Two identical loudspeakers $2.0 \mathrm{m}$ apart are emitting sound waves into a room where the speed of sound is $340 \mathrm{m} / \mathrm{s}$. Abby is standing $5.0 \mathrm{m}$ in front of one of the speakers, perpendicular to the line joining the speakers, and hears a maximum in the intensity of the sound. What is the lowest possible frequency of sound for which this is possible?