# Measurements and Analysis of Sound Reflections from Selected Building Facades
## 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 ofsound propagation for higher order reflections is via random scattering [15]. Geometrical changes of the facade in terms of depth and upward inclination show possibilities of noise reduction by up to 9 dB compared to a vertical facade [16]. The possible effect of facades on the acoustic environment is described in detail in [17]. This article focuses specifically on guidelines for positioning a measurement microphone near a building facade. Understanding the disturbances in the acoustic field caused by the building facade 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 facade 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 facade from the measurement microphone.