Wise and Dineen (1995) describe approaches to active noise control for energy-efficient HVAC systems.
One approach uses an...adaptive filter to compensate for the acoustic feedback from the canceling loudspeaker to the input microphone. With the...adaptive filter, the controller is not used to generate wave forms from the input frequency; rather, it creates an electronic representation, or model, of the duct acoustics. Any noise detected by the input microphone is processed by the controller that responds by playing the exactly appropriate canceling sound just as the noise reaches the speaker downstream.
