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A theoretical model is developed to investigate the influence of external mean flow on sound transmission loss (STL) through composite sandwich panels filled with porous materials. The equations of the motions for the composite laminate plates are established by adopting the first-order shear deformation theory. The porous materials in between the sandwich structures are characterized by an equivalent fluid model. Employing the fluid-structure coupling condition, the displacement continuity at fluid-structure interfaces is guaranteed. To validate the proposed theoretical model, a comparison among the present theoretical predictions, the existing theoretical and experimental results are executed, with overall agreements achieved. A systematical investigation is carried out to explore the influences of the external mean flow, incidence angle and laminate scheme on the coincidence frequency and sound transmission loss of the sandwich structures. This work provides a helpful guideline for the vibroacoustic design of composite sandwich structures.

As an acoustic metamaterial, Metal–organic frameworks (MOFs) can absorb sound energy abnormally. In this research, a thin and flexible acoustic material was prepared by growing MOF on the fabric. The successful growth of MIL-53(Fe) on the fiber surface was confirmed by SEM, FTIR, XRD and XPS. From the sound absorption and sound insulation test results of MIL-53(Fe)@fabric, the in-situ growth of MIL-53(Fe) greatly improves the sound absorption and sound insulation performance of the fabric, and gives the fabric an abnormal acoustic effect. From the calculation results of the theoretical model, the growth of the sub-wavelength scale MIL-53(Fe) significantly increases the flow resistance of the fabric, which is the root cause of the abnormal sound absorption of the material. It is worth noting that the sound transmission loss of the prepared flexible material doesn’t follow the mass law and exhibits excellent sound insulation performance. This is not only related to the increase in the sound energy reflected by the fabric, but also to the abnormal sound absorption of MIL-53(Fe). Here, the sound insulation performance of MOFs@fabric is reported for the first time. This work promotes the research and application of MOFs in the field of acoustics, and provides a method and theoretical basis for the design and preparation of acoustic protection textiles.

Ventilation ducts can have a negative effect on the sound reduction index between two rooms if they pass through the dividing structure without treatments. The overall sound reduction of a ventilation duct is dependent on several factors including the transmission loss when sound is breaking in and out from the duct. This study aims to model the sound reduction of a combined system with a separating wall and a ventilation duct through it. Three walls, characterized according to ISO 717-1, are combined with three different ventilation ducts, two circular and one rectangular with different dimensions. Laboratory measurement data are used to determine the sound reduction of the different configurations and the type of treatments needed for each configuration. A proposed model with existing theory for describing sound transmission losses of circular and rectangular ventilation ducts predicts the shape of the measurement data for many frequency bands. A new theory part is developed through an iterative process for circular ducts, which is based on measurements with previous methods and studies as a guide because the existing prediction scheme is somewhat perplexing. For rectangular ducts, the existing theory has been updated to better match measurement data. The application of the proposed theory and model in this article shows similar results when compared to measurements. The difference in weighted sound reduction index between developed theories and measurement data is 0–1 dB for every configuration.

The scope of this paper is to investigate the sound transmission loss of an acoustic package of glass wool with embedded periodic inclusions, considering the possibility to improve a standard configuration and inserting the innovative package in a practical configuration used in the aeronautic field for noise suppression. Periodic inclusions are introduced to enhance the sound transmission loss performance of the acoustic package in the mid-high range of frequencies. The main interest of the present work, with respect to the state of the art, is represented by the arrangement of the inclusions one respect to the others, then creating an inclusion pattern that improves the performance of the periodicity peak. To reach this goal, a numerical model of the package is studied, and the effect of the patterns of periodic inclusions is simulated. The pattern behavior is evaluated for eight configurations, which are different from each other for the cubic dimensions and the inclusion radii. Furthermore, an optimized configuration for aeronautical applications is designed starting from the studied acoustic package; then, the results in terms of mass and performance are discussed. Results are presented in terms of tables and graphs, which may constitute a good basis to perform preliminary design consideration that could be interesting for further generalizations.

Acoustic metamaterials are materials artificially engineered to control sound waves, which is not possible with conventional materials. We have proposed a design of an acoustic metamaterial plate with inbuilt Helmholtz resonators. The plate is made of Polylactic acid (PLA) which is fabricated using an additive manufacturing technique. It consists of Helmholtz resonator-shaped cavities of different sizes. In this paper, we have analyzed the acoustic properties of the Helmholtz resonators-based metamaterial plate experimentally as well as numerically. The experimental results are in good agreement with the numerical results. These types of 3D-printed metamaterial plates can find their application where high sound transmission loss is required to create a quieter ambience. There is an additional advantage of being lightweight because of the Helmholtz resonator-shaped cavities built inside the plate. Thus, these types of metamaterial plates can find their application in the design sector requiring lighter materials with high sound transmission loss.

Sound transmission loss (TL) through mechanically linked aircraft double-walls is studied with a statistical energy analysis method. An overview of the method is given with details on acoustic and structural transfer path analysis. The studied structure is composed of a thick composite sandwich panel representative of a skin panel, lined with an acoustic insulation layer (glass wool), and structurally connected via vibration isolators to a thin composite sandwich lining panel representative of a trim panel. Two types of vibration isolators are considered: a soft and rigid mechanical link. Various experimental methods were used to assess the accuracy of this model. This study shows the robustness of the simple four-pole modeling of isolators, which depends mainly on the importance of correctly determining the experimental dynamic stiffness of typical aircraft vibration isolators. The prediction of the TL while acceptable was, however, found less satisfactory for the soft configuration. This is traced to the uncertainties on the used coupling loss factor. Finally, a transfer path analysis is performed to identify the contribution of each transmission path in the entire frequency range of interest. Results show that non-resonant airborne transmission dominates in low frequencies, the airborne radiation is significant in the critical frequency region of the panels, while the structure-borne radiation increases the noise transmitted in the mid- and high-frequency ranges.

The present paper investigates a portable eustachian-tube-function testing device by sonotubometry based on pure-tone sound transmission via the eustachian tube (ET). The measured results obtained by the proposed method were validated through comparison with the existing testing technique based on broadband sound inspection. The measurement results for the ET opening time (Topen) and the sound pressure difference in the ear canal between open and closed ETs (ΔL) obtained using pure-tone sounds with tonal frequency components of 7.0 and 9.5 kHz generally agreed with the results obtained by the existing technique with broadband testing sound.

In this study, power spectral density and inverse analyses were performed to obtain the frequency characteristics and spatial distribution of temperature in the Qiongzhou Strait using reciprocal sound transmission data obtained in a coastal acoustic tomography experiment conducted in 2013. The results reveal three dominant types of internal tides (diurnal, semidiurnal, and terdiurnal). Spectral analysis of the range-average temperature deviation along the northern and southern transmission paths shows that along the northern path, the energy of the diurnal internal tides was significantly larger than that of the semidiurnal tides. The semidiurnal internal tides, in contrast, were more pronounced along the southern path. A terdiurnal spectrum with an energy level equivalent to that of the semidiurnal internal tide was discernable for both the northern and southern paths. These three types of internal tides can also be recognized in the time variation of the zonal-average temperature deviation. The diurnal internal tides were strengthened along the northern coast, implying their westward propagation and the existence of coastally trapped effects. The other two types of internal tides, which have smaller wavelengths than the diurnal internal tides, were less resolved over the entire tomographic domain due to the insufficient resolution of the inversion. The data quality was verified to be satisfactory by error estimation.

Technological advancements in computational building modeling have enable designers to conduct simulations at the component level. With the evolution of parametric modeling, designers can evaluate multiple design options and identify the best performing solutions before expending resources on physical testing and eventual construction. However, to conduct design space exploration or optimization, an objective function is necessary to evaluate performance. While defined objectives exist for design goals such as sustainability, energy usage, structural performance, and daylighting, there does not yet exist an encompassing objective that can accurately quantify the sound transmission of structures in building design. This paper proposes four transmission rating strategies that can describe air-borne and impact performance of floors, walls, or other acoustic barriers. The approaches consider air-borne and structure-borne sound for four floor constructions, revealing strengths and weaknesses across the methods. Implementation of the approaches in an optimization framework is discussed, along with practical methods for optimizing the objectives in early-stage design.

An analytical model for the forced sound transmission loss of finite single-leaf walls using a variational technique was previously developed and validated. As the double panel is one of the most used structures in building acoustics, the aim of this paper is to extend the analytical model to consider double panel structures. Analytical formulas for the forced part of the airborne sound insulation of finite sized double panel structures are derived using a variational technique based on the integral-differential equation of the fluid loaded panels. The formulas are valid in the entire audible frequency range. The results are compared to alternative analytical models and measurements, with reasonable agreement.

Considering Impact sound level requirements accomplishment in Brazil, floating floors are still considered as an inviable solution for building companies due to the implications in the total cost of building, mainly for social housing. Alternative and sometimes cheaper solutions are those undertaken in the receiver room. However, the lack of laboratory and field tests on the acoustic performance of this type of system is still a barrier for acoustic designing in Brazil. The aim of this paper is to study and validate different constructive solutions developed jointly with building companies for improving the impact sound insulation performance on the receiving room of new Brazilian housing constructions.

Background Although many studies have suggested that air cells may play an important role in sigmoid sinus diverticulum and/or dehiscence (SSDD)-induced pulsatile tinnitus (PT), the exact effects remain unclear. This study aims to quantitatively investigate the effect of different degrees of pneumatization of temporal bone on sound transmission from the sigmoid sinus to the tympanic cavity. Methods In the clinical study, 25 patients were enrolled to measure the sound intensity and frequency of SSDD-induced PT. In the experimental study, sound inputs at different frequencies at the dehiscent sigmoid plate were measured and compared among realistic object models of different degrees of pneumatization, when sound intensity in the tympanic cavity was fixed as the level of the PT sound intensity sensed by patients. Results The sound intensity sensed by PT patients was 34.0 ± 13.0 dB SPL, which represented the sound intensity in the tympanic cavity transmitted from the dehiscent sigmoid plate. In the experimental study, when sound received in the tympanic cavity was fixed at 34 dB SPL, the mean inputs of sound intensity at the dehiscent sigmoid plate were 46.9, 46.2, 45.2, 47.1, 57, 57.4, and 74.1 dB SPL in a hypo-pneumatized model; 42.6, 43, 41.5, 43.2, 47.3, 58.2, and 78.8 dB SPL in a moderately pneumatized model; 52.6, 52.8, 48.1, 61, 64.2, 82.4, and >87.3 dB SPL in a well-pneumatized model; and 47.2, 46.2, 45.4, 49.4, 54.9, 66.6, and 77.7 dB SPL in hyper-pneumatized model, with increased sound frequencies (125-8000 Hz). The mean sound transmission distances were 41.7 mm, 45.2 mm, 47.6 mm, and 48.4 mm in successively better pneumatized models. Conclusion Sound reduces while passing through air cells and attenuation is lowest in the moderately pneumatized temporal bone, followed by the hypo- and hyper-pneumatized temporal bones, and the highest in the well-pneumatized temporal bone. Lower-frequency sound attenuation (≤1000 Hz) is less than that of higher-frequency sound (>1000 Hz).

The performance improvements of SOnic Detection And Ranging (SODAR) necessitate designing efficient acoustic antennas for the Atmospheric Boundary Layer (ABL) measurements to enhance the data availability of weak echoes. An efficient acoustic antenna needs to optimize electrical to acoustic and acoustic to electrical conversion efficiency measured at the antenna axis. It also needs to provide a good directional response and to handle atmospheric noise. Acoustic antennas designed using moving-coil transducers, parabolic dish and acoustic baffle should provide better characteristics. In the present research work, several types of Acoustic Composite Material (ACP) for acoustic baffle have been tested to their characteristics Sound Transmission Coefficient (STC) and Noise Reduction Coefficient (NRC). Based on these characteristics, the whole testing is performed in the reverberation chamber and a comparative study of transmission loss and absorption is elaborated. It is concluded that baffle (ACP sample 2 with foam) is the suitable material with STC (34) and NRC (0.98). Also, an acoustic antenna has been designed using ACP sheets with foam and tested all the components i.e. transducer, disc and baffles in the acoustic anechoic chamber and reverberation chamber, to analyse the axial transmit and receive conversion efficiencies and directional response.

An imperfect sealing system would be the main path of the noise propagating into the interior compartment of a high-speed vehicle. The study on the sound insulation modeling of automotive door sealing systems, which involve complicated threedimensional sealing structures and gap cavities, has attracted more and more attention. This study employs hybrid finite element–statistical energy analysis (FE-SEA) models to predict the sound transmission loss of three simplified sealing specimens and an actual automotive door sealing system. For the actual sealing system under compression, a three-dimensional FE model is built to simulate the nonlinear compression, which can acquire the compressed geometries and pre-stress modal results of the seals for further prediction of the sound transmission loss. The hybrid FE-SEA method is firstly verified by the experimental result of a doubleplate vibro-acoustic system and another numerical method. Several factors concerning the modeling, including the boundary conditions, the equivalent elastic modulus for the hyper-elastic rubber, the specimen length, and the structural grid size, are considered to study their impacts on the sound transmission loss. The effects of using shell elements and using solid elements to model the sealing rubber layers are also compared. The results of this study can provide guides regarding the tradeoff between the modeling efficiency and accuracy, so that it has significance for engineering modeling, as well as the design and optimization of automotive door sealing systems. © 2021 Institute of Noise Control Engineering.

This paper presents a theoretical model based on Biot theory to investigate the sound transmission loss (STL) of a pyramidal lattice sandwich structure lined with porous material. This theory is mo...

A new sound insulation metamaterial (SIM) is designed by combining a Helmholtz resonator and a fractal structure for sound insulation in the frequency range of 600 to 1700 Hz. Using a fractal-based internal structure, the designed hybrid SIM shows a relatively constant value of sound transmission loss (STL) over the target frequency range. The basic concept of this work is to develop two functional parts working in each effective frequency range. One is a Helmholtz resonance structure that operates with a high value of STL from 600 to 1000 Hz, and the other is an internal fractal structure that shows a high STL at higher frequencies in the 1000 to 1700 Hz range. In this work, the proposed metamaterial has a mean of 16.34 dB with a standard deviation of 1.73 dB within the wide target range of 600 to 1700 Hz. Additionally, the proposed SIM is approximately 40 % smaller in size than the previous resonator and has a higher mean STL with a small ΔSTL of 1.7 dB between highest and lowest values.

Elastography emerges as a medical modality to map stiffness distribution of tissues and is expected to help identify malignant tumors. To this end, tissues are externally stimulated with dynamic waves, and thereafter mechanical responses are internally measured. However, internal measurements limit the resolution and accuracy due to wave scattering and frequency-dependence. Although models have been reported only with need for acquiring transmitted responses, the computational processes are time-consuming in the inverse analysis. Here we develop an architecture of deep learning-based convolutional neural networks (CNNs) to image elastography based on sound transmission. The proposed CNNs contain three branches, one of which considers the contribution of original features in input data. By comparison, the developed architecture not only maps elastography accurately, but also is more efficient than traditional CNNs in sequence.

Emergency alarm systems notify people in case of a fire hazard so that they can quickly escape to safe areas. As buildings become larger and taller, emergency alarm systems have been transitioning from alarm-at-once systems to priority alarm systems. The Korean National Fire Safety Code for the emergency alarm system (NFSC 202) states that if there is a fire on or above the second floor of a building, it is mandatory to sound an alarm on the fire floor and the floor directly above it. A previous study reported that as the fire alarm sound transferred to the upper and lower floor through escape stairways, the transferred alarm sound could also be recognized by residents on unintended floors. Consequently, there is a possibility that all of the residents in a building may try to attempt to escape simultaneously. Application of sound absorption material in the alarm sound propagation routes was proposed to reduce alarm sound transmission to unintended floors. However, a study on the prediction of alarm sound propagation through escape stairways connected to the elevator hall was not conducted. This study predicted the propagation of alarm sounds generated in the elevator halls of Korean apartment buildings to floors above and below the alarming floor using a standardized room acoustic simulation method. To control alarm sound transmission to the unintended floors, the application of sound absorption materials on the walls of the escape stairways and the sound insulation performance of fireproof doors was considered. To facilitate effective escapes from high-rise buildings, control of a situation in which the alarm sounds of a priority alarm system are transferred to unintended floors is necessary. Prediction results showed that to prevent alarm sound transmission though the escape stairways, installation of fireproof doors with high sound insulation performance at the entrance of escape stairways and application of incombustible sound absorption materials or sound-absorbing blocks on the walls of escape stairways are needed.

The present study is concerned with the buckling, vibration and sound transmission characteristics of the simply supported sandwich plate with trapezoidal corrugated core in thermal environment bas...

Acoustic metamaterials are becoming promising solutions for many industry applications, but the gap between theory and practice is still difficult to close. This research proposes an optimization methodology of acoustic metamaterial designs for sound insulation that aims to start bridging this gap. The proposed methodology takes advantage of a hybrid analytical-numerical approach for computing the sound transmission loss of the designs efficiently. As a result, the implementation of optimization techniques on numerical model designs becomes practically possible. This is exemplified with two test cases: (i) optimization of the sound transmission loss of a single gypsum board panel and (ii) optimization of the noise reduction of outdoor HVAC units. Two resonator designs, one used previously for sound radiation in flat panel speakers and the other for enhancing the sound transmission loss at the mass-air-mass resonance of double panels, are here optimized for the two test cases. This shows how an existing resonator can be adapted for new purposes, thus making the design of acoustic metamaterials efficient. The optimized metamaterials outperform the original designs as well as traditional approaches to sound insulation.

The propagation of animal vocalizations in water and in air is a well-studied phenomenon, but sound produced by bark and wood boring insects, which feed and reproduce inside trees, is poorly understood. Often being confined to the dark and chemically-saturated habitat of wood, many bark- and woodborers have developed stridulatory mechanisms to communicate acoustically. Despite their ecological and economic importance and the unusual medium used for acoustic communication, very little is known about sound production in these insects, or their acoustic interactions inside trees. Here, we use bark beetles (Scolytinae) as a model system to study the effects of wooden tissue on the propagation of insect stridulations and propose algorithms for their automatic identification. We characterize distance-dependence of the spectral parameters of stridulatory sounds, propose data-based models for the power decay of the stridulations in both outer and inner bark, provide optimal spectral ranges for stridulation detectability, and develop automatic methods for their detection and identification. We also discuss the acoustic discernibility of species cohabitating the same log. The species tested can be acoustically identified with 99% of accuracy at distances up to 20 cm and detected to the greatest extent in the 2-6 kHz frequency band. Phloem was a better medium for sound transmission than bark.

Bone conduction is an efficient pathway of sound transmission which can be harnessed to provide hearing amplification. Bone conduction hearing devices may be indicated when ear canal pathology precludes the use of a conventional hearing aid, as well as in cases of single-sided deafness. Several different technologies exist which transmit sound via bone conduction. Here, we will review the physiology of bone conduction, the indications for bone conduction amplification, and the specifics of currently available devices.

The sound absorption and sound transmission loss performances of the natural woods, hard and soft processed woods with attachment of the various natural or waste materials were investigated in the present study using impedance tube with American Society for Testing Material (ASTM) standards. The sound absorption performances of all natural and all hard processed woods were very poor. It was found that filter mat made by the coconut fibre was the best material for sound absorption improvement of the hard processed woods. The sound absorption performance of the soft processed wood (cork) was better than all natural and all hard processed woods. Among all tested woods, it was found that the cork with attached tea bag made by corn fibre is the best selection for sound absorption application. The transmission loss performances of all natural woods were good. The effects of various materials on the transmission loss performances of all hard processed woods were not very significant. For cork with and without attachment of various materials, their transmission loss performances were not as good as the hard processed woods. Among all tested woods, it was found that Pterocarpus soyauxii and Quercus spp. (natural woods) are the best woods to be used in those applications when prevention of sound transmission is needed. It is recommended that cork is the best wood to be used in those applications where sound absorption and prevention of sound transmission are needed at the same time due to its good sound absorption performance while its ability on prevention of the sound transmission is also acceptable.

Open acoustic barriers exhibit excellent sound transmission reduction property at a certain frequency/frequencies which highly depends on the configuration of its unit cell. Design of unit cell configuration for minimum sound transmission at predefined objective frequency remains an open question. This paper aims at providing an automatic design method for open acoustic barriers with multi-material unit cell. Firstly, a wave finite element method is developed to calculate the sound transmission through an infinite array of periodic scatterers. As the unit cell contains infinite fluid domain, the application of Floquet-Bloch theorem to the boundaries of perfectly match layers (PML) is necessary and has been resolved in this paper. This wave finite element method with the implementation of PML is validated by comparing to analytical solution of sound transmission through an array of steel cylinders. Then a genetic algorithm is employed to optimize the sound transmission loss with respect to material distribution of a bi-material unit cell. Finally, the effectiveness of this inverse design is demonstrated by examples with different predefined frequencies. Corresponding unit cell typologies are obtained and the dips of sound power transmission coefficient curve are successfully tuned to objective frequencies.

Using the active feedback control system on the elastic wave metamaterial, this research concentrates on the sound transmission with the dynamic effective model. The metamaterial is subjected to an incident pressure and immersed in the external mean flow. The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside. The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms. Based on the dynamic equivalent method, the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter. With the coupling between the fluid and structure, the expression of the sound transmission loss (STL) is derived. This research shows the influence of effective mass density on sound transmission properties, and the STL in both modes can be tuned by the acceleration and displacement feedback constants. In addition, the dynamic response and the STL are also changed obviously by different values of structural damping, incident angle (i.e., the elevation and azimuth angles) and Mach number of the external fluid with the mean flow property. The results for sound transmission by two methods are compared, i.e., the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one. This paper is expected to be helpful for understanding the sound transmission properties of both pure single- and double-plate models.

The mouse is an important animal model for hearing science. However, our knowledge of the relationship between mouse middle-ear (ME) anatomy and function is limited. The ME not only transmits sound to the cochlea in the forward direction, it also transmits otoacoustic emissions generated in the cochlea to the ear canal (EC) in the reverse direction. Due to experimental limitations, a complete characterization of the mouse ME has not been possible. A fully coupled finite-element model of the mouse EC, ME, and cochlea was developed and calibrated against experimental measurements. Impedances of the EC, ME, and cochlea were calculated, alongside pressure transfer functions for the forward, reverse, and round-trip directions. The effects on sound transmission of anatomical changes such as removing the ME cavity, pars flaccida, and mallear orbicular apophysis were also calculated. Surprisingly, below 10 kHz, the ME cavity, eardrum, and stapes annular ligament were found to significantly affect the cochlear input impedance, which is a result of acoustic coupling through the round window. The orbicular apophysis increases the delay of the transmission line formed by the flexible malleus, incus, and stapes, and improves the forward sound-transmission characteristics in the frequency region of 7–30 kHz.

It has been demonstrated recently via simulations in a duct that the sound transmission loss of porous materials can be increased with embedded periodic scatterers [Jena and Qiu, J. Acoust. Soc. Am. 147, 978-983 (2020)]. In this paper, the insertion loss (IL) of two types of finite size structures constructed by installing two parallel porous sheets within rows of periodic scatterers is investigated in free field. One structure uses rigid cylindrical shells, while the other uses split ring shells, which are obtained by making uniform vertical slits in cylindrical shells. The simulation results show that the mixed structure has larger IL than the summation of the ILs of the individual periodic scatterers and two parallel porous sheets in the frequency range after the first bandgap due to Bragg diffraction, and an additional peak in IL is introduced for the split ring scatterers due to their local resonance. The amplitude, frequency, and bandwidth of the resonance peak can be tuned by changing the geometry of the slit for some specific broadband sound absorption. Finally, the experiment results obtained in an anechoic chamber are presented to support the simulation results and analyses.

When applying the modal summation method to the sound transmission loss (STL) prediction of various plates, the assumption of the blocked sound pressure, or alternatively speaking, ignoring sound radiation terms, has obvious simplicity and is sometimes used for the single-layered panels, rib-stiffened plates or heavily damped sandwich plates. For light-weighted sandwich plates with honeycomb and foam cores, however, this assumption is somewhat in doubt and worth examining. Based on sixth-order differential equations governing the flexural vibration of sandwich plates, the prediction formula of STL is derived by the modal summation approach. Theoretical predictions were validated by measurement data. Next, the theoretical formula of STL under the assumption of the blocked sound pressure was examined. The STL discrepancies of sandwich plates caused by sound radiation terms are illustrated. It was found that the STL discrepancies of sandwich plates were closely related to frequency, reached their peak value at the coincidence frequency region. The results indicate that the sound radiation terms, or the couplings between the radiated sound pressure and the plate response, should not be ignored for the prediction of STL for sandwich plates with honeycomb and foam cores.

Environmental issues near roads become more and more important in our society daily life. One of the most critical environmental issues is traffic noise. The present paper study louvred noise barrier designed by authors. The louvred noise barrier provides sound attenuation while allowing airflow and sunlight through it. Since the airflow resistance of the barrier is low, it requires a shallow foundation compared to conventional noise barriers. The sound attenuation performance of the louvred noise barrier was tested experimentally in a sound transmission chamber. Airflow resistance simulated using a computational fluid dynamics model. The simulation and experimental study were done with different louvred noise barrier setup: change of louvre blade angle and sound-absorbing material thickness. The results showed potential for future development for the field testing. Sound attenuation was highest in 2500 Hz and 3150 Hz octave frequency bands. Depending on the louvred barrier setup, sound attenuation was up to 28 dB(A) in mentioned frequency bands. The equivalent sound pressure level reduced up to 17 dB(A). The results showed that an increase in the louvre blade angle increases sound attenuation and increases airflow resistance.

BACKGROUND: Sound normally enters the ear canal, passes through the middle ear, and stimulates the cochlea through the oval window. Alternatively, the cochlea can be stimulated in a reverse manner, namely round window stimulation. The reverse stimulation is not well understood, partly because in classic lumped-parameter models the path of reverse drive during the round window stimulation is usually not considered. OBJECTIVE: The study goal is to gain a better understanding of the hearing mechanism during round window stimulation. METHODS: A piezo actuator was coupled to the oval and round window of the guinea pigs. The auditory brainstem response produced by the forward and reverse stimulation at four frequencies was recorded. RESULTS: The results show that the input voltage of the actuator required at the hearing threshold in the round window drive was higher than that in the oval window drive. In order to understand the data, we designed a lumped-parameter cochlear model that can simulate both forward and reverse drive. The model-predicted results were consistent with the experimental results. CONCLUSIONS: The response of the auditory system to stimulus of oval window and round window was quantified through animal experimentation, and guinea pigs were used as experimental animals. When the same stimulus was applied to the oval window and round window of the cochlea, the ABR signals were compared. A lumped parameter model was designed to incorporate the sound transmission paths in both oval and round window stimulation. The simulated results are consistent with those of animal experiments. This model will be useful in understanding the inner-ear response in round window.

This study collects all of the existent papers in the field of acoustic transmission across multilayered plate constructions. Herewith, a comprehensive source is proposed wherein approximately 410 references are reviewed and described from the first [Formula: see text] to [Formula: see text]. In the first part, in addition to the presentation of a complete explanation about the importance of the acoustic analysis of these structures, appropriate formulations are also provided. Furthermore, an overview of the thematic correspondent is carried out. Since the type of material used in these constructions can be very important in sound insulation, the significance of this subject is remarked. The papers are then classified based on their acoustic excitation fields containing plane wave, diffuse, random, and point source. After analyzing the research approaches according to different environmental properties, the articles are ordered based on their boundaries as finite and infinite. To present reliable outcomes, it is necessary to investigate a proper theory proportional to the structure’s thickness. Herewith, this issue is also discussed in detail. The review is also expanded to focus on the different vibroacoustic solutions. Before concluding remarks, the authors' research works are presented wherein either optimization algorithms or control techniques improve the acoustic performance of these structures.

In the present work, vibroacoustic (VA) characteristics, namely sound transmission loss (STL), overall sound pressure levels (OASPLs) of aircraft panels made up of aluminum, composites and fiber me...

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Sound transmission characteristics of panels have been extensively examined which is often quantified by transmission loss. Although acoustic materials are usually applied to passive noise solutions. In the present paper, the influence of sound-absorbing materials on the transmission loss of double-walled panels has been studied theoretically. An analytical method based on statistical energy analysis technique (SEA) is employed for predicting the transmission loss of double-wall steel and aluminum panels. Three commercially available acoustic materials, ie., polyurethane, glass wool, and melamine foam are chosen for investigation.

This work deals with Experimental Modal Analysis and vibro-acoustic testing performed on several composite panels tested at Leonardo Laboratories, Pomigliano site. The main objective of this paper is to investigate the dynamical behaviour of the structure under test and to evaluate its acoustic properties. Several tests have been performed at the Trasmission Loss Facility of Leonardo. In a modal test, both the applied forces and vibration responses of the excited structure are measured in one or more locations. Exploiting this data, a Modal Model, that essentially contains the same information as the original vibration data, is derived by means of frequency-domain system identification techniques. A home-built Matlab algorithm, named “uMan”, is developed to perform a full Experimental Modal Analysis. Its performances, in terms of capability to build a useful stabilization chart and to curve-fit measured FRFs, are shown. Moreover, a comparison with respect to the state-of-art “Polymax” algorithm in LMS Test.Lab is provided. Finally, the numerical-experimental correlation is performed to verify consistency. The proposed algorithm identifies first mathematical polynomial models, rather than estimating the modal parameters directly from the measurements. Subsequently, these mathematical models are related to the modal parameters. Finally, the obtained Modal Model is compared to the analytical dataset. An acoustic test has been performed to experimentally investigate sound transmission. Two experimental methods have been adopted to evaluate the transmission loss. First, the method that includes measurements of the sound pressure levels using microphones is exploited. Then, the sound intensity method, in which the transmitted sound intensity is measured with a sound intensity probe, is used. By comparing both experimental techniques, the first showed better performance with respect to the other method at low frequencies, while the sound intensity method is more applicable in the medium and high frequency regions in order to predict the noise transmission characteristics.

This study aims to develop a novel acoustic panel that constitutes more natural fiber rather than a resin matrix, and the effect of perforation depth in the composite panel is investigated. Jute fiber-reinforced composite panels undergo partial perforation using a tapping machine of depth 7.5 mm, 15 mm, and 22.5 mm to the total thickness of 30 mm. The samples are tested experimentally in an impedance tube and sound transmission loss test setup to evaluate the acoustic capabilities for the frequency range of 100–1600 Hz. For validation, the intrinsic parameters are predicted from experimental sound absorption data using the inverse characterization technique. Insight of application aspect, the panel is modeled to be present in a rectangular acoustical cavity and analyzed numerically in COMSOL Multiphysics. The impedance tube test results indicate that the peak of the sound absorption coefficient increases with increases of perforation depth. Similarly, perforation depth influences the transmission loss of the panel, and significant results noticed. The use of a jute panel in rectangular enclosure results in a 3–6 dB reduction in the overall sound pressure level of one-third octave frequencies.

The hyacinth plant (Eichhornia crassipes) is an aquatic weed that causes the silting of swamps. The water hyacinth research was developed because of concerns over the threat of biodiversity in swamps by utilizing water hyacinth for ceramic and composite mixtures. This current research highlights the comparative acoustical performances of ceramic and composite with water hyacinth contents. Dried water hyacinth was added to the clay ceramic mixture with a weight percentage of 2, 6, 8, and 10 wt%. The ceramic dough was then shaped hexagonally with an interlock system and molded overlay respectively before burning and biscuits, while the composite dough consisted of 200 ml polyester resin: 25 mg water hyacinth: 20 ml catalyst. The acoustic test methods refer to ASTM 1050-98 and ASTM E2611-09 for sound absorption and sound transmission loss respectively. The result showed that the 8 wt% water hyacinth mixture of porous ceramic had an average absorption coefficient of 0.29 and a sound transmission loss of a wide range of frequencies with an average of 59.1 dB. Meanwhile, the resin composite has a poor average of sound absorption of 0.10 - 0.11 and 58.08 - 58.36 dB on its STL. The innovation of the water hyacinth-ceramic, however, had a promising character as a Helmholtz-based diffuser-absorber.

The paper discusses promising way of utilization of the buckwheat husks for production of noise abating epoxy based composites for transport infrastructure and buildings industry. Composites of different densities from 400kg/m3 up to 650 kg/m3 have been prepared. The measurements of normal coefficient of sound absorption and sound transmission loss in the range from 500 Hz up to 6400 Нz are carried out. The absorption coefficient posses local maximum depending on the density of composites approaching the value of 0.99 at 3120 Hz for the density 400 kg/m3. The sound transmission loss of composites increases with density from the mean value of 10 dB for 400kg/m3 up to 60 dB for 650 kg/m3 that is comparable with well-developed artificial materials. The pristine buckwheat husks is thermally stable of up to 200-250°С that gives thermogravimetric analysis in the range from 30°С up to 500°С. The husks is suggested as the filler for production of epoxy resin based noise abating composites.

Ocean fronts are mostly determined according to the horizontal temperature gradient, and various selection criteria may lead to different frontal zones. This study proposes a frontal zone delineation method based on sound speed profile. In this paper, the sound speed profile of the Kuroshio intrusion front in the Luzon Strait is classified via fuzzy cluster analysis based on transitive closure and fuzzy C-means algorithm. At the same time, considering that ocean fronts affect sound propagation, we verify the effectiveness of the two algorithms in terms of sound transmission loss. The results show that in different depth ranges, the effectiveness of the two algorithms differs in identifying the frontal zone. At depth below 300 m, the sound speed profile changes drastically, and fuzzy cluster analysis based on the transitive closure is more effective. At 300–700 m depth where the sound speed profile tends to be stable, the fuzzy C-means algorithm is more effective. At 700–1000 m depth near the SOFAR axis (the depth of the minimum sound speed), fuzzy cluster analysis based on the transitive closure is more effective. Finally, based on the sound speed profile, we combine both algorithms for the first time to obtain a three-layer geometric optimized structure of the Kuroshio intrusion front in the Luzon Strait. The classification of sound speed profiles via the two fuzzy cluster algorithms provides a new way to judge the frontal zone in different depth ranges and reconstruct geometric models of ocean fronts.

In this paper, the sound transmission loss by different materials at aircraft noise is measured experimentally. The main objective of this paper is to measure the acoustical or sound absorption properties of glass material, polypropylene material and glass fiber reinforced composite material. The composite material is manufactured at three different fiber volume fractions. The fiber volume fractions are 10%, 20% and 30%. A three dimensional wooden sound proof duct is manufactured in which a long duct is enclosed. An acoustic source is used to generate an aircraft noisy signal. The generated signal is passing through the samples of the different material to measure their sound absorption properties. It is observed that for each fiber orientation, glass material is absorbing more aircraft sound than neat polypropylene and composite specimens. It is concluded that composite material with 10% volume fraction of fiber is performing better than the rest of specimens. This is due to the fact that with the increase in volume fraction of fiber, porosity decreases due to which sound transmission loss decreases. Also, the sound transmission loss of composite specimen with 10% volume fraction of fiber is comparable with that of the glass material.

This is comprehensive study on sound absorption performance of coconut coir fiber using experimental and theoretical approaches. Samples of coconut coir fiber with different thickness and densities were prepared to get their effect on sound absorption coefficient. Measurement of sound absorption coefficient was done by using impedance tube set up based on ISO 10534-2 and ASTM E1050-98 standards. Delany- Bazley model was used to find effect of thickness and density. In this paper the result sound absorption coefficient of theoretical and experimental study presented and compared. The result of Delany- Bazley model shows promising results compared with experimental results up to 2700–2900 Hz, further deviation in results were observed. Sound absorption coefficient of 0.84 (2900 Hz) for 35 mm thick sample with density 220 Kg/m3 was recorded. Further Sound Transmission Loss (STL) for 21 mm, 28 mm, 35 mm thickness samples with 220 Kg/m3 were measured using transfer function method of impedance tube. It was established that coconut coir fiber samples effectively dissipitate the sound energy giving fair sound absorption properties.

The sound transmission losses (STL) of a metal panel with rib reinforcement (MPRR) are studied by both an experimental method and a simulation approach. The experimental method and data processing technique for obtaining STL are presented. Six MPRRs with different number of rib reinforcement and different geometry size of rib reinforcement, and six MPRRs with different type of the pasted damping material are designed and anufactured, and their STL performances are investigated by experimental method. The calculation model for STL of a MPRR is proposed and the calculated STL are compared favorably with the experimental data, which validates the proposed model. The analytical methods and conclusions are instructive for the design and the tuning of STL of MPRRs.