Abstract
Measurement of natural vibration of acoustic space is effective for noise reduction in the cabin room of vehicle (e.g. auto-mobile, railroad car and so on). In general, multi-point excitation is useful to measure natural vibration of three-dimensional acoustic space with high damping on boundary surface. However, multi-point excitation needs adjustment of amplitude and phase for each actuator. Thus, multi-point excitation is difficult to implement. In this paper, the measurement technique of natural vibrations of acoustic space by multi-point excitation using decentralized control with local feedback control is used. Local feedback control generates force in the direction of motion, which had been presented by authors. In this paper, influence of increasement of excitation point controlled by local feedback control is investigated. Firstly, decentralized control using local feedback control is introduced. Local feedback control can cancel the influence of damping in acoustic space. Thus, signal of multi-point excitation using speakers controlled by local feedback control are automatically adjusted synchronizing via natural vibration. Secondly, the problem of multi-point excitation using decentralized control is verified. It is clarified from the experiments by single-point, four-points and nine-points excitation that measurement accuracy of natural vibrations gets the influence of number of excitation points. Finally, natural vibration modes, which can not be measured by single-point and four-point excitation, can be measured by nine-point excitation.
