# Improving Engineering Design Using Smart Evaluation of Indoor Acoustical Climate of Dining Places
## 4 Acoustical Analysis of Dining Places
The influence of the reflecting barriers on the STI index is shown in Figure 4.  
Figure 3: STI values for a catering room with different ceiling absorption and capacities. The results of the simulations presented in Figure 3 indicate that both the capacity and sound absorption of the ceiling significantly influence speech intelligibility. As shown, the effects are not identical. As shown, speech intelligibility increases to a greater extent with the modification of sound absorption by changing the acoustical parameters of the ceiling. The simulation results show that the sound absorption of the materials in the enclosure plays a more significant role in the assessment of the acoustical climate of the restaurant during the early stages of design. Modification of the sound absorption parameters of the ceiling, from non-absorptive (\(\alpha_{\text{p}}=0.1\)) to highly absorptive (\(\alpha_{\text{p}}=0.8\)), changed the speech intelligibility parameter (STI), measured in the centre of the simulated restaurant, from 0.35 to 0.62 for low capacity (9 tables), from 0.40 to 0.65 for average capacity (25 tables), and from 0.50 to 0.70 for high capacity (42 tables). This results in a difference in results from \(\Delta\text{STI}\approx 0.27\) for low capacity to \(\Delta\text{STI}\approx 0.20\) for high capacity. This means that this parameter plays a fundamental role in changing the intelligibility of speech in dining places and should be considered the most. Variation in the number of tables (capacity)--from low capacity, with 9 tables, to high capacity, with 42 tables--changed the speech intelligibility (STI) measured in the centre of the simulated restaurant from 0.35 to 0.50 for non-absorptive ceiling with \(\alpha_{\text{p}}=0.1\), from 0.55 to 0.65 for average absorptive ceiling with \(\alpha_{\text{p}}=0.4\), and from 0.63 to 0.70 for highly absorptive ceiling with \(\alpha_{\text{p}}=0.8\). This results in a difference in results from \(\Delta\text{STI}\approx 0.15\) for low capacity to \(\Delta\text{STI}\approx 0.05\) for high capacity. The capacity influences the speech intelligibility in the enclosure to a lesser extent than the sound absorption coefficient; therefore, in the overall assessment of the acoustical climate of the dining enclosure, it is less important. Table 2 presents a comparison of the differences in the STI results. It is clear that the sound absorption of the ceiling has a more significant influence on speech intelligibility than the capacity of the restaurant. Figure 4: Influence of partitions in a restaurant with 25 tables on speech intelligibility. The barriers mounted between tables significantly influence the speech intelligibility of the sound generated by the loudspeaker (not by the guest sitting at the tables), from 0.65 for an enclosure without barriers to 0.55 for an enclosure with barriers (measured in the centre of the simulated enclosure). Simultaneously, the barriers decrease the sound pressure levels, which affect the speech intelligibility between the guests sitting at the table. Table 3 compares the results of the differences between the STI and SPL(A). Mounting barriers between tables negatively impacts the speech intelligibility of sounds generated by, for example, sound alarm systems in dining places. The speech might not be recognised by those sitting at the tables, especially those far away from the loudspeaker. Simultaneously, the speech intelligibility at the tables will increase because the sound levels generated by any noise source will affect the discussion less.