Reduction Of Sound Transmission Research Articles

Sound transmission reduction of double walls using porous and viscoelastic materials

Double-walled structures separated by an acoustic cavity are widely used in many applications for sound insulation purposes. Their sound transmission loss is estimated by calculating the ratio between the incident sound power on the first wall and the radiated sound power by the second. The introduction of a melamine foam associated with heavy masses brings a better sound insulation against external noise. In this context, this work deals with the numerical prediction of the sound transmission of a roller shutter box equipped with porous and viscoelastic materials. Such system can be modeled, at first approximation, as a double-walled structure. The proposed approach is based on the use of the finite element method for the modeling of the different solid and fluid domains of the problem. A mixed displacement pressure formulation of the Biot poroelasticity equations is used to model the poroelastic domain. The structure is excited by a diffuse field represented by a superposition of plane waves with random phases and directions. The acoustic power radiated by the second wall is calculated by applying the Rayleigh integral method. The results show the importance of optimizing the position of the porous and the heavy layers to maximize the sound insulation.

Active sound transmission reduction across acoustic window

In this study, the experimental method of transfer functions is employed to investigate the possibility of improving the sound transmission loss of acoustic windows using an active control technique. Twenty-five microphones, 20 of them located evenly over the acoustic window's indoor exit (provide error signals) and 5 fixed in the receiver room (capture the transmitted sound), and 19 small loudspeakers were used in the experiments. The loudspeakers acted as the canceling sources, and they were located along the window's interior perimeter (except the bottom part). The receiver room was made relatively “dead” using fiberglass linings. A loudspeaker array located in the source room acted as the primary sound source. The active control is implemented by minimizing the squared sound pressures at selected error microphones. Results show that the active noise control method can improve the sound transmission loss across acoustic window. The performance depends on the arrangement of the cancelling sources and the error microphone locations. It is found that an average of between 6 and 8 dB reduction of sound transmission within the frequency range from 100 to 1000 Hz can be achieved by an active control system with 4 or 6 error microphones and only three cancelling loudspeakers.

Optimization of sound transmission loss of open acoustic barriers with respect to unit cell topology

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.

How Stapes Ankylosis and Fracture Affect Middle Ear Dynamics: A Numerical Study.

Numerical models of the human middle ear have been developed throughout the last 30 years, for different purposes. While several types of pathologies have been studied, stapedial disorders were seldomly explored. This papers aims to clarify how stapes fracture and some forms of stapes ankylosis, such as stapedial tendon (ST) ossification, augmented pyramidal eminence (PE) and bony bar presence, affect the sound transmission through the middle ear. In addition, the stapes dynamics is also analyzed by means of total displacement and first principal strain. For the purpose of the study, first, a three-dimensional finite element model of the human middle ear is detailed and validated under normal (healthy) conditions. The model is then modified to represent the stapedial disorders of interest. A measure is established for evaluating how the disorders reduce sound transmission through the middle ear. Results of the reduction of sound transmission showed that the different forms of stapes ankylosis affect primarily low frequencies, while the stapes fracture mostly affects high frequency sound transmission. According to the results, an augmented PE does not restrict stapes movement unless followed by some ossification of the ST. In addition, the question whether the fracture is in the anterior or posterior crus and the distance of the fractured part from the stapes footplate have a relevant role in the reduction of the sound transmission. Finally, the analysis of total displacement and first principal strain of the stapes helped to highlight some differences among the stapedial disorders.

Reduction of Sound Transmission Through Finite Clamped Metamaterial-Based Double-Wall Sandwich Plates with Poroelastic Cores

Finite structures play a more realistic role in applications designed for sound and vibration isolation. Doublepanel structure with poroelastic cores is able to exhibit a superior sound insulation performance in mid-high frequency range, while is relatively inferior to isolate waves at low frequencies. In order to further reduce sound transmission at low frequencies and cater for the actual situation, this paper decides to introduce the metamaterial concept into finite double-wall sandwich plates and presents an analytical model to calculate the sound transmission loss through the metamaterial-based double-panel with fully clamped boundary conditions. The metamaterial-based double-wall sandwich plates are constructed by replacing the bare panel with the metamaterial plate, consisting of a homogeneous plate and periodically attached local resonators. Biot's theory is used to examine the wave propagation in the poroelastic medium. The vibro-acoustic problem of the proposed sandwich plate is solved by employing the modal superposition theory and the Galerkin method. Numerical results show that the sound transmission is significantly reduced at low frequencies. Unique phenomena caused by attached local resonators are explained and the eff ects of resonator inerter, incident angles and damping on the sound insulation properties are also studied.

Analysis of the effect of different patologies on the sound transmission through the middle ear by means of a finite-element model

The middle ear is part of the human auditory system and its function is to transmit acoustical energy to the inner ear by means of mechanical vibrations. Finite-Element (FE) models of the human middle ear have been studied since 90s, making it possible to evaluate its dynamic behavior in different ways. In this work, an accurate FE model of the human middle ear is described and used for assessing the relationship between the reduction of sound transmission through the ossicular chain and hearing loss due to three different pathologies: tympanic membrane perforation, stapedial tendon ossification and stapes fracture. For these three pathologies, case studies from the literature with experimental hearing loss data are reviewed and clinical results are compared to the FE model predictions. In all cases a good relationship between sound transmission reduction predicted by the FE model and the hearing loss measured through audiometric tests were found. Results show that an accurate FE model of the human middle ear can be a powerful tool for clinical applications and research in otology, allowing to predict the effect of middle ear pathologies and to evaluate the results of corrective surgeries on hearing.

Slow-wave metamaterial open panels for efficient reduction of low-frequency sound transmission

Sound transmission reduction is typically governed by the mass law, requiring thicker panels to handle lower frequencies. When open holes must be inserted in panels for heat transfer, ventilation, or other purposes, the efficient reduction of sound transmission through holey panels becomes difficult, especially in the low-frequency ranges. Here, we propose slow-wave metamaterial open panels that can dramatically lower the working frequencies of sound transmission loss. Global resonances originating from slow waves realized by multiply inserted, elaborately designed subwavelength rigid partitions between two thin holey plates contribute to sound transmission reductions at lower frequencies. Owing to the dispersive characteristics of the present metamaterial panels, local resonances that trap sound in the partitions also occur at higher frequencies, exhibiting negative effective bulk moduli and zero effective velocities. As a result, low-frequency broadened sound transmission reduction is realized efficiently in the present metamaterial panels. The theoretical model of the proposed metamaterial open panels is derived using an effective medium approach and verified by numerical and experimental investigations.

Reduction of sound transmission across plenum windows by incorporating an array of rigid cylinders

The potential improvement of plenum window noise reduction by installing rigid circular cylinder arrays into the window cavity is investigated numerically using the finite-element method in this study. A two-dimensional approach is adopted. The sound transmission characteristics and propagation within the plenum window are also examined in detail. Results show that the installation of the cylinders in general gives rise to broadband improvement of noise reduction across a plenum window regardless of the direction of sound incidence. Such acoustical performance becomes better when more cylinder columns are installed, but it is suggested that the number of cylinder rows should not exceed two. Results also show that the cylinder positions relative to the nodal/anti-nodal planes of the acoustic modes are crucial in the noise reduction enhancement mechanisms. Noise reduction can further be enhanced by staggering the cylinder rows, such that each cylinder row supports the development of a different acoustic mode. For the simple cylinder arrangements considered in this study, the traffic noise reduction enhancement observed in this study can be as high as 4–5 dB, which is already comparable to or higher than the maximum achieved by installing sound absorption into a plenum window.

Using Tuning-Fork Tests in Diagnosing Fractures.

Mugunthan K, Doust J, Kurz B, Glasziou P. Is there sufficient evidence for tuning fork tests in diagnosing fractures? A systematic review. BMJ Open. 2014;4(8):e005238. Does evidence support the use of tuning-fork tests in the diagnosis of fractures in clinical practice? The authors performed a comprehensive literature search of AMED, CAB Abstracts, CINAHL, EMBASE, MEDLINE, SPORTDiscus, and Web of Science from each database's start to November 2012. In addition, they manually searched reference lists from the initial search result to identify relevant studies. The following key words were used independently or in combination: auscultation, barford test, exp fractures, fracture, tf test, tuning fork. Studies were eligible based on the following criteria: (1) primary studies that assessed the diagnostic accuracy of tuning forks; (2) measured against a recognized reference standard such as magnetic resonance imaging, radiography, or bone scan; and (3) the outcome was reported using pain or reduction of sound. Studies included patients of all ages in all clinical settings with no exclusion for language of publication. Studies were not eligible if they were case series, case-control studies, or narrative review papers. Potentially eligible studies were independently assessed by 2 researchers. All relevant articles were included and assessed for inclusion criteria and value using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool, and relevant data were extracted. The QUADAS-2 is an updated version of the original QUADAS and focuses on both the risk of bias and applicability of a study through a series of questions. A third researcher was consulted if the 2 initial reviewers did not reach consensus. Data for the primary outcome measure (accuracy of the test) were presented in a 2 × 2 contingency table to show sensitivity and specificity (using the Wilson score method) and positive and negative likelihood ratios with 95% confidence intervals. A total of 62 citations were initially identified. Six primary studies (329 patients) were included in the review. The 6 studies assessed the accuracy of 2 tuning-fork test methods (pain induction and reduction of sound transmission). The patients ranged in age from 7 to 84 years. The prevalence of fracture in these patients ranged from 10% to 80% using a reference standard such as magnetic resonance imaging, radiography, or bone scan. The sensitivity of the tuning-fork tests was high, ranging from 75% to 92%. The specificity of the tuning-fork tests had a wide range of 18% to 94%. The positive likelihood ratios ranged from 1.1 to 16.5; the negative likelihood ratios ranged from 0.09 to 0.49. The studies included in this review demonstrated that tuning-fork tests have some value in ruling out fractures. However, strong evidence is lacking to support the use of current tuning-fork tests to rule in a fracture in clinical practice. Similarly, the tuning-fork tests were not statistically accurate in the diagnosis of fractures for widespread clinical use. Despite the lack of strong evidence for diagnosing all fractures, tuning-fork tests may be appropriate in rural and remote settings in which access to the gold standards for diagnosis of fractures is limited.

Active control of aircraft fly-over sound transmission through an open window

This paper presents an experimental work on active control of sound transmission through a restricted opening bottom hinged window. The main goal of the work is to demonstrate the feasibility of the active technique to limit the loss of attenuation due to the aperture of windows, and its application to aircraft fly-over incident noise. The experimental window is placed in an exposed façade of a dwelling close to an airport and subject to fly-by aircraft noise. The active control is configured to cancel the pressure at the aperture using a single-input single-output feedforward adaptive system. As a result, a reduction of sound transmission is achieved with low power consumption. In global terms, an increase of almost 3dB of transmission loss (with respect to the partially opened window insulation values) in the low frequency range (below 160Hz and according to the National Danish Method for evaluating low frequency noise) is demonstrated, which is equivalent to a reduction of 50% in the loss of insulation caused by opening the window.

Smart Double Panel for the Sound Radiation Control: Blended Velocity Feedback

In this paper an active damping method using blended velocity feedback for the reduction of sound transmission through a simplified aircraft double panel is considered. The double panel consists of a source and a radiating panel, which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The double panel is equipped with an array of nine voice-coil actuators that can react against the two panels. A velocity sensor is mounted at both panel junctions of each actuator. The outputs from the sensors on the source and radiating panels are weighted by factors α and 1 - α, respectively. The two weighted signals are then subtracted and combined into the error signal fed back to the actuator via a constant amplification gain. The stability and performance of such a decentralized velocity feedback system are analyzed experimentally as a function of the weighting factor α. Reductions between -10 and -18 dB in the radiated sound power have been measured at low-frequency resonances of the double panel, depending on the weighting factor implemented.

Reduction of Sound Transmission by Active Control of the Incident Sound to the Wall

Reduction of Sound Transmission by Active Control of the Incident Sound to the Wall

Smart Double Panel with Decentralized Active Dampers for Sound Transmission Control

This paper presents a theoretical study of decentralized velocity feedback control systems for the reduction of sound transmission through double panels. The system studied consists of two plates which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The geometrical and material properties of the double panel have been chosen so as to approximate a section of an aircraft fuselage skin. The outer panel of the skin (the source panel) is excited by oblique plane waves and the consequent sound power radiated from the inner panel (the radiating panel) is calculated. First, a parametric study of passive sound transmission of double panels with different geometrical and material properties is carried out. Second, active vibration control is implemented using 16 decentralized direct velocity feedback loops. Performance of such a control system is assessed for four control cases. The first two cases deal with skyhook force actuators with collocated velocity sensors, which implement active damping either on the source panel or on the radiating panel. In the third case, skyhook actuators and collocated velocity sensors are located on both panels. Finally, an approach using actuators that react between the two panels with collocated relative velocity sensors is considered.

Glass laminates for reduction of sound transmission

The present invention is a glass laminate having sound attenuation properties that make it suitable for use as acoustic glazing in architectural applications and/or in vehicles.

Vibration and Sound Radiation of Truss Core Panels

The dynamic response and the sound radiation of truss core panels are investigated in this paper. The spectral element model for the truss core panel is developed. The element model is established by employing shape functions derived directly from the solution of distributed parameter models for each beam element. Forced vibrations of a fluid-loaded beam in a rigid baffle are considered. The spectral formulation can be easily and efficiently coupled with the Fourier transform (FT) based analysis of the structure’s sound radiation in a surrounding acoustic medium. Hence the proposed formulation is an efficient numerical tool for the analysis of the dynamic and acoustic performance of the considered truss core sandwich panels. The comparison of the sound characteristics selected as sound transmission reduction index to the psychical parameters of the truss core beam is carried out.

Structural and Acoustic Behavior of Chiral Truss-Core Beams

This paper analyzes the structural and acoustic behavior of sandwich beams with a chiral truss-core. This particular core configuration is considered to exploit some of the unique properties of the chiral geometry and to explore their potential benefits in terms of sound-transmission reduction and vibration isolation. The chiral core is composed of circular elements or nodes, joined by ligaments or ribs. The arrangement of nodes and ribs is such that chiral assemblies exhibit in-plane negative Poisson’s ratio behavior as well as unique deformation patterns. The vibroacoustic performance of the considered beams is evaluated through a numerical model, formulated by employing dynamic shape functions derived directly from the distributed parameter model of beam elements. This formulation allows an accurate evaluation of the dynamic response of the considered structures at high frequencies with a limited number of elements. Furthermore, such a numerical model can be coupled with a Fourier-transform-based analysis of the sound radiated by the structure in a surrounding fluid medium. The structural-acoustic behavior of the proposed beams is investigated in terms of kinetic energy of the constraining layers and sound pressure levels corresponding to an incident pressure wave. A sensitivity study investigates the influence of core configuration and geometry on the beam performance. Moreover, the performance of the chiral core is compared to that of cores with “square” and hexagonal topologies. The results demonstrate the design flexibility offered by the proposed core design, whose configuration is defined by a number of independent parameters that can be modified and optimized to enhance the structural-acoustic performance of the beam.

Reduction of Sound Transmission by Active Control of the Incident Sound to the Wall

Reduction of Sound Transmission by Active Control of the Incident Sound to the Wall

Active control of glass panels for reduction of sound transmission through windows

This paper explores the development of thin glass panels that can be controlled electronically so as to act as transmission preventers that block the propagation of sound. Small rare earth voice coil actuators are used to control glass panel vibrations. The development of the control system is based on the use of a wave separation algorithm that separates incident sound from reflected sound. The incident sound serves the important purpose of providing an acoustic reference that is unaffected by the action of the control system speaker. This reference signal is used in an adaptive feedforward control system to drive the transmitted sound to zero. Detailed experimental results are presented showing the efficacy of the algorithms in achieving real-time control of acoustic transmission. The glass panels are able to effectively block transmission of sound, reducing sound transmission by 20 dB in the case of tonal frequencies and by 10–15 dB in the case of broadband noise. The glass panels can potentially be of great value in the development of noise-blocking glass windows for homes close to airports and noisy highways.

Vibration and sound radiation of sandwich beams with honeycomb truss core

Abstract The vibrations of and the sound radiation from sandwich beams with truss core are analyzed. The structure of the core is composed of a sequence of identical unit cells repeating along the beam length and across the core thickness. Each cell is composed of beam elements assembled to form a frame structure. Layouts with the typical honeycomb pattern arranged through the thickness of the core are here considered. This design represents an alternative with respect to the traditional application of honeycombs in sandwich construction. The proposed configuration provides sandwich beams with interesting structural as well as acoustic characteristics. A finite element model is developed to evaluate the structural and the acoustic behavior of the considered class of sandwich beams. The model is formulated by employing dynamic shape functions, derived directly from the distributed parameter model of beam elements. This formulation, often denoted as “spectral”, allows an accurate evaluation of the dynamic behavior of the considered structures at high frequencies and with a limited number of elements. In addition, the spectral model can be easily coupled with a Fourier transform based analysis of the sound radiated by the fluid-loaded structure. The model is used to analyze the performance of beams with various core configurations. The comparison is carried out in terms of structural response and sound transmission reduction index. In addition the sound pressure levels and distributions resulting from the beam vibration in an unbounded acoustic half-plane are evaluated and compared. Hexagonal and re-entrant configurations are considered in an effort to study the effects of core geometry on structural response and acoustic radiation.

Research in the field of active sound transmission control

Sound transmission through an unperforated partition may be described as the vibro-acoustic process in which fluid-borne sound waves incident upon the partition from the source side force it to vibrate and consequently radiate transmitted fluid-borne sound waves into the space on the opposite (receiving) side. Active reduction of sound transmission through partitions, or active sound transmission control (ASTC), denotes an active modification to this process. It may be defined as the reduction of transmitted sound through the action of electro-mechano-acoustical devices regulating any or all stages of the vibro-acoustic sound transmission process. In certain analyses, this branch of active noise control has referred to situations in which electro-mechanical actuation is applied only to a partition through which sound is transmitting. However, since ASTC may be achieved by other means, and since much research in the field has utilized other techniques, this limitation is clearly too restrictive. This paper reviews and categorizes many research efforts in the field, and provides a brief history of the efforts based on an extensive bibliography of the subject matter. It also identifies research areas that could be pursued in the future.