When the speaker S₁ is switched O N , the sound intensity at a point P in a room is 80 dB . But when the speaker S₂ is switched ON ( S₁ is switched OFF), the sound intensity at the same point P in the room is 85 dB . The sound intensity level (in dB ) at the same point P in the room, if the two speakers S₁ and S₂ are simultaneously switched O N , is (consider the speakers to be incoherent)