## 3 Evaluation Experiments  
### Experimental Conditions  
To demonstrate the effectiveness of the proposed method, we carried out evaluation experiments in a typical office room. The proposed method was implemented with Matlab R2023a. The sound reproduction and recording were carried out with Audio Toolbox from Matlab. Table 1 gives the conditions of the experimental environment. Compared with ideal environments like anechoic chambers, real-world environments can show the performance and practicality of the proposed method; however, reverberation may be a factor affecting the performance of the proposed method. Table 2 lists the equipment used in the experiments, which was generally the same as that used in conventional studies [22; 24; 25]. The experimental arrangement is shown in Figure 4. The secondary sound sources (PALs and EDLs) were set along the \(x\)-axis at intervals of 0.22 m. VSSs were constructed along the \(y\)-axis utilizing WFS, as the purpose of this study was to improve far-near perception. Figure 5 gives a photograph of the EDLs and PALs used in the evaluation experiments. The reference line described in Section 2.2 was set at \(y_{\text{Ref}}\) = 2.5 m, and the reference point described in Section 2.3 was set at (0 m, 2.5 m). To design the crossfade filter described in Section 2.3, we utilized a time-stretched pulse (TSP) [30] signal to measure the impulse response. In the preliminary measurement, we employed a monopole omni-directional sound source as the real sound source described in Section 2.3. The VSS constructed by the proposed method was expected to have frequency characteristics similar to those of a real sound source, because the impulse response of the real sound source has been utilized in the design of crossfade filters. Our preliminary study [25] showed that the contribution balance varies as the VSS position changes, and the frequency characteristics measured at the reference point became flatter utilizing crossfade filters. In this paper, the evaluation target is the entire sound field rather than a certain position. \begin{table}
\begin{tabular}{l l} \hline Ambient noise level & 28.4 dB (A) \\ \hline Reverberation time & 650 ms \\ \hline Sound velocity & 343 m/s \\ \hline Sampling & 96 kHz, 24 bits \\ \hline \end{tabular}
\end{table} 
Table 1: Conditions for the experimental environment. \begin{table}
\begin{tabular}{l l} \hline \hline
**Device** & **Type** \\ \hline EDLs & Pinbotronix, AT37 YF2655 MUI5112 \\ \hline PALs & Tristate, K02815 \\ \hline Monopole sound source & Qsources, Qmos2 \\ \hline Power amplifier for EDLs & Yamaha, P4050 \\ \hline Power amplifier for PALs & Yamaha, IPA8200 \\ \hline Audio interface & RME, MADIface \\ \hline D/A converter & RME, M-32 DA \\ \hline A/D converter & RME, M-32 AD \\ \hline Microphone & Sony, ECM-88B \\ \hline Microphone amplifier & RME, OctaMic II \\ \hline \end{tabular}
\end{table} 
Table 2: Equipment used in the experiments. In the following experiments, we prepared five patterns of VSS construction with WFS to compare with a real sound source. The comparison methods are listed as followd:  
* 'Baseline' stands for a baseline method [8] in which only EDLs are used as secondary sources. The total number of loudspeakers was 16, where \(I_{\text{EDL}}=16\) and \(I_{\text{PAL}}=0\). * 'Conv. PAL' stands for the conventional VSS construction method using only PALs as secondary sources [22]. The total number of loudspeakers was 16, where \(I_{\text{EDL}}=0\) and \(I_{\text{PAL}}=16\). * 'Conv. Hybrid' stands for the conventional VSS construction method with a hybrid control of EDLs and PALs [24], which can be regarded as the state-of-art method. In this method, VSS construction switches EDLs and PALs according to the VSS position. In the cases of \(\mathbf{r_{\text{S}}}=(0.0,0.5)\) and \((0.0,1.0)\), this pattern is equivalent to 'Baseline'. When \(\mathbf{r_{\text{S}}}=(0.0,1.5)\) and \((0.0,2.0)\), this pattern is equivalent to 'Conv. PAL'. * 'Prop. (8.8)' stands for the proposed method with a half-sized loudspeaker array.