bluuebunny/crossref_metadata_2025 huggingface dataset:
Volume reverberation in littoral waters
Authors: Love Richard H. , Thompson Charles H. , Nero Redwood W.
Published: October 2005

Until recently, virtually no low- and mid-frequency volume reverberation data were available from littoral waters. However, in the past few years, the Naval Research Laboratory has conducted volume reverberation measurements in deep, slope, and shelf waters in several oceanic regions. Deep ocean volume reverberation is relatively uniform over broad ocean areas at both low- and mid-frequencies. As water depths become shallower, many fishes responsible for deep ocean volume reverberation eventually disappear and the character of the reverberation changes. Measurements in littoral waters demonstrate that low- and mid-frequency volume reverberation levels can be very high and can vary greatly over short distances and from day to night. Results also show that changes in volume reverberation from deep to shallow water can be significantly different in different regions. Variability is the principal feature of volume reverberation in littoral waters.
A numerical study of time-domain backscattering from one-dimensional, rigid, random surfaces
Authors: Lupien Vincent
Published: October 2005

In certain high-resolution target detection systems, impulsive scatter from ocean boundaries gives rise to sonar clutter. In this work, the main objective was to identify the stochastic characteristics of rigid, one-dimensional rough surfaces which create backscatter containing spikes in the time domain. The interarrival time and amplitude statistics of impulsive events were determined numerically through Monte Carlo realizations of different surface types. For each surface the far-field impulse response in backscatter was determined using an exact integral equation method adapted from E. I. Thorsos [J. Acoust. Soc. Am. 83, 78 (1988)]. The impulse responses were convolved with the source spectrum to generate exact backscattered waveforms. Three sets of surfaces were investigated. In the first set, surfaces with a Gaussian correlation function were considered, which possess a single horizontal and vertical scale. In the second set, surfaces with a multiscale, power-law spectral density were investigated. The third set consisted of surfaces made up of adjacent straight line segments, or facets. The co-ordinates of the vertices of each facet were randomized through a discrete stochastic process. The results have provided insight into the physical mechanisms which generate spikes in the time domain and helped distinguish the contribution that localized scatterers make versus those that result from random interference of nonadjacent points on the surface. [Work sponsored by the Office of Naval Research.]
The effect of environmental parameters on surface scattering strength
Authors: Nicholas Michael
Published: October 2005

Throughout the Critical Sea Test (CST) experiments, a large body of quality surface scattering data was accumulated which was collected over a broad range of sea states using both explosive (SUS) charges (impulsive sources) and transmitting arrays (waveform sources). Simultaneously, an extensive suite of environmental measurements was also made, providing a unique data set with which to examine how the surface scattering strength changes with various environmental parameters. Historically wind speed has been the environmental descriptor of choice, but while this is the dominating factor, wind speed alone was found to be inadequate to fully describe all the observations. Other important environmental descriptors will be discussed, and some of their effects on surface scattering at both very high and very low sea states will be demonstrated. The latest empirical surface scattering strength algorithm based on all the CST SUS measurements will also be described, and the effect of current findings on future modifications to this algorithm will be discussed.
Modeling low-frequency surface scatter intensity statistics
Authors: Thorsos Eric I. , Percival Donald B. , Bader Kate M.
Published: October 2005

Low-frequency surface backscattering experiments (CST-7, ASREX) show that the surface scattered field statistics are non-Gaussian, which means the intensity statistics will be nonexponential. These data show the intensity distribution to be closer to log normal. In such cases the statistical distribution depends on the scattering area on the surface or, equivalently, on the number of scatterers. An analytical model has been developed for the intensity distribution that results when the scattering area contains multiple, spatially independent, identically distributed scatterers. The individual scatterers, e.g., bubble clouds, are assumed to yield a log-normal intensity distribution. The assumption that the scatterers are spatially independent leads to a Poisson distribution for the number of scatterers in a given surface area. The parameters to be specified are the standard deviation of the log-normal distribution and the average number of scatterers per unit area. Monte Carlo simulations yield estimated intensity distributions in very good agreement with the analytical model. Preliminary comparisons will be made with ASREX data. [Work supported by ONR.]
Rayleigh scattering from a plume of suspended particulates located near an ocean boundary
Authors: Palmer David R.
Published: October 2005

A number of experiments have been conducted to acoustically image plumes of particulates suspended in the ocean. In many cases the scattering is in the long-wavelength or Rayleigh region. A comprehensive framework was recently developed for calculating the intensity received by a monostatic sonar system due to backscattering in the Rayleigh region from a plume of suspended, nonspherical particulates [D. R. Palmer, J. Acoust. Soc. Am. 99, 1901–1912 (1996)]. This framework is extended to include the possibility that the plume is close to an ocean boundary. The distances of the particulates from the boundary are assumed to be small compared to the wavelength and the boundary surface is assumed to be planar. The scattering amplitude in the presence of a rigid or a pressure-release boundary surface is related to the amplitude in the absence of the surface. As a result the intensity can be averaged over the random orientations of the individual particulates and this averaged intensity can be bounded in terms of the intensity that would be measured if the particulates scattered the acoustic wave as if they were spherical.
Sound scattering by the complexly shaped objects within the sea waveguides
Authors: Oboznenko E. I. , Oboznenko I. L.
Published: October 2005

An algorithm for the sea waveguide located by arbitrary shaped objects’ echosignals computation is obtained. The problem is solved with the help of boundary integral equations for the potentials of a single (or double) layer on the surface of the object, that is located within the waveguide that has already been defined by a Green function for its object-free state. The Pekeris waveguide is taken as an example. The object’s wave dimensions were equal to 0.5–15 (low-frequency range of echolocation). Up to 12 modes could be present in the waveguide. Scattering patterns’ calculations have been made for the object’s azimuthal plane at the different distances between the source, the object, and the receiver and their mutual location’s different depths. Object scattering patterns (both in static and in dynamic object state) have been investigated, hydrodynamical effects have been ignored. The echosignal for the four-component receiver (pressure and particle velocity vector), as well as for the scattered wave intensity vector, has been determined. It is shown that velocity and intensity vector method usage when receiving the scattered wave in the waveguide increases substantially the echosignal informative content when compared to the free sound field measurements, and this is due to the modes interaction both in scalar and in vector waves. The scattering pattern for the azimuthal plane contains the information about the scattering within the two mutually orthogonal planes. The results of the scattered fields’ hydrophysical modeling (scaling factor 1:20–400 and 1:1) are presented. The theoretical and model investigation results are in good agreement.
Room acoustic properties of concert halls: Quantifying the influence of size, shape, and absorption area
Authors: Gade Anders Chr.
Published: October 2005

A large database of values of various room acoustic parameters has provided the basis for statistical analyses of how and how much the acoustic properties of concert halls are influenced by their size, shape, and absorption area (as deduced from measured reverberation time). The data have been collected over a 15-year period from about 50 concert halls in Europe and the U.S. In all halls the same measurement technique was used (1/1 oct sweep tones all pass filtered to form impulse responses per octave band). Due to the large range of geometric differences contained in the material, it has been possible to derive empirical regression formulas from which the influence of certain geometrical design variables can be quantified. The author has found these fairly simple relationships useful in teaching and as guidelines both in the early stages of physical hall design and in setting up electronic reverberation enhancement systems.
Consistent physical measures of auditory source width for various frequency components of reflections
Authors: Morimoto Masayuki , Setoyama Haruki , Iida Kazuhiro
Published: October 2005

At this writing, there is no physical measure that can evaluate consistently the auditory source width (ASW) perceived for sound fields consisting of a direct sound and reflections with various frequency components. In the experiments, a music motif is used as a source signal. The frequency components of reflections are varied by changing the cutoff frequency of low-pass, high-pass, and band-elimination filters, and simultaneously their directions are varied from ±18 to ±90 deg by steps of 9 deg. ASW and some physical measures are obtained for all sound fields in the experiments. The results on ASW indicate that any frequency component of lateral reflections contributes to create ASW almost equally. The comparisons of ASW with many physical measures show that ICCavg and Lfavg can evaluate ASW for all sound fields consistently with high accuracy. They are the average of the degrees of interaural cross correlation and the lateral energy fractions for 1/1-oct bands for 125 Hz to 8 kHz, respectively. Furthermore, the average of the degrees of cross correlation between two points 30 cm apart without using a dummy head for 1/1-oct bands for 125 Hz to 8 kHz is also adequate, although it is less accurate than ICCavg and Lfavg.
Influence of acoustic envelopment on spatial impression
Authors: Hanyu Toshiki , Kimura Sho
Published: October 2005

The spatial information of a sound field in various kinds of halls has been measured and studied. Through these measurements, it is clear that not only early lateral reflections (which relate strongly to spatial impression [M. Barron, J. Sound Vib. 15(4), 475–494 (1971)] but also acoustic envelopment were some of the characteristics of the spatial information. Therefore, quantifying acoustic envelopment, and examining the influence of acoustic envelopment on spatial impression by performing experiments has been tried. The results are as follows: (1) Acoustic envelopment influences spatial impression, especially in regards to subjective envelopment; and (2) there is a possibility that subjective envelopment can be explained by the values (e, b, A.E.) that have been introduced in order to quantify acoustic envelopment.
Some new considerations on the perception of subjective loudness in concert halls
Authors: Kahle Eckhard , Jullien Jean-Pascal
Published: October 2005

The link between the perception of subjective loudness and the total sound level, G, and, more generally, the ambient sound power level at the listener’s ears, has been established for some time. However, new results from laboratory experiments as well as real-hall listening tests indicate that the link is slightly more complicated. These studies suggest that the auditory system monitors the strength of the early part of the room response (corresponding to a perceptual factor of ‘‘presence‘‘) and the late part of the room response (corresponding to a perceptual factor of ‘‘room effect’’) separately. Evaluation of subjective loudness occurs only at a higher level of the auditory system. The results corroborate other investigations in showing that listeners can evaluate different contributions of the room in separate streams of attention.
Measuring the effectiveness of special acoustic provisions in a concert hall
Authors: Houtsma A. J. M. , Martin H. J. , Hak C. C. J. M. , van Donselaar C. J.
Published: October 2005

In a recently constructed concert hall in The Netherlands (14400 m3, 1250 seats), problems were encountered with solo piano performances. Music critics wrote that the instrument sounded unclear and appeared to be swimming in space. A 52-m2 on-stage wooden reflector and a 90-m2 curtain along the front wall, both removable, were applied to increase clarityC80 . This satisfied the critics. The acoustic effectiveness was measured by making KEMAR head recordings of short piano fragments, replayed by a Yamaha Disklavier, at various listening positions in the hall, both with and without the reflector and curtain in place. Two-alternative forced-choice discrimination experiments between comparable stimuli, with and without the provisions, were performed with listeners using insert earphones. The results showed that only a few listeners were able to score significantly above chance level for a few music fragments and recording positions. The average score over all listeners, music fragments and recording positions, however, was only 57% correct. This suggests that the apparent success of the reflector/curtain combination is attributable to factors other than purely acoustical ones.
A rigorous linear model for the local reverberation time
Authors: Stanzial Domenico
Published: October 2005

Recent advances in energetic analysis of sound fields show that three local sound field indicators η, ξ, σ accounting, respectively, for the sound radiation, the sound absorption, and the sound energy velocity at any given location of a general sound field can be usefully employed for modeling the reverberation process as a linear feedback system. The input and the output of this black-box model of a general reverberant field are the sound energy density of the associated free-field and the actual sound energy density of the reverberant sound field. It turns out that the energy transfer function of the model system is simply given by the time-average speed of the sound energy at the given location. The local reverberation time formula is obtained from this model by adding up how many ‘‘characteristic times of the acoustic system’’ are necessary in order to get an energy feedback contribution 60 dB lower than the steady-state sound energy level of the associated free-field.
A modest approach to enhancement of existing spaces for music performance
Authors: Wetherill Ewart A.
Published: October 2005

The combination of new acoustical analysis and evaluation techniques made possible by digital electronics has led to a greater understanding of construction and remodeling for music performance. However, the increas- ing complexity of acoustical analysis and design—as seen in several well-publicized recent examples—supports the belief of some music administrators that acoustical consulting is both costly and often the cause of high remodeling costs. At the same time, the performing arts, which 30 years ago enjoyed wide public and private support, are now desperately short of funds, as demonstrated by the demise of several once-prominent orchestras and other performing groups. Studies indicate that many smaller orchestras perform in halls that are fairly good but that could be improved acoustically at modest cost. Combining this newly acquired understanding of acoustics with better communication between consultants and administrators in relatively modest projects could significantly enhance public appreciation and support of orchestras.
Bubble distribution measurements—Theoretical aspects
Authors: Henyey Frank S.
Published: October 2005

Two theoretical topics in support of bubble cloud measurements are presented: (1) Corrections to Foldy’s effective medium theory. A very large class of multiple scattering contributions are summed to give a correction to Foldy’s formula for the index of refraction of a random collection of small scatterers. The result has a simple theoretical interpretation, and is a much smaller correction than that obtained by [Z. Ye and L. Ding, J. Acoust. Soc. Am. 98, 1629–1636 (1995)] due to cancellations between their multiple scattering contributions and others. The probable effect of neglected contributions is discussed, and contrasted to a claim that Foldy’s model gives infinite results [A. S. Sangani, J. Fluid Mech. 232, 221–284 (1991)]. The finiteness is due to a cancellation between multiple scattering terms. (2) The Kramers–Kronig integrals are applied to resonator data. (This work is done in collaboration with R. Goodman, D. Farmer, and S. Vagle.) The real and imaginary parts of the index of refraction are measured, and the Kramers–Kronig integrals give a prediction for each in terms of the other. Discrepancies between the measured and predicted functions indicate inaccuracies of the measurements, if enough bandwidth and fine enough sampling are included.
Acoustic measurement of bubble size distributions: Theory and experiments
Authors: Duraiswami Ramani , Prabhukumar Sankar , Chahine Georges L.
Published: October 2005

Among methods of measurement of bubble size distributions, a successful acoustic method has advantages in that bubbles are very responsive to sound, large volumes may be sampled, and the method can be inexpensive. However, inversion of the data to recover the bubble density is difficult. In the present work a model for sound propagation in bubbly liquids is used to develop two Fredholm integral equations of the first kind relating the attenuation and phase velocity to the bubble density. These equations are ill-posed, and require special solution. New solution algorithms based on a constrained minimization method were developed. These were first tested on analytical data with added noise, and were successful in recovering the bubble density. Bubble populations were then generated using electrolysis and air injection. Short bursts of sound at different frequencies were generated at a source, and received at a hydrophone after passage through the medium. The attenuation and phase velocity were obtained, along with other information, that are used to develop constraints on the solution. Results obtained for the bubble population are compared with microphotography and show that the method is accurate. In ongoing work an integrated PC-based instrument is being developed. [Work supported by NSF.]
Time-space characteristics of bubble clouds in the open ocean
Authors: Smith Jerome A.
Published: October 2005

In the spring of 1995, a ‘‘Doppler secscan’’ sonar system (200 kHz) was deployed from FLIP off Pt. Conception (1 month), San Clemente island (2 weeks), and Monterey (1 month), CA. This instrument provides backscatter intensity and radial velocity every 0.75 s, over a 450-m range by 30-deg azimuth. Dense temporal coverage means surface wave orbital velocities can be averaged out, and breaking events are not missed. A feature-tracking average was implemented, so longer averages can further reduce surface wave velocities without smearing features advecting past FLIP. In the first two segments, the instrument surveyed a horizontal sector, and winds ranged from 0 to 25 m/s. The evolving fields of intensity and velocity display some surprising relations, especially during higher winds. For example, the size and even orientation of intensity versus velocity features can differ. Off Monterey, a 2-D ‘‘vertical slice’’ was surveyed, yielding a new view of the time-space evolution of bubble clouds. In general, the clouds move sideways out of view before their temporal evolution can be tracked. However, it appears feasible to characterize some aspects of initial injection under breaking waves, and to characterize statistically the shapes of the clouds. A preliminary look indicates substantial asymmetry.
Nonlinear acoustic interactions in liquids with bubbles and their applications for bubble measurements at sea
Authors: Sutin Alexander M. , Ostrovsky Lev A.
Published: October 2005

It is known that, in comparison with homogeneous media (e.g., water, air), acoustical nonlinearity of a liquid with a small concentration of bubbles can be anomalously high. The influence of bubbles upon nonlinear properties of the medium is often much more significant than the simultaneous change of linear characteristics, such as sound speed. This paper presents a brief review of our investigations of nonlinear acoustic phenomena in bubble clouds, and some results concerning nonlinear acoustic methods of measurements of bubble radii and their distribution in water. (1) The theory of the bubble medium is based on summation of the fields scattered by separate bubbles. The scattered field consists of coherent and noncoherent parts, and the latter can be treated as a nonlinear reverberation signal which takes place at frequencies different from those of the incident acoustic wave: second harmonics in the case of a harmonic primary radiator, and sum- and difference-frequency signals for a bifrequency radiator. The formulas relating these signals to the bubble distribution in the layer have been obtained. (2) To observe nonlinear acoustic effects in a subsurface bubble layer and in sea sediments, two echosounders working at different frequencies were used. The sum- and difference-frequency components were observed in the signals scattered from sediments with bubbles and from the subsurface bubble layer. The theory of such nonlinear scattering is in good agreement with experimental data.
The significance of multiple scattering in bubble measurements near the sea surface
Authors: Bjo/rno/ Irina K. , Bjo/rno/ Leif
Published: October 2005

The acoustic interactions between gas bubbles in bubble plumes formed near the sea surface may significantly change the propagation and attenuation conditions for acoustical signals in the sea. The scattering properties of the bubble plumes have been studied extensively since Foldy’s formulation of the theory for isotropic scattering by randomly distributed scatterers. This theory, modified later by others [K. W. Commander and A. Prosperetti, J. Acoust. Soc. Am. 85, 732–746 (1989)] fails in the vicinity of individual bubble resonances and for high concentrations of bubbles in the population. A recent improvement of the scattering theory [C. Feuillade, J. Acoust. Soc. Am. 98, 1178–1190 (1995)], predicts a downward frequency shift and a suppression of the attenuation peak. His results emphasize the importance of the still unsolved problem on proximity thresholds for influence of multiple scattering in terms of bubble plume qualities. Available, but still unconfirmed, experimental data show the significance of multiple scattering in bubble plumes having void fractions ≳0.22%. This paper forms an attempt to illuminate and solve the proximity threshold question, forming the basis for the significance of contributions from multiple, linear scattering, by use of experimental data from laboratory and full-scale tests of bubble plume scattering.
Gas bubbles in phytoplankton
Authors: Didenkulov Igor N. , Selivanovsky Dmitry A. , Muyakshin Sergey I.
Published: October 2005

Phytoplankton plays a very important role in gas exchange in the ocean. But until now it has not been considered as acoustically significant as zooplankton. The existence of gas cavities in phytoplankton cells was suggested a long time ago but has not been detected so far because of early methods of observation. The review of recent works on acoustical investigations of gas bubbles associated with phytoplankton cells is given in this paper. Acoustical and related properties of phytoplankton suspensions were studied under laboratory conditions and in situ by several methods including acoustic 6.5-MHz backscattering under ordinary conditions with additional compression up to 5 atm. It was observed that, under the sharp compression gas cavities dissolve and recover under the light exposition. The volume of gas cavity associated with a phytoplankton cell was found to be up to 0.3 of the volume of a cell for different alga species. Such a bubble may increase the acoustical cross section of a pure cell by 2–3 orders. Roles of phytoplankton bubbles for sound propagation, for anomalous migration of some sound scattering layers, and for hydrodynamic cavitation in the subsurface layer and in wakes of sea animals are discussed. Experimental examples are given. [Work was supported by RFBR (Grant No. 95-05-15632).]
Subsurface bubble layers generated by extremely heavy rainfall
Authors: Nystuen Jeffrey A.
Published: October 2005

Acoustical evidence for the formation of subsurface bubble layers generated by extremely heavy rainfall will be presented. These bubble layers are associated with the presence of very large raindrops (over 3.4 mm diameter) within the rain, which in turn, tend to be associated with extremely heavy rainfall. The splash physics of very large raindrops include a turbulent downward propagating jet which has been shown to carry bubbles into the underlying water. These raindrops have also been shown to rapidly deepen a rain-induced mixed layer, suggesting that rain can generate a subsurface bubble layer. The bubble populations are measured by predicting the sound field generated at the surface and then measuring the acoustic extinction well below the surface. Vertically integrated bubble population densities equivalent to the bubble field generated by 10-m/s winds are observed. These bubble populations quickly dissipate when the very large raindrops are no longer present in the rain, suggesting that the bubble layer generated by extremely heavy rain is very thin (tens of centimeters at most). [Work sponsored by NSF and ONR.]
Magnetohydrodynamic fluid pump
Authors: Grant Anat , Garrett Steven
Published: October 2005

Magnetohydrodynamic transduction has been successfully demonstrated in the conversion of acoustic to electric energy in a thermoacoustic prime mover [Swift, J. Acoust. Soc. Am. 83, 350 (1988); Swiftet al., J. Acoust. Soc. Am. 78, 767 (1985)]. The reciprocal effect [Swift and Garrett, J. Acoust. Soc. Am. 81, 1619 (1987)]—the magnetohydrodynamic generation of sound—is also potentially attractive for production of high-amplitude standing waves in gases since the moving fluid does not require a flexure or piston seal. Results will be presented for an experimental device which compresses gases above a fluid-filled U-tube driven magnetohydrodynamically at resonance. Electroacoustic efficiencies for mercury and potassium chloride conductivity standards will be related to transducer parameters (e.g., magnetic induction, electrode dimensions, tube diameter, fluid viscosity, etc.). [Work supported by the Office of Naval Research.]
Magnetodynamic fluid pump
Authors: Poese Matthew , Garrett Steven
Published: October 2005

The total magnetic energy of a solenoid can be reduced by the introduction of a magnetic material. This effect is exploited in the operation of actuators used in a variety of applications ranging from automobile door locks to the clamping of airplane landing gear. FerrofluidTM is a stable colloidal suspension of magnetic particles in a liquid carrier with μ≤3μ0 and viscosities in the range from 10–6000 cp. A report will be made on a measurement of the resonant oscillations of the magnetically driven ferrofluid contained in a U-tube geometry. The ferrofluid ‘‘plug’’ functions as a double-acting piston which generates sound in the gas volumes which are above the fluid-free surface. [Work supported by the Office of Naval Research.]
Time-reversal property of acoustic phase conjugate waves and their applications to imaging systems
Authors: Yamamoto Ken , Kokubo Akira , Ohno Masahiro , Sakai Keiji , Takagi Kenshiro
Published: October 2005

High-efficiency generation of the acoustic phase conjugate waves with nonlinear PZT piezoelectric ceramics was successful. This method has advantages over other methods in its fast response and a weak dependence on incident angle. Efficiency of the phase conjugator, defined as the amplitude ratio of the phase conjugate wave to the incident wave, is strongly dependent on the nonlinear piezoelectric, elastic, and dielectric constants of the materials. These nonlinear constants were measured in some PZT ceramics with different compositions. The efficiency was calculated theoretically from these values. The results were in good agreement with the observed efficiency. In previous studies, a very small efficiency in LiNbO3 crystal was found. The phase conjugation efficiency in PZT ceramics is up to 20%, which is 20 times larger than that of LiNbO3, in which the nonlinear constants are much smaller than those of PZT ceramics. The time-reversal property of the phase conjugate waves was confirmed by visualizing their propagation with a stroboscopic schlieren technique. The phase conjugator was also applied to the acoustic imaging system: The image distortion caused by the inhomogenity in the medium was successfully eliminated.
Acoustic sensor pad for physiological monitoring
Authors: Scanlon Michael V.
Published: October 2005

An innovative physiological monitoring device allows passive acoustic detection of heartbeats, breaths, and other body sounds. Since the human body is mostly water, a liquid-filled bladder placed in contact with the torso acts as a fluid extension of the human body to form an acoustical conduit to a sensitive hydrophone within the pad that detects body sounds. Careful selection of interface material and internal fluid can help match acoustic impedance and transmission characteristics to that of a human body so that sounds travel easily through the coupling surface and fluid to the hydrophone. Acoustic analysis of the sensor-pad output can provide amplitude, phase, frequency, duration, rate, and correlative information that may be useful for medical diagnosis, patient care, and research. Joint time-frequency Fourier analysis of collected data shows that human cardiopulmonary function contains intricate spectral details that include infrasonic signals. Spectrogram representations of missed heartbeats, murmurs, held breaths, and fetal motion have demonstrated high sensitivity and SNR can be achieved through this coupling mechanism. The acoustic sensor pad can be useful for military and civilian casualty care, transport, performance evaluation, and continuous health monitoring of infants and the elderly.
DK model for electrostatic ultrasonic transducers with V-grooved backplates
Authors: Ge Li-Feng
Published: October 2005

A new model for electrostatic ultrasonic transducers with V-grooved backplates is developed. The model treats the diaphragm of the transducer as a plate supported by an air spring. Since the tension is usually not used and unnecessary, only the bending stiffness of the diaphragm, D, and the air-gap spring stiffness, K, are taken into account. It is revealed by the DK model that the first resonant frequency of the transducer stems from the air-gap spring, like a Helmholtz resonator, and the second resonant frequency corresponds to the first mode frequency of the diaphragm vibrating as a thin plate. The motion of the diaphragm can be described approximately by the combined contributions of the two parts. According to the theory, a wider bandwidth can be obtained by designing the second resonant frequency to be near the first one with an appropriate selection of geometric dimensions and material parameters. For a typical V-grooved transducer with an 8-μm-thick Mylar diaphragm and a 0.5-mm pitch air gap, the first resonant frequency predicted by the model is 50.9 kHz, and the second one is 78.6 kHz. The prediction is consistent with experimental results. [Work supported by Anhui Natural Science Foundation of China.]
Subjective investigation of a new sound reproduction system (stereo dipole)
Authors: Watanabe Yuko , Tokunou Hironori , Hamada Hareo , Kirkeby Ole , Nelson Philip A.
Published: October 2005

Recently, a new transaural sound reproduction system, referred to as a ‘‘stereo dipole’’ (SD) reproduction system, has been proposed, in which a closely spaced pair of loudspeakers is located in front of a listener. Theoretical investigation was carried out by computer simulations and it was reported that the SD system would be capable of providing a relatively large equalized area to the listener and robustness with respect to a listener’s head movement compared with those given by the standard loudspeaker arrangements. This paper deals with a subjective investigation of the SD system. It is known that the ordinary transaural system has a disadvantage in the quality of reproduced sound; that is, the reproduction of unnatural and antiphase virtual sound from the psychoacoustic point of view. Therefore, subjective listening tests were carried out, which aimed to compare the SD system with the ordinary system. The significance of the SD system on reproduced sound perception is suggested.
A study of the effect of visual images on three-dimensional sound localization
Authors: Motizuki Takahumi , Hamada Hareo
Published: October 2005

The purpose of this study is to develop a three-dimensional acoustic display, in which an interaction between a visual and a sound image is taken into account. To find out the characteristics of the interaction, it is useful to examine the effect of visual images on three-dimensional sound localization. In general, it is known that the visual image affects the location of sound images. It is particularly evident when both of the locations are close to each other. For instance, when a sound image located at a certain angle with respect to the listener is presented, the perceived position of the sound image would be shifted toward the image due to the interactions. This phenomena may lead to a simplification of the signal processing for sound localization, since now information from both a visual and a sound image can be used to localize the sound image at a certain position. In this paper, results of some basic experiments will be presented, and the influence of visual images on sound localization will be considered. The visual image was created by computer graphics and the sound images were reproduced using head-related transfer functions.
Sound generation by fluttering wings
Authors: Ohnuki Takeshi , Sakayanagi Masako , Kawachi Keiji
Published: October 2005

The flight mechanism of insects has not yet been understood. Their wings produce more lift than predicted by steady- or quasisteady theory. The importance of unsteady aerodynamic mechanisms is now recognized but, except for the specialized ‘‘flying’’ mechanism, the origin of the extra lift is unclear. An attempt is made to explain the unsteady aerodynamic forces by aeroacoustics approach. Sound generated by a moving surface can be physically understood as composition of wing thickness noise, loading noise, and other elements, such as vortex noise. In insect flight, the velocity of the wing tip is much smaller than the velocity of sound, and the compressibility of the air can be neglected. In this case, it becomes easy to calculate the fluttering noise from a given aerodynamic load on the wing surfaces. A new approach to understanding the lift generation mechanism is proposed.
The VL1 virtual acoustic synthesizer
Authors: Kunimoto Toshifumi , Kakishita Masahiro
Published: October 2005

McIntyre et al. [J. Acoust. Soc. Am. (1983)] suggested the idea of constructing electrical musical instruments based on physical models of natural musical instruments. The first product employing such an approach has been developed, the VL1, and the synthesis technique is called ‘‘virtual acoustic synthesis.’’ Differences and comparisons between conventional music synthesizers and the virtual acoustic synthesizer will be shown. Also, problems arising in the approximation of natural musical instruments and the realization of approximated models will be described to some extent. The VL1 synthesizer also contains a sound effects section and other common features found in commercial digital musical instruments. The system is realized using specialized DSP chips. The current VL/virtual acoustic synthesizer is expensive, so reducing the cost was the next goal. A low-cost version, the VL70-m, was also released this year. There will be a small demonstration to exhibit the sound of the instrument.
Time-domain simulation of aeroacoustic sources in flutelike instruments
Authors: Verge Marc-Pierre , Hirschberg A.
Published: October 2005

The sounding mechanism of flutelike instruments is based on the oscillations of an airjet on each side of the labium. This jet motion provides the ‘‘drive’’ which enables the maintenance of the acoustic oscillations in the resonator of the instrument. Sound is also produced by two other aeroacoustic sources, namely, vortex shedding at the edge of the labium and turbulence in the mouth of the instrument. Vortex shedding is crucial since it represents the main nonlinear amplitude limiting mechanism for the fundamental of the acoustic oscillations. The shedding of vortices also contributes to generate high frequencies in the spectrum and therefore determines the tone of the instrument. Turbulence in the mouth produces noise which constitutes, although it does not contribute fundamentally to the functioning of the instrument, an essential component of its tone. Simple and efficient hydrodynamic representations of these complex phenomena are presented. The influence on the tone produced by the instrument of the mouth geometry, which accounts for the work of the instrument maker, and the playing conditions is also discussed. These features are included in a one-dimensional simulation model of flutelike instruments which can be used for real-time sound synthesis.
Synthesis of brass tones using a driven lip model
Authors: Berners David P.
Published: October 2005

Typical physical modeling synthesis methods for brass instruments contain a lip dynamics model and an acoustic flow model for the lips. Both elements contain nonlinearities, leading to a nonlinear feedback loop. Problems that arise with this type of system include difficulty in predicting the pitch of the synthesized tone and lack of robust methods for getting tones to ‘‘speak.’’ Elimination of the lip dynamics model leads to replacement of the nonlinear feedback system with a simpler nonlinear filtering system. In this model the lip reed is replaced by a zero impedance regulating valve which moves at the frequency of the desired output, according to measured lip data. Whereas for the conventional synthesis model, the frequency of synthesized sound is neither the resonant frequency of the lips nor the resonant frequency of the bore; in the case of the driven lip model, the synthesized frequency is exactly the same as the frequency at which the lip valve is driven. The driven model also guarantees that synthesized tones will speak, because amplitude of lip oscillation becomes a direct control parameter. Since harmonic generation in brass instruments is not directly caused by lip dynamics, spectrally rich tones can be generated by this model.
Use of a simple control system for the improvement of simplified physical-modeling synthesis algorithms
Authors: Stilson Timothy S.
Published: October 2005

Efficiency requirements often cause physical models of musical instruments to be vastly simplified when implemented, sometimes to the point where the model loses certain ‘‘correct’’ behaviors, such as realistic attacks or even stability. In the case of instability, many implementations which use fixed-point arithmetic implicitly rely on the limiting behavior of the number system to contain the amplitude of the signal. Certain models, such as clarinet models, tend to continue to work well in the presence of this instability, due to the fact that the resulting clipping does not significantly alter the spectral content of the signal. Other models, however, are significantly altered by the limiting. In certain cases, a simple nonlinear control system can be placed into the model (without significantly increasing the computation requirements) to serve the oscillation amplitude to a desired amplitude envelope. This control system improves the stability of the system, which in saturating number systems also reduces distortion. The control system can also improve other performance behaviors, such as attacks.
The discontinuous conical bore as a Sturm–Liouville problem
Authors: Berners David P.
Published: October 2005

In some cases the reflection functions associated with the discontinuities in conical bores are growing exponentials [J. Martinez and J. Agul- ló, J. Acoust. Soc. Am. 84, 1613–1619 (1988)]. It is shown that discontinuities can be modeled by a Sturm–Liouville system using a pressurelike quantity as the dependent variable. For the subset of discontinuities exhibiting the growing exponential reflection function, the Sturm–Liouville potential function is an energy well. This well is shown to support exactly one trapped energy mode which corresponds to the growing exponential. It is shown that in the region surrounding the discontinuity for these systems, traveling Fourier components taken together with their reflected waves do not constitute a complete set and that the trapped mode is required to complete the set. On the other hand, for systems which do not exhibit the growing exponential, the Sturm–Liouville potential is an energy barrier with no trapped modes, and the Fourier components compose a complete set within the conical regions. Furthermore, a change of dependent variable can be used to go from a Sturm–Liouville description involving an energy well to one involving a barrier, thus eliminating the trapped mode.
Comparison of the directivity of woodwind instruments: Improvement of diffusion techniques in sound synthesis by physical modeling
Authors: Causse Rene , Rousseau Antoine
Published: October 2005

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.
Nonlinear vibration frequencies of a discrete model of a stiff string
Authors: Harazono Masahiro , Kuramoto Atsushi
Published: October 2005

Nonharmonic components in a string vibration generate beats, effect the sound quality of a musical instrument, and become a harmful component in the tuning. Therefore, one needs to grasp in detail the influence of various parameters such as inherent elasticity. In the present paper, influence of tension change acting as nonlinear with the displacement of the stiff string on vibration frequencies is analyzed by constructing a discrete model. In numerical calculations of the string vibration affected by a disturbance such as elasticity, it is impossible to get a rigorous solution from a finite-difference scheme, and particular consideration in evaluating vibration frequencies affected by nonlinear ingredients is needed. Because of this influence of vibration, frequencies are expected to be very small; the analysis has to be carried out with a sufficient grasp of digitizing errors. First string vibration frequencies of the discrete model are analyzed and then evaluated with a rigorous value for an ideal string and the case including inherent elasticity. In addition, the simulation of nonlinear string vibration is conducted by correcting the digitizing error. The vibration frequencies of the simulated response are obtained from the period of numerical solution by applying a digital filter. The results show that vibration frequencies fall slightly due to the effects of nonlinear components.
Consideration of a device for correcting string vibration frequency measured by an electromagnetic transducer
Authors: Kuramoto Atsushi , Harazono Masahiro
Published: October 2005

An electromagnetic transducer is used for measuring characteristics of string vibration and for tuning stringed instruments. Analysis shows that, in spite of weakness of magnetic coupling between the transducer and the string, partial tones are not harmonic because of the influence of the negative stiffness of the transducer. Therefore, beats occur because of interference among the fundamental and the partial tones, whose amplitudes are not so small. This problem is formulated by use of linearized attraction to the static component and the stiffness component, and a δ function is used to express the lumped force in the distributed system. The solution can be obtained by use of a Laplace transform, and the vibration frequency affected by the negative stiffness is analyzed exactly from the numeric calculation of characteristic equation. This paper describes approximated equations for the vibration frequency based on these analyses and the measured frequency through the electromagnetic transducer. A method is described to correct the influence of negative stiffness on the vibration frequency using the measured frequency. The corrected results obtained from the prototype system show sufficient precision for practical use. Furthermore, according to the method, construction of a measurement device making use of the electromagnetic transducer is considered.
The optimization of a single-stage valved pulse tube refrigerator
Authors: Ohashi Yoshimasa , Matsui Takayuki , Kawano Shin , Inoue Tatsuo
Published: October 2005

The pulse tube refrigerator, which has made great progress in the past couple of years, is a typical thermoacoustic device and has attracted attention because it may be replacing conventional cryocoolers, such as Stirling and Gifford–McMahon refrigerators. The pulse tube refrigerator is a very interesting system from the viewpoint of thermoacoustics because it consists of a regenerator where entropy is pumped with a reversible process by the progressive wave component of the oscillation, and a pulse tube where work flows adiabatically. A four-valve-type single-stage pulse tube refrigerator was constructed, which has a pressure switching valve system at the hot end of the pulse tube with a conventional GM compressor unit. The four-valve type is an active and easy way to evaluate the boundary condition of phase and displacement quantitatively. By the optimization of the phase shifting, driving conditions, and the shapes, the lowest temperature of 30 K and cooling power of 10 W (at 80 K) for 700 W of power consumption are obtained, at present. The key point of achieving higher performance is how to reduce the work dissipation in the regenerator and the heat transfer losses via the pulse tube. In this session, an actual approach to this viewpoint will be discussed.