An industrial ANC application for an enclosure

An unusual ANC approach using structural sensors and actuators is investigated for its effectiveness in actively attenuating the sound radiation from an irregular enclosure excited by an internal sound field. The intention of the control strategy is to control the enclosure vibrations in such a way that the radiated sound field is minimized. For the case considered here the interior noise spectrum has most of its energy below the first enclosure structural resonance frequency, thus complicating the control design. Here the design of a suitable control system for this problem is described. This is followed by a discussion concerning the type and reliability of the equipment which is most appropriate, after which experimental results illustrating the performance of this approach are presented. The experimental data show a direct correlation between the reduction in enclosure surface vibration and the reduction in noise radiation. INSTRUCTION Nowadays, noise reduction is still a main concern, both to improve the work environment and to reach new customers where noise is a choice factor between two products providing the same services. Although passive noise control is widely used in industry, there are relatively few industrial applications of active control, probably because of its unreliability (both in terms of control stability and in terms of embedded electronic devices) and because it is usually difficult and time consuming to implement. Here, it is shown how a simple robust active noise control system can be used to attenuate noise radiated from an irregular enclosure at frequencies below the first enclosure structural resonance frequency. The robustness comes from two system properties: only structural sensors/actuators have been used; and the choice of an adaptive feedforward controller using a simple FXLMS control algorithm. The controller developed here could easily be applied in industry as it is robust, simple and small in size. There are three main issues addressed in this paper: the use of structural sensors and actuators to control noise radiation, the type of control approach needed to drive the ANC system and the reliability of the real time system involved.