Traditionally, product development concerning acoustics in the building industry is measurement oriented.For lightweight floors, frequencies that are lower than the frequency range for heavy concrete floors are anissue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound inmulti-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It iswell known that a lower frequency range of interest makes finite element simulations more feasible. Strategiesfor reducing impact sound tend to be less straightforward for timber floors because they have a largervariation of designs when compared to concrete floors. This implies that reliable finite element simulations ofimpact sound can save time and money for the building industry. This study researches the impact soundtransmission of lightweight timber floors. Frequency response functions, from forces on excitation points tosound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflectionfreeboundary elements under the floors in the models, the transmission and insulation can be studied withoutinvolving reverberation. A floor model with a hard screed surface will have a larger impact force than a softerfloor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, thepoint mobilities of the impact points are also calculated and presented. The vibration and sound transmissionlevels are dependent on the selection of the excitation points.