## 5 Evaluation Experiment
### Experiment A  
Figure 7 depicts the setup of the sound source positions and the microphone array for Experiment A. We used M1 alone to evaluate the angular resolution as a preliminary experiment. The sound source comprises 26 positions: P1-P26. We divided these positions into two groups as P1-P13 and P14-P26 which were located, respectively, on the circumferences of half circles with radii of 10 m and 20 m. The angle interval of the respective positions from the origin was 15\({}^{\circ}\). Here, P1-P13 existed on the straight lines of P14-P26 from the origin. Let \(\theta_{g}\) denote the ground-truth (GT) angle of \(\theta\). Figure 8 depicts the angle estimation results for 16 positions at \(\theta_{g}=\pm 15^{\circ}\), \(\pm 30^{\circ}\), \(\pm 60^{\circ}\), and \(\pm 90^{\circ}\). The experiment results demonstrated a unimodal output distribution of \(G(\theta)\). Moreover, \(G(\theta)\) at positions with the radius of 10 m were found to be greater than those of 20 m. The purple-filled circles denote the vertices of the respective output waves. We let \(\theta_{m}\) represent the maximum angle of \(G(\theta)\) in \(-90^{\circ}\leq\theta\leq 90^{\circ}\) calculated from the Formula (21). \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameter** & **Experiment A** & **Experiment B** & **Experiment C** \\ \hline Date & 19 August 2020 & 26 August 2020 & 28 August 2020 \\ Time (JST) & 14:00–15:00 & 14:00–15:00 & 14:00–15:00 \\ Weather & Sunny & Sunny & Sunny \\ Air pressure (hPa) & 1008.1 & 1008.8 & 1007.2 \\ Temperature (\({}^{\circ}\)C) & 28.6 & 31.7 & 33.4 \\ Humidity (\%) & 65 & 53 & 58 \\ Wind speed (m/s) & 4.3 & 3.8 & 4.9 \\ Wind direction & WNW & WNW & W \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Meteorological conditions on the respective experiment days. Figure 7: Setup of sound source positions and the microphone array M1 for Experiment A. Table 6 presents \(\theta_{m}\) at the respective positions. The error \(E\) between \(\theta_{g}\) and \(\theta_{m}\) is calculated as:  
\[E=\sqrt{(\theta_{g}-\theta_{m})^{2}}. \tag{23}\]The experimentally obtained results demonstrated that \(E=0\) in \(-15^{\circ}\leq\theta_{m}\leq 15^{\circ}\). As an overall tendency, the increase of the angles and \(E\) demonstrated a positive correlation apart from the negative angles of the 10 m radius. Figure 9 presents the two-dimensional distributions of \((x_{m},y_{m})\) for comparison with \((x_{g},y_{g})\), which represents the GT coordinates of the respective positions. The theoretical distance between M1 and the respective sound source positions was unobtainable for this experimental setup. Therefore, provisional positions were calculated by substituting \(L_{1}\) as 10 m or 20 m.  
Figure 10 presents scatter plots of \(\theta_{g}\) and \(\theta_{m}\). The distribution results for \(L_{1}\) = 10 m and \(L_{1}\) = 20 m are presented, respectively, in the left and right panels. On the plus side, \(\theta_{m}\) for \(\theta_{g}\) exhibited smaller values as the angle increased. By contrast, on the minus side, it exhibited greater values as the angle increased. As the angle increased, the absolute \(\theta_{m}\) for absolute \(\theta_{g}\) tended to decrease. \begin{table}
\begin{tabular}{l c c c c c c c} \hline
**Position** & \(\theta_{g}\) & \(\theta_{m}\) & \(E\) & **Position** & \(\theta_{g}\) & \(\theta_{m}\) & \(E\) \\ \hline P1 & \(-90\) & \(-90\) & \(0\) & P14 & \(-90\) & \(-83\) & \(7\) \\ P2 & \(-75\) & \(-72\) & \(3\) & P15 & \(-75\) & \(-68\) & \(7\) \\ P3 & \(-60\) & \(-54\) & \(6\) & P16 & \(-60\) & \(-56\) & \(4\) \\ P4 & \(-45\) & \(-44\) & \(1\) & P17 & \(-45\) & \(-42\) & \(3\) \\ P5 & \(-30\) & \(-29\) & \(1\) & P18 & \(-30\) & \(-29\) & \(1\) \\ P6 & \(-15\) & \(-15\) & \(0\) & P19 & \(-15\) & \(-15\) & \(0\) \\ P7 & \(0\) & \(0\) & \(0\) & P20 & \(0\) & \(0\) & \(0\) \\ P8 & \(15\) & \(15\) & \(0\) & P21 & \(15\) & \(15\) & \(0\) \\ P9 & \(30\) & \(29\) & \(1\) & P22 & \(30\) & \(29\) & \(1\) \\ P10 & \(45\) & \(43\) & \(2\) & P23 & \(45\) & \(43\) & \(2\) \\ P11 & \(60\) & \(54\)