Honeycomb core structure with face sheets is commonly used in various lightweight applications and mobility industry. These structures have a very good stiffness to weight ratio, and their acoustic performance in terms of transmission loss needs to be estimated at the early design stage. The current study is focused on the estimation of random incidence Transmission Loss (TL) of honeycomb sandwich using the semi-numerical method. The proposed methodology is based on the Finite Element (FEM) and Boundary Element Method (BEM), where the modal superposition technique is used. Equivalent properties of the orthogonal honeycomb core of the sandwich panel are estimated theoretically and used for further numerical analysis. The predicted results of honeycomb panels are compared with a simple plate and later validated with measured results. Results show that the honeycomb sandwich panel has better acoustic performance with respect to a simple homogeneous plate. Further, the acoustic performance of sandwiched walls of square ducts is demonstrated. The proposed methodology in this work acts as a basic framework in the early estimation of acoustic performance of complex sandwiched structures. © International Institute of Acoustics and Vibration (IIAV), 2022.