# An Estimation of Speech Privacy Class Based on ISO Parameter
## 2 Background  
### Ambient Noise and Speech Level in the Room  
Figure 1 schematically depicts a typical scenario involving the positioning of two rooms, regardless of whether they serve as residential or business spaces. The assumption is that one room (the source room) is engaged in specific activities generating a sound field, while the other room (the receiving room) serves as the location for speech privacy analysis. The receiving room is described by the volume \(V\) and reverberation time \(T\). The rooms are separated by a partition construction with a surface area \(S_{12}\) and a sound reduction index \(R\). It is important to note that the sound reduction index is a frequency-dependent variable, signifying that it encompasses a range of values rather than a single numerical  
figure. Ambient noise, denoted by the level \(L_{b}\) in Figure 1, acts as a determining factor in the signal-to-noise ratio within residential premises, predominantly infiltrating them through three potential pathways:  
* As noise that passes through the elements of the facade from the outside environment (its level is denoted as \(L_{in}\) in Figure 1);
* As noise that passes through partition structures from neighboring rooms (its level is denoted as \(L_{2}\) in Figure 1);
* As the noise of devices and installations within the receiving room (its level is denoted as \(L_{onipip}\) in Figure 1). The external noise (indicated by the level \(L_{in}\)) infiltrates the room through the dividing elements of the facade. Primarily, these pathways involve sound transmission through the glass panes of windows, as illustrated in Figure 1, and possibly balcony doors. It is worth noting that facade walls exhibit significantly higher insulation power compared to glass (\(R_{wall}>>R_{win}\), as indicated by smaller arrows in Figure 1). The acoustic environment surrounding residential premises is largely influenced by traffic-generated sounds. The noise level \(L_{in}\) is contingent on factors such as traffic intensity, the type of traffic (cars, buses, trains, etc. ), and the configuration of buildings bordering the street, as well as facade structures. By contrast, the acoustic environment within the building surrounding the receiving room encompasses all sounds generated by human activities, denoted by the noise level \(L_{2}\). This acoustic backdrop is shaped by the everyday activities in neighboring apartments, but it can also result from various disruptive activities occasionally categorized as \"antisocial\" behavior [46]. Additionally, various operational mechanisms integral to the building's functionality may contribute to the ambient noise. It is important to note that regulations regarding the design of residential buildings explicitly prohibit the placement of rooms with such functionalities directly adjacent to living spaces [47]. In residential premises, in addition to the two mentioned noise components, there may also be equipment noise (\(L_{equip}\)) emanating from appliances within the receiving room, such as air conditioners, fans, computers, HVAC systems, etc. [48]. The dominant component in constituting ambient noise inside a room depends on the type and purpose of the building, the environment in which the building is located, the construction system employed, the equipment of the room with devices that potentially generate noise, the age of those devices, and various other factors. Speech from the neighborhood penetrates the receiving room through the partition construction that separates them. The starting point in analyzing this process is the level of speech (\(L_{1,speech}\)) created by the neighboring sound environment right next to the border wall. This sound environment is characterized by periodicity, non-stationarity, and significant variability over time. The sound power that reaches the receiving room depends  
Figure 1: Schematic representation of the components of ambient noise and how it reaches the receiving room.