Based on the transfer matrix method,the calculation of absorption of multi-layer micro-perforated panels(MPP)is conducted.Properly increasing the number of layers with different impedance in given cavity depths can improve sound absorption performance.The 4-layer and 5-layer micro-perforated panels with optimized parameters obtained by genetic algorithm can significantly broaden the sound absorption frequency bandwidth and improve the absorption coefficient of the whole frequency range,with an average absorption of 0.7 and 0.8 respectively in the range of 200-3 150 Hz which covers the main noise frequency range of high-speed train at 250-350 km·h-1.For 5-layer absorbers,absorption coefficients can be higher than 0.8 at 400-4 000 Hz.
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