扬声器中涡流的热效应

通过分析和比较两种扬声器涡流电学模型和两种扬声器热模型，提出一种分频段的非线性热模型类比线路，给出了对应的音圈稳态温度公式，并在高频段运用逐点测温的方法研究，论证了扬声器涡流随频率变化的规律及其对扬声器热效应的影响。     

An analytical model for a dodecahedron loudspeaker applied to the design of omni-directional loudspeaker arrays

The dodecahedron (12 sided) loudspeaker is used extensively for acoustic measurements as an approximation to an omni-directional sound source, for example in building acoustics and automotive applications. In many instances its use is favoured above other omni-directional source approximations e.g. open pipe because of its greater power. However, analysis by other authors has shown that the radiation deviates from omni-directional above a certain frequency. In this paper an analytical model of the sound pressure field generated by a dodecahedron loudspeaker is constructed. The sound pressure field generated by the model is then compared with measured data and good agreement is demonstrated. Having established and validated the model, it is adapted to form alternative spherical loudspeaker arrays based on Platonic and Archimedean solid geometry and also a number of spherical packing routines. The aim of the analysis is to determine the optimal geometry for an omni-directional source using pistonic loudspeakers.The analysis shows that constructive interference of the pressure field across the spherical baffle surface and not individual loudspeaker pistonic radiation characteristics is the most significant factor with respect to deviations from omni-directional radiation for a complete spherical array. Consequently, loudspeaker elements which physically occupy the spherical baffle surface to their maximum extent provide the most extended frequency range of omni-directional operation. The most optimal spherical array distribution is shown to be the dodecahedron.     

直接辐射式扬声器系统的低频效率计算公式*

效率是扬声器系统的重要性能指标,然而常用的标称效率在低频范围并不适用。本文研究直接辐射式扬声器系统的低频效率,推导了基于TS参数的低频效率计算公式。针对封闭式扬声器系统和倒相式扬声器系统,开展实验验证,结果表明本文提出的计算公式得到的低频效率与实验测量得到的低频效率较为相符。进一步对比分析低频效率和标称效率,结果表明低频效率能够适用于低频,能准确地展示扬声器系统参数对效率的影响。利用本文提出的计算公式,有助于进一步优化提升扬声器系统的低频效率。     

扬声器的优化设计

基于有限元法发展了扬声器的计算机辅助设计，由此分析了扬声器的振动特征，讨论了各参数对扬声器振动及声辐射的影响，最后地其声压频响的优化措施作了探讨。     

Transient modal radiation of axisymmetric sources: Application to loudspeakers

The present study proposes a transient model of the acoustic radiation of axisymmetric structures. The pressure field is approximated by the Rayleigh integral corresponding to a monopole source distribution over the non-planar vibrating surface. The displacement field is expanded on the linear modes of the structure and a change of variables in the Rayleigh integral is then proposed in the case of a monotonic profile function to compute the Spatial Impulse Response associated to each mode of vibration efficiently. The results are compared to the formulation obtained in the case of planar and spherical sources. The method of calculation is then derived in the case of a typical loudspeaker profile (association of a truncated cone with a spherical cap). Finally, the present approach is used to estimate the nonlinear radiation pattern of a prototype loudspeaker and predictions are compared to measurements in anechoic room.     

Sound radiation of panel-form loudspeaker using flat voice coil for excitation

A novel panel-form loudspeaker in which the panel of the speaker is excited by the forces generated through the flat voice coil of a rectangular electro-magnetic type exciter for sound radiation is presented. The exciter when properly designed has the advantage of exerting appropriate loads to the panel so that the major sound pressure level (SPL) dips of the speaker can be suppressed or even eliminated. For designing such panel-form speaker, a method formulated on the basis of the classical plate theory (CPT), Ritz method, and first Rayleigh integral is proposed for predicting the SPL curve of the speaker. An experimental investigation was performed to verify the feasibility of the proposed method. The effects of some system parameters on the major SPL dips of the proposed panel-form speakers are investigated by means of several numerical examples. The optimal locations of flat voice coils for exciting several panel-form speakers are determined to illustrate the important role of excitation location for enhancing sound quality of such speakers via the removal or suppression of the major SPL dips.     

MEMS electrodynamic loudspeakers for mobile phones

This paper presents a MEMS structure of electrodynamic loudspeakers dedicated to mobile phone applications. The major goals are to obtain a high electroacoustic conversion efficiency and a high fidelity acoustic quality. The originalities lie in a rigid silicon membrane and in its suspension by a set of silicon beams. The moving coil is a planar copper microcoil electroplated on the silicon membrane whose microstructure was optimized for providing both rigidity and lightness of the mobile part.This paper presents different magnetic structures of the motor for this MEMS loudspeaker. These structures are ironless, only made out of permanent magnets which are bonded on the substrate. They are studied and optimized thanks to analytical formulations of the magnetic field created by the permanent magnets. Results are presented for a deep RIE etched 7.5 mm radius silicon membrane structured with 40 stiffening ribs and on a 30 μm thick microcoil with 35 turns.     

Analytical solutions for axisymmetric vibration of loudspeaker cones in transitional range

The loudspeaker cone vibration in the transitional frequency range in which the governing equations have transition or turning points is studied by applying the uniformly valid solutions obtained in a previous paper. The solutions are presented analytically as well as the resonant and anti-resonant frequency equations, the associated patterns and the axial admittance. A new frequency equation for the non-bending effect is obtained. The results agree well with numerical results.     

优化扬声器阵列的指向性与声功率级

提出了同时优化扬声器阵列的指向性和声功率级的方法。运用该方法可以优化扬声器阵列的输入电压分布,获得指向性和声功率级二者兼顾的扬声器阵列。本方法不必使用复杂的与频率相关的信号处理装置。模拟结果和实验测量结果表明该方法是可行的和有效的。     

Resonance identification in loudspeaker driver units: A comparison of techniques

A number of techniques with the scope of identifying loudspeaker cone resonances have been examined. Namely, the waterfall plot, the wavelet transform and the empirical mode decomposition scheme were compared on the basis of time-frequency resolution and damping estimation. The commonly used waterfall plot is only acceptable at the upper range of the acoustic spectrum. The wavelet transform is especially well suited for the analysis of transient signals from loudspeakers and is a significant improvement over the waterfall method. The newly developed EMD scheme has the highest potential in separating the modal components. By application of the EMD both instantaneous amplitude and frequency can be accurately determined.     

扬声器锥形振膜环反谐振频率的计算

本文在求解扬声器锥形振膜低频振动的基础上,得到了计算扬声器锥壳环反谐振频率的精确公式,并借助特征频率反比于质量平方根的物理概念,推出了适于工程应用的近似公式,其偏差在３％以内。     

基于最小二乘法的均匀扩声技术研究

针对目前室外及超大型室内空间的扩声应用中声场分布不均匀的问题,本文提出了一种基于最小二乘法声场重建方法的扩声技术。该技术通过对目标声场的逼近来计算线性扬声器阵列各通道的输入参数,实现扩声区域内声压级的均匀分布,同时约束非扩声区域的声能量以获得较好指向性。本文通过仿真研究算法各参数的改变对控制结果的影响,探讨不同扩声区域和目标所对应参数的选取方法。仿真和实验比较了该算法以及未经控制的声场、相移法波束控制的效果,证明该方法可以获得更好的声场均匀度。     

Acoustic coupling between the loudspeaker and the resonator in a standing-wave thermoacoustic device

Thermoacoustic refrigerators work with high amplitude sound waves, which are often created using an acoustic source coupled to a resonator. This coupling can be calculated analytically using linear acoustic equations and a linear model of the loudspeaker. This paper makes a comparison between such a coupling and measurements obtained in a large-scale thermoacoustic resonator constructed at the University of Manchester. The resonator was driven from low to large pressure amplitudes, with drive ratios up to 10%. It is shown that a good agreement is obtained for small amplitudes and this progressively worsens as the amplitude is increased. In the absence of wave harmonics and loudspeaker nonlinearities, the increasing discrepancy is attributed to the presence of minor losses.     

Three-dimensional visualization of diffusion flame shapes under acoustic excitation using stereoscopic imaging and reconstruction technique

Stereoscopic imaging and reconstruction technique is introduced to reconstruct the flame structures that are subject to acoustic excitation. The laminar diffusion flame under investigation was created in a cylindrical tube and excited by a loudspeaker. Stereo images were taken at a shutter speed of 1/10000^th second using a ‘stereo camera’ and the depth cue of the flame structures along the camera viewing direction were then computed using machine vision methodology. By visualizing the computed three-dimensional flame models, as well as judging the corresponding attribute such as surface gradient, the understanding of the flame and acoustic wave interaction could be improved.     

A comprehensive discrete-time computer modeling of acoustic Transmission Line loudspeakers

The Transmission Line loudspeaker is an audio loudspeaker enclosure topology devoted to extending the low frequency range near the loudspeaker frequency resonance. A few models based on physical properties of damped pipes have been proposed to characterize the Transmission Line loudspeaker systems. Unfortunately, Thiele/Small parameters, which are usually employed in enclosure designs, are not useful as parameters of design for these loudspeakers. In this paper, a comprehensive numerical formulation of a Transmission Line loudspeaker is presented, which is based in a finite difference approach of the governing equations, including the effects of the absorbing material allocated inside the pipe. The influence of the main empirical parameters is tested on the proposed model, which is also compared to a real prototype for validation purposes.     

An active noise reduction earplug using a piezoelectric laterally radiating loudspeaker

This paper describes the electroacoustic behaviour of a new piezoelectric Active Noise Reduction (ANR) earplug device. The sensor is a microphone having suitable characteristics chosen from among commercially available electret microphones. The actuator is a cylindrical piezoelectric ceramic loaded with a thin fluid film. An analytic model of laterally radiating loudspeaker, based on fundamental equations of acoustics, which takes into account the effect of viscosity and heat conduction is adapted to describe the acoustic radiation of the actuator. Theoretical and experimental frequency responses in a small cavity and an example of the ANR that can be obtained with the earplug are presented.     

封闭式扬声器系统空气劲度的非线性研究

从理想气体多变过程的状态方程出发,推导了封闭式扬声器系统的非线性空气劲度的理论公式。研究发现,封闭式扬声器系统的非线性空气劲度与音圈运动位移、有效辐射面积、箱体有效容积和多变系数等主要因素有关。通过实验,分别测量了封闭式扬声器系统与扬声器单元的非线性劲度,二者相减获得封闭式扬声器系统的非线性空气劲度。实测数据与理论计算得到很好的吻合。     

数字化声学测量技术 Ⅲ.非消声室环境中扬声器的测试

由于建造消声室费用太高，如何在非消声室环境测量扬声器的特性是众多中小电声器材生产厂家极为关心的问题。本文介绍一种可在非消声室环境中进行测量的数字化的扬声器测量系统，本文论述了它的基本原理及两个关键问题，即激盛信号的选择以及对单位脉冲响应加窗的问题。本文还讨论了窗口的宽度和形状对所测扬声器频率特性的影响，及对测量房间的要求。     

Acoustic characteristics of an electrodynamic planar digital loudspeaker using noise shaping technology

The present study extends our previous work [Furihata et al., J. Acoust. Soc. Am. 114, 174-184 (2003)] by investigating our electrodynamic planar loudspeaker when driven by a 12 bit digital signal with noise shaping. Changing the structure of the loudspeaker can lead to improvement, but in this paper improvements that can be made using signal processing are investigated. Results show that the digital loudspeaker demonstrated good linearity over its 84 dB dynamic range from 40 Hz to 10 kHz. This shows that a 12 bit digital loudspeaker which is equivalent to a 16 bit one is possible.     

Strain imaging of a perpendicular recording head in a Hard Disk Drive

Imaging of magnetic-field-induced strains using scanning probe microscopy enables us to observe magnetic domain structures and magnetic force distributions. This method has an ability of observing magnetic structures in deep portions along with surface structures. We observed an air-bearing surface of a perpendicular recording head in a hard disk drive in large areas including the whole yokes, and investigated characteristics of the magnetic poles and layers subjected to magnetic fields produced by writing coil currents. Attractive forces independent of the field directions acted between the upper and lower yokes made by soft material, which generated surface displacements in the ABS. The signals were second-harmonic oscillations for alternating currents without a dc bias, and the amplitude images represented the field distribution. Meanwhile, fixed magnetic charges in both ends of the read sensor, which were produced by the hard-bias film, were subjected to the fields. The fixed charges, which hardly changed by the fields, lead to strains depending on the field directions, and generated specific contrasts of one pair of bright-dark spots in the strain images. In the absence of surface underlayer, the fields by the writing coil broke into the read sensor sandwiched by the shield layers.