## 5 Experimental Results and Discussion  
### Results  
The developed system was tested several times with the two quadrupoles placed at the two control positions. Among these experiments, the two optimal configurations for each dominant frequency are presented. The corresponding maximum noise reduction and optimal driving parameters for the longitudinal (Long) and the lateral (Lat) quadrupole setup are shown in Table 2.  
* MP 1: From Table 2, it seems that both quadrupoles offer the same maximum attenuation at 50 Hz when they are positioned at CP 2 and CP 1, respectively. At 100 Hz, the attenuation is much higher, reaching 32 dB, and the longitudinal prevails slightly over the lateral source, giving a 3 dB higher maximum attenuation. * MP 2: At 50 Hz, the longitudinal quadrupole at CP 2 attains a quite satisfying attenuation of 18.5 dB, while the lateral source at the same position achieves a reduction of 15.5 dB. At 77 Hz, the longitudinal quadrupole offers noise attenuation up to 29.5 dB, in which CP 2 has the advantage over CP 1. * MP 3: At 50 Hz, the longitudinal quadrupole at CP 1 offers high primary attenuation of 19.5 dB. At 108 Hz, it reaches a reduction of 32.5 dB at the same position. Again, the longitudinal source offers higher attenuation at both frequencies. In Table 3, the optimal attenuation results are given for the two control setups in each CP, MP, and frequency. In Figure 9, the same results are depicted with colored arrows to show the noise control efficiency between each pair of CP and MP. The results are divided into four groups: red color is used for noise attenuation of up to 8 dB (\"not sufficient\"), \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**MP**} & \multirow{2}{*}{**Freq. (Hz)**} & \multirow{2}{*}{**CP**} & \multirow{2}{*}{**Control Setup**} & \multirow{2}{*}{**Max Noise Reduction (dB)**} & \multicolumn{2}{c}{**Optimal Driving Parameters**} \\  & & & & & \\ \hline \multirow{2}{*}{\(1\)} & 50 & 2/1 & Long/Lat & 18/18 & 5.5, 1.5, 135/2.5, 0.5, 180 \\  & 100 & 1/1 & Long/Lat & 32/29 & 4, 3.5, 90/2.5, 2.5, 90 \\ \hline \multirow{2}{*}{\(2\)} & 50 & 2/2 & Long/Lat & 18.5/15.5 & 4, 7.5, 270/9, 8, 180 \\  & 77 & 2/1 & Long/Long & 29.5/28 & 1.5, 5, 180/3.5, 1.5, 135 \\ \hline \multirow{2}{*}{\(3\)} & 50 & 1/2 & Long/Long & 19.5/18 & 5.5, 1.5, 225/1.5, 2.5, 225 \\  & 108 & 1/1 & Long/Lat & 32.5/27.5 & 2, 5.5, 45/3.5, 8, 315 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The two optimal attenuation results for each MP and frequency, with the optimal driving parameters. Figure 8: The investigated room with the compound control source located at CP 2 and the microphone at MP 1: (**a**) longitudinal and (**b**) lateral setup. orange for up to 16 dB (\"sufficient\"), blue for up to 24 dB (\"satisfying\"), and green for higher reduction levels (\"very satisfying\"). It is derived that the dominant frequencies can be controlled sufficiently in every MP by using either the longitudinal or the lateral configuration. The longitudinal source can at least satisfyingly control all the problematic frequencies in each MP, especially when it is positioned in CP 2. This does not stand for the lateral source. Specifically, at CP 1, noise control is not sufficient at 50 Hz in MP 2 (6 dB), while it is slightly sufficient in MP 3 (8.5 dB). With the lateral source at CP 2, the attenuation at the same frequency is not sufficient in  
Figure 9: Optimal noise attenuation among each CP, MP, and frequency. For each MP, the first arrow represents the 50 Hz case, while inspecting the graph in a clockwise direction. The second arrow is for 100 Hz (MP 1), 77 Hz (MP 2), and 108 Hz (MP 3).