Active control of sound transmission into enclosure through a panel

The thesis is concerned with the effectiveness of active sound transmission control inside an enclosure under the potential energy, squared pressure and energy density control algorithms using a purely vibration actuator, a purely acoustic source and combined source system. The principal application is to effectively use various control algorithms and sources on the active control of sound transmission into an enclosure and control of its resultant sound fields. The main objective of this thesis is to clarify the role of acoustic and vibration actuators, as well as error sensors and sensing schemes, in the global and local control of harmonic sound transmission into a structural-acoustic coupled system with different strength of structural-acoustic coupling. The effects of the edge rotational and translational flexibility of the flexible structure on the active sound transmission control are investigated in detail. The objective is tackled by way of investigations into (i) the physics of structural-acoustic coupled systems and (ii) the physical limitation and control mechanisms of active sound transmission control. The investigations were performed by employing three concepts: sound-field visualization for the analysis of active noise control, normalized impedance and mobility for the analysis of structural-acoustic coupled systems, and the effects of the edge rotational and translational flexibility of the flexible structure on the active sound transmission control.; The present results also showed the occurrence of the detrimental effects and spillovers under the squared pressure control, while they can be removed by using the energy density control. The energy density control results in more uniform sound fields and a performance similar to the potential energy control. However, it is not effective if the error sensor is located near to the secondary sound source. Formulae based on the normalized impedance-mobility approach were developed for the active sound transmission control with consideration of flexible structures with edges elastically supported against translation and rotation. Full coupling between the flexible structure and the interior acoustic cavity is considered. Effective active control is obtained for pure vibration control at low frequency, while pure acoustic control gives a more uniform performance for various combinations of edge rotational and translational flexibilities.