. Clarity for sources located by the high altar is better, at about \(-5\) dB to about 2 dB. Figure 14: \(C_{80}\) in octave bands simulated for the recreated church, shown for 13 different receiver positions. The spatial mean (line) is also shown. (a) \(C_{80}\) when the sound source is located in the nuns’ gallery. One position produces significantly lower clarity. (b) \(C_{80}\) when the sound source is located in the choir. (c) \(C_{80}\) when the sound source is located by the high altar in the nave. Although \(C_{80}\) is not expected to be uniform in a space, the results in Figure 14 show that most values fall in clusters around the average value. However, there is one outlier in Figure 14a, when the source is located in the gallery. This estimate comes from the receiver located underneath the gallery, below point P1 in Figure 9. It is separated from the sound source by the physical structure of the gallery itself, and there is no direct line of sight. A review of the acoustic simulation reveals that the first sound energy reaching this location from the source in the gallery is a second-order reflection, showing that sound energy reaching this location from the gallery consists solely of reflections of order two or higher. This significantly decreases the cohesion and energy level in early parts of the impulse response, leading to a very poor clarity of sources in the gallery as perceived by listeners beneath it. The acoustic field in the naive is further analyzed to determine whether the spatial variations for sources in the choir and by the high altar, seen in Figures 13e,f and 14, are caused by acoustic subspaces.