## 5 Results
### Measurement Results  
The measurements results are presented in Figures 10-14, corresponding to the cases 1 to 5 in Table 2. In the figures (a) is the reverberation time \(T_{20}\) in seconds, (b) is the speech clarity \(\mathbf{C}_{50}\) in dB and (c) is the sound strength \(\mathbf{G}\) in dB. Comparisons are made between measurements, Sabine calculation and the non-diffuse calculation. For the non-diffuse calculation, both the empirical and the theoretical approaches, discussed in Section 3.2.3, are shown. Figure 10: Sparsely furnished room with dimensions \(7.35\times 7.50\times 3.50\) m. Ceiling treatment: 50-mm glass wool absorber at a mounting height (air cavity behind the absorber) of 750 mm. (**a**) Reverberation time \(\mathbf{T}_{20}\) in seconds, (**b**) speech clarity \(\mathbf{C}_{50}\) in dB, (**c**) sound strength \(\mathbf{G}\) in dB. Curves shown are (red) diffuse calculation (Sabine), (blue) measurement, (dashed) non-diffuse calculation, where the number of non-grazing modes is estimated by Equation (31), and (dash-dotted) non-diffuse calculation, where the number of non-grazing modes is empirically estimated, see Table 1.  
Figure 11: Sparsely furnished room with dimensions \(7.35\times 7.50\times 3.50\) m. Ceiling treatment: 15-mm glass wool absorber at a mounting height (air cavity behind the absorber) of 785 mm. (**a**) Reverberation time \(T_{20}\) in seconds, (**b**) speech clarity \(C_{50}\) in dB, (**c**) sound strength \(G\) in dB. Curves shown are (red) diffuse calculation (Sabine), (blue) measurement, (dashed) non-diffuse diffusion calculation, where the number of non-grazing modes is estimated by Equation (31), and (dash-dotted) non-diffuse calculation, where the number of non-grazing modes is empirically estimated, see Table 1.  
Figure 12: Sparsely furnished room with dimensions \(7.35\times 7.50\times 3.50\) m. Ceiling treatment: 15 mm glass wool absorber at a mounting height (air cavity behind the absorber) of 785 mm. 6.48 m\({}^{2}\) 40 mm glass wool wall absorber equally distributed on two adjacent walls and directly mounted on the walls, see Figure 7. (**a**) Reverberation time \(T_{20}\) in seconds, (**b**) speech clarity \(C_{50}\) in dB, (**c**) sound strength \(G\) in dB. Curves shown are (red) diffuse calculation (Sabine), (blue) measurement, (dashed) non-diffuse calculation, where the number of non-grazing modes is estimated by Equation (31), (dash-dotted) non-diffuse calculation, where the number of non-grazing modes is empirically estimated, see Table 1.  
Overall, the non-diffuse model fits better with the measurement results than the diffuse model. In particular, the overestimation of the absorption in the diffuse model is reduced in the non-diffuse model. The large differences between the diffuse calculations and the measurement results are typical for sparsely furnished rooms with an absorbent ceiling treatment. The cause of this is the lack of diffusion and the influence of the grazing sound field. Naturally, the empirical estimation given in Table 1 agrees better with measurements than the theoretical approach, according to Equation (31). This is more apparent at the higher frequencies. It is noticeable that the non-diffuse model captures the frequency behavior better than the diffuse one. Figure 14: Sparsely furnished room with dimensions 7.35 \(\times\) 7.50 \(\times\) 3.50 m. Ceiling treatment: 50 mm glass wool absorber at a mounting height (air cavity behind the absorber) of 150 mm. (**a**) Reverberation time \(\mathbf{T}_{20}\) in seconds, (**b**) speech clarity \(\mathbf{C}_{50}\) in dB, (**c**) sound strength \(\mathbf{G}\) in dB.