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Aircraft cabin noise control in the past has relief heavily on improving sidewall attenuation by passive ‘‘add-on’’ treatments. The conventional passive methods, such as adding mass, damping, or acoustic absorption, etc., not only impose a stiff weight penalty, they are also ineffective in improving the low-frequency sound transmission loss of an aircraft fuselage sidewall. Active control of sound inside aircraft cabins has been the focus of research in recent years and has shown considerable promise. Laboratory and in-flight tests of prototype active control systems for tonal noise reduction using secondary speakers have demonstrated the feasibility of active noise control (ANC) in aircraft cabins. In recent years active structural acoustic control (ASAC) has also been applied to aircraft fuselage structures in controlling low- to mid-frequency structural sound radiation. In the ASAC technique, control forces are applied directly to the vibrating structure by actuators (such as piezoelectric transducers) instead of using loudspeakers to minimize the radiated sound field. The ASAC approach is also important in the design of ‘‘smart structures,’’ which incorporate both sensors and actuators in the structure for noise and vibration control. This paper presents results of investigations (conducted at McDonnell Douglas) of application of both ANC and ASAC techniques to a full scale aircraft fuselage. Significant sound pressure reductions were achieved throughout the cabin for multiple tonal frequencies of excitation. The performance of the ASAC method is compared with that of the ANC system using speakers. The flight test results with a prototype ANC system in an MD-80 aircraft will also be presented.

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