Coiled quarter wavelength resonators for low-frequency sound absorption under plane wave and diffuse acoustic field excitations

To reduce their space requirement, quarter wavelength resonators are coiled up into a spiral to have the shape of a flat cylinder. The practical implementation of these resonators is tested using 3D printing, laser cutting and machining. Numerical simulations and impedance tube measurements are first compared for a normally incident plane wave excitation. This step allows to evaluate the effect of the resonator's inlet diameter, internal wall thickness, overall height as well as its constitutive material. A series of samples are then 3D printed following the identified optimal geometrical configuration. An array of resonators is tested alone and in combination with a glass wool layer under diffuse acoustic field excitation in a small reverberation chamber. The obtained results show that coiled quarter wavelength resonators can provide large sound absorption at their lowest resonance frequency and under both considered excita-tions, even if the largest external dimension of the resonators is only 1/18th of the targeted acoustic wavelength. (c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

To reduce space requirement, quarter wavelength resonators are coiled into spiral shape resembling a flat cylinder. Practical implementation involves 3D printing, laser cutting, and machining. Numerical simulations and impedance tube measurements are compared for normal incident plane wave excitation, evaluating the effect of inlet diameter, internal wall thickness, overall height, and constitutive material. 3D printing is used to produce samples with the optimal configuration, which are then tested in a small reverberation chamber under diffuse acoustic field excitation alone and in combination with a glass wool layer. The results show that coiled quarter wavelength resonators provide significant sound absorption at their lowest resonance frequency even with a much smaller size compared to the acoustic wavelength. (c) 2023 Elsevier Ltd. All rights reserved.