Impedance-based control system and its application in active noise control - Part II: Electro-impedance theory and measurement

By using electromechanic and acoustoelectric analogue theory, the law of electric and acoustic impedances variation for a sound source in noise reduction was studied. The expression of general input electric impedance of a coil driven loudspeaker was given, and the effect of radiation impedance of sound source on the electric impedance was analyzed. The law of electric impedance variation for the secondary loudspeaker were also studied under conditions of two noise reduction strategies, acoustic absorption and acoustic suppression. The relation of input voltage and vibratory output for loudspeaker was derived. The experiments in a semi-anechoic chamber were performed. It is shown that the measured electric impedance of secondary loudspeaker is in agreement to the predicted results.