## 4 Experimental Study  
Experimental validation was carried out in a semi-anechoic chamber of the Institute of Vibration, Shock, and Noise (IVSN) at the Shanghai Jiao Tong University (SJTU). The background noise level of the semi-anechoic chamber is 15.6 dB (A), and the cut-off frequency is 100 Hz. The floor of the semi-anechoic chamber is solid, which could act as a work surface for supporting heavy items. In the experiments, a 56-channel spiral array with 40 enabled microphones was placed 2.404 m in front of the measurement plane. Three Philips BT25 Bluetooth loudspeakers were arranged in the measurement plane as sound sources. The acoustic signals were captured by Bruel & Kjaer 4944-A microphones, which were calibrated by a Bruel & Kjaer 4231 94 dB sound pressure calibration before the measurements. The sound pressure analog signals were converted into digital signals using a 42-channel Mueller-BBM MKII sound measurement system, and the sampling rate was 16,000 Hz. A snapshot of the experimental setup is presented in Figure 12.  
As shown in Figure 12, the geometrical center of the spiral array, which was at a height of 1.39 m from the floor in the experiments, was set as the coordinate origin. Three sound sources, which were 1.752 m, 1.128 m, and 1.419 m from the floor, were supported by tripods. A laser level and the band tapes with a 0.001 m accuracy were utilized to measure the sound source locations. Accordingly, considering the length of the microphones, the coordinates of the three sound sources were (\(-\)0.800, 0.029, and 2.304 m), (0.007 m, \(-\)0.262 m, and 2.304 m), and (0.793 m, 0.362 m, and 2.304 m) in a near-field Cartesian coordinate system. The plane of the microphones was set as the x-z coordinate plane. Three randomly selected data pieces from the ST-CMDS data testing set were broadcast by loudspeakers on an endless loop in the measurements. A 40-channel mixed signal is shown in Figure 13.  
The beamforming maps of the localization results obtained by the proposed process are shown in Figure 14. By adopting the BW-MUSIC method and denoising DNNs, the localization performance was found to be acceptable with obvious main lobes, which  
Figure 12: Experimental setup: three loudspeakers and the spiral microphone array in a semi-anechoic chamber.  
Figure 13: Forty-channel measured mixed signal in the experimental study.  
indicate the location of the sound source. The side lobes could barely be noticed in all the three figures. However, the area of the hotspots was larger than in the simulation results. As the experimental chamber is semi-anechoic, the lower resolution in Figure 14, compared to Figure 9, can be attributed to the ground reflection of sound waves. Table 2 shows the corresponding errors in the absolute distance of localization by BW-MUSIC. It is indicated that the three sound sources are localized accurately, with a location error of less than 0.15 m.  
A comparison of the original signals from the dataset and the signals reconstructed by the proposed method is shown in Figure 15. The reconstructed signals shown in Figure 15(1b-3b) prove that the proposed method can successfully separate the three sound sources from the mixed measurement signal. However, the apparent discrepancy between the original and reconstructed signals indicates a worse performance of the signal reconstruction in the experimental study compared with the simulation results. As background noise is generated from the sound measurement system and the ground reflection interference of sound waves, in future work, a more robust denoising DNN for a lower SNR will be explored to improve the reconstruction performance.