Abstract: The control system of active noise attenuators in ducts. by processing the noise signal detected by the microphones, generates a signal exciting the secondary sound sources to radiate a sound wave cancelling the primary sound wave in the downstream. The desired frequency response function of the control system is determined by the frequency response of the loudspeakers and the detecting microphones as well as the configuration of them. In this paper, the desired frequency response function of control system corresponding to different configuration of secondary sources and detecting microphones were calculated. A method measuring the frequency response of microphone and loudspeaker in ducts was introduced. These measurements offer the basis to the design of the control system for active noise attenuators.