In this paper, a comparison is made between the measured and calculated vibration reduction indices (Kij ) and the engineering approximations in EN 12354-1. First, the existing expressions in EN 12354-1 for simple junctions of homogeneous elements are compared with a large data set of measured and calculated Kij spectra. For more complex junctions, not in EN 12354-1, like junctions with cavity walls (H-junctions) and junctions with different surface masses for in-line elements, a large number of FEM calculations have been made, from which new engineering approximations are derived.