虚拟声屏障的数值及实验分析

虚拟声屏障(Virtual Sound Barrier,VSB)由若干控制声源和误差传感器构成,使用有源噪声控制方法在噪声环境中产生局部安静区域,“阻隔”声音但不“阻隔”空气和光,像一个无形的屏障对声音起作用。本文建立立体结构的VSB系统模型,从数值模拟和实验两方面说明在噪声来自于多个方向的普通房间中,通过该系统产生人头大小的静区是可行的。数值模拟表明即使在中频VSB系统也有良好的降噪效果。实验给出一种实用的圆柱状分布的16通道的VSB系统,在中低频条件下产生人头大小的静区,降噪可达10 dB以上。     

人头散射对虚拟声屏障的性能影响分析

在噪声来自于多个方向的普通房间中,通过立体结构的虚拟声屏障(Virtual Sound Barrier,VSB)系统能够产生比人头大的静区。实际应用中人头处于系统包围的静区内,必须考虑人头的散射作用对系统的影响。数值模拟表明,由于人头的散射作用,在人头附近,声压降低量分布更为均匀,系统性能可能变好也可能变坏,与误差传感器包围区域的半径及噪声频率有关。系统性能随系统物理配置的变化趋势,与未引入人头时是一致的。人头可以在系统包围的静区内移动,随着人头偏离系统中心,降噪效果会下降,但即使人头偏离至系统包围静区的边缘,仍有10 dB以上的降噪。实验给出一种实用的圆柱状分布的16通道的VSB系统,引入人头后系统性能变好了。当人头在该系统包围的静区内移动时,即使频率达到500 Hz,降噪效果最差仍达13.3 dB。     

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。     

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。     

用于开口声辐射控制的虚拟声屏障实现 方法及机理研究*

建筑物通常留有开口以便人员物料的进出及室内的自然通风采光,但这些开口也是噪声传播的途径。传统被动噪声控制方法需要将开口封闭,且对低频噪声的控制效果不好,故引入有源噪声控制技术降低室内声源通过开口的声辐射。基于惠更斯原理,均布开口的次级源和误差传声器构成的平面型虚拟声屏障可以实现对开口声辐射的有效控制,数值仿真和实验已证明其有效性。将次级源安装在开口边界更有利于保留开口的功能且方便实际安装,但这样的单层边界虚拟声屏障降噪效果存在上限,仅能在低频段实现全局控制。和单层边界次级源相比,双层边界次级源可显著提高降噪量和有效降噪频率上限。该文回顾了开口声辐射有源控制的相关工作,并讨论了未来可能的研究方向。     

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。     

有源头靠中一种分布式虚拟传声器优化方法

有源降噪头靠系统中,远程虚拟传声器技术能够解决控制点处与误差传声器处降噪量不匹配的问题。在实际应用中,多通道虚拟传声器技术存在收敛速度慢和运算复杂度高等问题。针对这个问题,本文通过重新设计远程虚拟传声技术的离线优化过程,提出一种分布式远程虚拟传声器技术优化方法。该方法将虚拟次级通路矩阵作对角化限制,同时对观测传递函数矩阵进行联合寻优,以实现一种分布式的更新算法。有源降噪头靠实验结果表明,所提算法能够有效降低远程虚拟传声器技术算法的运算复杂度,并且提升了算法的收敛速度。     

局部空间自适应宽带有源消声

本文提出一个局部空间自适应宽带有源消声系统,该系统能实现有源消声所要求的任意带宽噪声在局部空间衰减,能自动补偿背景噪声及消声装置中不可控参数及噪声源变化对消声效果的影响.自适应滤波由TMS 32010数字信号处理器采用NLMS算法多路并行处理完成.实验结果表明:对普通房间中的单次级源布置方式,在主次级源前方1m,±30°扇面区域内,该系统对20—600Hz内的宽带噪声抵消,取得的最大降噪量在25dB(A)以上.     

充液管路系统流体声与结构声的复合有源控制

采用基于谐频自适应控制算法的有源消声与消振系统对充液管路系统突出的低频线谱噪声进行有源控制实验研究.建立了泵水循环管路实验系统,在管路中安装有源消声器对流体声进行控制,在管路出口障板上采用8×8通道有源消振系统控制结构声辐射。开展的低频线谱噪声与振动有源控制实验结果表明,在50~200 Hz频带内,通过结合有源噪声与振动控制可在多数频点取得10 dB以上的降噪效果。针对该实验系统,通过分别控制流体声和结构声分析了两者的贡献.实验结果验证了有源消声与消振系统具有较好的降噪性能,各频点处流体声与结构声占比情况不同,需要综合控制流体声与结构声才可以取得显著的降噪效果。      

有源噪声控制在隔声罩中应用的初步实验研究

本文以对液压泵降噪为例,对有源噪声控制系统在隔声罩中的应用进行了初步的实验研究。噪声的低频段由有源噪声控制系统降低,中高频段由隔声罩降低,从而发挥了有源噪声控制和隔声罩各自的优点。附加了有源系统后的隔声罩使液压泵的噪声从112.4dB降到了80.0dB,整个系统的降噪量达到了32dB。其中有源噪声控制系统采用了6个次级控制源,在600Hz以下频段新增13dB的插入损失。     

A moving zone of quiet for narrowband noise in a one-dimensional duct using virtual sensing

A frequent problem in active noise control is that the zone of quiet created at the error sensor tends to be very small. This means that the error sensor generally needs to be located close to an observer's ear, which might not always be a convenient or feasible solution. Virtual sensing is a method that can move the zone of quiet away from the error sensor to a desired location that is spatially fixed. This method has been investigated previously, and has shown potential to improve the performance of an active noise control system. However, it is very likely that the desired location of the zone of quiet is not spatially fixed. An active noise control system incorporating a virtual sensing method thus has to be able to create a moving zone of quiet that tracks the observer's ears. This paper presents a method for creating a moving zone of quiet based on the LMS virtual microphone technique. To illustrate the proposed method, it is implemented in an acoustic duct and narrowband control results are presented. These results show that a moving zone of quiet was effectively created inside the duct for narrowband noise.     

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.     

Performance of an independent planar virtual sound barrier at the opening of a rectangular enclosure

Planar virtual sound barrier systems have been used successfully to reduce noise radiation through an opening without affecting natural ventilation and lighting. However, the complexity of a fully coupled control system grows at the rate proportional to the square of the number of channels and this make the system implementation become impractical for enclosures with large openings. To reduce the system complexity, this paper proposes an independent planar virtual sound barrier, which is a multi-channel system consisting of many independent single channel active noise control systems. Each single channel system is “independent” in the sense that the control source output of the system is updated only with the signal from its own error sensor. Based on the analytical model of sound radiation through the opening of a rectangular enclosure, the transfer functions from both primary and control sources are calculated first. Then the noise reduction performance, the stability, and the convergence behavior of both fully coupled and independent planar virtual sound barrier systems are investigated. It is found that the independent system with no control output constraint becomes inherently unstable at some frequencies; however its stability can be improved by applying some control output constraint. Reducing the number of channels and the distance between secondary loudspeakers and error microphones can also increase system stability but at the cost of smaller noise reduction. When the system is inherently stable and there is no constraint on control output, the independent system can provide the same noise reduction as the fully coupled one but with faster convergence speed.     

Performance analysis of the virtual sound barrier system with a diffracting sphere

Since a practical virtual sound barrier (VSB) system has to be implemented surrounding a human’s head, the effects of such a diffracting sphere on the performance of the system are considered in this paper. It is found that the performance of the VSB system with a diffracting sphere might be improved or decreased depending on the size of the zone surrounded by the error sensors and the noise frequency, and the noise reduction distribution around the sphere tends to be uniform due to the diffraction of the sphere. Numerical simulations show that the tendency of the control performance with respect to the configuration of the system with a diffracting sphere is similar to that without the sphere. The diffracting sphere might move in the quiet zone of the VSB system, and the performance decreases with the increase of the distance between the sphere and the center of the system. However, the noise reduction level can remain more than 10 dB even when the sphere is near the border of the quiet zone. Experiments with a 16-channel cylindrical VSB system in a normal room validate the above conclusions.     

Active noise control with linear control source and sensor arrays for a noise barrier

A study is conducted on minimizing the sum of the squared acoustic pressures with a linear array of control sources and a perpendicular linear array of error sensors, placed above the top of a noise barrier. Particular angular orientations, with respect to the center of the barrier top, and spacings of the linear arrays of control sources and error sensors result in moderate to significant additional reduction of the acoustic pressure in the shadow zone. Visual inspection of the sound pressure field, with and without active noise control, found that uniform and significant additional insertion loss can be generated near the barrier. Numerical simulations were conducted to test the proposed method. For separations between control sources and error sensors much less than a quarter wavelength of the primary noise disturbance, results show that the angular orientation, of the combined linear control source and sensor arrays, is a weak factor for acoustic pressure reduction in the shadow zone. Weak angle dependence serves as an advantage to the proposed method, which yields uniform performance for any angular orientation. An angular orientation involving the alignment of the furthest error sensor with the first diffracting edge of the barrier and the primary source was observed to perform well for a variety of frequencies, since the spacing between error sensors and between control sources is of the order of a quarter-wavelength. Improved noise control in the shadow zone of a barrier is achieved by the use of two control sources and angular orientation as mentioned above. Further spatial extension of the area of reduced acoustic pressure is possible by utilizing an increased number of control sources.     

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.     

有源头靠系统中次级声源和控制电路的参数优化研究

在有源头靠系统中,针对次级声源和控制电路两部分对模拟反馈有源控制系统(ANC)参数进行优化。为了达到更好的噪声抑制效果,次级声源的有效辐射频带应和待控制噪声的主要频谱相近,在使用电动扬声器作为次级声源时,其谐振频率应在要控制噪声频谱的下端。在优化控制电路参数时,根据经典控制理论提出合适的目标函数,通过差分演化算法进行优化。在有源头靠系统中,可通过适当调整两通道间距离,或将两通道间耦合纳入参数优化算法中,以保证系统稳定性和抑制"水床效应"的影响。模拟和实验表明两种方法各有利弊。在实际应用中需根据不同需要采用不同的优化方法。     

Experimental results for multichannel feedforward ANC with noninvasive system identification

This paper presents experimental validation of a class of algorithms designed to enable active noise control (ANC) to function in environments when transfer functions change significantly over time. The experimental results presented are for broadband, local quieting in a diffuse field using a multichannel ANC system. The reverberant enclosure is an ordinary room, measuring approximately 1.4 x 2.4 x 2.4 m3 and containing a seated occupant, with six microphones defining the quiet zone near the occupant's ears. The control system uses a single reference signal and two error channels to drive four secondary sources. Using an ideal reference sensor, reduction in sound pressure level is obtained at the quiet-zone microphones averaged over the frequency range 50 to 1000 Hz with an occupant seated in the room. Two main results are presented: first for an adaptive cancelling algorithm that uses static system models, and second for the same algorithm joined with a noninvasive real-time system identification algorithm. In the first case better than 23 dB of performance is obtained if the occupant remains still through calibration and testing. In the second case, approximately 18 dB is obtained at the error microphones regardless of the motion of the occupant.     

Active control of radiation from a piston set in a rigid sphere

Active control of the sound radiated from a piston set in a rigid sphere with a set of control point sources around is considered in this paper, where the scattering sound field of the control sound from the rigid sphere has been taken into account to minimize the total radiated sound power. Analytic results of the sound power are obtained and numerical simulations show that it is possible to reduce the radiation from a small piston set in a rigid sphere similar to the size of a human head up to a certain frequency. It is found that the introduction of the scattering object makes significant differences from the active control without scattering objects. This being the case, the scattering object makes the active noise control easier. To increase the global reduction of sound-power output, the optimal number and locations of the control sources and the optimal number and locations of error sensors are discussed. Finally, experiments with one control source and one error sensor around a head simulator have been carried out to verify the simulation results.