Two loudspeakers, d1 = 2.00 m, are in phase. assume the amplitudes of the sound from the speakers are approximately the same at the position of a listener, who is d2 = 3.75 m directly in front of one of the speakers. consider the audible range for normal hearing, 20 hz to 20 khz. (a) what is the lowest frequency that gives the minimum signal (destructive interference) at the listener's ear? (b) what is the lowest frequency that gives the maximum signal (constructive interference) at the listener's ear?