In this research project,energy extraction methods for active noise control are developed. A major goal is to explore and design robust feedback control methods for rendering sound fields silent through energy extraction, and not via wave-cancellation. The technique developed are applicable to local as well as global silencing of sound fields. Further, these energy extraction methods are effective for progressive sound fields (for example, duct-borne noise) as well as reverberant noise configurations. Any selected resonant modes as well as broad-band noise are suppressed. In the context of duct-borne sound, sound energy is trapped (for extraction) in the region between the source and the control. The sound fields, downstream of the control are essentially silenced. Initial experimental work focuses on 1-D control of duct-borne noise with subsequent extension to the acoustic caging of 3-D sound sources. Using the proposed robust energy extraction methodology for noise silencing, in principle all noise configurations could be silenced: 1-D, 3-D, progressive wave fields or reverberant acoustic chambers. In all cases the noise could be confined to a small region near the source, rendering all space outside the confinement zone silent. Since the units do not exactly provide phase and amplitude matching for silencing, they will be simple, robust, and economical and have universal applicability.
