Two loudspeakers emit sound waves along the x axis. a listener in front of both speakers hears a maximum sound intensity when speaker 2 is at the origin and speaker 1 is at x = 0.50 m. if speaker 1 is slowly moving forward, the sound intensity decreases and then increases, reaching another maximum when speaker 1 is at x = 0.90 m. a. what is the frequency of the sound? assume the speed of sound is vsound = 340 m/s. b. what is the initial phase difference between the speakers?