Two loudspeakers are located 1.8 m apart. They play tones of equivalent frequency. When you stand 3.0 m in front of the speakers, and precisely between them, you hear a maximum of intensity. As you walk parallel to plane of the speakers, staying 3.0 m away, the sound intensity reduces until reaching a minimum if you are directly in front of one of the speakers. The speed of sound in the room is around 340 m/s. Determine the frequency of the sound?