Based on multi-layer Helmholtz resonators with extended necks (HREN), a compact sound-absorbing structure is developed for extra-broadband sound absorption. The structure of HREN with a single perforation is beneficial for low-frequency absorption under a thin thickness. However, it faces the problem of effectively attenuating noise only within a narrow frequency bandwidth near the resonance frequency. To widen its effective absorption bandwidth, two potential solutions are proposed and evaluated: (1) increasing the perforation number, and (2) adding extra layers in series. Results reveal that more perforations produce a wider half-absorption bandwidth, and the added layers induce more absorption peaks. Thus, a multi-layer HREN unit with multiple perforations is a favorable candidate for broadband sound absorption. On the basis of these, we design a broadband acoustic structure constructed by 11 coupled parallelly arranged double-layer HREN units with multiple perforations. The structure possesses an average sound-absorption coefficient of 0.9 in a prescribed frequency ranging from 800 to $3000\hspace{0.17em}\text{Hz}$. The absorption effectiveness of the structure is validated via experiments. What is more, the dimension of the absorber is only $50\hspace{0.17em}\text{mm}\hspace{0.17em}(\text{long})\times 50\hspace{0.17em}\text{mm}\hspace{0.17em}(\text{width})\times 41\hspace{0.17em}\text{mm}\hspace{0.17em}(\text{depth})$, indicating its compact characteristic. Hence, the developed extra broadband and compact sound-absorbing structure possesses a promising potential in various engineering applications.

中文翻译：

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一种由多孔双层谐振器组成的超宽带紧凑型吸声结构

基于带加长颈部的多层亥姆霍兹谐振器 (HREN)，开发了一种紧凑的吸音结构，用于超宽带吸音。HREN的单孔结构有利于薄厚度下的低频吸收。然而，它面临着仅在谐振频率附近的窄频带宽内有效衰减噪声的问题。为了扩大其有效吸收带宽，提出并评估了两种可能的解决方案：（1）增加穿孔数量，以及（2）串联增加额外的层。结果表明，更多的穿孔产生更宽的半吸收带宽，并且增加的层引起更多的吸收峰。因此，具有多个穿孔的多层 HREN 单元是宽带吸声的理想选择。在这些基础上，我们设计了一种宽带声学结构，由 11 个耦合平行排列的双层 HREN 单元构成，具有多个穿孔。该结构在规定的频率范围从 800 到 0.9 的平均吸声系数为 0.9$3000\hspace{0.17em}\text{赫兹}$. 通过实验验证了该结构的吸收效果。此外，吸收体的尺寸仅为$50\hspace{0.17em}\text{毫米}\hspace{0.17em}(\text{长})\times 50\hspace{0.17em}\text{毫米}\hspace{0.17em}(\text{宽度})\times 41\hspace{0.17em}\text{毫米}\hspace{0.17em}(\text{深度})$，表明其紧凑的特点。因此，开发的超宽带和紧凑的吸音结构在各种工程应用中具有广阔的潜力。