Research On Modulation And Nonlinear Distortion Compensation Algorithm Of Parametric Loudspeaker

Acoustic directional system,also called parametric acoustic array,uses nonlinear acoustic effect to generate audible audio beam from ultrasonic beam,which has high directivity in propagation process.In the process of self-demodulation,the nonlinear effect produces high order har-monics as well as audio beam,which greatly affects the quality of audio beam.Aiming at the nonlinear distortion caused by air self-demodulation in audio directional system,a new improved pre-distortion modulation al-gorithm based on traditional modulation algorithm is proposed in this paper.In addition,a new modeling scheme(Volterra filter modeling)for acoustic directional system is explored,and a second-order compensator model is designed based on Volterra filter and an adaptive second-order compen-sator model is designed to solve the inaccuracy of inverse system.The new preprocessing algorithm and the adaptive second-order compensator algo-rithm greatly improve the audio quality of the audio directional system and provide a new idea and scheme for the nonlinear compensation of the audio directional system.The main work completed in this paper is as follows:Westervelt theory and Berktay far-field solution are theoretically ana-lyzed and the KZK numerical solution model in time domain is established.The existing modulation algorithms DSBAM and MAM are theoretically analyzed,and an improved modulation algorithm is proposed.In order to analyze and compare the total harmonic distortion of the three modulation algorithms,the far-field solution and numerical solution are used to analyze the single frequency and compound frequency respectively,and the experi-ment proves that the improved modulation algorithm can effectively reduce the total harmonic distortion of the acoustic directional system.The data model(Volterra filter)is established and verified by iden-tification experiments that Volterra filter can well simulate the nonlinear characteristics of acoustic directional system.In order to further compen-sate harmonic distortion,a second-order compensator based on pth-order inverse theory and an adaptive second-order compensator based on adaptive inverse control theory are designed respectively for Volterra filter model.The simulation results show that when the linear part of the model is a non-minimum phase system,The adaptive second-order compensator has a good compensation effect.The experimental platform of audio directional system is designed,and the designed compensator is transplanted to the experimental platform.The feasibility of the two compensation schemes is verified through ex-periments.The advantages and disadvantages of the two schemes are dis-cussed.Both schemes can compensate the total harmonic distortion,while the adaptive second-order compensator can compensate the total harmonic distortion better when the linear part of the model is non-minimum phase system.It provides a new idea and scheme for the further research and development of audio directional system.There are 61 figures,1 tables,and 62 citations in this thesis.