## 5 Example Case  
The reverberation time has been measured in the Oslo Opera auditorium several times during 2023. This opera house was completed in 2007, and the main auditorium has a maximum of 1364 seats. The width of the stage opening is 16 m. Particularly interesting in this context are the measurements made in February and in July, because the air humidity was quite different. In July, the conditions were very close to the standard atmosphere (20.0 \({}^{\circ}\)C, 52% RH), and normalization of the results would not change anything. But, in February, the relative humidity was much lower (20.6 \({}^{\circ}\)C, 31% RH), and the normalization led to a significant difference at high frequencies. A photo from the auditorium is seen in Figure 9. The omni-directional sound source was just behind the orchestra pit and in front of the closed iron curtain. Microphone positions were in several places, and the one selected for this context was at the side on the second balcony, see Figure 10. Source and microphone positions were the same on the two measurement days, and the distance from source to receiver was approximately 15 m. However, the conditions in the auditorium were not the same during the two measurements; the orchestra pit was open and furnished with chairs and music stands in February. In July, the floor of the orchestra pit was raised as an extension of the stage and not furnished. This can explain some minor differences in the results. Figure 9: Photo from the opera house during one of the measurements. (Photo: [PERSON]). The results of the measured and normalized reverberation times \(T_{20}\) and \(T_{30}\) from 1 kHz to 8 kHz are presented in Figure 11. The full summation method was applied. At 4 kHz and 8 kHz, there is a significant difference between the measurement results at 52% RH and 31% RH. The measurements at 52% RH are shown without normalization, because this would make no difference. The measured reverberation times are shorter when the air is dry, but using the normalization of the impulse response brings the results from different atmospheric conditions very close. At 8 kHz, a tendency to over-compensate for the air attenuation is noted, especially for the \(T_{30}\) results. This will be discussed later in Section 6. Figure 11: Measured and normalized reverberation times in a position on the second balcony in the opera house. The full summation method was applied for the normalization. (**a**) Reverberation time \(T_{20}\). (**b**) Reverberation time \(T_{30}\). Figure 10: Measurement positions for the results in Figure 11. Source H1 in front of the stage and microphone M1 in the second balcony. The approximate normalization method has also been applied to these measurements, see Table 3. The reverberation times measured at 31% RH were normalized to 50% RH, and the approximate method yields results that are nearly as good as the those obtained by normalization of the impulse response with the summation method. The relative deviation from the reference results obtained with 52% RH is given in Table 4.  
Concerning the EDT results, the summation method applied for the normalization provides good agreement with the reference measurements (up to \(\pm\)5% deviation). But the approximation method does not work so well; the results are over-compensated from \(-15\)% deviation without correction to \(+29\)% with correction. Looking at the results for \(T_{20}\), both methods provide good results (up to \(\pm\)5% deviation). For the T30 results, the approximation method works fine in all octave bands, whereas the summation method over-compensates at 8 kHz (\(+10\)% deviation with correction). The distances of sound propagation related to the approximation method are presented in Table 5 for the octave bands 1 kHz to 8 kHz. It is noted that at 8 kHz, the distance to the knee point is shorter than \(r_{3}\) and \(r_{4}\), so \(T_{20}\) and \(T_{30}\) are both affected by the lower air attenuation beyond the knee point. At 4 kHz, this only yields \(T_{30}\).