## Low frequency sound generated vibration in buildings due to military training and air traffic

F. Løvholt, C. Madshus, K. Rothschild; NGI

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Low frequency sound, in addition to the effects of audible sound, contributes to human annoyance and building damage by inducing building vibration. This involves whole body vibration sensing of humans, and therefore frequencies down to approximately 1 Hz become important. Here, the results of study of outdoor low frequency noise induced building vibration and indoor noise are presented. The results originate from different field measurements and numerical simulations on military training and aircraft operations in eastern and northern Norway. The field measurements have shown that he first natural frequency of the whole building seem to be critical with respect to vibration transmission of sound into the buildings. Radiation from vibrating ceiling and walls seems to be the dominant source of the sound in the room. The measurements support the hypothesis that floor vibration are acoustically driven by the indoor sound pressure in the room rather than through moment-stiff coupling to the walls, making wall bending cause bending of the floor. Moreover, these field measurements have discovered that in many circumstances the vibration contribute more to the annoyance than the audible noise. Due to its low frequency characteristics, mitigation of this low frequency noise in buildings is difficult. Still, the effect of possible mitigation measures are illustrated through numerical Finite Element simulations of the low frequency sound and the building response, by altering the structure of the building in a typical Norwegian dwelling.