The Design Of The Parametric Loudspeaker System

When two sinusoidal beams are radiated from an intense ultrasound source, a spec-tral component at the difference frequency is secondarily generated along the beams due to the nonlinear interaction of the two primary waves. At the same time, spectral components such as a sum-frequency component and harmonics are generated. How-ever, only the difference-frequency component can travel an appreciable distance be-cause sound absorption is generally increased with frequency. Due to high directionality and strong penetrability, acoustic parametric array has broadly been applied to various technical fields such as detecting and identification of buried target,underwater com-munication and directional propagation of audio signal, etc. The paper is organized as follows.The first chapter reviews the background and significance of parametric acoustic array and the practical application of parametric acoustic array is introduced. Besides, This chapter concludes the main contents of this review paper.Based on the theory of nonlinear acoustic, combined with Lighthill wave equations, Westervelt wave equations and Berktay theory,etc,the principle of parametric acoustic array is introduced systemically in Chapter Ⅱ. Moreover, This chapter outlines some properties, such as the directivity of parametric acoustic array and the gain of difference frequency component.The third chapter highlights two important parts of parametric loudspeakers. One is signal processing and modulation techniques, another one is transmitting transducer array for parametric loudspeakers. By simulating the spectrum of the demodulated sig-nal in three modulation modes respectively,we can compare these three methods of sig-nal pre-processing and modulation. The results showed that the main distortion source of double-sideband modulation comes from harmonic distortion, and there are no har-monic distortion in the square-root amplitude modulation and single-sideband modula-tion.However, the ultrasonic emitter with large bandwidth is required to generate the infinite harmonics introduced by the square-root operation. In addition,the influences of the array element size, the number of element and interelement spacing on the trans-mitting transducer array are calculated and analyzed,which may be helpful for the con-trol of high directivity.In this section, we look into some of the implementation issues on developing the parametric loudspeakers in analog and digital circuits. In addition,square-root ampli-tude modulation are presented and analyzed using Simulink.The last chapter made a brief summary and outlook.In this paper, based on the theory of nonlinear acoustic, we introduced the impacts of acoustic source and transducer array on directivity and made a comparison among three signal processing schemes used in parametric acoustic array.