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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 38913

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Special Issue Editors

Dr. Edoardo Piana

E-Mail Website1 Website2
Guest Editor

Applied Acoustics Laboratory, Department of Mechanical and Industrial Engineering, University of Brescia, 25123 Brescia, Italy
Interests: vibro-acoustics; environmental noise control; room and building acoustics; experimental methods and in-field measurements; properties of conventional and unconventional acoustic materials

Dr. Paolo Bonfiglio

E-Mail Website
Guest Editor

Materiacustica s.r.l., 44122 Ferrara, Italy
Interests: porous material vibro-acoustic characterization and design; numerical modeling for the study of acoustical radiation and noise control; active noise control
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Monika Rychtarikova

E-Mail Website
Guest Editor

1. Faculty of Architecture, KU Leuven, 1030 Brussels, Belgium
2. Faculty of Civil Engineering, Slovak University of Technology in Bratislava, 810 05 Bratislava, Slovakia
Interests: building and room acoustics; environmental acoustics; virtual acoustics; perception of sound

Special Issue Information

Dear Colleagues,

A wide range of sound-absorbing elements are currently available to adjust the acoustic features of an environment, thanks to the progress made in materials research and to the introduction of innovative manufacturing technologies. Nowadays, performance is only one of the required specifications, together with environmental compatibility, longevity, and affordable cost.

“Acoustic Properties of Modern Sound-Absorbing Materials” will collect the most recent advances in the broad-spectrum characterization of sound-absorbing materials used in civil, industrial, and tertiary applications by means of experimental, numerical, or theoretical studies. Works related to the development of novel materials and meta-materials are also welcome.

Dr. Edoardo Piana
Dr. Paolo Bonfiglio
Prof. Dr. Monika Rychtarikova
Guest Editors

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Keywords

Sound absorption
surface acoustic properties
metamaterial
porous material
environmental compatibility
life cycle assessment
experiment
simulation
model

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Published Papers (13 papers)

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Editorial

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3 pages, 180 KiB

Open AccessEditorial

Acoustic Properties of Absorbing Materials

by Edoardo Alessio Piana, Paolo Bonfiglio and Monika Rychtarikova

Appl. Sci. 2022, 12(9), 4446; https://doi.org/10.3390/app12094446 - 28 Apr 2022

Cited by 1 | Viewed by 2066

Abstract

Thanks to the progress made in materials research and to the introduction of innovative manufacturing technologies, a wide range of sound-absorbing elements are currently available to adjust the acoustic features of an environment [...] Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

Research

Jump to: Editorial, Other

18 pages, 5508 KiB

Open AccessFeature PaperArticle

Comparison Failure and Successful Methodologies for Diffusion Measurements Undertaken inside Two Different Testing Rooms

by Lamberto Tronchin, Angelo Farina, Antonella Bevilacqua, Francesca Merli and Pietro Fiumana

Appl. Sci. 2021, 11(22), 10523; https://doi.org/10.3390/app112210523 - 9 Nov 2021

Cited by 3 | Viewed by 1875

Abstract

The scattering phenomenon is known to be of great importance for the acoustic quality of a performance arts space. The scattering of sound can be achieved in different ways: it can be obtained by the presence of architectural and/or decorating elements inside a room (e.g., columns, statues), by the geometry and roughness of a surface (e.g., Quadratic Residue Diffuser (QRD)) and by the diffraction effect occurring when a sound wave hits the edges of an obstacle. This article deals with the surface scattering effects and the diffusion phenomenon only related to MDF and plywood panels tested by disposing the wells both horizontally and vertically. The test results undertaken inside a semi-reverberant room and inside a large reverberant room have been compared to highlight the success and the failure of the measuring methodologies. In detail, according to the existing standards and regulations (i.e., ISO 17497—Part 2), diffusion measurements have been undertaken on a few selected types of panel: two QRD panels (made of Medium Density Fiberboard (MDF) and plywood) with and without a smooth painted solid wood placed behind the QRD. The panels have been tested inside two rooms of different characteristics: a semi-anechoic chamber (Room A) and a large reverberant room (Room B). The volume size influenced the results that have been analyzed for both chambers, showing an overlap of reflections on panels tested inside Room A and a clear diffusion response for the panels tested inside Room B. In terms of the diffusion coefficient in all the octave bands between 125 Hz and 8 kHz, results should not be considered valid for panels tested in Room A because they were negatively impacted by extraneous reflections, while they are reliable for panels tested in Room B. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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23 pages, 3258 KiB

Open AccessArticle

On the Determination of Acoustic Properties of Membrane Type Structural Skin Elements by Means of Surface Displacements

by Daniel Urbán, N. B. Roozen, Vojtech Jandák, Marek Brothánek and Ondřej Jiříček

Appl. Sci. 2021, 11(21), 10357; https://doi.org/10.3390/app112110357 - 4 Nov 2021

Cited by 5 | Viewed by 2903

Abstract

The article focuses on the determination of the acoustic properties (sound transmission loss, sound absorption and transmission coefficient under acoustic plane wave excitation) of membrane-type of specimens by means of a combination of incident plane wave sound pressure and membrane surface displacement information, measuring the sound pressure with a microphone and the membrane displacement by means of a laser Doppler vibrometer. An overview of known measurement methods and the theoretical background of the proposed so-called mobility-based method (MM) is presented. The proposed method was compared with the conventional methods for sound transmission loss and absorption measurement in the impedance tube, both numerically and experimentally. Finite element model (FEM) simulation results of two single layer membrane samples of different shape configurations were compared, amongst which six different variations of the backing wall termination. Four different approaches to determine the sound transmission loss and two methods to determine sound absorption properties of the membranes were compared. Subsequently, the proposed method was tested in a laboratory environment. The proposed MM method can be possibly used to measure the vibro-acoustic properties of building parts in situ. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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14 pages, 3545 KiB

Open AccessArticle

A Perforated Plate with Stepwise Apertures for Low Frequency Sound Absorption

by Xin Li, Bilong Liu and Chong Qin

Appl. Sci. 2021, 11(13), 6180; https://doi.org/10.3390/app11136180 - 2 Jul 2021

Cited by 4 | Viewed by 3315

Abstract

A perforated plate with stepwise apertures (PPSA) is proposed to improve sound absorption for low frequencies. In contrast with an ordinary perforated plate with insufficient acoustic resistance and small acoustic mass, the perforated plate with stepped holes could match the acoustic resistance of air characteristic impedance and also moderately increase acoustic mass especially at low frequencies. Prototypes made by 3D printing technology are tested in an impedance tube. The measured results agree well with that of prediction through theoretical and numerical models. In addition, an absorber array of perforated plates with stepwise apertures is presented to extend the sound absorption bandwidth due to the introduced multiple local resonances. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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17 pages, 5134 KiB

Open AccessArticle

The Influence of Floor Layering on Airborne Sound Insulation and Impact Noise Reduction: A Study on Cross Laminated Timber (CLT) Structures

by Federica Bettarello, Andrea Gasparella and Marco Caniato

Appl. Sci. 2021, 11(13), 5938; https://doi.org/10.3390/app11135938 - 25 Jun 2021

Cited by 20 | Viewed by 3787

Abstract

The use of timber constructions recently increased. In particular, Cross Laminated Timber floors are often used in multi-story buildings. The development of standardization processes, product testing, design of details and joints, the speed of construction, and the advantages of eco-sustainability are the main reasons why these structures play a paramount role on the international building scene. However, for further developments, it is essential to investigate sound insulation properties, in order to meet the requirements of indoor comfort and comply with current building regulations. This work presents the results obtained by in field measurements developed using different sound sources (tapping machine, impact rubber ball, and airborne dodecahedral speaker) on Cross Laminated Timber floors, changing different sound insulation layering (suspended ceiling and floating floors). Results clearly show that the influence on noise reduction caused by different layering stimulated by diverse noise source is not constant and furthermore that no available analytical model is able to correctly predict Cross Laminated Timber floors acoustic performances. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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20 pages, 6208 KiB

Open AccessArticle

Acoustic Characterization of Some Steel Industry Waste Materials

by Elisa Levi, Simona Sgarbi and Edoardo Alessio Piana

Appl. Sci. 2021, 11(13), 5924; https://doi.org/10.3390/app11135924 - 25 Jun 2021

Cited by 5 | Viewed by 2125

Abstract

From a circular economy perspective, the acoustic characterization of steelwork by-products is a topic worth investigating, especially because little or no literature can be found on this subject. The possibility to reuse and add value to a large amount of this kind of waste material can lead to significant economic and environmental benefits. Once properly analyzed and optimized, these by-products can become a valuable alternative to conventional materials for noise control applications. The main acoustic properties of these materials can be investigated by means of a four-microphone impedance tube. Through an inverse technique, it is then possible to derive some non-acoustic properties of interest, useful to physically characterize the structure of the materials. The inverse method adopted in this paper is founded on the Johnson–Champoux–Allard model and uses a standard minimization procedure based on the difference between the sound absorption coefficients obtained experimentally and predicted by the Johnson–Champoux–Allard model. The results obtained are consistent with other literature data for similar materials. The knowledge of the physical parameters retrieved applying this technique (porosity, airflow resistivity, tortuosity, viscous and thermal characteristic length) is fundamental for the acoustic optimization of the porous materials in the case of future applications. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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13 pages, 3606 KiB

Open AccessArticle

Optimization of Shunted Loudspeaker for Sound Absorption by Fully Exhaustive and Backtracking Algorithm

by Zihao Li, Xin Li and Bilong Liu

Appl. Sci. 2021, 11(12), 5574; https://doi.org/10.3390/app11125574 - 16 Jun 2021

Cited by 9 | Viewed by 1972

Abstract

The shunted loudspeaker with a negative impedance converter is a physical system with multiple influencing parameters. In this paper, a fully exhaustive backtracking algorithm was used to optimize these parameters, such as moving mass, total stiffness, damping, coil inductance, force factor, circuit resistance, inductance and capacitance, in order to obtain the best sound absorption in a specific frequency range. Taking the maximum average sound absorption coefficient in the range of 100–450 Hz as the objective function, the optimized parameters of the shunted loudspeaker were analyzed. Simulation results indicated that the force factor and moving mass can be sufficiently reduced in comparison with that of a typical four-inch loudspeaker available on the market. For a given loudspeaker from the market as an example, the four optimized parameters of the shunted loudspeaker were given, and the sound absorption coefficient was measured for verification. The measured results were in good agreement with the predicted results, demonstrating the applicability of the algorithm. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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19 pages, 2464 KiB

Open AccessArticle

Sound Absorbing and Insulating Low-Cost Panels from End-of-Life Household Materials for the Development of Vulnerable Contexts in Circular Economy Perspective

by Manuela Neri, Elisa Levi, Eva Cuerva, Francesc Pardo-Bosch, Alfredo Guardo Zabaleta and Pablo Pujadas

Appl. Sci. 2021, 11(12), 5372; https://doi.org/10.3390/app11125372 - 9 Jun 2021

Cited by 17 | Viewed by 4322

Abstract

From a construction point of view, neighborhoods with residents living at or below the poverty threshold are characterized by low energy efficiency buildings, in which people live in acoustic discomfort with no viable options for home improvements, as they usually can not afford the materials and labor costs associated. An alternative to this is to use low-cost insulating elements made of non-conventional materials with acceptable acoustic properties. Given that household materials at their end-of-life (EoLHM) are free of costs and available also to the more disadvantaged population, they can be used to build acoustic panels for such contexts. This approach embraces several benefits since it reduces the amount of waste produced, the footprint deriving from the extraction of new raw materials and, by highlighting the potential of the EoLHM, discourages the abandonment of waste. In this paper, the acoustic properties of EoLHM, such as cardboard, egg-cartons, clothes, metal elements and combinations of them, are investigated by means of the impedance tube technique. The measured sound absorption coefficient and transmission loss have shown that EoLHM can be used for the realization of acoustic panels. However, since none of the analyzed materials shows absorbing and insulating properties at the same time, EoLHM must be wisely selected. This innovative approach supports the circular economy and the improvement for the living condition of low-income households. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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20 pages, 9361 KiB

Open AccessFeature PaperArticle

More Than Just Concrete: Acoustically Efficient Porous Concrete with Different Aggregate Shape and Gradation

by Louena Shtrepi, Arianna Astolfi, Elena Badino, Giovanni Volpatti and Davide Zampini

Appl. Sci. 2021, 11(11), 4835; https://doi.org/10.3390/app11114835 - 25 May 2021

Cited by 9 | Viewed by 2673

Abstract

The interest in the use of resistant acoustic materials has put further attention on the use of porous concrete in the building industry. This work investigates the acoustic properties of four different mix designs of porous concrete obtained with two types of aggregates, that is, normal weight and lightweight aggregates. The assessment of the sound-absorbing performances has been conducted in the small-scale reverberation room (SSRR) at Politecnico di Torino (Italy), in agreement with the procedure indicated in the ISO 354 Standard. For each concrete type, three panel thicknesses, i.e., 20 mm, 40 mm, and 60 mm, were tested. Moreover, different mounting conditions were investigated, considering the combination of single panels in multiple layers, adding an air gap between the panel and the backing, and inserting a layer of rock wool in the air gap itself. The results show weighted absorption coefficients (α_w) in the range of 0.30 to 0.75 depending on the thickness and mounting conditions. These encouraging values make these materials useful for efficient practical applications in indoor and outdoor environments. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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12 pages, 10212 KiB

Open AccessArticle

Acoustical Properties of Fiberglass Blankets Impregnated with Silica Aerogel

by Hasina Begum and Kirill V. Horoshenkov

Appl. Sci. 2021, 11(10), 4593; https://doi.org/10.3390/app11104593 - 18 May 2021

Cited by 11 | Viewed by 3395 | Correction

Abstract

It is known that aerogel impregnated fibrous blankets offer high acoustic absorption and thermal insulation performance. These materials are becoming very popular in various industrial and building applications. Although the reasons for the high thermal insulation performance of these materials are well understood, it is still largely unclear what controls their acoustic performance. Additionally, only a small number of publications to date report on the acoustical properties of fibrous blankets impregnated with powder aerogels. There is a lack of studies that attempt to explain the measured absorption properties with a valid mathematical model. This paper contributes to this knowledge gap through a simulation that predicts the measured complex acoustic reflection coefficient of aerogel blankets with different filling ratios. It is shown that the acoustic performance of a fibrous blanket impregnated with aerogel is generally controlled by the effective pore size and porosity of the composite structure. It is shown that there is a need for refinement of a classical Biot-type model to take into account the sorption and pressure diffusion effects, which become important with the increased filling ratio. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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14 pages, 8587 KiB

Open AccessArticle

Development of a Panel Membrane Resonant Absorber

by Yaw-Shyan Tsay, Jui-Yen Lin and Faxin Ma

Appl. Sci. 2021, 11(4), 1893; https://doi.org/10.3390/app11041893 - 21 Feb 2021

Cited by 3 | Viewed by 4921

Abstract

The bass ratio describes the relationship between the reverberation energy in the low frequency region and that of the middle frequency. An appropriate bass ratio can create a warm sound; however, too much bass can influence speech clarity (C₅₀) and work efficiency and can even cause listeners to feel tired or exhausted. Using perforated plate resonance theory and membrane resonance theory, this research developed the panel membrane resonant absorber (PMRA), which not only provides an outstanding continuous absorption spectrum in the broadband range of 100–800 Hz but also presents an aesthetic appearance at a low cost. We divided this study into two parts: (1) PMRA development and experiment and (2) field application and measurement to confirm the sound absorption performance of the PMRA. In part 1, PMRA was developed by combining different materials and thicknesses of the air cavity. In the field study of part 2, the PMRA with the appropriate sound-absorbing curve was installed in a small auditorium, where we conducted field measurements for reverberation time (RT) and speech clarity (C₅₀). According to the experimental results, the PMRA had great absorption performance at a low frequency. In the field validation, the PMRA was found to effectively decrease the low-frequency RT while also maintaining the RT of middle-high frequency. The C₅₀ of the auditorium was also improved. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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11 pages, 1953 KiB

Open AccessArticle

Investigation of Acoustic Properties on Wideband Sound-Absorber Composed of Hollow Perforated Spherical Structure with Extended Tubes and Porous Materials

by Dengke Li, Zhongcheng Jiang, Lin Li, Xiaobo Liu, Xianfeng Wang and Mu He

Appl. Sci. 2020, 10(24), 8978; https://doi.org/10.3390/app10248978 - 16 Dec 2020

Cited by 9 | Viewed by 2365

Abstract

Traditional porous media such as melamine foam absorb sound due to their three-dimensional porous struts. However, the acoustic properties at low frequencies are greatly related to its thickness. In this paper, a novel type of thin and lightweight sound absorber composed of melamine foam and hollow perforated spherical structure with extended tubes (HPSET) is introduced to enhance the sound absorption performance at low frequencies. A theoretical model for the normal absorption coefficient of the HPSET with melamine foam is established. Good agreements are observed between the simulated and the experimental results. Compared with the virgin melamine foam, the proposed absorber can greatly improve the low-frequency sound absorption and retain the mid- to high-frequency sound absorption, while the thickness of the proposed absorber is less than 1/28 of the wavelength. Full article

(This article belongs to the Special Issue Acoustic Properties of Absorbing Materials)

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