Abstract: Active sound absorbers are more effective for canceling the low frequency noise in ducts. In this paper, a new active sound absorber is presented, which consists of an unidirectional microphone, a time delay device and an unidirectional loudspeaker. This new absorber can achieve an attenuation of 35-55 dB for tone signal in the frequency range of 100-315 Hz; an attenuation of 14-24 dB for third octave noise; and for wide band noise, an attenuation of 8-20 dB is achieved within one octave band.