Two powerful speakers, separated by 15.00 m, stand on the floor in front of the stage in a large amphitheater. An aisle perpendicular to the stage is directly in front of one of the speakers and extends 50.00 m to an exit door at the back of the amphitheater. The speed of sound in air is 344 m/s.

If the speakers produce in-phase, coherent 440.0 Hz tones, at how many points along the aisle is the sound minimal?