A new formulation is derived for obtaining the modal frequency response (MFR) of a coupled acousticstructural system by using an orthogonality condition of a coupled system that was presented earlier by the authors. An improved compensation technique is then proposed for compensating for the effect of truncated modes, which are the lower and/or higher modes beyond the frequency domain of an MFR analysis. A coupled acoustic-box model is used in the analysis to confirm the applicability of the proposed method to actual coupled analysis problems. It is demonstrated that the use of this technique greatly improves convergence, and makes it possible to determine the frequency response with better accuracy than the mode-displacement method, the mode-acceleration method, or Hansteen-BelPs method. Moreover, it does not increase the computational effort.