Question

Two loudspeakers radiate in phase at `170 H_(Z)`. 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`.
(a) Find the observer intensity when both speakers are on together.
(b) Find the observer intensity level when both speakers are no together but one has its leads reversed so that the speakers are `180^(@)` out of phase.
(c ) Find the observer intensity level when both speakers are on and in phase but the frequency is `85 H_(Z)`.

Answer 1

Correct Answer - A::B::C::D
`Delta phi = (2 pi)/(lambda) (Deltax) = ((2 pi f)/(nu))(Delta x)`
`= ((2 pi) (170))/(340) (11 - 8)`
`= 3 pi = phi` (say)
`I = 4l_(o) cos^(2) (theta)/(2)` ..(i) Subsituting value of `phi`, we get
`I = 0`