## 4 Results
As shown in the left part of Table 2, which summarizes the data associated with measurements when the masking system remained disabled, for the data associated with measurement point #3, at the frequency of 250 Hz, the module of the arithmetic difference of the results of measurements performed in the central band and in the respective adjacent bands only meets the criterion for the value 9.2 dB (49.3 dB-40.1 dB), which is not true for the value 6.4 dB (49.3 dB-42.9 dB), thus not confirming the tonal hypothesis. The superposition of masking sounds, as a strategy to eliminate the tonal characteristics of acoustic noise, proved to be effective at the substation studied. In addition to the benefits caused by masking, it should be noted that the superposition of the masking signal to the acoustic field generated by the operation of the substation does not always increase \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**Measurement Point \#**} & \multicolumn{3}{c}{**Frequency Bands (Hz)**} & \multicolumn{3}{c}{**Measurements with the Masking System Disabled**} & \multicolumn{3}{c}{**Measurements with the Masking System Activated**} \\ \cline{2-9}  & \multirow{3}{*}{
\begin{tabular}{c} **Cental** \\ **Band (cb)** \\ \end{tabular} } & \multicolumn{3}{c}{**Adjacent**} & \multicolumn{3}{c}{\(L_{\infty}\) (dB)**} & \multicolumn{3}{c}{\(L_{\infty}\) (dB)} \\ \cline{3-9}  & & **Band** & **Band** & **(cb)** & **Adjacent** & **Adjacent** & **Adjacent** & **Adjacent** & **Adjacent** \\  & & **Band** & **Band** & **(cb)** & **Band** & **(cb)** & **Band** & **(cb)** & **Band** & **(cb)** \\ \hline \multirow{3}{*}{Meas.Point \#2} & \multirow{3}{*}{125} & \(100\) & 63.7 & 45.1 & 18.6 & 62.3 & 61.4 & 0.9 \\  & & 160 & & 39.0 & 24.7 & 47.5 & 14.8 \\ \cline{2-9}  & & 200 & & 38.3 & 4.8 & 44.7 & 42.3 & 2.4 \\  & & 315 & & 40.5 & 2.6 & 42.9 & 1.8 \\ \cline{2-9}  & & 400 & & 45.4 & 40.5 & 4.9 & 42.9 & 4.6 \\  & & 500 & & 40.8 & 4.6 & 41.8 & 5.7 \\ \hline \multirow{3}{*}{Meas.Point \#3} & \multirow{3}{*}{125} & \(100\) & 62.2 & 47.5 & **14.7** & 59.7 & 53.4 & 6.3 \\  & & 160 & & 42.4 & 19.8 & 47.6 & 12.1 \\ \cline{2-9}  & & 200 & & 40.1 & **9.2** & 48.5 & 1.6 \\  & & 315 & & 42.9 & 6.4 & 46.9 & 47.2 & 0.3 \\ \cline{2-9}  & & 400 & & 46.1 & 42.9 & 3.2 & 51.4 & 47.2 & 42 \\ \hline \multirow{3}{*}{Meas.Point \#6} & \multirow{3}{*}{125} & \(100\) & 53.9 & 38.4 & 15.5 & 58.7 & 49.4 & 9.3 \\  & & 160 & & 36.3 & **17.6** & 58.7 & 48.9 & 9.8 \\ \cline{1-1} \cline{2-9}  & & 250 & & 36.9 & 7.1 & 45.5 & 44.8 & 0.7 \\ \cline{1-1} \cline{2-9}  & & 315 & & 40.6 & 3.4 & 45.5 & 37.4 & 8.1 \\ \cline{1-1} \cline{2-9}  & & 315 & & 40.6 & 3.3 & 37.4 & 2.9 \\ \cline{1-1} \cline{2-9}  & & 500 & & 39.1 & 4.8 & 40.3 & 38.6 & 1.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Processing of measurements to identify the tonal component of noise. The red color indicates values that exceed the criteria defined in Table 1.  
the intensity of the acoustic pressure associated with the combined acoustic field. This fact is exemplified by the comparison of the results of the measurement of acoustic pressure at the frequency of 125 Hz, carried out at measurement points #2 and #3, in which the value of the acoustic pressure decreased by 1.4 dB (from 63.7 dB to 62.3 dB at measurement point #2) and has fallen by 2.5 dB (from 62.2 dB to 59.7 dB at measurement point #3). In contrast, the masking effect increased 4.8 dB (from 53.9 dB to 58.7 dB at measurement point #6 furthest from the substation) at the same 125 Hz frequency. Contrary to what should be expected when the masking signal is superimposed on other acoustic noises in an open field, the reduction in the intensity of the sound pressure at points #2 and #3 can be explained by an adverse action of masking on standing waves that can be formed in confined environments, as occurred at measurement points #2 and #3, closest to the access gate of the substation.