The Research On The Theory And The Experiment Of The Directional Speaker

In this dissertation, the directional speaker has been studied both theoretically and experimentally. The ultrasonic carrier signal is modulated by an audio signal and sent by the ultrasonic transducers along specified direction. During the propagation of the sound wave, the audio signal is regenerated by self-demodulation due to the nonlinearity of air.Firstly, the basic principle, history and present progress of the development of the directional speaker are briefly introduced. The KZK equation and the Berktay' s far-field solution are discussed. Based on above discussions, three preprocessing methods, preprocessing method of double-sideband, preprocessing method of square root and preprocessing method of single-sideband are discussed respectively in detail.Secondly, the characteristic of directional sound in the air is numerically simulated using the KZK equation. The model of ultrasonic transducers used in the simulations is taken from the measured data of the transducers.Lastly, a directional speaker has been developed based on the theoretical analysis and computation simulations. The experiment results show that there is little difference among the directivity of three processing methods and the distortion of method of single-sideband is the smallest, method of square root is in the middle, and method of double-sideband is the largest.The theoretical analysis, computer simulations and experimental results in the dissertation give a comprehensive understanding to the directional speaker. The progress is important to the design of the directional speaker.