Estimating Impact noise through Cross Laminated Timber floors using the Transfer Matrix Method

Abstract

In 1994 the Swedish building regulations was updated, allowing tall buildings to be built with wood as load bearing material. However, the sound protection regulations was not changed, which meant that wooden buildings would be acoustically evaluated according to the old standard, which was developed for heavy construction materials, e.g. concrete. Light and heavy constructions behave different acoustically. Due to this, wooden constructions struggles to keep up with the standard’s requirements in low frequencies, where they are bad at attenuating sound compared to heavy constructions. In order to start building more with wood, it is necessary to be able to estimate the acoustical behaviour of wooden constructions - especially in the lower frequencies. The aim of the thesis is to investigate if the transfer matrix method is suitable when estimating the impact noise through cross laminated timber (CLT) floors and if it provides a reliable estimation compared to measured and simulated results. The transfer matrix method can be used to calculate impact sound trough a stratified medium. Each layer is expressed with a transfer matrix which is coupled together in a global transfer matrix. The acoustical parameters on the output side is obtained by solving the global transfer matrix. The final result is size corrected with the radiation efficiency factor of a corresponding equivalent baffled plate. The calculated results are first validated for heavy constructions with measurements and simulated results from Bastian, a computer program used for e.g. estimating impact noise through a building element. Then the transfer matrix method is used to calculate the impact noise through CLT floors, which is compared to measured and simulated data. The results show that the transfer matrix method is suitable for estimating the acoustical behaviour of bare CLT floors and multiple layers. It is especially reliable in lower frequencies but show larger differences in higher frequencies compared to calculations on heavy constructions.