0.1~20Hz低失真度激光活塞发声器的设计与实现

为实现次声频段传声器的准确校准,研制了低失真、低泄漏的激光活塞发声器。激光活塞发声器采用具有空气轴承和位移反馈控制的超低频振动台驱动的活塞-腔体组合获得低失真度的声压信号;采用气浮自对中技术的小间隙缸塞配合以及大体积的腔体设计,获得了低泄漏的活塞发声器。在0.1~20 Hz,声压波形总谐波失真低于0.8%,实现高达50 s的腔体泄漏时间常数,使其适用于更低频段的传声器校准。在0.1~20 Hz频率范围内,激光活塞发声器的测量不确定度不超过0.58 dB (k=2)。与耦合腔互易法、关联传声器法的比较结果表明,激光活塞发声器法获得的传声器灵敏度与其他方法之间具有很好的一致性。      

考虑基底热传导的石墨烯薄膜热声理论

主要基于热声效应对石墨烯薄膜发声进行理论研究。首先建立了石墨烯薄膜耦合热振动模型,推导出了石墨烯薄膜发声器的声压表达式。在此基础上,进行了不同基底石墨烯薄膜发声器的声压测试,并将测试值与理论计算结果对比,二者随频率变化趋势基本吻合,测试值略低于理论值,验证了推导出的声压表达式的正确性。研究表明石墨烯薄膜发声器有很宽的频域响应,在低频段声压级随频率增大而增大,在高频段响应平稳,具有作为优秀的热致发声器的潜力。基底材料蓄热系数越小,石墨烯薄膜的声压值越大;声压级随薄膜热容量的增大而减小。研究结果对于石墨烯的发声机制探索及其在扬声器设计等方面的应用具有指导意义。      

高声压传声器校准器的校准

本文对高声压传声器校准器,腔内声压级受传声器前腔体积的影响进行了计算和测量,并叙述了校准方法。结果表明,保持校准器插入电压不变的条件下,在其工作频率范围内,传声器前腔体积变化,会使校准器腔内的声压级随频率产生不同程度的变化。若不对传声器前腔体积的影响进行修正,会带来多达几分贝的校准误差。本文采用前腔体积已知的标准传声器和激光测振仪测量腔体积,并采用激光测振仪测量活塞振幅的方法来校准高压传声器校准器.校准的声压级范围为124dB—164dB,校准精确度为±0.27dB。     

航天飞行器实验室的高声强噪声产生能力

加拿大NAE空气动力装备、结构和材料实验室设置了总声压级为157dB的航天飞行器混响室,总声压级为167dB的行波管和总声压级为150—155dB的高声强小型混响室,它们的噪声谱可以用不同截止频率喇叭和噪声发声器组合来进行控制,这是根据1980年要求对加拿大航天飞行器的质量鉴定需具有低频分量的高声强噪声环境而改建的。气源为300Psig,50001~3。     

高声强下传声器灵敏度校准

本文对CH16和BK4136等型号的电容传声器在高声强声波作用下,其灵敏度变化作了估算和校准。用BK4221型高声压传声器校准器对上述型号的传声器作灵敏度校准,声压级从140dB至161.6dB,这些传声器之灵敏度变化一般不超过0.3dB。与活塞发生器校准结果比较,两者最大差值一般在0.4dB之内。另外,在168dB至173dB的高声强环境中做了类似实验,结果一致。实验结果和理论分析相符,证实了用活塞发生器校准得到的传声器灵敏度值,来校准高声强(声压级在170dB以下)是可行的,这对高声强测试工作提供了方便。     

声学测量用电火花式脉冲声源及其声学特性

电火花发出的声脉冲具有脉冲宽度小、无方向性和声级高等特点,因此它是研究厅堂音质的脉冲响应,混响时间和模型试验的理想声源.当声级足够高而稳定时,还可作为隔声测量和高声强冲击波换能器近场校正之用.这里我们采用了高电压小电容放电的方式.在控制电路方面设有自动、手动和遥控装置,便于使用.本脉冲发声器电路简单,性能稳定,装置紧凑,使用方便. 本文主要介绍火花发声器的原理,电路设计的特点,声源的声学特性以及应用等.     

烟火药和压缩氮气声源水下声辐射特征对比研究

为研究烟火药水下燃烧声辐射机理,采用烟火药和压缩氮气喷射声源对比的方法,利用水声测试系统,通过实验研究不同体积流量下两种声源装置的声辐射规律。结果表明,烟火药水下燃烧声源与压缩氮气声源的声辐射特征相似,辐射频率主要集中在0～1000 Hz内,峰值频率均位于100 Hz附近,总声压级、峰值声压级均随着气体流量增加而增强。当气体流量从60 ml/s增加到84 ml/s时,烟火药峰值声压级由155 d B增加到163 d B,0～1000 Hz内总声压级由159 d B增加到165 d B;当喷气流量从70 ml/s增加到141 ml/s时,压缩氮气源峰值声压级由136 d B增加到139 d B,0～1000 Hz内总声压级由144 d B增加到147 d B。当气体流量相近时,烟火药相比压缩氮气声压级相差显著,其声压级均高于同频率下压缩氮气源,两者的峰值声压级分别为157 d B、139 d B,0～1000 Hz内总声压级分别为160 d B、147 d B。     

静电激发器

静电激发器是一种声学计量设备,它主要用于传声器、声级计和其他各种声学测量仪器的声压级频率响应特性的校准.该设备在声学计量、声学测试、环境保护以及生产线校准中都得到了广泛地应用.近年来,以该发明为中心所组成的声压级校准装置与互易法、活塞发生器法等灵敏度校准方法相结合,广泛地用于我国地方级计量部门和测试单位.该发明的主要技术指标达到了国际同类设备的水平,井通过采用高分子介质层和梯形栅格断面结构解决了提高校准精度与电击穿之间的矛盾,改善了激发器的结构动力学特性和降低了声反射所引起的误差,从而为我国填补了一项空…     

有限长号筒中非线性声传播的数值模拟研究

研究了大振幅活塞声源经有限长号筒向外辐射声波的非线性声学问题。采用具有频散保持特性的高精度计算格式求解了适用于变截面管道的一维非线性声场模型,并考虑到声波的非线性畸变及管口处的声反射,加入了宽频时域声阻抗边界条件。宽频阻抗模型的共轭复数系数采用优化拟合方法近似求解,并采用递推卷积算法快速求解出时域声阻抗。在弱非线性条件下模拟指数形号筒中的声传播取得了与已有实验相一致的结果,表明模型能够描述声波非线性畸变带来的宽频特性。进而采用本模型数值模拟了大振幅活塞声源在双曲形、锥形、指数形和正弦形号筒中的非线性声传播问题,结果表明号筒出口声压级受活塞振动速度、频率以及号筒形状的影响,并分析讨论了波形畸变与号筒几何形状之间的关系。     

有限长号筒中非线性声传播的数值模拟研究

研究了大振幅活塞声源经有限长号筒向外辐射声波的非线性声学问题。采用具有频散保持特性的高精度计算格式求解了适用于变截面管道的一维非线性声场模型,并考虑到声波的非线性畸变及管口处的声反射,加入了宽频时域声阻抗边界条件。宽频阻抗模型的共轭复数系数采用优化拟合方法近似求解,并采用递推卷积算法快速求解出时域声阻抗。在弱非线性条件下模拟指数形号筒中的声传播取得了与已有实验相一致的结果,表明模型能够描述声波非线性畸变带来的宽频特性。进而采用本模型数值模拟了大振幅活塞声源在双曲形、锥形、指数形和正弦形号筒中的非线性声传播问题,结果表明号筒出口声压级受活塞振动速度、频率以及号筒形状的影响,并分析讨论了波形畸变与号筒几何形状之间的关系。      

声诱饵仿真试验系统

文章介绍了声诱饵仿真试验系统中的有关问题，包括：系统的组成、工作原理、对接装置结构等。建立了对接装置声耦合状态下的数学模型，对近场声压分布进行了仿真计算，得出了匹配材料厚度、发射和接收换能器的选取原则。     

Optical fiber coupler array for multi-point sound field measurements

A pressure-sensitive device using an optical fiber coupler is proposed, and is integrated into an array system to measure sound field distributions. The optical coupling between two optical fibers is modulated by the applied sound field with the use of a membrane mechanically connected to the coupler. In the array system, a large number of the optical coupler sensors are connected two-dimensionally, and sound pressure at each sensor can be read out by switching the input light sources in turn. A prototype of the basic array system based on this principle was made, and its performance was demonstrated. The signal discrimination between each element was confirmed in a 2x2 array; then, using a four-element linear array, we demonstrated the steering of beam based on the phased array method.     

A laser pistonphone based on self-mixing interferometry for the absolute calibration of measurement microphones

A laser pistonphone for the absolute calibration of microphones at low frequencies has been developed at UME. The motion of an electro-dynamically driven piston in a small close cavity produces a sound pressure. Accurate measurement of the piston displacement, by self-mixing interferometry, enables this sound pressure to be calculated, and consequently the pressure sensitivity of a microphone, exposed to this sound pressure, to be determined. Absolute calibrations of type LS1P and WS1P microphones have been carried out with an uncertainty of less than 0.15 dB. The performance of the laser pistonphone has been validated by comparing the measured microphone sensitivities with those obtained by the closed coupler reciprocity method.     

Design parameter investigation of industrial size ultrasound textile treatment bath

Design requirements for industrial size ultrasound bath for textile treatments have been determined. For this purpose, effects of sound pressure level, bath temperature, bath volume, textile material type and hydrophility degree of fabric were examined extensively. Finite element analysis (FEA) was used to investigate spacing and alignment of the ultrasound source transducers to reach effective and homogenous acoustic pressure distribution in the bath. It was found that textile material type, bath temperature and volume led to significant changes at sound pressure level. These parameters should be taken into consideration in designing of industrial size ultrasound bath for textile treatments. Besides, wettability of textiles is highly dependent to the distance from the transducers.     

Coupling of earphones to human ears and to standard coupler

A standardized acoustical coupler should enable the calibration of audiometric earphones which ensures that the hearing thresholds determined in the audiometric measurement are independent of the earphone type. This requires that the coupler approximates the average human ear closely. Nevertheless, the differences among earphones as well as between human ears and the coupler affect the results of the audiometric measurements inducing uncertainty. As the mentioned differences are related to the coupling of different earphones to human ears and to a standardized coupler, the effects of this coupling are investigated by measuring the transfer functions from input voltage of the earphone terminals to the pressure at the ear canal entrance in two situations: open and blocked canals. Since the "ear canal entrance" is not well-defined for the coupler, transfer function measurements in the coupler were carried out in a similar way but at different depths. In order to describe and compare the earphone couplings, the pressure divisions at the entrance of the ear canal are calculated from the measured transfer functions. The results indicate that significant difference appears among sound pressures generated in different individuals' ears. Also, the earphone couplings to human ears and to the coupler differ considerably.     

Potential solutions to improved sound performance of volume based lightweight multi-storey timber buildings

Lightweight building systems in general suffer from poor sound insulation, especially in the low frequency region. Since no reliable mathematical models that can predict the impact sound pressure level exists, the lightweight building design is to a high extent based upon previous experience and upon measurements. A special difficulty is related to experimental measurements since the variation among identical units must not be neglected. A modern volume based lightweight wooden building concept has here been tested by numerous well controlled measurements, in laboratory as well as in more field like conditions. The volume construction technique offers new possibilities and challenges to improve sound insulation in light weight timber construction. The main purpose was to investigate how different constructional solutions in the floor, like plaster board, mineral wool, elastic glue, dividing board, floating floor etc., affect the sound insulation. Many of the tested modifications resulted in only marginally changed impact sound pressure level but parameters that substantially can improve the sound insulation were found in using elastic glue to mount the floor boards, to install extra board layers and to use floating floors.     

MP3 player listening sound pressure levels among 10 to 17 year old students

Using a manikin, equivalent free-field sound pressure level measurements were made from the portable digital audio players of 219 subjects, aged 10 to 17 years (93 males) at their typical and "worst-case" volume levels. Measurements were made in different classrooms with background sound pressure levels between 40 and 52 dBA. After correction for the transfer function of the ear, the median equivalent free field sound pressure levels and interquartile ranges (IQR) at typical and worst-case volume settings were 68 dBA (IQR?=?15) and 76 dBA (IQR?=?19), respectively. Self-reported mean daily use ranged from 0.014 to 12 h. When typical sound pressure levels were considered in combination with the average daily duration of use, the median noise exposure level, Lex, was 56 dBA (IQR?=?18) and 3.2% of subjects were estimated to exceed the most protective occupational noise exposure level limit in Canada, i.e., 85 dBA Lex. Under worst-case listening conditions, 77.6% of the sample was estimated to listen to their device at combinations of sound pressure levels and average daily durations for which there is no known risk of permanent noise-induced hearing loss, i.e.,?≤ 75 dBA Lex. Sources and magnitudes of measurement uncertainties are also discussed.     

渐开线斜齿轮短齿廓修形降噪分析*

为了降低特定工况下减速箱的噪声特性,找到相对最佳的渐开线斜齿轮修形方式,该文基于专业的齿轮修形软件Kisssoft和多学科一体化软件LMS Virtual Lab,根据短齿廓修形可以改变渐开线斜齿轮的端面、轴向重合度的原理,比较了未修形和经过不同短齿廓修形方式达到特定重合度后的渐开线斜齿轮减速箱声功率级的大小。分析了经过短齿廓修形后的减速箱声功率级在转速500~2000 r/min之间显著下降的原因,并对经过短齿廓修形后的减速箱声功率级在2500 r/min和3000 r/min时并未明显下降的原因做了解释。最后根据减速箱声功率级在转速500~2000 r/min之间的平均降幅,认为通过齿形鼓形修形使得渐开线斜齿轮的端面、轴向重合度分别为1.516、0.864时,减速箱声功率级降幅最大,降噪效果最好。     

基于声压场描述的扩散声场多自由度互易原理研究

应用于复杂结构中频声振分析的扩散场多自由度互易原理采用位移变量描述系统,实质为弹性波场互易原理,应用于声波场时会造成模型自由度数不必要的增加。建立基于声压描述的扩散声场受挡模型,利用声辐射模态描述扩散声场中结构的表面受挡声压;据此提出基于声压描述的扩散声场多自由度互易原理,发现扩散声场中结构表面受挡声压的互谱矩阵与该结构在自由空间中振动辐射声波的声阻矩阵成正比。该互易原理与传统的单自由度互易原理表达形式相似,但适用于任意自由度结构。该互易原理可用于扩散声场中复杂结构的表面受挡声压的自谱及相关分析,仿真研究表明当边界元网格尺寸小于声波波长的1/6(线性单元)或1/3(二次单元)时,数值解与理论解完全吻合。      

Instability of the voltage transfer function for an MR103 microphone in a coupler calibration technique

MR103 microphones are commonly used laboratory standard microphones in Japan. When the pressure sensitivity of MR103 is calibrated by using a coupler calibration technique, higher accuracy is difficult to achieve due to deviations in the measured voltage transfer function. These deviations are peculiar to MR103, but not to B&K4160, which is also a commonly used laboratory standard microphone throughout the world. Such deviations occur even when the measurements are done consecutively under the same measurement conditions, such as polarization voltage, temperature, and static pressure.This study experimentally and theoretically considered one of the possible reasons for this deviation. The results reveal that (a) this deviation can be explained by changes in the microphone’s parameters, such as the distance between a microphone’s membrane and back-plate, and the tension of the membrane, (b) grease used to prevent leakage of gas and sound out of the coupler might be one of the reasons for this deviation, and (c) insertion of polished sapphire spacers between the microphones and the coupler might help diminish this deviation.