Active control is applicable to resonators to improve noise control performance. Many active resonators depend on transfer functions from secondary sources to sensors to generate destructive interference in noise fields. These transfer functions are sensitive to the variance of acoustical parameters in noise fields where the sensors locate. An alternative strategy is to control resonators internally. This approach focuses on the internal dynamics of a resonator and uses an equivalent primary source with unknown strength and impedance to model the external noise field. A robust controller is designed on the basis of the internal dynamics model. It is independent of external parameters and able to minimize resonator reflection for the improved absorption performance. The active resonator is implemented in a set of experiment tests to achieve near perfect absorption performance in a wide frequency range. The closed-loop system is robust with respect to significant variations of acoustical parameters in the external field.