声强探头相位误差的电补偿技术

以双传声器技术为基础的声强测量方法对两个传声通道的相位特性非常敏感，本文介绍了对声强探头进行相位匹配以及使用精密相位计进行测量的方法和实例，通过在声强探头后级电路中采用一种称相网络进行相位补偿，在大部分频段上减少了相位误差，可以改善声强测量的精度。文中提供了基本的电路原理图和典型的实验数据。     

双水听器水声声强测量系统的误差分析和校准

基于双水听器互谱测量法,研制的水声声强测量设备可用于测量水下声源产生的声场中任意点的声强量值或任意面上的声强量值分布。根据双水听器测量声强法原理进行了误差分析,提出了该双水听器声强测量系统的校准方法。对系统测量水声声强量值的不确定度进行了估计并进行了实验验证。验证表明,理论分析评定与实测结果一致。     

室内脉冲声场中声强的测量研究

采用多次重复发射的声源配合装置在缓慢转动平台上的接收传声器所组成的测量系统(简称为RRS),它等效于多个完全匹配的传声器组成的圆型阵列.文中着重阐述了借助此技术测量房间内脉冲声场中声强的时间与空间分布特性.阐明了以RRS测量入射脉冲声强的理论基础,分别对离散的脉冲声场及扩散声场提出了测量声强的定量关系式,对实验结果及应用作了分析与讨论.     

阵列式双水听器平面扫描声强分布测量和声功率计算实验研究

根据双水听器法测量声强的基本原理，本文提出了基阵在湖中的布放及测量声强分布的实施步骤。通过对试验数据的处理与分析，给出了声强分布的三维力和等值曲线图，并利用扫描平面上的声强分布。计算出声源辐射的声功率。实验表明，本文提出的用列阵式双水听器声强测量系统，作平面扫描测量声强分布的方案是合理的；利用所测得的双平面近场声强分布来计算源的辐射也是可行的。     

FFT分析仪-微机声强测量系统及其应用

本文讨论用HP 3562A动态信号分析仪与HP9000/320微机联机所组成的声强测量分析系统,利用自编软件进行声强的测量和分析。系统的输出功能有:50Hz—10kHz范围内各种频率分辨率的声强谱和声功率谱(线性或A计权,窄带或1/3倍频程分析),表面的三维声强图和等声强线图。以B＆K4205标准声功率源和电动机为测量对象,与在半消声室内按ISO 3745测得的结果进行对比表明,本声强测量系统的精度能满足一般工程要求。最后还提供了应用本测量系统对一台车床的噪声幅射进行分析的实例。     

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。     

机械阻抗测量的一种新方法

本文介绍了一种新的机械阻抗测量方法－声强法，由定义出发将机械阻抗表为功率流和加速度响应谱的函数，应用结构声强技术测量功率流，声强法不需要测量作用力信号，可以用于测量任意结构中的各类机械阻抗，实验结果表明，声强获得的测量值与直接获得的测量值相近，声强法能较准确地测量一维和二维匀质结构中机械阻抗。     

声强的有旋性与表面声强

本文应用复声强的概念,讨论了复声强的实部即有功声强的有旋性质。指出:在声场中真正传递声能量者仅是有功声强中的无旋分量。所以在应用双传声器声强测量法测量声功率时将受到有旋性的影响。有功声强的无旋分量与表面声强有关,因此测量表面声强可避免有旋性的影响。本文从自功率谱的角度给出了表面声强的有关计算公式,为表面声强测量提供了理论基础。     

用简易声强计测量声强

本文介绍作者装置的一台简易声强计,实测误差与理论分析结果符合良好。组成声强计传感器的两个传声器之间的相对相移对测量结果有明显的影响,特别是在频率低端会产生很大的误差,作者通过使用倒向平均法降低了误差。消声室和混响室里的模拟实验结果证实了声强测量能可靠地在现场确定声源的声功率。     

声强测量技术在水下结构辐射噪声近场测量中的应用

本文介绍了强测量技术在水下结构辐射近场测量中的实际测量系统，特别是水下声系统的扫描平面的实现方法及定位误差控制方法，最后讨论和分析了实际测量结果，从而说明该系统用水下声强测量是可行的。     

Fundamentals of the direct measurement of sound intensity and practical applications

Sound intensity is a measure of the magnitude and direction of the flow of sound energy. Developments in sound intensity measurement capabilities in the last quarter century have occurred because of several reasons. The main ones include the derivation of the cross-spectral formulation for sound intensity and developments in digital signal processing. This paper begins with a brief historical introduction of sound intensity measurements. Then elementary theory for sound intensity is presented. A section on sound intensity measurements is then included. The next section of the paper discusses sources of measurement error; the major sources of error are described in some detail. The paper continues with a discussion of the main applications of sound intensity measurements: sound power determination, noise source identification, and transmission loss measurements. The paper concludes with a discussion of ISO and ANSI intensity related standards and relevant references.     

多路噪声测量系统的研制

本描述了多路噪声测量系统的建立,该系统是一以微机为中心的数字化系统,可实现对４路稳态宽带噪声的测量,测量参数是线性声压级和倍频带声压级。系统由微机、ＴＭＳ３２０Ｃ３０板、多路ＡＤ板、传感器、放大器等设备构成硬件系统,并通过编制Ｃ３０板嵌入式软件和微机主控程序实现系统功能。在软件编制中结合数字信号处理技术,并结合硬件特性优化程序设计,本系统测量方法简易,快捷和精度高,在噪声测量领域具有较高实用价值     

以虚拟仪器为平台的声学实验

基于计算机声卡和Adobe Audition软件制作了声学虚拟仪器,可实现示波器、信号发生器和频率计算仪器功能,并介绍了此声学虚拟仪器在双音多频信号DTMF的研究、声速的测量和变音钟实验中的具体应用.     

A wave field synthesis approach to reproduction of spatially correlated sound fields

This article discusses an open-loop wave field synthesis (WFS) approach for the reproduction of spatially correlated sound fields. The main application concerns laboratory reproduction of turbulent boundary layer wall pressure on aircraft fuselages and measurement of their sound transmission loss. The problem configuration involves reconstruction of random sound pressure distributions on a planar reproduction surface using a planar array of reproduction monopoles parallel to the reproduction plane. In this paper, the WFS formulation is extended to sound fields with imposed time and spatial correlation properties (or equivalently imposed cross-spectral density in the frequency and wave number domains). Numerical examples are presented for the reproduction of a propagating plane wave, diffuse acoustic field and wall pressure in subsonic or supersonic turbulent boundary layers. The reproduction accuracy is examined in terms of the size of the source plane and reproduction plane, their separation, and the number of reproduction sources required per acoustic wavelength. While the reproduction approach cannot reconstruct sub-wavelength correlation scales of subsonic turbulent boundary layers, it effectively reconstructs correlation scales larger than the acoustic wavelength, making it appropriate for diffuse acoustic field and supersonic turbulent layers.     

A high-temperature acoustic field measurement and analysis system for determining cavitation intensity in ultrasonically solidified metallic alloys

A high-temperature acoustic field measurement and analysis system (HTAFS) was self-designed and developed to achieve real-time acoustic field analysis and quantitative cavitation characterization within high-temperature liquids. The acoustic signal was acquired by a high-temperature resistant waveguide and calibrated by separate compensation of line and continuous spectra to eliminate frequency offsets. Moreover, a new method was proposed to derive from the continuous-spectrum sound intensity and line-spectrum sound intensity in the frequency band above 1.5 times the fundamental frequency to characterize the intensity of transient cavitation and stable cavitation. The acoustic field characteristics within solidifying liquid Al-7 %Si alloy were successfully determined by this system. With the increase of ultrasound amplitude, the acoustic pressure in the alloy melt increased to be stable, the transient cavitation intensity first rose and then declined, and the stable cavitation intensity remained unchanged. Combined with the structural evolution of the primary α(Al) phase, the transient cavitation intensity was determined to be the dominant factor for the ultrasound-induced grain refinement effect.     

Determining the direction to a sound source in air using vector sound-intensity probes

This paper is concerned with probes for measuring vector sound intensity in air using the minimum number of sound-pressure sensors. The probes consist of an arrangement of four small microphones at the vertices of a regular tetrahedron. They are connected to a digital signal processor, which determines the sound-intensity vector, using the cross-spectral formulation based on finite-difference approximations. Determining the direction of a sound source is an obvious application. To do this accurately the probes should be omnidirectional. This implies that the microphones in the probe have to be omnidirectional and to have the same response. Results in the paper show that the direction of a sound source can be determined with an accuracy of a few degrees. Two types of probes are described. One measures the sound-intensity vector in three-dimensional space. The other measures the vector in a half space such as would occur above the ground or in front of a wall.     

超声吸收体物理参数对红外热成像测量高强度聚焦超声声场的影响

超声吸收体的物理参数对利用水听器和红外热成像技术的高强度聚焦超声(High-Intensity Focused Ultrasound,HIFU)声场测量结果具有重要影响。为了探索超声吸收体的物理参数(密度、声速、衰减系数、热扩散系数、定压比热容)对测量结果的影响规律,本文根据层状模型计算出相同声源功率输出时不同物理参数对应的超声吸收体内部声场和热场,利用有限差分法计算出超声吸收体表面在辐照过程中的温度变化;利用基于水听器和红外热成像技术的聚焦声场测量方法测量出焦域内不同位置上声场特征值(轴线声强和-6 dB声束宽度),与通过理论计算得到的声源在纯水中声场特征值进行比较,分析了不同物理参数对测量结果的影响。超声吸收体的声、热学参数中除了声速外,其它物理参数的变化引起声场特征值的测量造成最大相对差异率小于15%。因为声波传播速度的改变会导致超声吸收体内部热场分布变化,使测量结果与理论计算值有较大偏差,其中-6 dB声束宽度和轴线声强最大相对差异率为95.37%和69.97%。因此在选择超声吸收体的声、热学参数时应重点关注声波在吸收体内声速的影响。超声吸收体的声学参数与水的声学参数相近时,可以在焦域内获得较好的测量结果。      

基于LabVIEW的微小电容测量

针对电容层析成像技术中的微小电容测量的问题,以数字相敏检波原理为基础,LabVIEW软件及NI采集卡为核心设计了微小电容测量系统。LabVIEW程序控制NI采集卡产生激励信号加在微小电容两端,C/V转换电路将其转换为电压信号,NI采集卡将采集的电压信号传送到PC机中,并在LabVIEW程序中通过数字相敏检波算法对数据进行处理及显示。最终,通过对数据进行线性化,得到相应的测量电容值。实验结果表明,该系统具有精度高,线性度好,稳定性好等优点,可以满足电容层析成像系统中对微小电容的测量的要求。     

Flat-response sound source technique for using the two-microphone method in an impedance tube

In this letter, to improve the acoustic impedance measurement in a tube using the two-microphone method, a sound source technique is developed that is capable of generating incident sound waves of uniform intensity over the entire frequency range of interest. The basic principle is to use a digitally synthesized compensation input signal to achieve a flat response of the sound source provided by one or more loudspeakers. The present sound source technique has been demonstrated to be very effective and easily implemented with the current impedance tube testing systems.     

Application of the ISO 13472-1 in situ technique for measuring the acoustic absorption coefficient of grass and artificial turf surfaces

This paper presents the applicability of an in situ technique based on ISO 13472-1 standard for measuring the acoustic absorption coefficient of grass and artificial turf surfaces for normal incidence from a sound source. The in situ method is based on acoustic impulse response measurement of the material surface. A maximum length sequence (MLS) signal is played through a loudspeaker and the acoustic response from the surface is recorded using a single microphone. The fast Hadamard transform and fast Fourier transform based digital signal post-processing algorithm provides the acoustic absorption coefficient of the surface under test. The normal incidence acoustic absorption coefficient of a commercial artificial quash surface of Dow Co. obtained from this method was compared with the results from the ASTM E1050 impedance tube method for the same surface. The acoustic absorption coefficients of a test-site grass surfaces were measured for 30 mm and 100 mm length of grass blades in wet and dry soil conditions. Substantial difference in the acoustic absorption coefficient was observed for a similar grass-like artificial surface used for estimating sound power of commercial garden equipments and lawnmowers. The advantage of the in situ method lies in its ability to measure the normal incident acoustic absorption coefficient of any planar surface as installed or in situ. Additionally a quick testing time of less than a minute with the use of a laptop sound card based inexpensive data acquisition system is the main feature of this robust method.