This paper presents a theoretical and experimental study on the implementation of active noise and vibration control on a ventilation duct. Ventilation systems radiate noise at the duct outlets and from the duct walls. In many practical applications, ventilation ducts are installed without shielding, although, they often run through corridors and adjacent rooms or halls to be ventilated. Thus both air- and structure-borne disturbances are a cause of acoustic discomfort for the occupants. In this study the combined active control of air- and structure-borne noise is examined. For the theoretical study, a section of a circular ventilation duct is modeled via structural-mobility and acoustic-impedance formulations, where the interior fluid-structure coupling and sound radiation to the outside is modeled using an elemental approach. The control performance is evaluated in terms of the far field sound power radiated from the duct outlet and from the duct wall. For the experimental study, a laboratory duct set-up equipped with an axial ventilator and a ring of four control loudspeakers is used. The theoretical and experimental analyses show that active noise and vibration control systems can be effectively combined to reduce the low frequency noise radiated both by the outlet and the walls of the ventilation duct.
