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1

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

Numerical directivity simulations of speaker arrays for omnidirectional sound source quality assessment

Chojnacki Bartłomiej

Vibrations in Physical Systems

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2022

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Vol. 33, nr 1

art. no. 2022101

EN

Omnidirectional sound sources are standard devices used in numerous acoustic measurements, such as the ones described in ISO3382, ISO140, or ISO354 standards. They are used when information on the sound diffraction at an object is required. State of the art findings describe several engineering designs of omnidirectional sound sources; some commercial applications can be also found. However, there is no universal design method for this kind of sound sources, neither in terms of the size and number of the transducers nor any general electroacoustic principles. This paper describes the use of Finite Elements Method (FEM) to derive the directivity patterns of different speaker arrays, such as spherical speaker arrays and the most popular polyhedrons. The number of transducers studied in the paper varies from 4 to 36. The influence of transducer size and the enclosure size was also preliminarily investigated. The simulation results were assessed with new strict omnidirectionality quality measures, and the influence of the transducers' number or size on a final omnidirectional sound source performance was verified.

3

Miniature omnidirectional sound sources used in acoustic scale modeling - measurements and validation

Chojnacki Bartłomiej

Vibrations in Physical Systems

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2022

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Vol. 33, nr 2

art. no. 2022201

EN

Acoustic measurements such as scale modeling measurements require a particular type of miniature omnidirectional sound source. The most important aspects of those devices are small sizes (usually below 100 mm in diameter) and different frequency ranges compared to traditional, omnidirectional sound sources used in room acoustics. The required frequency range differs regarding the used scale factor in different models, which leads to the troubles in frequent source changes and the need for a unique source design for every model. The project will present the recent achievement in miniature omnidirectional sound sources development. The optimal sound sources for the given measurement functions were developed based on the previous numerical simulations and experiments such as FEM sound directivity simulations or transducers' parameters tolerance testing. The sound sources presented are used for applications such as acoustic sound insulation scale measurements (frequency range 800 ÷ 63 000 Hz), scaled reverberation chamber measurements (300 ÷ 80 000 Hz), or acoustic reduction models measurements (400 ÷ 70 000 Hz). The paper will cover a detailed technical explanation of the laboratory environment's source construction aspects and validation measurements.

4

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.

5

Durability of paving concrete produced in a laboratory setting and obtained in field at expressway construction site

Kubissa Wojciech, Dąbrowski Mariusz, Chojnacki Bartłomiej, Glinicki Michał A.

Roads and Bridges - Drogi i Mosty

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2021

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Vol. 20, no. 4

397--412

EN

The article describes an experimental study of the properties of concrete designed for the construction of the bottom layer of two-layered road pavement with the exposed aggregate surface. Two types of materials were studied: industrially-produced concrete placed on a highway trial section using slip form technology and concrete produced in a laboratory setting, containing CEM II/A-V and CEM II/A-S Portland cement. The tested mixes contained granite or limestone coarse aggregate. The following basic performance properties were studied: compressive strength and split tensile strength, air void characteristics, freeze-thaw resistance, water absorption rate and chloride penetration. The mechanical properties and freeze-thaw resistance results obtained on the laboratory specimens were similar to those obtained on the cores drilled from the pavement. Despite the observed changes in the air void system parameters, mineral admixtures to Portland cements did not reduce the freeze-thaw resistance of concrete. The compressive strength was higher by up to 19% and sorptivity decreased by up to 22% in concrete containing cement with mineral admixtures.

PL

W pracy przedstawiono badania doświadczalne właściwości betonu projektowanego na dolną warstwę nawierzchni drogowej. Porównano właściwości betonu dolnej warstwy w nawierzchni dwuwarstwowej z eksponowanym kruszywem, wbudowanego na odcinku próbnym drogi ekspresowej, z właściwościami betonu wykonanego w laboratorium z użyciem cementów typu CEM II/A-V i CEM II/A-S. Zakres badań objął mieszanki betonowe zawierające kruszywo granitowe i wapienne. Przeanalizowano podstawowe właściwości techniczne betonu: wytrzymałość na ściskanie i rozciąganie przy rozłupywaniu, charakterystykę porów powietrznych, mrozoodporność, szybkość absorpcji wody i głębokość penetracji jonów chlorkowych. Próbki laboratoryjne i próbki-odwierty z nawierzchni wykazały zbliżone właściwości mechaniczne i odporność na działanie cyklicznego zamrażania i rozmrażania. Stosowanie cementów portlandzkich z dodatkami mineralnymi nie pogorszyło mrozoodporności betonu pomimo zaobserwowanych zmian w charakterystyce porów. Stwierdzono zwiększenie do 19% wytrzymałości na ściskanie oraz zmniejszenie do 22% sorpcyjności betonu.

6

Sposoby integracji systemu HVAC w budynkach użyteczności publicznej

Chojnacki Bartłomiej

Chłodnictwo i Klimatyzacja

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2020

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nr 9

34--35

PL

W krajach wysoko rozwiniętych, człowiek izoluje się od świeżego powietrza, spędzając około 90% czasu w pomieszczeniach zamkniętych. Nie jest to zatem czas poświęcony jedynie na sen czy odpoczynek w domowym zaciszu, lecz także na pracę. Według rankingu OECD Polacy spędzają w biurach około 2000 godzin rocznie, co za tym idzie - długotrwały wpływ na nasze samopoczucie ma bardziej jakość powietrza wewnątrz budynków niż na zewnątrerz.

7

Integracja oraz sterowanie systemem HVAC w inteligentnym domu jednorodzinnym

Chojnacki Bartłomiej

Chłodnictwo i Klimatyzacja

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2020

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nr 5

53--55

PL

Nie ma dziś domu, w którym nie spotkalibyśmy rozmaitych automatycznie sterowanych urządzeń. W dążeniu do wygody i ekonomicznego gospodarowania wodą, prądem a także własnym czasem, ludzie coraz chętniej wykorzystują możliwości dostarczane przez producentów. Inteligentny, oszczędny dom to jednak coś więcej niż zbiór automatycznie sterowanych aparatów. Pełną "inteligencją" swoich domów będą się cieszyć pewnie dopiero nasze dzieci lub wnuki, ale już dziś można i warto!) wiele zrobić, aby zintegrować w jeden sprawnie działający system urządzenia, które grzeją, chłodzą i wentylują przestrzeń domową. To ważne zarówno dla środowiska, jak i dla portfeli nawet tak drobnych inwestorów, jak właściciele domów jednorodzinnych.

8

Coupled speakers directivity measurements for small acoustic omnidirectional source development

Chojnacki Bartłomiej, Kamisiński Tadeusz, Juros Klara, Kaczor Daniel

Vibrations in Physical Systems

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2019

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Vol. 30, nr 1

art. no. 2019128

EN

Acoustic monopole construction is unsolved task, which engineers try to solve for many years. In the past they constructed many innovative solutions, such as spark or laser-gap sound sources, but those concepts caused many equipment troubles. It is impossible to select type of the measurements signal for this kind of sound sources, also any sparks and laser beams can provide strong electromagnetic distortions around the operation zone. In current state of art we are trying to provide non-standard solutions while traditional omnidirectional sound source, based on spatial configuration of electroacoustic transducers, is not described correctly and can be expanded. Paper presents concept of acoustic monopole source based on coupled configuration for electrodynamic loudspeakers, similar to isobaric setup but non-constant volume between the speakers. By using FEM modelling we will present directivity patterns and project ideas, describing how overall results corresponds with geometrical parameters of speaker configuration and parameters. Presentation summary contain results of prototype device directivity patterns measurements. Received characteristics shows big potential in using cone-to-cone coupled speaker setup to reach acoustic monopole in frequency range defined by distance between transducers. Achieved knowledge allows to provide broadband, easy to build and small acoustic monopole with many possible applications.