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This paper investigates the acoustic performance of stone wool sandwich panels with steel facings at two different thicknesses. Sound transmission loss is predicted using a poroelastic model based on Biot theory, which accounts for the anisotropic structure of stone wool. Three modeling approaches are compared to assess the effect of material parameters: a simplified poroacoustic model using JCA or Delany-Bazley parameters, an isotropic Biot poroelastic model, and an orthotropic Biot poroelastic model that captures directional material properties. Finite element simulations predict sound transmission loss across different frequencies, incorporating both steel plate and stone wool poroelastic parameters. Boundary conditions are also explored to understand the best approach to predict experimental results. Experimental measurements of airborne sound transmission loss for the two sandwich panel thicknesses are compared with the numerical predictions. The study evaluates how accounting for full poroelastic parameters, boundary conditions, and material anisotropy affects prediction accuracy and identifies the influence of each modeling assumption. Results demonstrate the relevance of poroelastic modeling over simplified poroacoustic approaches and provide guidance on when material anisotropy must be considered for accurate acoustic design of sandwich panels.