## 3 Experimental Results  
The dual-zone ANC experiments are carried out in an anechoic chamber (Figure 3a). The TMS320C6678 DSP is utilized as the controller and a feedforward control is realized. The secondary loudspeaker array consists of eight speaker units spaced 0.12 m apart (Figure 3b). There are 11 microphones: a reference microphone, five control points and five noncontrol points. The spacing between the control points and the noncontrol points is 0.08 m. The center of the secondary loudspeaker array is taken as the origin. The distance between the center of the control points and the origin is 1.5 m. The noncontrol points have the same configuration as the control points. The control points and noncontrol points are located in the \(-30^{\circ}\) and \(30^{\circ}\) directions deviated from the center of the secondary loudspeaker array, respectively. The primary source is placed 1.5 m from the origin. The sampling frequency of the dual-zone ANC system is 8000 Hz. The loudspeakers are positioned on the same horizontal plane. The transfer function between the secondary loudspeaker array and the control points and the noncontrol points are initially measured with white noise. Then, a white noise signal is emitted by the primary source, which can be obtained by the reference microphone as a reference signal \(\mathbf{X}\). The algorithms proposed in this paper and the reference signal \(\mathbf{X}\) are used to obtain the wideband filter coefficient in the frequency domain. Then, the time domain filter coefficient can be acquired by inverse Fourier transformation. The frequency range of interest is from 300 to 1200 Hz. The time domain experimental results measured at discrete frequencies with 50 Hz spacing of the proposed three algorithms are shown in Figure 4 when \(\lambda=10^{-4}\). Figure 4a,b shows that the algorithms proposed in this paper have a good wideband performance. From 300 to 1200 Hz, the average noise reduction in the control point is more than 10 dB and the average sound power increase is less than 1 dB. From Figure 4b, the increase of sound power of LS algorithms is much larger than that of the algorithms proposed in this paper, which verifies that the three wideband algorithms proposed in this paper can realize directional ANC, where the secondary loudspeaker array processes only noise reduction in the control zone, without changing the initial sound field of the noncontrol zone. Although, the algorithm based on ACC has a smaller noise reduction in the control zone, it has better directivity. Therefore, the increase of sound power in the noncontrol zone is the smallest of the three proposed algorithms. The algorithm based on CLS has better noise reduction. At 900 Hz, the noise reduction difference between LS and the CLS is small, which means that the constraint to the LS does not affect the robustness of the LS algorithm. In addition, the experimental results of the proposed algorithm, based on SFR-ACC, can also realize dual-zone ANC with directivity, which verifies its feasibility in ANC systems. From the noise reduction curve in Figure 4a, the trend of the  
Figure 4: The experimental results of the dual-zone ANC from 300 to 1200 Hz: (**a**) is the results of reduction (Re) in the control zone; and (**b**) is the increase of sound power (Isp) in the noncontrol zone. Figure 3: The dual-zone ANC system and the secondary loudspeaker array: (**a**) is the dual-zone ANC system; and (**b**) is the secondary loudspeaker array. SFR-ACC algorithm is the same as the results of the LS algorithm. However, because this algorithm combines the LS algorithm and the ACC algorithm, the robustness of SFR-ACC is determined by both of them. Therefore, the noise reduction level is smaller than in the LS algorithm. In addition, the small noise reduction at 300-400 Hz and 1100-1200 Hz is caused by data truncation when the inverse Fourier transform is utilized.