Active open-loop control
Active noise control - theoretical basis

The electrical block diagram of a single-channel open-loop active control system is shown in figure 6 . It takes into account the measurement noiseN _r (ω ) and N _e (ω ) (due to turbulence, for example) present on the reference and error microphones, as well as a feedback path between the secondary source and the reference microphone, characterized by its frequency response H _f (ω ).