In propeller driven aircraft the main source for internal noise are tonal disturbances caused by the propeller blades that are passing the fuselage. In a certain four propeller military transport aircraft the maximum sound level in the cabin can reach up to 110 dB(A), not taking into account any noise control treatments. Inside the semi closed loadmaster working station (LMWS) the sound level must be reduced down to 86 dB(A). It is proposed to reach this goal with an active noise control system, because passive solutions are to heavy at low frequencies.
Optimal positions of the loudspeakers are found by finite element calculations. These positions have been realized in a full-scale test bed. A reduction of the sound pressure level of more than 30dB within a specified volume was achieved at a frequency of 100 Hz.
HiFi speakers are used as secondary actuators in this test bed. These speakers are heavy and have unsuitable geometric dimensions for an aircraft. Therefore, other actuators, e.g. flat panel speakers, will be investigated with respect to the application in a mock-up of the LMWS.