A feedback control algorithm based on the internal model principle is proposed to solve the active noise control (ANC) problem in ducts. Because of its infinite open-loop gain at selected frequencies, the controller is able, at the cancellation speaker position, to block noise transmission of these frequencies. In other words, the speaker acts like a totally reflective boundary. Stability analysis of the closed-loop system is performed using the Nyquist criterion. Experimental results confirm the theoretical analysis, showing an average noise level reduction of 30 to 40 dB at the target frequencies.