Electromagnetic Speaker Research Articles

Transparent piezoelectric film speakers for windows with active noise mitigation function

Noise pollution has a significant negative effect on psychological health and quality of life. The building envelop, particularly windows often constitute to the primary path for external noise sources to travel into the buildings. Here we have designed and fabricated transparent piezoelectric film speakers as secondary area sound source for active noise mitigation for window application with ventilation function. The performance properties of the obtained transparent speaker and its effectiveness for active noise mitigation are evaluated through numerical simulations as well as experimental measurements. The produced transparent piezoelectric film speaker exhibited enhanced overall sound pressure level (SPL) and broader frequency response range with a significantly improved SPL at frequencies below 300 Hz. Furthermore, compared to an electromagnetic speaker as a point secondary sound source, using the transparent piezoelectric film speaker as an area source resulted in more uniform noise mitigation with substantially larger averaged SPL reduction. The results presented here show the potentials and advantages of transparent piezoelectric film speakers for active noise mitigation.

Fully direct write dispenser printed sound emitting smart fabrics

Direct write dispenser printed sound-emitting smart fabrics are reported for creative applications and wearable electronics. Using dispenser printing, sound emission can be easily added to various fabric substrates, from industrial coated architectural fabrics to everyday woven polyester cotton fabrics. Two different types of sound emission have been realised on fabrics: a piezoelectric buzzer and an electromagnetic planar spiral speaker with an external magnet. These two planar sound emitting devices are flexible and simpler than conventional three-dimensional electromagnetic and electrostatic sound emitting devices. Furthermore, the spiral-based planar electromagnetic speakers allow interactive applications by changing the distance between the magnet and the speaker. The theory and the manufacturing technology of the direct write printed fabric buzzer and speaker are reported.

Modelling with gradient information

Response surface models (RSMs) can be used to model expensive simulations or real measurements [1]. An RSM is constructed by simulating solutions at systematic points in a design space and fitting a model to them. The RSM is then employed in subsequent calculations (for instance in optimization) effectively replacing the original expensive simulator, which leads to considerable savings in time and money. A novel technique is presented here which uses the gradient of a function as well as the function itself to construct the RSM. Such an approach is possible because, for many types of simulations, gradient information is simple and cheap to obtain. The design of an electromagnetic speaker assembly is used to illustrate the new approach. The finite element method (FEM), on which the simulation is based, can provide gradient information at little extra cost and hence the benefits of using gradient information are considerable, being especially marked in higher-dimensional spaces.

Method of making and using microphones for recording telephone conservations

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Electromagnetic speaker with bucking parallel high- and low-frequency coils drives sounding board and second diaphragm or external apparatus via magnetic coupling and having adjustable air gap and slot pole piece

An electro-acoustic transducer having a bass and treble coil wound on a single magnetizable core positioned to activate a magnetizable armature at one end of the core and to supply magnetic energy at the other end of the core for the operation of other energy requiring apparatus.

Acoustic particle agglomeration due to hydrodynamic interaction between monodisperse aerosols

The experimental verification of the theory on the hydrodynamic collisions in acoustic agglomeration is reported. Measurements are carried out on the time-dependent particle size distribution function using relatively monodisperse aerosols. These data are then used to determine the acoustic agglomeration constant which agrees well with the theoretical prediction. Two different experimental acoustic sources are used: one is a low frequency electromagnetic speaker and the other is a high frequency siren. Results show that acoustic agglomeration by hydrodynamic collision is important for particles radii larger than 0.5 μm in the audible frequency region (less than 10 k Hz). It is found that the acoustic agglomeration of these large particles is relatively insensitive to the frequency change, in contrast to the orthokinetic interaction whose effectiveness is sensitively dependent on the acoustic frequency.

Acoustic Stimulator for Rats

The ear bar of a stereo-taxic instrument was modified to permit the introduction of acoustic stimuli to the rat's eardrum during acute experiments on the auditory nervous system. For measurement of the sound pressure of pure-tone stimuli, a probe microphone was attached to the hollow ear bar so that the probe tube tip is placed near the eardrum. Pure tones are led through a fiber tube in the wall of the experimental chamber to the hollow ear bar. Tones between 100 and 15 000 Hz are produced by an electromagnetic speaker, while higher frequencies are generated by an electrostatic transducer. Acoustic transients are produced by a 1-in. condenser microphone operated as a loudspeaker attached to the hollow ear bar inside the experimental chamber. The acoustic waveform of these transients was measured with a 14-in. condenser microphone situated at the end of a 0.08-cc coupler, which is placed on the hollow ear bar to take the place of the rat's bulla. The three sound-producing devices can be interchanged without disturbing recording electrodes or the probe microphone. [Research was supported by the National Institutes of Health and Middlebury College.]

Generator Impedance of Power Amplifiers Used with Horn-Loaded Loudspeakers

The radiation resistance of a finite exponential horn fluctuates between wide limits in the region near the cut-off frequency. The variations in sound power output caused by these fluctuations can be minimized by choosing the correct generator impedance for the power amplifier used with a horn-loaded loudspeaker. This impedance is shown to be a function of the efficiency of the electromagnetic speaker unit. For speakers with greater than 50 percent efficiency a positive generator impedance is required, and the amplifier designer can secure the right value by a proper choice of negative feedback. For speakers with less than 50 percent efficiency a negative generator impedance is required, and this makes more severe demands on the amplifier design.

Acoustic Impedance of Sample from Motional Impedance Diagrams

If the electrical impedance of an electromagnetic speaker is plotted as a vector when the acoustic loading consists of an air column of variable length terminated by a rigid plug, a circle diagram results. If the air column is terminated instead by an acoustic sample, a second circle diagram results. Various relationships between the two circles have been worked out which yield the acoustic impedance of the sample with considerable precision. The method inherently averages many individual readings and automatically checks the self-consistency of the data. It is applicable to samples with little absorption since full advantage is taken of the possibility of coupling such a sample most effectively to the speaker by means of the air column. The method has been used to determine the acoustic impedance of commercial materials at low audiofrequencies, where the absorption is quite small.

A Continuously Variable Acoustic Impedance

The mechanical impedance of an electromagnetic speaker is affected by current flowing in the electrical elements, just as the electrical impedance is influenced by the motion of the mechanical system. This paper gives the relation between mechanical impedance and electrical load impedance, making use of the three complex speaker constants evaluated by the motional impedance method presented earlier by R. D. Fay. Measurements are given showing that the mechanical impedance of a WE555 horn driver can be varied over a fairly wide range.

A Continuously Variable Standard Acoustic Impedance

The mechanical impedance of an electro-mechanical device is affected by current flowing in the electrical elements, just as the electrical impedance is influenced by the motion of the mechanical system. The purpose of this paper is to determine over what limits the mechanical impedance of electro-magnetic loudspeakers and horn driver units can be varied by varying the load impedance across the terminals. A simple extension of the motional impedance analysis presented by R. D. Fay provides a means of calculating the mechanical impedance of an electro-magnetic speaker as a function of electrical load. The speaker when used in this way may be considered a continuously variable acoustic impedance. It is a secondary standard, since electrical measurements provide a means of calculating the impedance in terms of the surge impedance of a column of air. The calculated impedances were checked by direct measurement using the standing wave, or hyperbolic tangent, method. By means of a horn driver, the impedance of an area equal to approximately one square inch can be varied over fairly wide limits. The range of variation for cone speakers, with correspondingly larger areas, is much more restricted.

Motional Impedance Analysis Applied to a Dynamic Microphone

The receiver analysis developed by R. D. Fay gives a method for calculating the complete performance of an electromagnetic speaker from a plot of electrical impedance measured when the speaker is loaded by a closed tube of variable length. This of course includes the performance of the speaker as a microphone, although the statement is not explicitly made. The present article applies the above analysis to a dynamic microphone and compares the sensitivity thus obtained with an independent calibration at lower audiofrequencies. This method yields a primary calibration, in that neither calibrated source nor comparison microphone is required. The high mechanical resistance of a dynamic microphone and its low coupling constant, as compared with an electromagnetic speaker, result in a much smaller variation in electrical impedance, with changing air load. The variation is of the order of 5 percent of the minimum impedance, as compared with perhaps 80 percent change in speaker impedance. The cross-sectional area of the terminating tube is found to be of considerable importance. The effect of this choice of tube area on over-all accuracy is discussed.

Motional Impedance Analysis Applied to a Dynamic Microphone

An article by R. D. Fay presents a method for calculating the complete performance at any frequency of an electro-magnetic speaker from a plot of its electrical impedance measured when the speaker is loaded by a closed air column of variable length. The present article applies this method to a dynamic microphone, yielding pressure sensitivity at lower audiofrequencies and providing a means of calculating microphone mechanical impedance and other characteristics. Improvement in accuracy which may be achieved by proper choice of area for closed air column is discussed.