# Indoor Acoustic Requirements for Autism-Friendly Spaces
## 3 Results and Discussion  
From the above-mentioned literature review (Sections 2.1 and 2.2), the range RT = 0.4 \(\div\) 0.7 s (mean values for the octave frequency bands of 500 Hz, 1000 Hz, and 2000 Hz) appears to be optimal for both the application of microphones and for subjects particularly sensitive to auditory stimuli. From the point of view of C\({}_{50}\), the literature also suggests aiming at C\({}_{50}\)\(\geq\) 2 dB (same RT frequency range), while for D\({}_{50}\), the selected range is, as for RT, the one comprising all the found limits: D\({}_{50}\)\(\geq\) 0.7. Graphical results are reported in Figure 3, where the grey rectangles highlight the chosen reference ranges. The measured RT frequency trends (average of six positions) for each room are reported in Figure 4. As above-mentioned, these values were used to calibrate 3D models. In Table A1, the measurement accuracy is depicted, highlighting very small variations in the tested results. The RT frequency trend in each analyzed room was quite linear only for a specific room (Soft room); small rooms (Th. Room nos. 1, 3, 4, and bedroom) presented RT frequency values between 0.5 and 0.8 s; the largest rooms (Th. Room no. 2 and atelier) depicted a volcano-shape pattern with higher values (RT > 1 s) at 500 Hz. In terms of arithmetic (RT) and logarithmic (C\({}_{50}\) and D\({}_{50}\)) mean values, three out of seven rooms resulted in being out of the optimal considered ranges for the reverberation time parameter. It is worthy to remark here that every room was equipped with some sound absorbing panels. In Appendix A, Figure A2a-g describes the room models considered for the acoustic simulations, furnished as in the real conditions, while, in Figure A3a-g, the results in terms of the Q-Q plots referring to reverberation time (octaves bands) are reported, demonstrating a very good agreement between the measured results and simulated ones. The calibration of 3D models permits the consideration of also clarity C\({}_{50}\) and definition D\({}_{50}\). The results in terms of the averaged values related to the frequency range 250 \(\div\) 2500 Hz of all the investigated parameters are reported in Table 1. Results are listed considering the average of all receiver positions for RT, while values were retrieved at a distance of 2 m from the  
Figure 4: Measured reverberation time (T\({}_{30}\)) for different rooms. Figure 3: Grey rectangles highlight the chosen ranges in this work. Arrows indicate the range or points associated with selected literature papers (highlighted with squared brackets), used as support. source for C\({}_{50}\) and D\({}_{50}\). This range was chosen in accordance with the work of [PERSON] and [PERSON] (2018). It is evident how some rooms do not respect the selected ranges depicted in Figure 3 and thus some measured environments should be acoustically improved to achieve better indoor acoustic comfort. By means of 3D simulations, the indoor sound field distribution related to the objective parameters could be investigated, permitting the search for focusing phenomena, other scattering issues, and the material distribution inside rooms. These events may affect operative sensor conditions and speech clarity and definition. Accordingly, if reverberation increases, the difficulty in identifying and recognizing a sound signal will rise. For example, the spatial distribution of the reverberation time included in therapy room no. 2 (Figure 5) shows how the corner positions do not represent the optimal device locations. Even if corners could embody good places where no obstacles to such furnishings, chandeliers, curtains, or other objects are present, they are unfortunately the room points where reverberation is higher and different from the source area. The sound field analysis of C\({}_{50}\) and D\({}_{50}\) (Figures 6 and 7) shows that the optimal positions for the acoustic recognition devices are located in the proximity of the spaces most likely to be occupied by users (e.g., on top of a table, near the center of the ceiling or walls, etc.).