## 5 Validation of the Proposed Method  
To verify the proposed method, different measurements were carried out on the facade of a corner room using four different loudspeaker positions. The obtained results made it possible to experimentally determine the standardized level differences and to compare them with the simulations. The measurements were performed on a room at the ground floor of the Mathematics Department--University of Brescia, having dimensions of 6 m \(\times\) 4 m \(\times\) 2.9 m (Figure 6). An omnidirectional source was placed in four positions outside the room (1a, 1b, 2a, 2b in Figure 7) and a Larson & Davis 831 analyzer was used to measure the sound pressure levels. The reverberation time was measured using the sound level meter and an impulsive source. The standardized level difference \(D_{\text{ls,2m,nT}}\) was computed for the individual loudspeaker positions and for pairs of loudspeaker positions (1a-2a; 1a-2b; 1b-2a; 1b-2b) using Equation (2). Figure 8a shows the results of the measurements for each position of the sound source, while Figure 8b shows the results for the considered pairs of sound source positions. The overall weighted values derived from the measurements in the two cases are shown in Table 5.  
It is worth noting that, as expected from the previous discussion, the results depend on the loudspeaker positions. For example, the difference between positions 1a and 2b was 7 dB while the difference between 1a-2a and 1b-2b combinations was 2 dB. During the experimental campaign, the attenuations due to the diffraction of the building or to the different distances from the facade were evaluated through sound pressure level measurements at 5 cm from the facade (Figure 9). The building is surrounded by other buildings on both sides, at a distance of 12 m and 13 m from the building facades. Comparing measured and predicted attenuations in the case of an isolated building and in the case of a building placed at 10 m from the facade (Figure 10), one can observe that the measurements are better  
To evaluate the reliability of the method, further comparisons between predictions and measurements were carried out. Considering the previous tables and the dimensions of the measured room, calculations using the weighted indices can be performed. The same calculations can be done in octave or one-third octave frequency bands. On the basis of the datasheets of the facade elements (20-cm-thick precast panel wall and windows with 4-20-4 glasses), the following weighted sound reduction indexes can be adopted for the calculations: \(R_{\text{w\_wall}}=50\) dB, \(R_{\text{w\_window}}=35\) dB. As concerns the windows surfaces, the areas for the two different sides are \(S_{\text{window\_1}}=8.7\) m\({}^{2}\) and \(S_{\text{window\_2}}=4.35\) m\({}^{2}\). A level difference due to facade shape \(\Delta L_{\text{fs}}=0\) was also considered. The correction for flanking transmission was set to \(-2\) dB. By applying Equation (3), the following results can be obtained:  
\[D_{2m,nT,w11}=R^{\prime}{}_{1}+\Delta L_{fs}+10\text{lg}\bigg{(}C_{sab}\frac{V }{T_{0}S_{1}}\bigg{)}=36.9\text{ dB} \tag{12}\]  
\[D_{2m,nT,w22}=R^{\prime}{}_{2}+\Delta L_{fs}+10\text{lg}\bigg{(}C_{sab}\frac{ V}{T_{0}S_{2}}\bigg{)}=39.9\text{ dB} \tag{13}\]  
When dealing with in situ measurements, the loudspeaker can be positioned in four possible configurations: (a) 1a-2a; (b) 1a-2b; (c) 1b-2a; (d) 1b-2b (Figure 7). If case \"a\" is considered, the attenuations due to the diffraction, for a room having dimensions 4 m \(\times\) 6 m, are given in Table 6 (\(\Delta D_{\text{21a}}\) is obtained by linear interpolation). \begin{table}
\begin{tabular}{c c c} \hline \multirow{2}{*}{**F0**} & \multicolumn{2}{c}{\(\Delta D_{\text{12a}}\)} & \(\Delta D_{\text{21a}}\) \\ \cline{2-3}  & \(6\times 4\) & \(4\times 6\) \\ \cline{2-3}  & 2.1 & 1.4 \\ \hline \end{tabular}
\end{table} 
Table 6: Attenuation \(\Delta D_{\text{FL}}\) (case “a”).