Development of real time simulator for acoustic field based on discrete Huygens' model

将离散惠更斯模型(DHM)应用于实时声场模拟器。为了实现实时仿真，采用了现场可编程门阵列(FPGA)器件。现场可编程门阵列是一种包含可编程逻辑元件和可编程互连的半导体器件。基于DHM或传输线矩阵法TLM，建立了适用于现场可编程门阵列器件的声场数字等效电路。DHM是一种数值模型，它将波的传播和散射模拟为传输线网络上的脉冲散射序列，符合惠更斯原理。DHM元件用硬件描述语言(VHDL语言)描述，并配置在一片FPGA芯片上。对于三维情况，DHM元件所需的现场可编程门阵列逻辑单元的数量估计约为400。为了减小DHM元件的电路规模，在DHM计算中采用了定点算法。讨论了基于现场可编程门阵列的DHM定点算法的数值精度。估算了实际精度的声场模拟所需的数据长度。当数据长度为28bit或更长时，由于数值误差比空气吸声引起的衰减小得多，因此可以达到实际精度。通过引入符号校正电路，避免了溢出误差。利用现场可编程门阵列(FPGA)技术，在硅片上制作音乐厅的声场实时模拟器--“硅音乐厅”。

The discrete Huygens' model (DHM) is applied to real time simulator for acoustic field. To achieve real time simulation FPGA (Field Programmable Gate Array) device is applied. FPGA is a semiconductor device containing programmable logic components and programmable interconnects. The digital equivalent circuit of the sound field for FPGA device is developed based on the DHM or the transmission line matrix method TLM. DHM is a numerical model in which propagation and scattering of waves are simulated as the sequences of impulses scattering on the transmission line network as Huygens' principle states. DHM elements are described in hardware description language (VHDL) and configured on a FPGA chip. The number of FPGA logic cells required for a DHM element is estimated at about 400 for three dimensional case. To reduce the circuit scale of a DHM element, the fixed-point arithmetic is taken in the DHM calculations. Numerical accuracy of FPGA based DHM using the fixed-point arithmetic is then discussed. The data length required for sound field simulation in practical precision is estimated. When the data length is 28bits or longer, the practical accuracy can be achieved because the numerical error is small enough than the attenuation caused by the sound absorption of air. The overflow error can be avoided by introducing sign correcting circuit. Using the FPGA technique, the real time simulator named "Silicon Concert Hall" will be created in which sound field of a concert hall is fabricated on a silicon wafer.