# Measurements and Analysis of Sound Reflections from Selected Building Facades
## 3 Results and Discussion  
Tables 3 and 4 show the average sound levels together with the mean difference and standard error stored in measurements taken simultaneously at three points. All measurement results included in the analyses are shown graphically in Figures 9-14. Table 3 contains the averaged sound level results from the three measurement microphone locations for the three different facade claddings. Table 3 summarizes the averaged difference results individually for each of the three measurement locations. The presented results of sound level differences for the location of microphones on the facades of buildings (M1, M2) strongly deviate from the \(-3\) dB correction recommended in [20] (see column 2, Table 4). Only in two measurement positions (A1, B1) was a difference greater than \(1\) dB obtained, and the maximum difference was \(1.6\) dB. The values of sound level differences for the locations of microphones M1 and M3 without normalization are in the range of \(1.3\) to \(3.3\) dB. After normalization, the differences obtained are in the range of \(0.8\) to \(2.8\) dB. At the two locations A1 and B2, the results of the obtained differences are close to the \(-3\) dB correction as suggested in [20]. However, please remember that the \(-3\) dB correction applies only to measurements taken at the facade of buildings. Figure 10: Measurement results for cycle A2: (**a**) microphones M1, M2; (**b**) microphone M3. Figure 9: Measurement results for cycle A1: (**a**) microphones M1, M2; (**b**) microphone M3. It was observed that normalization of the results at point M3 showed a lack of the expected convergence with the results at points M2 and M2F. Despite the fact that, in the sense of the standard [20], both points were located in a non-reflectance-induced sound field. Differences in the average values of the equivalent sound level \(L_{\alpha\beta M2}\) - \(L_{\alpha\beta M3n}\) were obtained, ranging from 0.6 to 2.2 dB. Despite the stable sound source used, only two time courses (A1 and B1) of sound level changes maintain a similar difference in results for all 10 pairs. The results of measurements at the facade of the buildings at locations A and B show a similar relationship. At a height of 2 m (A1, B1), that is, at the height of the sound source, the differences are greater than those obtained at a height of 6 m (A2, B2). At location C, regardless of the measurement height, the differences obtained are similar and do not exceed 0.2 dB on average. Figure 11: Measurement results for cycle B1: (a) microphones M1, M2; (b) microphone M3. Figure 12: Measurement results for cycle B2: (a) microphones M1, M2; (b) microphone M3. At the first measurement level (2 m above ground level), the highest sound reflections were recorded at the facade A made of clinker brick, with a \(L_{eqM1}-L_{eqM3n}\) difference value of 2.8 dB. The smallest sound reflections were registered at elevation C made of HPL panels, with a \(L_{eqM1}-L_{eqM3n}\) difference value of 0.8 dB. At the second measurement level (6 m above ground level), the highest sound reflections were recorded at the facade B made of mineral plaster, with a value of difference \(L_{eqM1}-L_{eqM3n}\) equal to 2.5 dB. The sound reflections recorded at the elevations A and C were equal with a value of the difference \(L_{eqM1}-L_{eqM3n}\) equal to 1.2 dB. During the tests, an additional measurement microphone was installed at a considerable (50 m) distance from the nearest reflecting surfaces (buildings). The purpose was to check whether there is a significantly disturbed sound field at a distance of 3 m from the elevation. The results obtained clearly indicate that the differences between microphones M2 (3 m from the elevation) and M3 (50 m from the elevation) equally distant from the source  
Figure 14: Measurement results for cycle C2: (**a**) microphones M1, M2; (**b**) microphone M3. Figure 13: Measurement results for cycle C1: (**a**) microphones M1, M2; (**b**) microphone M3. are significant.