混响室中扩散体的总面积和测得的吸声系数

按混响室法作吸声系数测量时,人们总是用在混响室内尽可能无规地悬挂扩散体的办法来获得必要的声扩散。     

混响室中悬挂扩散板和试件面积对吸声测量结果的影响

混响室中的扩散程度通常对材料吸声系数测量值有较大影响,悬挂无规取向的扩散板可改善声场的扩散性能。我们的经验是在100m³左右的小混响室内,扩散板占地面面积的60—70％即可达到足够的扩散。但是这里也发现如软质纤维板（不论其表面处理及穿孔情况如何）之类材料的吸声系数与扩散条件关系不大,可解释为它们随入射角不同只有很小变化,因此不适宜用来判断声场扩散的改善程度。
多种常用吸声材料的测试结果表明,如果试件长宽比在0.7—1.0之间,试件面积从10m²改变至6m²对吸声系数测量值的影响并不太明显,其差异约小于0.02,个别吸声系数很高的材料,其差异也不超过0.06,与一般测试误差相接近。因而可以把最小试件面积规定为6m²,以便利测试,也能满足一般工程要求的测试精度。     

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。     

伪随机扩散体的吸声性能及其应用

本文介绍伪随机扩散体吸声性能的应用，提出减少扩散体结构厚度的实用设计，并应用于剧场观众厅以减少混响时间．     

赝随机扩散体吸声性能的理论分析

本文对赝随机扩散体的吸声性能提出了一个新的分析理论,该理论中假定相邻闭管管口间的声压一般并不保持相等,引入了\     

混响室中扩散声场统计特性的实验研究

一、引 言 频率足够高的声信号可在房间中同时激发起许多简正方式,这些简正方式相互叠加结果可使不规则房间中的声场变得十分复杂,以致一般不能用确定方法加以描述,而必须采用统计法。这就是统计声学。 从五十年代到现在,许多学者在统计声学领域中做了大量的研究工作,发表了一系列理论结果。相对说来,支持理论的实验工作却较少。正是这种理论与实验之间不平衡的状况,使我们有兴趣完成了本文的实验研究工作。     

基于二次剩余序列的扩散吸声体的研究

本文对基于二次剩余序列的声学结构的吸声性能进行实验研究，并定性分析了它的吸声机理．研究表明，除了结构振动所产生的损耗之外，更重要的吸收源是结构表面由于声干涉所形成的附加声阻抗的影响．     

赝随机扩散体吸声性能的数值分析与实验研究

本文根据前文[3]提出的理论,通过数值计算以及实验研究,进一步分析了赝随机扩散体整体结构表面的平均声压与振速,得出了结构表面处的平均声阻抗率,着重分析了非线性耦合声阻率的影响。实验采用二维声学结构,在低频驻波管中测得法向吸声系数,实验结果与理论计算相吻合。这为解释伪随机扩散体的吸声规律提供了有力的依据,并为今后指导工程设计提供了理论基础。     

电子自旋弛豫时间测量中电子自旋扩散的影响

在光注入电子自旋包的不同位置进行时间分辨的泵浦-探测实验时,发现电子自旋信息的退化率不同.揭示了电子自旋扩散对准确测量电子自旋弛豫时间的影响,获得了自旋输运动力学方程的解.对该解进行研究发现,电子自旋扩散对电子自旋弛豫时间测量值的影响可以归结为两个含时间的因子,其中一个因子与泵浦光斑中心和探测光斑中心的距离有关,另一个因子与泵浦光斑尺寸有关.提出了自旋弛豫时间测量实验中消除扩散影响的条件:1)泵浦光斑和探测光斑中心重叠;2)泵浦光斑尺寸足够大.结果表明,泵浦光斑尺寸越大,探测光斑中心越接近于泵浦光斑的中心,则扩散对自旋弛豫时间测量值所造成的影响就越小.     

The effect of stationary diffusers in the measurement of sound absorption coefficients in a reverberation room: An experimental study

It has not yet been established if stationary diffusers are effective in the measurement of the sound absorption coefficients of materials in a reverberation room. Although the results of such measurements may be strongly influenced by the use of diffusers, the conditions under which diffusing panels must be used and the number of such panels required have still not been ascertained exactly.In this paper we report the results of a series of measurements on different kinds of materials, performed in a reverberation room in both the presence and absence of diffusers, in order to establish the effect of diffusing elements on the absorption coefficient values. In some cases variations greater than 40 per cent were observed.     

室内声场简正波法的数值计算方法和混响场中声强测量的误差

简正波法是求解室内声场的一种较准确的数值计算方法,准确度由所取级数的项数而定,本文详细讨论了数值计算方法、级数的收敛性,并以图线来表明在声源点级数的发散及在声源附近计算的困难,本文还讨论声强测量的理论误差,用一般声强计在混响场中测量声强,误差是很大的,以致所得结果完全不可信任,如将传声器易位、前后两次测得的声强取平均,测量误差就可大大减小,若能采用精密仪器,使两个通道的相位差小于0.05°,则测量结果的统计误差可控制在合理范围内。     

双频激光干涉测角中角锥镜的不对称性对测角精度影响的分析

对双频激光干涉测角中反射镜组内两角锥镜的不对称性进行了分析,包括两反射角锥镜的制造工艺误差——两反射角锥镜的厚度偏差,以及安装偏差——两反射角锥镜前表面不平行度。推导出了由于该类误差带来的测角影响,建立了精确的角度测量模型。     

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab?sorbing structure(DiflFsorber) has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers(QRD) structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.     

The measurement of sound radiation from room surfaces in lightweight buildings

When investigating the transmission of sound within a building it is useful to measure the sound powers being radiated by individual room surfaces. This is normally accomplished using the ‘accelerometer method’. This method is shown to be unsuitable for use in lightweight buildings, and a new ‘direct’ method, suitable for general application, is described. The equipment required by the direct method is detailed, and the magnitudes of the inaccuracies involved in its use are estimated. An account is given of the successful testing of the method on lightweight panels radiating into an anechoic chamber, and the application of the method to actual constructions is described.     

Influence of wall absorption on low-frequency dependence of reverberation time in room of irregular shape

In this paper, a modal analysis was used to describe a reverberation phenomenon in a room of complex shape. A theoretical model was limited to low sound frequencies, when eigenmodes are lightly damped, thus they may be approximated by uncoupled normal acoustic modes of a hard-walled room. A utility of this method was demonstrated in a numerical example where the enclosure in a form of two coupled rooms was considered. A reverberation time was evaluated from a time decay of spatial root mean square pressure, the overall measure of room pressure. The results of calculations, performed for three different distributions of absorbing materials on room walls, showed how various location of the material can effect a dependence of the reverberation time on a frequency of sound source.     

The influence of absorption on possible nucleon-antinucleon resonances and bound states

We study analytically the effect of an absorptive potential on bound states and resonances in the N$\text{N}$ system. We show that these states are destroyed by moderate absorption. Thus, only N$\text{N}$ channels which are weakly absorptive can exhibit resonant behaviour.     

波束开角对多普勒测频结果的影响*

具有不同波束开角的声学多普勒测速设备未标定的测速结果存在偏差。基于水底椭圆散射模型研究了波束开角对声学多普勒测速结果的影响,对提高声学测速性能具有实际意义。水底椭圆散射模型下,足印上不同方位传播损失和散射强度存在差异,导致频谱不对称,测频结果偏小。利用不对称系数量化频谱不对称程度,若波束开角增大,方位不对称系数随之增大,测频偏差增大,推导了波束开角导致的测频偏差解析式。分析仿真和外场试验数据测频结果可知,不同多普勒频移下测频偏差和理论计算值相符,不同波束开角下实际测频偏差与理论公式计算的测频偏差均随波束开角增大而增大。     

混响室条件下环境场强测量位置选取准则

针对在混响室条件下进行辐射敏感度测试时电磁环境场强难以度量的问题,分析了混响室内电场强度的统计特性,理论推导了有损混响室内场强空间相关系数表达式,并通过仿真分析验证了表达式的正确性。根据表达式得出有损混响室内相对距离大于半波长的两点间场强相互独立的结论,并由此推断出,混响室内环境场强测试位置与受试设备(EUT)距离应大于0.5倍波长,且应以此作为测量位置选取准则。采用仿真计算与实验验证相结合的方法分析了相对误差随测试点与EUT间相对距离的变化规律,对该准则进行了验证,结果表明,当测试点与EUT相对距离大于0.5时,相对误差能够保证在1.5 dB以内,可应用于实际混响室环境场强测试。