## 3 Results
### Objective Results
\(\Delta T_{30}\) represent the parameter differences between the configurations Df-Dm, Df-Dr, Dm-Dr in the reflective (-R) and absorptive (-A) conditions. Differences equal \(\pm 1\)JND of the parameters are highlighted through a gray area. Figure 8: \(D_{50}\) parameter averaged over 500 Hz and 1000 Hz for S1 and S2 source-to-receiver distance. \(\Delta D_{50}\) represents the parameter differences between the configurations Df-Dm, Df-Dr, Dm-Dr in the reflective (-R) and absorptive (-A) conditions. Differences equal \(\pm\)1 JND of the parameters are highlighted through a gray area. Figure 7: C\({}_{80}\) parameter averaged over 500 Hz and 1000 Hz for S1 and S2 source-to-receiver distance. \(\Delta\)C\({}_{80}\) represents the parameter differences between the configurations Df-Dm, Df-Dr, Dm-Dr in the reflective (-R) and absorptive (-A) conditions. Differences equal \(\pm\)1 JND of the parameters are highlighted through a gray area. A statistical analysis has been performed on the data shown in Appendix A to investigate the main factor (that is the absorptive/reflective conditions, source S1 and S2, source-to-receiver distance) effects on the variability of the objective acoustic parameters in the comparisons between the tested configurations (Df-Dm, Df-Dr, Dm-Dr). To this aim, only differences above the JND have been considered since it is not meaningful from an acoustic point of view to investigate data lower than the perceived ones. Thus, _EDT_, which resulted in the most affected parameter, was retained suitable for a statistical analysis given the relatively high number of receiver locations that showed differences above the JND. However, it was not possible to apply an ANOVA analysis since the assumptions of normality of data distribution and homogeneity of variance are violated. Given this result, the Kruskal-Wallis (KW) test, which is a non-parametric test and an extension of the Mann-Whitney U Test for more than two groups, has been applied [34]. The Kruskal-Wallis test did not show a statistically significant result (\(p>0.05\)) for the differences due to the diffusers location variations. Table 3 shows the differences in the spatial mean values of each parameter obtained in the conditions with the three different locations of the diffusive surfaces (Df, Dm, and Dr) with respect to the absorptive (All-A) and reflective (All-R) conditions. It can be noticed that the overall results show significant differences for the _EDT_ in all the configurations (Df, Dm, and Dr) and also for T\({}_{30}\) in the Df and Dm configurations with respect to All-A. However, this might be due to the variation of the equivalent absorption area, which decreases when one part of the lateral absorptive walls is set into a diffusive condition. This effect is not evident with respect to the reflective condition (All-R). A more detailed analysis of the objective parameters has been performed at the head positions. Table 4 gathers the differences of the objective parameters between each compared pair for source position S1 and S2 in the subjective test. The objective parameters at the head position have been evaluated as the values of the parameters obtained at the nearest microphone positions, i.e., microphone position 18 for head 1 and average values of microphone positions 14 and 15 for head 2. The conditions Df and Dr, i.e., the subjectively compared conditions, that lead to differences between the objective parameters above the JND are highlighted in bold. Figure 9: \(T_{\rm s}\) averaged over 500 Hz and 1000 Hz for S1 and S2 source-to-receiver distance. \(\Delta T_{\rm s}\) represent the parameter differences between the configurations Df-Dm, Df-Dr, Dm-Dr in the reflective (-R) and absorptive (-A) conditions. Differences equal \(\pm 1\) JND of the parameters are highlighted through a gray area. The combination of the listening position head 1 and source location S1 presents a greater number of parameters (_EDT_, \(D_{50}\), and _IACC_L) that reveal differences above the JND in the comparison of Df-A towards Dr-A.