# Courtyard Sound Field Characteristics by Bell Sounds in Han Chinese Buddhist Temples
## 2 Research Methods
### An Acoustic Model of Han Chinese Buddhist Temples  
The outdoor courtyard spaces of Han Chinese Buddhist temples were simulated in this study using acoustic software (Odeon). Based on geometrical acoustics, the software uses a hybrid approach that combines both the image source and the ray-tracing method in conjunction with the secondary source method to perform computer-aided sound field simulation on the absorption, scattering, and diffraction of sound waves. Aside from enclosed buildings, the software is applicable to open plazas and semi-enclosed buildings as well. The software calculation settings were set to the most accurate mode: 'precision'. Quick and global estimate functions were used to estimate the reverberation time of the acoustic models. The computation results, including multiple acoustic parameters, such as EDT, T\({}_{30}\) (reverberation time extrapolated from the time required for sound to decay by 30 dB, from \(-5\) dB to \(-35\) dB), C\({}_{80}\), and SPL, provided comprehensive reference data for acoustic analysis [37; 38]. According to the basic layout proposed by [PERSON] [3] for ancient Han Chinese Buddhist temples (Figure 1) and a field survey on temple typicality, this study established an acoustic model for standard forms of Han Chinese Buddhist temples (Figure 2). Geometric dimensions of the model were set by referring to the reported survey results of key Han Chinese Buddhist temples throughout China. In all, 70% of Buddhist temples are less than 100 m wide, 33% have a depth of 50 m to 100 m, and 47% have a depth of 100 m to 200 m [39]. In this study, the model's temple width was set to 50 m, depth was set to 150 m, and there were four courtyards along the central axis. In the model, sound receivers were placed on a grid of 10 m \(\times\) 10 m cells in each courtyard; each receiver was situated 1.5 m above the ground and more than 3 m from the building boundary. Four sound receivers were placed in the first courtyard, wherein the bell tower and drum tower were located, and 15 were placed in the second. This second courtyard was the front courtyard of the Great Buddha Hall--the largest hall in the temple. Ten sound receivers were placed in each of the third and fourth courtyards. Sound receiver locations are illustrated in Figure 2, denoted by dots. Considering that Odeon software is typically used to simulate the sound field of indoor spaces, the sound field model of a semi-closed courtyard in a Chinese Buddhist temple in this study was placed in a cube larger than the courtyard (Figure 2); subsequently, sound absorption coefficients of this cube's surfaces at each frequency were set to 1 (the sound was completely absorbed). With this setting, the sound field of a semi-closed courtyard could be more accurately simulated. For an acoustic parameter in a given courtyard, calculation results were averaged over all sound receivers, and different courtyard sound fields' averages were compared. A weighted sound pressure level (SPL(A)) was measured in place of SPL, since SPL(A) closely mimics the auditory characteristics  
Figure 1: Layout of Buddhist temples in ancient China. (**a**) Layout during the [PERSON] dynasty. (**b**) Layout during the Qing dynasty. of human ears. RT was measured as T\({}_{30}\) and EDT, and comparison and analysis were performed on the average results at typical middle frequencies (which are averages of values on the bands of 500 Hz and 1000 Hz, denoted in this paper by the subscript \"m\"). In addition, three other acoustic parameters were included as references to enable the comparison of temple sound fields: C\({}_{80}\) and the interaural cross-correlation coefficient (IACC). C\({}_{80}\) describes musical clarity, which is defined as the logarithmic ratio of early-to-late sound energy, where \"early\" refers to sound arriving in the first 80 ms, and \"late\" refers to sound arriving after this period. Generally, the shorter the RT, the bigger the C\({}_{80}\) and the greater the musical clarity.