The Design And Realization Of Parametric Acoustic Source Control System Based On Adaptive Inverse Control

As a new conceptual sound source, the parametric loudspeaker can generate highly directional audible sound by the nonlinear effects of air. At present the analytical relationship between the demodulated signal and ultrasonic sound waves in the parametric loudspeaker still rely on the theory of Berktay’s far field solution. But Berktay’s far field solution can only obtain the two-order approximation when the nonlinear effects, scattering, and absorption effect are not taken into account. Therefore the audible sound after demodulated must exist sound distortion.According to the phenomena of the parametric loudspeakers’ distortion, this paper proposes to establish the adaptive inverse controller of the parametric loudspeaker, and the inverse controller series before the parametric loudspeaker, through the feedback of the inverse controller to reduce the distortion of the parametric loudspeaker. Using MATLAB simulation the effectiveness of the system is verified. The algorithm of adaptive inverse control is implemented in DSP platform, and the performance of algorithm realization is verified finally.In order to build the adaptive inverse controller of the parametric loudspeaker, this paper elaborates the working principle of the parametric loudspeaker, and establishes the function model of the parametric loudspeaker to facilitate the verification of the simulation of adaptive inverse control. Then focus on the adaptive inverse control in the forward model and inverse model construction method. According to adaptive algorithm, the forward model and inverse model using adaptive filter is established, and the validity of proposed model is analyzed.Based on the models of the parametric loudspeaker established, this paper analyzes the common structures of adaptive inverse controller, and focuses on the X-filter LMS algorithm and ε-filter LMS algorithm. Establishes adaptive inverse control algorithm of the parametric loudspeaker using ε-filter LMS algorithm, and constructs inverse control model of the parametric loudspeaker by Simulink. Analyzes the control precision and the tracking speed of adaptive inverse control model, and compares the control algorithm of traditional PID control algorithm with the control algorithm of adaptive inverse control to prove the better performance with adaptive inverse control algorithm of the parametric loudspeaker source than traditional PID control algorithm.Finally, according to the theory and analysis of simulation results, the adaptive inverse control algorithm of the parametric loudspeaker is achieved in DSP platform. This paper presents the hardware implementation of the system, and makes a detailed analysis of some key circuits. Then gives the software flow chart of the system as well as some part of the program codes, analyzes realization of adaptive inverse control algorithm and builds up related test platform of experiments. The test results show that the adaptive inverse control system proposed in this paper can effectively reduce the voice distortion of the parametric loudspeaker.