Cross-laminated timber (CLT) has experienced significant growth in popularity due to among others high structural stiffness and low weight. However, these two properties lead to potentially poor acoustic performance. In order to suppress flanking sound, where vibrational energy is transmitted from one wall or floor to another through their common junction, elastic interlayers are typically included in the design, but the potential improvements are not straightforward to assess. In the present work, the vibration reduction index Kij for wave transmission between two connected elements i and j is predicted based on analytical wave theory for semi-infinite thin homogeneous plates. Both isotropic and orthotropic equivalent material models are considered and the junctions themselves can be rigid or contain elastic interlayers modeled as distributed springs or flexible waveguides. The proposed methodology is validated with on-site experiments on a T- junction consisting of CLT-panels with a resilient interlayer. Static equivalence is used to obtain the model input parameters. The model predictions are in reasonable agreement with the experimental results for the entire frequency range, especially for the flexible interlayer models with deviations of Kij generally below 10 dB. The differences between the equivalent isotropic and orthotropic plate model predictions remain small.