Low frequency noise control using coupled loudspeaker and negative impedance circuit

It remains a technical challenge for low-frequency duct noise control devices to combine compact and broadband features at same time. A semi-active noise control approach is introduced to solve this problem. The device consists of a main pipe and two loudspeakers connected by a circuit containing a negative impedance network. Due to the effect of the negative impedance circuit, the virtual bypass is composed of the coupled loudspeaker and the circuit has sound transmission characteristics close to a physical duct in a certain frequency range. The effect of the negative impedance network and circuit on the performance of the silencer is studied by using the transfer matrix method. Through the design of the circuit, the sound transmission process of the virtual bypass can be realized. If the proper circuit network and parameters are selected, the virtual bypass HQ tube can achieve compact broadband noise control at low frequencies. A semi-active noise control device has 10dB noise reduction in the range of 100-300Hz.