Active noise control (ANC) is achieved by introducing a cancelling "antinoise" wave through an appropriate array of secondary sources. These secondary sources are interconnected through an electronic system using a specific signal processing algorithm for the particular cancellation scheme. ANC has application to a wide variety of problems in manufacturing, industrial operations, and consumer products. The emphasis of this paper is on the practical aspects of ANC systems in terms of adaptive signal processing and digital signal processing (DSP) implementation for real-world applications. In this paper, the basic adaptive algorithm for ANC is developed and analyzed based on single-channel broad-band feedforward control. This algorithm is then modified for narrow-band feedforward and adaptive feedback control. In turn, these single-channel ANC algorithms are expanded to multiple-channel cases. Various online secondary-path modeling techniques and special adaptive algorithms, such as lattice, frequency-domain, subband, and recursive-least-squares, are also introduced. Applications of these techniques to actual problems are highlighted by several examples.

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Active noise control: a tutorial review

Active control of interior noise in model aircraft fuselages using piezoceramic actuators is experimentally studied. The actuators are bonded directly to the structure and error information is taken from up to two microphones located in the interior acoustic field. The results demonstrate that global attenuation of the order of 10 to 15 dB of interior noise can be achieved with piezoceramic actuators, irrespective of whether the shell system is vibrating at an acoustic or structural resonant frequency. The work also proves that active control using vibration (moment) inputs works well when a floor simulating that of an aircraft is installed in the model. This result suggests that the technique will be successful in controlling interior noise in realistic aircraft structures.

Active control of interior noise in model aircraft fuselages using piezoceramic actuators

This paper presents a review of active techniques for aerospace vibro-acoustic control. First, the mechanisms of airborne or structure-borne sound generation and transmission in aerospace vehicles are briefly reviewed. The main approaches of passive and active noise/vibration control are then summarised, and three examples of active systems that have already been developed into practical aerospace applications are briefly described. Finally the actuator, sensor, and control system requirements for aerospace applications are discussed.

Review of Active Techniques for Aerospace Vibro-Acoustic Control

Control of sound radiation with active/adaptive structures

This paper presents a theoretical study of the active control of both structure-borne and airborne noise transmission through a double-panel system. The physical and geometrical characteristics of the system were chosen to be similarto those of the fuselage of a civil aircraft. The total sound power transmitted by the double-panel system was used to evaluate the active control performance of four different strategies for the control system: e rst, active mounts connecting the two panels and loudspeakers placed between the two panels were driven to minimize the total sound powerradiated by thepanel (thereference case );second, activemounts connecting the two panels were driven to cancel the out-of-plane velocities at the connecting points on the radiating panel; third, loudspeakers placed between the two panels were driven to cancel the acousticpressure at points neareach control loudspeaker; and fourth, active mount and control loudspeaker systems were used simultaneously as already stated. The simulations show that the control loudspeakers are able to produce large attenuation of the sound transmission at low frequencies close to the mass-air-mass resonance of the double panel. The performance is signie cantly better if the loudspeakers are driven to minimize radiated sound power, rather than cancel pressure between the panels. The active mount cone guration studied in this paper does not producesignie cant reductions of the sound transmission except in the case where it is used in combination with the control loudspeakers. I. Introduction

Active Control of Structure-Borne and Airborne Sound Transmission Through Double Panel

We report the results of tests conducted to demonstrate the effectiveness of active vibration control techniques in reducing structure borne noise in aircraft cabins. A prototype active vibration control system was tested in the Douglas Aircraft Company Fuselage Acoustic Research Facility, using the aft section of a DC-9 aircraft as the test article

Full-scale demonstration tests of cabin noise reduction using activevibration control

A simplified cylindrical model of an aircraft fuselage is used to study experimentally the effect of an internal floor on low-frequency sound transmission into aircraft cabins. A geometrically scaled lattice floor support and floor skin are designed based on selected characteristics of a business aircraft. The pressure amplitude at various interior locations is presented along with a modal decomposition of the associated shell response. Results indicate that the main effect of the floor on interior pressure levels is due to a modification of the interior acoustic mode shape and not due to the structural modification of the fuselage model caused by the lattice floor support. Thus, the model provides a simplified procedure for studying the influence of various structural modifications as well as other important effects.

J. D. Jones

Papers

Full-scale demonstration tests of cabin noise reduction using activevibration control

Influence of a floor on sound transmission into an aircraft fuselage model

Full-scale demonstration tests of cabin noise reduction using activevibration control