# Measurements and Analysis of Sound Reflections from Selected Building Facades
## 2 Materials and Methods  
### Sampling Points Selection  
This study was conducted at three buildings (A, B, C) located outside the center of a medium-sized town in the northern part of Poland. The selected buildings have different exterior facade claddings. Building A (Figure 1) has a facade made of clinker bricks. Clinker bricks usually have a volumetric density of 1.5 to 2.0 kg/m\({}^{3}\). The exterior walls of building B (Figure 2) are made of precast reinforced concrete parts. They were further insulated with polystyrene foam and plastered. Mineral plaster has a volumetric density of 1.5 to 1.8 kg/m\({}^{3}\). The facade of building C (Figure 3) is a wall of aerated concrete blocks insulated with mineral wool with an exterior cladding of HPL panels. The HPL board consists of pressure-pressed cellulose fibers impregnated with thermosetting phenolic resins. The product's volumetric density is 1.4 kg/m\({}^{3}\). Figure 1: The building facade A. The average values of sound absorption coefficients of building and finishing materials used in the analyzed facades are presented in Table 1[46]. Figure 3: The building facade C.  
Figure 2: The building facade B. There were no reflective surfaces other than the ground within a 50-m radius of point five (M3). Meteorological measurements were conducted simultaneously at point five--Figure 6.  
A portable, foldable measurement stand was designed to facilitate noise assessments both on and near a building facade, irrespective of the height of measurement. The stand was required to support simultaneous measurements directly on the facade (at distances ranging from 0.5 m to 2.0 m) and at a distance of 3.0 m away from the facade. A more detailed description of the stand can be found in [44]. A schematic diagram of the stand is shown in Figure 7. The stand's frame is constructed from a 5 mm thick aluminum plate measuring 0.5 \(\times\) 0.7 m, to which a horizontal mast is secured. The mast is composed of two thin-walled pipes with a diameter of 20 mm, connected using sockets. Microphone holders, which can be adjusted and positioned along the mast, are mounted on the pipe. During the measurements, a point omnidirectional sound source emitting pink noise at a height of 2 m above the terrain was used, with a sound power of 96 dB. The selection of measurement points took into account the recommendations of the standard [20] and Appendix B. In particular, the main issue was the location of the measurement microphones in relation to the reflecting surfaces. The A1 measurements were conducted at buildings having facades on the side of the sound source that were as flat as possible. The finishing materials of the facades were hard and met the criteria contained in the standard [20]. Using the provisions of Anne B of the standard [20], the extreme distances (minimum  
Figure 6: View of the fifth (M3) measuring point. Figure 7: Test stand scheme. and maximum) of the M1 microphone from the facade was determined, for which the noise measurement results must be corrected by 3 dB. It was checked that the measuring microphone was located beyond the immediate vicinity of the facade, having the correction of \(-6\) (5.7) dB. The least distance of \(d^{\prime}=1.0\) m of the microphone from the facade was established. The maximum distance of the microphone from the facade of the building \(d^{\prime}\) allowing the \(-3\) dB correction to be subtracted was determined as follows:  
* It was assumed that the minimum distance of the measurement point from the sound source was \(a^{\prime}_{min}=24\) m and \(d^{\prime}\leq 0.05\cdot a^{\prime}\leq 1.2\) m. Ultimately, \(d^{\prime}=1.0\) m was selected for the measurements. Having established the maximum distance \(d^{\prime}\), the location of the measurement microphone in relation to the edge of the building was determined. Distances \(b\geq 4\cdot d\geq 4\) m and \(c\geq 2\cdot d\geq 2\) m were maintained.