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The potentialities of active strategies based on boundary condition control are investigated for globally reducing the noise in cavities. Two active systems previously developed [Furstoss, Thenail, and Galland, J. Sound Vib. 203, 219–236 (1997)] are exploited in order to assign the most suited wall impedance for noise reduction: the first is referred to as ‘‘direct’’ control and permits precise realizations for harmonic excitations, the second is a hybrid passive/active feedback control well suited for random noise treatments. Experimental analysis and numerical developments are conducted on a rectangular three-dimensional cavity closed by a simply supported elastic plate. Noise is generated by an external load applied to the plate. Different impedance values are successively assigned, and their effect is estimated on the global sound-level reduction. Attention is also given to plate vibration changes, which may occur. Different typical behaviors of the plate-cavity system are first investigated for harmonic excitations. The hybrid control system appears to be a good compromise for all cases, and shows promising behavior when dealing with broadband excitations.