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

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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.