The Design Of Audio Directional System

Audio directional system is a new kind of loudspeaker, which can project the audible sounds onto a given region. It is developed by the parametric acoustic array theory and the amplitude modulation technology. The ultrasonic carrier is modulated by the audio signals and then radiated into the air from transducers. Due to the nonlinearity of the air medium, the original audio signals will self-demodulate continuously in the propagation process and be heard by human. This thesis explores the basic principles and the key system implementation technologies of audio directional system, and designs the principle prototype, on which the relevant experimental tests are taken. The main research contents are summarized as follows:1. Based on the basic working principles of audio directional system, the associated theories and equations of nonlinear acoustic are analyzed. The two important parametric acoustic array theories, Westervelt equation and"Berktay far-field solution"are also explained. Furthermore, the KZK equation is solved, and some discussions are made about the related conclusions.2. For the main signal processing methods, the theoretical formulas for calculating the demodulated signals'sound pressure and signal distortion are derived from their theoretical self-demodulation models. The main signal processing methods, with the single-frequency signal input and dual-frequency signal input, are simulated by Matlab respectively. Based on the simulation results, the influential factors on signal distortion and the different signal processing method's characteristics are analyzed.3. Based on the piston transducer sound field theory, combined with the theories of attenuation and parametric acoustic array, the mathematical model of the demodulated signals'sound field is established. The three-dimensional sound field of the system is simulated using Matlab, and then the influential factors on the sound field distribution are explored by analyzing the simulation results. The sound field of transducer rectangular array is also simulated to provide theoretical guidances for system design.4. The signal processing system is realized using analog circuits and digital circuits respectively. Besides, a transducer square array is designed based on simulation results. Finally, the prototype is implemented by assembling the components. In summary, the results of experimental tests show that the sound field directivity and signal harmonic distortion and other indicators meet the design requirements. So the design methods proposed in this thesis are verified to be effective.