# An Estimation of Speech Privacy Class Based on ISO Parameter
## 4 Results and Discussion  
### Analyzed Rooms  
In this paper, tests were conducted using rooms of varying purposes, volumes, and shared wall surfaces to assess the proposed method. These rooms also exhibited differences in reverberation times. A total of 43 measurements of the sound reduction index of partitions between rooms were performed following the ISO standard [50]. All analyzed partitions were wall-mounted without doors or windows. The differentiation among rooms based on their purpose primarily involves the spatial organization and the quantity of furniture. Bedrooms and living rooms, for instance, feature a plethora of furniture items such as beds, sofas, bar tables, wardrobes, carpets, heavy curtains, and more. In contrast, classrooms typically house tables and chairs, with hard floors lacking carpets, and may have acoustic treatment on the ceiling or walls. Offices primarily contain chairs and desks, with additional items like smaller wardrobes and computer equipment. The analyzed case-scenario rooms included 12 living rooms (27.9% of the total number analyzed), 6 bedrooms (14%), 8 hotel rooms (18.6%), 5 classrooms (11.6%), and 12 office spaces (27.9%). In the conducted measurements, the rooms differed not only in terms of their intended purpose but also varied in size. Furthermore, the surface of the shared wall between the rooms, whose sound reduction index was measured, was also variable. Figure 2 illustrates the relationship between the volume of the receiving room \(V\) and the surface area of the shared wall \(S_{12}\) whose sound reduction index was measured. Each point on the graph represents a distinct measurement location. It is evident that the volume of the receiving rooms spans from 23 m\({}^{3}\) to 130 m\({}^{3}\), indicating significant variations in room dimensions. The surface area of the common wall ranges from 8 m\({}^{2}\) to 35 m\({}^{2}\). These diverse conditions provide a robust foundation for testing _SPC_ estimation methods in different real-world scenarios. The \(x\)-axis represents different rooms (labeled from 1 to 43). The room order is not arranged by categories but follows the naming convention of the measurement locations. This order will be maintained throughout the remainder of the manuscript. In Figure 3, the \(y\)-axis represents frequency bands, and the reverberation time values are depicted using a color scale, where warm colors (including red) indicate larger values, while cooler colors (including dark blue) indicate smaller values. The reverberation time varies between 0.25 s and 3 s. Figure 3 illustrates that a considerable number of rooms exhibit a relatively short reverberation time, around 0.5 s. This is attributed to the presence of furniture with higher absorption coefficients, particularly in bedrooms, living rooms, and hotel rooms. Conversely, longer reverberation times were observed in office spaces and classrooms with larger volumes, such as those numbered 32, 33, and 35. To further analyze the acoustic properties, Figure 4a displays the measured values of the sound reduction index for all measurement locations. In the majority of locations, the sound reduction index exceeds 50 dB, indicating relatively good insulation. However, in some cases, the insulating power of the partitions falls below 35 dB. These lower values suggest potential issues in the construction of the partitions. Measurement locations with low values of reverberation time (13, 14, 15, 16, 42, and 43) exhibit the lowest insulation values. This could imply that, in addition to the structural characteristics of the partition, the reverberation time is also a dominant factor. However, based on measurements at other locations, such a conclusion was dismissed. The reverberation times for measurement locations 6 and 7 are also short, but the insulation power in these cases is over 50 dB. These measurement locations are characterized by a small partition wall surface and small receiving room volume, resulting in a high insulation value.