Sound localization of stereo reproduction with parametric loudspeakers

A parametric loudspeaker radiates an audible signal by the interaction of the primary wave that is amplitude modulated and is known as a super-directivity loudspeaker. The parametric loudspeaker is one of the prominent applications of nonlinear acoustics. So far, the applications have been limited monaural reproduction sound system for public address in museum, station, street etc. In this paper, we investigated sound localization of stereo reproduction using two parametric loudspeakers in comparison with that using two ordinary dynamic loudspeakers. In subjective tests, the binaural information ILD (Interaural Level Difference) or ITD (Interaural Time Delay) was focused on. To investigate the characteristics of sound localization in a wide listening area, three typical listening positions were picked up. Signals were 500 Hz, 1 kHz, 2 kHz and 4 kHz pure tones and pink noise. The used parametric loudspeaker was an equilateral hexagon. The subjective test led to the results that when the parametric loudspeakers were used, the listeners at the three typical listening positions perceived the correct sound localization of not only pure tone but also pink noise and when the ordinary dynamic loudspeakers were used, except for the case of pure tone with ITD, the tendency was almost similar to those using the parametric loudspeakers. The second subjective tests were conducted in order to investigate in details the difference between parametric loudspeakers and ordinary dynamic loudspeakers by increasing the number of subjects. In the case of ITD and 500 Hz using the ordinary dynamic loudspeakers, three types of sound localization were categorized, in which the reversed type was major and the normal and the other types were minor. The ILDs which were measured with a dummy head and were calculated with several formulas were almost the same and indicated the reasons of the reversed typed sound localization and a serious influence of the crosstalk. It was found that in the case of pure tone with ITD, the contradiction between the binaural information ILD and ITD is remarkable, because the directivity of the ordinary dynamic loudspeakers was so dull that the crosstalk components had a serious influence on sound localization. It was determined the parametric loudspeaker could transmit correct binaural information to the listener, because the directivity of the parametric loudspeakers was so sharp that it suppressed the cross talk components.     

Study of vertical sound image control with parametric loudspeakers

A parametric loudspeaker utilizes nonlinearity of a medium and is known as a super-directive loudspeaker. In this paper, the sound localization in the vertical direction using the upper and lower parametric loudspeakers is confirmed by listening tests and physical measurements. The differences in levels between the upper and lower parametric loudspeakers are varied as a parameter. The direction of sound localization in the vertical plane can be controlled not only when the acoustical axis is set to the right ear but also when it is set to at 5 deg to the right of the right ear. The effect of the level difference between the upper and lower loudspeakers is weaker than the differences observed when using ordinary loudspeakers. We obtained interesting characteristics of the left-right sound localization in the horizontal plane with the upper and lower parametric loudspeakers in the vertical plane. It is found that by setting the parametric loudspeaker at the right ear (that is, the horizontal angle of a listener to it is only 3 deg to the right), the direction of sound localization in the horizontal plane moved approximately 10 deg to the right. Moreover, by setting the parametric loudspeaker 5 deg to the right, the direction of sound localization moves approximately 20 deg to the right. The ILD (Interaural Level Difference) using a dummy head is calculated from the measured left and right sound signals. It is determined that ILDs of the parametric loudspeaker are larger than those of the ordinary loudspeaker. A simple geometrical acoustic model is introduced and analyzed. The analysis helps to explain the measured characteristics.     

基于Volterra滤波器的参量阵扬声器互调失真补偿研究

针对单边带调制方法预处理的参量阵扬声器系统在复杂信号输入情况下存在明显互调失真的问题,引入Volterra滤波器模型和简化的一维Volterra滤波器模拟了其互调失真。设计了相应的逆滤波器,并对其抑制系统互调失真的性能进行了实验对比。结果表明,所设计的逆滤波器都能有效降低系统的互调失真,而后者具有较低的计算复杂度。     

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。     

FPGA-based implementation of steerable parametric loudspeaker using fractional delay filter

Parametric loudspeaker enables high directivity sound along the radiation direction to be generated by the nonlinear effects of ultrasonic waves in air. Based on the theory of phased array, the beams of parametric loudspeakers can be steered to other directions. In this paper, the Fractional Delay (FD) filter is introduced to generate any arbitrary delay to accurately control the steering angle of the beam. Field Programmable Gate Array (FPGA) is a better choice for the system of steerable parametric loudspeaker due to its strong capability of parallel and real-time processing. The algorithms have been realized easily and quickly by combining the tools of Matlab simulink and DSP Builder. Finally, the validity of the system is verified through comparing the theoretical simulations with the experimental results.     

Three-dimensional acoustic sound field reproduction based on hybrid combination of multiple parametric loudspeakers and electrodynamic subwoofer

Auditory Mixed Reality (MR) systems that reproduce Three-Dimensional (3-D) acoustic sound fields have recently become a research focus because the combination of visual and auditory MR systems can achieve a greater sense of presence than conventional visual MR systems. General auditory MR systems usually use a headphone-based system with a Head-Related Transfer Function (HRTF), which is a major system for reproducing 3-D acoustic sound fields. However, the localization accuracy of sound images with a HRTF depends on the individual. On the other hand, we have already proposed a system for reproducing a 3-D acoustic sound field with parametric loudspeakers instead of headphones. The 3-D acoustic sound field reproduced by this system has achieved a highly accurate localization of sound images. However, one problem is that it is difficult to reproduce lower frequency sounds using parametric loudspeakers, which causes a poorer sound quality. We tried to accomplish a greater sense of presence for 3-D acoustic sound fields based on a hybrid combination of an electrodynamic subwoofer and the parametric loudspeakers by improving the sound quality. Sound images were formed at the target location using the parametric loudspeakers, and a lower frequency sound was compensated for by using the electrodynamic subwoofer. Subjective evaluation experiments were conducted to verify the effectiveness of the proposed system. We confirmed the improved sound quality while maintaining a higher accuracy of sound image localization by using the proposed system. We also confirmed the optimum parameters of the proposed system to achieve a greater sense of presence.     

相位差法波前传感系统自身误差的分析及消除方法

 针对附加像差为离焦的情况,对焦面位置误差、离焦量误差、图像对准误差以及图像噪声等因素带来的波前传感误差进行了数值模拟,并给出了确定焦面位置、对准焦面图像和离焦面图像、精确计算分光比、确定离焦量以及处理图像噪声的方法。使得传感结果的均方根误差分别由0.088 8λ,0.059 0λ,0.128 4λ,4.170 6λ,0.152 6λ降为0.002 1λ,0.002 1λ,0.002 1λ,0.002 1λ,0.029 2λ。结果表明:这些方法可以有效地减小传感误差,大大提高了传感精度,为相位差法的实际应用提供了重要的技术支持。     

相位差法波前传感系统自身误差的分析及消除方法

针对附加像差为离焦的情况,对焦面位置误差、离焦量误差、图像对准误差以及图像噪声等因素带来的波前传感误差进行了数值模拟,并给出了确定焦面位置、对准焦面图像和离焦面图像、精确计算分光比、确定离焦量以及处理图像噪声的方法。使得传感结果的均方根误差分别由0.088 8λ,0.059 0λ,0.128 4λ,4.170 6λ,0.152 6λ降为0.002 1λ,0.002 1λ,0.002 1λ,0.002 1λ,0.029 2λ。结果表明:这些方法可以有效地减小传感误差,大大提高了传感精度,为相位差法的实际应用提供了重要的技术支持。     

点源透过率测试系统精度标定与分析

点源透过率(PST)测试系统是评价光学系统杂光抑制水平高低的关键设备, 其系统精度的标定是研制难点, 针对此设计了一套用于点源透过率杂散光测试系统精度标定的校准镜头. 利用Tracepro建模分析了校准镜头在不同离轴角下的PST值, 并用此系统对校准镜头不同离轴角下的PST值进行了实测, 与其理论分析值进行比对完成设备精度的标定, 同时通过实测数据分析了测试误差, 给出了系统测试精度和测试极限水平. 结果表明, 在双柱罐内洁净度为ISO 7级的环境水平下, 系统的可见光PST测试极限水平为10^-8, 测试精度对数值优于0.5, 测量重复性为7.9%, 根据对探测系统探测能力的评估, 系统的PST极限测试水平为10^-10.     

有内共振时的扬声器分谐波和混沌

研究了当轴对称模态由驱动力共振激发,并且轴对称模态和非轴对称模态存在2:1内共振时的扬声器辐射体薄壳的分谐波和昆沌。采用多尺度法分析了非线性模态方程的稳态解及其稳定性,由此进一步确定了驱动频率和驱动力平面上的分岔集。给出了所考虑情形下扬声器分谐波的阈值电压公式,该阈值电压低于无内共振时的阈值电压。除出现非轴对称模态的1/2分谐波振动外,2个模态的振幅经Hopf分岔后作极限环运动,并经倍周期分岔进入混沌运动。混沌出现是由于2个模态间能量的强烈交换。理论结果和实验结果基本吻合,该一致性表明了所建扬声器非线性薄壳模型的正确性。     

Comparative measurements of loudspeakers in a listening situation

Comparison of loudspeakers is a major concern during design or product selection. There are several standards for the measurement of loudspeaker characteristics, but none of them provides hints for a rigorous comparison between devices. In this study, different ways of evaluating acoustical dissimilarity between loudspeakers were compared. Several methods of signal analysis were used, and for each method a metric evaluating the dissimilarity between two signals was defined. The correlation between the different dissimilarity evaluations over a significant panel of loudspeakers led to identified classes of measurements. A specific aspect of this work is that measurements were performed in a standard listening environment, rather than in an anechoic or reverberant one. It allowed the use of the recorded signals for a simple listening test, providing a perceptual metric which was compared to the acoustical ones. It also allowed the introduction of auditory models in the computation of some acoustical metrics, so defining a new class of measurements which gave results close to the perceptual ones.     

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。     

A method to retrieve blackbody temperature errors in the two points radiometric calibration

Measurements of the atmospheric thermal emission using an infrared Fourier transform spectrometer need to be radiometrically calibrated. As for several existing instruments (IASI-MetOp, IASI-balloon, NAST-I, AERI, etc.), the two points radiometric calibration is generally performed using two well-characterized blackbodies at two different temperatures (or one blackbody and the cold space), which allow to determine the response and the self-emission of the instrument. To perform an accurate radiometric calibration, the emissivity and the temperature of each blackbody should be known accurately. The blackbody temperatures are chosen to fit the characteristics of the instrument. The measurement of these temperatures is essential. This paper proposes a method to perform an accurate radiometric calibration even when one of the two blackbodies temperatures is not perfectly measured, by numerically retrieving this erroneous temperature.     

Chen系统的非共振参数控制

本文利用非共振参数策动实现对Chen系统的非反馈方式混沌控制.使用远大于系统平均频率的周期信号作为控制输入,将控制系统中的系统变量分解为按系统平均频率变化的慢变量和按外加控制信号频率变化的快变量,然后利用平均法对控制系统进行处理得到慢变系统;根据慢变系统的动力学性质,得出所用控制参数应满足的条件.数值仿真结果表明此方法可以使控制系统迅速达到目标状态,并且在控制信号受到噪声干扰时,在一定信噪比范围内仍能对系统进行有效的控制,证明了该方法的可行性. 关键词： 平均法 Chen系统 混沌控制     

Dynamical measurements on viscoelastic behaviors of spiders in electro-dynamic loudspeakers

Spiders in electro-dynamic loudspeakers are most commonly concentrically corrugated fabric disks, and their viscoelastic behaviors affect the loudspeaker reproductions. A noncontact dynamic measuring technology is presented by a subwoofer closed box to excite the tested spiders pneumatically with a Laser Doppler Vibrometer (LDV) to measure the velocity of the moving spiders. Correlation techniques were employed to get an accurate and reliable acoustical transfer function between the measured velocity and sound pressure. The Young’s moduli of the tested spider composite materials were derived from the measured vibration modes. The creep effect and the level dependent behaviors of tested spiders were investigated. The results indicate that, the Young’s moduli of the tested spiders are frequency dependent. The mechanical stiffness increases with a small slope in low frequency range while a large slope in high frequency range. The loss factor exhibits the maximum around the resonance frequency, and after that it decreases with increasing frequency. The effective stiffness has a monotonic decrease with input voltage levels and the harder the spider, the less stiffness changes with input levels.     

电子白板系统中参数标定方法的研究

为了避开复杂繁琐的摄像机标定过程,提出了一种基于CCD摄像机的电子白板系统参数标定新方法,实现了开机自动标定系统参数的功能。采用Harris角点检测算法成功提取了参考点的像素坐标,并直接运用射影变换交比不变性,推导出白板边框图像像素距离与实际物理距离的映射关系式,进而获得了摄像机的光心坐标。简要分析影响系统标定精度的因素,并设计出减小标定误差的方案,最后搭建实验平台标定系统参数。实验结果表明:该标定方法实现简单,应用方便,且对于单位长度为1 cm的标定块而言,标定误差小于0.04 cm。     

Development and application of automated vicarious calibration system

In order to improve the frequency and precision of radiometric calibration, the automated vicarious calibration system(AVCS) is developed and deployed at the Dunhuang test site to perform vicarious calibration without the in situ manned measurements. The surface and atmospheric parameters are automatically collected by AVCS.An absolute radiometric calibration approach based on AVCS is proposed. Six successful calibrations of the Aqua Moderate Resolution Imaging Spectroradiometer(MODIS) are conducted. The results are in good agreement with the on-board calibration system with all the relative differences less than 4%. It enables us to monitor the change of a sensor over long time scales.     

前方空间环绕声的四扬声器虚拟重放

考虑头部转动带来的动态因素对听觉垂直定位的贡献,提出了前方空间环绕声的四扬声器虚拟重放方法。4个扬声器分别布置在水平面左前、右前以及高仰角的左前上、右前上方向,并采用听觉传输信号处理的方法将多通路空间环绕声信号转换为4个扬声器的重放信号。以9.1通路空间环绕声虚拟重放为例,采用头相关传输函数对双耳声压及其包含的定位因素进行分析表明,该方法可以产生正确的双耳时间差及其随头部转动的变化,从而产生合适的侧向定位双耳因素和垂直定位的动态因素。而心理声学实验结果表明,该方法可以重放稳定的前方空间的水平和垂直虚拟源。因此,四扬声器布置结合听觉传输处理足以重放前方空间环绕声的垂直定位信息,实现多通路空间环绕声的向下混合与简化。