用空气柱共鸣法测量声波波长

在学习“声音的共鸣”时，我们知道，音叉发声时，下面的共鸣箱发生共鸣，使音叉的声音增强．用音叉也可以使空气柱发生共鸣．对一端开口的玻璃管内的空气柱来说，跟某一声波共鸣的空气柱的最短长度等于该声波波长的1/4．也就是说，利用空气柱的共鸣可以测定声波的波长，并且，在空气柱长度等于声波波长的1/4，3/4，5/4，…倍时，都会发生共鸣现象．     

如何用量筒和音叉测定声波的波长

中师物理教材"声音的共鸣"一节的练习中有一道实验题:用量筒和音叉测声波的波长.题的意图是让学生根据本节实验的结论:"空气柱跟某声波发生共鸣的最小长度等于该声波波长的1/4"来测定声波的波长.     

空气柱共鸣实验的改进

空气柱共鸣实验的改进孙振海（河北元氏师范学校０５１１３０）中师《物理学》第一册３０９页中空气柱共鸣演示装置有以下不足之处。１．所需粗而高的玻璃容器和长玻璃管不易找到，若玻璃管较短，演示时只能听到一次共鸣声，只说明空气柱的最短长度等于声波波长的１／４，...     

基于手机Phyphox软件设计“共鸣管测声速”居家实验

为了让学生居家完成空气中声速的测量,基于手机Phyphox软件设计了"共鸣管测声速"实验。本实验根据共鸣管的原理,利用手机Phyphox软件测量一端封闭,一端开口的奶茶管发出共鸣音时的基频,理论上声速大小是基频与空气柱长度乘积的4倍,但实际上有效空气柱长度是实际空气柱长度加上"管口校正量"。通过公式变形,得出实际空气柱长度与基频的倒数成正比例的关系公式,采用线性拟合数据直接得出声速,从而巧妙避免了"管口校正量"的干扰,同时理论上也给出了一种得到"管口校正量"的方法,这是本实验的创新点。实验以内直径为12.0mm的奶茶管进行测量数据,通过线性拟合得到声速值,并进一步讨论了线性拟合得出的截距的物理意义和含义。     

声学实验‘共鸣管’的改进——声的驻波和行波

从老的物理实验“共呜管”的启发下改变为现在可闻声波的波动实验。在实验原理上避免了以空气柱的共振为必要条件,并且大大地丰富了有关波动的实验内容。本实验不仅能测定空气中声波的波长和声速,以及能显示驻波的振幅分布,并且试验成功用相位比较法显示驻波中各点振动的相位关系。后者两个内容可能是本实验的特点。在实验装置中采取措施以防可闻声波的相互干扰。本实验只要在装置上略加改变就能用行波相位比较法测定声波的波长和声速。     

浅析声音在空气中的传播

声波在液体、气体和固体中以纵波的形式向四周传播.当置于空气中的发声体振动时,造成了周围空气的被压缩,使空气形成了周期性的疏密状态变化,这种疏密状态由发声体向外传播,这就形成了空气中的声波(见图1),并遍布于整个传播波的三维空间中.     

对共鸣管实验的改进

用音叉和玻璃管来演示空气柱的共鸣现象是高中物理声学部分的一个实验。笔者根据多年的实践经验,采用如下方法较理想。实验装置如图所示。其中玻璃管的长度约为30cm左右,口径约为2cm左右。如果实验室不备有此管,可采用废旧8W日光灯管改制。改制的方法是将废旧灯管两端灯丝小心卸下,用砂子冲刷管内荧光物质,冲刷干净以后用水冲洗透明,再用砂石磨平灯管两端。管底端通过软木塞、导管与大号注射器相连,管身一侧可贴上有标度的纸条,用来记录空气柱的长度。将管固定于铁架台上,往管内注水,由于注射器容量可达90ml,通过活塞足以使管内空气柱的长度在30cm     

径向声子晶体隔声特性*

该文构造了由两种匀质材料交替分布的径向声子晶体柱壳模型。首先,针对声波在其中的轴对称传播情况进行了理论分析,建立了声波由内向外传播的传递矩阵,进而导出了声压透射系数和隔声量表达式。采用数值分析的方法系统地讨论了径向声子晶体柱壳的隔声特性,并与单一材质柱壳的传播规律进行对比分析,其次,借助有限元仿真分析的手段对数值结果进行了验证。最后,详细分析了内外流体的特性阻抗对径向声子晶体柱壳隔声特性的影响,得到了相应的参数影响规律。研究表明,径向声子晶体柱壳存在声波带隙,导致其在带隙范围内的隔声效果远远优于单材质柱壳,并且该结构的固有特性突破了质量定律的限制;声波带隙内表面局域态现象出现与否由内外声场和结构场共同决定。     

两种共鸣结合测空气中的声波波长

共鸣管法测空气中声波波的实验中,用水调空气柱长度,用耳辨别波节波腹。由于水流动时的惯性加上环境噪声的干扰,往往不容易得到很准确的数据,且弄得不好水易溢出。如果将管平放用活塞调空气柱长,在管口处连一橡皮管(或听诊器)插在耳中来进行实验,可以使实验效果得到改进。现在如果再在共鸣管口上安上一个共鸣器,再接橡皮管(图1),调节共鸣器使之和空气柱中的声音发生共鸣,可以使在波节     

探究钢管中声音节点的位置

每根钢管都有一个声音节点,在此节点上固定钢管敲击时,就会发出特别清脆悦耳的声音.实验发现节点位置处于钢管长度的三分之一处,声音频率反比与钢管长度.空气柱与钢管的共振可以说明这个现象.     

Transmission of low-frequency sound through the water-to-air interface

L.M. Brekhovskikh revealed and studied the important role played by inhomogeneous waves emitted by a point source when they pass through an interface with a medium in which the velocity of sound is lower, for example, from water to air. This paper studies the energy characteristics of sound emitted into air by an underwater point source. The energy transfer due to inhomogeneous waves is shown to cause the phenomenon of anomalous transparency of the interface for low-frequency sound. The anomalous transparency manifests itself in that the energy flux through the interface increases with decreasing frequency of sound and, at sufficiently low frequencies, almost all of the acoustic energy produced by the underwater source is emitted into air. Conversely, at high frequencies, when the contribution of the inhomogeneous waves becomes negligible, the water-to-air interface is similar to a perfectly reflecting surface and almost all of the acoustic energy produced by the source is emitted into water. The anomalous transparency phenomenon changes the conventional opinion on the possibility of acoustic coupling between points in water and air and on the role played by physical processes evolving in the water column in generating atmospheric acoustic noise.     

The metre

A musical wind instrument transforms a constant pressure input from the player's mouth into a fluctuating pressure output in the form of a radiating sound wave. In reed woodwind and brass instruments, this transformation is achieved through a nonlinear coupling between two vibrating systems: the flow control valve formed by the mechanical reed or the lips of the player, and the air column contained by the pipe. Although the basic physics of reed wind instruments was developed by Helmholtz in the nineteenth century, the application of ideas from the modern theory of nonlinear dynamics has led to recent advances in our understanding of some musically important features of wind instrument behaviour. As a first step, the nonlinear aspects of the musical oscillator can be considered to be concentrated in the flow control valve; the air column can be treated as a linear vibrating system, with a set of natural modes of vibration corresponding to the standing waves in the pipe. Recent models based on these assumptions have had reasonable success in predicting the threshold blowing pressure and sounding frequency of a clarinet, as well as explaining at least qualitatively the way in which the timbre of the sound varies with blowing pressure. The situation is more complicated for brass instruments, in which the player's lips provide the flow valve. Experiments using artificial lips have been important in permitting systematic studies of the coupling between lips and air column; the detailed nature of this coupling is still not fully understood. In addition, the assumption of linearity in the air column vibratory system sometimes breaks down for brass instruments. Nonlinear effects in the propagation of high amplitude sound waves can lead to the development of shock waves in trumpets and trombones, with important musical consequences.     

Effect of the Refraction of Sound Waves in the Sediment Layer on the Sound Field Levels in the Ocean at Short Ranges

On the basis of the results of an acoustic experiment, which was carried out in the Indian Ocean with the use of explosive sources of sound, the effect of the refraction of sound waves in the sediment layer on the levels and the structure of the sound field formed in the water column at short ranges, namely, in the first geometric shadow zone and in the insonified zone below the channel axis, is considered. The length of the acoustic track under study is 45.0 km, and the frequency range is 10–500 Hz.     

用DIS数字化信息系统测量金属棒中声速的有效方法

本文设计了一种将驻波法与声波传感器相结合测定金属棒中声速的有效方法.将金属棒固定在中点,沿轴向摩擦激励纵振动并在棒中形成驻波而发声,用DIS数字化信息系统接收声波信号,得到波形图,由此测得棒中声波的基频和声速.本文分别测定了铝、钢、黄铜、紫铜4种不同金属材料棒中的声速.结果表明,同种材料、不同长度金属棒中声速的测量结果基本相同;各种金属棒中声速的测量值与公认值的相对误差小于6.00%.此方法的特点是将声波信号变成可视波形,并可从波形图中直接提取准确的计算参数.     

A theoretical study of passive control of duct noise using panels of varying compliance.

It is theoretically demonstrated that, in a duct, a substantial amount of sound energy can be transferred to flexural waves on a finite wall panel when the upstream portion of the panel is made to couple strongly with sound. The flexural wave then loses its energy either through radiating reflection sound waves or by internal friction. The effectiveness of the energy transfer and damping is greatly enhanced if the panel has a gradually decreasing in vacuo wave speed, which, in this study, is achieved by using a tapered membrane under tension. A high noise attenuation rate is possible with the usual viscoelastic materials such as rubber. The transmission loss has a broadband spectrum, and it offers an alternative to conventional duct lining where a smooth air passage is desired and nonacoustical considerations, such as chemical contamination or cost of operation maintenance, are important. Another advantage of the tapered panel is that, at very low frequencies, typically 5% of the first cut-on frequency of the duct, sound reflection occurs over the entire panel length. This supplements the inevitable drop in sound absorption coefficient, and a high transmission loss may still be obtained at very low frequencies.     

Sound radiation into air by a point source moving underwater

Based on the discovery that the majority of radiated energy of a stationary sound source in shallow water is into the air at infrasonic frequencies, the sound transmission into air from a point source moving underwater is investigated in this letter. It is found that a moving sound source can radiate more acoustic energy into the air than a stationary one and the amount of energy radiated into the air increases with the speed of the moving source. Simulations show that the sound transmission into air is dominated by the inhomogeneous waves generated by the moving source.     

管束穿孔板的管腔耦合共振吸声机理研究

为了揭示管束穿孔板共振吸声结构的吸声机理,利用热黏性条件下基于有限元算法的管束穿孔板仿真模型,研究了平面声波正入射条件下,管束穿孔板内部声场分布特征,并利用阻抗管对吸声系数的理论仿真结果进行了试验验证.结果表明,管束穿孔板在低频主要靠腔体共振吸声,在高频主要靠管共振吸声,管束穿孔板整体呈现出较为明显的管腔耦合共振吸声特征。管束穿孔板共振时管中声强和质点法向振速较大,高频次吸声峰频点处管中和腔中均有驻波形成,频率越高驻波数量越多.管束穿孔板的耦合共振受到管长、腔深、穿孔率和管内径等参数变化的影响,管长对高频耦合共振的影响最大,管长增大使高频主吸声峰频点移向低频,并使相邻主吸声峰之间的间距减小.      

Nonlinear acoustic wave generation in a three-phase seabed

Generation of an acoustic wave by two pump sound waves is studied in a three-phase marine sediment, which consists of a solid frame and the pore water with air bubbles in it. To avoid shock-wave formation, the interaction is considered in the frequency range where there is a significant sound velocity dispersion. Nonlinear equations are obtained to describe the interaction of acoustic waves in the presence of air bubbles. An expression for the amplitude of the generated wave is obtained and numerical analysis of its dependence on distance and resonance frequency of bubbles is performed.     

A Helmholtz resonator buried in the ground as a source of seismic waves and low-frequency sound in the atmosphere

The procedure is given for calculating the total power of low-frequency sound and seismic waves produced by a Helmholtz resonator in the form of an air-filled spherical cavity buried in the ground and supplied with a hole through which it is connected with the atmosphere. The sound is generated by air oscillations in the resonator’s neck section that is open to the atmosphere, while the compression and shear elastic waves are generated in the bulk of the ground by cyclic pressure fluctuations that act on the spherical walls of the cavity. Calculations show that the coincidence of the resonance frequencies (within approximately ten to hundred hertz), at which both the sound radiation to the atmosphere and the elastic seismic radiation in the form of longitudinal and transverse bulk waves are maximum, can occur only when the resonator is placed in a loose ground characterized by reduced elastic characteristics. In these conditions, the power of transverse waves exceeds the sound power by a factor of two and the power of longitudinal waves is smaller than the sound power by a factor of several tens.     

Transmission of low-frequency internal sound through pipe walls

Transmission loss measurements are reported for long steel pipes of circular crosssection, with air inside and out, excited by internal sound. At low frequencies (wavelength greater than the pipe diameter), most of the radiated sound is accounted for by pipe bending waves. In order to approach the much higher transmission loss predicted for pure breathing motion of the pipe, bending waves must be suppressed; this has been achieved for a straight pipe by careful isolation. A sharp 90 bend in the pipe is shown to cause significant bending-wave excitation when plane waves are incident on the bend.