This work explores the application of the finite transfer matrix method (FTMM) for evaluating the sound transmission loss, of a double wall incorporating a porous layer. In order to optimize the acoustic performance of the system, a global sensitivity analysis using Sobol indices incorporating 11 parameters is performed, encompassing both material and geometric factors. Recognizing the computational demands of this sensitivity study with the FTMM model, the use of metamodels is proposed. A kriging metamodel is implemented to efficiently reduce the computation time while preserving accuracy. The sensitivity analysis results obtained from the original FTMM model are compared to those derived from the kriging metamodel. The study demonstrates that the acoustic performance of the double wall depends on the thickness of each layer, varying in importance across frequencies, and Young's modulus of the porous material at specific frequencies.