Non-resonant sound transmission through double walls using statistical energy analysis

Although SEA is a suitable framework for predicting sound transmission through double walls it has been found that the standard method of computing the non- resonant coupling loss factor from a room to cavity underestimates the coupling. A revised model for computing this coupling loss factor is presented which gives much better agreement with measured data. This allows better predictions to be made of sound transmission through lightweight double walls.     

The transmission of sound through a cavity-backed finite plate

This paper is concerned with the influence of a finite cavity backing a finite panel on the transmission of sound through the panel and on the vibration of the panel. Such phenomena as negative transmission loss, combined panel and cavity resonance, coincidence and cavity resonance are readily identified from the final expressions. A graphical technique, first used in a one-dimensional study of this case, is shown to be applicable in the three dimensional case to predict frequencies of interest. The theoretical analysis is compared with experimental results and with the predictions of other workers.     

Exact solution for guided sound transmission through a double partition

The exact solution is obtained for the problem of the transmission of a symmetric sound wave through a double partition contained in a parallel-plane waveguide with rigid walls. A membrane model is used for the two leaves of the partition. The solution involves a number of infinite series which converge rapidly. It is not necessary to make any special assumptions regarding the parameters describing the model. In particular no modifications are necessary for the region of the critical frequencies. Full details are given for the particular case of an incident plane wave. The result, which is suitable for computation, involves four converging infinite series. In general there are no frequencies of complete transmission or reflection. Similar analysis applies to the case of a circular waveguide.     

The effect of workmanship on the transmission of airborne sound through light framed walls

A study of the airborne sound transmission in a multi-tenanted building has shown that elements of the building which are nominally identical do not have the same acoustic performance. It was seen that some of this variation in performance could be attributed to visually-observable differences in the constructions. Some of the variation could not be explained however, and it was concluded that this variation was due to workmanship. The level of this variation was seen to be approximately 1 dB for a light steel framed construction. This variation is considerably less than that measured previously for a monolithic construction.     

Feedback control of sound transmission through a double glazed window

One way to tackle the control of stochastic noise in three dimensions is to reduce the sound transmission to the zone of interest. In buildings, windows are often the weak link in protecting the interior from outside noise. In particular, double glazed windows have a poor sound insulation at low frequency around the mass-air-mass resonance (double wall resonance). Since passive means for windows are exhausted, an active controller that increases the transmission loss in the low-frequency range is an attractive approach to reduce the noise level in buildings. Previously suggested feedforward controllers need reference microphones to measure the disturbance outside and error microphones for the adaptation somewhere in the room. For a real window this is unpractical or even unfeasible. These limitations can be overcome with the feedback controller presented here, which only uses sensors and actuators in the cavity of the double glazed window. Four different controllers—two feedforward and two feedback strategies—are designed, implemented and compared. With feedback the noise transmission around the mass-air-mass resonance can be reduced by , compared to with a feedforward controller.     

The effects of external lagging on low frequency sound transmission through the walls of rectangular ducts

Previous work by the author [1], on the transmission of internally propagated acoustic noise through the walls of rectangular ducts, is extended here in an investigation of the effects of external “lagging” (consisting of a layer of porous sound-absorbing material, and an impervious external covering) on the duct walls; this type of treatment is commonly applied as a noise control measure. A simple theoretical model, based, as before, on a coupled acoustic/structural wave system, is devised and shown to give reasonably accurate predictions in comparison with measurements of the wall transmission loss (though not in the case of lagging in which an external covering of very non-uniform thickness is incorporated). The conclusion is reached that external lagging used as an acoustic treatment is not, in general, particularly satisfactory.     

A method to predict the transmission of sound through corridors

This paper describes research carried out to provide a method by means of which sound levels in rooms adjacent to a corridor, produced by the transmission of sound through the corridor from another room, can be predicted. This has been done by using an acoustic scale model to show how the physical parameters of the corridor affect the transmission of sound into, out of and along the corridor. From analysis of the experimental results, empirical formulae are obtained to predict: (1) sound levels along a corridor produced by a sound source in the corridor or an adjacent room, (2) sound levels along a side corridor produced by a sound source in the main corridor and (3) sound levels in rooms adjacent to the corridor produced by a sound source in another room.     

Modeling the sound transmission between rooms coupled through partition walls by using a diffusion model

In this paper, a modification of the diffusion model for room acoustics is proposed to account for sound transmission between two rooms, a source room and an adjacent room, which are coupled through a partition wall. A system of two diffusion equations, one for each room, together with a set of two boundary conditions, one for the partition wall and one for the other walls of a room, is obtained and numerically solved. The modified diffusion model is validated by numerical comparisons with the statistical theory for several coupled-room configurations by varying the coupling area surface, the absorption coefficient of each room, and the volume of the adjacent room. An experimental comparison is also carried out for two coupled classrooms. The modified diffusion model results agree very well with both the statistical theory and the experimental data. The diffusion model can then be used as an alternative to the statistical theory, especially when the statistical theory is not applicable, that is, when the reverberant sound field is not diffuse. Moreover, the diffusion model allows the prediction of the spatial distribution of sound energy within each coupled room, while the statistical theory gives only one sound level for each room.     

Optimal poroelastic layer sequencing for sound transmission loss maximization by topology optimization method

Optimal layer sequencing of a multilayered acoustical foam is solved to maximize its sound transmission loss. A foam consisting of air and poroelastic layers can be optimized when a limited amount of a poroelastic material is allowed. By formulating the sound transmission loss maximization problem as a one-dimensional topology optimization problem, optimal layer sequencing and thickness were systematically found for several single and ranges of frequencies. For optimization, the transmission losses of air and poroelastic layers were calculated by the transfer matrix derived from Biot's theory. By interpolating five intrinsic parameters among several poroelastic material parameters, distinct air-poroelastic layer distributions were obtained; no filtering or postprocessing was necessary. The optimized foam layouts by the proposed method were shown to differ depending on the frequency bands of interest.     

Phase relations for a sound wave at its reflection and transmission through a plane layer

A property never considered before in acoustics is established: in the case of a sound wave incidence on a plane layer bordered by two liquid media with identical elastic properties, the phase difference between the reflected and transmitted waves is equal to π/2 irrespective of the physical constants of the layer and the media contacting it, as well as of the frequency of the incident wave.     

双层板腔结构声传输及其有源控制研究

利用子系统模态综合方法,结合阻抗-导纳矩阵法,建立了双层板腔结构向自由空间声传输及其在入射板PZT控制、辐射板PZT控制,和腔中次级声源作动等多种控制策略下,系统物理模型的统一的分析模型,导出了系统模态响应及最优次级源强度的统一的阻抗-导纳矩阵表达式。该模型表达式各部分物理意义清晰、明确,便于进行系统耦合理论、有源控制及其机理的分析和数值研究。然后,在此基础上对双层板腔结构声传输有源控制进行了全面深入的数值计算和分析研究,重点探讨了控制方法策略及系统参数对有源控制效果的影响及其对应的控制机理。结果表明:入射板PZT作动辐射声功率最小控制策略是通过入射板、声腔和辐射板三个子系统的模态抑制或重组达到消声的目的,涉及多种复杂控制机理,对入射板、辐射板和声腔模态均有效,但对入射板模态更有效;在低频段声腔(0,0,0)模态在系统耦合响应中起主导作用,因此利用腔中次级声源作动能获得较理想的控制效果,是一种较好的控制策略;由于声腔模态与结构模态间复杂的耦合关系,使得某些频率处腔中声势能一定程度上的降低并不一定导致系统声传输损失的增加,因此,腔中声势能最小控制策略不一定能够获得理想的声传输控制效果。     

Experimental study for control of sound transmission through double glazed window using optimally tuned Helmholtz resonators

This paper presents an experimental investigation of passively control of sound transmission through a double glazed window by using arrangement of Helmholtz resonators (HRs), which are commonly used for narrow band control application. The laboratory experiments were performed placing the window between reverberation chamber and anechoic chamber. The window was subject to diffuse field, approximate normal wave and oblique wave acoustic excitations. Three sets of HRs were designed and installed in cavity of window. The sound control performances at far-field were measured. The control performances from varying the number of HRs, incident acoustic field, excitation sources (band-limited white noise and traffic noise examples) are presented and discussed in detail. It is shown that a considerable reduction of the transmitted sound pressure levels has been achieved around the mass–air–mass resonance frequency (50–120 Hz). The obtained reductions in the transmitted sound pressure illustrate the potentials of HRs for improving the sound insulation characteristics of double glazed window. The experimental results also indicate that only tuning the HRs to the mass–air–mass resonance frequency does not guarantee the best possible insulation of the sound transmission.     

A finite difference scheme for acoustic transmission through the walls of distorted circular ducts and comparison with experiment

A numerical method is developed to find the structural response of the walls of cylindrical distorted circular ducts to internal plane acoustic travelling waves, and hence the internal/external sound transmission loss. Comparisons are made between experiment and theory for two “long-seam” air conditioning ducts and a squashed spiral-wound air conditioning duct. In general, reasonable agreement is obtained, when the accuracy of the geometrical specification of the ducts is taken into account. The generality of the computing code allows the method to be applied to cylindrical ducts of virtually any geometry where the radius of curvature and its first and second derivatives can be considered continuous around the duct perimeter. It is concluded that “mode-coupling” effects appear to offer a plausible explanation for the effect of wall distortion in lowering the duct wall transmission loss.     

Transmission of low-frequency internal sound through pipe walls

Transmission loss measurements are reported for long steel pipes of circular crosssection, with air inside and out, excited by internal sound. At low frequencies (wavelength greater than the pipe diameter), most of the radiated sound is accounted for by pipe bending waves. In order to approach the much higher transmission loss predicted for pure breathing motion of the pipe, bending waves must be suppressed; this has been achieved for a straight pipe by careful isolation. A sharp 90 bend in the pipe is shown to cause significant bending-wave excitation when plane waves are incident on the bend.     

The transmission of finite amplitude sound beam in multi-layered biological media

Based on the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation, a model in the frequency domain is given to describe the transmission of finite amplitude sound beam in multi-layered biological media. Favorable agreement between the theoretical analyses and the measured results shows this approach could effectively describe the transmission of finite amplitude sound wave in multi-layered biological media.     

The effect on sound insulation of small holes through solid masonry walls

Nominally identical examples of most types of building construction have been found to provide different levels of sound insulation. A possible reason is that different standards of workmanship introduce differences that cannot be seen when the building has been completed. For example, if mortar between bricks or blocks is omitted, holes right through the wall may result. An experiment has been conducted to investigate the effect of small holes through a solid wall when it is plastered or dry-lined. The results showed that the single-figure insulation ratings of the wall were not changed by the presence of holes.     

Low-frequency sound transmission through a gas-liquid interface

Typically, sound speed in gases is smaller and mass density is much smaller than in liquids, resulting in a very strong acoustic impedance contrast at a gas-liquid interface. Sound transmission through a boundary with a strong impedance contrast is normally very weak. This paper studies the power output of localized sound sources and acoustic power fluxes through a plane gas-liquid interface in a layered medium. It is shown that, for low-frequency sound, a phenomenon of anomalous transparency can occur where most of the acoustic power generated by a source in a liquid half-space can be radiated into a gas half-space. The main physical mechanism responsible for anomalous transparency is found to be an acoustic power transfer by inhomogeneous (evanescent) waves in the plane-wave decomposition of the acoustic field in the liquid. The effects of a liquid's stratification and of guided sound propagation in the liquid on the anomalous transparency of the gas-liquid interface are considered. Geophysical and biological implications of anomalous transparency of water-air interface to infrasound are indicated.     

Transmission of sound through pipe walls in the presence of flow

The transmission of sound through pipe walls was studied experimentally under no-flow conditions as well as with steady air flow velocities up to 120 m/s. The test specimens were commercial pipe and tube of diameter ranging from 0·07 to 0·3 m, and thickness-to-diameter ratios from 0·12 to 0·2. The technique involved two reverberant rooms, one traversed by the test pipe to measure externally radiated sound, and one in which the test pipe terminated to measure internally propagated sound. Vibration of the pipe wall was also monitored to determine radiation efficiency.The results show that no-flow transmission loss (TL) is higher than predicted by available theoretical expressions, but that TL decreases strongly with increasing flow velocity. A qualitative explanation for the latter is offered. Radiation efficiency was found to be independent of flow velocity. The scaling of results between “similar” specimens was moderately successful. The results are documented in sufficient detail to permit their use for forming empirical models as well as for testing future theoretical predictions.     

Low-frequency sound transmission through a gas-solid interface

Sound transmission through gas-solid interfaces is usually very weak because of the large contrast in wave impedances at the interface. Here, it is shown that diffraction effects can lead to a dramatic increase in the transparency of gas-solid interfaces at low frequencies, resulting in the bulk of energy emitted by compact sources within a solid being radiated into a gas. The anomalous transparency is made possible by power fluxes in evanescent body waves and by excitation of interface waves. Sound transmission into gas is found to be highly sensitive to absorption of elastic waves within a solid.     

Time-domain impedance formulation for transmission line matrix modelling of outdoor sound propagation

Outdoor sound propagation modelling has attracted considerable attention in the past and has lead to many analytical and numerical models. More recently, the increase of computational power has led to consider time-domain methods that enable to consider transient phenomena. Among these models, the transmission line matrix (TLM) method has been proposed, but the sound absorption at boundaries appears to be a somewhat underdeveloped aspect of this approach. In this paper, a specific implementation of impedance boundary condition is proposed. The method is based on the approximation of the impedance as a sum of linear systems, which allows the formulation of an equivalent impedance model in the time-domain. The proposed implementation is applied for two common impedance models of porous material. Numerical simulations have been carried out in the case of sound propagation over a flat ground with and without an impedance discontinuity, and for several values of specific airflow resistivity. TLM numerical predictions expressed in terms of excess attenuation relative to free field show a good agreement with analytical solutions.