The intensity of sound at a point P is I₀ , when the sounds reach this point directly and in same phase from two identical sources S ₁ and S ₂ . The power of S ₁ is now reduced by 64 % and the phase difference ( ) between S ₁ and S ₂ is varied continuously. The maximum and minimum intensities recorded at P are now I_ max and I_ min such that