# Courtyard Sound Field Characteristics by Bell Sounds in Han Chinese Buddhist Temples
## 2 Research Methods
### Acoustic Parameter Settings of Simulation Software
Based on this strategy, determinations were made for reference values of the absorption and scattering coefficients of materials that are commonly used in ancient temples (Table 2). For courtyard sound fields that were simulated using the parameters in Table 2, differences between the simulated and measured values are shown in Figure 5. For most SPLs, differences for each frequency ranged from \(-10\) dB to \(10\) dB, with differences in middle frequencies mostly ranging from \(-5\) dB to \(5\) dB. For most reverberation times, the ratio of the difference between the simulated and measured EDT to the measured EDT ranged from \(-30\%\) to \(30\%\), and from \(-20\%\) to \(20\%\) for middle frequencies. In general, errors were lower for middle and high frequencies than for low frequencies. Figure 3: Survey mapping and sound-field simulation diagram of the West Palace. (**a**) The top view and cross-sectional view of the West Palace. (**b**) The acoustic model diagram and sound pressure level (SPL) distribution diagram of the West Palace. The simulation accuracy of this study did not entirely meet the common acoustic criteria in interior space, which requires that the simulated error of RT should be less than its JND [41]. However, we considered the errors in this study to be within an acceptable range based on the following reasons: (1) There was a lack of related research about standard acoustic parameters of materials in ancient Chinese architecture. The sound absorption coefficients of ancient materials used in our simulation research were from those of relevant building materials in acoustic reference books, which may be different from the actual sound absorption coefficients of the site's materials; (2) The measurements were conducted in outdoor spaces, the courtyard scale was large, reverberation resulted from multiple reflections, and the acoustic model simplified the building and the courtyard in the simulation process. These factors would affect the measurements and simulation accuracy in this study; (3) Relative values from courtyard sound field simulation results were compared and analysed, and the results of the middle frequency (the bands of 500 Hz and 1000 Hz, which also is the main frequency range of human language), wherein errors were relatively small, were chosen as representative data; (4) The purpose of this study was not to obtain acoustic results for engineering calculations but to analyse characteristics of the courtyard sound field in Chinese Buddhist temples by means of comparing changing trends of the sound field. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{3}{c}{**Sound Absorption Coefficient at the Following Frequency (Hz)**} & \multirow{2}{*}{
\begin{tabular}{c} **Scattering** \\ **Coefficient** \\ \end{tabular} } \\ \cline{2-2} \cline{5-8}  & **125** & **250** & **500** & **1000** & **2000** & **4000** & \\ \hline Glazed tile roof [46] & 0.01 & 0.01 & 0.01 & 0.01 & 0.02 & 0.02 & 0.50 \\ Glass window [47] & 0.35 & 0.25 & 0.18 & 0.12 & 0.07 & 0.04 & 0.1 \\ Rendered wall [47] & 0.03 & 0.03 & 0.03 & 0.04 & 0.05 & 0.07 & 0.05 \\ Red brick wall * & 0.11 & 0.08 & 0.07 & 0.06 & 0.05 & 0.05 & 0.10 \\ Stone step * & 0.01 & 0.01 & 0.02 & 0.02 & 0.02 & 0.05 & 0.15 \\ Hard paving * & 0.01 & 0.01 & 0.02 & 0.02 & 0.02 & 0.05 & 0.05 \\ Wooden door [48] & 0.16 & 0.15 & 0.10 & 0.10 & 0.10 & 0.10 & 0.20 \\ Bucket arch [47] & 0.19 & 0.43 & 0.44 & 0.40 & 0.42 & 0.40 & 0.40 \\ Wooden eave column [45] & 0.1 & 0.07 & 0.05 & 0.05 & 0.05 & 0.05 & 0.30 \\ Mud floor [46] & 0.15 & 0.25 & 0.40 & 0.55 & 0.60 & 0.60 & 0.70 \\ Lawn [46] & 0.11 & 0.26 & 0.6 & 0.69 & 0.92 & 0.99 & 0.60 \\ \hline \hline \end{tabular} Note: The sound absorption coefficient of the material marked with * was obtained by referring to similar material suggested by Odeon software.  
\end{table} 
Table 2: Sound absorption coefficient and scattering coefficient of outdoor enclosure courtyard materials. Figure 4: Average values of measured EDT in three traditional courtyards.