Andreas Linderholt

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 an issue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound in multi-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It is well known that a lower frequency range of interest makes finite element simulations more feasible. Strategies for reducing impact sound tend to be less straightforward for timber floors because they have a larger variation of designs when compared to concrete floors. This implies that reliable finite element simulations of impact sound can save time and money for the building industry. This study researches the impact sound transmission of lightweight timber floors. Frequency response functions, from forces on excitation points to sound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflection-free boundary elements under the floors in the models, the transmission and insulation can be studied without involving reverberation. A floor model with a hard screed surface will have a larger impact force than a softer floor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, the point mobilities of the impact points are also calculated and presented. The vibration and sound transmission levels are dependent on the selection of the excitation points.

Elastomers are commonly used to decrease the sound transmission between apartments in timber framed houses. In previous studies, different types of connections have been evaluated. However, the frequency dependent dynamic properties in different directions of a connection including elastomers are not fully investigated yet. Previous studies have actually shown that elastomers cause the vibrations to increase in the direction perpendicular to the applied load within the low frequency span. The properties of the elastomers are needed in order to model the dynamic behaviour and thereby be able to predict sound and vibration transmissions in wooden houses in the future. With known properties, the elastomer connections can be modelled using springs and dashpots. In this study, dynamic experiments have been made on elastomer strips half embedded. The test setup has been subjected to various loads using an electromagnetic shaker. The responses have been measured and evaluated using modal analysis. With different loads, non-linear characteristics of the elastomers’ behaviour have been obtained. The elastomers have also been tested quasi-statically, to obtain a load-deflection curve. Finally, the estimated properties of the elastomers have been included in an FE model using springs and the analytical results are compared with the experimental results.