Abstract: Theoretical analysis of sound field within a tube with an aperture on its wall is presenced in this peper.Equivalent circuit is obtained for calculation of sound waves propagating within the tube.The aperture on tube wall can be represented by a lumped circuit impedance in the eqaivalent circuit.The impedance is written in terms of aperture impedance and an inertance due to the disturbance of sound field by the aperture.Expressions for caculation of the impedance are given for a rectangular aperture.The effect of sound source is also discussed