# A Planer Moving Microphone Array for Sound Source Localization
## 3 Experiment and Results  
In this section, we describe an experiment conducted to compare the performance of FPMMS with a 1 \(\times\) 4 linear rotation microphone array, a circular rotation microphone array, and a 4 \(\times\) 4 rotation microphone array (summarized as the contrast groups). We also build the microphone array displayed in Figure 10 (left). In addition to the different active microphone arrays used for comparison, we also used three major SSL algorithms--TF-WISE, SRP-PHAT, and MUSIC--to assess the performance of the active microphone arrays. The signal used for the experiment was derived from the LibriSpeech dataset [43; 44; 45; 46; 47]. Three experiments, one each for azimuth, distance, and height, were conducted in one normal classroom, as depicted in Figure 10. The classroom was 8 m long, 10 m wide, and 3 m high. Each experiment was conducted in a very common classroom environment, with \(T_{60}=240\) ms and \(SNR=15\) dB. In addition, for each experiment, we developed a corresponding flow chart to explain the procedures for direction, distance, and height estimation. In Figure 11, the 1 \(\times\) 4 microphone array uses one row of the 4 \(\times\) 4 microphone array. The radius of the circular microphone array is 10 cm. The length of the 4 \(\times\) 4 microphone array is 20 cm, and the height of the 4 \(\times\) 4 microphone array is 15 cm, where the horizontal inter-mic distance is about 6.67 cm, and the vertical inter-mic distance is 5 cm. Figure 9: Parallel line pattern forms of FPMMS. The lines connecting two MEMS microphones mean the two microphones are paired for subsequent height estimation. (**a**,**b**) are two symmetric patterns that FPMMS can form individually. All motors are synchronously controlled by high- and low-level clock signals emitted by the Arduino board, i.e., PWM-based control was used. Before the experiment, the speed of the conveyor belt with the matching gear under the maximum PWM power was measured (with the microphone installed). Based on this, the durations for which the high and low levels were required for translation and rotation were set. Continuous movement and sound acquisition would increase internal noise pollution. Due to the fixed timing control, the time interval positions of the microphone movement in the audio could be calculated from the sampling and timing, allowing them to be cut out. The Arduino board generates high-/low-level clock signals for PWM-based control. The Arduino's internal clock and the configured baud rate (command transmission frequency) were also considered. This experiment used 9600 baud serial communication. For the number of angle directions at the same distance, we chose K targets from five directions to form a multiple-sound source scenario. K is 2 and 3 here. For the angle directions at different distances, we picked K targets, but no direction was focused on; rather, we picked both 1.5 m and 2 m as the target at the same time. K was 2, 3, 4, or 5 for different distance cases. For the FPMMS, the movement time was 0.5 s, and the stationary time was 1 s, always facing directly forward relative to the robot. For the 1 \(\times\) 4 and 4 \(\times\) 4 microphone arrays, 0\({}^{\circ}\) was set as facing directly forward (robot front). The rotation angles, from left to right, were \(-15^{\circ}\), 0\({}^{\circ}\), and 15\({}^{\circ}\), with a rotation control time of 0.1 s and a stationary time of 1 s. For the circular microphone array, 0\({}^{\circ}\) was set with the first reference mic aligned to the robot's front. The rotation angles, from left to right, were \(-15^{\circ}\), 0\({}^{\circ}\), and 15\({}^{\circ}\), with a rotation control time of 0.1 s and a stationary time of 1 s.  
Figure 11: Real image of the circular microphone array and 4 \(\times\) 4 microphone array. Figure 10: (**Left**) Schematic of experiment setting (normal classroom) and real image from experiment. (**Right**) FPMMS is mounted on service robot and collects data from the speaker at 60\({}^{\circ}\), 2 m distance.