Numerical modelling of interior sound fields due to external vibratory forces

There is increasing concern about the indoor acoustical environment affected by the rooftop vibratory equipment. Although vibration isolators are normally employed to reduce the structure-borne sound power transmitted to the building, a large amount of vibrational energy at some frequencies is occasionally transmitted to the roof and emitted as sound to the room underneath. The aims of this preliminary study are to model the interior sound fields due to vibratory forces; and to investigate the possibility of controlling the sound fields by numerical modelling at design stage. The interior sound fields are evaluated using commercial ANSYS software. The numerical results show that the vibration of roof structure and the amplitude of coupled interior sound pressure are related to the structural resonant frequencies and the acoustic resonant frequencies of the room. In order to reduce the interior noise levels, large modal coupling coefficients should be reduced by proper selection of structural and acoustic modal modifications.