The paper addresses the active control of the sound transmission through a double panel partition. A literature survey indicates that active cavity control is much more efficient than active structural control. The vibro-acoustic behaviour of the double wall is analysed in light of this observation. This analysis shows that the sound transmission through the double panel is larger than that through a single panel at the resonances of the coupled eigenmodes with the strongest vibro-acoustic coupling between the plate motion and the pressure in the cavity. At frequencies where the double panel radiates much sound energy, the acoustic energy in the cavity is also high. Active control simulations illustrate that the cavity control approach, reducing not only the uncoupled (0,0,0) mode, achieves a considerable reduction of the sound transmission over a large frequency band. Depending on the desired noise reduction, the complexity and the cost of the control system can be reduced by a proper diagonalisation of the controller and by a clustering of the sensors and the actuators.