The formulation and implementation of a low-order vibration controller using Linear Quadratic (LQ) modern control theory is demonstrated. The controller is implemented to reject persistent disturbances of the fundamental mode of a simply supported plate. The plate is excited by a 60 Hz harmonic excitation, a narrowband excitation centered at 60 Hz, and an impulse excitation caused by an impact hammer. The extraction of the eigen-properties of the first four modes of the plate is presented. The eigen-properties form the basis of the modal model of the plate. Also, a brief discussion of the control law is provided. Simulated and experimental results are presented for the transputer-based, parallel-processing control system. The steady-state fundamental modal amplitude is attenuated by more than an order of magnitude at the disturbance frequency, and the modal damping is doubled. Additionally, the implementation issues of applying the LQG controller are addressed including temporal and spatial aliasing considerations. / Master of Science