A Review of the Applications of Hybrid Active / Passive Noise Control Systems in Ducts

The hybrid passive/active control system is a practical choice sometimes in duct noise control, where the tonal or narrowband noise at low frequencies is typically reduced by the active noise control technology. This paper reviews the applications of the hybrid passive/active systems in ducts and introduces two applications for locomotive exhaust noise and ventilation noise control in detail. As the reference signal affects both the control stability and noise reduction of feedforward active noise control systems, attentions are paid to the reference sensing strategy and several methods for dealing with the acoustic feedback from secondary sources to the reference microphone are discussed.