Global control of propeller-induced aircraft cabin noise using active sound absorbers

Abstract

A method to attenuate the global acoustic pressure of low-frequency harmonic acoustic disturbances in the interior of a small aircraft cabin mockup is proposed herein. This method is based on the well-known active sound absorption technique, which employs a wave-separation method to separate acoustic waves into incident and reflected waves. The shape identification of the low-frequency acoustic modes, both analytically and via the finite element method (FEM), allows the precise placement of four active sound absorbers in the cabin mockup to achieve global acoustic pressure attenuation. The key advantage of this approach is that acoustic pressure attenuation occurs via the dampening of acoustic modes, thus resulting in a global reduction in the sound pressure level (SPL), instead of creating quiet zones locally. Simulations and experiments for an aircraft cabin mockup show that a SPL attenuation exceeding 9 dB can be achieved in most of the cabin locations. Furthermore, the SPL reduces by up to 20 dB in certain regions. Finally, the surfaces of the active absorbers cover only 2% of the inner surface of the enclosure to achieve these results, thus necessitating only a few transducers.