Low-frequency sound absorption of elastic micro-perforated plates in a parallel arrangement Hyun-Sil Kim * , Pyung-Sik Ma, Bong-Ki Kim, Sang-Ryul Kim, Seong-Hyun Lee Acoustics and Noise Research Team, Korea Institute of Machinery & Materials, 156 Gajeongbuk-Ro, Yusung-Gu, Daejeon, 34103, South Korea article info Article history: Received 4 March 2019 Received in revised form 8 July 2019 Accepted 3 August 2019 Available online 7 August 2019 Handling Editor: L. Huang abstract In this paper, the low-frequency sound-absorbing performance of parallel-arranged micro- perforated plates (MPPs) is investigated, where elastic MPPs with different MPP parame- ters and cavity depths are set in a parallel-arrangement with a checkerboard pattern. Under the plane wave condition, a low-frequency formula for sound absorption coefficient is derived by means of a structural-acoustics analysis with two different elastic MPPs in the aforementioned parallel-arrangement. The accuracy of the proposed method is confirmed by comparisons with finite element method (FEM) results. The present method is based on the velocity average over different MPPs and does not assume any interactions among different MPPs. However, the FEM considers interactions among MPPs. The basic arrangement of the MPPs consists of two different MPPs and cavity depths in parallel. To smooth out the interactions, the cross-section of the MPPs is subdivided into small sec- tions like a checkerboard pattern so that no immediate neighboring sections would have the identical MPPs and cavity depths. As the number of the sections increases, the FEM results converge to the prediction due to the cancelling out of the interaction. When two rigid MPPs are arranged in parallel, the equivalent impedances are derived by modeling the MPPs as equivalent electrical circuits. When a partition between two different MPPs exists, the equivalent impedance using the analytical method is found to be identical to that based on an equivalent electrical circuit analogy. However, in the absence of a partition, the two results show a small difference, which is negligible in the plane wave approximation. The effect of the partition is discussed. When the partition between two MPPs is removed, acoustic fields separated by the partition form a single field, which in turn yields a single peak. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction Micro-perforated panels or plates (MPPs) have received much attention as a new generation of sound absorbers. MPPs have several advantages over conventional fibrous or porous sound absorbers. For instance, MPPs are resistant to humidity and are environmentally-friendly. Moreover, they can be designed to provide wide-band sound absorption for an intended frequency range by changing MPP parameters such as the hole diameter, thickness, and perforation ratio. Maa [1,2] presented a simplified impedance formula for an MPP. Maa's formula is considered as a useful tool in many studies of MPPs and related * Corresponding author. E-mail address: hskim@kimm.re.kr (H.-S. Kim). Contents lists available at ScienceDirect Journal of Sound and Vibration journal homepage: www.elsevier.com/locate/jsvi https://doi.org/10.1016/j.jsv.2019.114884 0022-460X/© 2019 Elsevier Ltd. All rights reserved. Journal of Sound and Vibration 460 (2019) 114884