A stepped honeycomb design improves sound absorbers

Our world is increasingly technology-infused, and as a result, increasingly noisy. Low to mid frequency noise poses health risks, especially in transportation, aviation, and marine industries. Mitigating noise in engineering systems is important for both human safety and equipment reliability, but traditional noise absorbers and existing acoustic metamaterials are typically too thick for many practical applications, or only cover a small noise bandwidth.

To provide a solution for real-world, low-frequency noise control applications, Song et al. present a thin, lightweight material with an innovative design that integrated a stepped Helmholtz resonator (SHR) — a cavity geometry good for reducing low to mid frequencies —with a honeycomb configuration, which provides mechanical strength and improved low frequency blocking.

The researchers first optimized the SHR-honeycomb design of the material, which had spatially partitioned cavities to help with low-frequency sound absorption, with an acoustic impedance model to dissipate energy and improve sound absorption. They then fabricated it using additive manufacturing with the assistance of simulations and theoretical analysis. They tested samples of the material in an impedance tube and benchmarked against conventional honeycomb designs.

“By incorporating a stepped configuration, we achieved substantial low-frequency sound absorption within an ultra-thin profile of only 17 millimeters,” said author Wei Chen. “In contrast, comparable low-frequency absorption in prior studies typically required structures with average thicknesses exceeding 25 millimeters — often reaching over 40 millimeters in thicker variants — and usually without the use of internal fillers.”

By dramatically reducing the size of low-frequency absorbers, the material could be used in many applications that don’t have space for bulky absorbers, such as the interiors of high-speed trains and aircraft compartments, and industrial equipment enclosures. The researchers intend to continue with the research to improve performance and readiness of their laboratory findings.

Source: “Enabling broadband low-frequency sound absorption with a stepped Helmholtz-honeycomb metamaterial,” by Ziming Song, Wei Chen, Shengzhe Jin, Feihu Shan, Kui Liu, Hongwei Zhang, and Sichao Qu, Journal of Applied Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0306216 .