## 3 Results and Discussion
For the smallest of the analyzed frequencies, that is, 14 Hz, the minimum power required was equal to 125 W. In turn, for the largest of the analyzed frequencies, that is, 21 Hz, the recorded minimum power was almost equal to 350 W.  
The results obtained for the modulated waveforms are presented in Table 4.  
Similarly to the unmodulated waveform, it can be observed that as the frequency increases, an increase in the minimum electrical power values that had to be delivered to the sound source to observe complete flame extinguishment was observed. For the lowest frequency analyzed, that is, 14 Hz, the required level of minimum electrical power was equal to 200 W. In turn, for the highest of the analyzed frequencies, that is, 20 Hz, a power level almost double that of the unmodulated waveform was recognized--it was equal to 700 W if no temporary change in weather conditions was noted (it is worth noting that if temporary changes in atmospheric conditions or gusts of wind affect the results \begin{table}
\begin{tabular}{c c} \hline \hline
**f (Hz)** & **P (W)** \\ \hline
14 & 200 \\
18 & 305 \\
20 & 700 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Minimal electrical power values (P) necessary to extinguish flames as a function of frequency (f) for a sinusoidal wave AM modulated by a square waveform (f\({}_{\text{MOD}}\) = 0.125 Hz). Figure 4: SPL [dB] vs. f [Hz] for modulated and unmodulated acoustic waves. \begin{table}
\begin{tabular}{c c} \hline \hline
**f [Hz]** & **P [W]** \\ \hline
14 & 125 \\
18 & 155 \\
21 & 345 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Minimal electrical power values (P) necessary to extinguish flames as a function of frequency (f) for a sinusoidal wave. obtained, experiments need to be repeated). The results allow us to see that there is a correlation between the increase in the minimal electrical power values that had to be delivered to the sound source to observe complete extinguishment of the flames as the frequency increases. Moving away from the resonant frequency results in a deviation from the resonant optimum, which translates into an increase in the minimal electrical power values that had to be delivered to the sound source to observe complete extinguishment of the flames. The summary diagrams of P [W] vs. f [Hz] for modulated and unmodulated waves are presented in Figure 5.  
During fire extinguishing tests, the smallest tested frequency, that is, 14 Hz, showed the highest fire extinguishing effectiveness. For this frequency, the difference in power level that had to be supplied to the sound source of the extinguisher to observe the effect of completely extinguishing the flames was less than 100 W during the measurements. For low frequencies, the electrical power required to supply the fire extinguisher was the lowest. Increasing the frequency translates into an increase in electrical power that must be supplied to the acoustic extinguisher to observe the effect of extinguishing the flames. On the other hand, the benefit is then a greater directional concentration of acoustic energy, as well as practical considerations (limiting the size of the waveguide). For the middle frequency, that is, 18 Hz, the required power to extinguish the flames increased and was equal to 150 W, while for the largest of the frequencies analyzed (that is, 20 Hz for the modulated waveform and 21 Hz for the unmodulated waveform, respectively), it was about 350 W. This means almost twice the level of power that had to be delivered to observe the effect of completely extinguishing the flames compared with the unmodulated wave (i.e., sinusoidal). In practice, for the assumed conditions, the level of power that had to be delivered to the sound source of the extinguisher to observe the effect of complete extinguishment of the flames for the modulated wave was higher than for the unmodulated wave. It is worth noting that despite the low power, the amplitude of the speaker's vibration may limit its effective use for flame extinguishing.