Two Loudspeakers Are Placed Facing Each Other and Driven by the Same

Multiple Choice

Two loudspeakers are placed facing each other and driven by the same source at 680 Hz.A listener is positioned between the two speakers on the line separating them,thus creating a constructive interference at the listener's ear.What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s. )

A) 0.13 m
B) 0.25 m
C) 0.50 m
D) 1.00 m