Recent works have demonstrated the potential of small-scale membrane-type acoustic metamaterials for low-frequency (<500 Hz) noise control. Such a phenomenon is attributed to the resonant behavior of the overhanging membrane in each unit cell. Considering industrial applications, large-scale designs may be preferred. This study presents a large-scale (0.8 × 0.8 m2) membrane-type acoustic metamaterial (or the meta-panel), which was evaluated experimentally and verified numerically. Experimental results showed that a broadband sound transmission loss (STL) improvement could be achieved by the incorporated membrane (up to 7.4 dB at 380 Hz). Numerically, parametric studies showed that the broadband STL performance of the meta-panel was due to not only the resonant behavior of the overhanging membrane but also the resonant behavior of the sandwiched membrane along the boundaries of the unit cells. If properly designed, this resonant behavior of the sandwiched membrane could complement membrane-type acoustic metamaterials to achieve an extended good STL performance across a broader frequency bandwidth.

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Membrane-type acoustic metamaterials generally involve a heavy platelet attached to a pretensioned membrane. Their acoustical performance is characterised solely based on the resonant behaviour of the membrane-platelet assembly. However, typical designs may pose manufacturing issues if extended in scale for industrial applications. Examples include the spatial consistency of the platelet(s), the uniformity of the membrane pretension, and the durability of the membrane—not to mention stress relaxation. As large-scale designs are recently gaining interest, it is imperative to address the shortcomings for manufacturability. This study presents a proof-of-concept design using tensionless membranes without any platelets. The results showed that the acoustical performance could be complemented by the coupling effect between two enclosed cavities via an orifice. The orifice diameter could serve as a tuning parameter for broadband or narrowband transmission loss at selected frequencies. Consequently, the proposed design could address the shortcomings of membrane-type acoustic metamaterials and complement their acoustical performance with the additional feature.

The aim of this paper is to provide an overview of the existing industrial practices used for cabin noise control in various industries such as automotive, marine, aerospace, and defense. However, emphasis is placed on automobiles and armored vehicles. Generally, automobile cabins usually constitute of thin structural panels, where the fundamental frequency typically falls below 200[Formula: see text]Hz. If a specific structural mode couples with a specific acoustic mode of the cabin, booming noise occurs. As such, discomfort may be felt by the occupants. Fundamentally, vibroacoustics problems may be minimized if the acoustic modes and the structural modes are decoupled, which is achieved usually by structural modifications or acoustical treatments. However, if excessively performed, the weight limitation of an automobile design will be exceeded; not to mention the adverse effect of increased weight on several factors such as fuel efficiency, mileage life of tires and acceleration of the vehicle. Moreover, current solutions have several drawbacks in low frequency noise control. In light of this, it is of great interest to explore the feasibility of acoustic metamaterials as an alternative with hope to improve cabin noise.

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