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This paper investigates the prediction of low-frequency impact sound insulation for a solid timber floor formed from dowel-connected joists with Swiss hardwood.
A finite element model was developed for the dynamic response of the floor as it is neither homogeneous nor isotropic and has complex connections.
With point force excitation, a FEM model for the dynamic response of the floor was validated using experimental modal analysis in the laboratory.
Two different FEM models were developed, one using spring connectors and the other using join connectors. Good agreement between FEM and measurements in terms of the Modal Assurance Criterion (MAC) and eigenfrequencies was achieved for the first 14 modes with the spring connector model and for the first 7 modes with the join connector model.
However, for the vibroacoustic analysis it was necessary to use the join connector model due to the computational instabilities of the spring model above 100 Hz when it was coupled to the acoustic medium.
With mechanical excitation the radiated sound power from the underside of the timber floor was measured with sound intensity in order to calculate the radiation efficiency. Comparison of measurements and FEM showed reasonable agreement between 20Hz and 200Hz
An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.