应用于有源声辐射控制的一种组合次级声源

在分析多通道单极子次级源控制系统的基础上,提出一种幅度调节型组合次级声源,这种组合源由两个单极子声源构成,单极子声源的间距远小于声波的波长。文中就组合次级源在自由场中对不同初级声源辐射噪声的控制进行理论分析和实验验证,并与同等条件下的单极子次级源控制系统的降噪性能进行了比较分析。数值计算和实验结果均表明,对于不同的初级声场,在次级通道数相同的情况下,组合次级源控制系统可以得到比单极子次级源控制系统高的降噪量。     

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。     

管道噪声的自适应抵消及其计算机模拟

本文提出一种采用自适应抵消的管道噪声有源降噪系统，自适应滤波器为有限冲激响应的横向结构，系统中采用了辅助滤波器和补偿滤波器，它们保证了最小均方算法的正确收敛，消除了声反馈效应，计算机模拟证实了该系统的可行性，通过对具有不同物理参数的管道的计算机模拟，得到了这些参数的变化对总降噪量的影响，这些参数包括温度、气流速度、管内的吸声情形、次级声源的Q值及次级声源到检测传声器的距离，模拟的结果有助于实际管道有源降噪的系统的设计。     

有源声屏障中误差传感器的位置优化

有源声屏障利用有源控制系统提高声屏障低频段的降噪效果。有源控制系统中误差传感器的位置对整个系统的降噪效果有较大的影响。通过数值模拟和实验研究误差传感器的位置优化问题,得出了有源控制系统中误差传感器摆放位置的两条结论:(1)所介绍的三种摆放中,误差传感器的位置在次级声源的正上方时,有源控制系统在屏障后方声影区引入的新增插入损失最好,特别是对于距离屏障较远的区域;(2)当误差传感器的位置在次级声源的正上方时,误差传感器与次级声源间的距离存在一个最优距离使得屏障后方声影区的衍射声得到最好的降低。     

一种有源头靠系统中虚拟传声器技术的改进方法

对人头移动导致有源头靠降噪效果下降的问题进行了理论分析,得到了残余噪声的预测表达式,提出了一种通过设计次级通道模型改进虚拟传声器技术性能的方法。分析表明,人耳位置处降噪量取决于虚拟传声器方法中采用的次级通道模型与人头移动到不同位置处的真实次级通道之间的匹配程度。通过设计合理的次级通道模型,可有效扩大人耳获得有效降噪量的人头允许移动范围。仿真分析和实验结果验证了该方法的有效性。     

贯流风扇气动声场数值模拟及分析

针对贯流风扇气动噪声传播特性,采用基于非结构网格的CE/SE算法对其气动流场进行数值模拟,并模拟了气动噪声的传播.湍流模拟采用大涡模型,搭接式滑移网格模型处理动静干涉.噪声传播采用完全欧拉方程作为控制方程,远场采用无反射边界条件.将使用该方法得到的远场噪声频谱与实验数据进行对比分析,结果表明与实验测量得到宽带频谱不同,采用大涡模拟湍流模型进行声源模拟时,会加强部分离散频率上的声级,从而产生误差.     

管道有源噪声控制中壁面分布次级声源的空间分布优化

为了改进管道中高阶模式声波的有源控制效果,研究了壁面分布次级声源的空间分布优化问题。首先提出管道中次级声源独立控制高阶模式声波的理论模型,然后推导次级声源在管道中各方向上空间分布对控制高阶模式声波的贡献,得到了次级声源空间分布的优化准则。通过将空间分布离散化,采用最小化管道中声能流的控制策略得到次级声源的最优驱动强度,最后通过数值仿真对比最优驱动强度时各种次级声源空间分布对控制性能的影响,验证了通过优化次级声源空间分布能显著提高控制效果。仿真结果表明,当次级声源分布于管道所有壁面且沿管道轴向分布范围较大时,高阶模式的控制效率最高。     

军用运输机机舱有源消声实验系统的设计与实现

为验证有源消声技术在军用运输机机舱低频噪声消除方面的有效性,设计和实现了一套机舱有源消声实验系统。采用“激振器+舱壁板”方式实现了飞机螺旋桨对机舱诱导噪声的声源模拟,设计了基于前馈控制结构的自适应有源噪声控制系统,构建了基于FX-LMS算法的自适应消声控制器,采用监测麦克风组对舱内空间的消声效果进行监测。实验结果验证了自适应有源噪声控制技术在军用飞机舱室消声降噪领域的有效性,并表明初、次级声源间距对自适应有源消声系统的消声效果具有重要的影响。     

鲁棒性有源头枕系统的设计方法*

为了降低舱室内休息区域乘客双耳处的低频宽带噪声,采用最优维纳滤波器的设计准则,设计出一种基于局域空间有源降噪的多通道前馈有源头枕系统。实验对比了人工头在不同位置处和不同转动角度时两通道和四通道有源头枕系统在人耳处的降噪效果;进一步地,针对人头转动时控制效果变差的情况,提出了一种低复杂度的鲁棒性算法。仿真和实验表明,通道数量增加可使该系统在人耳附近获得更大的降噪量,使用鲁棒性算法的头枕系统在人头转动时有更好的控制性能。     

基于平面声源实施结构声辐射有源控制的理论研究

研究了利用分布式平面声源对结构声辐射进行有源控制的问题。首先建立了系统的数学模型,然后推导了有源控制条件下次级声源的强度和声功率降低的计算公式。在实际应用中,次级声源参数(面积大小、安放位置、个数等)对控制效果有重要影响,本文基于有源控制的物理机理和数值仿真研究这些问题。结果表明:一般情况下,次级声源板的振动模态分布与初级结构振动模态分布不相同,因此,在低频范围内,需要至少4个分布式次级声源,方能有效地控制初级结构声辐射。     

复杂声学环境中人耳附近空间有源降噪研究综述

复杂声学环境中人耳附近空间降噪是有源噪声控制研究的重要课题,目前采用的主要方法为有源降噪头靠(AHR)和虚拟声屏障(VSB).本文简述AHR与VSB的发展历史和研究现状,介绍其物理原理和设计方法,评述其在实际应用中的优缺点,讨论了目前存在的问题与未来相关的研究方向.已有理论、数值仿真和实验研究验证了相关技术在人耳附近空间产生静区的可行性. AHR系统需要较少控制源,系统相对简单易实现,但静区范围较小,结合虚拟传声器技术和人头跟踪技术后可实现随人头移动的静区,降噪频率可达中高频; VSB产生的静区范围较大,但控制源个数较多,系统复杂和成本高,可通过代价函数和控制源优化,以及主被动混合控制技术来提高有效降噪频率范围和减少控制源个数.     

平板扬声器用于结构声有源噪声控制实验研究

对NXT技术的分布式平板扬声器和集中参数扬声器的频响和指向性等进行了对比测量，通过对组合平板扬声器的声场研究及有源消声实验，证明了平板扬声器用于有源噪声控制的可行性。综合平板扬声器和集中参数扬声器的物理特点和声场特性，根据基于平面声源有源噪声控制的已有的理论研究结果和本文的实验结果，可以认为，NXT平板扬声器适合作有源噪声控制的次级源，有利于有源噪声控制的工程推广应用。     

Binaural active noise control using parametric array loudspeakers

This paper reports the binaural active noise control (ANC) system developed to deal with factory noise. The control points are located in the vicinity of the left and right ears of a worker sitting along the production line. Due to the complicated safety requirements in the factory, secondary sources and error microphones are not allowed to be placed near the worker. Therefore, the proposed ANC system employs the feedforward structure and adopts the parametric array loudspeakers (PALs) as the secondary sources. The PAL is a type of directional loudspeaker that generates a much narrower sound field as compared to the conventional loudspeaker. Once the proposed ANC system has been trained offline, the error microphones can be removed. The performance of the binaural ANC system is successfully demonstrated based on a digital signal processor (DSP) implementation.     

Broadband performance of an active headrest.

This paper presents a study of the attenuation of broadband random acoustic disturbances, when using a feedback active headrest system, as originally suggested by Olson and May. Previous studies showed that a practical active headrest can be designed for tonal disturbances using feedforward controllers. However, many applications, such as jet aircraft and cars, require feedback systems to control random disturbances over a wide frequency bandwidth. In this work, robust feedback controllers are designed to control broadband random disturbances in the low-frequency range based on measured data from a laboratory headrest system. The results show that a practically useful performance can be achieved, but only if the controller is designed to minimize the pressure at a "virtual microphone" close to the listener's ears, and that the performance is maintained reasonably well with movements of the listener's head. The paper emphasizes the importance of both the acoustics and the control in the design of broadband active headrest systems.     

Active noise control in finite length ducts

A simple technique for the active control of sound in ducts, initially suggested by Olson and May [1], is investigated in detail. A simple, “virtual earth” principle, feedback loop is used to drive the sound pressure to a minimum at a microphone placed close to a loudspeaker in the duct wall. This produces a reflection of downstream travelling plane waves. A detailed investigation of the loudspeaker near field has enabled the optimum position of the microphone to be identified. The system is shown to be especially effective at the frequencies of the longitudinal duct resonances, where the acoustic response of the duct produces a high loop gain. Results are presented which show a reduction of up to 20 dB in the amplitude of low frequency broadband noise at a position downstream of the cancelling source.     

次级源近场和管壁弹性对充液管路有源消声性能的影响EI北大核心CSCD

建立了含次级源结构的充液直管有源消声系统数值模型,重点分析了声激励下次级源近场和管壁弹性对有源消声性能的影响。结果表明:次级源近场为非均匀声场,误差点位于该区域时部分频点控制效果较差甚至放大,而处于声场均匀区域时可使降噪量提高10 dB以上,增加误差点数量可使绝大多数频点的降噪量提高5 dB以上;管壁弹性使次级源与管壁间的耦合较强,非对称分布的次级源容易激起管壁振动,导致降噪谷值的出现,采用对称分布的次级源可显著提升控制效果;增加次级源数量能够提高系统的有源无源复合控制效果,但使得管内声场变得复杂,多次级源模型的有源消声效果随频率升高而有所降低。     

Investigation of spherical loudspeaker arrays for local active control of sound

Active control of sound can be employed globally to reduce noise levels in an entire enclosure, or locally around a listener's head. Recently, spherical loudspeaker arrays have been studied as multiple-channel sources for local active control of sound, presenting the fundamental theory and several active control configurations. In this paper, important aspects of using a spherical loudspeaker array for local active control of sound are further investigated. First, the feasibility of creating sphere-shaped quiet zones away from the source is studied both theoretically and numerically, showing that these quiet zones are associated with sound amplification and poor system robustness. To mitigate the latter, the design of shell-shaped quiet zones around the source is investigated. A combination of two spherical sources is then studied with the aim of enlarging the quiet zone. The two sources are employed to generate quiet zones that surround a rigid sphere, investigating the application of active control around a listener's head. A significant improvement in performance is demonstrated in this case over a conventional headrest-type system that uses two monopole secondary sources. Finally, several simulations are presented to support the theoretical work and to demonstrate the performance and limitations of the system.     

A study of sound intensity control for active noise barriers

Active noise control systems have been applied to increase the insertion loss of noise barriers where the squared sound pressure or the total acoustic energy density is used as the cost function in previous works. The absolute value of the mean active sound intensity is chosen as the cost function to obtain extra sound insertion loss in the dark area of a hybrid active noise barrier system in this note. The strategy of minimizing the near-field sound intensity at discrete locations along the edge of the passive barrier is shown to be able to provide better far-field noise reduction than that of minimizing the squared sound pressure control. Both numerical simulations and off-line experiments are carried out with a three-channel demonstration system, where the locations of the secondary sources and the error sensors are optimized and comparisons are made between the extra sound pressure attenuation of the sound intensity control and that of the squared sound pressure control.