Countermeasures against noise and vibrations in lightweight wooden buildings caused by outdoor sources with strong low frequency components

Low frequency sound may contribute to human annoyance by inducing building vibration involving both rattling and whole body vibrations. The basic mechanism, verified by a series of field measurements, is that transmitted low frequency noise excites floor vibrations. Hence, improved sound insulation at the lowest frequencies will also mitigate floor vibrations. While techniques for sound insulation at higher frequencies are well known, there is a lack of knowledge on how to design countermeasures providing good low frequency sound insulation, especially for lightweight structures. To close this knowledge gap, a broad research program on low frequency sound transmission and sound induced vibrations has been performed. The aim of the study has primarily been to develop cost-effective countermeasures against low frequency noise for lightweight building structures, which also has a good effect in the frequency range that determines the A-weighted sound level. A countermeasure with stiffening of the walls and roof using steel sheet profiles screwed to the existing studs in combination with plywood panels was proposed. The study involved laboratory measurements, Finite Element simulations, proposal and design of countermeasures, as well as full-scale field testing of the proposed countermeasures in a typical Norwegian wooden building. In this paper we present an overview of the results from the laboratory measurements and the full scale field testing. The study showed that the proposed countermeasure combined with improvements of windows and balanced ventilation gives about 10 dB reduction of the A-weighted indoor sound level from F-16 aircrafts and 30-70% reduction of the floor vibrations.