# Measurements and Analysis of Sound Reflections from Selected Building Facades
## 4 Conclusions  
Considering the results obtained during this study, it can be said that they are consistent with previous findings of other researchers. The sound level correction proposed in ISO 1996-2 of \(-3\) dB measured at a distance of up to 2 m from the building facade is overestimated. Based on field measurements, the value of this correction is about 1 dB. At no measurement point at the facade (M1, M2 and M1F, M2F) did the measurement difference results approach the \(-3\) dB correction for microphone distances of 1 m and 3 m from the building facade (see column 2, Table 4). The recommendations of the EU directive [21] and the ISO 1996-2 standard do not indicate the need to apply a \(-3\) dB correction for measurement results obtained at distances higher than 2 m from the facade. However, it is certainly difficult to consider that placing the microphone 3 m away from the building facade ensures measurement in a free sound field. Due to the fact that there is a disturbed sound field at a distance of 3 m from the facade of a building, it is recommended that a correction of \(-3\) dB is not applied to the results of environmental noise measurements regardless of whether the measurement is made at a distance of 1 m or 3 m from the facade. In any case, people in the acoustically protected area near the building facade are exposed to real noise uncorrected by 3 dB. Based on our own measurements and by analyzing the results of other researchers, it can be concluded that the increase in sound level caused by reflections at a distance of up to 2 m from the building facade is less than 1 dB. The use of a \(-3\) dB correction creates a temptation to manipulate the results of measurements when assessing the behavior of noise limits in the environment. A small difference in the distance of the microphone from the building facade, e.g., 2.2 m \(-\) 1.7 m = 0.5 m, causes, by virtue of the recommendations of the EU directive [21] and the ISO 1996-2 standard, a difference of 3 dB in the received sound level. According to the authors, the suggestion of not correcting the results of noise measurements at a distance of 0.5 to 2.0 m from the building facade formulated in the German guidelines [42; 43] is correct. Sound reflections from three different structures of the facades of selected buildings were studied. Due to the significant disturbance of the sound field found at a distance of 3 m from the facade of the buildings, only the differences \(L_{eqM1}-L_{eqM3n}\) were evaluated. However, it is important to note that the \(-3\) dB correction is applicable only to measurements taken at the facades of buildings (\(L_{eqM1}-L_{eqM2}\)). Due to the almost identical meteorological conditions recorded during the tests at the three locations, an influence of the meteorological parameters on the sound measurement results obtained was excluded. Referring to the material of external facade cladding of the analyzed buildings, the following can be concluded:  
* Facade C made of HPL boards generates the smallest sound wave reflections. The differences between the results \(L_{\text{aqM1}}-L_{\text{aqM3n}}\) and \(L_{\text{aqM1}}-L_{\text{aqM2}}\) are the smallest of the three facades tested. At the same time, HPL hard panels have the lowest sound absorption coefficient among those tested (see Table 1). This means that the sound wave is much more dispersed by the HPL board cladding compared to the plastered and brick facades;
* Facades A and B, made of clinker brick and mineral plaster, respectively, absorb sound in a similar amount. The differences in reflections on facades A and B appear depending on the angle of incidence of the sound wave. At a distance of 2 m from the ground level, greater wave reflections were recorded on facade A. Facade B generated greater wave reflections at a measurement height of 6 m.  
This research will continue in two aspects. A study of sound reflections from identical building facades located in areas with similar hard and soft coverings will be performed.