What is the lowest frequency for a microphone interference maximum?

[rsu]

A microphone is located on the line connecting two speakers that are 0.537 m apart and oscillating 180° out of phase. The microphone is 2.00 m from the midpoint of the two speakers. What is the lowest frequency that produces an interference maximum at the microphone's location?

 

[alphysicist]

Hi rsu,

A microphone is located on the line connecting two speakers that are 0.537 m apart and oscillating 180° out of phase. The microphone is 2.00 m from the midpoint of the two speakers. What is the lowest frequency that produces an interference maximum at the microphone's location?

What have you tried so far?