17. You stand next to one sound source, which emits sound of frequency 680Hz. A second sound source, which emits sound of the same frequency in air with a speed of sound of 340m/s is 5.5m away. You walk a distance x along a straight line perpendicular to the line joining the two loudspeakers. a. For how many values of x will you encounter a minimum of sound level (destructive interference)? b. What are those values of x? C. How would this change if the emitted frequency was 510Hz?