Noronha Castro Pinto F., Souza Pacheco W.

Active noise control is becoming a major noise reduction strategy, specially when dealing with one-dimensional propagation as in ducts for instance. Nevertheless it imposes very stringent restrictions on the processing capabilities of the control system. An alternative approach is the use of semi-active control systems. The article presents the design and implementation of a semi-active noise control system for ducts based on Helmholtz resonators. The control system actively tunes the passive, dynamical, absorbing characteristics of a Helmhotz resonator by varying its parameters like the resonator volume through a computer controlled mechanism. The system is useful for the cases where the noise exhibits predominant frequency components, which can be used as a target for the resonator tuning. The control system is modeled through simple equations describing the resonator behavior and as FEM-model. The practical implementation of the system as an experimental setup is discussed together with the processing characteristics needed for the system. An application example for the case of an exhaust system is presented.