Adaptive feedforward broad-band noise compensation is currently used when a correlated measurement with the disturbance (an image of the disturbance) is available. Most of the active feedforward noise control systems feature an internal "positive" acoustical feedback between the compensation system and the disturbance measurement which has to be taken into account. Adap-tive algorithms for active feedforward noise attenuation have been developed since 1985 from a local optimization point of view. This paper presents two classes of adaptive configurations for active feedforward noise compensation developed from a stability point of view. The first class uses a standard IIR(FIR) compensator structure while the second class uses the Youla-Kucera parametrization of the feedforward noise compensator. This allows to separate the problem of stabilizing the internal positive feedback loop from the minimization of the residual noise. These adaptive schemes have been developed in the context of active vibration control but, as it will be shown, they can be used also in active noise control. The paper presents in a unified manner the available algorithms and compensator structures for adaptive feedforward noise attenuation and provides a comparative experimental evaluation on a relevant experimental test-bench (a duct silencer). Index Terms-active noise control, adaptive feedfor-ward compensation, Youla-Kucera parametrization, positive feedback coupling.