# Measurements and Analysis of Sound Reflections from Selected Building Facades
## 1 Introduction
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; 40; 41]. The validity of including a \(-3\) or \(-5.7\) dB correction due to the location of the microphone relative to the facade 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 facade (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 facade 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 facades. 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 facade. 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 facades are minimal, measuring significantly less than 1 dB [41]. To further support these studies, a portable test stand for positioning measurement microphones near building facades was developed and tested [44]. It was determined that flat facades would be tested first to avoid interference from balconies [45]. It was assumed that facades 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 facades with various external claddings. Key aspects of this study include examination of sound reflections from three types of facade structures: facade A: clinker brick, facade B: mineral plaster, and facade C: HPL hardboard. All facades 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 facade structure (exterior cladding material) on the amount of sound reflection. * Determine whether a distance of 3 m from the building facade provides an undisturbed reflected sound field comparable to that of free space.