Active Control of Transmission Noise in a Bell 407 Helicopter

Cabin noise is a major source of discomfort for helicopter passengers. One of the main sources of noise is the main rotor drive and gearbox assembly, whose structural vibrations are primarily transmitted through supporting struts and mounts to the airframe, which then radiates sound into the cabin. The vibration and resulting noise occur mainly at discrete gear meshing frequencies in the frequency range [1-3] kHz. The objective of this work was to establish the feasibility of an active control system to reduce multi-harmonic transmission noise in helicopter cabins. The system development, implementation and testing were conducted on a Bell 407 aircraft.