## 2 Subjective Experiment Using Full-Scale Room Models
### Results and Discussion  
Figure 5 shows the results of the subjective experiments on a psychological scale. Error bars represent 5% significant yardsticks. We can evaluate statistical significance (\(p<0.05\)) between two average cores by comparing with the other's yardstick. The largest difference in psychological value was observed for \"reverberance\". All evaluation spaces were found to have significantly different reverberances. The participants could distinguish one space from the others. With the increase in the absorber area, the psychological values of \"feeling of silence\", \"feeling of serenity\", \"sense of quality\", and \"user preference\" also tended to increase. However, the changing ranges of these items were not larger than that of \"reverberance\". Regarding \"feeling of silence\" and \"sense of quality\", the largest change in psychological value was observed between evaluation spaces \"C\" and \"D\". These results indicate that a certain threshold of absorption area must be exceeded to feel the difference in these sensations. An analysis of variance (ANOVA) was performed between the average absorption coefficients of the five patterns and eight evaluation items. The main effect of changing the absorption area was not significant in terms of \"sense of room volume\", \(F\) (4, 20) = 2.20, \(p\) = 0.11 and \"feeling of oppression\", \(F\) (4, 20) = 0.28, \(p\) = 0.89, but showed 1% significance for the other six evaluation items. The correlation coefficients of these six items were calculated and are listed in Table 3. The absorption installation may influence \"difference in feeling of silence\", \(r(5)\) = 0.81, \(p<0.01\), \"reverberance\", \(r(5)\) = -0.94, \(p<0.01\), \"feeling of silence\", \(r(5)\) = 0.97, \(p<0.01\), \"feeling of serenity\", \(r(5)\) = 0.98, \(p<0.01\), \"sense of quality\", \(r(5)\) = 0.94, \(p<0.01\), and \"user preference\", \(r(5)\) = 0.90, \(p<0.01\) (all values at 500 Hz). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Item** & **125 Hz** & **250 Hz** & **500 Hz** & **1000 Hz** & **2000 Hz** & **4000 Hz** \\ \hline Difference in feeling of silence & 0.79 * & 0.77 * & 0.81 * & 0.80 * & 0.80 * & 0.72 \\ Reverberance & \(-\)0.93 ** & \(-\)0.97 ** & \(-\)0.94 ** & \(-\)0.97 ** & \(-\)0.97 ** & \(-\)0.99 ** \\ Feeling of silence & 0.97 ** & 0.98 ** & 0.97 ** & 0.99 ** & 0.99 ** & 0.96 ** \\ Feeling of serenity & 0.93 ** & 0.98 ** & 0.98 ** & 0.98 ** & 0.97 ** & 0.99 ** \\ Sense of room volume & - & - & - & - & - & - \\ Feeling of oppression & - & - & - & - & - & - \\ Sense of quality & 0.99 ** & 1.00 ** & 0.94 ** & 0.98 ** & 0.99 ** & 0.99 ** \\ User preference & 0.94 ** & 0.97 ** & 0.90 ** & 0.95 ** & 0.95 ** & 0.99 ** \\ \hline \hline \end{tabular}  
\end{table} 
Table 3: Correlation coefficients between the average absorption coefficients and psychological values of each evaluation item. We analyzed the relationship between objective measurements and subjective experiments in detail. Only for \"reverberance\", the absorption pattern \"B\" with an arithmetic average of the absorption coefficients of 0.12 from 500 to 4000 Hz significantly differed from pattern \"A\". This shows that an absorption coefficient of 0.12 is not sufficient to create the auditory effect of the room. Similarly, the absorption pattern \"C\" (arithmetic average of absorption coefficient: 0.17) could provide a lower \"reverberance\" and higher \"feeling of serenity\" and \"user preference\". However, it could not provide a \"feeling of silence\" and \"sense of quality\". Absorption pattern \"D\" (arithmetic average of the absorption coefficient: 0.25) could provide a higher \"feeling of silence\" and \"sense of quality\", considerably lower \"reverberance\", and considerably higher \"feeling of serenity\" and \"user preference\". Thus, the effect of the absorbent material was increased at an absorption coefficient of 0.17 and was further increased at an absorption coefficient of 0.25. Figure 5: Results of psychological experiments using the full-scale room model.