## 5 Results and Discussion
### Measurement Results Undertaken inside Room B--Reverbearant Room Facility at the University of Parma  
Another set of measurements was performed inside Room B, a reverberant chamber that represents one of the laboratory facilities at the University of Parma. From the results in Section 5.1, the difference of the scattering coefficients between the QRD composed ofplywood and MDF is minimal; as such, the authors for this campaign preferred to test theplywood QRD only, with and without the backing panel, in both horizontal and vertical configurations. As anticipated in Table 1, this campaign also consists of measuring the RIRs with the presence of the backing reflecting panel. This latest one has been introduced as a totally reflecting surface, representing a reference for making any comparison with the other configurations. Figure 10 shows theplywood QRD that has been tested inside Room B, with and without the backing reflecting panel. Figure 9: Matching between numerical and experimental data for the horizontal plywood and MDF panels inside Room A at mid-frequencies. The graphs in Figure 11 report the scattering coefficient obtained for each band of frequency between 125 Hz and 8 kHz, and for the configurations of the plywood QRD described above. These results were compared to those obtained by testing the reflecting panel only. The results of the acoustical coefficients are obtained by considering the average values of all the measuring points related to each microphone. At 125 Hz, all the configurations are similar and comparable, with a broad diffusion between channels 8 and 20. At the extremities, the peaks appear at channels 4 and 22, having a symmetrical trend with respect to channel 13 that is placed at the center. The graph relative to 250 Hz shows an increase in sound levels at channels 11 and 16, with the best performance equal to 71 dB registered by measuring the plywood QRD with the backing reflecting panel. Other peaks are found at channels 4 and 22, with comparable sound levels recorded at 125 Hz. The downward peaks belong to channels 2, 7, 13, 19 and 24. At 500 Hz, the sound level of channel 13, relative to the presence of the reflecting panel only, reaches 76 dB, equal to 5 dB above the plywood QRD in the horizontal configuration and with the backing reflecting panel. Other peaks are revealed at channels 9 and 17 with minor energy floating between 65 and 70 dB for all the configurations. The downward peaks recorded at 250 Hz, are herein increased up to 15 dB at the same channels. The graph relative to 1 kHz shows a flatter trend of the results across all the microphones, with the elimination of the fluctuations registered at side channels. In particular, since the performance of the horizontal configuration with the backing reflecting panel resulted, in the best case, between 125 and 500 Hz, in this frequency band the vertical configuration with the backing reflecting panel gives higher sound levels, especially at channels 8 and 15, while at channel 13 the result is equal to the horizontal configuration having the backing panel. From 2 kHz onwards, the performance of the only reflecting panel is the best only relative to channel 13, while it results lower than all the other configurations at the other microphone positions. The best performance across all the channels is given by the vertical configuration having the backing panel, especially at channel 13, but with small peaks registered at channels 7 and 20, recording 76 dB at these two positions. The results at 4 and 8 kHz are very similar in trend line and maximum scattering sound energy, the only difference consists of the peaks registered at channels 7, 10, 12, 14, 16 and 18, resulting in the more accentuated at 8 kHz. Other than the scattering coefficient, the directional diffusion coefficient has been calculated by the results obtained inside Room B. Figure 12 shows the values of the diffusion coefficient, correlated to the frequency range between 125 Hz and 8 kHz.