Vibration transmission between coupled plates using finite element methods and statistical energy analysis. Part 2: The effect of window apertures in masonry flanking walls

Part 1 of this paper demonstrated the validity of predictions of vibration transmission across junctions of masonry walls using Finite Element Methods (FEM). Part 2 uses numerical experiments with FEM to calculate the vibration transmission between masonry walls with window apertures at different positions in the flanking wall(s). Results from the numerical experiments are used to assess a simple “rule-of-thumb” estimate for calculating the change in the coupling parameters due to the introduction of an aperture into a flanking wall. Conclusions are drawn concerning use of the “rule-of-thumb” estimate for the coupling loss factor in Statistical Energy Analysis and the vibration reduction index in European standard EN 12354.     

实验室隔声测量中试件洞填隙墙传声影响的检验

文章探讨了实验室建筑构件隔声测量中填隙墙传声影响的检验与修正方法。通过实验分析,给出了三种可用于不同隔声量构件的门、窗和玻璃试件隔声测量的填隙墙构造方式。     

Prediction of airborne sound transmission across a timber–concrete composite floor using Statistical Energy Analysis

This paper concerns the development and experimental validation of prediction models using Statistical Energy Analysis (SEA) to calculate the airborne sound insulation of a timber–concrete composite floor. The complexity in modelling this floor is due to it having (1) a multilayer upper plate formed from concrete and Oriented Strand Board (OSB), (2) multiple types of rigid connector between the upper plate and the timber joists and (3) a resiliently suspended ceiling. A six-subsystem model treats the concrete–OSB plate as a single subsystem and three different five-subsystem models treat the combination of concrete, OSB and timber joists as a single orthotropic plate subsystem. For the orthotropic plate it is suggested that bending stiffnesses predicted using the theories of Huffington and Troitsky provide a more suitable and flexible approach than that of Kimura and Inoue. All SEA models are able to predict the weighted sound reduction index to within 2 dB of the measurement. The average difference (magnitude) between measurements and predictions in one-third octave bands is up to 4 dB. These results confirm that SEA can be used to model direct transmission across relatively complex floor constructions. However, this requires the inclusion of measured data in the SEA model, namely the dynamic stiffness of the resilient isolators and the cavity reverberation time.     

Prediction of sound flanking transmission through two adjacent rooms within a residence building

Flanking transmission has significant effects on the overall sound insulation of two adjacent rooms within a residence building. This study investigates the mechanism of the sound flanking transmission by dividing it into several subsystems with the statistical energy analysis method. The sound energy equations of these subsystems are obtained first, and then,the sound transmissions on each flanking path are predicted and the dominant sound transmission path is determined by solving these equations and calculating the total loss factors of the subsystems and coupling loss factors between subsystems. With respect to a masonry building with heavy-weight homogeneous structure, the results show that:(1) the flanking transmission paths instead of the separating wall may become the dominant ones at low frequencies;(2) all sound transmissions on the flanking paths tend to be consistent at medium and high frequencies, so the sound insulation between two adjacent rooms depends on the direct path of the separating wall;(3) heavy-weight separating walls can be used to reduce the frequency range of the flanking transmission.     

Effect of woodwool shuttering in party floors on the flanking transmission of sound between maisonettes

The sound insulation of party walls in a four storey block of maisonettes was found to be considerably lower at first floor level than at other floor levels in the frequency range of approximately 600 to 3000 Hz. The rooms at first floor level lie immediately below the party floor which is built of dense concrete cast on woodwool shuttering, plastered beneath; the other floors are timber joist floors and this seems to be the only major difference in construction at different floor levels. Vibration measurements indicated that appreciable flanking transmission of sound was occurring through the ceiling in the frequency range 600 to 3000 Hz and it seems probable that the use of woodwool shuttering has led to a resonance effect producing these high vibration levels.     

The effect of construction material, contents and room geometry on the sound field in dwellings at low frequencies

An experimentally validated finite element method is used to model the sound level in rooms at low frequencies. It is demonstrated that the dimensions of rectangular rooms strongly influence the sound pressure level difference. Additional factors were investigated which are not normally considered in the frequency range where diffuse sound field conditions can be assumed. Three effects were investigated: room damping due to wall vibrations, furniture, the effect of small deviations from simple rectangular shapes. It is confirmed by field measurements that the vibrations of masonry walls and floors introduce less damping than surfaces of lightweight construction. Assigning to the FE model a damping equivalent to a surface absorption of 0.02 reproduces the effect of walls of heavyweight construction. Damping equivalent to a surface absorption of 0.15 reproduces the effects of plastered timber-frame walls, floors and ceilings. The work was briefly extended to a room pair built with heavyweight and lightweight material of construction. The modification of the shape of the room frequency response highlights well the effect of material of construction. In-situ and laboratory measurements show that furniture has little effect on steady-state room response below 100 Hz. Modelling a wall recess smaller than 0.5 m improved the agreement between prediction and measurements but the assumption of a simple rectangular room remains appropriate.     

A homogenised vibratory model for predicting the acoustic properties of hollow brick walls

The prediction and the physical understanding of sound transmission through masonry walls made of hollow bricks remain an open question. To solve this problem a semi-analytical approach is proposed. The inhomogeneous structures of the brick wall are homogenised and a simplified analytical model is established to calculate the transmission loss of an equivalent finite and multilayered anisotropic plate. An efficient numerical homogenisation technique is derived to define the equivalent anisotropic brick. This process only needs the knowledge of the elastic tensor of the brick material that has been determined using ultrasonic measurements. The features of the simplified brick wall have been then investigated through Lamb waves dispersion curves. Finally, the model has been used to explain the transmission loss curve of a wall and a good agreement between predictions and test data is obtained.     

Establishing a new acoustical laboratory, planning, experiments, experiences

A significant part of the input data for planning the acoustical quality of building is the result of laboratory measurements. Detailed modelling of complex phenomena of sound transmission, like structure borne sound propagation can be solved based on on well planned laboratory experiences. However it seems the constructional details of the testing facilities have important effect on the measured results. The paper describes the process of planning the testing facilities of the Laboratory of Building Acoustics, TU Budapest, which operate as a standardised laboratory, a modelling “tool” for flanking transmission in research and development and which is utilised in teaching too. Some results and conclusions of recent experiments are also reported and discussed here related to the sound reduction index of a heavy brick wall without and with flanking transmission, to the impact sound insulation between the rest of a stair and an adjacent room and also to a possibility to determine the reduction of impact sound transmission of floor coverings.     

电磁波穿透墙体的衰减特性

 应用平面电磁波理论和菲涅耳公式分析了电磁波穿透不同介质的衰减特性,对不同的极化方式、入射角、介电常数、电导率、损耗角正切和频率下,电磁波在介质间的透射性能及介质中的传输衰减特性进行了分析,对常见的普通混凝土墙、37砖墙、24砖墙、石膏空心板、水泥泡沫板、木板和玻璃与频率的衰减特性进行了数值仿真,比较了新砌混凝土墙、实心粘土砖墙和多孔粘土砖墙的损耗特点,将仿真结果与实际测量及参考文献测量结果进行了比较,结果表明仿真的墙体频率衰减趋势与实际测量结果一致,衰减数值接近并略低于实测结果。     

Calculation of the sound transmission between dwellings by partitions and flanking structures

A calculation model is presented for the sound transmission between dwellings by partitions and by flanking structures, based on the application of classical theory.The most important data needed are the sound reduction index for direct transmission of the different structures and the vibration level differences across junctions. Information on the reduction index is given, based on theory, taking into account the influence of boundary conditions by means of the structural reverberation time in situ. The vibration level differences have been determined for different junctions on the basis of in situ measurements. Under some—reasonable—restrictions this model gives the same results as would be achieved by applying the so-called Statistical Energy Analysis (SEA).Comparison between calculation and measurement for seventy-five different situations shows good agreement, the average predictions being correct with a standard deviation of 1·5 dB.     

Sound transmission at low frequencies through the walls of distorted circular ducts

A theoretical treatment of sound transmission through the walls of distorted circular ducts is given, for plane mode transmission within the duct. The transmission mechanism is essentially that of “mode coupling”, whereby higher structural modes in the duct walls are excited, because of the wall distortion, by the internal sound field. The theory is in two parts: an approximate analytical model for the structural response of the walls to the internal sound field, and a structural radiation model. Computed results, based on the theory, are compared to measurements on “long-seam” air conditioning ducts. Where the duct geometry can be reliably specified, reasonably good agreement is obtained between theoretical and experimental data. It is concluded that mode coupling effects serve to account for the discrepancies between ideal and observed behaviour in sound transmission through duct walls.     

Reduction of external noise by building facades: tolerance of standard EN 12354-3

The European standard EN 12354-3 describes a calculation model designed to estimate the reduction of outdoor sound by facades of buildings. The accuracy of the prediction method is not specified in the standard. In this paper, the tolerance of the method is studied by comparing the calculation results to the laboratory and field measurement results of different types of facades. For the weighted sound reduction index, the mean and standard deviation of the difference between the calculated and measured values of nineteen facades is 0.3±0.4 dB in laboratory conditions. In field conditions, the mean and standard deviation of the difference between the calculated and measured values of twelve facades is 3.8±3.8 dB. The tolerance is considerably larger compared to the laboratory measurements because the sound insulation of the single building facade elements have been evaluated based on the empirical estimations and not on measurement results.     

住宅建筑中相邻房间的侧向传声预测

侧向传声作为建筑中声传递的组成部分,对住宅的整体隔声效果具有重要的影响,通过将建筑中相邻房间的各建筑构件划分为若干子系统,应用统计能量分析(Statistical Energy Analysis,SEA)理论,从系统的声功率平衡的角度建立侧向传声的预测模型,在描述各路径的传声规律的同时确定主要传声路径。研究结果表明:当外围护结构为重质结构,且为匀质单一材料构造时,(1)在低频处,全程通过两相邻房间的侧墙或楼板的非通过隔墙的侧向路径成为主要侧向传声路径;(2)在中高频,各侧向路径的声压级差趋于一致,此时的建筑隔声性能取决于通过隔墙的直接路径上的声传递;(3)采用重质隔墙可以缩小侧向传声影响的频率范围。本研究为改善住宅的声环境质量及建筑隔声设计提供了理论依据。      

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.     

建筑墙体对电磁脉冲响应的FDTD分析

 采用时域有限差分法和傅里叶变换对电磁脉冲作用于建筑墙体后发生的反射和透射进行了比较全面的研究分析。采用周期边界实现了不同建筑墙体对电磁脉冲响应的数值计算，对计算的结果进行了讨论分析，研究结果表明：钢筋阵对低频段的屏蔽效果很好，当频率增加时，屏蔽效果变差。混凝土墙的频域波形具有明显的周期性，存在许多谐振频率，谐振时透过很大，谐振频率由墙的厚度、磁导率和介电常数决定，要提高墙的屏蔽效果必须增加墙的电导率，以达到一个比较好的屏蔽效果。钢筋混凝土墙的屏蔽效果和反射特性由钢筋和混凝土墙共同调制决定。     

建筑物墙壁电磁耦合截面建模及应用

电磁波照射下的建筑物室内电磁环境具有混响效果,因此可采用功率平衡法（PWB）快速评估室内电磁环境水平。然而目前PWB方法中电大腔壁耦合截面（CCS）的计算模型建立在腔内电磁波不穿透腔壁的条件下,无法直接用于电磁波可穿透室内建筑物墙壁的耦合截面计算。为此,提出了一种适用于电磁波穿透有限厚度建筑物墙壁的CCS计算新模型。该模型考虑实际建筑物墙体的厚度和材料电磁特性,能够充分反映电磁波因有限厚度墙壁多次反射对室内电磁环境水平的影响。将该模型应用于室内电场水平的快速评估,预测结果与实际测量结果吻合较好,证明了所提有限厚度建筑物墙壁CCS模型的合理性。     

Measures for assessing architectural speech security (privacy) of closed offices and meeting rooms

Objective measures were investigated as predictors of the speech security of closed offices and rooms. A new signal-to-noise type measure is shown to be a superior indicator for security than existing measures such as the Articulation Index, the Speech Intelligibility Index, the ratio of the loudness of speech to that of noise, and the A-weighted level difference of speech and noise. This new measure is a weighted sum of clipped one-third-octave-band signal-to-noise ratios; various weightings and clipping levels are explored. Listening tests had 19 subjects rate the audibility and intelligibility of 500 English sentences, filtered to simulate transmission through various wall constructions, and presented along with background noise. The results of the tests indicate that the new measure is highly correlated with sentence intelligibility scores and also with three security thresholds: the threshold of intelligibility (below which speech is unintelligible), the threshold of cadence (below which the cadence of speech is inaudible), and the threshold of audibility (below which speech is inaudible). The ratio of the loudness of speech to that of noise, and simple A-weighted level differences are both shown to be well correlated with these latter two thresholds (cadence and audibility), but not well correlated with intelligibility.     

Sound transmission in multilayered structures – Introducing finite structural connections in the transfer matrix method

The transfer matrix technique is an efficient tool for calculating sound transmission through multilayered structures. Recent developments, as to the calculation of the sound reduction index, have given better fit to measurement data, e.g. due to the simulation of finite size samples by the spatial windowing technique. In practice, however, finite size structural connections (points or lines) normally do exist between leaves in wall constructions and these are not “natural” elements in the transfer matrix method. The paper describes a simple method to account for the effect of point- and line-connections in double-leaf constructions in a transfer matrix setup. To cover the frequency range above the critical frequency of the constituent plates, some new developments as to the forced radiation from plates were needed. Predicted results compare favorably with measurement results for a number of different cases, also including a heavy wall.     

Measurement of sound insulation with a sound level meter

The present technique for measuring the airborne sound insulation of walls and floors, involving measurements in 16 one-third octave bands, is tedious and expensive. The method provides more information than is needed for most purposes, and is more suited to research.Several investigators have proposed the measurement of the overall A-weighted sound level difference using a sound level meter, with a broad band source of white or pink noise. Consistent results have been obtained but their relation to accepted rating methods such as STC is rather empirical.The reference curves used for airborne sound insulation, i.e. STC and HPGW are very similar to the A weighting curve, and if the latter were adopted as the reference curve, there would be a firm theoretical basis for measurement with a sound level meter. Measurement of the difference between the linear sound level of a source of white noise, and the A weighted received level, would in practice be a test of the conformity to the A weighting curve of the transmission loss curve of the partition. Adverse deviations would show as a higher received level. Favourable deviations would have little effect.A study of practical walls and floors, taken from National Building Studies Research Paper 33, showed that there was good correlation between the sound level difference calculated as if it had been measured directly with a sound level meter, and a proposed rating method similar to ISO R717, but using the A weighting curve as the reference curve. Ninety-six per cent of results were within ±1 dB.The practical difficulties of achieving a reasonably flat transmitted spectrum, and of correcting for room absorption will reduce this precision, but bearing in mind the practical success of other short tests, the proposed test should provide a rapid test which is adequate for approval purposes.