## 7 Conclusions  
In this study, we investigated the influence of sound absorption in general dwellings on the subjective evaluation of acoustics. First, a subjective experiment was conducted using a full-scale room model. \"feeling of silence\" and \"feeling of serenity\" could be felt at an absorption coefficient above 0.17 and were clearly felt above values of 0.25. Second, we used the recorded binaural sounds obtained in the full-scale room model for a subjective test because this model examination required considerable time and human resources. This test showed that \"reverbearance\", \"feeling of silence\", and \"feeling of serenity\" can also be evaluated using headphone listening. We also measured the reverberation time and recorded the sound environment in the bedrooms, LD rooms, and child rooms in three modern Japanese dwellings to verify the results of the former experiments. The reverberation times of LD and child rooms in this study were longer than the other reported furnished rooms by approximately 0.1-0.2 s [1; 2; 3; 4; 5; 6; 9; 10]. In particular, those of the child rooms were long, despite the small room volume of approximately 30 m\({}^{3}\). The wooden floor and lack of absorption materials could be the cause of longer reverberation times. The average absorption coefficients of the LD and child rooms were smaller than 0.17, in the range of 500 Hz to 4 kHz. Therefore, we analyzed the subjective effect of the absorption by a psychological test using the binaural recorded sounds in the nine rooms and observed that the bedrooms with absorption coefficients of 0.18 to 0.23 were significantly less reverberant, quieter, and serener than the other rooms. The results may be caused by the wooden floor and low absorption of the ceiling and walls in all LD and child rooms. From the discussion, it was revealed that the absorption coefficient above 0.25 may become one of the criteria for creating a silent and serene space when a room has low background noise level. As you feel stiffening in an anechoic room, considerable absorption may not make us comfortable. There may be upper limit of the absorption area to provide a feeling of comfort and serenity in a room. Further studies are required to clarify this aspect. Additionally, to prevent booming or fluttering echo in a small room, the amount and position of the absorption area are important factors to be considered. Although scattering treatment does not reduce reverberant energy by itself, it can induce an adequate absorption effect. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Item** & **125 Hz** & **250 Hz** & **500 Hz** & **1000 Hz** & **2000 Hz** & **4000 Hz** & **A-Weighted** \\ \hline Reverberance & \(-\)0.05 & 0.37 & 0.40 & 0.53 & 0.47 & 0.35 & 0.45 \\ Feeling of silence & 0.19 & \(-\)0.33 & \(-\)0.36 & \(-\)0.53 & \(-\)0.50 & \(-\)0.42 & \(-\)0.40 \\ Feeling of serenity & 0.21 & \(-\)0.32 & \(-\)0.38 & \(-\)0.58 & \(-\)0.51 & \(-\)0.40 & \(-\)0.42 \\ Sense of room volume & 0.20 & 0.60 \({}^{*}\) & 0.50 & 0.56 & 0.60 \({}^{*}\) & 0.63 \({}^{*}\) & 0.58 \\ Feeling of oppression & \(-\)0.46 & \(-\)0.24 & 0.25 & 0.36 & 0.22 & \(-\)0.01 & 0.13 \\ Sense of quality & 0.27 & \(-\)0.27 & \(-\)0.36 & \(-\)0.57 & \(-\)0.49 & \(-\)0.37 & \(-\)0.38 \\ User preference & 0.39 & \(-\)0.22 & \(-\)0.38 & \(-\)0.61 \({}^{*}\) & \(-\)0.53 & \(-\)0.37 & \(-\)0.38 \\ \hline \end{tabular} \({}^{*}\)_p_ \(<\) 0.05.  
\end{table} 
Table 12: Correlation coefficients between the background noise levels in nine rooms in modern Japanese dwellings and the psychological values of each evaluation item. Therefore, moderate acoustic scattering treatment could be important for creating a serenity room and should be further investigated. Conceptualization, K.H., T.H., and D.W.; methodology, T.H. and D.W.; software, K.H., T.H., and R.S. ; validation, K.H., T.H., and R.S. ; formal analysis, T.H. ; investigation, K.H., T.H., R.S., and D.W.; resources, T.H. and D.W.; data curation, K.H., T.H., R.S., and D.W.; writing--original draft preparation, K.H. and T.H.