Simplified Characterisation Of Structure-borne Sound Source With Multi-point Connections

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. In order to simplify the description , people produce each viewpoint to conducted the simplification description research from the different aspects, for instance polar method, no-coupling method and so on ,but they all exist involve the element excessively or the description precision insufficiently accurate, lacking the enough feasibility in the practical application. Under the loses in the precision is not very large , it have the vital significance to seek the simple approximate forecast method .The mobility matrix is one of usual physics parameters to characterize structure-sound source. Studying the statistical description of the mobility matrix element has good benefits to simplify characterization of structure-sound source. The results of the work has shown the mobility matrix element have a log10nalmal magnitude description. Such the mean value of the mobility matrix element (here we use are average characteristic value, their difference is not big) relatively concentrate in a quite narrow scope , this scope is much narrow than it's expected by theoretically forecast. Thus it has laid a good foundation for the average characteristic value theory proposed .It provide a simplified analysis tool to use the use the mobility matrix in practical.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 is better than other approximate methods.In order to further explained the superiority of the characteristic value theory , we take into account that it exit error in the structure -borne sound measurement in practical, the influence of this kind of error is big regarding the precision measuring ,but to the average characteristic value method forecast the influence is quite small. We knew the existence of the erroneous is unavoidable, in such situation, the eigenvalue theory appeared very good superiority to absorptive bigger erroneous. In the measuring accuracy request is not very accurate, the simplification characteristic of the eigenvalue theory is more prominent, it uses a quite simple way to achieve even surpass the measurement result which the precision measuring method obtains, even more satisfies in the actual building facilities engineering to the forecast of structure accoustical power rate. The forecast method of the simplification description for the structure accoustical power rate has provided one feasible method.