Modellisation of an active control system for exhaust noise emission.

An original prototype for vehicle exhaust gas pipe noise reduction is proposed: the system is based on an active noise control technique. A loudspeaker generates the canceling noise which is generated by a DSP based numerical algorithm. Canceling noise signal is emitted inside a custom pipe which is coaxial to the final segment of vehicle exhaust duct; disturbing noise and canceling noise destructively interfere at the exhaust duct outlet section; outgoing noise is thus reduced. The theoretical investigation upon the acoustic performances of the prototype has been carried out by adopting the electrical equivalent circuit approach; each acoustic element has been associated to an equivalent electrical component: air volume canceling noise propagates through has been modeled by an equivalent electrical circuit. Exhaust gas duct behavior is associated to an electrical inductance. Prototype transfer function has been estimated by an electrical circuit simulation software. Acoustical performances have been improved by optimizing equivalent electrical parameters.