Analysis of the sound transmission loss of panels with resonant systems on the basis of equivalent representations

Effects of increasing the sound transmission loss of panels with the help of resonant systems on the basis of equivalent representations are analyzed. Emphasis is placed on the least-studied resonant systems, the inertial bodies of which simultaneously interact with media on each side of the panels. A universal expression for the sound transmission loss of panels with an arbitrary system of resonant elements with one degree of freedom is presented. It includes the parameters common to all types of resonators (the total mass, compressibility, quality factor, and characteristic frequencies). The expression can be directly used to compare the efficiency of different types of resonant systems mounted on a panel and to determine their optimum parameters.     

Sound transmission loss of foam-filled honeycomb sandwich panels using statistical energy analysis and theoretical and measured dynamic properties

Comparisons between the experimental and predicted sound transmission loss values obtained from statistical energy analysis are presented for two foam-filled honeycomb sandwich panels. Statistical energy analysis (SEA) is a modeling procedure which uses energy flow relationships for the theoretical estimation of the sound transmission through structures in resonant motion. The accuracy of the prediction of the sound transmission loss using SEA greatly depends on accurate estimates of: (1) the modal density, (2) the internal loss factor, and (3) the coupling loss factor parameters of the structures. A theoretical expression for the modal density of sandwich panels is developed from a sixth-order governing equation. Measured modal density estimates of the two foam-filled honeycomb sandwich panels are obtained by using a three-channel spectral method with a spectral mass correction to allow for the mass loading of the impedance head. The effect of mass loading of the accelerometer is corrected in the estimations of both the total loss factor and radiation loss factor of the sandwich panels.     

Experimental estimation of the transmission loss contributions of a sound package placed in a double wall structure

The objective of this paper is to propose a practical impedance tube method to optimize the sound transmission loss of double wall structure by concentrating on the sound package placed inside the structure. In a previous work, the authors derived an expression that breakdown the transmission loss of a double wall structure containing a sound absorbing blanket separated from the panels by air layers in terms of three main contributions; (i) sound transmission loss of the panels, (ii) sound transmission loss of the blanket and (iii) sound absorption due to multiple reflections inside the cavity. The sound transmission loss contributions of the blanket can thus be estimated from three acoustic measurements using impedance tube techniques: two reflection coefficients at the front face and the rear face of the blanket placed in specific positions characteristic of its position inside the double wall structure and its sound transmission coefficient. The method is first validated in the case of a double wall structure filled with a 2 in. foam material. Next, it is applied to investigate (i) the effect of frame compression of a 2 in. fibre glass in an aeronautic-type double wall structure and (ii) the effect of double porosity with or without porous inclusions in a building-type double wall structure.     

Analytical Study on the Rate of Sound Transmission Loss in Single Row Honeycomb Sandwich Panel Using a Numerical Method

Honeycomb structures have recently, replaced with conventional homogeneous materials. Given the fact that sandwich panels containing a honeycomb core are able to adjust geometric parameters, including internal angles, they are suitable for acoustic control applications. The main objective of this study was to obtain a transmission loss curve in a specific honeycomb frequency range along with same overall dimensions and weight. In this study, a finite element model (FEM) in ABAQUS software was used to simulate honeycomb panels, evaluate resonant frequencies, and for acoustic analysis. This model was used to obtain acoustic pressure and then to calculate the sound transmission loss (STL) in MATLAB software. Vibration and acoustic analysis of panels were performed in the frequency range of 1 to 1000 Hz. The models analyzed in this design includes 14-single row-honeycomb designs with angles of −45°, −30°, −15°, 0°, +15°, +30°, +45°. The results showed that a-single row and −45°cell angle honeycomb panel in the frequency range of 1 to 1000 Hz had the highest STL as well as the highest number of frequency modes (90 mods). Furthermore, the panel had the highest STL regarding the area under the STL curve (dB∙Hz). The panels containing more frequency mods, have a higher transmission loss. Moreover, the sound transmission loss is more sensitive to the cell angle variable (θ). In other studies, the STL was more sensitive to the number of honeycomb cells in the horizontal and vertical directions, as well as the angle of cells.     

Active control of acoustic reflection,absorption, and transmission using thin panel speakers

This paper explores the development of thin panels that can be controlled electronically so as to provide surfaces with desired reflection coefficients. Such panels can be used as either perfect reflectors or absorbers. They can also be designed to be transmission blockers that block the propagation of sound. The development of the control system is based on the use of wave separation algorithms that separate incident sound from reflected sound. In order to obtain a desired reflection coefficient, the reflected sound is controlled to appropriate levels. The incident sound is used as an acoustic reference for feedforward control and has the important property of being isolated from the action of the control system speaker. In order to use a panel as a transmission blocker, the acoustic pressure behind the panel is driven to zero. The use of the incident signal as a reference again plays a key role in successfully reducing broadband transmission of sound. The panels themselves are constructed using poster board and small rare-earth actuators. Detailed experimental results are presented showing the efficacy of the algorithms in achieving real-time control of reflection or transmission. The panels are able to effectively block transmission of broadband sound. Practical applications for these panels include enclosures for noisy machinery, noise-absorbing wallpaper, the development of sound walls, and the development of noise-blocking glass windows.     

Sound transmission across duct constrictions with and without tapered sections

The sound power transmission loss across duct constrictions with linearly tapered sections is studied with the finite element method. Results show that the acoustic energy distributions of transmitted waves at high frequency depend critically on the exit configuration of the constriction. The corresponding strengths of these waves are very much affected by the entrance setup of the constriction. The difference between inlet and outlet impedance of a constriction leads to weaker resonant sound transmission.     

An analytical study of sound transmission through unbounded panels of functionally gradedmaterials

The problem of sound transmission and reflection from unbounded panels of functionally graded materials is studied using an analytical approach. By means of matrix manipulation and Fourier component analysis, the three-dimensional (3-D) governing equations of elastodynamics are converted into a system of ordinary differential equations with variable coefficients in the frequency and wavenumber domain. Integration of the ordinary differential equation system across the panel thickness leads to a closed-form solution for the transfer matrix. Analytical expressions are then obtained for sound reflection and transmission coefficients for panels of functionally graded materials. The present model is used to predict sound transmission losses for various panel examples. The results compare well with published data from other methods, thereby validating the accuracy of the formulation developed in this study.     

Sound transmission across lightweight all-metallic sandwich panels with corrugated cores

The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. To check the validity of the model, it is used first to study the sound insulation properties of double-panel structures with air cavity, and the analytical predictions agree well with existing experimental data. The model is then employed to quantify the influence of sound incidence angle and the inclination angle between facesheet and core sheet on sound transmission loss （STL） across sandwich panels with corrugated cores. The results show that the inclination angle has a significant effect on STL and it is possible to avoid STL dips by altering the inclination angle. Moreover, it is found that sandwich panels with corrugated cores are more suitable for the insulation of sound waves having small incidence angles.     

浅海空气声入水传播特性分析

结合射线和波数谱积分方法,对空气声入水传播途径进行了分析,利用海上试验数据进行了比较检验。结果表明,在浅海环境中,对水下声场有主要贡献的空气声入水传播途径,主要是透射穿过海面边界的折射直达声以及后续的海底反射声途径,其中折射直达声途径的贡献主要集中在声源正下方附近区域,当距离较远时,由于声线扩展损失效应以及直达声影区两方面的限制,折射直达声传播损失显著增加,对接收声场起主要贡献的是可以到达更远水平距离上的海底反射声,包括海底海面多次反射声。      

Sound transmission prediction by 3-D elasticity theory

The problem of sound transmission through layered panel structures is studied with the exact theory of three-dimensional (3-D) elasticity. The exact solution to the 3-D elasticity equations is obtained by the use of the Fourier spectral method. Based on this analytical solution, a transfer matrix is derived that relates the spectral displacements and stresses on the one surface of the panel to those on the opposite panel surface. The transfer matrix is then used to develop the analytical solutions for sound reflection and transmission coefficients. Explicit, concise expressions are obtained for the analytical solutions of the acoustic transmission and reflection coefficients under the general conditions of layered anisotropic panels. Examples are given for both single-layer and sandwich panels. Predictions on sound transmission from the 3-D elasticity theory are compared with available data from other methods, and the results are discussed.     

Mechanism and calculation of the niche effect in airborne sound transmission

The goal is to interpret and calculate the "niche effect" for the airborne sound transmission through a specimen mounted inside an aperture in the wall between the source and receiving reverberation rooms. The low-frequency sound insulation is known to be worse for the specimen placed at the center than for the specimen mounted at either edge of the aperture. As shown, the aperture with a tested specimen can be simulated at low frequencies as a triple partition where the middle element is the specimen and the role of the edge leaves is played by the air masses entrained at the aperture edges. With a centrally located specimen, such a triple system is symmetric and has two main natural frequencies close together. In this case, the resonant transmission is higher than for the edge arrangement simulated as a double system with one natural frequency. Analogous resonant phenomena are known to reduce the low-frequency transmission loss for symmetric triple windows or solid walls with identical air gaps and lightweight boards on both sides. The theoretical results obtained for the mechanical and acoustical models are in a good agreement with the experimental data.     

Reflection and transmission of phonons at a planar interface between two dissimilar solids

Two semi-infinite dissimilar crystals with, however, the same crystal structure and lattice parameter are in contact at a planar interface. Using a simple force constant model, restricted to near-neighbour interaction reflection and transmission coefficients for sound waves propagating along one solid are calculated. At low frequencies the reflection and transmission coefficients are determined solely by the force constants and the atomic masses in the two media. At high frequencies the transmission coefficient becomes small if the force constant at the interface between the two media is weak. Information of the local force constant in the interface region can be gained at least in principle, by measuring the reflection and transmission coefficients at high frequencies.     

Calculation methods for the transmission loss of single,double and triple partitions

Methods of calculating the transmission loss for single and double walls are presented. These methods are developed using a statistical energy analysis (SEA). In principle the methods are based on separate calculations of resonant and non-resonant transmission for frequencies less than the critical frequency, $\text{f}{}_{\mathrm{c}}$, of the panels and calculation of only resonant transmission for frequencies equal to, and greater than, $\text{f}{}_{\mathrm{c}}$.Comparisons between calculated and measured results show good agreement.A calculation method is also presented for the transmission loss of triple panels for frequencies greater than the cut-off frequency for the cavities. For frequencies less than the cut-off frequency for the smallest cavity depth it is shown that, in most cases, the effect of the middle panel is very slight.     

Volume Fresnel reflection of electromagnetic waves in three-dimensionally inhomogeneous media

Eikonal approximation is used to derive equations describing propagation of monochromatic electromagnetic waves in a three-dimensionally inhomogeneous medium, including volume Fresnel reflection from inhomogeneities. The analysis is based on a locality principle. Separation into reflection and transmission effects is performed. The former effects are found to be isotropic, whereas the latter are anisotropic and depend on interference phenomena. Interference effects lead to violation of the Rytov law of polarization rotation. Brewster phenomena in layered and three-dimensionally inhomogeneous media are shown to occur under different conditions.     

Solid-perforated panel layout optimization by topology optimization based on unified transfer matrix

This paper presents a numerical method for the optimization of the sequencing of solid panels, perforated panels and air gaps and their respective thickness for maximizing sound transmission loss and/or absorption. For the optimization, a method based on the topology optimization formulation is proposed. It is difficult to employ only the commonly-used material interpolation technique because the involved layers exhibit fundamentally different acoustic behavior. Thus, an optimization method formulation using a so-called unified transfer matrix is newly proposed. The key idea is to form elements of the transfer matrix such that interpolated elements by the layer design variables can be those of air, perforated and solid panel layers. The problem related to the interpolation is addressed and bench mark-type problems such as sound transmission or absorption maximization problems are solved to check the efficiency of the developed method.     

The influence of sills and reveals on sound transmission loss

A review is made of existing works concerning the effects of sills and reveals on the transmission of sounds through windows and panels. New data is presented which supplements our knowledge base and a sill and reveal design guide is proposed for the purpose of increasing the sound transmission loss of windows or light panels.     

Positive and negative refraction of magnetoinductive waves in two dimensions

Previous studies of magnetoinductive waves in homogeneous media with resonant elements consisting of capacitively loaded metallic loops are extended to the case when a single wave from one medium is incident upon another one. The relationship between the input and output angles and the reflection and transmission coefficients are determined with the aid of the dispersion equation for different scenarios. An expression is obtained for the power density vector, and it is shown that its component perpendicular to the boundary is conserved across the boundary. Using different configurations of the elements it is shown that both positive and negative refraction may occur.     

A theoretical study of passive control of duct noise using panels of varying compliance.

It is theoretically demonstrated that, in a duct, a substantial amount of sound energy can be transferred to flexural waves on a finite wall panel when the upstream portion of the panel is made to couple strongly with sound. The flexural wave then loses its energy either through radiating reflection sound waves or by internal friction. The effectiveness of the energy transfer and damping is greatly enhanced if the panel has a gradually decreasing in vacuo wave speed, which, in this study, is achieved by using a tapered membrane under tension. A high noise attenuation rate is possible with the usual viscoelastic materials such as rubber. The transmission loss has a broadband spectrum, and it offers an alternative to conventional duct lining where a smooth air passage is desired and nonacoustical considerations, such as chemical contamination or cost of operation maintenance, are important. Another advantage of the tapered panel is that, at very low frequencies, typically 5% of the first cut-on frequency of the duct, sound reflection occurs over the entire panel length. This supplements the inevitable drop in sound absorption coefficient, and a high transmission loss may still be obtained at very low frequencies.     

南海北部海域内波环境下声传播损失起伏统计特性

浅海内波会引起声传播能量随时间的起伏变化,进而影响水声设备的工作性能.本文利用2015年南海北部一次浅海声场起伏实验数据,对比分析了浅海线性内波和孤立子内波条件下的声传播损失统计特性.在孤立子内波条件下,声传播损失起伏明显加剧,可达11 dB,且分布明显展宽,相对于线性内波的环境,声传播损失起伏可增加5 dB.从简正波...     

多孔弹性介质三层夹心板的隔声性能研究

应用Biot关于流体饱和多孔弹性介质的声传播理论,采用传递矩阵的分析方法,就复合多孔弹性材料夹心三层板在不同结构情况下的隔声性能进行了理论研究和实验分析,并与同等条件下双层夹心板的隔声性能进行了比较。数值计算和实验结果均表明,与双层夹心板相比,三层夹心板在中高频段隔声性能有明显优势,但低频段隔声性能有一定程度上的下降。研究还表明不同结构的复合三层夹心板在隔声效果上也各有特色。