## 3 Results
### Reverberation Time  
The frequency characteristics of the reverberation time of each one octave band are shown in Figure 12. The reverberation time in the 500 Hz one octave band is 0.95 s for the lobby, 0.98 s for the entrance hall, and 1.00 s for the mezzanine. The results for each room were obtained by averaging the values of the measurement points in Table 6, but if two results were obtained for one measurement point, the following values were used: The measurement point of D3 is sound source S1, E5 is sound source S2, and C8 and E8 are sound source S2. Each reverberation time of the measurement point is the average value of seven measurement values. In addition, the signal peak level to background noise level ratios are 30 dB at 63 Hz and more than 45 dB in the other frequency bands.  
Next, it was confirmed whether the sound source position was affected by the reverberation time. The reverberation time was compared to measure the points of the lobby (D3), entrance hall (E5), and mezzanine (C8 and E8) with each sound source position. The differences in the reverberation time for 63 Hz to 8000 Hz of the one octave band are 1-15% for the lobby, 1-29% for the entrance hall, and 1-25% for the mezzanine. Though mainly studying music sources, [PERSON] et al. [17] suggested that the reverberation time discrimination threshold in an actual indoor sound field is  
Figure 11: Relationship between the sound pressure level distribution and theoretical values in the lobby and entrance hall.  
about 10% for 500 Hz-1000 Hz of the one octave band. This study corresponds to the conclusions of [PERSON] [18]. The differences that exceeded 10% in this measurement were mainly around 63 Hz and 8000 Hz of the one octave band. In these frequency bands, the assumption of a diffuse sound field possibly does not hold because a low frequency range is generally susceptible to the influence of the normal mode of vibration of a room, and the high frequency range obtains much sound absorption due to air absorption. For the other frequencies, the 500 Hz in the lobby and the 2000 Hz in the mezzanine of C8 have a difference greater than 10%. The difference in the lobby is not significant, with the reverberation time of sound source S1 being 12% and that of sound source S2 being 10%. The difference in the mezzanine is also not great, with the reverberation time of sound source S1 being 14% and that of sound source S2 being 13 %. Although the source position may affect the reverberation time, this survey did not determine whether there is an audible difference.  
We compared the values of the reverberation time at 500 Hz with the values of the optimum reverberation time [19], which was proposed both empirically and theoretically by many researchers as a function of the room volume. The values of the reverberation time at 500 Hz are comparable to the values that [PERSON] recommended for the conference room and those that [PERSON] recommended for lectures and conversations in the main rooms. The reverberation times of the lobby and the entrance hall were found to be suitable for rooms in which conversations are the main purpose. This tendency is seen when the lobby and entrance hall are regarded as separate rooms and also when the rooms are regarded as an integrated room. This result corresponds to the reputation of the sound environment of the lobby. The appropriateness of the reverberation time with respect to the space use is one of the factors evaluated for the sound environment of the lobby.