Prediction of vibration transmission across finite double wall junctions using a hybrid diffuse-deterministic approach

Predicting the sound insulation between two rooms is a complex problem since not only the direct path through the separating element but also the flanking transmission paths can largely influence the sound insulation of the system. An important parameter for calculating flanking transmission is the vibration reduction index, which relates to the transmission coefficient between the connected plates. The international building acoustics standard ISO 12354-1/2 provides prediction formulas for the vibration reduction index of single wall junctions, but not for double wall junctions. A new hybrid diffuse-deterministic approach is proposed to calculate flanking transmission across double wall junctions. The walls and floors are modelled as diffuse subsystems while the connection between the double wall is modelled deterministically. In the derivation of the transmission coefficient between two diffuse subsystems, the diffuse field reciprocity relationship is employed, such that the finite size and structural details of the junction are taken into account. The diffuse field reciprocity relationship relates the vibration transmission to the direct field dynamic stiffness of the diffuse subsystems (walls and floors), i.e., the dynamic stiffness of the equivalent infinite subsystem as observed at the junction. The new approach is applied to different types of double wall junctions to determine simplified regression formulas for practical sound insulation design.