Sound Insulation Performance Research Articles

Plate-type metastructure with low-frequency sound insulation and high stiffness properties

According to the mass law, it is impossible to increase sound transmission loss (STL) of conventional structures at low frequencies without increasing their weight. Metastructures are capable to break the limits of the mass law at low frequencies. However, many existing sound insulation metastructures need to be constructed using a host structure with low-stiffness properties, such as a thin plate and a thin membrane. As a result, the metastructures normally have large exposed areas with low-stiffness characteristics and are unable to bear heavy loads, which limits their practical applications. In this work, we propose a high-stiffness plate-type metastructure (HSPM) with both low-frequency sound insulation performance and high stiffness properties. The STL performance of the HSPM is demonstrated analytically, numerically and experimentally, indicating that the HSPM can deeply break the mass law at low frequencies. Owing to the simple construction, high stiffness properties, and high sound insulation performance at low frequencies, the proposed HSPM has promising applications in practical noise control engineering.

An Investigation of the Acoustic Enclosure of an Air Conditioning Compressor Using Response Surface Analysis and Topological Rigidity Optimization

A novel split-type air conditioning system is introduced to balance usability and portability. Unlike conventional split-type systems, where the compressor is typically placed outside, this system situates the compressor within the indoor unit, which may expose users to compressor noise. There are prominent peaks in the compressor noise spectrum, particularly at the compressor operating frequency and its harmonics, notably the second and third harmonics. The research presents a multilayered acoustic enclosure specifically designed for air conditioning compressors to address this issue without modifying the compressor or indoor unit casing. In order to get better sound insulation performance, a response surface methodology (RSM) is applied to optimize the thickness ratio, open area ratio, and open area height of the acoustic enclosure with predefined thickness. In addition, topological optimization is employed to strengthen weak areas of the acoustic enclosure. Then, experimental trials using the proposed acoustic enclosure are conducted in a semianechoic chamber. Results demonstrate significant reductions in noise levels, including 7.99 dB(A), 5.69 dB(A), and 5.19 dB(A) reductions in the fundamental frequency, second harmonic, and third harmonic noise of the compressor’s operating frequency, respectively.

Enhancing sound insulation performance with active constrained layer damping plates at low frequencies

In this paper, the normal incident sound transmission loss characteristics of active constrained layer damping (ACLD) plates are investigated numerically and experimentally. The sound insulation performance of the ACLD plate configuration with a centrally positioned 30 mm × 30 mm patch is initially examined in both passive and active control states. The analog feedback control strategy is employed to physically demonstrate that the ACLD treatment can effectively improve airborne sound insulation performance at low frequencies. To enhance control efficiency and mitigate control spillover effects, an edge-enhanced ACLD (EACLD) plate configuration is proposed, which enables a direct electrical connection between the PZT layer and base plate. Control mechanism is further analyzed from the perspectives of mean quadratic normal velocity and deformed modal shapes. Results show that, in the passive state, the formation of sound insulation peaks of the ACLD and EACLD plate configurations are attributed to structural anti-resonance effects. By applying active control, the shear deformation degree of the viscoelastic layer can be further increased, and the advantages of active and passive hybrid damping are formed. Therefore, the sound insulation performance of the EACLD plate configuration in the first-order resonance region around 190 Hz can be enhanced by approximately 20 dB. The proposed EACLD plate configuration demonstrates a broad low-frequency sound insulation bandwidth and holds strong potential for engineering applications.

Improving low-frequency sound transmission loss of double panels with a plate-type acoustic metamaterial

The sound insulation performance of double-leaf partitions is crucially affected by the mass-air-mass resonance phenomenon, whose frequency reduction can shift the high sound insulation to lower frequencies. In this work, an alternative strategy for exceeding the low limit of the mass-air-mass resonance frequency of conventional double panels is proposed in terms of the effective surface mass density. An equivalent spring-mass model based on the effective medium theory is implemented to intuitively understand the characteristics. A simple double-panel metamaterial is designed by replacing one of the panels with a single-plate metamaterial attached strip masses to decrease the structural complexity. The extended semi-analytical method is applied to predict efficiently the sound transmission loss in the low-frequency range, which is verified by the coupled vibro-acoustic finite element method with excellent agreement. The results demonstrate that the proposed double-panel metamaterial can reduce the minimum of the resonant frequency without changing the areal mass density and panel spacing. The sound insulation can be significantly improved between the reduced mass-air-mass resonance and the anti-resonance frequencies. To provide a better understanding of the sound transmission loss improvement, parametric studies are conducted. The design strategy is validated through experiments conducted in an impedance tube, and the results corroborate the findings. This study is instrumental in designing double-panel partitions that require sound insulation in specific low-frequency regions.

Sound insulation performance of different built-in acoustic materials for new multifamily residential

ABSTRACT The Building Technical Regulations in Taiwan, Article 46–6, Section 1. require that the impact sound insulation performance △LW be greater than 17 dB. Although the regulation has been in effect for over 2.5 years, installations of qualified acoustic materials have not yet been found in the market, as they are not required to be listed for building permit applications until 2021. Owing to the slow increase in new home construction, sound insulation mats are estimated to take five to seven years to be widely adopted. To characterize the material performance, the built-in permanent sound insulation layers of various materials were tested in an unfinished residential building. Practical experiments were conducted as per the CNS 15160-7:2021standard on the 7th floor of new buildings in northern Taiwan. Eleven insulation materials were selected from different manufacturers. The insulation mats made from these materials were placed in the same environment of approximately 10 M2, then incorporated underneath the mortar substrate of the polished floor tile using the wet construction method; the 6th floor of the building was utilized to evaluate sound reduction in accordance with the CNS 8465–2:2019 standard for different materials.

Research Progress on Thin-Walled Sound Insulation Metamaterial Structures

Acoustic metamaterials (AMs) composed of periodic artificial structures have extraordinary sound wave manipulation capabilities compared with traditional acoustic materials, and they have attracted widespread research attention. The sound insulation performance of thin-walled structures commonly used in engineering applications with restricted space, for example, vehicles’ body structures, and the latest studies on the sound insulation of thin-walled metamaterial structures, are comprehensively discussed in this paper. First, the definition and math law of sound insulation are introduced, alongside the primary methods of sound insulation testing of specimens. Secondly, the main sound insulation acoustic metamaterial structures are summarized and classified, including membrane-type, plate-type, and smart-material-type sound insulation metamaterials, boundaries, and temperature effects, as well as the sound insulation research on composite structures combined with metamaterial structures. Finally, the research status, challenges, and trends of sound insulation metamaterial structures are summarized. It was found that combining the advantages of metamaterial and various composite panel structures with optimization methods considering lightweight and proper wide frequency band single evaluator has the potential to improve the sound insulation performance of composite metamaterials in the full frequency range. Relative review results provide a comprehensive reference for the sound insulation metamaterial design and application.

An investigation on synergistic resonances of membrane-type acoustic metamaterial with multiple masses

Membrane-type acoustic metamaterials (MAM) represent a class of materials that are lightweight, compact, structurally simple, and simultaneously offer flexibility and moldability, all while demonstrating exceptional sound attenuation properties in the low-frequency range. As a continuation, this study focuses on membrane-based acoustic metamaterials with synergistic resonance of multiple loaded mass blocks. By varying the unit shape, arrangement method, radius and material of the loaded mass blocks, the low-frequency sound insulation performance of membrane-based acoustic metamaterials with synergistic resonance of multiple loaded mass blocks was calculated using a numerical model that are experimentally validated. The results indicate that the peak transmiss loss (TL) frequencies can be tuned to specific values. The optimized membrane-type acoustic metamaterial could achieve a TL bandwidth up to 844 Hz (>5dB) and a TL bandwidth up to 376 Hz (>10 dB) within the low-frequency range. Acoustic-membrane analysis further revealed the vibration patterns of the structure under different frequency excitations, providing profound physical insights into the mechanisms of low-frequency sound insulation. Moreover, by altering the relative angles between the loaded mass blocks could further broaden the effective noise reduction bandwidth which can benefit the understanding on the optimized membrane-acoustic interactions.

Low shrinkage polyimide aerogel cross-linked with amino-functionalized hollow glass microbeads for thermal and acoustic insulation

As a nanoporous material, polyimide (PI) aerogels have excellent thermal and acoustic properties. However, their high air flow resistance is detrimental to the development of their acoustic properties. To enhance the thermal and acoustic insulation properties of PI aerogels, we have selected hollow glass microbeads (HGM) with a low thermal conductivity coefficient to be combined with the PI aerogel, leading to the fabrication of PI/HGM aerogel composite materials. In this study, there are two preprocessing methods for HGM: untreated and aminized (HGM-NH2). These were then individually combined with PI aerogel to fabricate two distinct PI/HGM composite aerogels: a physically blended variant (PIHGM) and a chemically bonded one (PHN). The thermal insulation and acoustic properties of these two composite aerogels were compared. The results show that HGM-NH2 not only functions as a cross-linking agent but also plays a key role in forming the three-dimensional network structure, which effectively reduces the shrinkage rate and density of the composite aerogel. Moreover, the thermal conductivity of PHN reached a low of 27.92 mW m⁻1 K⁻1, which is a reduction compared to PIHGM's thermal conductivity of 29.83 mW m⁻1 K⁻1. Moreover, the PHN composite aerogel with 10% HGM addition exhibited an average sound insulation level that was 120% higher than that of PIHGM. The method of incorporating pore structures with different scales also offers valuable insights for enhancing the sound insulation performance of other materials.

Effects of waste rubber particles on workability, mechanical, and sound insulation properties of recycled aggregate mortar

The influence mechanism of waste rubber particles (WRPs) on the workability, mechanical properties, and sound insulation performance of recycled aggregate sound insulation mortar (RCM) were investigated. According to the principle of volume fraction replacement of recycled fine aggregate by 0 to 50%, WRPs with a particle size of 1–4 mm were incorporated in various mixtures of RCM. Each RCM mixture was tested for workability, mechanical, and sound insulation performance. Mercury intrusion porosimetry was used to analyze the distribution of pores and their sizes inside the material, and X-ray diffraction and scanning electron microscopy were used to analyze the characteristics of the interfacial transition zones (ITZs) between the rubber particles and the cement paste. The results showed that, owing to the hydrophobicity of WRPs, greater WRPs content led to greater fluidity of the mortar mix and a smaller water retention rate. Notably, the rubber in the mortar did not contribute to the hydration reactivity of the cement paste, but it changed the crystal morphology and pore structure of ITZ hydration products. The RCM incorporating 3–10% WRPs produced the optimal pore structure through the aggregate effect, which increased its overall compactness and mechanical performance. Further increase of WRP content significantly improved the sound insulation performance while significantly reducing the strength. Moreover, there was a clear logarithmic relationship between the strength and impact sound level index. This new knowledge can be used to prepare RCM that meets the actual strength and sound insulation requirements of the floor. Thus, the resource utilization of solid waste can be expanded.

Evaluating Airborne Sound Insulation in Dwellings Constructed with Hollow Ceramic Blocks under Brazilian Housing Policies

In Brazil, there is a shortage of approximately 5.80 million residences, a challenge that intensified during the pandemic. Since 2013, there has been a mandate to implement specific performance criteria in residential constructions. However, many construction firms face difficulties in meeting these standards, especially concerning sound insulation in partition elements. This work aims to assess the airborne sound insulation performance and compliance with legal standards in new residential buildings through measurements and simulations. In particular, subsidized housing units for low-income populations are studied, which are eligible for reduced taxes on building loans. These buildings are typically made of hollow ceramic blocks with vertical perforations as separating walls, a commonly used national building material. Three buildings located in Guarapuava, a southern city in Brazil with a population of approximately 183,000 residents, were selected for this purpose. Measurements were conducted following ISO 16283-1 guidelines, whereas simulations were performed using ISO 12354-1, initially assuming a uniform plate but also exploring an alternative model that considers orthotropic behavior with analytical expressions. The calculations considered both static and dynamic moduli of elasticity. The results indicated that all the units failed to meet the specified standards. The measured DnT,w values were below the required thresholds, obtaining 42 < 45 dB for Building B1, 40 < 45 dB for Building B2, and 38 < 40 dB for Building B3. The predicted DnT,w values agreed well with the measured values when considering orthotropy with a dynamic elastic modulus. However, discrepancies were observed in the spectral analysis, especially at lower and higher frequencies. The findings suggest refraining from employing single-leaf partition walls made of vertical hollow ceramic blocks in such buildings. Improving sound insulation necessitates embracing a comprehensive strategy that takes into account the separating element, flanking paths, and the room geometries.

Impact sound insulation performance of mass timber floors

Mass timber floors are being used increasingly in both mass timber and hybrid timber buildings due to its dry and rapid construction. Bare mass timber structural slabs have relatively low impact sound insulation performance. Though certain floating floor assemblies on mass timber slabs can provide adequate single number ratings, such assemblies are mainly effective in the middle to high frequency range. This paper will provide an overview of the research on the impact sound insulation perforamnce of mass timber floors with exposed ceiling and floating floor assembies conducted at the Universtiy of Northern British Columbia. The test data of bare mass timber floors, with continous floating concrete toppings, with raised discrete floating floor assemblies will be presented and compared. The effect of interlayer, concrete thickness and excitation sources on the single number ratings and frequency spectra will be discussed. Recommendations for future reseach will be given based on the discussion.

Vibroacoustic performance of a mass timber cassette floor through mock-up tests

Though cross laminated timber slab floors are being used increasingly in mass timber construction, solid mass timber slab floors are limited to short-to-medium span applications. The sound insulation performance of solid mass timber slab floors is often achieved through assemblies on the floor surface as exposed wood ceilings are often prefered by achitects and occupants. A mass timber cassete floor system has been recently designed and tested for its structural, vibrational and acoustical performance. This paper reports the vibroacoustic performance of the proprietary floor system through mock-up building tests. In particular, the natural frequency and mode shapes of the floor under 200 Hz was measured by experimental modal tests. The effect of floating concrete topping on the dynamic properties of the floor was assessed by experimental modal testing. The impact sound insulation performance of the bare cassette floor was first measured, and then with floating concrete toppings. The airborne sound insulation performance of a partition wall was measured to reveal the effect of flanking sound casued by the exposed continous mass timber ceiling. Detailed results will be presented in the full paper.

Sound flanking through common low-voltage electrical conduit in multi-family residential buildings

Sound flanking between suites in multi-family residential buildings is a prevalent issue in architectural acoustics and building construction that can decrease the sound insulation performance of suite-demising partitions, compromising acoustical privacy and comfort for residents. In recent times, a specific deficiency regarding the sealing of common low-voltage electrical conduit routed between residential suites has been increasing in frequency in construction of residential buildings, resulting in otherwise appropriately designed suite demising configurations performing poorly in situ, and in some cases, even failing Ontario Building Code requirements for sound insulation between dwelling spaces during site testing. This article presents test data sampled from multiple residential buildings in Ontario, highlighting the extent of this issue and its implications, along with discussion regarding the proactive prevention and post-construction rectification of this issue.

Sound insulation enhancement of polyvinyl butyral film by blending polyurethane and its laminated safety glass

Laminated glass based on PVB film is widely used in military industry and life depending on its excellent safety performance. However, the insufficient sound insulation performance of PVB film restricts its practical application and has gained much more attention. In this work, a PVB-TPU composites with high strength and excellent sound insulation acoustic performance was designed by melt blending method which is attributed to their molecular entanglement and hydrogen bonding interactions between PVB and TPU molecule chains. It has been showed that the maximum tensile strength and elongation at break of the PVB-TPU blending film reached 34 MPa and 235 % respectively when 10 wt% content of TPU in the system. In addition, 20–41 dB of the sound transmission loss (TL) for the composite film with 1 mm thickness in the range of 2000–6000 Hz was achieved, which was obvious enhanced compared with the existing laminated glass intermediate film. The high impact resistance of the laminated glass based on the PVB-TPU film was confirmed by the falling ball impact test. The high sound insulation and safety laminated glass prepared here will be widely used in more fields.

Designing and experimental validation of single-layer mixed foil resonator acoustic membrane to enhance sound transmission loss (STL) within low to medium frequency range

This study presents a novel design for an acoustic membrane structure that employs a parallel-arrangement of mixed foil sound resonators to improve sound absorption and insulation capabilities in the low to medium frequency range. The structure is composed of a single layer of parallel-arranged mixed foil wedge-shaped coffers and a bottom flat panel separated by an air cavity. The mixed thickness-based foil resonators are treated as a combination of independent resonators with unique resonance frequency, resulting in improved sound insulation with broadband efficacy. A comprehensive parametric analysis was carried out using the Finite Element Method (FEM) based COMSOL Multiphysics, yielding the anticipated outcomes. The study revealed that the broadband Sound Transmission Loss (STL) can be tailored by varying the thickness of the top and side walls, the bottom plate thickness, and the depth of the rear air cavity. The findings suggest that existing acoustic membrane design can be highly efficient, achieving, and average STL of over 40 dB ∼ 45 dB across the low to medium frequency range of 500 Hz to 3000 Hz. The experimental validation was conducted in an anechoic chamber, and the results were found to be in close agreement with the FEM simulation results. In comparison to conventional uniform foil sound resonator based acoustic membrane structure, this mixed single-layer square wedge-shaped foil resonator based acoustic membrane exhibits outstanding sound insulation performances in the low to medium frequency range, owing to its lightweight structure and availability of conventional manufacturing techniques. This advanced version of the foil sound resonator based acoustic membrane holds immense promise for the use in acoustics and noise control applications across domestic, commercial, and industrial environments.

A convenient approach to manufacturing lightweight and high-sound-insulation plywood using furfuryl alcohol/multilayer graphene oxide as a shielding layer

ABSTRACT With the requirement of green construction, the building envelope system urgently needs lightweight material with high sound insulation performance. In this study, a kind of plywood with furfuryl alcohol/multilayer graphene oxide (FA/MLGO) layer was prepared by lamination. The four-microphone impedance tube method measured the sound insulation to evaluate optimal process parameters. At the same time, the acoustic impedance, damping performance, interface microstructure, and chemical components were characterized to discuss the sound insulation mechanism of FA/MLGO as a shielding layer. It showed that the weighted transmission loss of plywood with different FA/MLGO layers was enhanced, and acoustic impedance increased while the acoustic radiation damping coefficient decreased. In addition, considering economic costs, the optimal preparation process was three layers with 0.5 wt.% MLGO concentration and 50 wt.% FA concentration, followed by curing for three h. The surface properties, micromorphology, and chemical composition results indicated that FA/MLGO layer formed more complex sound propagation paths in the plywood, thereby increasing the loss of sound energy inside. Thus, the sound insulation of the plywood was improved.

Inverse design of laminated plate-type acoustic metamaterials for sound insulation based on deep learning

The laminated plate-type acoustic metamaterial (LPAM) has designable low-frequency sound insulation performance and ultrathin and ultralight characteristics. However, the complexity of LPAM design increases significantly as the number of layers increases. An inverse design method is proposed to determine the topology and design parameters of LPAM based on deep learning. To train the deep learning model, the finite element and analytic models are combined to generate sufficient training data. The experimental validation of the finite element model and the acoustic impedance model are carried out to reduce the deviation between the experiments and simulations. The LPAM design system contains the pre-processing, inverse design and post-processing modules. The pre-processing module can produce candidate targets based on the required sound-insulation design target. For each candidate target, the inverse design module utilizes convolutional neural networks to autonomously design topology and parameters of LPAM. Finally, the pre-processing and post-processing modules are combined to choose the optional LPAMs meeting the sound-insulation target. To verify effectiveness of the LPAM design system, typical cases, involving the sound insulation targets of one and two sound insulation peaks, and uniform sound insulation in a broadband from 50 Hz to 600 Hz, are designed successfully and efficiently.

Sound insulation performance of cylindrical sandwich structure improved by membrane-type metamaterials

Cylindrical sandwich structure with excellent mechanical properties has attracted extensive attention from researchers and been applied in various fields. The cylindrical sandwich structure meets the mechanical requirements of the application and new requirements emerge at this time. The structure should have multifunctionality which can withstand multiple different loads simultaneously. To improve its sound insulation ability while maintaining its mechanical properties, membrane-type metamaterials are introduced into cylindrical sandwich structure in this article. A theoretical model according to the harmonic expansion method is established. Then, the sound transmission loss (STL) of the structure is predicted. Besides, the influence of boundary conditions on its STL is analyzed and the sound insulation mechanism of the structure is investigated by discussing various parameters effect on the STL curve.

Multi-Objective Prediction of the Sound Insulation Performance of a Vehicle Body System Using Multiple Kernel Learning–Support Vector Regression

The sound insulation performance of an electric vehicle’s body system serves as a critical metric for evaluating the noise, vibration, and harshness (NVH) quality of the vehicle. The accurate and efficient prediction of sound insulation performance is foundational for undertaking noise reduction design and optimization. Current engineering practices predominantly rely on Computer-Aided Engineering (CAE) methodologies to address this challenge. However, inherent shortcomings such as low modeling efficiency and difficulty in ensuring prediction accuracy often characterize these approaches. In an effort to overcome these limitations, we propose a decomposition framework for predicting the sound insulation performance of the electric vehicle body system. This framework is established based on a comprehensive analysis of the noise transmission paths within the system. Subsequently, the support vector regression (SVR) method is introduced to construct a machine learning model specifically designed for predicting the sound insulation performance of the body system. This approach aims to mitigate the inherent weaknesses associated with the conventional CAE processes using a ‘data-driven’ paradigm. Furthermore, the Multiple Kernel Learning (MKL) method is used to enhance the processing efficacy of the SVR model. The proposed method is validated using practical application and testing on a specific electric vehicle. The results demonstrate commendable performance in terms of prediction accuracy and robustness. This research contributes to advancing the field by presenting a more effective and reliable approach to predicting the sound insulation performance of electric vehicle body systems, offering valuable insights for noise reduction strategies and optimization efforts in the automotive industry.

Sound insulation performance of membrane-type acoustic metamaterial based on defect state structure

Although conventional Membrane-type Acoustic Metamaterial(MAM) has good sound insulation performance in low frequency bands, the sound insulation performance in middle and high frequency bands is not as good as conventional sound insulation materials with the same quality. This problem still persists by using the double-layer MAM structures. To solve this problem, the defect state is introduced into the double-layer MAM structure. Although the ideal periodic structure is destroyed, the sound insulation performance will also change greatly, and it has a strong creativity. In this paper, the sound insulation performance of MAM with defect states is studied. Firstly, the theoretical model of sound insulation of double-layer membrane-type acoustic metamaterial with eccentric composite mass block (MAMEM) structure is calculated by using modal superposition method and transfer matrix method. Secondly, the influence of different defect locations on the sound insulation of membrane-type acoustic metamaterial with eccentric composite mass block(MAMECM) structure is discussed. The results show that the sound insulation peaks of the angular defect structure appear at 300 Hz, 320 Hz, 1040 Hz and 1410 Hz. The average sound insulation in the whole study frequency band of the angular defect structure is 4.23 dB higher than the non-defect structure. In addition, the experiment verifies the accuracy of the results. Thirdly, based on genetic algorithm, the area enclosed by the sound translation loss (STL) curve of the double-layer MAMECM structure above the mass law curve is taken as the optimization target to optimize the structure topology. The results show that the optimal structure not only has good sound insulation performance in the low frequency band, but also reaches the sound insulation peak at 1230 Hz, 1300 Hz, 1430 Hz and 1450 Hz. Besides, the optimal structure heaviness is reduced by 12%.