Synthesis and analysis of model-based controllers for an acoustic system require the state-space formulation of the system. The use of modal data, i.e. resonant frequencies, model damping ratios, and mode shapes, in constructing state-space model of an aoucstic system is described in this paper. Moreover, a simple, low-order feedback controller for adding damping to and/or cancelling offending noise in an acoustic system is introduced. State-space modeling, as well as the effectiveness of the proposed feedback controller are demonstrated through numerical and experimental, illustrative examples.