Abstract: Sound emission from mounting points transmitting into support structures is an important physical parameter in characterization of structure-borne sound.The mobility method provides a complete and mathematically rigorous way for predicting the sound emission value,but is inconvenient as it contains too many elements.From the eigenvalue theory,a simplified method is proposed for building equipment,in which mobilities of structure-borne sound sources are considerably greater than those of the supporting structure.With two typical fans as an example,sound power predicted using proposed method is compared with that predicted with other approximate methods.Results show that the proposed method gives ±4dB error with respect to the precise value,better than other approximate methods.