Research And Realization Of Signal Processing Method For Screen Directional Loudspeaker

The screen directional loudspeaker based on the principle of parametric array is a new type of screen loudspeaker which can present the picture and produce highly directional audible sound at the same time.Because the self-demodulation process of the medium is nonlinear,it is influenced by many factors such as temperature,humidity,signal processing algorithm and the characteristics of the screen directional loudspeaker itself,which leads to the distortion of the audible sound demodulated by the screen directional loudspeaker,it has a great influence on the sound quality of the equipment,so this thesis mainly studies the harmonic distortion of the screen directional loudspeaker,and provides a feasible scheme to realize the high fidelity sound quality of the screen directional loudspeaker of the portable equipment.According to the nonlinear acoustics theory,this thesis explains the basic principle of the parametric array screen directional loudspeaker,and analyzes the distortion of the common signal processing and modulation algorithms of the parametric array loudspeaker,the harmonic distortion of the screen directional loudspeaker and the shortcomings of the existing acoustic model are also discussed.The harmonic distortion of the screen directional loudspeaker is analyzed.In order to solve the problem of harmonic distortion of screen directional loudspeaker caused by the nonlinear effect of medium,the mathematical model of parametric array screen directional loudspeaker is established by means of system identification,based on the model and the double sideband modulation algorithm,a predistortion compensation algorithm is proposed,which is based on the basic theory of Nonlinear acoustics and adaptive filtering.The influence of the parameters and parameters on the performance of the improved algorithm proposed in this thesis is discussed theoretically,compared with the traditional LMS algorithm,NLMS algorithm and SVSLMS algorithm,the proposed algorithm has faster convergence speed and better stability.According to the results of the above theoretical research,this thesis designs the hardware platform of screen directional loudspeaker based on FPGA,and builds the test system of screen directional loudspeaker with the parametric array screen directional loudspeaker as the sound generating device and the corresponding chip,the ultrasonic frequency response test,audible frequency response test,directivity test,sound field shape test and distortion test were carried out.The results of ultrasonic frequency response test,audible frequency response test,directivity test and sound field test show that all the indexes meet the use standard,compared with the modulation algorithm without pre-distortion compensation,the high-order harmonics of the proposed algorithm are reduced by 7.49%,and the test results verify the effectiveness of the proposed algorithm.Based on the theoretical research and experimental results,it can be concluded that the proposed compensation algorithm can reduce the harmonic distortion of the screen directional loudspeaker and improve the sound quality of the portable equipment.