REDUCTION OF THE NOISE TRANSMITTED BY AN ENCLOSURE THANKS TO ACTIVE ABSORBERS

This paper investigates the potential of active absorbers for reducing low-frequency noise transmission through an enclosure. Active absorbers are intended to obtain a purely real prescribed impedance at the front face of a porous layer. This is achieved by an active control system which cancels the acoustic pressure at the rear face. The test bench was a simplified enclosure: a rigid-wall cavity coupled to a baffled elastic plate. The system was excited by a point source inside the cavity, and the absorbers were located on the rigid walls. Modeling was based on an analytical modal approach, and the absorbers were modeled by an impedance boundary condition applied on the cavity walls. The radiated sound power was calculated from the velocity field induced on the plate. The purpose of this simulation was first to calculate the optimal impedance, providing maximal reduction in radiated power, and then to define a sub-optimal strategy for actual absorber production. A 3-cell configuration was implemented on the test bench. Active control used a multichannel feedforward algorithm. In line with prediction, the absorbers provided a 5.5dB overall reduction while covering only 2 % of the cavity surface