IN-FLIGHT EXPERIMENTS ON THE ACTIVE CONTROL OF PROPELLER-INDUCED CABIN NOISE

Results are presented of a series of in-flight experiments on the active contrl of propeller-induced passenger cabin noise in a B.Ae. 748 aircraft. Twenty-six configurations of up to 16 loudspeakers and 32 microphones were investigated at the first three harmonics of the blade passage frequency. Two loudspeaker distributions, which were either evenly distributed or partly concentrated in the plane of the propellers, gave similar reductions in the sum of the squares of the measured pressures at the fundamental blade passage frequency (88 Hz) of about 13 dB. Concentrating the loudspeakers near the propeller plane increased the reductions in the second and third harmonics (176 Hz and 264 Hz) from about 9 dB and 6 dB respectively for the equally distributed system, to about 12 dB for both harmonics. Subjective reductions in noise level with all three harmonics being simultaneously controlled were pronounced, with reductions of over 7 dB(A) being recorded at some seat locations. Also reported are additional experiments, with a local (two-loudspeaker, two-microphone) control system used for a single seat, and with the 16 loudspeaker, 32 microphone control system used to control the noise inside the cabin when the engines were run-up on the ground. © 1990.