Sound source A is located at x = 0, y = 0, and sound source B is located at x = 0, y = 3.10 m. The two sources radiate coherently and in phase. An observer at x = 19.0 m, y = 0 notes that as he takes a few steps from y = 0 in either the +y or -y direction, the sound intensity diminishes. What is the lowest frequency f of the sources that can account for that observation? f = TOOLS What is the second-lowest frequency f2 of the sources that can account for that observation? x10 f2= kHz kHz