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-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. This approach relies on the diffuse field reciprocity relationship, which relates the vibration transmission to the direct field dynamic stiffness of the subsystems (walls and floors), i.e., the dynamic stiffness of the equivalent infinite subsystem as observed at the junction. In contrast to existing approaches, the finite size of the junction is properly taken into account in this way. The new approach is applied to different types of double wall junctions to determine simplified regression formulas for practical sound insulation design.