SOUND TRANSMISSION THROUGH ELASTOMERIC BULB SEALS

The sound barrier performance of elastomeric vehicle weather seals was investigated. Experiments were performed on a single bulb seal specimen using a reverberation room method. The seal wall velocity was measured using a laser Doppler vibrometer. The sound pressure near the velocity measurement location was measured simultaneously, which allowed the sound intensity on both sides of the seal and the sound transmission loss to be determined. The vibration response and the sound transmission loss of the bulb seal were then computed using finite element analysis. Acoustic-structure interactions were considered for a partially coherent spatially distributed pressure excitation. The experimental data obtained using the reverberation room method allowed the validation of the numerical models. The resonance frequency due to the mass-air-mass mode of vibration was accurately predicted. The model was then used to numerically investigate the influence of various design parameters. It was found that the elastic modulus significantly affects the bulb seal resonance frequency, and that the loss factor of the material has major effects on the sound transmission loss around resonance.     

板结构的声辐射模态分析及其高分辨率法向振动速度重建

提出了一种基于声辐射模态的速度基向量构建方法,该速度基向量不受网格划分的影响,可用于高分辨率的板结构法向振动速度重建。首先对板表面稀疏网格的声辐射模态进行计算,再以声辐射模态和模态系数构建板法向振动速度分布的基向量,然后由声场测量声压求解基向量系数,最后由该系数和加密网格的速度基向量重建高分辨率的板法向振动速度分布。以简支板声源进行仿真计算,当测量声压信噪比为30 dB时,低频的法向振动速度重建误差最低可达3.7%;以固支板声源在消声室中进行实验验证,131.5 Hz振动频率下的重建误差低于7%。该方法实现了只需要少量声压测量点即可精确重建板声源更高分辨率的法向振动速度分布。      

Spatial cross-correlation of acoustic pressures in steady and decaying reverberant sound fields

From the equation for the steady state sound pressure distribution produced in a rectangular reverberation chamber by a point source, and by using the usual high frequency approximations, it is shown that, for a random source position, the cross-correlation function for two points not too far apart approaches that of Cook et al. in the reverberant field of the chamber. When the same approach is used on the equation for sound pressure decay when the point source excitation is cut off, the cross-correlation function obtained for the initial portion of the decay corresponds with that determined experimentally by Balachandran and Robinson.     

Adaptive wave field synthesis for active sound field reproduction: experimental results

Sound field reproduction has applications in music reproduction, spatial audio, sound environment reproduction, and experimental acoustics. Sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. The room response thus reduces the quality of the physical sound field reproduction by WFS. In recent research papers, adaptive wave field synthesis (AWFS) was defined as a potential solution to compensate for these quality reductions from which WFS objective performance suffers. In this paper, AWFS is experimentally investigated as an active sound field reproduction system with a limited number of reproduction error sensors to compensate for the response of the listening environment. Two digital signal processing algorithms for AWFS are used for comparison purposes, one of which is based on independent radiation mode control. AWFS performed propagating sound field reproduction better than WFS in three tested reproduction spaces (hemianechoic chamber, standard laboratory space, and reverberation chamber).     

An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation

~~An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation1 Zhang, R.. Jin. G. Normal-mode theory of average reverberation intensity in shallow water, Journal of Sound and Vibration, 1987 19(2):215-223 2. Ellis, D. D., A shallow-water normal-mode reverberation model, J. Acoust. Soc, Am., 1995, 97(5): 2804-2814. 3. McDaniel, S. T., Seafloor reverberation fluctuations, J. Acoust. Soc. Am., 1990, 88(3): 1530-1535. 4. Abraham, …     

Vibration measurements in the classical guitar

Some measurements are described that pertain to the high frequency behaviour of the vibrations of the string and soundboard of the guitar.Three isolated soundboards of different woods were compared with respect to their early decay times (by means of measurements of their vibrational impulse responses), in order to assess its possible use as an objective measure of the reverberation time of the plates. The results of all these measurements show that high frequency vibrations and radiation occurs significantly from 1 to 14 kHz, but that the sound radiation has harmonics at frequencies up to 20 kHz. This report does not produce any experimental evidence as to the importance of the high frequency region from the subjective point of view, or to the correlation of the subjective impression of reverberation of the plates with measured data of early decay times, as these aspects were not addressed at this point.     

Development of an optimised, standard-compliant procedure to calculate sound transmission loss: design of transmission rooms

A numerical procedure to estimate the transmission loss of sound insulating structures is proposed based upon the technology of acoustic measurements and standards. A virtual laboratory (VL), namely, a numerical representation of a real laboratory consisting of two reverberation rooms meeting certain sound field quality criteria is designed. VL is to be used for the numerical simulation of standardised measurements under predefined, controlled, acoustic conditions. In this paper, the design and optimisation of VL is investigated. The geometry of the transmission rooms is designed following first principles, in order for diffuse field conditions and sufficiently smooth primary mode distribution in the low frequency to be achieved. A finite element-based optimisation procedure, introduced by the author in previous work, is extended to arbitrarily shaped rooms. It is used to predict the appropriate local geometric modifications so as for improved mode distribution and smoother sound pressure fluctuations of the transmission rooms in the low-frequency range to be achieved and low-frequency measurement reproducibility and accuracy to be increased. Steady-state acoustic response analysis is performed in order to quantify the acoustic field quality of the virtual transmission rooms in the frequency range of measurements. A method to calculate the total absorption, A, of the receiving room is introduced by simulation of the reverberation time measurement procedure using Transient acoustic response analysis. The acoustic performance of VL is overall considered and is shown to meet in a sufficient degree, relative laboratory measurement standards in the frequency range of 100÷704 Hz.     

微型无刷直流电机位置系统的过程控制

为了实现机械相控阵列天线的波束扫描,采用微型无刷直流电机驱动螺旋天线单元转动来到达预定的辐射相位。设计了一种新型微型无刷直流电机位置控制系统,构建了比例滑模面-超螺旋二阶滑模控制器用于速度控制,利用结合速度剖面策略的PID控制算法实现了转动位置的中间过程控制。建立了基于Simulink的系统仿真模型,验证了方案的可行性,并构建了FPGA硬件实验平台。仿真和实验结果均表明,微型无刷直流电机驱动天线单元精确按照预设的速度剖面曲线运行,在50 ms控制周期内转动角度达到180°,中间控制过程的位置跟踪误差和平衡位置处的残余震荡误差均小于±3°。     

非线性内波存在下的浅海远程混响模型

研究了浅海非线性内波对远程混响场的影响。通过分析非线性内波活动引起声源到海底散射元以及散射元到接收点之间的声传播变化,给出了非线性内波引起远程混响强度变化的表示,建立了非线性内波存在下的浅海远程混响模型,数值计算了非线性内波运动引起远程混响强度的变化。理论和数值计算表明,非线性内波的活动能够引起远程混响强度的变化,在某些情况下会导致远程混响强度增强。通过讨论非线性内波引声简正波的耦合效应,给出了其引起远程混响强度增强的原因。      

体积速度匹配分布源边界点法的特解源位置优化方法研究

在分布源边界点法中,选择特解源及特解源位置对声场计算的精度具有很大的影响。为减小声场计算的误差,提出了一种确定特解源位置的优化方法。在该方法中,采用三极子作为特解源,以1%体积速度相对误差对结构声辐射计算的上限频率进行预测,然后在计算上限频率范围内通过体积速度匹配搜索,得到体积速度相对误差最小意义下的特解源优化位置,在该优化位置处构造声压与表面体积速度之间的传递矩阵来计算声场,以减小计算误差。数值仿真结果表明:在求取的计算上限频率范围内,特解源处于优化位置时,计算误差得以显著减小。当振速测量存在一定误差时,采用该方法仍可将计算误差控制在5%以内。      

High frequency dynamics in a monatomic glass

The high frequency dynamics of glassy selenium has been studied by inelastic x-ray scattering at beam line BL35XU (SPring-8). The high quality of the data allows one to pinpoint the existence of a dispersing acoustic mode for wave vectors (Q) of 1.5相似文献   

频率搅拌混响室原理及应用

从理论上分析了混响室采用频率搅拌的可行性,仿真计算和试验测量了频率搅拌混响室内部电场的均匀性和统计特性,探索了在屏蔽效能测试中的应用。研究结果表明:频率搅拌方法能够得到空间统计均匀的电场分布,电场直角分量的模值服从瑞利分布,并且频率越高电场的均匀性和统计特性越好。在频率搅拌混响室内部测试得到开缝小尺寸屏蔽体在1~10GHz频段的屏蔽效能约为15dB,与机械搅拌混响室测试结果基本一致。     

炉内管阵列中声源辐射特性数值研究

炉内换热器结构类似于声子晶体,基于声子晶体理论,采用数值计算与软件模拟得到管阵列中声源不同方向的声传播特性,并将两种方法所得结果进行对比分析,研究声源在管阵列中不同位置处的辐射特性.结果表明：声指向性特性与声源通过管排数量,声源频率是否处在声波禁带有关.     

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。     

Position optimization of particular solution sources for distributed source boundary point method by volume velocity-matching

Choosing particular solution source and its position have great influence on accuracy of sound field prediction in distributed source boundary point method.An optimization method for determining the position of particular solution sources is proposed to get high accuracy prediction result.In this method,tripole is chosen as the particular solution.The upper limit frequency of calculation is predicted by setting 1%volume velocity relative error limit using vibration velocity of structure surface.Then,the optimal position of particular solution sources,in which the relative error of volume velocity is minimum,is determined within the range of upper limit frequency by searching algorithm using volume velocity matching.The transfer matrix between pressure and surface volume velocity is constructed in the optimal position.After that,the sound radiation of structure is calculated by the matrix.The results of numerical simulation show that the calculation error is significantly reduced by the proposed method.When there are vibration velocity measurement errors,the calculation errors can be controlled within 5% by the method.     

Calculation of vibrational relaxation times in gaseous cyanogen

A calculation of vibrational relaxation times in gaseous cyanogen at 300°K is presented. It is suggested that two well separated dispersion regions should be found in sound velocity measurements at ultrasonic frequencies, the higher frequency region being associated with the relaxation of the combined vibrational specific heat contributions of the two lowest modes and the lower frequency region being associated with the relaxation of the corresponding contribution of the next highest mode.     

低频混响信号中的简正波衰减系数提取方法

提出一种从低频混响信号中提取简正波衰减系数的方法。利用简正波过滤技术对垂直阵混响信号进行分析,获得单阶简正波混响声场。假设海底反向散射矩阵可分离,从单阶简正波平均混响强度中提取出有效海底反向散射矩阵元素,最后利用不同距离上的有效海底反向散射矩阵元素计算出简正波的衰减系数。利用该方法从混响信号中提取出的简正波衰减系数预报的声传播损失和相同海域实测声传播损失一致。该简正波衰减系数提取方法有效避免了海底散射衰减和简正波传播衰减耦合的问题,同时对海底参数反演和水声环境的快速评估也具有重要的意义。      

利用正弦调频信号的宽带速度敏感特性抑制混响

有源声呐探测水中低速目标时,混响与目标回波的频率接近,目标回波与混响分离困难.根据运动目标与产生混响的散射体在速度域的差异,利用正弦调频信号(SFM)的速度敏感特性实现目标回波与混响的有效分离.推导了 SFM信号宽带混响抑制能力与速度分辨模糊之间的约束关系,建立了波形优化设计的搜索模型.通过多普勒滤波处理将数据从频率域...     

Improved prewhitening method for linear frequency modulation reverberation using dechirping transformation

This letter presents an autoregressive (AR) prewhitener for linear frequency modulation (LFM) reverberation to enhance the target signal. The proposed method uses a dechirping transformation to inversely compensate the frequency chirp rate of the LFM and give the LFM reverberation a stationary frequency property in each data block. The left or right beam signal adjacent to the current beam is then used as the reference signal, and the frequency response of each data block modeled using the AR coefficients. Finally, these coefficients are used to implement the inverse filter and efficiently prewhiten the LFM reverberation of the current beam.     

Sound strength and reverberation time in small concert halls

Sound strength and reverberation time measurements have been carried out in six small concert halls in Cambridge, UK. The sound strength G is a measure of the physical sound level in a concert hall and is closely related to the subjective sensation of loudness. It compares integrated impulse responses at a point in the measured room with that measured at ten metres distance in the free field.The aim of the measurements is to investigate the acoustic characteristics of the halls concerning sound strength and reverberation time. Furthermore the effect of the variable acoustics in the halls on these parameters is discussed in this paper. Especially for bigger ensembles it is often desirable to reduce the sound level in a small concert hall. The measurement results show that for a fixed hall volume, this can primarily be achieved by decreasing the reverberation time in the hall. However, with regard to the sound quality of a hall and the recommended reverberation times for chamber music, reverberation time cannot be reduced by an arbitrary extent. Therefore reverberation time and strength have to be balanced very carefully in order to obtain sufficient reverberation whilst at the same time avoiding excessive loudness. Finally the measured strength levels are compared to values derived from traditional and revised theory [Barron M, Lee L-J. Energy relations in concert auditoriums. J Acoust Soc Am 1988;84(2):618-28] on strength calculations in order to assess the accuracy of the theory for small chamber music halls. Possible reasons for the low measured strength levels observed are discussed with reference to related design features and objective acoustic parameters.