A method for room acoustical simulations has been developed in order to compute the sound field in acoustic cavities with compound absorbers, mounted at the walls.To reduce the number of degrees of freedom and therefore the numerical effort, a model reduction method, based on a Component Mode Synthesis (CMS), is applied. Macrostructures are assembled out of single substructures applying shape functions at the interfaces. These substructures contain acoustic components like porous absorbers or resonators. They are calculated separately in the frame of the CMS approach. The acoustic fluid is modeled with the Spectral Finite Element Method (SFEM) and coupled with plate-like compound absorbers at the interfaces via wavenumber- and frequency-dependent impedances using Hamilton's Principle and a Ritz approach, where phase correct coupling conditions are ensured. The porous foam in the absorber is modeled with the Theory of Porous Media (TPM) and the impedances are calculated with the help of the Integral Transform Method (ITM). The application of the method is presented in several examples.