Full-scale experiments on the reduction of propeller-induced aircraft interior noise with active trim panels

Results are presented of full-scale experiments on the active reduction of rotor-induced passenger cabin noise in a Dornier Do728 aircraft. Two active sidewall panels (smart linings) are used to reduce the sound pressure in a control region in front of the linings. The fuselage pressure distribution associated with the first five harmonics of a generic counter-rotating open rotor (CROR) engine is emulated with a loudspeaker array. Each smart lining is equipped with two inertial force actuators. It uses up to eight error microphones and implements an adaptive feedforward controller. The two smart linings are driven in parallel. A maximum SPL reduction of 11.3 dB is achieved in the controlled area. The mean SPL reduction over 18 microphones is 6.8 dB. At the most critical second frequency, a mean SPL reduction of 9.3 dB is achieved by the two smart linings working in parallel. It is observed that the SPLs near the lining (at the window seat positions) are significantly higher than the SPLs near the aisle. This leads to the conclusion that the major part of the sound energy is transmitted through the linings, which is seen as an argument for the suitability of the smart lining concept