# Courtyard Sound Field Characteristics by Bell Sounds in Han Chinese Buddhist Temples
## 3 Results and Discussion
### Courtyard Interface Materials  
The building materials used in Han Chinese Buddhist temples include bricks, wood, tiles, and stones. Temple courtyard walls are mostly made from smooth bricks with small sound absorption coefficients. In the sound field simulation model, the sound absorption coefficients of temple courtyard walls at various frequency bands were set in the range of 0.01 to 0.03. The scattering coefficient was set to 0.15. Studies show that when the courtyard wall is made from different materials or with different climbing plants, its sound absorption and scattering coefficients will change [49]; a vegetation-covered wall will have a sound absorption coefficient of 0.6 to 0.7 at frequencies of 125 Hz to 4 kHz [50]. In the interest of research simplification, this study assumed that at each frequency band the sound absorption coefficient of the temple courtyard wall was 0 for smooth brick walls, 0.3 for brick walls that were covered to some extent with climbing plants, and 0.6 for walls covered with greenery growing in soil. Moreover, if hedges of sparse foliage enclosed the temple, the sound absorption coefficient would be assumed as 0.9, since sound can easily pass through hedges, and each scattering coefficient was set to 0.1. Courtyard sound fields were simulated for the aforementioned four types of temple courtyard walls. As shown in Figure 10(a), for every increase of 0.3 in sound absorption coefficient, the SPL(A) of the second and third courtyards decreased by 1.2 to 4.0 dBA, and that of the fourth courtyard decreased by 2.2 to 4.6 dBA. In particular, when the sound absorption coefficient increased from 0.6 to 0.9, the SPL(A) dropped significantly. Figure 10(b) shows that increases in courtyard wall sound absorption coefficients increased the standard deviation of SPL(A), resulting in the non-uniform distribution of SPL(A) in courtyards. As shown in Figure 10(c), for every increase of 0.3 in the sound absorption coefficient, T\({}_{30m}\) decreased by 9% to 32%, 5% to 14%, 5% to 6%, and 9% to 18% in the first, second, and fourth courtyards, respectively. For every increase of 0.3 in the sound absorption coefficient, EDT\({}_{\text{m}}\) decreased by 5% to 12%, 2% to 7%, 7% to 21%, and 11% to 28% in the first through fourth courtyards, respectively, with most of the decreases exceeding the JND. Figure 10(d) shows that if the sound absorption coefficients of temple courtyard walls increased from 0 to 0.9, C\({}_{80}\) increased by 2.1 dB, 1.9 dB, 4.4 dB, and 3.6 dB in the first through fourth courtyards, respectively. This shows that when compared with various vegetation-covered walls or hedges, smooth brick walls lead to higher SPL(A) with more uniform distribution in sound fields of Buddhist temples, while increasing RT and decreasing C\({}_{80}\). Figure 11: _Cont._Courtyard grounds of traditional Buddhist temples are generally paved with hard bricks or stones, with partial areas of natural vegetation (greenery) or bare soil. In this study, each courtyard's sound field was simulated with three different courtyard ground compositions: 100% greenery, 100% bare soil, or 100% stone pavement. Figure 12a shows that there was almost no difference in SPL(A) between courtyard sound fields with ground compositions that were either greenery or bare soil. The sound level was higher in the stone pavement courtyard than in courtyards that had the other two types of ground, by about 1.6 dBA in the first courtyard; furthermore, the SPL(A) was higher by about 1.3 to 3.8 dBA in the second through fourth courtyards compared with the other two types of ground. Figure 12b shows that greenery and bare soil exhibited very similar results with regard to the first courtyard's EDT\({}_{\text{m}}\) value; however, for stone pavements, the first courtyard's EDT\({}_{\text{m}}\) was about 13% higher than in the other two scenarios.