Measurements and Analysis of Sound Reflections from Selected Building Façades

Abstract

This paper presents a study of the effect of the type of exterior cladding material of a building façade on the amount of sound reflection. It was verified whether there is a sound field undisturbed by reflections, similar to the free field, at a distance of 3 m from the building façade. Sound reflections from three building façade structures were tested: clinker brick, mineral plaster, and hard HPL. An equal geometry of the measuring field at selected real objects was used. It was determined that the differences in sound level results measured at distances up to 2 m and more than 2 m from the building façade are lower than the −3 dB correction specified in ISO 1996-2. Significant differences were observed comparing the measured sound level values in the undisturbed sound field with the levels recorded at a distance of 3 m from the building façade. It was proposed that the results of measurements made to control the levels of permissible noise in the environment should not be subject to the −3 dB correction.

1. Introduction

Noise is one of the pollutants that has a negative impact on the environment, thus constituting a significant social problem. With the development of civilization and intensification of human activities, noise pollution is increasing. Noise in the environment causes annoyance to the recipients and sleep disturbance but also increases the risk of many diseases [1,2,3,4,5]. The greatest danger is noise generated by road, rail, and air traffic [6]. Noise increases particularly rapidly in large cities and highly urbanized areas. The increase in noise levels in suburban areas is due to the migration of young families to the suburbs due to real estate prices [7]. The predominant reasons for moving to the countryside, however, are the features attributed to rural areas, such as peace, beautiful landscapes, and recreational opportunities [8,9]. A consequence of this situation is the increasing volume of traffic. An analysis of WHO documents [10,11] indicates that, in EU countries, the largest percentage of the population is exposed to road traffic noise. As a result, it is estimated that 40% of the EU population is exposed to noise levels exceeding 55 dB. The fact that 30% of the EU population is exposed to road noise levels greater than 55 dB at night is particularly significant and disturbing.

In order to determine the intensity of sound levels in the environment, it is necessary to accurately conduct a field noise survey. Planning and conducting a field study is a complex process that involves considering numerous variables. The measurement results at the study location must account for existing sound sources, the area’s usage, and prevailing atmospheric conditions—factors that are beyond the operator’s control [12,13]. Field measurements of sound levels in the surrounding environment are conducted for various purposes. Most commonly, they are used to determine whether established limits are being met. Additionally, they can be used to validate computational models. Cases of multiple reflections are also analyzed [14], and it is suggested that the dominant mechanism of sound propagation for higher order reflections is via random scattering [15]. Geometrical changes of the façade in terms of depth and upward inclination show possibilities of noise reduction by up to 9 dB compared to a vertical façade [16]. The possible effect of façades on the acoustic environment is described in detail in [17]. This article focuses specifically on guidelines for positioning a measurement microphone near a building façade. Understanding the disturbances in the acoustic field caused by the building façade is essential to ensure that the resulting control measurements provide a reliable assessment of noise pollution [18].

The guidelines set forth in the ISO 1996 international standards [19,20] are used widely in performing environmental sound measurements. The recommendations in the documents [19,20] are applied to the analysis of emissions from various sources of environmental sound. The main sources of emissions include noise from transportation (rail, road, aviation) and industrial noise. The basic assessment procedures and methods, as well as the definitions and indicators used in environmental noise analyses, are described in ISO 1996-1 [19]. The standard also addresses the problem of chronic exposure to environmental noise and describes ways to predict the potential annoyance to the population caused by it.

ISO 1996-2 [20] describes how to determine the sound pressure level as a basis for assessing exceedances of permissible noise levels in the environment or confronting the results obtained from measurements and simulations. An important part of the measurement is to establish the position of the microphone in relation to the reflective surfaces present in the area. One of these surfaces is often the façade of a building located in an area subject to acoustic inspection and evaluation. The normative part of the standard [20] refers only to the distance of the building façade from the measurement microphone. Only the informative part of the standard (non-normative) in Appendix B indicates the need to take into account other factors arising from the land use of the study area.

Directive 2002/49/EC of the European Parliament [21] refers to the guidelines given in the standard (ISO 1996-2) and relates to the assessment and management of environmental noise. The document provides guidelines obliging European Union countries to produce strategic noise maps for cities. As an extension to measurements that enable validation of data for acoustic mapping [22,23,24], the standard [20] is used as a set of recommendations when carrying out control measurements for maintaining permissible noise levels in the environment [25,26,27,28]. Having the above in mind, the guidelines provided in the standard [20] have become the subject of interest for many researchers [29,30,31,32,33,34,35,36,37,38,39,40,41]. The validity of including a −3 or −5.7 dB correction due to the location of the microphone relative to the façade was examined. In the analyses on various case studies, researchers determined the size of the correction. In particular selected measurement cases, a few researchers managed to estimate an increase in noise level near the façade (0.5–2.0 m) of about 3 dB [26,32]. It should be pointed out that the increase in noise level associated with sound reflection from the façade did not exceed 1 dB for most of the studied cases.

The inclusion or exclusion of the amendment significantly influences the index value that determines the intensity of environmental noise, either halving it or doubling it. For instance, German guidelines [42,43] recommend that measurement results should not be adjusted for sound reflections from façades.

Through extensive noise measurements conducted as part of environmental monitoring, the authors observed a difference of less than 3 dB between measurements taken at distances of 1 m and 3 m from a building façade. In 2020, the authors initiated a series of studies in this area, analyzing two types of noise sources: road traffic (an extended source) and industrial activity (a point source). Using the equivalent sound level index A, it was determined that actual sound reflections from building façades are minimal, measuring significantly less than 1 dB [41]. To further support these studies, a portable test stand for positioning measurement microphones near building façades was developed and tested [44]. It was determined that flat façades would be tested first to avoid interference from balconies [45]. It was assumed that façades with different exterior finishing materials would be selected for testing. It was decided that, during the tests, an additional microphone would be placed well away from the vertical reflective surfaces.

This study introduces an innovative approach by employing equal geometry in the measurement polygon to analyze sound reflections from real building façades with various external claddings. Key aspects of this study include examination of sound reflections from three types of façade structures: façade A: clinker brick, façade B: mineral plaster, and façade C: HPL hardboard. All façades were plain (without balconies) and featured acoustically protected windows commonly used in residential buildings.

The main objectives of this study were defined as follows:

• Assess the impact of façade structure (exterior cladding material) on the amount of sound reflection.
• Determine whether a distance of 3 m from the building façade provides an undisturbed reflected sound field comparable to that of free space.

2. Materials and Methods

2.1. 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 façade claddings. Building A (Figure 1) has a façade made of clinker bricks. Clinker bricks usually have a volumetric density of 1.5 to 2.0 kg/m³.

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/m³.

The façade 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/m³.

The average values of sound absorption coefficients of building and finishing materials used in the analyzed façades are presented in

Table 1. Absorption coefficients.

Material	125 Hz	250 Hz	500 Hz	1 kHz	2 kHz	4 kHz
Brickwork, 10 mm flush pointing	0.08	0.09	0.12	0.16	0.22	0.24
Mineral plaster (rough finish)	0.14	0.10	0.06	0.05	0.04	0.04
Hard panels with smooth surface	0.01	0.01	0.01	0.02	0.02	0.02

[46].

For this study, sites with less human activity were chosen to maximally eliminate the influence of background noise on the measurement results. It was ensured that the background sound level was 10 dB lower than the measured levels of the sound source. Between consecutive measurement series, the sound source was turned off, and the background noise level was checked through measurement. The average result of the acoustic background at locations A, B, and C was 44.3 dB, 45.5 dB, and 44.8 dB, respectively. The average result of the measurement of the acoustic background level at individual measurement points was lower than the result of the measurement of the point source from 12.5 dB to 15.8 dB. Five measurement points were established at each location for this study. Four measurement points were located on the façade of buildings using a portable test stand [43]: M1, M2 at a height of 2 m, and M1F, MF2 at a height of 6 m (Figure 4). The fifth measurement point, M3, was fixed and located at a distance of 50 m from the building façade (Figure 5).

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 façade, irrespective of the height of measurement. The stand was required to support simultaneous measurements directly on the façade (at distances ranging from 0.5 m to 2.0 m) and at a distance of 3.0 m away from the façade. 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 × 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 façades on the side of the sound source that were as flat as possible. The finishing materials of the façades were hard and met the criteria contained in the standard [20]. Using the provisions of Annex B of the standard [20], the extreme distances (minimum and maximum) of the M1 microphone from the façade 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 façade, having the correction of −6 (5.7) dB. The least distance of d′ = 1.0 m of the microphone from the façade was established. The maximum distance of the microphone from the façade of the building d′ 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′_min = 24 m and d′ ≤ 0.05 · a′ ≤ 1.2 m. Ultimately, d′ = 1.0 m was selected for the measurements.

Having established the maximum distance d′, the location of the measurement microphone in relation to the edge of the building was determined. Distances b ≥ 4 · d ≥ 4 m and c ≥ 2 · d ≥ 2 m were maintained.

Distance markings were adopted in accordance with Figure B.2 of the standard [20]—Figure 8.

Measurements at the building façade were conducted at two heights of 2 m and 6 m from the ground, mounting microphones on a portable measuring mast [44]. The fifth measurement point was fixed and located 4 m above the ground at a distance from the vertical reflecting surfaces. Bearing in mind the guidelines from Appendix B of the standard [19], it can be concluded that microphones M2 and M2F 3 m away and M3 50 m offset from the building façade were in the free sound field.

2.2. Measurement Procedure and Equipment

Measurement of sounds at the façade of buildings was carried out using two microphones (M1 and M2 or M1F and M2F) 1 m and 3 m away from the façade, respectively. During measurements at both heights of 2 m (M1, M2) and 6 m (M1F, M2F), 10 one-minute samples were taken each. This activity, at both heights, was repeated twice at each location. The result was a record of the history of sound pressure changes with time-weighted fast. The measurement set-up is illustrated in Figure 4. The position of microphone M3 allowed additional measurement in the free sound field as defined by Appendix B [20]. The ground was the only reflecting surface for this case. In addition, it was ensured that there was no reflecting surface behind the microphone (at least at a distance d ≥ 2 · a′) and in the direction normal to the direction of incidence of the sound wave (at least at a distance b ≥ 4 · d′). Distances were measured using a Leica DISTO A5 laser meter (Leica, Wetzlar, Germany) with a measuring range of 200 m and an accuracy of ±3 mm. Recordings of measured sounds were made using two SVANTEK noise analyzers (SVANTEK, Warsaw, Poland) with Class 1 windshields: the SV 977A (M3) and SV 958A (M1 and M2). Three GRAS 40AZ microphones (GRAS, Copenhagen, Denmark) were used, with a range of measured sound frequencies from 0.5 Hz to 20 kHz. The microphones were mounted at a height of 4 m using a tripod (M3) and at elevation (M1 and M2) using a portable measuring stand [44]. The measuring instruments and the reference sound source used during the tests had valid calibration certificates. During the tests, periodic calibration of the measurement paths of the microphones used was carried out using an external standard SV03 class 1 sound source. During the calibration of the measurement paths, no deviation greater than 0.1 dB in relation to the reference sound was observed. During the data acquisition process, the environmental conditions were monitored using an SV 205 weather station (SVANTEK, Warsaw, Poland) positioned on a tripod at a height of 3 m from the ground under the M3 microphone. Tests at selected building façades were conducted on different days with similar meteorological conditions:

• Temperature 17 ÷ 21 °C;
• Humidity 55 ÷ 70%;
• Average wind speed 0 ÷ 2 m/s.

2.3. Analysis Methodology

Sound sampling occurred at one time on three microphones located according to the measurement cycle. Based on the history of sound pressure changes obtained from measurements, the equivalent sound level A for each measurement minute L_Aeq1min was determined. The obtained values of equivalent sound level L_Aeq1min were compiled into 20 pairs of results for each measurement cycle. The measurement cycles carried out are summarized in

Table 2. Summary of measurement cycles.

Façade Type	Cycle Name	Height of Measurement at Elevation [m]	Parameters Measured in Each Cycle
A	A1	2 (M1 and M2)	LeqM1, LeqM2, LeqM3
	A2	6 (M1F and M2F)
B	B1	2 (M1 and M2)
	B2	6 (M1F and M2F)
C	C1	2 (M1 and M2)
	C2	6 (M1F and M2F)

. Then, from each cycle, 10 pairs of differences not containing interference were selected. Disturbances are understood as environmental noises such as dog barking, shouting, or passing vehicles. During the measurements, the occurrence times of such clearly audible events were recorded. These records allowed the elimination of samples laden with interference. Initially, results differing by ±2 dB from the mean were discarded. Finally, 10 pairs remained, each differing from the average result by less than 0.6 dB. The goal of the work was to establish the differences in the results recorded by the three microphones. The differences of L_eqM1 − L_eqM2 and L_eqM1 − L_eqM3 were analyzed and compared with a standard correction value of −3 dB. A statistical evaluation of the results was carried out. The standard error was reported, and the non-parametric Wilcoxon signed-rank test was performed. This test determines whether the mean values of the differences are not remarkably different from zero.

Differences in the distance of the measurement microphone from the source were taken into account. Measurement microphones M2 and M3 were not equidistant from the sound source by a₁′. For example, at the first measurement level, microphone M2 was 3 m closer to the sound source. Therefore, the results obtained at M3 were normalized (standardized) and converted to a₁′ distance using Formula (1).

$$L_{eqM3n}=L_{eqM3}+10log\left({\displaystyle \frac{a_2\text{'}}{a_1\text{'}}}\right), \left[\mathrm{d}\mathrm{B}\right],$$

(1)

where

L_eqM3n—normalized (standardized) equivalent sound level;

L_eqM3—measured equivalent sound level;

a₂′—distance from the sound source to the point M3;

a₁′—distance from the sound source to the point M2.

3. Results and Discussion

Table 3. Measured average values of the equivalent sound level.

Location Number	${\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}1}$ [dB]	${\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}2}$ [dB]	${\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}3}$ [dB]	${{\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}3\mathit{n}}}^{\mathit{*}}$ [dB]
A1	60.3	58.7	57.0	57.5
A2	58.3	58.2	56.8	57.1
B1	61.0	59.9	58.6	59.2
B2	61.3	61.0	58.6	58.8
C1	59.3	59.1	58.0	58.5
C2	59.6	59.4	58.1	58.4

* With sound source normalization.

and

Table 4. Statistical parameters for the differences in bandwidth between the measurements: mean values, standard error, significance of mean values.

Location Number	$\overline{\mathit{x}}\left\{{\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}1}-{\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}2}\right\}\pm {\mathit{\sigma }}_{\overline{\mathit{x}}}{,}^{\left(\mathit{p}\text{-}\mathbf{v}\mathbf{a}\mathbf{l}\mathbf{u}\mathbf{e}\right)}$	$\overline{\mathit{x}}\left\{{\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}1}-{\mathit{L}}_{\mathit{e}\mathit{q}\mathit{M}3}\right\}\pm {\mathit{\sigma }}_{\overline{\mathit{x}}}{,}^{\left(\mathit{p}\text{-}\mathbf{v}\mathbf{a}\mathbf{l}\mathbf{u}\mathbf{e}\right)}$
		Without Sound Source Normalization	With Sound Source Normalization
1	2	3	4
A1	1.6 ± 0.1 *	3.3 ± 0.1 *	2.8 ± 0.1 *
A2	0.1 ± 0.1 (n.s.)	1.5 ± 0.3 *	1.2 ± 0.3 *
B1	1.1 ± 0.1 *	2.4 ± 0.1 *	1.8 ± 0.1 *
B2	0.3 ± 0.1 *	2.7 ± 0.1 *	2.5 ± 0.1 *
C1	0.2 ± 0.2 (n.s.)	1.3 ± 0.3 *	0.8 ± 0.3 *
C2	0.2 ± 0.2 (n.s.)	1.5 ± 0.5 *	1.2 ± 0.5 *

^(n.s.) Indicates a non-significant difference (p > 0.05). * Indicate the level of significance of the differences (p ≤ 0.05).

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 Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14. Table 3 contains the averaged sound level results from the three measurement microphone locations for the three different façade 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 façades 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 façade of buildings.

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_eqM2 − L_eqM3n 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 façade 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.

At the first measurement level (2 m above ground level), the highest sound reflections were recorded at the façade 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 façade 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 are significant. Differences in average values of equivalent sound level L_eqM2 − L_eqM3n in the range of 0.6 to 2.2 dB were obtained. This means that at a distance of 3 m from the façade of the building there is a reflection-disturbed sound field.

In the conducted measurements, the location of the microphones and the sound source were determined to be the same in relation to each other and the analyzed building façade. However, the ground cover at the surveyed locations varied and was not affected by the investigators. At location A, the ground cover was 80% soft (grass), while, at locations B and C, the ground cover was 80% hard (concrete paving stones). The results of the measurements at the examined locations may include the influence of sound reflected from the ground, which is difficult to estimate. It should be noted that the ISO standard does not condition the −3 dB correction value on the type of ground. The greatest impact of this phenomenon should be observed on the first measurement level (A1, B1, C1). However, no such confirmation was obtained in tests at elevation C. The average values of differences at a height of 2 m (C1) are less than or equal to those obtained at a height of 6 m (C2). It is interesting to note that at location A with soft cover, the largest tested differences L_eqM1 − L_eqM2 and L_eqM1 − L_eqM3 were obtained, as well as differences between the results at 2 and 6 m height (A1 and A2).

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 façade is overestimated. Based on field measurements, the value of this correction is about 1 dB.

At no measurement point at the façade (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 façade (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 façade. However, it is certainly difficult to consider that placing the microphone 3 m away from the building façade 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 façade 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 façade. In any case, people in the acoustically protected area near the building façade 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 façade 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 façade, 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 façade formulated in the German guidelines [42,43] is correct.

Sound reflections from three different structures of the façades of selected buildings were studied. Due to the significant disturbance of the sound field found at a distance of 3 m from the façade 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 façades 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 façade cladding of the analyzed buildings, the following can be concluded:

• Façade C made of HPL boards generates the smallest sound wave reflections. The differences between the results L_eqM1 − L_eqM3n and L_eqM1 − L_eqM2 are the smallest of the three façades 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 façades;
• Façades A and B, made of clinker brick and mineral plaster, respectively, absorb sound in a similar amount. The differences in reflections on façades 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 façade A. Façade 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 façades located in areas with similar hard and soft coverings will be performed. There will be a verification of at what distance from the building façade the impact of sound wave reflections is less than 0.5 dB. It is planned to perform simulations (calculations) reflecting measurement situations using algorithms from various standards used in the world.