Study of acoustic field modulation in the regenerator by double loudspeakers method

A model to modulate acoustic field in a regenerator of a thermoacoustic system by the double loudspeakers method is presented in this paper. The equations are derived for acoustic field modulation. They represent the relations among acoustic field (complex pressure p(0), complex velocity u(0), and acoustic impedance Z(0)), driving parameters of loudspeakers (voltage amplitude and its phase difference), and operating parameters involved in a matrix H (frequency, temperature of regenerator). The range of acoustic field is adjustable and limited by the maximal driving voltages of loudspeakers according to driving parameters. The range is simulated and analyzed in the amplitude-phase and complex coordinate planes for a given or variable H. The simulated results indicate that the range has its intrinsic characteristics. The expected acoustic field in a regenerator can be obtained feasibly by the modulation.     

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.     

Comparison between voltage and current driving methods of a micro-speaker

Since its inception, most audio amplifiers control the loudspeaker in voltage. However previous studies highlighted the importance of the loudspeaker control in current. These studies have been done only with large size loudspeakers (bass or midrange loudspeakers) and this is certainly not transposable for the type of loudspeaker in interest i.e. micro-speaker. First of all, this paper describes a model of loudspeaker (voltage driven and also current driven) represented by a comprehensive set of data based on a minimal number of measurements. Simulation results based on these models are presented using single frequency signals such as multi-frequencies signals to compare the two driven methods. At this level of modelling, simulation results show that, contrary to the woofer applications, current driving of micro-speaker does not affect significantly in terms of harmonic distortions, intermodulation distortions and transient behavior.     

Influence of rigid wall on the nonlinear pulsation of nearby bubble

This paper mainly focuses on the nonlinear pulsation of a bubble near the rigid wall. Dynamics of near-wall bubble and free bubble are discussed and compared in details. Investigation reveals as the driving acoustic pressure amplitude increases, nonlinear pulsation of bubble becomes intense gradually. Besides, decreasing the viscosity of host liquid is advantageous for the nonlinear pulsation of bubble. Bifurcation diagrams of bubble radius show acoustic reflection of the rigid wall makes the initial bifurcation appear at low driving acoustic amplitude and on bubble with small ambient radius, and makes the bifurcation still exist for bubble in high-viscosity liquids. That indicates the rigid wall will produce enhancement on the nonlinearity of nearby bubble. As the bubble approaches the wall, the enhancement becomes strong. Moreover, research on the influence of driving frequency shows the rigid wall makes the frequency band corresponding to chaos around the resonant frequency of free bubble shift downward.     

Model and estimation method for predicting the sound radiated by a horn loudspeaker - With application to a car horn

This paper deals with a new car horn device made of a sound synthesizer and an electrodynamic horn loudspeaker. It presents an one-dimensional model allowing to predict the loudspeaker efficiency and a specific method to estimate experimentally the model parameters. First, this model aims at reducing the time spent in the design process. Second it aims at correcting the sound emitted by the sound synthesizer in order that the listener hears the sound designed for creating the warning message. The study gives a survey of the vast loudspeaker literature. It is based on the conventional electroacoustic approach used for electrodynamic loudspeakers and on wave propagation models used for characterizing acoustic horns. The estimation of the model parameter values is performed using measurements of the electrical impedance of the loudspeaker and of the acoustic impedance of the horn. The model is assessed by comparing the calculated and measured electrical impedances and horn efficiencies. Results show that the model predicts well the horn efficiency up to 2500 Hz, the limitation being due to the horn radiation impedance modelization.     

水听器校准器的开发研究

本文所介绍的水听器校准是由一动圈活塞式换能器和由它激励的一端开口的水柱组成。水柱中的声压由驱动电流的大小来控制。在校准器的水柱中用比较法来校准水听器的低频接收电压灵敏度。     

Frequency spectrum of the nonlinear magnetoimpedance of multilayer film structures

Magnetization reversal by high-frequency current in FeCuNbSiB/Al/FeCuNbSiB three-layer film structures is studied. The frequency spectrum of the voltage arising in a coil wound on the sample as a function of a permanent magnetic field (nonlinear magnetoimpedance) is taken. It is shown that the frequency spectra of the voltage are qualitatively different for the longitudinal and transverse orientations of the field with respect to the direction of the current. Frequency spectrum harmonics are demonstrated to be highly sensitive to a magnetic field. A simple electrodynamic model to describe experimental data is suggested.     

声腔对电动式换能器工作特性的影响

传统的电动式换能器设计理论中,未考虑压力补偿系统等声腔结构对声学性能的影响,声源级理论设计结果与实测结果存在较大差别.研究中将电动式换能器内部的三段气腔视为突变截面声腔结构,给出了声腔的四端网络等效电路,将其作为辐射面的负载添加到电动式换能器的传统等效电路中,获得了电动式换能器改进的等效电路.基于改进的等效电路求解了带...     

含气泡液体中的非线性声传播

考虑到分布在液体中的气泡是声波在含气泡液体中传播时引起非线性的一个很重要的因素,本文研究了声波在含气泡液体中的非线性传播.将气体含量的影响引入到声波在液体中传播的方程中,从而得到声波在气液混合物中传播的数学模型.通过对该模型进行数值模拟发现,气体含量、驱动声场声压幅值及驱动声场作用时间均会影响到气液混合物中的声场分布及声压幅值大小.液体中的气泡会"阻滞"液体中声场的传播并将能量"聚集"在声源附近.对于连续大功率的驱动声场来说,液体中的气泡会"阻滞"气液混合物中声场及其能量的传播.     

电动声源热声致冷机声学和计算实例

我们将各种热声致机简化为一包括声学终端在内的声管道系统，并通过实例讨论了致冷机的声学特性，该管道系统与一般声管道不同：１．在热声堆中热波和粘滞波不可不计。２．在热声堆与声管连接时，必需考虑合成波的体积流；而热声堆内只需考虑传播波的体积流。本文对此提出了阻抗连接条件的修正。实例使用电动扬声器为声源，给出了热声行波和驻波致冷的声学计算方法以及它们的声学特性，所用扬声器的标称伏安为１００ＶＡ，可为热声致     

压电陶瓷非线性对大功率换能器结构参数匹配影响的计算分析

在Guyomar非线性模型基础上,通过机电等效法将晶堆前向负载作为等效质量和阻尼加入振动方程的质量项和阻尼项,推导了换能器振速、辐射声压级和谐振频率偏移率等表达式,计算分析了压电陶瓷非线性参数和结构参数对换能器声辐射性能的影响,研究了压电陶瓷的非线性对换能器结构参数匹配的影响。结果表明,换能器节面靠前,前盖板厚度越小,前盖板大径越小,都可以减少压电陶瓷非线性引起的换能器频率偏移。当设计频率确定时,压电陶瓷处于非线性工作域的换能器的结构参数有所减小。换能器加入辐射端匹配后,可以改善压电晶堆前向负载匹配,降低换能器的谐振频率偏移率。换能器激励电流也会出现频率偏移现象。在提高换能器激励电压时,换能器的结构参数应适当减小。得到的结论可为换能器设计提供理论依据和帮助。     

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。     

Linear and nonlinear 2D finite element analysis of sloshing modes and pressures in rectangular tanks subject to horizontal harmonic motions

The influence of nonlinear wave theory on the sloshing natural periods and their modal pressure distributions are investigated for rectangular tanks under the assumption of two-dimensional behavior. Natural periods and mode shapes are computed and compared for both linear wave theory (LWT) and nonlinear wave theory (NLWT) models, using the finite element package ABAQUS. Linear wave theory is implemented in an acoustic model, whereas a plane strain problem with large displacements is used in NLWT. Pressure distributions acting on the tank walls are obtained for the first three sloshing modes using both linear and nonlinear wave theory. It is found that the nonlinearity does not have significant effects on the natural sloshing periods. For the sloshing pressures on the tank walls, different distributions were found using linear and nonlinear wave theory models. However, in all cases studied, the linear wave theory conservatively estimated the magnitude of the pressure distribution, whereas larger pressures resultant heights were obtained when using the nonlinear theory. It is concluded that the nonlinearity of the surface wave does not have major effects in the pressure distribution on the walls for rectangular tanks.     

Time-varying non linear modeling of electrodynamic loudspeakers

This paper deals with the time-varying nonlinear analytical modeling of the electrodynamic loudspeaker. We propose a model which takes into account the variations of Small signal parameters. The six Small signal parameters (R_e, L_e, Bl, R_ms, M_ms, C_ms) depend on both time and input current. The electrodynamic loudspeaker is characterized by the electrical impedance which, precisely measured, allows us to construct polynomial functions for each Small signal parameter. By using this analytical model, we propose to compare two identical electrodynamic loudspeakers. One of them is supposed to be run in and the other one is not. The experimental methodology is based on a precise measurement. In all the paper, the time scale is assumed to be much longer than one period of the harmonic excitation.     

Research on coupling between thermoacoustic resonance pipe and piezoelectric acoustic source

Piezoelectric loudspeakers have been used in thermoacoustic refrigerators for operating at the high frequency to miniaturize the system. Then the coupling between the piezoelectric loudspeaker and resonance pipe becomes an important factor for improving the performances of the system. By the equivalent circuit model, the expressions of the acoustic output power and electroacoustic transfer efficiency at a low operating frequency are obtained, and then the structures of the piezoelectric loudspeaker and resonance pipe, as well as the operating frequency, are optimized to achieve a high electroacoustic transfer efficiency and a large acoustic output power. It is also shown that when the total reactance of the system equals zero, the resonance frequency of the resonance pipe is the optimized operating frequency and a high acoustic output power can be achieved. However, the highest transfer efficiency and largest acoustic power cannot be obtained simultaneously, therefore a trade-off condition must be adopted.     

Experiments and simulations for large-amplitude vibrations of rectangular plates carrying concentrated masses

Large-amplitude (geometrically nonlinear) forced vibrations of a stainless-steel thin rectangular plate carrying different concentrated masses are experimentally studied. The experimental boundary conditions are close to those of a clamped plate. The plate is vertically and horizontally tested in order to investigate the gravity effect. Harmonic excitation is applied by using electrodynamic exciter and the plate vibration is measured by using a laser Doppler vibrometer with displacement decoder. The harmonic excitation is controlled in closed-loop in order to keep constant the desired force and is increased (or decreased) by very small discrete steps. Numerical simulations on reduced-order models, obtained by using Von Kármán nonlinear plate theory and global discretization, are also carried out and compared to experiments in order to better understand the system. Results show that concentrated masses have no effect on the trend of nonlinearity of the vertical plate, while they play a role in case of horizontal plate due to the static flexural deflection caused by gravity, which reduces the hardening-type nonlinearity. Initial geometric imperfection (deviation from flat surface in vertical position) of the plate is measured and taken into account; it plays a significant role.     

Profiles of initially sinusoidal waves propagating in nonlinear microinhomogeneous materials

The asymptotic analytical theory predicting acoustic wave profiles in microinhomogeneous materials with hysteretic quadratic nonlinearity and attenuation proportional to an even power of frequency is developed. The theory predicts that the influence on the nonlinear wave of the Rayleigh scattering of acoustic waves, which is proportional to the forth power of frequency, results in the net diminishing of wave attenuation. This is due to the suppression (diminishing) by scattering of the nonlinear hysteretic losses which is more important than direct increase in linear losses added by scattering.     

All-optical probing of the nonlinear acoustics of a crack

Experiments with an all-optical method for the study of the nonlinear acoustics of cracks in solids are reported. Nonlinear acoustic waves are initiated by the absorption of radiation from a pair of laser beams intensity modulated at two different frequencies. The detection of acoustic waves at mixed frequencies, absent in the frequency spectrum of the heating lasers, by optical interferometry or deflectometry provides unambiguous evidence of the elastic nonlinearity of the crack. The high contrast in crack imaging achieved by remote optical monitoring of the nonlinear acoustic processes is due to the strong dependence of the efficiency of optoacoustic conversion on the state of the crack. The highest acoustic nonlinearity is observed in the transitional state of the crack, which is intermediate between the open and the closed ones.