面向目标的定向声辐射技术及其应用研究

面向目标的定向声辐射是指利用声源特性和阵列信号处理技术,将声波传送至目标方向或区域的声场控制方法。本文介绍了定向声辐射技术的原理和进展,重点阐述了普通扬声器阵列和参量阵扬声器这两种声源形式的理论、算法和应用研究。其中,针对扬声器阵列,主要分析了基于声能量对比度控制的声聚焦技术;针对参量阵扬声器,综述了利用非线性效应产生高指向性可听声的计算方法、信号预处理和应用等进展。面向目标的定向声辐射技术的研究对实现智能声场控制有着重要意义。     

虚拟声屏障在变压器低频降噪中的实验研究

针对开口房间内的变压器,在开口处布放若干扬声器和误差传声器构成虚拟声屏障,实验研究了虚拟声屏障对通过开口向外辐射的低频线谱噪声的控制效果。将15个次级源近似均匀分布在面积为2 m′ 2.7 m的开口面上,左右间距约58.5 cm、上下间距45-65 cm,15个误差传声器分别位于对应的次级源正前方1 m,系统采用自适应谐波降噪算法。结果表明：虚拟声屏障系统在误差点100 Hz、200 Hz和300 Hz的平均降噪量分别达到12.7 dB、19.9 dB和22.2 dB,虚拟声屏障对100 Hz、200 Hz、300 Hz线谱噪声的控制效果与单层封闭窗户相当,且内部合成参考信号,无需外接参考传声器。采用虚拟声屏障对开口房间内的变压器降噪的好处是实现室内外的自然通风,便于变压器的散热。     

参量阵扬声器在管道噪声控制中的研究*

为了解决管道有源噪声控制中声反馈造成的系统复杂度和计算量的增加,文中引入参量阵扬声器作为次级声源,利用其强指向性减小控制系统的声反馈。为了验证该方法可行性,本文分别在直管和L管中,对600 Hz单频噪声和频率范围为500 Hz~1000 Hz的窄带噪声进行了管道有源噪声控制,同时测量了参量阵扬声器的管内声场和降噪范围。结果表明,参量阵扬声器声反馈小,在没有声反馈补偿的条件下对单频噪声的降噪效果基本达到了声反馈补偿条件下普通扬声器的降噪效果,对窄带噪声的降噪效果稍差。此外,通过测量管道声场和降噪量,确定了参量阵扬声器的降噪区域为误差传感器下游整个管道,降噪面积为管道整个截面。这说明参量阵扬声器作为次级声源降低了系统的复杂度和算法的计算量,并取得了较好的降噪效果。     

次级声源优化布放的局部空间有源降噪

针对区域有源降噪问题,为获得更优降噪效果,根据实际次级通路传递函数,提出次级声源优化布放的有源控制系统并详细比较了两种次级声源优化布放算法与次级声源均匀布放的实际降噪效果。应用的第一种次级声源优化算法是l2范数约束的约束匹配追踪算法,第二种次级声源优化算法是l1范数约束的稀疏正则化方法。在全消声室中利用扬声器线阵进行多通道有源降噪实验研究,实验结果表明,在200~1000 Hz,次级声源优化布放的控制系统的平均降噪量比次级声源均匀布放的控制系统的平均降噪量多5 dB左右;在1100~1900 Hz,次级声源优化布放的控制系统的平均降噪量比次级声源均匀布放的控制系统的平均降噪量多11~13 dB左右,次级声源优化布放的控制系统的降噪量分布更加均匀且次级声源输出能量更小。此外,两种优化算法中,稀疏正则化方法的降噪效果更佳。     

基于平板冲击声的声源特性表征及自动识别*

以平板结构导纳函数为纽带,建立冲击声信号特征与声源特性之间的关联,获得与声源属性密切相关的特征用于目标分类。针对四边简支矩形被击板,借助信号参数识别算法获得与声源物理属性有关的6维导纳特征,并从冲击声样本中提取80维音色特征,将音色特征和导纳特征做相关性分析,获得与声源物理属性相关的信号特征集。利用BP神经网络进行分类,结果表明,当采用与特定声源物理属性相关的信号特征子集时,分类效果达到同组最优。     

北极冰下双轴声道传播特性研究

本文利用第六次北极科学考察的所得的楚科奇海温盐深数据,开展了北极海域声传播特性研究。通过引入Diachok海冰散射模型,将海冰界面模拟为无限椭圆形半圆柱体在自由界面的随机分布,利用Twersky散射理论计算了海冰的反射系数。使用简正波中的KRAKENC模型,结合海冰参数,进行了传播损失仿真分析。研究表明,北极的双声道波导中表面声道的传播特性与声源频率和收发深度紧密相关。深海声道与北极典型声速结构的传播特性一致,具有频率选择特性,在20 Hz左右时传播特性较为理想。此外,在远程传播时,深海声道的传播特性要优于表面声道。     

二维声子晶体平板成像中的通道特征

利用多重散射理论分析了钢/水声子晶体平板成像过程.发现平板成像中的散射波会聚具有散射通道特征.对于确定的声源位置,不同入射角信号对应不同的通道;耦合进入通道的信号强度也不相同.小角度入射波能较强地耦合进入通道;大角度入射波在入射表面受到强烈散射,较弱地耦合进入通道.非理想成像情况下,不同入射角信号通过平板成像的位置不同,因而形成像差.声源位置改变,对应的通道亦随之改变.散射通道与声子晶体的各向异性能带结构和多重散射密切相关.     

两扬声器虚拟声重放的双耳声压控制与定位性能

在两扬声器虚拟声重放中,通过精确重构双耳声压而产生不同的空间听觉感知。其重放的定位性能应该是由双耳声压控制的代价和稳定性所共同决定的。过去研究主要对双耳声压控制的稳定性进行分析,并以此作为扬声器布置和信号处理的依据。该文研究表明仅对双耳声压的稳定性分析是不足以完全衡量扬声器虚拟声重放的定位性能的。进一步采用虚拟声信号处理滤波器响应平均功率对双耳声压控制的代价进行分析。结果表明,缩窄左右对称扬声器布置的张角或采用非对称扬声器布置会明显增加产生侧向目标虚拟源时的双耳声压控制代价。虚拟源(虚拟声像)定位实验表明,双耳声压控制代价增加会引起虚拟源定位缺陷。实际应用中,为了有效产生侧向虚拟源,应避免采用过窄张角(如立体声偶极)和非对称的扬声器布置。     

光学系统受迫振动的激光测量方法

将激光信号与高帧频CCD结合,解决了光学系统中振动信号和激光信号之间的转换问题,不仅能够测量振动对系统光束指向稳定性的影响,而且能够得到振动信号本身的频率特性。利用该方法对振源为150 Hz和200 Hz两种条件下的光学系统受迫振动进行测量,得到了与输入信号相吻合的振动信号属性。通过实验与分析得知:时域振幅测量精度为6.25 m,频域分辨力为2 Hz,方法简便高效,测量结果准确,已应用于角多路准分子激光主振荡功率放大器系统打靶试验平台光束指向稳定性的研究中。     

变工况下轴流泵装置振动特性实验研究

对不同工况下轴流模型泵装置各主要测点处的振动加速度信号进行动态测量和分析,获得了特定频域范围内振动加速度均方根值随流量的变化规律。实验结果表明:10～8000 Hz频域范围内振动加速度均方根值随流量的变化趋势和泵扬程随流量的变化趋势基本一致,运行工况从大流量降至小流量的过程中其装置振动水平可分为低水平区、快速增长区及高水平区;10～350 Hz频域范围内低水平区中振动最低点对应的流量和泵最优工况流量基本一致。研究结果为轴流泵多工况下的稳定运行及最优工况判定提供了一定的理论和技术基础。     

Smart panel with active damping units. Implementation of decentralized control

This paper contains the second part of a study on a smart panel with five decentralized velocity feedback control units using proof mass electrodynamic actuators [Gonzalez Diaz et al., J. Acoust. Soc. Am. 124, 886 (2008)]. The implementation of five decentralized control loops is analyzed, both theoretically and experimentally. The stability properties of the five decentralized control units have been assessed with the generalized Nyquist criterion by plotting the loci of the eigenvalues of the fully populated matrix of frequency response functions between the five error signals and five input signals to the amplifiers driving the actuators. The control performance properties have been assessed in terms of the spatially averaged response of the panel measured with a scanning laser vibrometer and the total sound power radiated measured in an anechoic room. The two analyses have shown that reductions of up to 10 dB in both vibration response and sound radiation are measured at low audio frequencies, below about 250 Hz.     

Comparison of decentralized velocity feedback control for thin homogeneous and stiff sandwich panels using electrodynamic proof-mass actuators

Theoretical and experimental work is presented to compare the effect of decentralised velocity feedback control on thin homogeneous and sandwich panels. The decentralised control system consists of five control units, which are composed of a proof-mass electrodynamic actuator with an accelerometer underneath its footprint and an analogue controller. The stability of the feedback loops is analysed by considering the sensor-actuator open-loop frequency response function of each control unit and the eigenvalues of the fully populated matrix of open-loop frequency response functions between the five sensors and five actuators. The control performance is then analysed in terms of the time-averaged total kinetic energy and total sound power radiated by the two panels. The results show that for a stiff sandwich panel higher stable feedback gains can be implemented than on a thin homogeneous panel of comparable weight per unit area. Moreover the implementation of decentralised velocity feedback can offset some of the undesirable sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.     

Active vibroacoustic control with multiple local feedback loops

When multiple actuators and sensors are used to control the vibration of a panel, or its sound radiation, they are usually positioned so that they couple into specific modes and are all connected together with a centralized control system. This paper investigates the physical effects of having a regular array of actuator and sensor pairs that are connected only by local feedback loops. An array of 4 x 4 force actuators and velocity sensors is first simulated, for which such a decentralized controller can be shown to be unconditionally stable. Significant reductions in both the kinetic energy of the panel and in its radiated sound power can be obtained for an optimal value of feedback gain, although higher values of feedback gain can induce extra resonances in the system and degrade the performance. A more practical transducer pair, consisting of a piezoelectric actuator and velocity sensor, is also investigated and the simulations suggest that a decentralized controller with this arrangement is also stable over a wide range of feedback gains. The resulting reductions in kinetic energy and sound power are not as great as with the force actuators, due to the extra resonances being more prominent and at lower frequencies, but are still worthwhile. This suggests that an array of independent modular systems, each of which included an actuator, a sensor, and a local feedback control loop, could be a simple and robust method of controlling broadband sound transmission when integrated into a panel.     

Use of high-rate envelope speech cues and their perceptually relevant dynamic range for the hearing impaired

The ability of hearing-impaired (HI) listeners to use high-rate envelope information in a competing-talker situation was assessed. In experiment 1, signals were tone vocoded and the cutoff frequency (f(c)) of the envelope extraction filter was either 50?Hz (E filter) or 200?Hz (P filter). The channels for which the P or E filter was used were varied. Intelligibility was higher with the P filter regardless of whether it was used for low or high center frequencies. Performance was best when the P filter was used for all channels. Experiment 2 explored the dynamic range over which HI listeners made use of high-rate cues. In each channel of a vocoder, the envelope extracted using f(c)?=?16?Hz was replaced by the envelope extracted using f(c)?=?300?Hz, either at the peaks or valleys, with a parametrically varied "switching threshold." For a target-to-background ratio of +5?dB, changes in speech intelligibility occurred mainly when the switching threshold was between -8 and +8?dB relative to the channel root-mean-square level. This range is similar in width to, but about 3?dB higher in absolute level than, that found for normal-hearing listeners, despite the reduced dynamic range of the HI listeners.     

融合多尺度特征的短时音频场景识别方法EI北大核心CSCD

为解决短时音频场景识别任务中识别性能差的问题,提出一种融合多尺度特征的音频场景识别方法。首先将双声道音频中左右声道的和差作为输入,并使用长时帧长进行分帧处理,以保证提取出的帧级特征中包含足够多的音频信息。然后将特征逐帧输入到融合多尺度特征的一维卷积神经网络中,以充分利用网络中不同尺度的浅层、中层和深层嵌入特征。最后综合所有帧级软标签得到短时音频的场景分类结果。实验结果表明,该方法在国际声学场景和事件检测与分类挑战赛(DCASE) 2021短时音频场景数据集上的准确率为79.02%,实现了该数据集上目前为止的最优性能。     

立体声技术近年来的进展

本文总结和评论了立体声技术近年来的进展，包括声像定位理论和实验，传统的双通路立体声系统的改进，环绕产系统，高清晰度电视声系统，假头型立体声系统，数字声频技术在立体声的应用等．文中最后还叙述了对立体声今后发展的展望．     

调控明区声场重建性能和暗区声能量的综合控制方法

采用扬声器阵列的空间局部声场重建是指控制扬声器阵列输入的幅值和相位,使得目标声场聚焦于特定区域(明区)内,同时降低其他区域(暗区)的声能量。为满足车内乘客对独立视听环境需求的不断提高,研究车内局部声场重建。考虑到扬声器有驱动功率限制和传递函数存在测量误差,提出一种调控明区声场重建性能与暗区声能量平衡的鲁棒性控制方法(PSR-RC,Personal Sound Reproduction with Robust Control),采用路径跟踪法获得不同频率下的最佳权重因子。仿真结果与实车测试性能显示,PSR-RC算法保证明区重建声场性能的基础上,通过最小化暗区能量,获得了较好的明暗区声能量对比度。仿真与实车试验结果保持了较好的一致性,控制点区域的控制效果与非控制点区域的控制效果也保持了较好的一致性,验证了PSR-RC算法的正确性和可靠性。      

The effect of frequency change on discrimination of pulse bursts in an electrocutaneous tactual vocoder

Tactual vocoders (artificial hearing systems) transduce the acoustic energy of speech into patterns of stimulation that are presented to the skin. In an electrocutaneous tactual vocoder, energy within an acoustic-frequency band is generally represented at a particular skin locus by the rate or frequency of brief electrical pulse bursts. At present little is known about tactual sensitivity for changes in the frequency of brief, bipolar electrical pulses used in several current electrocutaneous vocoder designs. Accordingly, discrimination of frequency change of electrocutaneous bipolar signals was evaluated for standard frequencies of 48, 100, 148, 200, and 248 Hz at signal durations of 50, 100, and 250 ms. Bipolar pulses (height = 10 mA, width = 13 microseconds) were presented on a single electrode placed slightly above and 8 cm to either the left or right of the navel. In a same-different task, three practiced subjects judged pairs of stimuli separated by an interstimulus interval (ISI) of 300 ms. For standard frequencies of 48 and 100 Hz, psychometric functions were similar for all subjects and all signal durations. For these frequencies, delta f/f was constant at approximately 0.3. By contrast, for standard stimuli greater than 100 Hz, the Weber fraction was found to increase dramatically as a function of both standard frequency and signal duration. In a second, similar experiment the Weber fraction for a 248-Hz standard increased as ISI was decreased below 300 ms. By contrast, ISI had little effect on sensitivity for standard stimuli of 48 and 100 Hz. Overall, these results suggest guidelines for possible intensity coding schemes for future electrocutaneous vocoder designs.     

三维浅海下弹性结构声辐射预报的有限元-抛物方程法

利用多物理场耦合有限元法对结构和流体适应性强、抛物方程声场计算高效准确的特点,提出了三维浅海波导下弹性结构声振特性研究的有限元-抛物方程法.该方法采用多物理场耦合有限元理论建立浅海下结构近场声辐射模型,计算局域波导下结构声振信息,并提取深度方向上复声压值作为抛物方程初始值;然后采用隐式差分法求解抛物方程以步进计算结构辐射声场.重点介绍了该方法对浅海下结构声辐射计算的准确性、高效性以及快速收敛性后,对Pekeris波导中有限长弹性圆柱壳的声振特性进行了分析.研究得出,当圆柱壳靠近海面(海底)时,其耦合频率比自由场下的要高(低),当潜深达到一定范围时,与自由场耦合频率基本趋于一致;在低频远场,结构辐射场与同强度点源声场具有一定的等效性,且等效距离随着频率增加而增加;由于辐射声场受结构振动模态、几何尺寸和简正波模式影响,结构辐射场传播的衰减规律按近场声影响区、球面波衰减区、介于球面波和柱面波衰减区、柱面波衰减区四个扩展区依次进行.     

基于最优滤波器的强混沌背景中谐波信号检测方法研究

强混沌背景中的微弱谐波信号检测有重要的工程研究意义. 目前的检测方法主要是基于Takens理论的混沌相空间重构方法, 然而这些方法往往对信干噪比要求高, 且对高斯白噪声敏感等. 本文注意到混沌信号的二阶统计特性是不变的, 根据这个特点提出了一种基于最优滤波器的强混沌背景中的微弱谐波信号检测方法. 该方法首先构建一个数据矩阵, 在频域上对每个频率通道分别检测谐波信号, 从而将信号检测问题转化为最优化问题, 然后利用最优化理论设计滤波器, 使待检测频率通道的信号增益保持不变, 而尽量抑制其他频率通道的信号, 最后通过判断每一频率通道的输出信干噪比来检测谐波信号. 与传统方法相比, 本文方法有如下优点: 1)可以检测更低信干噪比下的微弱谐波信号; 2)可检测的信号幅度范围更大; 3)抗白噪声性能更强. 仿真结果证明了本文方法的有效性.