Enhanced sound absorption with the combined sonic black holes

In this study, a combined sonic black hole (SBH) structure is proposed to improve the sound absorption performance of the traditional SBH. The proposed combined SBH consists of multiple SBHs with different lengths by space division. The transfer matrix method (TMM) is used to analyze the sound absorption performance of the proposed combined SBH. Furthermore, the proposed SBH is fabricated by the additive manufacturing. The experimental sound absorption coefficients are obtained from an impedance tube setup. The absorption coefficients from TMM and experiments show a reasonable agreement. Comparing to the traditional SBH, the main advantage of the proposed combined SBH is that lower cut-off frequency and higher sound absorption coefficient can be achieved.