# Historically Based Room Acoustic Analysis and Auralization of a Church in the 1470s
## 4 Room Acoustic Analysis  
The sound field in the reconstructed church was evaluated from room acoustic simulations. Three questions were specifically examined. First, three different visitor conditions were evaluated. The three conditions corresponded to an empty church, an ordinary sext (about 30 individuals), and a more festive event (about 140 individuals). The sext condition corresponds to the situation targeted in the auralization, with twelve nuns in the gallery, eight monks in the choir, and about ten other visitors in the central-eastern part of the nave. In the festive condition, denoted \"full\", there were 70 nuns in the gallery, 13 monks in the choir, and about 70 visitors in the nave. Second, the sound fields within the choir and gallery are examined. These locations are important for the religious practices of the order, and acoustic analysis of these spaces may provide new insights. Third, the sound field in the nave is examined. The auralizations are provided as supplementary material, and are not further analyzed in this text. Four room acoustical parameters are presented, as defined in ISO 3382-1:2009 [52]. The reverberation time \(T_{20}\) is presented, due to its traditional importance in acoustics. It is primarily useful as a tool for comparison to other spaces, as the reverberation time is a commonly measured acoustic characteristic. The early decay time (EDT) is also presented. It describes the rate of sound energy decay in the first parts of the impulse response, and is closely related to perceived reverberation and the presentation quality of Gregorian chant. Figure 9: Top-down view of the digital reconstruction of the abbey. North is up in the figure. The monks’ choir is the red area to the left, and the nuns’ gallery is the red area in the center. Three source positions—P1, P2, and P3—are marked. According to guidelines proposed by [PERSON] et al. [4], EDT values in the range 2.1 s to 4.2 s are appropriate for churches. In addition, \(C_{80}\) is presented as an indicator of the clarity and intelligibility of chant. As the liturgical practices of this region and time do not contain significant spoken elements, \(C_{50}\) (speech clarity) is not presented separately. For concert halls, \(C_{80}\) values of above 0 dB are usually considered \"good\", but no such guidelines have been defined for worship spaces. Finally, the sound strength (G) is presented. This value shows the total sound pressure level (SPL) at the receiver, as compared to what would be perceived from the sound source in free field at a distance of 10 m. G is positive in enclosed spaces. A summary of the results is shown in Table 1. This table gives values for \(T_{20}\), \(C_{80}\), EDT, and G, averaged according to ISO 3382-1:2009 [52]. In addition, the results are divided into categories based on the location of sources and receivers. If the source and the receiver are both within the gallery (point P1 in Figure 9), the data is denoted \"Gallery\". If both source and receiver are in the chair (point P2 in Figure 9), the data is denoted \"Choir\". Finally, if the sound has travelled through the naive, the data is categorized as \"Nave\". This includes when either the source or the receiver is located in the naive, but also the conditions where one is in the chair and one is in the gallery. One result seen in Table 1 is that the number of visitors and the visitor condition have an impact on all room acoustic parameters presented. There are no or almost no differences between the empty and the sext condition, but the full condition leads to significant decreases of EDT and \(T_{20}\). This is an expected result of the increased amount of absorption when the number of visitors increase. Increased absorption should also lead to an increased \(C_{80}\) and a decrease in G. These patterns can be seen, but are weak. The only differences larger than 1 JND are seen for \(C_{80}\) in the gallery and G in the naive.