Simulation of feedback systems in active noise control

Feedback systems are used in several applications of active noise control (ANC). Applications vary from active hearing protectors to active improvement of transmission loss in structures. The benefit of feedback systems is that no reference signal is needed. This usually means reduced system complexity and lower costs. Feedback systems are, however, inherently sensitive to instability. They also tend to increase noise level around the attenuated frequency band due to waterbed effect. Simulation plays an important role in designing feedback active noise control systems. With proper simulations, time and costs can be remarkably saved. Simulations can be used to choose appropriate structure for the controller and to evaluate the operation of the control algorithm. Simulations also give the optimum performance of the system in ideal conditions. This paper concerns system-level simulation of feedback active noise control systems. Different aspects including modeling of the plant and effect of the control loop delay are discussed. Simulation models of internal model control (IMC) based single-channel feedback systems are used as examples