Two loudspeakers radiate in phase at 170 Hz. An observer sits at 8 m from one speaker and 11 m from the other. The intensity level from either speaker acting alone is 60 dB. The speed of sound is 340 m/s.
(1) Find the observed intensity when both speakers are on together.
(2) Find the observed intensity level when both speakers are on together but one has its leads reversed so that the speakers are 180∘ out of phase.
(3) Find the observed intensity level when both speakers are on and in phase but the frequency is 85 Hz.