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Recently, research on an electronic sound cancellation system that is able to cancel noise using sound of the opposite phase has been conducted. This kind of noise control technique is referred to as active noise control (ANC). In order to realize a practical working ANC system, it has been considered desirable to apply the LMS (least-mean-square) algorithm to such a system's control, especially the VS (variable step)-LMS algorithm due to its high speed of convergence. The realization of an ANC system of the stand-alone type is presented. Experiments were conducted in actual air-conditioning ducts having a cross section of 500 × 500 mm by using the realized stand-alone type active noise control system with the VS-LMS algorithm. Below the cross-mode frequency, more than 15 dB of attenuation was obtained for broadband random noise, even in the presence of an air flow of 3.7 to 9.0 m/s.