## 3 Results and Discussion
distance--380 W (however, it should be noted that for the 19 Hz frequency, the maximum distance was 70 and not 80 cm due to the safety of the woofer). The implication of this is that the deviation from the resonant frequency affects the increase in the electrical power required to extinguish the flames, which for a distance of 70 cm exceeded 1 000 W. Therefore, for the frequency of 19 Hz, the experimental results are limited to distances up to 70 cm. The sound pressure level at which complete extinguishment of the flames occurred for both frequencies was similar (it was in the 120-130 dB range), with a greater spread of its values recorded for the first of the analyzed frequencies, i.e., 15 Hz. For the smallest distance, i.e., 20 cm, the sound pressure levels obtained were the same. For distances of 40 and 60 cm, differences of less than 1 dB (0.9 and 0.2 dB, respectively) were recorded. Comparable results were also obtained for the last distances analyzed between the flame source and the waveguide outlet, i.e., 80 and 70 cm, respectively. An analysis of the experimental attempts allows one to note a relationship between the measured sound pressure levels and the distance from the waveguide outlet. An inversely proportional decrease in the sound pressure values is observed with an increase in the distance of the flame source from the waveguide outlet. Since the diagrams (Figures 3-6) were obtained under the same environmental conditions, the shapes of the characteristics are similar. The presented results have experimentally confirmed the validity of the theory that acoustic waves can be successfully applied to extinguish flames. In principle, low-frequency acoustic waves are particularly useful and effective in extinguishing flames due to the significant turbulence they cause in the flame. The benefit then is the low power that must be delivered to the sound source to observe the complete extinguishment of the flames. On the other hand, their use is associated with the significant vibration of the diaphragm of the sound source due to the mismatch of waveguide and loudspeaker conditions. At slightly higher frequencies, the better focusing of the propagated acoustic beam is observed. In practice, as shown in Figures 7 and 9, the acoustic extinguisher requires the delivery of more power than the thermal power obtained by burning the substance. Therefore, taking into account energy issues and power consumption, for a sound source, such as a woofer (as an electroacoustic transducer) that converts electric current into an acoustic wave, the efficiency is low (on the order of a few percent). For this reason, in the future, the acoustic method assumes the search for other, more efficient and sophisticated, sound sources than the speaker. It should also be noted that during the experiments performed, much lower powers than the nominal power of the loudspeaker were applied, with successful extinguishing attempts. Therefore, using higher powers, it will become possible to obtain an energy reserve to effectively extinguish the flames in the event of an unfavorable change in conditions at the flame extinguishing site. Taking into account the advantages of using this technique in relation to other traditional methods of fire protection, including its versatility of use, environmental friendliness (acoustic waves are not a chemical creation), the unlimited operation time of the extinguisher being dependent only on the supply of electricity to it, the absence of the cyclic pressure tests of the tank, the absence of a human presence in the place of extinguishing, and many others, it is assumed that this method can be used especially to extinguish firebreaks, effectively preventing the spread of fire.