## 2 Methods
### Numerical Method
#### 2.2.3 Reflection-Based Scattering
Having in mind this constraint, a compromise has been made in order to stop the calibration process when differences between simulated and measured _EDT_, \(T_{30}\), \(C_{80}\), and \(D_{50}\) reached values of about one JND. The results of the material calibration are shown in Table 1 and Figure 5, and the results of the objective acoustic parameters after calibration are depicted in Figure 6. It can be observed that the differences between the simulated and measured results for \(C_{80}\) and \(D_{50}\) are slightly above one JND. This result was still considered acceptable, based on the restriction of the absorption coefficients variations, and on the fact that the degree of tolerance for the parameters that present values of the spatial standard deviation comparable to the JND should realistically be extended beyond one JND ([PERSON] and [PERSON], 2017). 4. **Case study models:** The absorptive surface properties obtained after the calibration have been assigned to the respective surfaces (type A and B) in the models of the case study (RF, DF, DM). The same properties have been used in both 3D prisms and flat surface models (DM and DF). This has been considered acceptable since the difference in volume may be considered negligible (\(\mathrm{V_{DM}}-\mathrm{V_{DF}}=7.77\) m\({}^{3}\)). The other surfaces such as doors, floor, and glass windows have remained the same as those used in the calibration model. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & & & & \\ \hline \multicolumn{2}{c}{**Frequency [Hz]**} \\ \hline  & **Materials** & **125** & **250** & **500** & **1000** & **2000** & **4000** & **8000** \\ \hline \multicolumn{2}{c}{**Fixed**} & Floor (linoleum on concrete) & 0.12 & 0.10 & 0.10 & 0.08 & 0.05 & 0.05 & 0.05 \\ \multicolumn{2}{c}{**material**} & Doors (hard metallic panels) & 0.13 & 0.11 & 0.07 & 0.05 & 0.05 & 0.05 & 0.05 \\ \multicolumn{2}{c}{**properties**} & Windows (single glazing sheet) & 0.18 & 0.06 & 0.04 & 0.03 & 0.02 & 0.02 & 0.02 \\ \hline \multicolumn{2}{c}{**Diffusive surface (3D panels) and**} & **Structure (metallic)** & **0.10** & **0.10** & **0.10** & **0.10** & **0.10** & **0.10** & **0.10** \\ \multicolumn{2}{c}{} & Diffusive surface (3D panels) and & 0.16 & 0.16 & 0.09 & 0.09 & 0.14 & 0.14 & 0.14 \\ \multicolumn{2}{c}{} & Structure (metallic), (cally. all models) & 0.16 & 0.16 & 0.09 & 0.09 & 0.14 & 0.14 & 0.14 \\ \multicolumn{2}{c}{**Varied**} & **Type A ([PERSON], 1978)** & **0.75** & **0.90** & **0.70** & **0.30** & **0.10** & **0.05** & **0.05** \\ \multicolumn{2}{c}{**material**} & Type A (Calib. DM1) & 1.00 & 0.95 & 0.75 & 0.20 & 0.10 & 0.10 & 0.05 \\ \multicolumn{2}{c}{**properties 1**} & Type A (Calib. RF) & 1.00 & 0.95 & 0.75 & 0.35 & 0.25 & 0.20 & 0.20 \\ \multicolumn{2}{c}{} & Type A (Calib. DM and DF) & 0.80 & 0.90 & 0.70 & 0.20 & 0.10 & 0.10 & 0.05 \\ \multicolumn{2}{c}{} & Type B (Peutz, 1978) & **0.20** & **0.40** & **0.70** & **0.90** & **0.85** & **0.90** & **0.95** \\ \multicolumn{2}{c}{} & Type B (Calib. DM1) & 0.45 & 0.47 & 0.60 & 0.70 & 0.65 & 0.90 & 0.95 \\ \multicolumn{2}{c}{} & Type B (Calib. RF) & 0.30 & 0.50 & 0.55 & 0.72 & 0.68 & 0.98 & 1.00 \\ \multicolumn{2}{c}{} & Type B (Calib. DM and DF) & 0.35 & 0.37 & 0.50 & 0.68 & 0.65 & 0.90 & 0.95 \\ \hline \hline \end{tabular}  
* Type A and type B material properties have also been plotted in Figure 5 for a clearer visualization of their variation during the calibration process.  
\end{table} 
Table 1: Absorption coefficients assigned to the different surfaces of the hall. “Fixed materials properties” have not been varied during the calibration process. Materials in the group of “Varied material properties” have been modified starting from the values signed in bold to the gray ones.