The Peterson‐Bogert model of the cochlea [J. Acoust. Soc. Amer.22, 369–381 (1950)] specifies, as one of its boundary conditions, zero pressure at the round window. This specification is equivalent to eliminating the round‐window membrane. We have substituted a new boundary condition, representing the round‐window membrane with an acoustic stiffness. With the new boundary condition, the equation forp+(x) requires a new solution, and a new value ofp−(x) atx= 0 is needed. The solution forp+(x) and the necessary value ofp−(0) are given as a function of frequency for sinusoidal stimulation. The latter value is used as the input to the Peterson‐Bogert type of model of the basilar membrane. The model's input impedance as well as the relative displacement between the oval and round windows are also given. These relationships are compared with experimental findings.