Efficiency of floating floors on CLT or concrete plate in the low frequency region

Abstract

In order to fulfil requirements regarding impact sound insulation between two ver-tically adjacent rooms, a floating floor construction is a commonly used technique. However the understanding of the acoustical performance of the floor construction at low frequencies is limited. This thesis aims to evaluate which physical parame-ters in the different layers of a floating floor construction that are important for the improvement of impact sound insulation below 200 Hz. Two different kinds of base floors are tested, concrete and cross laminated timber, CLT. The impact sound insulation improvement is evaluated using a numerical model developed in the finite element software COMSOL Multiphysics for extraction of vibration levels below the floor. The floor is considered being placed in an infinite baffle and the sound radiation is calculated using the Rayleigh integral. Applying a floating floor to a structural plate of either concrete or CLT changes the radiated sound power from the floor in different ways. Below the mass-spring-mass resonance frequency created by the three layers, the efficiency of the floating floor is mainly controlled by how the modal content of the floor is changed, both in frequency and amplitude. Above the resonance the efficiency of the floating floor follows expected theoretical improvements to different extent. The most important physical parameters in a floating floor construction are accord-ing to this study the stiffness of the interlayer as well as the density and thickness of the floating floor slab. The study shows that the density of the interlayer as well as the damping of the floating slab is less important for the efficiency of the floating floor. When increasing the thickness or the density of the floating floor slab, the sound insulation improvement at the lowest frequencies (f < 30 Hz) is better for the CLT plate, attenuating the radiated sound power to almost the same amplitudes as for the corresponding concrete case. Above the floating floor resonance the slope of the sound insulation improvement is in general steeper for the concrete cases. However no other general tendency can be seen when studying the difference between applying the same floating floor construction to the different structural plates.