Two Small Identical Speakers Are Connected (In Phase) to the Same

Multiple Choice

Two small identical speakers are connected (in phase) to the same source. The speakers are 3 m apart and at ear level. An observer stands at X, 4 m in front of one speaker as shown. The sound she hears will be most intense if the wavelength is:

A) 5 m
B) 4 m
C) 3 m
D) 2 m
E) 1 m