Electroacoustic Devices Research Articles

Global players in acoustic standardization

The World Trade Organization has identified international standardization as a key to realization of worldwide free trade. This identification underlined the importance of the work by nongovernmental international standardization bodies such as IEC and ISO as well as by governmental bodies such as the International Organization of Legal Metrology (OIML). In acoustics, each of these organizations deals with technical harmonization in a certain field: The work of both IEC/TC 29 ‘‘Electroacoustics’’ and OIML/TC 13 ‘‘Measuring instruments for acoustics and vibration’’ focuses on specification of performance characteristics and testing procedures for electroacoustical devices. Standardization of measuring methods for industrial products either emitting or reducing noise is the primary activity of ISO/TC 43 ‘‘Acoustics.’’ This lecture presents an introduction to how international standards in acoustics are developed along with a survey of the scopes and work programs of these three closely cooperating committees. Guidance on the estimation of the uncertainty inherent in standardized acoustical tests and measurements is a major technical issue. The role of national and regional standardization in acoustics will be noted. The European standards bodies, CEN and CENELEC, have clearly defined tasks within the European Economic Area related to acoustics.

Conduction Behavior of Doped Polyaniline Under High Current Density and the Performance of an all Polymer Electromechanical System

AbstractIn many device applications, such as electro-acoustic transducers and actuators based on high strain electroactive polymers, there are many advantages to utilize conductive polymers as electrodes. However, in these applications, a high electric power usually is required which translates to high voltage and high current in the system. Hence, the maximum current density which a conducting polymer can carry is of great interest and importance. In this paper, the conduction behavior at high current density of doped polyaniline(PANI) is reported. It was found that the current density deviates strongly from the ohmic relation with the electric field in high current density region and a saturation of the current density was observed. The maximum current density Jm observed is proportional to the conductivity of the samples and for PANI doped with HCSA, Jm can reach as high as 1200 A/cm2. Making use of the conducting polymer as the electrodes for the electrostrictive P(VDF-TrFE) copolymer, an all-polymer electromechanical system was fabricated. The all-polymer films exhibit similar or larger electric field induced strain responses than those from films with gold electrodes, presumably due to reduced mechanical clamping from the electrodes. In addition, the all-polymer system also exhibits comparable dielectric and polarization properties to those of gold-electroded P(VDF-TrFE) films in a wide temperature (from −50°C to 120°C) and frequency range (from 1Hz to 1MHz). These results demonstrate that polyaniline can be used for many electro-acoustic devices and provide improved performance.

Acoustical imaging in air by a low-cost system working in the audio band

In order to generate a two-dimensional acoustic image of an aerial scene, a system working in the audio band and composed of low-cost conventional electroacoustic and computation devices has been developed and tested. Such a system uses a loudspeaker for the emission of acoustic pulses, eight microphones for the reception of backscattered waves, a generation/acquisition digital board, and a personal computer. As in medical echography, the adopted algorithm for the image formation is a wideband coherent beamforming followed by a scan conversion in order to display the image in a Cartesian format (as a top view of the imaged scene). Robotic vision and remote measurement are potential applications of the system developed. Two major problems that were faced are the calibration of the microphones and the study of the best configuration in terms of pulse waveform and microphone placement. A simple calibration algorithm was achieved by comparing the obtained point spread function with the theoretical expectations, whereas the best configuration was obtained by taking into account the constraints imposed by the instrumentation and the application addressed. The obtained images are of good quality, also considering the low-cost instrumentation and the highly reverberant environment in which the experiments were performed.

Dead Rooms and Live Wires: Harvard, Hollywood, and the Deconstruction of Architectural Acoustics, 1900-1930

In 1900 Wallace Sabine, a physicist at Harvard University, published a mathematical formula for calculating the reverberation time in a room, a measure of how quickly or slowly sound energy dies away in an enclosed space. In 1930 Carl Eyring, a physicist working in the Sound Motion Picture Studio at Bell Telephone Laboratories, revised Sabine's equation. This essay examines material changes in the practice of architectural acoustics in order to explain how and why Eyring was motivated to reformulate the Sabine equation. Sabine's equation was the product of experimentation in highly reverberant rooms. Eyring worked in a world increasingly constructed of sound-absorbing building materials--a world of acoustically dead rooms in which Sabine's original assumptions were no longer valid. Further, Eyring's world was filled with electroacoustic devices that had not existed in 1900. Live wires powered new tools for producing, measuring, and controlling sound, and the new electroacoustic technologies additional...

The past, present and future of audio signal processing

The article reviews, with technical depth, the history of research in audio and electroacoustics, including electroacoustic devices, noise control, echo cancellation, and psychoacoustics. It also reports on processes in signal processing technologies that are widely used in hearing aids, the consumer electronics area, and professional audio equipment. It provides an effective review of the history of signal processing.

Comparison of the directivity of woodwind instruments: Improvement of diffusion techniques in sound synthesis by physical modeling

Sound synthesis by physical models is based on the simulation of the sound production by the instrument. Recently, progress has been made in the modeling of auto-oscillations and in the internal acoustic field of woodwinds. The modeling of the external field, however, its reproduction by electroacoustic devices as well as the control of this type of synthesis, describing the action of the musician, are usually too simple or not even considered. The development of software calculating the sound radiation of woodwinds (far-field) from a precise description of their geometry, has enabled us to compare the directivity of the principal instruments of this family as, for example, the oboe, the clarinet, and the flute. Different diffusing systems of sounds obtained from physical modeling will be presented; each of these systems using different principles for the reproduction of the directivity from the virtual sound recordings. In a previous study [Causse etal ., J. Acoust. Soc. Am. 95(A) (1994)], the perceptual difference between a real instrument and such a programmable radiation pattern loudspeaker system simulating a real instrument was investigated. In this talk, results of simple listening tests with these different systems of reproduction will be presented.

Application of parametric and non-parametric techniques to electroacoustic transfer function analysis

Electroacoustic devices or systems transfer functions are usually described by means of amplitude and phase Bode plots. They are obtained from usually large data series of excitation and response values. Acoustic set-up requirements vary considerably, from normal room to anechoic conditions, from complex instrumentation to simple sweeping ensembles. Filter frequency analysis, cross-spectral estimation by means of the discrete Fourier transform, time-delay spectrometry and the cepstral analysis methods are non-parametric examples. Model based techniques can be classified as identification techniques. They usually employ a limited set of parameters and achieve high information compression ratios and non-redundancy, flexibility and adequacy to convert to other types of models. In the present paper the most important established techniques for electroacoustic transfer function measurement are surveyed in their principles, possibilities, instrumentation and set-up requirements. A comparison is made with an input-output rational model based parametric technique, developed in the F.E.U.P. Practical results are reported, showing the accuracy obtained through this technique when applied to the measurement of a real full-range loudspeaker system. Nevertheless some difficult aspects still persist. In our point of view, a promising new way is ahead for measurement techniques in the electroacoustic field

Dipole horn piezoelectric electro-acoustic transducer design

A piezoelectric electro-acoustic device for converting an electric signal into an acoustic vibration and/or for converting acoustic vibrations into an electric signal is disclosed. The device employs at least two opposing concave membranes having a single axis of elongation tangent to the curvature thereof. The membranes face each other and are connected to electrodes. Upon changes in electric current provided to the membranes, the membranes will vibrate towards one another to thereby displace air located between the surfaces thereof. This dipole horn structure provides a high conversion efficiency as well as a true 360° acoustic response.

Acoustic aspects related to the performance of teleconference facilities

Room acoustic design and electroacoustic system integration are paramount to the performance, and therefore effectiveness, of teleconferencing facilities. Some key elements that need to be considered during the design and implementation stages are (a) the effects of room acoustics on transmitted, received, and in‐room speech communications; (b) the effect of transmission bandwidth on intelligibility and audio quality in the teleconference suite; (c) the naturalness of interaction over a telephone network; (d) the impact of acoustic and electroacoustic devices in a visual communications medium; (e) room ambient noise and potential noise sources. These elements are examined in light of the recent design, implementation, and operation of 12 teleconference (audio and video) suites. Details of design choices and acoustic measurements of these teleconference suites will be presented.

Novel piezoelectric materials

The unique properties of piezopolymersendow them with particular advantages for use in electroacoustic devices such as the self‐supporting dome hydrophone shown in the Figure. Thin or especially thick films can be fabricated, and three‐dimensional forming of the materials can be accomplished by standard techniques. Further interesting possibilities offered by incorporating a ferroelectric ceramic into a non‐electroactive polymer matrix are sketched.

Electroacoustic device for hearing needs including noise cancellation

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New method to characterize the surface-generated bulk acoustic waves in piezoelectric substrates

A new method is proposed to characterize the bulk acoustic waves (BAWs) that can be excited by electrical sources at the surface of a piezoelectric substrate used in electroacoustic devices for signal processing. Using the concepts of harmonic source and of acoustic radiation admittance and impedance, the method allows one to compute, as a function of the acoustic slowness, the absolute magnitude of BAW radiation efficiency. Moreover, a relationship is established, giving the individual contributions to the real part of the surface admittance or impedance due to each BAW mode. Numerical applications of the method are carried out for a number of substrates currently used in surface acoustic wave devices, such as YZ-LiNbO3, 128° YX-LiNbO3, XZ-LiNbO3, and 36° YX-LiTaO3, as well as a 42.5° YX-quartz. It is found that the radiation efficiency of BAWs depends on not only the piezoelectric coupling constant, but also on the mode coupling between them. The analysis of the results obtained may lead to a deeper understanding of the mode-interaction mechanisms of the surface-generated bulk waves.

The dynamic mobility of nonspherical particles

This paper is concerned with the electrophoretic mobility of particles in alternating electric fields. We refer to this mobility as the “dynamic mobility,” to distinguish it from the standard electrophoretic mobility, which is defined for static fields. This dynamic mobility can now be measured at frequencies up to 1 MHz with the aid of electroacoustic devices. In this paper we present formulae for calculating the dynamic mobility of spheroidal particles with thin double layers. With the aid of these formulae it should be possible to obtain information on particle charge, size, and shape from electroacoustic measurements on dilute suspensions.

Active reverberation time control: A sound intensity based approach.

The control of reverberation time is certainly one of the outstanding problems in Architectural Acoustics. Besides the classical techniques, some control techniques using electroacoustical devices for artificial reverberation are available today. Commonly, these devices merely supply the ‘‘reverberation’’ to an enclosed space so as to simulate the sound queue phenomenon instead of actually controlling the proper reverberation time of the room in such a way to make it longer, but in this case, even shorter. This paper presents an intensity-based approach to the reverberation time control using the total transfer function of the acoustic system constituted by the room and by the control device itself. As the energy transfer function of an enclosed space is simply related to the reverberation time [D. Stanzial, J. Acoust. Soc. Am. Suppl. 1 88, S185 (1990)], an alternative criterion for the local active control of the reverberating acoustic field is readily obtained.

Electroacoustic device for hearing needs including noise cancellation

A device for performing electroacoustic functions including noise cancellation, hearing aid, communication interface, headset, feed for recording device, and headphone functions. The device includes composite transducers connected to a control unit. The composite transducers can be mounted on a headband and are configured to include input transducers for converting acoustic waves into electrical signals for processing by a control unit, and output transducers for converting the processed electrical signals to processed sound waves. The control unit includes an inverter/amplifier and a mixer/output amplifier for inverting the electrical input and controlling the gain for either adjusting the gain to maximize a noise cancellation function or increasing the gain beyond the minimum level heard by the ear to a desired level for a hearing aid function. Connectors for connecting recorders and a boom microphone, and function selection switches are provided by the control means for connecting circuit components of the control unit selectively for performing the above functions. The input and output transducers have oppositely oriented diaphragms mounted in a common plane to provide an inverted acoustic wave in real time for combining with and substantially cancelling an incoming acoustic wave. 1

Eyeglass frame with electroacoustic device for the enhancement of sound intelligibility

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Electroacoustic device with broad frequency range directional response

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Diaphragm comprising at least one foil of a piezoelectric polymer material

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Waves-scatter bond graphs for electroacoustic systems

Electroacoustics was born as a twin to the telephone 110 years ago. Today electroacoustic transduction involves a sophisticated science and technology. Early in this evolution alternating currents and electrical oscillations were compared to the better-understood mechanical vibrations, but electro-technology advanced so rapidly that mechanical systems were soon treated conversely by analogous electrical circuits. Yet because a strict correspondence does not exist at the microscopic and continuum levels, several alternative analogies emerged so that now engineers confront a lack of uniform methodology, particularly when dealing with distributed transducers. Bond graphs were developed to meet just such needs by treating all physical systems as a set of multiport elements richly interconnected by another set of power bonds, which together enforce continuity-conservation laws for mass, momentum, charge, and energies. Furthermore, to provide self-consistent signal causality and detailed balances of power dissipation and entropy production, scattering variables can be employed at all ports, and wave variables on all bonds. Such characteristic variables and their methods of use were first introduced by Bernhard Riemann in 1860 for finite amplitude sound waves and later reintroduced in the 1940s for microwave circuitry. Some applications are given of this powerful approach to practical electroacoustical devices and systems.

Unified analysis of sound field involving the driving system in time domain

AbstractRecently, it has become important, with the development of electroacoustic devices, to provide a systematic analysis of the electrical circuit, the electromechanical transducer part and sound field, taking their interactions into consideration. When the boundary condition of the sound field or the shape of the scattering object is complicated, numerical computation is more effective, especially when the analysis of time variation is required. This paper presents a numerical method of computation for the electrical circuit, transducer part and sound field, in which the entire system is represented by an electrical equivalent circuit. A formulation is made of the wave propagation and circuit element characteristics by Bergeron's method, with the time‐axis analyzed by the node equation. As a result, it became possible to analyze the entire system by electrical circuit analysis, clearly indicating the interactions among various parts. The method is based on the time‐response analysis, and the response to the pulse wave, for example, can be calculated on the time axis. As examples, some basic problems with sinusoidal input in two‐ and three‐dimensional space are analyzed, and the results are compared with those of theoretical analysis. A computation is also made for the case where the voltage and current at the transducer input are affected by the reflected wave of the sound field through the vibrating membrane, indicating the feature of the proposed method where the interactions in the system can clearly be demonstrated.