Low frequency noise breakout through duct walls of the ventilation system is a serious problem. The addition of sound absorbing materials such as fiberglass inside the duct wall to improve sound absorption performance at high frequency is a well-known technique. The experiment presented in this paper is to investigate and analyze the duct noise reduction at low frequency. The range of effective sound absorption frequency band and maximum sound absorption are also predicted in terms of the thickness of face sheet absorption material inside the cavity and the lateral dimensions. The feasibility of simultaneous optimization of acoustic properties of panel absorber for such applications is discussed. It is found that the new design of duct with panel absorber is more effective than conventional fiberglass blanket.