Abstract:

Drum-like silencers commonly require a back cavity with sufficient volume to achieve low-frequency sound absorption, which is not allowed in many practical applications. In this study, a drum-like silencer with tunable property for low-frequency sound absorption is designed and analysed. The concept of symmetrical magnetic device is introduced to reduce the cavity volume. On the one hand, the dynamic effect of the magnetic forces on the silencer is used to reduce the stiffness of the whole system, so as to transfer the effective absorption frequency band to low frequency range without increasing the cavity volume. On the other hand, the equivalent reverse magnetic forces neutralize each other, eliminating its static effect on the silencer. Besides, in order to maintain the system in the controllable range of positive stiffness, the structural design of the silencer is a challenge. In this study, two methods of the tapered membrane structure and the sandwich structure are proposed to meet the requirements of the positive stiffness of the system, of which the reliability is being explored theoretically and experimentally. Up to now, the basic theoretical analysis has been carried out, and the test platform has been built for some preliminary experiments. This presentation focus on the modal analysis of the sandwich structure.