# Tunable Perforated Panel Sound Absorbers for Variable Acoustics Room Design
## 4 Results and Discussion
### Case Study: Application to Variable Acoustics Room Design  
Next, the use of the TS-A variable solution was analyzed under diffuse field conditions using the ray tracing method in the case study room, as described in Section 3.2. For this  
Figure 4: Measured sound absorption coefficients for each of the analyzed configurations: (**a**) TS-A and (**b**) TS-B. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Variable Solution**} & \multicolumn{8}{c}{**Open Area Ratio (\%)**} \\ \hline \multirow{3}{*}{TS-A} & A\#1 & A\#2 & A\#3 & A\#4 & A\#5 & \\ \cline{2-9}  & 0.6 & 1.2 & 1.4 & 2.7 & 5.6 & \\ \hline \multirow{3}{*}{TS-B} & B\#1 & B\#2 & B\#3 & B\#4 & B\#5 & B\#6 & B\#7 & B\#8 \\ \cline{2-9}  & 0.7 & 1.7 & 2.7 & 3.9 & 6.1 & 8.7 & 10.6 & 14.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Open area ratio for each of the analyzed configurations of both types of solution. purpose, the Reverberation Time (RT), the Definition (D50), and the Clarity (C80) were calculated from the impulse response obtained at each of the receiver positions for different room occupancy levels: empty, one-third occupation, and full occupation. As mentioned previously, diffuse field values of the sound absorption coefficient were estimated from the measured values depicted in Figure 4a by using the methodology described in [3], the resulting data being presented in Table 4.  
This analysis was intended to show how the presence of the proposed variable acoustics system may help in controlling the acoustic environment inside the room, acting in conjunction (and eventually compensating) with the occupation by people. Besides the full and empty room cases, an intermediate case has been introduced, showing the effect of the system for one-third of occupation to further illustrate the effect of the system in in-between occupancy conditions. Figure 5 shows the average results for the three parameters mentioned above as a function of octave frequency bands. Results are shown for a reference case (i.e., without a tunable absorber solution) and different occupancy levels for each of the five configurations of variable solution TS-A analyzed in the previous section. It should be noted that, due to the small volume of the room and its RT being around 1.2 s at lower frequencies, the expected value of Schroeder's frequency (below which the room is expected to exhibit a modal behavior) is around 185 Hz. Thus, simulations using the ray tracing process are only expected to provide meaningful results above this frequency and, consequently, although the results at 125 Hz are presented in the plots, a gray area has been added to indicate that they are outside the range of validity of the model. For lower frequency analysis, more accurate results may only be obtained by using alternative approaches based on numerical methods to solve the wave equation, such as the finite element method or boundary element method, and also include more detailed properties such as complex surface impedance. An example of this approach can be found in the recent work by [PERSON] et al. [29]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Frequency (Hz)**} \\ \hline
**TS-A Variable Solution** & **125** & **250** & **500** & **1 k** & **2 k** \\ \hline A\#1 & 0.18 & 0.30 & 0.62 & 0.39 & 0.25 \\ A\#2 & 0.23 & 0.22 & 0.46 & 0.59 & 0.27 \\ A\#3 & 0.26 & 0.23 & 0.39 & 0.64 & 0.30 \\ A\#4 & 0.07 & 0.11 & 0.17 & 0.56 & 0.28 \\ A\#5 & 0.16 & 0.16 & 0.13 & 0.21 & 0.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sound absorption coefficients used in the diffuse field simulations for TS-A variable acoustics solution. As expected, results show that, as the occupancy level of the room increases, a reduction in the RT and, consequently, an improved Definition and Clarity, are achieved due to the extra sound absorption linked to the higher number of people in the room.