# A Planer Moving Microphone Array for Sound Source Localization
## 3 Experiment and Results
The first experiment focused on estimating the angle of multiple targets in multiple directions. The FPMMS result was compared with the ones derived from the contrast groups. FPMMS was mounted on a robot at a height of 1 m from the floor. The directions of the targets were 30\({}^{\circ}\), 60\({}^{\circ}\), 90\({}^{\circ}\), 120\({}^{\circ}\), and 150\({}^{\circ}\). Sound sources were set at two different distances, 1.5 m and 2 m. Thus, unlike in [21], wherein the authors set only one distance, our multi-target system was more complex. Figure 12 depicts the procedure of the experiment. The direction estimation results are shown below. The figures denote the gaps between each microphone array estimation result and the ground truth directions. In Figures 13-24, the horizontal axes represent location distances, and the polar axes are in degrees. From the results, we can see that, in angular estimation, FPMMS generally makes estimations that are much closer to the actual performance of a 16-microphone array than other forms of active microphone array. At 90\({}^{\circ}\), FPMMS performs better than at other angles. The accuracy at a distance of 1.5 m is generally better than that at a distance of 2 m. FPMMS works better in all five directions and two distances than the 1 \(\times\) 4 linear rotating microphone array. Regarding the different SSL algorithms, the TF-WISE group generally performs better, though it is not as useful in scenarios that feature fewer targets. When the number of targets is around three, four, or five, TF-WISE displays its advantages. In addition, the number of microphones affects each SSL algorithm's recognition ability. In theory, TF-WISE, MUSIC, and SRP-PHAT can recognize \"k \(-\) 1\" number of targets. \"k\" is the number of microphones. Indeed, FPMMS moves four times, and the others rotate three times. Sometimes, the FPMMS and 1 \(\times\) 4 linear microphone array can recognize all targets but do not always succeed. Thus, below are reference tables showing the success rates of the FPMMS, the 1 \(\times\) 4 linear microphone array, and the circular microphone array in recognizing all targets. The 4 \(\times\) 4 microphone array had almost no failures and started with a three-target scenario. From Tables 1-3, we can ascertain that the circular microphone array has a huge advantage over the others because it has six microphones. The FPMMS enables greater data collection, meaning it shows better performance than the 1 \(\times\) 4 linear microphone array, and its performance is not far behind that of the circular microphone array. Figure 12: The flow chart of the first and second experiments. The audio signal is multi-channel; Thus, the Audio signal part would be overlapped by different colors. The small black dots represent microphones on circular mic array and linear mic array. The four deep blue squares represent collected four microphone data at time spot 1. The dash squares following the timeline represent data collected after planar moving of FPMMS. The second FPMMS experiment focused on distance estimation for SSL. From the 2D polar localization view, the first experiment gave us an angle estimation \(\mathbf{\varphi}\), and we used the same data collected by microphones in pairs/groups, as stated in Section 3, to facilitate planar distance estimation. Thus, no tables showing success rates are needed here. Figure 12 shows the procedure of this experiment. Figure 14: TF-WISE angular estimation results derived from an experiment featuring 3 sound sources (at angles of \(30^{\lx@math@degree},\,60^{\lx@math@degree},\,90^{\lx@math@degree},\,120^{ \lx@math@degree},\,\) and \(150^{\lx@math@degree}\) at distances of 1.5 m (**a**) and 2 m (**b**) and a height of 1.5 m). The error between the estimated sound source angles and the true sound source angles is also shown.