扬声器低频谐波失真的数值分析

扬声器作为一种非线性振动系统，在低频段仅考虑力学恢复力非线性可用经典的Duffing方程来描述；同时考虑恢复力和磁场非线性可用广义的Duffing方程来表征。Yoshinisa研究了仅含恢复力非线性扬声器低频非线性现象中的低频谐波失真现象，但对恢复力和磁场非线性同时存在的扬声器低频谐波失真问题未作研究。西方利用Matlab软件求解扬声器非线性振动系统的广义Duffing方程的数值解，又利用Spectra Plus频谱分析软件得到扬声器低频谐波失真与频率的关系曲线，通过分析低频谐波失真与频率的关系曲线，并着重讨论磁场的非线性对扬声器低频谐波失真的影响，得出一些有价值的结论。     

基于PCI-1712卡的参量扬声器算法验证平台设计与实现

针对参量扬声器的算法快速验证与开发问题,采用PCI-1712高速数据采集卡作为信号输入/输出设备,以Labview作为算法快速建模与仿真工具,在PC机上设计并实现了参量扬声器的算法快速验证平台.利用该平台,对SSB算法及DSB算法进行了快速验证与开发,发现:在1.5kHz以上频段,SSB算法输出声波的声压级明显大于DS...     

前馈型低频非线性失真补偿器的仿真与实验

扬声器工作在大振幅时声信号中存在显著的非线性失真,该失真可通过常规非线性失真补偿技术减少.对一种基于反馈线性化理论的前馈型非线性失真补偿器进行了分析讨论,通过仿真得到了单个扬声器参数变化对补偿器性能的影响情况,并通过对扬声器样品的实验评估了补偿器的实际性能.实验结果表明,使用补偿器后扬声器声响应的低频部分谐波失真减少约...     

用互调法测量解调失真

用频偏仪测量调频波的频偏时,在输入纯正弦信号调制的调频波后,由于仪器本身存在非线性,通过混频器、鉴频器、低频放大器后会引起所谓解调失真,它是频偏仪性能的一项指标。本文介绍用于测量频偏仪解调失真的互调法,该法利用双音频调频,然后进行解调,并测量因通过频偏仪后所产生的互调成分,用以表征它的失真。     

聚焦参量阵原频声场抑制方法的研究

在近距离海底底质原位探测中,使用多阵元聚焦技术能弥补参量阵中差频信号能量较低的不足,但也会使得声焦点处的原频信号能量过高,导致接收系统信号波形限幅,引起波形失真,此外在声场测量时也容易造成传感器损坏.基于KZK(Khokhlov-Zabolotskaya-Kuznetsov)方程和Berktay包络自解调理论,以声焦点...     

“Bi—Amp”探讨

双功放驱动(Bi-Amp)是由双线分音连接(Bi-Wire)发展而来的。虽然“Bi-Wire”有着不少的优点,但仍不能完全抵消低音单元音圈运动时产生的反电动势对高频信号的调制作用。此外,尽管双线连接减小了高、低频之间的互调失真,但功放输出的仍是全频带的大电流信号,互调失真仍然存在。而“Bi-Amp”则是使用两台功放并用两对喇叭线分别连接到音箱中的高、低音单元上,由于各频段的驱动功放完全分开,就完全消除了前述反电动势造成的干涉现象,互调失真也被进一步降低。     

超指向性扬声器的系统设计与测试

超指向性扬声器是一种利用声波在空气中传播的非线性由不可听超声产生可听声的参量阵装置,这种声源相比相同大小的传统扬声器,可以产生非常强的指向性、像聚光灯光束一样的宽带可听声束.文章介绍了超指向性扬声器的基本原理,给出了一个基于模拟电路的系统实现方案,并着重介绍了基于所完成的工程样机所做的频率响应、总谐波失真和指向性测试及相关实验分析,还讨论了进一步工作的发展方向.     

遗传算法用于电子枪发射系统的全局最优化设计

常用的优化设计方法 ,如单纯形法、Powell法等 ,易陷入局部最优解。而遗传算法是一种新兴的直接搜索最优化算法 ,它模拟达尔文遗传选择与自然进化的理论 ,根据“适者生存”和“优胜劣汰”的原则 ,借助“复制”、“交换”、“突变”等操作可以得到全局最优解。本文将遗传算法运用于电子枪发射系统的最优化设计 ,得到了使交叠点半径尽可能小的发射系统的最佳结构和相应电参量     

接收机三阶截点原理分析及测试方法探讨

介绍接收机存在的两种互调失真及其测试方法，针对最新数字超短波接收机的技术特点，提出一种实用的三阶截点测试方法，并分析该方法的测试原理。     

遗传算法用于电子枪发射系统的全局最优化设计

常用的优化设计方法，如单纯形法、Powell法等，易陷入局部最优解，而遗传算法是一种新兴的直接搜索最优化算法，它模拟达尔遗传选择与自然进化的理论，根据“适生存”和“优胜劣汰”的原则，借助“复制”、“交换”、“突变”等操作可以得到全局最优解，本将遗传算法运用于电子枪发射系统的最优化设计，得到了使交叠点半径尽可能小的发射系统的最佳结构和相应电参量。     

Grating lobe elimination in steerable parametric loudspeaker

In the past two decades, the majority of research on the parametric loudspeaker has concentrated on the nonlinear modeling of acoustic propagation and pre-processing techniques to reduce nonlinear distortion in sound reproduction. There are, however, very few studies on directivity control of the parametric loudspeaker. In this paper, we propose an equivalent circular Gaussian source array that approximates the directivity characteristics of the linear ultrasonic transducer array. By using this approximation, the directivity of the sound beam from the parametric loudspeaker can be predicted by the product directivity principle. New theoretical results, which are verified through measurements, are presented to show the effectiveness of the delay-and-sum beamsteering structure for the parametric loudspeaker. Unlike the conventional loudspeaker array, where the spacing between array elements must be less than half the wavelength to avoid spatial aliasing, the parametric loudspeaker can take advantage of grating lobe elimination to extend the spacing of ultrasonic transducer array to more than 1.5 wavelengths in a typical application.     

有源噪声控制次级声源的非线性建模

基于电动扬声器的顺性、磁力因子和音圈自感三个非线性参数,建立了基于电力声类比线路方法的次级声源非线性时域模型.采用该模型对次级声源总谐波失真(THD)进行仿真,并与测试结果进行比较,结果表明在较低频率范围、较大输入信号幅值的情况下,该非线性模型是可行的.将该模型引入有源噪声控制系统,并以滤波-XLMS算法为例,对采用次级声源理想模型、线性时域模型和非线性时域模型的控制系统分别进行仿真,结果表明采用非线性模型系统的降噪量远低于采用其他模型的系统,并且非线性失真度大小对降噪量也具有明显的影响.     

一种用于水声运动目标成像的空间散射模型

水声成像过程中为了分析所接收的运动目标回波、理解接收信号的形成机理,提出了一种用于该情况的空间散射模型,并利用此模型仿真了"T"型阵成像声呐接收的回波信号。对信号的分析说明了空间散射模型的正确性。以空间散射模型为基础,利用傅里叶变换波束形成算法对不同条件下的球体目标进行了水声成像,并分析了成像性能。性能分析说明了水声目标大小、距离等因素对成像的影响情况,还特别强调了在运动情况下目标的成像情况。以上工作完成了对"T"型阵水声成像过程的模拟,为成像过程回波信号研究和成像声呐研制提供了理论基础和仿真手段。     

基于短时傅里叶变换的异常音检测方法

提出一种基于短时傅里叶变换的扬声器异常音检测方法,该方法首先对由扫频信号激励的扬声器声响应信号进行短时傅里叶变换,然后根据扬声器异常音信号的特点将所获得的时频图分割为若干区域,并提取各个区域内的时频图所对应的矩阵,最后通过计算被测扬声器声响应信号所对应区域内的矩阵与黄金样品所对应的矩阵之间的距离来判断该扬声器是否存在异常音。还简要介绍了基于该方法实现的扬声器异常音在线检测仪,实验室及企业生产线初步检验结果表明,该方法简单有效,可用于部分种类扬声器的异常音在线检测。     

Modeling of finite-amplitude sound beams: second order fields generated by a parametric loudspeaker

The nonlinear interaction of sound waves in air has been applied to sound reproduction for audio applications. A directional audible sound can be generated by amplitude-modulating the ultrasound carrier with an audio signal, then transmitting it from a parametric loudspeaker. This brings the need of a computationally efficient model to describe the propagation of finite-amplitude sound beams for the system design and optimization. A quasilinear analytical solution capable of fast numerical evaluation is presented for the second-order fields of the sum-, difference-frequency and second harmonic components. It is based on a virtual-complex-source approach, wherein the source field is treated as an aggregation of a set of complex virtual sources located in complex distance, then the corresponding fundamental sound field is reduced to the computation of sums of simple functions by exploiting the integrability of Gaussian functions. By this result, the five-dimensional integral expressions for the second-order sound fields are simplified to one-dimensional integrals. Furthermore, a substantial analytical reduction to sums of single integrals also is derived for an arbitrary source distribution when the basis functions are expressible as a sum of products of trigonometric functions. The validity of the proposed method is confirmed by a comparison of numerical results with experimental data previously published for the rectangular ultrasonic transducer.     

Helmholtz resonance technique for measuring liquid volumes under micro-gravity conditions

The Helmholtz resonance technique has been investigated for measuring liquid volumes under micro-gravity conditions. We proposed a theoretical model of the Helmholtz resonance phenomenon induced in a closed container, and carried out a micro-gravity experiment to confirm the applicability of the measurement technique using water as a test liquid. A swept frequency signal was added to a loudspeaker, and together, a microphone and the loudspeaker picked up the sound of the Helmholtz resonance. The liquid volume was calculated from the Helmholtz resonance frequency using an equation derived from the theoretical model. The liquid volume obtained from the micro-gravity experiment agreed well with the liquid volume obtained under terrestrial conditions. Thus, it was confirmed that the Helmholtz resonance technique was applicable for measuring liquid volume under micro-gravity conditions.