Ning Han

Active control of one-dimension impulsive reflection based on a prediction method

An approach for predicting the reflected sound pressure is proposed in one-dimensional sound field. For a duct ended with a rigid reflective surface, only one microphone is required to measure the total sound pressure on the surface, which is further used as the error sensing strategy in an active noise control (ANC) system to reduce the in-duct reflection. Experiments are carried out to validate the prediction method, and a broadband feedforward ANC system is implemented to suppress the impulsive reflection. It is found that the ANC system based on the reflected sound prediction is effective, and 12.2 dB attenuation of the one-dimension impulsive reflection is obtained after the active control.

Time-domain simulation for active noise control in a two dimensional duct

1 Time-Domain Simulation for Active Noise Control In a Two Dimensional Duct Ning HANa,b, Chunqi WANGa,c This paper presents a time-dependent simulation scheme which emulates the real-time acoustic wave propagation controlled by an active noise control (ANC) system. The proposed numerical scheme models the electrical control system (including the secondary loudspeaker, the reference and error sensors, and the adaptive control algorithm) and its interaction with the acoustic field as a whole, which contrasts existing simulation schemes that usually concern only one aspect of them. An accurate time-domain pseudo-spectral method (Chebyshev collocation) is used to solve the acoustic wave equation so that the numerical error in the acoustic field is minimized and will not adversely affect the ANC simulation. Experimental studies are carried out to validate the numerical scheme. Good agreement is observed between the experimental results and the numerical simulations. The numerical model is used to examine the controlled acoustic impedance of a single-channel feedforward ANC system in ducts. It is found that the major function of the control algorithm is to adjust the negative equivalent mass of the ANC system so as to cancel the inertial radiation reactance of the secondary loudspeaker as much as possible. For broadband noise control, the controlled impedance of the ANC system oscillates around the target value, resulting in worse noise reduction performance than in the situation of tonal noise control.

Unidirectional acoustic boundary through active control system in one dimensional duct

The unidirectional acoustic boundary has broad application prospects. Besides the strongly nonlinear acoustic medium, which can be applied in the realization of the unidirectional acoustic boundary, the present paper proposes a new approach through the active control method, where the secondary source has the property of single directivity. In order to validate its effectiveness in onedimensional duct, experiments are implemented in three steps: 1. construct the secondary source with the single directivity by two loudspeakers; 2. design the steady unidirectional acoustic boundary by the secondary source in step 1; 3. implement the adaptive unidirectional acoustic boundary by the secondary source in step 1, and through FXLMS algorithm. Results show that the presented approach is feasible and effective for one-dimensional unidirectional acoustic boundary, and the system only contains two traditional loudspeakers and two traditional microphones; thus it will be more feasible for practical realizations of the unidirectional acoustic boundary, compared with the acoustic diode.