A study on feedback control of the vibration of a clamped elastic plate in the audio frequency range is presented in this paper. The study is specified by a discretization method based on an inverse modal analysis approach, through which a new lumped parameter system can be established to represent the dynamics of the low-order modes of the actual structure. With the discrete model the standard linear quadratic optimal control theory can be formulated in physical state space to design a controller, that will be later implemented in experiments to control the real structure. As an illustration, a lumped parameter model with 9DOFs has been created for the clamped plate. It is demonstrated by experiments under both impulse excitation and stationary random excitation that the corresponding nine vibration modes of the plate are quite well controlled with a collocation of two electromagnetic actuators and five sensors.