Audio Directional Loudspeaker Signal Processing System Based On Fpga Design

Audio directional loudspeaker is a brand-new device based on parametric acoustic theory and is also called parametric loudspeaker. The principal of audio directional speaker is fundamentally different from that of the traditional ones. The directional audible signal generated by audio directional loudspeaker is achieved by the nonlinear interaction of ultrasonic signal in the air. This paper mainly deals with the realization of the hardware signal processing platform and the signal processing algorithms, which are the two crucial parts of audio directional loudspeaker. Signal processing algorithms are researched based on the hardware signal processing platform which is designed in this paper.Theoretical basis and principles of audio directional loudspeaker is analyzed based on the principle of nonlinear acoustics, Westervelt acoustic parametric array theory and the Berktay broadband parametric acoustic theory. According to the audio directional signal processing algorithms, this paper introduced the design of the power supply and configuration circuit of the FPGA-based signal processing platform. The design of external signal acquisition circuit and signal filter circuit are also presented in this paper.The DSB modulation and SSB modulation algorithm which have been widely used in the audio directional loudspeaker are introduced in this paper. A PPM generating method, different from the existing double-sideband modulation and single-sideband modulation, is also proposed in this paper, which generates PPM signal by sampling the input signal. The output is a two-level square wave signal which can be amplified directly by class D Power Amplifier. The amplified signal could be used to drive the transducer after being reconstructed by the reconstruction filter. Realization of the DSB, SSB, PPM algorithms are all achieved, through programming with VHDL language, at the designed hardware platform, In addition, based on the amplitude-controlled PPM generating method in this paper, another PPM signal generating method is also proposed, which generates PPM signal through comparison of input signal and carrier. This paper not only provides a detailed introduction of its principles and solving process, but also, through emulation in Matlab, gives verification of its prominent advantages. The derivation and simulation results of the improved-PPM algorithm adopted in this paper improved that PPM algorithm does have a small distortion. Through the comparison of actual result of the three modulation methods, it can be inferred that the system involving PPM algorithm obtaining a higher level of sound pressure whit the same power consumption. This result proves the assumption that PPM method enjoys superiority over others in reducing power consumption of audio directional system.