Arow of seats is parallel to a stage at a distance of 90 m from it. at the center and front of the stage is a diffraction horn loudspeaker. this speaker sends out its sound through an opening that is like a small doorway with a width d of 0.070 m. the speaker is playing a tone that has a frequency of 4.00 x 10 hz. the speed of sound is 343 m/s. what is the separation between two seats, located near the center of the row, at which the tone cannot be heard?