The modeling and active control of acoustic pressure in a 2-D cavity with a flexible boundary (a beam) is considered. Control is implemented in the model via piezoceramic patches on the beam, which are excited in a manner so as to produce pure bending moments. Approximation techniques are discussed and, by writing the resulting system as an abstract Cauchy equation, the problem of reducing interior pressure fluctuations can be posed in the context of an LQR time domain state space formulation. Examples illustrating the dynamic behavior of the coupled system, as well as demonstrating the viability of the control method on a variety of problems with periodic forcing functions, are presented.