At the Fraunhofer Institute for Building Physics, the source data of sanitary installations for predictions according to DIN EN 12354-5 in solid construction has been determined and used for some time. However, for timber and lightweight constructions, additional structure borne source data is required in addition to the blocked force.This article presents the initial measurements of the free velocity as well as the calculation of the source mobility especially on shower trays and bathtubs, in order to use them for predictions in lightweight constructions.The main problem of the measurements lies in the practical implementation, as the shower trays and bathtubs do not generate any structure-borne sound on their own and only become a source with usage. This means that the source data must be measured with simulated shower processes and user noises, as it is done for measurements in a practical setup. However, a fully practical installation cannot be performed here, and simplifications must be made.The obtained source data were subsequently used to create predictions with laboratory-measured transfer functions and compared with actual measurements from a practical setup on the same solid wood ceiling in the ceiling test facility at the IBP in Stuttgart.