We have two speakers on the x-axis and they are positioned such that one is behind the other. Both speakers emit a wave with the same frequency and amplitude, along the x-axis, which we denote as f and a. The sound intensity is maximum, with amplitude 2a, when speaker 2 is 10 cm behind speaker 1. The intensity decreases as speaker 2 is moved forward and first reaches a minimum when it is 20 cm in front of speaker 1.

What is:

1. The frequency of the sound? Assume air temperature is 20C.

2. The phase difference between the two loudspeakers?

3. The amplitude of the sound (as a multiple of a) if the speakers overlap? Yes, I know it's physically impossible, but use your imagination.