## 4 Comparison between the Simulation and Experimental Results  
Experiments were conducted in an anechoic room with a reduced system having five error microphones and five loudspeakers according to Esquations (1) and (4) by using NI CRio-9039, Labview FPGA, and Realtime OS. The sound pressure was acquired through Labview FPGA using microphones and sent to Realtime OS. The FxLMS algorithm was implemented via Realtime OS through the data received. The calculated value was again passed to the FPGA to generate sound through the speaker. The experimental geometry is shown in Figure 9(a). We used 11 measurement microphones (at 0.045 m intervals) to measure the quiet zone; these microphones were placed in a linear array configuration with an offset of 0.015 m in the normal direction. The inside of the quiet zone was measured at intervals of 10\({}^{\circ}\) through the rotational stage, and the 396 measurement points, measured by rotating each microphone in the linear array, are shown in Figure 9(b). To approximate the simulation result in which the loudspeaker is modeled as a point source, an experiment was conducted using a loudspeaker with a circular membrane having a radius of 0.03 m. The noise source generated a periodic 200-Hz signal at two positions: (1.97 m, 0.35 m, and 0 m) and (\(-1.8735\) m, \(-1.8735\) m, and 0 m). As shown in Figure 11, case 1 = [\(R_{mic}=0.5\) m, \(R_{s}=1.5\) m],  
Figure 10: (a) Experimental geometry and (b) measurement points. Figure 9: Average noise reduction with respect to the noise source angle. According to the change of \(R_{mic}\) (a) and \(R_{s}\) (b). case 2 = [\(R_{mic}\) = 0.5 m, \(R_{s}\) = 1.0 m], and case 3 = [\(R_{mic}\) = 0.5 m, \(R_{s}\) = 0.7 m] were considered, and adaptive feedback FxLMS ANC was performed. Table 1 shows the noise reduction performance outcomes for the measurement points in Figure 10b. As indicated, the performance is high in the order of case 1 \(>\) case 2 \(>\) case 3. Therefore, we proved that the radius of the loudspeaker affects the ANC performance. To compare the noise reduction between the simulation and the experiment, average noise reductions for each case are shown in Figure 12 for each rotation angle of each microphone constituting the line array. The experimental and simulation results show differences in noise reduction owing to various error factors in the experiment, such as the heights and positions of all microphones, loudspeakers, and noise speakers, or the fact that the loudspeaker is not a perfect monopole, and secondary path estimation errors. However, when the simulation and experimental results were compared, the noise reduction patterns at all set angles appeared to be similar. The amount of noise reduction with respect to the angle varied owing to the aforementioned factors, but the peak occurrence frequency and noise reduction trends according to \(R_{s}\) were similar between the experiments and simulations. This proves that the noise reduction pattern expected from the wave field reproduction error is similar to the actual experiments. [PERSON] et al. [19] used 12 microphones and 20 speakers to achieve a 9 dB noise reduction at the level of the dummy head within a 0.25 m hemisphere in a reverberant room using noise sources operated at 150 Hz and 200 Hz. In this study, the experiment was conducted in a free field, and five speakers and microphones were used to control the inner parts of a 0.5 m circle for a noise source operated at 200 Hz. In the case of \(R_{mic}\) = 0.5 m, \(R_{s}\) = 1.5 m, maximum and minimum noise reductions of 29.4 and 10.2 dB, respectively, were obtained. If the location of the noise source is on the plane of interest, the proposed ANC system is simpler than the ANC system wherein 3D spatial information is used; however, additional research is needed on the performance degradation caused by the vertical components of the noise source in the reverberant room. Figure 11: Experimental setup, (**a–c**) cases 1–3. Figure 12: Experimental and simulation noise reduction performance.