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Metals are excellent conductors for phonon transportation such as vibration, sound, and heat. Generally, metal sound insulators require multimaterial structure or defects and unimetal sound insulators are challenging. Therefore, a design of a defect‐free sound insulator made by single alloys with multiple friction stir processes (FSPs) is proposed. Periodic friction stir processing can induce superlattice‐like local mechanical properties' modifications. By experimental acoustic characterization, it is observed that FSP can introduce clear acoustic–elastic property contrast on an aluminum plate by the presence of stir zone and heat‐affected zones. In numerical simulations, the signature FSP‐induced property profile is periodically and parallelly arranged on a long aluminum plate. The transmission gap frequencies are present on the frequency spectrum with the sound propagation direction perpendicular to the FSP paths. Disorder offsets on FSP periodicity are further introduced. Anderson localization is found on a resonance frequency, which provides −11 dB sound reduction by an exponential decay. Due to the finite design length, the slight disorder can also enhance sound insulation in the periodic transmission gap frequency. With analysis and comparison with different configurations, the best performance in the models can achieve −30 dB sound insulation in the 350 mm‐long aluminum alloy plate with 14 parallel FSPs. [ABSTRACT FROM AUTHOR]

The sound insulation of the façade and its elements is a very important characteristic, as it largely determines the degree of sound protection of the building's interior from external noise sources. This feature, therefore, has a great influence on the acoustic comfort and health of the occupants. For this reason, it is very important that the way in which the sound insulation of the façade is quantified and represented corresponds to the way it is perceived. Although there have long been regulations describing how it should be measured and expressed through Single-Number Quantities (SNQs), there is much scientific debate about the appropriateness of current standardised methods for expressing sound insulation, in terms of whether they accurately represent human-perceived comfort. In this regard, much of the debate centres on the frequency range to be considered when expressing sound insulation, with no consensus as to whether the low-frequency bands (i.e., 50, 63, and 80 Hz) should be used for the calculation of façade sound insulation SNQs. In order to contribute to this knowledge, we conducted a listening test using a Two-Alternative Choice (2-AC) protocol on a sample of 100 participants to test whether participants' annoyance with urban noise changed significantly with variations in window sound insulation only in the low-frequency range. The results of the experiment, analysed using Thurstonian models, showed that the influence of low frequencies is limited for the sound insulation of the tested window façade elements and urban-type noise of aircraft and mixed urban traffic at low speeds and only becomes relevant when the sound insulation of the elements is exceptionally low in the low-frequency range. [ABSTRACT FROM AUTHOR]

The airborne sound insulation performance of finite sandwich panels is often significantly worsened by resonant transmission components in low and middle frequencies. In this paper, damping contribution of viscoelastic core on sound transmission loss (STL) of finite constrained layer damping (CLD) panels is studied in narrow frequency bands. A fully coupled layer-wise approach is used with a generalized high-order shear deformation hypothesis that accounts for all types of deformations in the core. The influence of several parameters is investigated extensively. Results show that the adverse impact of the first-three odd-odd order modes, namely (1,1), (3,1), and (1,3) modes, as well as some higher-order modes on STL cannot be disregarded. The constrained viscoelastic core plays a crucial role in enhancing, or even eliminating, dips of STL spectrum at resonant frequencies. Additionally, it can considerably counterbalance a relatively broadband reduction of STL caused by the inter-modal coupling in middle frequencies. The damping mechanism can be divided into two aspects: (i) the reduction of modal amplitude by vibration energy dissipation, and (ii) the change of bending modal shapes. CLD treatment is a concise and effective way to achieve stable sound insulation performance. [ABSTRACT FROM AUTHOR]

In this study, a design method of broadband low-frequency muffler based on NN method and Helmholtz resonators with helical necks is proposed, which ensures almost perfect ventilation and broadband sound insulation in the low- and medium-frequency range. First, the sound insulation performance of the muffler is improved by adding a helical structure at the port. The slit Helmholtz resonator with a helical structure is able to reduce the cross-sectional area of the resonator port and increase the contact area of thermal viscosity loss, thus reducing the peak frequency of sound insulation and increasing the sound energy loss. Using finite element analysis software, the structural transmission loss is simulated. At the same time, the neural network method is used to predict the combined structure, then, the combined structure can be designed quickly and reasonably to achieve the sound insulation of medium- and low-frequency broadband. Experimental and simulation results show that in the target range of 430 Hz–2220 Hz, the overall TL exceeds 30 dB and the maximum exceeds 60 dB. In addition, when a helical structure is added, the overall pipeline remains unchanged; and when a muffler is added on the basis, the perfect ventilation effect can be achieved. The proposed structural model and the idea of rapid design lay a great foundation for the design and optimization of broadband muffler. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical model to study sound transmission through a micro-perforated double-walled sandwich cylindrical shell with emphasis on the potential of internal gap flow to improve the sound insulation performance. This model adopts Donnell's thin shell theory to govern the shell motions and a simplified model based on Biot's theory to describe sound propagation in the porous lining. The mean acoustic particle velocity model with the grazing flow effect is applied to define the coupling condition between the fluid medium and the perforated shell. Transmission loss (TL) through the configuration with one gap flow is numerically calculated using the mode superposition method when subjected to an oblique plane wave in the presence of an external mean flow. Results reveal that the gap flow in the opposite direction to the external flow would elevate the mid-frequency TL. Gap depth has a complicated effect on TL since it influences the aerodynamic damping of the gap flow and sound dissipation in the porous layer. The average TL in 20–20 000 Hz is then optimized with a genetic algorithm, and an increase of 17.82 dB is finally achieved. The possibility of tuning the structural sound insulation performance by the gap flow has been verified. [ABSTRACT FROM AUTHOR]

Due to the influence of mass law, traditional lightweight sandwich structures have struggled to surpass solid structures in sound insulation performance. To this end, we propose an acoustic metamaterial structure with a sandwich configuration based on the re-entrant negative Poisson's ratio (NPR) structure and systematically investigate its sound transmission loss (STL) performance under incident plane wave conditions. We used the acoustic impedance tube method to experimentally study the sound insulation performance of the re-entrant NPR sandwich structure under free boundary conditions, and then established an acoustic analysis simulation model based on COMSOL Multiphysics software, which verified that the results obtained by the experiment and the numerical simulation were in good agreement. The results show that the sandwich structure exhibits excellent sound transmission loss performance in the studied frequency range (250–4000 Hz), and the overall sound insulation performance exceeds the curve of the mass theorem, basically achieving more than 20 dB when the sandwich thickness is 2 cm. Finally, we conduct parametric studies to establish a correlation between the geometric design of NPR sandwich structures and their sound transmission loss performance. The research shows that the changes of the length of the ribs, the distance from the ribs to the center of the unit, and the length of the upper wall and the lower wall have a significant impact on the sound insulation performance of the re-entrant NPR sandwich structure, while the change of the wall thickness basically will not affect the sound insulation performance of the sandwich structure. This research can provide practical ideas for the engineering application of noise suppression designs of lightweight structures. [ABSTRACT FROM AUTHOR]

Light-duty vehicles are increasingly incorporating plastic materials to reduce production costs and achieve lightweight designs. On average, a conventional car utilizes over 200 kg of plastic, comprising more than 23 different types, which often present challenges for recycling due to their incompatibility. Consequently, the focus on plastic recycling in end-of-life vehicles has intensified. This study aims to analyze critical car parts based on the plastics used, employing a novel thermodynamic approach that examines the embodied exergy (EE) of different plastics. Six vehicles from various segments, years, and equipment levels were assessed to understand their plastic compositions. The findings reveal that, on average, a vehicle contains 222 kg of plastic, accounting for 17.7% of its total weight. Among these plastics, 47.5% (105 kg) are utilized in car parts weighing over 1 kg, with plastics comprising over 80% of the part's weight. The identified critical car parts include the front door trim panel, front and rear covers, fuel tank, floor covering, front lighting, dashboard, rear door trim panel, plastic front end, backrest pad, door trim panel pocket, plastic foam rear seat, rear lighting, window guide, molded headliner, bulkhead sound insulation, foam seat part, and wheel trim. Regarding their contribution to EE, the plastics with the highest shares are polypropylene—PP (24.5%), polypropylene and ethylene blends—E/P (20.3%), and polyurethane- PU (15.3%). Understanding the criticality of these car parts and their associated plastics enables targeted efforts in design, material selection, and end-of-life management to enhance recycling and promote circularity within the automotive industry. [ABSTRACT FROM AUTHOR]

This paper describes a method to construct a movable virtual sound source (VSS) from a linear array of parametric loudspeakers. In the proposed method, wave field synthesis is used to construct a focused VSS at any position in air without moving the loudspeakers. The motion of the VSS can be realized by constructing VSSs successively along the moving path. Parametric loudspeakers realize a sharp directivity by exploiting the straightness of ultrasound; therefore, a VSS constructed by the proposed method is expected to be easy to perceive. Compared with a VSS constructed from conventional electro-dynamic loudspeakers, the proposed method can achieve a higher precision when the VSS is moving parallel to the loudspeaker array. [ABSTRACT FROM AUTHOR]

Copyright of Materiały Budowlane is the property of Wydawnictwo SIGMA-NOT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The bulk density of AAC determines many of its properties like compressive strength, thermal conductivity, sound insulation, and so on. It is described by the solid mass divided by the volume. The volume again is determined by the volume of the slurry in the mixer plus the rising volume. The rising volume is mainly caused by the hydrogen generation of the aluminum reaction. In practice, the rising volume is controlled by dosing of the aluminum, based on experience. This article shows that the rising volume cannot be calculated resp. controlled by the aluminum reaction only. Other influence parameters like casting temperature, final temperature and air pressure must be considered. The magnitude of this influence parameters is described, and some practical consequences are shown. [ABSTRACT FROM AUTHOR]

Due to the low density and stiffness of wood, traditional timber floor systems are prone to producing large vibration responses. By combining timber beams with concrete floors, timber–concrete composite (TCC) floor systems show stronger bearing capacity, higher bending stiffness, and better thermal and sound insulation behaviors when compared with traditional timber floor systems. In this study, the vibration performance of TCC beams with crossed inclined coach screw connectors was investigated using dynamic tests. The influence of the screw diameters and slab dimensions on the dynamic performance of the composite beams was evaluated. The test results demonstrated that TCC beams show good dynamic performance when used as a floor component and meet the preliminary requirements of floor vibration comfort for fundamental frequency. The fundamental frequency and damping ratio of TCC beams decreases with the increase in slab dimensions. The bending stiffness and natural frequency of TCC beams decrease smoothly when reducing the screw diameter from 16 to 12 mm. Additionally, two theoretical models were used to predict the natural frequencies of the TCC beams, and the predicted values show good consistency with the measured ones. [ABSTRACT FROM AUTHOR]

This study used ethylene‐propylene diene monomers (EPDM), an elastomer, to develop foams incorporating clay as filler using simple compounding, chemical foaming, and peroxide‐mediated light crosslinking methods. The low‐temperature batch mixer was employed for compounding azodicarbonamide (ADC) as a foaming agent, dicumyl peroxide (DCP) as a crosslinker, followed by compression molding for sheet preparation and the high‐temperature foaming process. Fourier transform infrared spectroscopy (FTIR) equipped with a hot stage attenuated total reflection (ATR) was employed to elucidate the ADC decomposition and foaming. The DCP (0.25 phr) content was optimized based on the foaming expansion ratio (>4) and stability, which was further optimized in conjuncture with clay to generate high‐performance composite foams. The incorporation of 1% organoclay enhances the expansion ratio and specific tensile strength by >7 and ~ 270%, respectively, compared with EPDM foams without clay while displaying a density of 0.11 g/cm3. Overall, the developed foaming process can be extended to other elastomeric polymers for various applications such as protective gears (e.g., helmets and shin guards), thermal/sound insulation, packaging/containment, footwear soles, oil absorption, etc. [ABSTRACT FROM AUTHOR]

Porous materials and metamaterials play a key role in sound absorbing and insulation solutions in acoustics. With the growing interest in additive manufacturing techniques, recent work has focused on the printing of porous and resonant structures for acoustic purposes. Usual metaporous surfaces/interfaces are generally built by periodically inserting resonant elements in an existing porous layer. This complex manufacturing process can be significantly simplified by using additive manufacturing techniques, which also eases the design and optimization of the metaporous surface. In this work, the acoustic properties of the metaporous surface are controlled by simple geometric parameters defining both the anisotropic porous layer and the shapes of the resonators. Hence, we focus on optimizing split-ring resonators embedded in a micro-treillis porous layer, which are built in a single part using additive manufacturing techniques. A finite-element method together with Bloch wave decomposition provides a numerical model used to predict the reflection and absorption coefficients under normal incidence. The geometric parameters of the anisotropic metaporous surface are then optimized by non-linear minimization techniques to maximize acoustic absorption. An optimal metaporous surface is 3D printed by fused-deposition modeling, and its acoustic properties are measured in an impedance tube. The measurements are in good agreement with the predicted optimal broadband absorption coefficient. This work demonstrates the benefits of additive manufacturing for designing metaporous acoustic surfaces. [ABSTRACT FROM AUTHOR]

A novel practical design of sheet-like acoustic metamaterials is described, which comprise a two-dimensional array of mutually connected cylindrical stubs with embedded metallic weights that can be processed with a simple integral molding. We investigate the elastic wave band dispersion of the acoustic metamaterial sheets to design the connected structure of the stubs so that each stub can work as spring–mass local resonators to open the out-of-plane acoustic bandgaps. For properly integrated materials, remarkable noise insulation performance over the mass law at the resonant frequencies is experimentally demonstrated. The sound insulation mechanism is numerically analyzed in association with the sound fields, the vibrational fields, and the dynamic effective mass using the finite element method by coupling the structures with acoustics. Furthermore, we show that the insulation frequency is tunable over a wide range of frequency by designing the physical and structural parameters of the resonator. The practically designed acoustic metamaterial sheets will pave the way for industrial use of acoustic metamaterials as advanced lightweight and compact sound insulators that can be tailored to meet individual needs on problems related to noise. [ABSTRACT FROM AUTHOR]

Soundproofing ventilation devices can block sound while allowing free airflow simultaneously, which have many important applications in daily lives. In this work, we theoretically design and experimentally implement a broadband low-frequency acoustic meta-window. The meta-window is composed of a central rectangular open area and 12 surrounding identical channels. The total ventilation area is 220 cm2. Interestingly, with a deep subwavelength thickness of 4 cm, such a meta-window can exhibit a large acoustic bandgap, leading to the effective blocking of more than 90% of the incident sound energy in the broad range of 605–1050 Hz. By cascading such acoustic devices, the sound blocking effect can be further improved. Our work realizes a large-area and ultrathin ventilative meta-window with the function of broadband low-frequency acoustic insulation. [ABSTRACT FROM AUTHOR]

Acoustic ventilation barriers (AVBs) constructed from metamaterials can effectively insulate sound waves while maintaining airflow, but previous schemes suffer from complex geometric structures. Here, we propose a reconfigurable AVB with subwavelength thickness (0.15λ), which is composed of simple zigzag structures with regular intervals and can be assembled into a full enclosure with an arbitrary shape. It is the interaction between the scattered wave of the zigzag structure and the un-scattered wave through the air channel that leads to a transmission dip and hence a sound insulation. Numerical simulations and experimental demonstrations consistently verify that the AVB possesses excellent omnidirectional sound insulation, while the width of the air channel can reach three times the unit width. As the number of cavity increases, the acoustic insulation bandwidth is broadened from 0.875/λ to 2.75/λ. As an example, a circle AVB is further demonstrated to shield acoustic waves emitting from either the interior or exterior. Experimental measurements indicate that the average sound transmission losses can reach roughly 19 dB and 15 dB, respectively. We believe that the proposed AVB may find potential applications in architectural acoustics, room acoustics, and duct noise control. [ABSTRACT FROM AUTHOR]

This study details the synthesis and performance evaluation of a novel lightweight thermal and acoustic insulation material, resulting from the combination of a scleroglucan-based hydrogel and recycled rigid polyurethane waste powder. Through a sublimation-driven water-removal process, a porous three-dimensional network structure is formed, showcasing notable thermal and acoustic insulation properties. Experimental data are presented to highlight the material’s performance, including comparisons with commercially available mineral wool and polymeric foams. This material versatility is demonstrated through tunable mechanical, thermal and acoustic characteristics, achieved by strategically adjusting the concentration of the biopolymer and additives. This adaptability positions the material as a promising candidate for different insulation applications. Addressing environmental concerns related to rigid polyurethane waste disposal, the study contributes to the circular economy.

This document is an editorial published in Frontiers in Materials, discussing the topic of acoustic and mechanical metamaterials for various applications. Metamaterials are artificial microstructures designed from natural materials that possess extraordinary physical and mechanical properties. They have important application value in fields such as aviation, aerospace, ships, automobiles, and architecture. The editorial highlights the achievements and challenges in the engineering applications of metamaterials, particularly in sound absorption, vibration attenuation, and isolation of seismic waves. The document also mentions the inclusion of seven papers in Volume II, covering topics such as bionic metamaterials, tunable acoustic metasurfaces, and ultrasonic damage localization. Overall, the editorial provides an overview of the current state and potential of acoustic and mechanical metamaterials in various industries. [Extracted from the article]

Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight building material that gained popularity from the 1950s to the mid-1990s. It offers thermal and sound insulation, but is weaker than traditional concrete due to the presence of air voids. This weakness makes RAAC more susceptible to damage from water ingress, freeze-thaw cycles, corrosion, overloading, and structural defects. Poor design, construction practices, and neglecting maintenance can also contribute to RAAC failures. The UK government has recently taken steps to address concerns about the safety of RAAC roofs in schools, but some critics argue that more needs to be done to protect people from the risk of collapse. [Extracted from the article]

Phononic crystals are a kind of artificial acoustic metamaterial whose mass density and elastic modulus are periodically arranged. The precise and efficient design of phononic crystals with specific bandgap characteristics has attracted increasing attention in past decades. In this paper, an improved adaptive genetic algorithm is proposed for the reverse customization of two-dimensional phononic crystals designed to maximize the relative bandwidth at low frequencies. The energy band dispersion relation and transmission loss of the optimal structure are calculated by the finite-element method, and the effective wave-attenuation effect in the bandgap range is verified. This provides a solution for the custom-made design of acoustic metamaterials with excellent low-frequency bandgap sound insulation or other engineering applications. [ABSTRACT FROM AUTHOR]

Corrugated structures are widely being used in industrial applications, which raises the demand for careful analysis of their behavior. To fill the gap for vibroacoustic characteristics, this paper focuses on proposing a model to investigate sound transmission through double-walled cylindrical shells with a circumferentially corrugated core. The structure is composed of outer and inner isotropic layers and a corrugated core. The outer layer is subjected to an oblige plane wave, and also a subsonic flow is traveling outside the double-walled shell. An equivalent method is applied to replace the corrugated core as axial, radial, and rotational springs with specific stiffness coefficients. The first-order shear deformation theory (FSDT) is applied to describe the behavior of isotropic shells. A considerable parametric study is established concerning both the incident wave and structural characteristics. The results show that the presence of the corrugated core improves sound transmission loss (STL) of the structure in the mass-controlled region, and it has a negative effect on STL in the coincidence-controlled region; therefore, using such a core for sound insulation depends on the desired frequency domain. [ABSTRACT FROM AUTHOR]

Various interior non–metal materials contained in the automobiles, mainly such as textiles, synthetic textiles, leather, synthetic leather and foam– based materials, are suitable for the production of sound and thermal insulation products. The presented contribution deals with the proposal of reusing and recycling of these components for the utilization of these non–metal materials for the production of new products, which, due to their sound and thermal insulation properties, will be widely applicable in various fields of industry as civil engineering, transport. [ABSTRACT FROM AUTHOR]

The new draft DEGA Guideline 103‐1: Sound insulation in residential buildings – Sound insulation classes and increased sound insulation This paper presents the draft of DEGA‐Richtlinie 103‐1 : 2023‐05 "Schallschutz im Wohnungsbau Teil 1: Schallschutzklassen und erhöhter Schallschutz" [1]. This draft is based on DEGA recommendation 103 version 2018. Comments to this draft can be sent to DEGA until 09. 10. 2023. Part 1 presented here deals with the sound insulation classes with the associated requirements. Part 2, which is to be prepared, will then deal with the sound insulation certificate. The draft continues the concept of the seven sound insulation classes from DEGA recommendation 103. The main change is the introduction of a parallel concept of building component‐related and room‐related single number values (SNV) for sound insulation. With regard to the subjective perception of noise, the use of room‐related SNV (DnT,w, L'nT,w and LAF,max,nT) is recommended. The classification is carried out on the basis of these SNV, but can also be carried out with the help of the usual SNV for the sound insulation of building components (R'w, L'n,w). The currently discussed changes in the planned revision of the DIN 4109 series were taken into account. [ABSTRACT FROM AUTHOR]

Elastic materials can be used to improve the impact sound insulation performance of the floating floor. In this study, the foam rubber damping pad and polyurethane foam board were used to improve the sound insulation performance in floating floors; the main performance parameters such as thickness, dynamic stiffness, resonance frequency and damping ratio of the foam rubber damping pad and the polyurethane foam board were tested and analyzed under different loading systems. Besides, a reinforced concrete residential compartment was used as experimental background, the foam rubber damping pad and polyurethane foam board were used as elastic damping materials to form the different structures of floating floors with different thicknesses; then the impact sound pressure level and its variation rule were tested under different conditions, and the influence of the reduction of impact sound pressure level on the floating floor was compared and analyzed. The results show that before the pavement, the thickness of the polyurethane foam board is 2 times the thickness of the foam rubber damping pad in the natural state; After pavement, under the action of the load, the thickness of the polyurethane foam board is 1.39–1.42 times that of the foam rubber damping pad. The sound insulation and damping performance of the polyurethane foam board are lower than that of the foam rubber damping pad. When the thickness of the floating plate is increased from 32 to 80 mm, the sound insulation performance of the floating floor structure made of polyurethane foam board and foam rubber damping pad has a deterioration tendency. This study provides a basic reference for the sound insulation of floating floors with the foam rubber damping pad or polyurethane foam board as the elastic damping cushion. Highlights: Under load, the cumulative thickness of polyurethane foam plate reached about 35% of its total thickness at 2 days. After 8–10 days, it tended to be stable, with a total deformation of about 45%. For the floating building sound insulation floor system made of foam rubber damping pad, the frequency varies from 69.8–145.3 Hz, the reduction of impact sound pressure level is 18.7–23.6 dB, the change of frequency is 51%, and the reduction range of impact sound pressure level is 27%; The floating floor of polyurethane foam board has a frequency change of 137.7–254.8 Hz, the reduction of impact sound pressure level is 11.1–17.3 dB, the frequency change is 46%, and the reduction range of impact sound insulation is 35%. The thickness of the polyurethane foam board is about 1 times the thickness of the foam rubber damping pad, but its sound insulation and vibration absorption performance is low. It can be seen that the insulation board used as sound insulation board, its sound insulation and vibration reduction performance can not achieve the expected effect. [ABSTRACT FROM AUTHOR]

Aiming at the insulation of low-frequency acoustic sound, a 100 mm crescent disc asymmetric membrane-type acoustic metamaterial structure was designed in this paper, which was composed of aluminum material as the frame and iron material as the mass attached to the surface of flexible ethylene-vinyl acetate copolymer film. The finite element method was adopted to calculate its transmission loss and displacement field. The asymmetric structure, the structure parameters and the mass block's eccentricity together with the vibrational modes analysis were investigated in this study for a better sound insulation performance. The results show that, compared with the symmetric membrane-type acoustic metamaterials, the design of the asymmetry in a single cell makes the low-frequency sound insulation band widened by 23 Hz. Meanwhile, more vibrational modes are generated which illustrates that the coexistence of Lorentz resonance and Fano resonance promotes a better sound insulation performance of the crescent disc asymmetric structure. The large-size asymmetric membrane-type acoustic metamaterial structure designed in this paper can reduce the sound insulation frequency to 10 Hz with a wide low-frequency sound insulation performance within 10 ~ 500 Hz. It provides a new method for improving the low-frequency sound insulation effect of sound barriers in terms of structural optimization design. [ABSTRACT FROM AUTHOR]

A new two-dimensional phonon crystal structure was designed and studied deeply by finite element method and equivalent model method. It is found that the structure has good low-frequency sound absorption performance. Through theoretical derivation and simulation calculation, it is found that the structure has a complete four band gap within 0 ~ 800 Hz under the condition of lattice constant of 21 mm. The lower limit of the first band gap is as low as 40. 28 Hz, and the bandwidth is approximately 93 Hz. Sound transmission loss calculation shows that the structure has a good acoustic insulation effect in the low frequency domain, and the maximum sound insulation amount can reach 87. 31 dB. After analyzing the multiple vibration modes of the structure, the corresponding equivalent model is established, and the influence of different factors on the band gap is explored based on the equivalent model. The general regularities of the new two-dimensional phonon crystal are summarized. The results show that increasing the scatterer density and reducing the matrix density can increase the bandwidth, and increasing the filling rate and properly opening the scatterer can improve the band gap characteristics. The research may provide some ideas for solving low-frequency noise control problems in engineering application. [ABSTRACT FROM AUTHOR]

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Materiały Budowlane is the property of Wydawnictwo SIGMA-NOT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The EN 1793-5 and EN 1793-6 standards have been in use for many years as a method for measuring the intrinsic characteristics of noise barriers installed along highways and railways. They require a sound source and a grid of microphones, to be placed near the barrier and in free field conditions, according to predetermined distances. In principle, small errors in positioning the sound source and microphone grid may affect the results obtained. An international round-robin test was carried out in 2012 to evaluate the repeatability and reproducibility of the method, but until now no studies have been carried out to evaluate and compare the repeatability of laboratory versus in-place measurements performed with the same equipment and its variance when an imperfect positioning of sound source and microphones is taken into account. In the present work, multiple series of sound reflection index and sound insulation index measurements performed on noise barriers of the same kind installed in the laboratory or along a highway are presented. The measurements were repeated in different ways: (1) in the laboratory, leaving the source and microphones unmoved to assess the repeatability of the results and of the measurement system under controlled conditions; (2) in the laboratory, repositioning for each measurement the source and microphone grid to assess the robustness of the method under real conditions but in a controlled environment; (3) in situ, along a highway open to traffic, repositioning for each measurement the source and microphone grid to assess the repeatability of the method under real conditions in a critical environment. In both reflection index and sound insulation index measurements, the standard deviation on single-number ratings in all cases examined is well below the value presented in EN 1793-5 and EN 1793-6, which was obtained from statistical analysis of the international round-robin test performed a dozen years ago, suggesting that expert operators with state-of-the art equipment can achieve much better results now. [ABSTRACT FROM AUTHOR]

The acoustic performance of a CLT-based building mockup was investigated within the scope of the ADIVBois acoustic technical commission with the objective of defining wood building constructions fulfilling requirements. The CLT-based building is a three-floor construction with four rooms on each level. Measurements from junction characterization to airborne and impact sound insulations were taken. The implemented floor systems were first tested in a laboratory to evaluate their acoustic performance. Predictions based on the EN ISO 12354-1 and -2 standards were compared to building acoustic measurements. The effect of using the tapping machine and the rubber ball as impact sources was investigated both in laboratory and in the CLT-based building mockup. The effect of the apparent post between rooms is also presented with an associated simple approach to take it into account in predictions. This paper summarizes the obtained results. [ABSTRACT FROM AUTHOR]

Extreme impedance mismatch causes sound insulation at water–air interfaces, limiting numerous cross‐media applications such as ocean‐air wireless acoustic communication. Although quarter‐wave impedance transformers can improve transmission, they are not readily available for acoustics and are restricted by the fixed phase shift at full transmission. Here, this limitation is broken through impedance‐matched hybrid metasurfaces assisted by topology optimization. Sound transmission enhancement and phase modulation across the water–air interface are achieved independently. Compared to the bare water–air interface, it is experimentally observed that the average transmitted amplitude through an impedance‐matched metasurface at the peak frequency is enhanced by ≈25.9 dB, close to the limit of the perfect transmission 30 dB. And nearly 42 dB amplitude enhancement is measured by the hybrid metasurfaces with axial focusing function. Various customized vortex beams are experimentally realized to promote applications in ocean‐air communication. The physical mechanisms of sound transmission enhancement for broadband and wide‐angle incidences are revealed. The proposed concept has potential applications in efficient transmission and free communication across dissimilar media. [ABSTRACT FROM AUTHOR]

Acoustic materials embed with inorganic fillers in viscoelastic polymers have promising applications in industrial settings. However, optimizing the sound insulation of composites by adjusting the microstructure of nanofillers remains a challenge. In this study, we synthesize adjustable hollow hierarchical Zeolite Socony Mobil #5 (ZSM‐5) which can be used as nanofillers in a sound insulation nanocomposite based on the polyacrylate (PA). The results show that the nanocomposites with 0.5 wt% hierarchical hollow ZSM‐5 can increase the sound transmission loss (STL) by 33.4%. The maximum STL value reaches as high as 40 dB. The damping properties of the nanocomposites were also improved by adding ZSM‐5 into the PA matrix. When the loading of hollow ZSM‐5 is 0.5 wt%, the storage modulus increased by 44%, as high as 4486.7 MPa. This strategy opens up a promising way for the sound insulation of composites based on controllable inorganic nanofillers. [ABSTRACT FROM AUTHOR]

To meet objectives such as the sound insulation characteristics of timber structures and the comfort of residents, this study assessed an ordinary floor and three kinds of floating floors (Portuguese cork, graphite polystyrene sound insulation boards and expanded polypropylene plastic foam boards) in the same bedroom of a two-storey light wooden building. Adopting standard white noise and music noise excitation, structural design, theoretical checks and sound insulation tests of the floors were conducted. For the four floor structures, the sound insulation volume, sound pressure distribution characteristic spectrum of the building floor under different noise source environments, the frequency characteristics of the noise source, the multiple relationship of the sound insulation sound pressure level and the sound insulation mechanism were analysed. It was found that the sound pressure multiple of the space separating the upper and lower floors of the building was 8–18 times greater than that of the light wooden floor structure. The airborne sound insulation volume–frequency curves of the four floors, calculated by the transfer matrix method, were consistent with the actual measured values. The sound insulation effect was better in the low and middle frequencies. [ABSTRACT FROM AUTHOR]

The article discusses the outcomes of the 51st Winter School on Wave and Quantum Acoustics and the Lth Winter School on Environmental Acoustics and Vibroacoustics, which took place in Szczyrk, Poland, from February 27 to March 3, 2023. Topics discussed include structural active noise control algorithms, the thermal properties of ionanofluids with functionalized carbon nanotubes, and innovative solutions for protecting against rail traffic noise.

Sound insulation of the finite double-panel structure (DPS) inserted with a cylindrical shell array is investigated by varying the sound incidence direction to improve its applicability. The effects of the vibro-acoustic characteristics of its constituents on the sound transmission loss (STL) are estimated in one-third octave bands from 20 Hz to 5 kHz for different incidence conditions. It shows that the first acoustic mode in the direction parallel to two panels (longitudinal modes) produces both the sudden variation of sound insulation with frequency and a large dependency on the incidence angle. Mineral wools are placed on two boundaries perpendicular to the panels, and the sound insulation is explored for different thicknesses of the porous materials. An absorbent layer with a certain thickness (more than 30 mm in our work) sufficiently eliminates the longitudinal mode, resulting in the improvement in the sound insulation by more than 15 dB and the decrease of its large variation with incidence direction. STLs with varying shell thicknesses are also assessed. It shows that the natural vibrations of the thin shells can give an enhancement in sound insulation by more than 10 dB in the frequency range of 1600-3700 Hz, corresponding to constructive interference. [ABSTRACT FROM AUTHOR]

Due to the dynamic and acoustic characteristics of functionally graded microplates in micro- and nano-electro-mechanical systems, this paper established the vibro-acoustic governing equation of functionally graded (FG) sandwich microplates, which contains one material length scale parameter. Two types of FG sandwich microplates are studied, and the effects of different parameters on the vibro-acoustic characteristics are discussed. The results show that the size effect is significant when the thickness of microplate is close to the material length scale, especially at the higher order mode and for the thicker plate. Moreover, the sound insulation performance with the size effect increasing becomes better. [ABSTRACT FROM AUTHOR]

Purpose: Maintaining static balance is a process coordinated by central integration of visual, vestibular and somatosensory information. Whether or not hearing and spatial acoustic information contributes to the maintenance of static postural balance is unclear. Methods: A prospective observational pilot study was performed. Twenty-five normal hearing adults (68% female; 19–31 years) underwent a computerized dynamic posturography test battery including the Sensory Organization Test (SOT), the Motor Control Test (MCT), and the Adaptation Test (ADT). The balance tests were performed two times, in a randomized sequence without or with acute hearing loss. Earplugs (sound insulation 37 dB) or headphones with white noise (sound volume 75 dB) induced the conductive hearing loss. Hence, all participants passed through four sequences of the balance test battery. A repeated-measures analysis of variance (ANOVA) was used to analyze the results. Results: The ANOVA revealed no difference for any SOT and ADT subtest without hearing loss and simulated hearing loss (either earplugs or headphones; all p > 0.05). The ANOVA showed no longer latencies with simulated hearing loss compared to no hearing loss in both experiments with one exception: the reaction of the right foot during large forward translation was longer with hearing loss than without hearing loss in both experiments (p = 0.025). Conclusions: Overall, a simulated acute conductive bilateral moderate or severe hearing loss did not disturb the static balance function in normal hearing younger adults in this first small pilot study. [ABSTRACT FROM AUTHOR]

In response to the demand for high sensitivity and stability during respiratory dust detection, photoacoustic spectroscopy is proposed for real-time monitoring of respiratory dust. The influence of the background noise generated by the inlet flow and the small suction pump on the experiment was analyzed, and noise reduction was carried out by physical methods such as adding a sound insulation layer to the small suction pump, as well as the Kalman filtering method was added to the LabVIEW software to further reduce the influence of noise. To carry out the detection of respirable dust in the ambient atmosphere. The detection under 0.2 μm filter membrane can filter out the effect of environmental dust, and the collection efficiency of 5 μm diameter dust is 50%; therefore, 5 and 0.2 μm filter membranes were added at the air inlet for respiratory dust detection, and two groups of experiments were carried out by using 5 and 0.2 μm filter membranes to obtain the change curve of the respiratory dust by the differential method. Through experimental validation, it is shown that the detection system can further improve the detection accuracy and stability of respiratory dust with the processing of physical noise reduction and Kalman filtering and can meet the monitoring of respiratory dust in the environmental atmosphere. [ABSTRACT FROM AUTHOR]

Ceramic nanofibrous aerogels have attracted great interest because of their extraordinary multifunctional properties. Herein, a facile strategy was proposed to create SiO 2 nanofibers-BN nanoribbons assembled binary aerogel with excellent temperature-invariant super-flexibility, as well as low thermal conductivity, low infrared radiation and excellent sound absorption properties. In addition, the unique structure of the nanofibers-nanoribbon aerogel acts as the thermal insulation layer, combined with Al foil acting as an infrared reflection layer, forming a component that can effectively hide high infrared targets. The nanofibrous-nanoribbons binary aerogel possess low thermal conductivity (0.0288 W/(m⋅K)) and outstanding sound-absorption ability (NRC value of 0.43), as well as excellent infrared stealth ability, which makes it an ideal candidate for thermal insulation and sound absorption in multi fields. [ABSTRACT FROM AUTHOR]

In order to achieve a balance between sound insulation and ventilation, a novel acoustic metamaterial of air-permeable multiple-parallel-connection folding chambers was proposed in this study that was based on Fano-like interference, and its sound-insulation performance was investigated through acoustic finite element simulation. Each layer of the multiple-parallel-connection folding chambers consisted of a square front panel with many apertures and a corresponding chamber with many cavities, which were able to extend both in the thickness direction and in the plane direction. Parametric analysis was conducted for the number of layers nl and turns nt, the thickness of each layer L2, the inner side lengths of the helical chamber a1, and the interval s among the various cavities. With the parameters of nl = 10, nt = 1, L2 = 10 mm, a1 = 28 mm, and s = 1 mm, there were 21 sound-transmission-loss peaks in the frequency range 200–1600 Hz, and the sound-transmission loss reached 26.05 dB, 26.85 dB, 27.03 dB, and 33.6 dB at the low frequencies 468 Hz, 525 Hz, 560 Hz, and 580 Hz, respectively. Meanwhile, the corresponding open area for air passage reached 55.18%, which yielded a capacity for both efficient ventilation and high selective-sound-insulation performance. [ABSTRACT FROM AUTHOR]

Bio-based composites are increasingly used. One of the most frequently used materials is hemp shives, which is agricultural waste. However, as the quantities of this material are lacking, there is a tendency towards finding new and more available materials. Corncob and sawdust are bio by-products that have great potential as insulation materials. In order to use these aggregates, it is necessary to examine their characteristics. New composite materials based on sawdust, corncobs, styrofoam granules, and the mixture of lime and gypsum as the binder were tested in this research. This paper presents the properties of these composites obtained by determining the porosity of samples, volume mass, water absorption, airflow resistance and heat flux, which was followed by the calculation of the thermal conductivity coefficient. Three of the new biocomposite materials, whose samples were 1–5 cm thick for each type of mixture, were investigated. The aim of this research was to analyze the results of different mixtures and sample thicknesses in order to determine the optimum composite material of the proper thickness so that the best possible thermal and sound insulation could be obtained. Based on the conducted analyses, the biocomposite with a thickness of 5 cm, composed of ground corncobs, styrofoam, lime, and gypsum, proved to be the best in terms of thermal and sound insulation. New composite materials can be used as an alternative to conventional materials. [ABSTRACT FROM AUTHOR]

Polyimide foam (PIF) is a rising star in high-end applications such as aerospace thermal insulation and military sound absorption. However, the basic rule on molecular backbone design and uniform pore formation of PIF still need to be explored. In this work, polyester ammonium salt (PEAS) precursor powders are synthesized between alcoholysis ester of 3, 3′, 4, 4′-benzophenone tetracarboxylic dianhydride (BTDE) and aromatic diamines with different chain flexibility and conformation symmetry. Then, a standard "stepwise heating" thermo-foaming approach is used to prepare PIF with comprehensive properties. A rational thermo-foaming program is designed based on in situ observation of pore formation during heating. The fabricated PIFs have uniform pore structure, and PIFBTDA-PDA shows the smallest size (147 μm) and narrow distribution. Interestingly, PIFBTDA-PDA also presents a balanced strain recovery rate (SR = 91%) and mechanical robustness (0.051 MPa at 25% strain) and its pore structure maintains regularity after 10 compression–recovery cycles, mainly due to high rigidity of the chains. Furthermore, all the PIFs possess lightweight feature (15–20 kg∙m−3), good heat resistance (Tg at 270–340 °C), thermal stability (T5% at 480–530 °C), thermal insulation properties (λ = 0.046–0.053 W∙m−1K−1 at 20 °C, λ = 0.078–0.089 W∙m−1K−1 at 200 °C), and excellent flame retardancy (LOI > 40%). The reported monomer-mediated pore-structure control strategy can provide guidelines for the preparation of high-performance PIF and its industrial applications. [ABSTRACT FROM AUTHOR]

This study examines a lightweight thermal and acoustic insulation material, produced starting from a hydrogel‐based mixture composed by renewable biopolymer and fiberglass waste powders. The gel 3D porous network is preserved after water removal by sublimation, resulting in a lightweight thermal and acoustic insulation material with good overall performance. Mechanical, thermal, and acoustic properties can be tuned as a function of biopolymer and additives concentration. This material addresses environmental concerns both in terms of secondary raw sources use and fiberglass waste disposal. Moreover, contrary to mineral wools currently on the market, it can overcome the problem of fiber release, with significant human health benefits. Thanks to its good properties and its fabrication process based on a circular economy approach, it can be appealing for thermal and acoustic insulating applications in building and industrial sectors and also in terms of environmental footprint. [ABSTRACT FROM AUTHOR]

Low-frequency interior noise tends to tire passengers and affect their health, the wheel/rail vibration and rolling noise are crucial noise sources. For a metro vehicle, the wheel/rail vibration transmits to the car body through the primary and secondary suspensions, causes the car floor vibration, the wheel/rail rolling noise transmits to carriage. An original study tries to predict low-frequency interior noise and reveal the acoustic law of panel contribution and improve ride comfort combining a wheel/rail rolling noise model, a rigid-flexible vehicle-track coupled dynamic model and detailed car body structural/acoustic finite element models. The results show that, based on the acoustic transfer vector method, the critical element contribution areas to the low-frequency noise were found; after removing the impact of critical elements, the sound pressure level peak at 80 Hz and 110–200 Hz decreased. The thickness increase can improve sound insulation level, but change the lower natural frequency, improve the structure's stiffness, suppress the amplitude of the transfer function. Based on element contribution analysis, the damping optimization method shows that the global SPL peak decreases by 4.3, 6.4, 7.8, 1.8, 3.5, and 5.2 dB (A,) respectively, from position 1 to 6. [ABSTRACT FROM AUTHOR]

Due to the complexity of the working conditions and the diversity of application scenarios, the normal operation of a fan, whether volute tongue, volute shell surface, or blade, often encounters some unavoidable problems, such as flow separation, wear, vibration, etc.; the aerodynamic noise caused by these problems has a significant impact on the normal operation of the fan. However, despite the use of aerodynamic acoustics to design low-noise fans or the use of sound absorption, sound insulation, and sound dissipation as the main traditional noise control techniques, they are in a state of technical bottleneck. Thus, the search for more efficient methods of noise reduction is looking toward the field of bionics. For this purpose, this paper first analyzes the mechanism of fan noise in the volute tongue and blades, and then, this paper reviews the noise control mechanism and improvement research using the bionic structures in the volute tongue structure, the contact surface of the volute shell, and the leading and trailing edges of the blade in the centrifugal fan. Finally, the current challenges and prospects of bionic structures for aerodynamic noise control of centrifugal fans are discussed. [ABSTRACT FROM AUTHOR]

This study focuses on sound isolation performances of original timber-framed interior wall and floor components in traditional-framed dwellings in Turkey and 19th century mud-brick samples used as infill within the timber frame. The acoustical ramifications of some retrofits proposed in the contexts of minimum intervention and refunctioning the traditional dwellings are assessed in reference to the relevant standards. Field measurements show that sound isolation performances of the original timber-framed wall and floor are ineffective. The results of this study show that acoustical retrofits applied on the original wall keeping its wood lath and mud-brick infill are about 5–7 dB in the weighted sound reduction index (RW) and are more effective than those applied on the reconstructed wall. Sound transmission loss values of 50- and 100-mm-thick authentic mud samples are 22–38 and 30–43 dB, respectively, between 125 and 4,000 Hz. The sound absorption coefficient at mid frequencies and the noise reduction coefficient of 50-mm-thick mud samples are 0.28 and 0.23, respectively. These results signal the importance of keeping traditional construction techniques of wall and floor during retrofits to improve the sound isolation performance. Adobe mixtures similar to the 19th-century mud-bricks can be of guidance for the production of innovative soundproofing earth-based building materials. Occupants living in traditional timber-framed houses suffer from noise-related problems even after these dwellings undergo repair works. According to field measurements, traditional timber-framed wall and floor components in these dwellings have inadequate sound isolation properties. On the other hand, studies show that mud-brick used as infill within the timber walls and floors, as well as mud plaster covering the wood lath, are important layers and help reduce noise transmission between the rooms in the dwellings. This means that traditional mud-based materials should be kept during retrofit works. Laying carpets or filling the voids at door edges and timber floor surfaces are minimum interventions but not enough to eliminate the noise passage. If one side of the timber-framed wall is covered with thin and insulated drywall, it provides sufficient sound insulation between the rooms. When enhanced sound isolation is needed, for instance, when a room is refunctioned as a meeting room during renovations, a separate mounting of drywall and separate mounting of timber ceiling are required to be done. This means that drywall or timber ceiling is attached in a way that does not touch the existing sublayer. [ABSTRACT FROM AUTHOR]

With the development of modern industrial technology, it is an essential problem to calculate the noise reduction performance of the flexible partition walls. The sound insulation measurement model is modeled by the Spectral geometry method (SGM). Compared with the traditional ones, it is a method with higher calculation accuracy and faster convergence speed. The displacement of the panel and the sound pressure field inside the rooms are expressed as Fourier series with additional items. In order to simulate the real measurement environment, the sound source room and the receiving room are set as a reverberation chamber and an anechoic chamber with impedance boundaries, respectively. The coupling relationship is established by the Hamilton's principle. Then the natural frequencies and the sound pressure level are compared with those derived by the finite element method (FEM). The results show that the analytical method has good accuracy and convergence. Moreover, the sound transmission loss (STL) of the partition could be obtained by the sound pressure method. Considering there is no accurate method for measuring the STL, this paper studies some factors affecting the sound insulation performance of the model by the parametric analysis method, such as the thickness of the panel, the length of the receiving room, the impedance of the receiving room and the parameters of medium. [ABSTRACT FROM AUTHOR]