Three sources of sound S
1, S
2 and S
3 of equal intensity are placed in a straight line with S
1S
2 = S
2S
3. At a point P, far away from the sources, the wave coming from S
2 is 120° ahead in phase of that from S
1. Also, the wave coming from S
3 is 120° ahead of that from S
2. What would be the resultant intensity of sound at P?