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The effect of sound-absorbing walls on the acoustic properties of the modelled unit cell of a sound-absorbing metamaterial

Chojak Aleksandra, Binek Wojciech, Chojnacki Bartłomiej, Pawlik Jan, Idczak Julia

Vibrations in Physical Systems

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2023

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Vol. 34, nr 2

art. no. 2023212

EN

Cavity-based metamaterials are usually designed for sound absorbing or sound scattering properties. They are built of combinations of ducts and slits, which in the case of acoustic absorbers are designed to maximize the sound absorption at resonance frequencies through the appearance of the viscothermal losses. The unit cells are designed under the assumption of perfectly rigid walls, shared by all the analytical models. Sound absorbing properties of the structures result from viscothermal losses in small ducts. The paper discusses the influence of adding sound absorption to the walls in the numerical model on the results of the observed sound absorption coefficient. It is demonstrated that the resulting sound absorption of the structure varies with changing sound absorption coefficient of the walls of the structure. The same observations are made for 3D-printed measurement samples, showing the importance of including the sound absorption of the walls in the modelling process.

2

Experimental verification of similarity criteria for sound absorption of simple metamaterials

Chojak Aleksandra

Vibrations in Physical Systems

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2022

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Vol. 33, nr 2

art. no. 2022211

EN

The paper concerns the dimensional analysis of simple acoustic metamaterials and its experimental verification in a computer model. Due to their decreased thickness possible because of the thermoviscous losses and sound dispersion that occur in acoustic metamaterials, such structures are gaining popularity, both as sound absorbers and diffusers. This implies the need to find their equivalents to be used at scale - both for modeling interiors with metamaterials and developing more complicated structures. The paper discusses the dimensional analysis performed for a generalized unit cell of a metamaterial with a resonator. The dimensional analysis shows the need for scaling both the geometrical dimensions of the structure and the parameters of the medium - air. The dimensional analysis was derived based on the transfer matrix method and was proven correct with the finite element method model. The paper also discusses the consequences of neglecting the air criteria, which are impossible to be fulfilled. This opens the question of finding new criterial numbers allowing the correct reflection of acoustic metamaterials at scale.

3

The use of Tranquility Rating for urban spaces

Idczak Julia, Juros Klara, Chojak Aleksandra, Mleczko Dominik

Vibrations in Physical Systems

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2021

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Vol. 32, nr 1

art. no. 2021104

EN

The Tranquility Rating coefficient (TR) is a tool proposed for assessing the quality of urban green areas, which considers both visual and acoustic aspects. This paper aims to verify how the proposed TR coefficient works for the assessment of the audiovisual quality of a typical urban space in a vicinity of an arterial road. Three different versions of the same urban space are considered: loud and visually unappealing (current state), quiet and visually unappealing (after considerable traffic reduction), and visually appealing and quiet (after redesigning). The values of noise levels required for the calculation of TR are taken from the noise maps based on the in-situ measurements, and the values of the percentage ratio of the features which are natural or man-made but contained within the visual scene (NCF) are taken from a survey conducted in the research. The results show that for the urban areas, even with very low noise levels, the TR is described as “unacceptable”. This may indicate the need for introducing an amendment for TR to be used in typical urban areas.

4

The impact of the sound reflection model on the ray tracing simulation variability

Binek Wojciech, Chojak Aleksandra, Kamisiński Tadeusz

Vibrations in Physical Systems

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2021

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Vol. 32, nr 2

art. no. 2021203

EN

Geometrical acoustics is the most commonly used method of room acoustics prediction. Its efficiency can be improved by explicit calculation of ray contribution to each receiver during reflection called algebraic reflection. The aim of this research is to analyse the applicability and impact of reflection model choice on algebraic reflection calculation using the ray tracing with next event estimation. The tested reflection models include the specular and Lambert reflection combination and the Phong reflection model. Classical ray tracing algorithm, without algebraic reflections, is used as a reference. Based on simulation results and statistical analysis we conclude that the change of the reflection model significantly affects the acoustics conditions within the simulation changing echograms in early reflections region and the reverberation times. Statistical analysis proved that echograms obtained with the combination of ray tracing with next event estimation and Phong reflection model have lowest simulation to simulation variability.