Experimental Realization of a Sound Radiation Filter for Feedforward Control to Improve Active Structural Acoustic Control Systems

Abstract

Due to the strengthened CO2 and NOx regulations, future vehicles have to be lightweight and efficient. But, lightweight structures are prone to vibrations and radiate sound efficiently. Therefore, many active control approaches are studied to lower noise radiation besides the passive methods. One active approach for reducing sound radiation from structures is the active structural acoustic control (ASAC). Since the early 90’s, several theoretical studies regarding ASAC systems were presented, but only very little experimental investigations can be found for this alternative to passive damping solutions. The theoretical simulations show promising results of ASAC systems compared to active vibration control approaches.So, for that reason in this paper an experiment is conducted to investigate the performance of an ASAC system in the frequency range up to 600 Hz. A regular sensor grid of 24 accelerometers that are interconnected to establish six radiation signals is applied to an aluminum plate. The plate is excited by a point force and the feedforward control system counteracts these vibrations with 2 inertial actuators. The radiated sound power can be reduced by 4 dB integrated over the targeted frequency band. Compared to an active vibration control system which results only in a 0.2 dB decreased sound radiation, the ASAC system is beneficial. Furthermore, the filter length and the causality aspect of the experiments are analyzed in order to investigate the digital signal processing requirements. It can be shown that short filters are sufficient for an ASAC system compared to the filter length needed for an AVC system.In the last part of this paper some technical simplifications are investigated in order to reduce the complexity of the sound radiation filters. It is shown that the high pass filters needed to model the radiation efficiency can be neglected with a very small loss of performance.