The use of in-situ test method EN 1793-6 for measuring the airborne sound insulation of noise barriers

The in situ measurement of the airborne sound insulation, as outlined in EN 1793-6:2012, is becoming a common means of quantifying the performance of road traffic noise reducing devices. Newly installed products can be tested to reveal any construction defects and periodic testing can help to identify long term weaknesses in a design. The method permits measurements to be conducted in the presence of background noise from traffic, through the use of impulse response measurement techniques, and is sensitive to sound leakage. Factors influencing the measured airborne sound insulation are discussed, with reference to measurements conducted on a range of traffic noise barriers located around Auckland, New Zealand. These include the influence of sound leakage in the form of hidden defects and visible air gaps, signal-to-noise ratio, and noise barrier height. The measurement results are found to be influenced by the presence of hidden defects and small air gaps, with larger air gaps making the choice of measurement position critical. A signal-to-noise ratio calculation method is proposed, and is used to show how the calculated airborne sound insulation varies with signal-to-noise ratio. It is shown that the measurement results are influenced by barrier height, through the need for reduced length Adrienne temporal windows to remove the diffraction components, prohibiting the direct comparison of results from noise barriers with differing heights.     

墙体设置接线盒隔声性能影响的实验室研究

在轻质墙体(轻钢龙骨类板墙)及重质墙体(240 mm砖墙)上设置不同数量的接线盒前后,对墙体的空气声隔声性能的影响进行了实验室试验。并对试验结论进行了分析,得出了不同类型墙体设置接线盒后,对墙体空气声隔声性能的影响因素及处理方法。     

Standardised acoustic characterisation of sonic crystals noise barriers: Sound insulation and reflection properties

This work presents sound insulation and sound reflection measurements conducted over sonic crystal noise barriers according to the European standards EN 1793-2, EN 1793-5 and EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to window out all diffraction components and to verify the points of strength and weakness of the application of standardised measurements to sonic crystals. Diffuse field measurements in laboratory are also done for comparison purposes. Since the target frequency range for traffic noise spectrum is centred at around 1000 Hz, a finite element based parametric investigation is performed to design unit cells capable of generating band gaps in the one-third octave bands ranging from 800 Hz to 1250 Hz. Then, 3 × 3 m sonic crystal noise barriers are installed in the Laboratory of the University of Bologna and sound insulation and sound reflection measurements are performed according to the mentioned active standards for normal incidence. Sound insulation is measured for diffuse incidence too. The two methods give different results. The method more directly comparable to calculations is the free-field one. However, if on the one hand the application of a time window allows to compute the transmitted or reflected component only, on the other hand the time window itself limits the maximum width of the sample for which all reflections of the n-th order having a significant spectral content are included, and thus results critical in the analysis of this kind of noise barriers. Nevertheless, the standardised measurements allow a direct comparison between the performance of sonic crystals and common noise barriers.     

The sound insulation of wood joist floors in timber frame constructions

The results of an investigation of the sound insulation provided by wood joist floors between timber frame dwellings are described. The investigation was mainly concerned with impact transmission since available field data showed that the impact performance was, in general, worse than the airborne performance. The effects of changing various aspects of the floor design are discussed and limited guidance is given on the values of some floor parameters. Some tests have been carried out with the resilient layer bridged by nails and with the floor loaded. Suggestions are given for further research which is required to improve the understanding of sound transmission processes in wood joist floors.     

A new laboratory facility for the determination of airborne sound insulation of party walls

The laboratory test chamber described in this paper was designed to provide a test facility for the measurement of airborne sound insulation of party walls and their associated flanking construction. Initially developed as a research tool to overcome the need to carry out field measurements on new dwelling types, the results obtained in the chamber were found to be in close agreement with the results of field measurements in dwellings with similar constructional detailing. It is concluded that a chamber of this type provides a simple and economic means of assessing in the laboratory the airborne sound insulation of dwellings.     

A survey of the sound insulation between dwellings in modern building constructions

A major survey of sound insulation between dwellings in modern constructions is being carried out by the Building Research Station. The results of this survey will provide information on the operation of a performance-based building regulation and should lead to improved predictions of sound insulation. Some preliminary results are given for the performance of party walls in timber-framed dwellings.     

A model comparison of the absorption coefficient of a Microperforated Insertion Unit in the frequency and time domains

The absorption coefficient of acoustic materials can be measured either in the frequency or the time domain. At normal incidence, a sample of the material is fitted within an impedance tube and the absorption coefficient is calculated in the frequency domain from the measurement of the transfer function between two microphones [ISO 10534-2. Acoustics - determination of sound absorption coefficient and impedance in impedance tubes - Part 2: transfer function method. ISO, Geneva, Switzerland; 1996]. When the acoustic material must be characterized at oblique incidence or in situ (noise barriers, for instance) the absorption coefficient is calculated from measurements of the loudspeaker-microphone impulse response in the time domain, both in free field and in front of the sample [CEN/TS 1793-5. Road traffic noise reduction devices - test method for determining the acoustic performance - Part 5: intrinsic characteristics - in situ values of sound reflection and airborne sound insulation. CEN, Brussels, Belgium; 2003, ISO 13472-1. Acoustic measurement of sound absorption properties of road surfaces in situ - Part I: extended surface method. ISO, Geneva, Switzerland; 2002]. Since the absorption is an intrinsic property of the acoustic material, its measurement in either domain must provide the same result. However, this has not been formally demonstrated yet. The aim of this paper is to carry out a comparison between the absorption coefficient predicted by the impedance model of a Microperforated Insertion Unit and the absorption coefficient predicted from a simulated reflection trace taken into account the finite length of the time window.     

利用混合FE-SEA方法的前围隔声性能优化设计*

为了提升某重型商用车前围的隔声性能,建立了用于分析前围传递损失的有限元-统计能量分析(FE-SEA)模型。针对前围结构复杂的特点,依据FE-SEA模型建模原则,提出了通过在表面创建声腔来确保能量在模型中的正确传递路径。将仿真结果与测试值对比,二者误差小于1.6 dB(A),验证了FE-SEA方法的准确性。用吸声材料与隔声材料复合设计前围声学包,采用正交试验法对前围声学包进行优化设计并对各个试验方案进行仿真计算。对仿真结果进行极差分析与方差分析,选出了在传递损失、重量和厚度三方面达到最佳平衡的声学包:毛毡(10 mm)+EPDM隔声垫(2 mm)。结果表明,优化后的前围传递损失在测试频率315 Hz～2000 Hz范围内最小提升了3.8 dB(A),最大提升了7 dB(A),前围的隔声性能得到较大的提升。     

分布式通风消声板特性研究*

在隔声板结构中,分布式内嵌大量小型消声单元,在入射声波被消声单元有效衰减的同时,气流可均匀通过整个板结构,形成一种分布式消声板结构。利用平面波理论和修正传递矩阵法,建立消声板简化模型,并预测模型传递损失。加工消声板样件,实验室内测试并验证其声学及通风性能。对比隔声测试结果与预测结果,验证修正传递矩阵法针对该结构的准确性,同时验证消声板结构的实际效果。结果显示,该分布式消声板结构具有良好的声学效果,修正传递矩阵法可应用于该结构的声学性能预测以及结构设计。     

On the uncertainty of building acoustic measurements – Case study of a cross-laminated timber construction

If variations and uncertainty in building acoustic measurements can be controlled, construction costs can potentially be reduced since the building will not have to be acoustically over-designed. Field measurements of impact and airborne sound insulation were carried out for an industrially prefabricated cross-laminated timber (CLT) system of plate elements. The results from 18 rooms, forming three groups with respect to size, were compared to a similar study dealing with a prefabricated Volume Based Building (VBB) system. Large variations were found at frequencies below 100 Hz which is crucial for the low frequency adaptation terms connected to the weighted sound insulation indices. The measurement uncertainty was investigated by analysing the repeatability, measurement direction and the time dependence of the sound source. The variations due to the measurement procedure were found to be small compared to the total variations. It was also indicated that the variations in sound insulation are smaller with a prefabricated system compared to on-site production, since less work is required at the building site.     

A short method for the determination of airborne sound insulation characteristics in buildings

This paper presents the results of experiments made on a sample of 40 different facades to evaluate the characteristics of airborne sound insulation in buildings. On the basis of these results, some relationships are proposed for correlating the airborne sound insulation index, R_w (ISO 717/3-1982), with the measurements in the field of the equivalent sound pressure level made in dB(A).     

NUMERICAL MODELLING OF MEDIAN ROAD TRAFFIC NOISE BARRIERS

Outdoor sound propagation from road traffic is modelled by solving a boundary integral equation formulation of the wave equation using boundary element techniques in two dimensions. In the first model, the source representing a traffic stream can be considered as a coherent line source of sound. The results can then be transformed to derive a pseudo-three dimensional solution to the problem. In the second model the line source is incoherent. For receivers near the ground, the second model predicted significantly higher values of ground attenuation than the first. The first model generally produced better agreement with ground attenuation results obtained using the U.K. traffic noise prediction model. For conditions when a noise barrier was present and the ground was absorbent, the incoherent line source model generally predicted significantly higher values of attenuation than those from the barrier and ground attenuation calculated separately. Over a range of receiver positions and barrier heights a similar, but less marked effect was observed when the coherent line source model was used. On dual carriageway roads, it is possible to incorporate barriers on the central reservation as a noise control measure. These are “median” noise barriers. The incoherent line source model is used to assess the performance of median barriers in reducing noise when installed alone and also with associated roadside barriers. A sound absorbent median noise barrier 1m in height produced consistent values of insertion loss of between 1 and 2dB over the range of receiver positions and ground conditions considered. When the median barrier was used in conjunction with a roadside barrier it produced a consistent improvement in insertion loss of between 1 and 2 dB over the range of conditions considered.     

Sound insulation of domestic roofing systems: Part 1

The three parts of this paper are to be published in three issues of Applied Acoustics. The present part discusses the experimental facilities of the measuring laboratory and gives details of tests conducted on ceiling specimens. In Part 2 the work on various types of roof component will be presented. In Part 3 will follow the results of tests carried out on the roof and ceiling components combined. It will also consider the ability of the roofing system to provide sound insulation, as a component of the whole building envelope, from typical external noise spectra. The availability of sound insulation values obtained by laboratory measurements does provide the building industry with guidance in building design, even though values for actual buildings may vary considerably from laboratory-measured values.     

An analytical model to estimate the performance of an indoor barrier at low-medium frequencies

Indoor barriers are now widely used for sound insulation. This paper examines the performance of indoor barriers in the low-medium frequency range and analyses the interaction between different natural modes of a room-barrier-room system. Morse proposed a theoretical model to calculate the sound field in a coupled-room, but this model neglects the surface integral of the boundary values of sound pressure. To estimate the performance of a barrier in an indoor environment, an analytical model is proposed that modifies the Green’s function for a non-rigid boundary enclosure and approximates the surface integral by a pre-estimated sound pressure based on Morse’s model. An additional approximation has been made in the proposed model to neglect the coupling area in the calculation of the surface integral. The proposed model used to predict the insertion loss of the barrier is verified by the experimental results using a 1:5 scale model. The predicted results agree well with the measured results at lower frequencies.     

Noise control measures in the new Singapore International Airport

This paper describes some of the noise control measures incorporated in the passenger terminal building at the new Singapore International Airport at Changi. As the acoustics adviser to the Changi Airport Development Division of the Public Works Department, the overall consultant of this multi-billion dollar project, the author reviews some of the special steps taken to incorporate some of the latest acoustics techniques in this airport.These include the establishment of norms for various factors such as permissible background noise levels to each of the rooms, offices, arrival and departure halls, etc. Specifications called for include optimum sound absorption and reverberations times, airborne sound insulation for internal and external building partitions and structureborne sound insulation, as well as a sophisticated sound reinforcement system.Because of the stringent requirements following some of these specifications, the factor of the skill and workmanship of the contractors involved in the erection of the partitions had to be allowed for. As a result, all suppliers and contractors were requested to send their building proposals for testing. This was done in the newly established Acoustics Laboratory of the National University of Singapore at Kent Ridge. Some of the tests carried out, based on International Standards ISO R140 and ASTM E90 on sound transmission loss and ISO R354 and ASTM C423 on sound absorption, are evaluated.     

Noise from neighbours and the sound insulation of party walls in houses

Nine-hundred-and-seventeen residents in a sample of attached houses constructed since 1970 were interviewed in the course of a national survey dealing with nuisance occasioned by noise from neighbours. The airborne sound insulation of the party walls, measured prior to occupation, ranged from zero to 120 dB AAD. Two-thirds of the respondents heard noise from their neighbours and even at performance levels meeting or exceeding the minimum requirements of the Building Regulations nearly 50% did so. Of the total sample, some 18% were seriously bothered by neighbours' noise. Highly significant relationships were found between physical performance rated in dB AAD (Aggregate Adverse Deviation) and a variety of subjective responses. These include reports of hearing neighbours' noise, of being bothered by it, hearing neighbours' conversation, and, in particular, the direct rating of sound insulation quality by respondents, which last appears to provide the most reliable and consistent indication of the likelihood of experiencing nuisance from neighbours' noise. These results provide, for the first time, empirical validation of the U.K. performance rating procedure. In addition, the survey findings emphasize the importance of impact noises, not included in the standardized performance measurements, but which contribute substantially to nuisance, particularly between houses where airborne sound insulation is comparatively good. Other findings indicate that occupants were very satisfied with their general environment and only slightly less so with their homes. Poor sound insulation was a prominent criticism of the dwellings, being ranked third among spontaneous adverse comments and first in a ranking of nine commonly encountered building defects. These results indicate the importance of sound insulation to occupants of recently built houses, placing this aspect of design and construction within a wider context. The overall results of the survey provide a practical guide to estimating the consequences, in terms of occupants' attitudes to noise from neighbours, of raising or lowering standards of sound insulation performance between houses.     

预测声屏障插入损失的抛物方程法及其初始声场研究

Salomons建立的抛物方程(CNPE)方法可以预测非均匀环境中的声屏障插入损失。但是该方法在声屏障与声源距离较近时会产生较大误差。文中通过理论分析发现产生该问题的原因在于CNPE方法所使用的Gauss初始场仅适用于小仰角(10°以内)范围内的声波。为解决Gauss初始场引起的问题,推导了可以用于较大仰角声波的更高阶数的Gauss初始场。通过数值仿真对比了不同阶数的初始场在CNPE方法中的效果。结果表明:4阶初始场是最适合CNPE方法的初始场,将该初始场与CNPE方法相结合,可以准确预测当声屏障与声源距离较近时的插入损失.      

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。