Sameer I. Madanshetty
Aerosp. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215
Yale University, New Haven CT 06520
A method of controlling the noise level in duct flows is described. The method is based on the principle of energy extraction by active source(s), rather than by wave cancellation as in ``antisound.'' As such the method of energy extraction is robust; it does not need the delicate signal processing, perfect phase, and amplitude matching, crucial to sound cancellation. Two useful modes of control are discussed, one for quieting low frequencies and the other effective for higher frequencies. The possibility of perfect ``noise trapping'' in a finite region is also considered, even though it is difficult to implement such complete control in practice. A preliminary experiment that substantiates the concept is described. Extension of this method of noise control to three-dimensional cases is also briefly discussed.