Active Control of Aircraft Cabin Noise

The noise levels in the passenger cabin of turbopropeller-driven aircraft are typically higher than the noise levels in comparable turbofan-powered aircraft. The sources of noise in a turboprop aircraft include boundary layer flow noise, structure-borne noise due to engine vibration, and acoustic excitation of the fuselage due to the propeller, with the latter being dominant for most turboprop aircraft. Possible noise reduction approaches encompass passive methods, such as structural modification, damping treatment, and active methods, which range from synchrophasing of the propellers to control of either the acoustic field or the structural vibration transmission path. An active noise control approach discussed in this paper is designed to weaken the coupling between the exterior and interior acoustics of turboprop aircraft. In this approach, the transmission of sound is impaired before it enters the cabin, which is superior to treating the problem further down the transmission path. Piezoceramic elements were used for structural actuation and vibration and/or acoustic sensing was employed. Full-scale testing was performed to evaluate the performance of the active noise control system. Significant reductions in noise level of up to 28 dB were achieved. Moreover the reduction in noise was global, leading to lower noise throughout the cabin. The results of this investigation demonstrate that Active Structural Acoustic Control Systems are capable of providing significant noise reduction and vibration suppression of aircraft to improve the habitability of the cabin.