The present paper describes the investigation of an active feedback noise control system in an enclosure surrounded by rigid walls. A large number of operations is required for active control in a rigid-walled sound field because lots of acoustic paths between multiple sensors and multiple secondary sources can exit. The rigid-walled sound field can be expressed by the superposition of a large number of orthogonal acoustic modes. It is expected that single-input single-output(SISO) model can be achieved for each mode independently using the modal decomposition and generation techniques and that various previously developed SISO control methods can be used. Therefore, I propose an active control system with SISO H∞ controllers to suppress multiple mode amplitudes independently based on the modal decomposition and generation techniques. In the present paper, the characteristics of the proposed system to control four modes are verified numerically and experimentally. The obtained results show that significant noise reduction in practical use can be achieved without mode couplings.