# An Active Indoor Noise Control System Based on CS Algorithm
## 4 Experiment and Discussion
### Experimental Test and Discussion  
We activated the artificial noise source outside the room during the test. For comparative purposes, the error microphone was utilized to assess the indoor ambient noise at this time without activating the ANC system, and after activating the ANC system, the error microphone's influence on the audio noise reduction was observed. First, the impact of a single tone signal on noise reduction was evaluated. Figure 12 displays the single-tone signal's noise reduction outcome (500 Hz). It has been discovered that the system's noise reduction impact is around 13 dB more pronounced for single tone signals. The findings of the further testing of monophonic sounds at various frequencies are shown in Table 4. The test findings demonstrate that a single tone signal has a greater than 7 dB noise reduction impact. The actual environment has many unpredictable characteristics; therefore, the outcomes are significantly different from the simulated findings. To reduce the discrepancy  
Figure 11: (**a**) Experimental environment; (**b**) equipment setup; (**c**) error microphone and noise source; (**d**) the input/output board; (**e**) the front door; (**f**) the desk.  
between the simulation and the actual scenario, we can further enhance the system model in the future.  
Finally, noises that replicated the real environment were produced using a synthetic noise source. The difference in audio levels between the interior environment before and after the ANC system was activated revealed a 6-7 dB decrease in noise, as shown in Figure 13. It is important to note that the benchmark for determining the effectiveness of noise reduction should be revised properly when the interior volume increases. People may be positioned randomly across the room (this paper presumes that a person spends most of his/her time at his/her desk), and noises may originate from various locations. Given the aforementioned elements, more thought must be given to the actual application design. To enhance the effectiveness of noise suppression, the number of sensors may be raised while the canceling speaker's power may be increased. This study examined a single case. Finally, there is a strong correlation between the microphone's performance and the noise the system collects. Different microphones have varying effects on the sensitivity of the sound and the caliber of the sound captured during the real test procedure. As a result, the aim with respect to audio acquisition should be the microphone with the best performance. Meanwhile, the performance that the sound box produces also has a certain impact on how well the noise is reduced. For example, single-directional loudspeakers can only emit sound waves in one direction but surround stereo speakers can emit sound waves in all directions.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Frequency (Hz)** & **Reduction (dB)** \\ \hline
200 & 9 \\
500 & 8.8 \\
1000 & 10.8 \\
2000 & 11.5 \\
3000 & 11.2 \\
5000 & 8.3 \\
10,000 & 7.8 \\
20,000 & 7.6 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Noise suppression performance for various frequencies in experiment.  
Figure 12: 500 Hz single tone signal acquisition noise: (**a**) ANC off; (**b**) ANC on.