Finding Maximum Sound Intensity: How to Determine the Two Lowest Frequencies?

[sopi]

Hello. I am totally stuck on this question. I don't even know where to begin. Any help would be appreciated:
A spherical sound source is placed at P1 near a reflecting wall and a microphone is located at P2. The frequency of the sound source is variable. Find the two lowest frequencies for which the sound intensity, at P2, will be a maximum. There is no phase change on reflection; the angle of incidence equals the angle of reflection. A diagram is attached.
Thanks,
Mike

 

[pseudovector]

I haven't seen the sketch of the system, but I think I know how to solve this one. Try ignoring the reflective surface, and replace it with another sound source, identicle to the first, and place it so the middle of the line connecting the two sources would be on the reflecting surface boundary (the second source should look like a mirror-image of the first, when the mirror is set on the boundary of the reflecting surface). Then you're left with a simple two sources interference.