A Study on Micro-Perforated Panel Absorber with Multi-Layered and Parallel-Arranged Structure to Enhance Sound Absorption Performance

Abstract

Micro-perforated panel absorber (MPPA) can be manufactured using various materials and can be applied to various fields. There are restrictions on applying MPPA because of the narrow sound absorption bandwidth. To solve this problem, the design parameters are controlled or the MPPA is constructed in parallel or multilayer structures. However, It is not easy to make holes of diameter of 0.1 mm or less in a general method. If there are constraint conditions, MPPA may not be designed for the target frequency band. We propose MPPA combined with multi-layer structure and parallel arrangement to effectively enhance the sound absorption performance. A calculation method for the absorption coefficient of the proposed MPPA is derived and the validity of calculation results is confirmed through the experiments. The sound absorption characteristics according to change of design parameters and structural change are analyzed and the following results are obtained. First, MPP with one kind of hole and various cavity depths is more effective in enhancing the sound absorption performance than MPP with various types of holes and one type of cavity depth. Second, in double-layer MPPA, it is confirmed again that the absorption performance is improved when the hole diameter and porosity of the MPP from the source are higher than those of the MPP from a rigid wall. Third, when MPPA with multi-layer structure and parallel arrangement is designed, both MPP properties and cavity depths should be considered to achieve good performance of MPPA. Based on the results, we design the prototype MPPA. Result of reverberation room test shows that prototype has a good sound absorption performance. We will improve the prototype MPPA and conduct a field test to reduce railway noise such as squeal noise.