Research On Directional Audio System Based On DSB Signal Modulation

Directional Audio System(DAS)is a novel sound source which can produce high directivity audible sound wave.DAS modulates the audio signal to the ultrasonic frequency carrier signal and then transmits it through the ultrasonic transducer.Due to the self-demodulation phenomenon of the sound wave in the air,the audio signal in the modulation signal can be heard by ears.Compared with the traditional loudspeaker,DAS has the advantages of strong directivity,long emission distance,and virtual sound source effect.Therefore,DAS has a bright perspective in industry,military,culture,education,commerce,and other fields.We design a complete directional audio system.The main contributions are:First,the sound field radiation model in space is derived based on the wave equation of the single-point source.Then the sound pressure equation and directivity function of the circular piston transducer are calculated.Next,we propose the acoustic field model of the array transducer based on the spatial position of each transducer in the ultrasonic array and the superposition property of the sound wave.The visual simulation of the ultrasonic array is carried out using MATLAB,in which the factors affecting the directivity of the sound field are analyzed.Second,the self-demodulation model of DAS is established using the AM and DSBAM signal processing methods.The circuit simulation based on Multisim demonstrates the effectiveness of the proposed model.Based on Berktay’s far-field solution,we derive the equations of sound pressure and harmonic distortion in the medium under the inputs of the single-frequency signal and the double-frequency signal,respectively.Then we have studied the main factors and mechanisms that can influence the self-demodulation signal sound pressure.Finally,a complete directional audio system is designed and analyzed qualitatively and quantitatively.Experiments on impedance characteristics,ultrasonic directivity,and self-demodulation audible sound pressure level of the transducer are carried out.The experimental results show the DSB-AM method has advantages in directional effect.However,there are differences between the experimental results and theoretical results calculated by the self-demodulation theory and Berktay’s far-field solution.We analyze the reasons that can lead to the errors and propose feasible solutions for the future optimal design of DAS.