Active trim panel with improved sound transmission loss under stochastic acoustic excitation

Abstract

The application of feedback control for the active reduction of stochastic broadband disturbances is widely recognized as being superior compared to feedforward control. This holds particularly true in the case of stochastically excited primary fuselage structures, since there is no practically realizable way of measuring time advanced and coherent reference signals. Since a considerable amount of acoustic energy is transmitted through the sidewall panels into the cabin, the transmission loss of a conventional double-wall fuselage structure can be improved by active structural acoustic control (ASAC) of the secondary lining structures (trim panels). The extension of the system boundary from an active primary structure to an active double-panel system with enclosed fluid enhances the spatial and temporal correlation of sensor signals and permits the implementation of a causal feedforward controller. If a causal control configuration is achieved, both resonant and forced structural vibration can be reduced. This potentially leads to a superior performance of a feedforward controlled ASAC system compared to an ASAC system implementing a feedback control law. In this work an aircraft relevant double-wall structure was mounted in the test opening of a sound transmission loss facility. The primary curved and stiffened CFRP-structure was augmented by accelerometers, microphones were placed in the cavity and the sidewall panel was augmented by actuators and sensors. The broadband performance of the active feedforward controller was tested under different stochastic acoustic excitations. A diffuse sound field was generated by means of a reverberation room and a distributed stochastic acoustic excitation of the primary structure with several independent noise sources was realized by means of an acoustic loudspeaker array. Experimental results show a considerable broadband reduction of structural vibration and radiated sound power.