# Edge-Computing Meshed Wireless Acoustic Sensor Network for Indoor Sound Monitoring
## 6 Discussion
### Microphone  
The type of microphone mostly used for acoustical WASN is condenser or condenser-electret according with the comparison made in Table 6. The microphone integrated in the presented work increases the frequency response from previous prototypes [16] and enables to obtain more frequency resolution for event detection algorithms meanwhile has less deviation in SPL measurements. It is observed in Table 6 that the author proposal is the only plug-and-play electret microphone that offers calibrated SPL values and has a lower price with a cost of EUR 29, compared to the other plug-and-play microphone [9] with a significant cost of EUR 140 as of September 2022. In addition, if the sizes of these two microphones is compared, the one selected in this work is significantly smaller, resulting in a smaller sensor. Another aspect to take into account is the signal-to-noise ratio (SNR) of the microphones. Furthermore, the SNR obtained by the proposed microphone is low enough so as not to mask the sounds to be monitored. Even though MEMS microphone technology has improved over the year, one of the main problems with this typology of microphones is the electrical background noise that they generate (see [47]).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**WASN** & **Microphone** & \
\begin{tabular}{c} **Frequency** \\ **Response** \\ \end{tabular} & **Calibration** &
\begin{tabular}{c} **Plug and** \\ **Play** \\ \end{tabular} \\ \hline MESSAGE 2013 [8] & Condenser & 20 Hz–20 kHz & Yes & No \\ \hline SONYC 2017 [23] & MEMS & 10 Hz–10 kHz & Yes & No \\ \hline [PERSON] et al., 2021 [9] & Electret & 20 Hz–20 kHz & No & Yes \\ \hline [PERSON] et al., 2021 [16] & Condenser & 20 Hz–16 kHz & Yes & Yes \\ \hline Proposed approach & Electret & 50 Hz–18 kHz & Yes & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparative table of different microphones implemented in each WASN. The last row represents the approach proposed in represents the approach proposed in this paper.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**WASN** & **Microphone** & **Connectivity** &
\begin{tabular}{c} **Computing** \\ **Unit** \\ \end{tabular} & **Power** & **Price** \\ \hline MESSAGE 2013 [8] & Condenser & ZigBee & Microcontroller & D Battery or \\
2013 [8] & microphone & + GPRS & PIC18F4620 & external power \\  & & & (around EUR 5) & connection & \\ \hline SONYC & Custom & WiFi direct & Tronsmart & 120 V outlet \\
2017 [23] & MEMS & connection & MK908 ii & + PSU & \\  & & to router & (EUR 50) & & \\ \hline [PERSON]. [PERSON] et al., & miniDSP & WiFi mesh & Raspberry Pi & Battery \\
2021 [9] & UMIK-1 & OLSR & 3B & (EUR 20) & \\  & (EUR 140) & protocol & (EUR 31) & & \\ \hline [PERSON] et al. & LYM00002 & WiFi direct & Raspberry Pi & 5 V–3 A & EUR 78 \\ approach & (EUR 11) & connection & 3B+ & charger & \\
2021 [16] & & to router & (EUR 37) & (EUR 12) & \\ \hline Proposed & Sandberg & WiFi mesh & Raspberry Pi & 5 V–3 A & EUR 120 \\ approach & 126-19 & HWMP & 4B-4 GB & charger & \\
2022 & (EUR 29) & protocol & (EUR 64) & (EUR 12) & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparative table of different WASNs. The last row represents the approach proposed in this paper. The last column indicates the price per node of each node of the network. Unavailable (N.A.) or missing prices have not been included in the table.