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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.

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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.

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Statistical analysis with Kolmogorov-Smirnov distance for reflections’ directions of arrival and amplitudes for sound field diffuseness estimation

Chojnacki Bartłomiej, Przysucha Bartosz, Kamisiński Tadeusz, Binek Wojciech

Vibrations in Physical Systems

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2021

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Vol. 32, nr 1

art. no. 2021101

EN

Many parameters are used for rating the quality of the sound field inside qualified acoustic halls describing the strength, clarity, and definition of the sound. Sound field diffuseness level and spatial impression parameters are used rarely because of the problem in their measurements and interpretation. Previous research on that topic provided some sound field diffuseness coefficients. Some of them are complicated in estimation and measurement. This paper presents a method for the sound field diffuseness level estimation basing on example measurements of the Arthur Rubinstein Philharmonic in Łódź, Poland. New directional parameters are proposed based on the statistical analysis of the sound reflections’ incidence angles and their amplitudes with Kolmogorov-Smirnov distance. The paper contains a discussion on the quality evaluation with the proposed method, including analysing the sound field diffuseness and non-uniform spatial distributions of sound reflections. The usability of the selected parameters and their importance for the spatial impression is discussed. The performed experiments allow setting the direction of future work in the field taken of the study, especially applying the proposed method for extended sound field diffuseness ratings with methods based on different physical principles, including directional, energetic, and time coefficients.