Effect of a honeycomb on the sound absorption characteristics of panel-type absorbers

Panel-type sound absorbers are commonly used to absorb low-frequency sounds. Recently, a new type of panel/membrane absorbers has been proposed as a next-generation sound absorber free from environmental problems. On the other hand, it is known that placing a honeycomb structure behind a porous layer can improve sound absorption performance and a similar effect can be obtained for microperforated-panel absorbers. Herein, the sound absorption characteristics of a panel sound absorber with a honeycomb in its back cavity are theoretically analyzed. The numerical results are used to discuss the variations in the sound absorption characteristics due to the honeycomb as well as the mechanism for sound absorption.     

Factors influencing the sound preference in urban open spaces

In this paper, based on a large scale survey in Europe and China as well as corresponding laboratory studies, the influencing factors on the sound preference evaluation, considering social, demographical, physical, behavioural and psychological facets, have been systematically examined based on statistical analyses for each of the 19 case study sites. Various sound types have been considered, including natural, human, mechanical and instrumental sounds. In terms of social/demographical factors, the results suggest that age and education level are two factors which universally influence the sound preference significantly, although the influence may vary with different types of urban open spaces and sounds. With increasing age or education level, people tend to prefer natural sounds and are more annoyed by mechanical sounds in general. It has also been found that gender, occupation and residence status generally would not influence the sound preference evaluation significantly, although gender has a rather strong influence for certain sound types such as bird sounds, especially at certain case study sites. In terms of physical factors (season, time of day), behavioural factors (frequency of coming to the site, reason for coming to the site), and psychological factors (site preference), generally speaking, their influence on the sound preference evaluation is insignificant, except for limited case study sites and certain sound types. The influence of home sound environment, in terms of sounds heard at home, on the sound preference has been found to be generally insignificant, except for certain sounds. It is noted that there are some correlations between social/demographical factors and the studied physical/behavioural/psychological factors, which should be taken into account when considering the influence of individual factors on sound preference.     

Sound image method and sound energy vortex in rectangular room

1.TntroductionMostprob1emsofsolvingsoundficlds,suchassoundpressuredistributionsinroomsareclassiia1.lllIn10wfrequencyrange,wavemotionmethodisapplied.Inthemethod,thenorma1modesofroomaresolvedandthensummeduptocvaluatetheirunknownamplitudesbymatchingsoundsource.Inhighfrequencyrange,thenumberofnormalmodesneedcdisnumer0usandtogetfina1solutionwouldbeimpossiblebecauseofthetimeconsumptionincomputation.Hence,ther0omacousticsbasedongeometri-calacousticsandthestatisticswasdevcloped.Thewavemotionmethodcan…     

Definition of a labelling code for the noise emitted by machines

It has been increasingly realised that traditional parameters, such as A-weighted sound levels, sound power and noise spectra in octaves or third octaves are not enough to describe a sound and that machine labels should show more subjective information about the emitted noise. A new labelling system based on empirical data is proposed. The methodology of the study used as the basis for the proposal is explained, as well as the objective and subjective characteristics to be included in the new label. The uses and applications of the label are discussed briefly.     

Study on the effect of sound duration on the annoyance of helicopter noise by applying a technique of time compression and expansion of sound signals

The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise.     

Experimental study on sound absorption performance of microperforated panel with membrane cell

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, a composite MPP sound absorber with membrane cells (MPPM) is introduced. Sound absorption properties of the MPPM are studied by the impedance tube experiment. Results show that the membranes have a significant influence on the sound impedance. The sound absorption performance of MPPM gradually increases with the increase of the membrane area. The single-layer MPP with some small area membrane cells may have the same effect and single large area membranes. By adjusting the size of the membrane cells, one can implement a sound absorber with a wider absorption bandwidth and higher absorption peaks than the single-layer MPP.     

水声声强测量分析系统及其在水下噪声鉴别中的应用

本文将空气中能形成测量分析系统的声强测量技术引入到水介质中，建立了一套水声声强测量分析系统，讨论了此套水声声强测量分析系统的硬，软件组成及特征，实验验证了本系统的可靠性，利用此声强分析系统对水下双噪声源的近场作了平面扫描测量，可以定位和鉴别这两个噪声源。     

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.     

点噪声源在近程声场中传播损失的仿真研究

在分层介质条件下，用本征声线法仿真计算了点声源这距离噪声场的传播损失曲线，仿真结果表明，其传播损失不仅依赖于声速分布，海区深度，海底反射特性等环境条件，也依赖于声源及接收水听器的深度，声传播损失显著不同于球面波衰减规律，其传播损失率差别可达８ｄＢ，这表明在测量舰船目标的辐射噪声声源级时必要的声场校正测量是必须的。     

一种强指向性基阵的设计及声场计算

提出了一种新的基阵:将90个小圆环分布于半径不同的5个同心圆周上,对每个小圆环采用了抛物型的振速加权。通过改变阵元尺寸、间距等参数研究了声场特征的变化。计算结果表明,该基阵模型具有非常高的指向性和抑制旁瓣的能力。通过优化阵元组合方式和参数,可获得最佳的声压分布效果。     

扩散吸声体的优化设计

由于扩散吸声体(Diffsorber)同时兼顾了扩散和吸声两方面的性能,在小房间的声学环境控制中有着特殊的功能。在比较成熟声吸收和声扩散理论的基础上,结合数论中的伪随机理论,提出利用吸声材料本身的声阻抗实现伪随机分布的新优化设计手段,并利用计算机编程实现,由此设计了多种不同吸声效果的扩散吸声体,以满足不同场合的需要。实验结果表明新方法的有效性。同时探讨了新型吸声扩散体的应用潜力。     

A method for determining the sound reduction index of precast panels based on point mobility measurements

Precast panels are widely used for the construction of large industrial buildings, trade centres and apartment houses. These buildings have to comply with prescribed noise and thermal requirements, so the possibility to accurately estimate the sound reduction index of such panels is of vital importance. The sound reduction index can be determined through measurements carried out in a laboratory or on an already mounted real-scale panel, but both solutions present problems. For example, precast structures consisting of two concrete panels coupled via an interlayer can be very bulky and heavy, and measurements in standard sound transmission laboratories may be impossible to carry out. In some countries, predictions based on theoretical models are accepted in lieu of measurements. Following this approach, the application of simple models, not accounting for the influence of coincidence and of losses, is not sufficient to make acceptable predictions. In this paper, an alternative method to estimate the sound reduction index of precast panels is proposed. Different panels have been considered in the study, each of which has been modelled by a mathematical representation found in the literature. It will be shown that all of these models can be synthesised by a common mathematical formulation, allowing the sound reduction index to be determined from point mobility measurements. The effectiveness of the new method has been investigated by comparing predicted and measured results, obtained in a sound transmission laboratory satisfying existing ISO standards.     

Towards standardization in soundscape preference assessment

The study of soundscapes involves diverse fields of practice, diverse approaches and diverse disciplinary interests. The field overlaps with the much larger and established field of environmental noise management, and also intersects, to various degrees, with other areas of acoustics such as sound quality, human acoustic comfort in buildings, and music—and also with non-acoustic fields such as wilderness and recreation management, urban and housing design, and landscape planning and management. Working Group 54 of ISO/TC 43/SC 1 has been formed with a remit of standardization for perceptual assessment of human sound preference (in outdoor space) using questionnaires. The working group began its work in 2009, with considerable and wide-ranging discussion amongst its members. This paper makes a range of observations, and sometimes suggestions, on matters pertinent to eventual definition of the soundscape; on outcomes of interest arising from experience of a soundscape; on the role of context in assessment; on sound sources in different places; and on relevant lessons for soundscape assessment from experience of questionnaire measurement of noise annoyance. It represents a personal view, though informed by a range of opinions from the Working Group meeting and from literature.     

Sound field prediction in long enclosures with branches: A combined method

The propagation of sound in long enclosures with branches has been studied theoretically and experimentally, and an efficient combined method is proposed to predict the sound field in long enclosures with branches. Based on the wave-acoustics theory, the theoretical analysis of the sound field of the long enclosures with branches is performed. This paper also investigated the sound field prediction of long enclosures with branches, by using the acoustic modeling program, ODEON. The results obtained by the theoretical analysis and the numerical simulation ODEON are compared with the experimental measurements, and the characteristics of the two methods for predicting the sound field of long enclosures with branches are analyzed. Compared with the experimental results, it is found that: (1) the results predicted by the theoretical analysis fluctuate relatively large with respect to the source-receiver distance, and the sound pressure level (SPL) attenuation obtained is smaller than that measured; and (2) the results predicted by the numerical simulation is smoother, and the calculated SPL attenuation is larger than that measured. To effectively predict the sound field of long enclosures with branches, a combined numerical method is thus proposed. The effectiveness of the proposed combined method is demonstrated by the scale-model experiments.     

Measurement of the sound velocity in fluids using the echo signals from scattering particles

With conventional methods the sound velocity c in fluids can be determined using the back wall echo. This paper proposes a novel technique, in which the signals reflected by scattering particles suspended in a fluid are analysed instead. The basic idea is that the particles generate the strongest echo signal when being located in the sound field maximum. Therefore the position of the echo signal maximum is a measure for the propagation time to the sound field maximum. Provided that calibration data or sound field simulations for the ultrasonic transducer are available, this propagation time suffices to determine both sound velocity and the location of the sound field maximum. The feasibility of the new approach is demonstrated by different kinds of experiments: (i) Measurements of the sound velocity c in four fluids covering the wide range between 1116 and 2740 m/s. The results show good agreement with values published elsewhere. (ii) Using the dependence of the sound velocity on temperature, it is possible to vary c over the comparatively small range between 1431 and 1555 m/s with increments of less than 10 m/s. The measured statistical variation of 1.4 m/s corresponds to a relative uncertainty not worse than 0.1%. (iii) The focus position, i.e. the distance of the maximum of the sound field from the transducer, was varied by time-shifted superposition of the receive signals belonging to the different elements of an annular array. The results indicate that the novel method is even capable of measuring profiles of the sound velocity along the ultrasonic beam non-invasively.     

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.     

Measurement of sound absorption coefficients of flat surfaces in a workshop

To improve the acoustic treatment of facings and provide appropriate solutions for noise control at workplace, it is necessary to develop methods of acoustic characterization of the walls in industrial halls. Sound absorption coefficient measurement in industrial rooms is however quite a difficult task because of the partially reverberant conditions. This work describes the measurement of the sound absorption coefficient of flat panels subject to small angle sound incidence, in an industrial hall using an experimental device equipped with an acoustic array. The directivity of this array has been optimized so that the major part of the received acoustic energy would come from one portion only of the investigated facing, this, in turn attenuating the reflected beams due to the reverberation. This new device includes an impulse sound source targeting the panels. The present article focuses mainly on the sound source design and implementation. It also describes some sound absorption measurements carried in a semi-anechoic chamber and in an industrial hall in order to examine the performance of the device. Sound absorption coefficients of several standard liners obtained through this device have been compared to those resulted from the two microphone technique.     

频率对环绕声声像定位的影响

本文考虑双耳相位差的高级近似，导出了中频情况下适用的具有更普遍意义的平面环绕声声像定位公式。在低频时该式将化为通常的环绕声声像定位公式，而随着声音频率的增加，声像位置将与频率有关。将新的公式用到方型排列和棱型排列的４－４－４环绕声系统，得到了同实验相一致的结果。文中着重指出，声像随频率而变化是导致环绕声重发中侧向声像不稳定的重要在而为今后改进环绕声系统提供了理论基础。     

头部尺寸对虚拟声像定位的影响

本利用立体声像的相关理论分析方法，分析了用扬声器重发虚拟声时，倾听的头部尺寸对声像定位的影响。结果表明,当实际倾听的头部尺寸与虚拟声信号处理所用头部模型的尺寸有差别时，前方范围内的声像位置畸变较小，但侧向的声像位置畸变较大，因而本特别指出，倾听头部尺寸的不同是虚拟声重发时侧向的声像位置畸变的重要原因，声像定位实验证实了理论分析。     

Determination of the sound power levels emitted by various vehicles using a novel testing method

This paper presents a new and efficient method to determine sound power levels (PWLs). PWLs, generally used for modeling outdoor sound simulations, are obtained from sounds that are emitted by various types of vehicles and cause road traffic noise. Other models, such as HARMONOISE and the ASJ Model, are also based on PWLs. However, a more efficient method is required for determining PWLs from sound pressure levels (SPLs) that typically are measured by field testing and evaluating the influence of different vehicles and road surfaces. The statistical pass-by (SPB) of ISO 11819-1 is used for SPL measurements; however, numerous SPBs must be carried out to reduce measurement uncertainty as well as to satisfy requirements related to meteorological conditions and background noise. In order to alleviate this problem and to make the determination of PWLS more efficient, a testing approach is presented that uses both the novel close proximity (NCPX) method and the pass-by method to determine PWLs.