## 6 Experimental Results  
To verify the accuracy of the conclusions mentioned above, experiments are conducted in an indoor environment, and the experiments met the requirements of the standard of HJ/T 90-2004 [25]. The height of the barrier used in the experiments is 1.2 m, and the distance between the top of the barrier and the roof is 2.4 m. The SPLs are measured by 1/2\" microphones (MAT231T, made by BSWA (Beijing, China), and the microphones met  
Figure 8: The overall SPLs at \(R\) when the height of the barrier is 1.5 m. (**a**) The primary source is located at 0.5 m above the ground. (**b**) The primary source is located at 1 m above the ground.  
the requirements of the standard of IEC 61260-1:2014. Random noise is selected as the primary source, and the primary source is located at 0.3 m from the surface of the barrier, 0.8 m above the ground. The additional source is attached to the surface of the barrier. According to the location of the additional source, the experiments are divided into three groups, and three receivers are set in each group. The receivers are located on a circle with a radius of 0.4 m centered on the top of the barrier, and the anglea formed by the line connecting the receiver and the top of the barrier with the horizontal line are 30\({}^{\circ}\) (Receiver R1), 60\({}^{\circ}\) (Receiver R2) and 90\({}^{\circ}\) (Receiver R3). In the first group, the additional source \(S_{a1}\) is located at 0.08 m above the ground. In the second group, the additional source \(S_{a2}\) is located at 0.2 m above the ground. In the third group, the additional source \(S_{a3}\) is located at 0.4 m above the ground. When the additional source is located at 0.2 m above the ground, the height of the additional source is 0.2 times the product of the height of the barrier and the primary source. The scheme of the experiments is shown in Figure 9.  
The overall SPLs at each receiver are shown in Table 2. As can be seen from Table 2, the SPLs measured in the second group are the lowest among the three groups. The comparison of the SPLs at the frequencies of 125 Hz, 250 Hz, 500 Hz, and 1000 Hz, measured at receiver R1 and receiver R2, are shown in Figure 10.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Group\(\backslash\)Receiver** & **R1 (dBA)** & **R2 (dBA)** & **R3 (dBA)** \\ \hline first & 55.52 & 57.73 & 52.63 \\ second & 54.56 & 52.78 & 51.78 \\ third & 57.64 & 54.88 & 53.58 \\ \hline \end{tabular}
\end{table}
Table 2: The overall SPLs measured at the receivers.  
Figure 9: The scheme of the experiments.  
It can be seen from Figure 10 that at the frequency of 125 Hz, the SPLs are almost the same, especially at the receiver R1, and the additional source location has less influence on the low-frequency noise. At the frequency of 250 Hz, the SPLs are the smallest both at the receiver R1 and receiver R2 when the additional source is \(S_{a2}\). At the frequency of 500 Hz, the SPL is the smallest for the additional source \(S_{a1}\) at the receiver R1, and the difference is 1.1 dB compared with the additional source \(S_{a2}\) and the SPL is the smallest for the additional source \(S_{a2}\) at the receiver R2. At the frequency of 1000 Hz, the SPLs are the smallest for the additional source \(S_{a2}\) both at the receiver R1 and receiver R2.  
It is obvious from the experimental results that when the additional source is located at 0.2 m above the ground, where the height of the additional source is 0.2 times the product of the height of the barrier and the primary source, the values of the SPLs are the smallest in the area above the barrier, and it is conducive to obtaining a good noise reduction effect in the large spaces behind the barrier. The experimental results agree well with the conclusions mentioned above.  
Figure 10: The SPLs measured at the frequency of 125 Hz, 250 Hz, 500 Hz, and 1000 Hz.