Two speakers, one directly behind the other, are each generating a 264-Hz sound wave. What is the smallest separation distance between the speakers that will produce destructive interference at a listener standing in front of them? Take the speed of sound to be 342 m/s.

Answer 1

The basic requirement for destructive interference is that the two waves be shifted by half a wavelength.

Now, as you know, v = λν, so just plug in your numbers.