A row of seats is parallel to a stage at a distance of 8.6 m from it. At the center and front of the stage is a diffraction horn loudspeaker that has a width D of 0.074 m. The speaker is playing a tone that has a frequency of 2.0 multiplied by 104 Hz. The speed of sound is 343 m/s. What is the separation between two seats, located on opposite sides of the center of the row, at which the tone cannot be heard?