Extremely tortuous sound absorbers with labyrinthine channels in non-porous and microporous solid skeletons

Zielinski, Tomasz G.; Opiela, Kamil C; Dauchez, Nicolas; Boutin, Thomas; Galland, Marie-Annick and Attenborough, Keith (2023). Extremely tortuous sound absorbers with labyrinthine channels in non-porous and microporous solid skeletons. Applied Acoustics, 217, article no. 109816.

DOI: https://doi.org/10.1016/j.apacoust.2023.109816


An assembly of additively-manufactured modules to form two-dimensional networks of labyrinthine slits results in a sound absorber with extremely high tortuosity and thereby a relatively low-frequency quarter wavelength resonance. Fully analytical modelling is developed for the generic design of such composite acoustic panels, allowing rapid exploration of various specific designs. In addition to labyrinthine channels in a non-porous solid skeleton, a case is also considered where the skeleton has microporosity such that its permeability is very much lower than that due to the labyrinthine channels alone. The analytical modelling is verified by numerical calculations as well as sound absorption measurements performed on several 3D printed samples of modular composite panels. The experimental validation required overcoming the non-trivial difficulties related to additive manufacturing and testing samples of extreme tortuosity. However, due to the two-dimensionality and modularity of the proposed design, such absorbers can possibly be produced without 3D printing by assembling simple, identical modules produced separately. The experimental results fully confirmed the theoretical predictions that significant sound absorption, almost perfect at the peak, can be achieved at relatively low frequencies using very thin panels, especially those with double porosity.

Plain Language Summary

The paper reports theoretical and experimental investigations of ways of 3D printing a thin sound absorbing layer by incorporating a labyrinth of narrow slits in a soid matrix that includes very small pores. The combination of sound reduction mechansisms inside the layer creates a useful peak absorption at a frequency with a wavelength much larger than the sample thickness.

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