Active control of a sound field with a state feedback electro-acoustic transducer

Abstract

This study presents an alternative control system in which the acoustic impedance of the diaphragm of an electro-acoustic transducer can be manipulated by modifying the design parameters of the control system. This system involves a state-space description of an electro-acoustic transducer that is derived from its electrical equivalent circuit using modern control theory. The optimal quadratic regulator was used in the control system design, and the quadratic performance index was formulated to relate to the square of the sound pressure near the diaphragm of the control system. Computer simulations were performed to test the proposed control system and indicated that significant reductions in the acoustic impedance density could be achieved near the assumed vibration frequency that was used in the formulation of the quadratic performance index. A computer model of the proposed control system was used to illustrate effective active noise control in a duct and indicated that the control system brings about an effect similar to that of a resonator type muffler.