bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal waves measurements with a ship-mounted, 300-kHz acoustic Doppler current profiler
Authors: Trump C. L. , Marmorino G. O.
Published: October 2005

Acoustic Doppler current profiler (ADCP) data from the upper few hundred meters in the open ocean have been analyzed for evidence of the relationship between high vertical shear in horizontal currents and small-scale mixing (detected with a simultaneous towed thermistor chain). The shear resolved by the ADCP generally occurs in thin, horizontal layers. Often the shear vector rotates with depth indicating packets of near-inertial internal waves with down- and upgoing energy propagation. Other times, the shear is more jetlike with little rotation. While patches of mixing and short waves occur on similar scales to the shear layers, it has not yet been proven that the mixing is due to a specific process such as Kelvin-Helmholtz billows. In contrast, higher frequency, ∼ 1-km wavelength, internal waves are poorly resolved except that they sometimes vertically displace the high shear layers. Only in coastal waters has the internal-wave-induced velocity been clearly resolved, and, in this case, the waves induced ∼ 5-m vertical oscillations in “echo strength,” high shear, and spectral width.
Oceanic turbulence measurements using a coherent bistatic acoustic Doppler profiler
Authors: Stanton Timothy P.
Published: October 2005

A 300-kHz acoustic Doppler profiler has been developed to measure turbulent processes in the upper ocean. Acoustic energy from scatterers ensonified by a single, narrow-beam, pulsed transmitter is received by four fan beam response hydrophones placed radially around the transmitted transducer. The present system allows three-component velocity profiles to be estimated every 10 cm over a 5- to 20-m range with high temporal resolution and adequate velocity range by using a dual interpulse period coherent sampling method. Examples of the high spatial and temporal resolution velocity fields are shown from recent measurements immediately below open ocean waves and a sub-ice boundary layer. Both the advantages and limitations of this current measurement technique will be discussed. [Work supported by ONR Physical Oceanography.]
Acoustic Doppler measurement of internal waves: New techniques and observations
Authors: Pinkel Robert , Sherman Jeffrey T.
Published: October 2005

In the mid 1970s, acoustic Doppler techniques were first applied to the internal wave measurement problem. Since then, both pulse-to-pulse coherent (short-range) and incoherent (long-range) sonars have been developed. Recently, a 161-kHz device that can operate in either mode, as well as a hybrid coded mode, has been created. In the hybrid mode, broadband pulses are transmitted. Doppler shift is estimated from the phase progression within individual returns. Incoherent averaging from pulse to pulse further improves the precision of the velocity estimate. Velocity error variance is reduced by a factor of 10 relative to uncoded pulses. The hybrid sonar was first operated in the Arctic, north of Svalbard, in conjunction with the 1989 ONR experiment, Cearex. While the under ice boundary layer was examined using a fully coherent operating mode, the large-scale internal wave field was sampled to depths of 500 m using the hybrid transmission scheme. Strong baroclinic subinertial motions were seen at diurnal tidal frequency. These occasionally became unstable, producing borelike events with amplitudes in excess of 50 m. Toward the end of the experiment, an eddy drifted under the ice camp. The precision of the sonar was sufficient to resolve a “crown” of internal waves trapped to the dome of the eddy.
Acoustic mode-coupling loss caused by internal wave packets in shallow water
Authors: Zhang Xue-zhen , Zhou Ji-xun , Rogers Peter
Published: October 2005

Previous work has shown that there is a strong interaction between acoustic waves and internal wave solitons in shallow water [Zhou et al., J. Acoust. Soc. Am. Suppl. 1 86, S8 (1989)]. The characteristics of internal waves in the coastal zone (deterministic, shoreward propagating packets with a well-defined wavelength and highly correlated with the local tides) are such that this interaction could possibly explain the anomalous, anisotropic frequency response of shallow-water sound propagation that is often observed in the summer. This anomalous propagation is a strong function of time and sometimes exhibits an abnormally large attenuation over some frequency range. By decomposing the acoustic field obtained using PE into normal modes, it is found that the additional “mode-coupling” loss caused by internal waves is a sensitive function of the signal frequency and the internal wave-packet parameters. The acoustic transmission loss is a “resonancelike” function of the number and wavelength of the solitons (with all other parameters held fixed). Hence, low-frequency acoustic measurements, including modal filtering, could be a powerful tool for remote monitoring of internal wave activity in the coastal zone in places such as the Massachussetts Bay, the New York Bight, and the Gulf of California and the Yellow Sea. [Work supported by ONR, IAAS, and GA Tech.]
Ted Schultz' contributions to aircraft acoustics
Authors: Haight Norris L.
Published: October 2005

Ted Schultz' contributions to aircraft acoustics began in 1955 during the initial design of the DC-8 jet transport airplane at the Douglas Aircraft Company in Santa Monica, CA. As Assistant Chief of the Acoustical Engineering Staff, he was directly involved in theoretical and environmental work in interior and exterior acoustics and provided challenging leadership to other Douglas employees. Ted's work in aircraft cabin acoustics included design and testing of: fuselage sidewalls with high sound transmission loss against the pressure fluctuations in the turbulent boundary layer (whose characteristics were not well understood at that time); interior sound-absorbing surfaces; and methods to control the noise produced by aircraft equipment items (e.g., hydraulic pumps, fans, venturi flow-control devices, and air-conditioning system components). During much of this experimental work, he found it necessary to develop unique acoustical laboratory test facilities and techniques which became an expertise widely sought after throughout his later professional career. In exterior acoustics, he worked closely with Alan Powell (consultant to Douglas Aircraft Company) to develop theoretical descriptions of the characteristics of noise resulting from the mixing processes in aircraft jet engine exhausts, as well as in the boundary layer along an aircraft fuselage. He provided insight and guidance in evaluation of results from model and full-scale jet noise suppressor concepts. Ted also helped in the early development of methods to evaluate community noise impact from operation of jet aircraft. His expertise on rating community noise response considering aircraft and other exterior sounds is recognized worldwide. His highly developed skills in aircraft acoustics were called upon again in the 1984–1988 period as a consultant to McDonnell Douglas in the design of state-of-the-art acoustical test facilities to study methods to minimize cabin noise levels in propfan-powered transport aircraft. Ted's innovative contributions to all aspects of aircraft acoustics formed technical foundations that will be utilized in establishing acoustical designs for commercial transport aircraft for years to come.
T. J. Schultz' contributions to sound-intensity measurement and theory
Authors: Crocker Malcolm J.
Published: October 2005

In the mid 1950s, during and following his doctoral research at Harvard University, Ted Schultz contributed significantly to the early development of sound-intensity measurement techniques. By using back-to-back pressure transducers, he was able to develop a sound-intensity probe that satisfactorily measured sound intensity. However, in explaining his observed results, he was impeded by the paucity of theoretical understanding of complex sound-intensity fields. Ted and other researchers in the late 1950s and early 1960s eventually dropped further development of the early “acoustic watt meter” on which Ted held a U.S. patent, after frustrating and disappointing research results. Later, Ted and others came to understand that great care must be taken to correct the errors between transducer channels or to use phase-matched transducers. In any event, Ted's pioneering experiments in sound intensity contributed immensely to later developments and to the current more advanced state-of-the-art.
Acoustic echo cancellation in subbands
Authors: Kellermann Walter
Published: October 2005

Acoustic echo cancellation for teleconferencing or hands-free telephony constitutes a challenging task for today's digital signal processing techniques. Compared to the well-established line echo cancellation in telephone networks, the problem takes on a considerably larger size: The impulse response of the echo path to be compensated is longer and may vary more rapidly in time. Moreover, larger bandwidths are often desirable. Therefore, acoustic echo cancellation requires algorithms that adapt far more coeffecients and converge faster than those commonly used in line echo cancelers. On the other hand, direct implementation of sufficiently advanced adaptive filtering algorithms is usually prohibited because of their computational complexity and inherent numerical difficulties. As a way out, the subband approach realizes a “divide and conquer” strategy and promises a reduction of computational complexity and favorable circumstances for fast convergence at the cost of some extra delay. After comparing several possible subband structures, the frequency subband structure is discussed in some detail. For adaptation using LMS-type algorithms, reasons for the improved convergence behavior compared to a fullband implementation are explained. Design examples are presented to illustrate the effectiveness of the method.
A client's view of Theodore J. Schultz
Authors: Filoni Albert L.
Published: October 2005

This paper describes how the author met Ted Schultz and their joint approach to a study of reverberation problems in the Olin Fine Arts Center at Washington and Jefferson College. This introduction led to collaboration on the remodeling of Benedum Center for the Performing Arts, with particular emphasis on design of the Proscenium and Rehearsal room A. Subsequent projects included the successful remodeling of Swasey Chapel at Denison University (from Church to Concert Hall). The presentation includes slides of drawings and actual realized designs, light studies of models and in full-scale buildings, and examples of Ted adjusting panels at Denison University.
Theodore J. Schultz and acoustical test standards
Authors: Brown Steven M.
Published: October 2005

This paper reviews Theodore J. Schultz's contributions in developing architectural acoustics test standards. Ted brought to this work the same enthusiasm, skill, and understanding that he brought to his other acoustical activities. His efforts in standards development were, in fact, strongly informed by his work and experience in other areas of acoustics. The result was a series of North American and international standards on measuring sound transmission and sound propagation in the laboratory and in actual buildings. This paper reviews both Ted Schultz's work in developing these standards and current work in extending and augmenting the standards. Throughout this work, the goal has been to develop practical, technically correct standards that help create better acoustical environments.
Acoustical variation within a large modern concert hall
Authors: Hook Julian L. , Gullerud Arne S. , Schomer Paul D.
Published: October 2005

Four acoustical parameters—sound level, 80-ms early-to-late sound ratio, initial time delay, and a simplified version of interaural cross correlation—were measured at 52 locations in a modern 2100-seat concert hall. All four were found to exhibit systematic variation from one part of the hall to another. A subjective study, involving questionnaires returned by musicians after attending concerts in the hall, was also undertaken. Of the four measures, early-to-late ratio correlated most strongly with overall preference in seat-to-seat comparisons. Of the subjective attributes rated in the questionnaires, “intimacy” correlated most strongly with preference. The hall studied, while generally highly regarded, has large areas with low early-to-late ratios and/or poor intimacy ratings. The suggestion is therefore advanced that in seat-to-seat comparisons within one hall, the objective and subjective attributes most strongly correlated with preference are likely to be those attributes in which the hall, taken as a whole, is poorest. In addition, listeners who have attended many concerts in the hall were found to give higher preference ratings than those less familiar with the hall.
Psychoacoustical demonstrations—Potential and peril
Authors: Hartmann William Morris
Published: October 2005

As a study of human sensation, psychoacoustics would seem to mesh well with appealing lecture demonstrations. To be meaningful, the study demands that students experience sounds personally. At the same time, the psychoacoustics literature offers a rich source of sonic effects, paradigms, and illusions. However, there are potential problems. Whereas psychoacoustical experiments normally involve trained subjects listening to headphones in an acoustically ideal environment, lecture demonstrations involve naive subjects listening to a loudspeaker in a room that may be far from ideal. There is always a risk that an important psychoacoustical effect will fail as a demonstration, either because listeners are not prepared to recognize the effect or because of the acoustical properties of the room. For example, rooms effects can seriously compromise demonstrations of the asymmetry of masking; room effects do not compromise critical-bandwidth measurement by masking. Some demonstrations (pitch shift effects and pitch ambiguity, for example) risk failure because of individual differences. Other demonstrations incorporate sequencing, required to make an effect apparent, which itself introduces unexpected artifacts. These points are discussed with particular reference to the auditory demonstrations on compact disc, now distributed by the Acoustical Society of America. [Work supported by the National Institutes of Health.]
Acoustic levitation and manipulation
Authors: Wang Taylor G. , Allen James L. , Anilkumar A. V.
Published: October 2005

The unique microgravity environment of space offers scientists and engineers a new tool to use in many areas of research. One set of experiments that takes the fullest advantage of the new tool is containerless science experiments. However, in performing containerless experiments, even in space, one must actively prevent the sample from drifting to the wall due to the microgravity force. Therefore, a set of levitation (or positioning) systems has been developed, namely, acoustic, electromagnetic, and electrostatic. In this session concentration will be on the acoustic approach and its capabilities.
Demonstration of nonlinear acoustics phenomena
Authors: Blackstock David T. , Maynard J. D.
Published: October 2005

The following experiments done with very intense sound in an air-filled, plane-wave tube are described: (1) progressive distortion of traveling waves of finite amplitude, both tones and noise; (2) saturation, which is the limit set by nonlinear effects on the amplitude (and intensity) of sound that may be transmitted a given distance; (3) interaction of a tone with noise; (4) suppression of sound by sound; and (5) acoustic levitation. Some of the experiments are illustrated by live demonstrations, others by descriptions and reported data. [Work supported by the Office of Naval Research.]
High-speed flash photography with sound triggers
Authors: Winters Loren M.
Published: October 2005

High-speed flash photography requires that the light from an electronic flash be brief but intense. Sound triggers that respond selectively to events producing loud and sharp noises can be built easily and inexpensively [L. M. Winters, Phys. Teach. 28, 12–19 (1990)]. With a single-flash unit, such events as the smash of a tennis ball struck by a tennis racket or the cavitation produced by a BB entering a tub of water can be demonstrated in the classroom. With two flash units and a simple timing device, the rip speed of a balloon can be measured. Multiple flash units, controlled by a computer with a photogate trigger, can be used to study the vibrational motion of a plucked cord [L. M. Winters, paper OO1 at this meeting] and other phenomena. The apparatus will be demonstrated and an assortment of photographs shown.
Interactive acoustics exhibits at the Science Place
Authors: Leto Glenn K. , Chiaverina Chris
Published: October 2005

The Science Place, Barrington School's interactive science center, consists of over 60 hands-on exhibits, displayed in thematic programs on a rotating basis. The Science Place attempts to generate a positive attitude toward science and alleviate science anxiety by allowing visitors to explore natural phenomena in a nonthreatening environment. Through support from the Acoustical Society of America, a number of exhibits illustrating acoustical phenomena have been developed. This paper will discuss these exhibits as well as the development and operation of the Science Place.
Effect of a backing plate on the transfer function of a flow noise reduction coating
Authors: Ko Sung H.
Published: October 2005

A theoretical model was developed to evaluate the transfer function of an elastomer layer bonded to a steel plate of finite thickness. The elastomer layer is designed to reduce pressure fluctuations due to turbulent flow over the elastomer (or other types of excitation). The effectiveness of the elastomer layer in discriminating against flow noise depends on the transfer function of the composite structure. Theoretical analysis is made using the theory of elasticity and pertinent boundary conditions. Due to the backing structure, the transfer function is affected by the flexural vibration of the plate. The contribution of the flexural wavenumber to the transfer function is discussed and numerical results are presented.
The damped acoustic pressure response of a thin diaphragm in close proximity to an arbitrarily shaped backplate
Authors: George Wallace R. A.
Published: October 2005

It is assumed that the damped behavior of the diaphragm is controlled by the motion of the gas in the space between the diaphragm and the neighboring backplate (i.e., the diaphragm to backplate distance is small but varying). The diaphragm could, in general, be a membrane type (as in typical capacitance microphones) or a plate type. The modeling is done for plate diaphragms, although the methods can, in general, be easily applied to membrane diaphragms. An explicit normal-mode expansion solution for the nonlinear fourth-order PDEs describing this plate-diaphragm's motion is discussed. The expansion is carried out in terms of the normal modes of the unbacked diaphragm. The nonlinear coupled fourth-order backspace pressure is derived in terms of the diaphragm displacement. The first explicit relations for the spatially dependent damped natural frequencies and associated damping factors for the diaphragm response are derived. The effect of the static gas-film pressure and thickness and a criterion for truncating the infinite sum solution are discussed.
Why acoustic sources are unique and how they can be identified from the fields they produce
Authors: Doak P. E.
Published: October 2005

The general Green formula solution of the inhomogeneous linear differential system for the general problem of acoustic motion in a uniform medium in an arbitrary space-time domain is presented. “Acoustic sources” are thereby seen to be exclusively the specified inhomogeneous terms of the differential system. The problem solution is seen to exist and to be unique; formal existence and uniqueness are retained even when nonanalytic generalized function type terms are present. The acoustic source distribution and the field it produces are seen to be in a one-to-one, and thus unique, relationship. The complete set of two, mutually exclusive, types of source distributions, active and reactive, is identified. An active distribution can be precisely reconstructed from knowledge of its farfield. A reactive distribution produces a zero field everywhere outside the region in which it is nonzero. Explicit results for one-dimensional examples are presented to provide some physical insight into why this one-to-one source/field relationship exists and how acoustic sources can be identified in practice.
Critical angle scattering: An asymptotic series approximation
Authors: Dean Cleon E. , Marston Philip L.
Published: October 2005

The critical light scattering angle at 82.8° from an air bubble in water locates the transition from partial to total reflection from elementary geometrical optics (EGO). A physical-optics approximation (POA) has been applied to analogous critical angle phenomena for sound reflected from a fluid sphere [P. L. Marston and D. L. Kingsbury, J. Acoust. Soc. Am. 70, 1488–1495 (1981)]. The present research gives a novel asymptotic series approximation for scattering amplitudes at the critical angle that is an improvement over both EGO and the POA. The series describes the breakdown of EGO at the critical angle: The leading correction to the scattering amplitude relative to the perfect reflection amplitude is found to be O[(ka)−1/4], where a is the radius of the reflector and the wavelength is 2π/k. A modified Watson transformation was applied to the exact Mie partial wave series for the case of light scattered from a bubble. A series was derived for the resulting integral special functions which is asymptotic for large ka [C. E. Dean, Ph.D. dissertation, Washington State University (1989)]. The series was confirmed by comparison (as a function of ka) with smoothed Mie computations for bubbles. It clarifies a relationship between scattered irradiance and bubble radius that has been used in optical studies of bubble dynamics and suggests how to improve the POA for critical angle reflection of sound. [Work supported by ONR.]
Localization of sources by two pattern-match methods
Authors: Eschenberg Kent E.
Published: October 2005

Two methods for the localization of sources were developed and applied to a simulation of point sources located near and behind barriers. Both methods are extensions of the concept of a “fictitious scatterer” and the approach used by acoustical holography and beamforming. The pattern-match point of view leads directly to a straightforward, though computationally demanding, method for dealing with cases where the radiation passes through nonisotropic but known disturbances. A second variation of pattern match has been explored that uses the mismatch, rather than the match, between the receiver and processing signal. Results for noise-free simulations of one and two point sources, in free space and near a barrier, indicate that these methods can extract information not available through holographic methods. Some situations may also lead to a number of false detections, indicating that the pattern-matching methods may need to be combined with more robust imaging in actual application.
Finite-difference approximations for transient acoustic waves in a pipe
Authors: Davis Sanford
Published: October 2005

A new formulation using compact higher-order finite differences is used to compute the propagation of a sound pulse in a pipe. The sound is generated by the arbitrary motion of a piston, and the pulse is free to radiate at its open end. After many reflections, conventional finite differences suffer severe phase distortion, which results in a scrambled signal. The new formulation is shown to maintain phase integrity. An expression for the open-end impedance that is appropriate for transients is used to compute the farfield radiation.
Comparison of four high-precision pitch extraction methods
Authors: Liang Haixiang , Titze Ingo R.
Published: October 2005

The accuracies of four pitch extraction methods are introduced and compared for high-precision perturbation measurement. They include combinations of peak-picking, zero-crossing, and waveform-matching strategies. The effects of sampling frequency, signal-to-noise ratio, pitch frequency, and signal modulation on the accuracies are explored. It is shown that methods with the waveform-matching technique give the best results for most cases. For near-sinusoidal stimuli (e.g., EGG signals), the zero-crossing technique gives higher accuracy than the peak-picking technique. At a low signal-to-noise ratio, a higher sampling frequency does give better results for the waveform-matching technique, but the accuracy of the peak-picking method may reduce as sampling frequency increases. As the signal-to-noise ratio increases, the effect of sampling frequency on accuracy diminishes when interpolation is used. A variety of waveforms are currently being tested to check the suitability of these methods for different applications. [Work supported by NIH.]
Experimental comparison of standardized sound-power measurement procedures for fans
Authors: Neise Wolfgang , Holste Fredi
Published: October 2005

An experimental study is described in which the sound power of six fans of different designs was measured using three different standardized measurement procedures, i.e., the free-field method ISO 3744, the reverberation room method ISO 3741/3742, and the in-duct method ISO/DIS 5136. The one-third-octave sound-power spectra obtained using the free-field method and the reverberation room method show excellent agreement in the frequency range from 100–10 000 Hz. The sound-power spectra determined according to the in-duct method show higher levels than the other two methods in the frequency region of plane-wave sound propagation in the ducts. This is due to the reflection of the sound waves at the fan inlet or outlet when the duct is removed. In the frequency range of high-order mode sound propagation, the in-duct sound-power levels are lower than the free-space levels. So far, there is no definite explanation for these differences; however, it is assumed that two frequency correction terms in the in-duct method need to be revised.
Means for quieting electric power transformers
Authors: Allen Clayton H.
Published: October 2005

An invention, now under development, comprises means that, without affecting the insulating or cooling capacity of the transformer design, create regions of low acoustic impedance at appropriate locations to facilitate the accommodation of oscillatory movement of the oil proximate to the source of any such movement. This significantly reduces the pressure fluctuations developed in conventional transformer designs where any movement of the core or windings must be accommodated by a combined movement of the tank walls and oscillatory flow of oil back and forth over relatively long and restricted paths from the expanding to the contracting regions. The physical concept and experimental designs will be discussed.
Pitch-synchronous analysis/synthesis using models of speech production
Authors: Gupta S. , Schroeter J.
Published: October 2005

Articulatory analysis/synthesis results, using a fixed frame length of 20 ms, have previously been reported [e.g., Schroeter, Larar, and Sondhi, J. Acoust. Soc. Am. Suppl. 1 82, S54 (1986)]. There, the Ishizaka/Flanagan self-oscillating two-mass model was employed to generate the glottal excitation. It was found, however, that this model causes the analysis-by-synthesis procedure to make a trade-off between pitch accuracy and match of spectral tilt. In this paper, a pitch-synchronous scheme using a parametric model of the time derivative of the glottal area function is presented. As with the two-mass model, the glottal flow is computed taking into account the current tract input impedance (acoustic source-tract interaction). Vocal-tract optimization, too, is done pitch synchronously. For this purpose, an improved articulatory codebook is searched for an optimal time sequence of start-up shapes. In the codebook search, a modified cepstral distance measure assures a good spectral match, and a properly chosen geometric cost function provides tract shapes that vary smoothly over time.
Amplifying musical nuance
Authors: Puckette Miller
Published: October 2005

A technique for computer music accompaniment of human instrument players is described, which emphasizes the use of control and sound information from the player to affect the computer's response. The intensities, microtuning, or timbre of certain notes can become parameters in sound synthesis, or the sounds themselves can be transformed by the computer. Alternatively, the player can play the computer as a keyboard instrument, with the computer supplying hidden parameters to the notes. The computer must follow the player's progress through the score, carrying out its various tasks in the desired places. Allowance must sometimes be made for notes coming in a nonpredetermined order. A multiprocessor currently under development at IRCAM for realizing these algorithms is described, as well as an example from a recent piece of music using them.
Active techniques for the suppression and reproduction of sound fields
Authors: Nelson P. A. , Elliott S. J.
Published: October 2005

The active suppression of unwanted sound and the reproduction of a desired sound field are very similar problems. Recent work on the active control of sound has successfully used multichannel adaptive filters in the feed-forward control of periodic and quasiperiodic low-frequency sound in aircraft [S. J. Elliott et al., J. Sound Vib. 128, 355–357] and automobiles [S. J. Elliott et al., Proc. Inter Noise '88 2, 987–990 (1988)]. The essence of the approach can be extended to deal with temporally random sound fields generated by multiple primary sources. The necessary extension of the existing theory will be described and some practical applications of the technique will be discussed. The same theory will also be shown to provide an appropriate framework for dealing with problems in multichannel sound reproduction. In particular, the formulation of the problem allows the specification of the optimal inverse filters that give the minimum mean-square error in reproducing a sound field recorded at multiple points. Some experimental results will be presented from the implementation of this approach in the two-channel case by Hamada et al. [Proc. IEEE Workshop on Applications of Signal Processing to Audio and Electroacoustics (1989)].
Hands-free telephone using compact echo cancelers and voice-switched attenuators
Authors: Ohga Juro , Masuda Hiroyuki , Fujii Kensaku , Sakai Yoshihiro
Published: October 2005

An all-in-one type hands-free telephone set was constructed by using a single chip digital signal processor integrated circuit (DSP IC). It includes a compact acoustic echo canceler, a sidetone echo canceler, and voice-swilched variable attenuators. An echo canceler whose length is only 16 ms (128 taps for an 8-kHz sampling) can suppress the power of an impulse response of the loudspeaker-microphone acoustic coupling path by more than 15 dB, because the major part of the path for an all-in-one telephone set is due to short direct paths. Most of the sidetone can also be suppressed by more than 20 dB by using an echo canceler of 8-ms length. A speech circuit including these echo cancelers and conventional voice-switched variable attenuators was composed of only one medium-performance DSP IC (75-ns machine cycle, 2K words of ROM and 512 words of RAM, and an additional 1000 ASIC gates}, CODEC IC's, and a few analog IC's. Complete simultaneous conversation is feasible with this hands-free telephone circuit because the voice-switched attenuation could be reduced to 10 dB or less.
Feature classification and related response in a real-time interactive music system
Authors: Rowe Robert
Published: October 2005

Cypher is a real-time interactive music system that has two halves: a listener and a player. The listener listens to and analyzes external musical input. The player uses various algorithmic techniques to produce new musical output. The two halves are each hierarchical, where higher levels correspond to longer spans of time. The listener classifies for the player features detected in the input and their behavior over time, and the player uses this information to produce music in response. Features characterized include speed, density, harmony, and duration. A graphic interface allows the user to specify relations between feature classifications and types of response. Collections of relations can be saved and recalled during performance by a score orientation section that tracks human performance and executes state changes at predetermined points in the score. Cypher plays composed music in a manner that is sensitive to live human performance cues. It is able to analyze and respond creatively to unknown music. Finally, it can compose without input, using algorithms to either transform remembered material, or generate new musical output.
Musical performance by the handicapped generated from bioelectric signals
Authors: Lusted Hugh S. , Knapp R. Benjamin , Nagler Joseph
Published: October 2005

Recently, the use of bioelectric signals to generate MIDI was reported [H. S. Lusted and R. B. Knapp, J. Acoust. Soc. Am. Suppl. 1 84, S179 (1988)]. Currently, the Biomuse system is being developed for use by movement-impaired individuals to produce music from standard MIDI instruments. The system detects bioelectric signals that are then analyzed for specific intensity and spectral characteristics, and then mapped to MIDI output commands to produce desired effects from a synthesizer. The system can utilize the electrical signals from muscle (EMG), brain activity (EEG), and eye movements (EOG). Through the use of flexible front end software, the Biomuse can accommodate the needs of many diverse populations of handicapped users. In so doing, the Biomuse will open doors to independent music making and renewal of the creative process. A quadriplegic user, for example, can utilize residual upper extremity EMG and eye movements to directly control various MIDI parameters in order to produce synthesizer sounds or access the functions of PC-based software. Therapeutic interactions using this technology can help people to overcome barriers and lead richer and more productive lives.
Decomposition of the farfield form function for studying the characteristics of an insonified object
Authors: Yen Naichyuan , Dragonette Louis R.
Published: October 2005

The characteristics of an insonified object are generally present in the signal carried by the returning scattered wave. Because an echo contains only a partial result of the wave interaction with a material structure, the inverse acoustical scattering process is an ill-posed mathematical problem that may not have unique solutions. However, by decomposing the normalized echo signature (the form function), certain features that appear in the joint time and frequency domains can be exploited to relate the scatterer's acoustical signature to its structural response. The approach of the form function decomposition is based on the frequency domain Wigner distribution function formulation. A computer algorithm extended from image processing techniques is then implemented to depict the numerical results in a two.dimensional (t vs ω) display. From the interpretation and understanding of scattering phenomenon, the physical parameters of the scatterer can be extracted from the graphical representation. Examples from numerically simulated models and laboratory measurements are illustrated for estimating the general physical size and the corresponding elastic properties of the insonified object.
High-frequency acoustic scattering from sinusoidal and doubly periodic ellipsoidal surfaces with a Dirichlet boundary condition: Numerical results
Authors: Smith Judy , Bishop Garner C.
Published: October 2005

Numerical results are obtained for exact and approximate solutions for the scatter of a plane wave from sinusoidal and doubly periodic ellipsoidal surfaces with a Dirichlet boundary condition. The farfield is obtained as an exact solution to the Helmholtz-Kirchhoff integral, and the surface field is obtained as an exact solution to Fredholm integral equations of the first and second kinds and as an approximate solution to the Fredholm integral equation of the first kind. Numerical calculations are performed to determine the accuracy of approximate techniques, the effects of geometric parameters and surface roughness type on the scattered field, and the dependence of the surface field on the type of Fredholm integral equation.
Sound radiation from cylinders: Modal analysis effect of curvature, and guidelines of noise reduction
Authors: Guyader Jean-Louis , Laulagnet Bernard
Published: October 2005

The paper will present a review of works by the authors in sound radiation from a cylindrical shell including theoretical predictions and experimental results. The present analysis of shell vibroacoustic behavior essentially deals with global quantities like power radiation, shell quadratic velocity, and radiation factor; however, the farfield directivity pattern and nearfield pressure, velocity, or intensity can be calculated. The theoretical model is a finite baffled cylindrical shell, immersed in light or heavy fluid, excited by driving point forces. Ring stiffeners and the viscoelastic coating layer can be taken into account. The calculations use the in-vacuo modal basis of the shell without stiffeners to expand shell displacements and boundary pressure, and the fluid loading is introduced by modal radiation impedances. Numerical implementation requires truncation of modal expansion, and criteria are necessary to select the modes governing vibroacoustic phenomena. This was established [B. Laulagnet and J. L. Guyader, J. Sound Vib. 131, 3 (1989)] and will be used to explain peaks of power radiation and critical frequency phenomena for light and heavy fluids. Examples of numerical convergence will conclude this point. The effect of curvature on sound radiation is known to be strong below the ring frequency as the membrane effect dominates the flexure. To put this tendency in concrete form, radiation from plates [A. Berry, J. Nicolas, and J. L. Guyader (submitted to J. Acoust. Soc. Am.)] will be compared with that of shells of same thickness, material, and area. Cases of stiffened and unstiffened plates and shells will be shown. Numerous industrial structures, for example in the aerospace or marine fields, can be modeled by a stiffened cylinder. In these fields, radiated noise presents a very important problem and therefore methods of minimizing it are of interest. To achieve this goal, understanding the influence of stiffeners, force location and direction, damping, and, for a heavy fluid, the viscoelastic coating layer, is fundamental. The coating effect was studied under the assumption of locally reacting stiffness [B. Laulagnet and J. L. Guyader (submitted to J. Am. Soc. Mech. Eng.)] and with three-dimensional elasticity. Other parameters were examined previously [B. Laulagnet and J. L. Guyader provisionally in J. Sound Vib. 137 (2) (1990)]. A synthesis of the main tendencies will be presented giving some guidelines of noise reduction. To conclude the paper a comparison between theoretical prediction and experiment will be shown in cases of stiffened and unstiffened shells radiating in air. In general, the agreement is quite satisfactory; however, for thin unstiffened shells, resonances of shell internal volume, neglected in the theory, are clearly involved in the power radiation phenomenon. [Work supported by D.R.E.T. and CERDAN, Ministère de la Défense, France.]
Triaxial acoustical characteristics of submerged cylindrical shells
Authors: Sandman B. E. , Harari A.
Published: October 2005

Cylindrical shells by the nature of their curvature exhibit coupling of extensional and flexural wave fields. This coupling produces unique characteristics when the shell is dynamically excited and subjected to acoustic radiation loading due to the interaction with a surrounding infinite fluid field. This paper outlines the governing equations of motion for the cylindrical structure and surrounding medium. The results of the coupled equations are presented in terms of acoustic power transmission. The acoustic power quantifies radiation loss, structural loss, and input power. Results are presented that describe the radiation efficiency of cylindrical shells under radial, axial, and circumferential point excitation. Parametric studies of structural loss, circumferential stiffening, and directional excitation are examined relative to the radiated acoustic power created in the farfield. A brief comparison of the theoretical calculation with an experimental result is presented as a validation benchmark for the theoretical calculations.
Transient response of fluid-loaded shells of revolution
Authors: Stepanishen Peter R.
Published: October 2005

The transient response of fluid-loaded shells is important from both a radiation and a scattering viewpoint. Numerous methods, which include integral transform and doubly asymptotic methods have been developed to address such problems; however, in general the integral transform methods are restricted to specific simple geometries and the doubly asymptotic methods are approximate in nature. During the past several years new time-domain methods of addressing transient radiation and scattering from heavily fluid-loaded shells of revolution have been developing. These methods are based on the marriage of finite element methods for shell analysis and boundary element methods for acoustic field analysis. A brief review of previous methods of addressing the transient problem will be presented. An overview of efforts in this area will then be presented including both past and present studies. Numerical results for several types of shells will be presented and discussed. [Work supported by ONR.]
Ray acoustics models for sound radiation from vibrations of fluid-loaded circular shells
Authors: Pierce Allan D. , Manley Martin G.
Published: October 2005

A theory of sound radiation by shells is developed using the canonical model of an elastic coaxial cylinder, with inner radius R − 12h and outer radius R + 12h immersed in a compressible fluid. As can be constructed from the earlier work of Pochhammer, Mindlin, Herrmann, Miklowitz, Greenspon, Veksler, and others, this dynamical system admits guided wave solutions of constant angular frequency ω, in which all of the appropriate field variables vary with azimuthal angle θ and axial coordinate xthrough a common factor Eih einθ Admissible solutions that do not grow at large positive x or at large r are governed by a dispersion relation of the form F(ω,kv, n) = 0, where F is a highly transcendental function involving Bessel and Neumann functions of various orders and with various arguments. In the present paper, n is not required to be an integer and kv = n/R is identified as another wavenumber component. In various limits, all with h/R ⩽ 1, simpler analytic approximations for possible dispersion relations result, which can be cast in the form k = k (ω,θλ), where wavenumber k for phase propagation in direction θλ has a positive non-zero imaginary part, which is interpreted in terms of sound radiation into the surrounding fluid. For length and frequency scales relevant to structural acoustics, the most important dispersion relations are those that correspond to longitudinal, shear, and flexural waves on plates, only with corrections to account for fluid loading and curvature. All modes radiate sound. [Work supported by ONR and by the William E. Leonhard endowment to Penn State Univ.]
Some interesting acoustic signals from backscattered echoes of submerged elastic objects
Authors: Werby M. F. , Gaunaurd G. C.
Published: October 2005

Acoustic signals scattered from submerged elastic targets have produced interesting backscattered signals in the appropriate frequency region particularly because of the presence of resonances. Considerable work has been done for spherically and cylindrically shaped objects out to moderate frequencies for both solids and shells. Only recently, however, have researchers been reporting on results for elongated objects such as spheroidal solids and shells. Further, the higher frequency region for spheres has not been investigated extensively. Reported on here is a series of calculations that are characteristic of elongated targets or of spherical shells at the higher frequency region. Some of the results discussed involve bending resonances due to obliquely incident plane waves on elongated objects and their relation to flexural resonances of beams; classes of resonances that are related to waves creeping along the longest and shortest meridians of a spheroid; flexural resonances (Ao resonances) for shells in the time domain at coincidence frequency, and high-frequency thickness effects when scattering from shells and their prediction based on flat plate theory. In the process a new background for elastic shells will be utilized. Several numerical examples will be shown.
Rigorous spectral theory for azimuthally dependent source-excited fields in a fluid in the presence of a thin elastic spherical shell: Formulation and high-frequency asymptotics
Authors: Felsen L. B. , Ho J. M.
Published: October 2005

A general theory, in terms of complex wavenumber spectra, has been developed for point-source-excited wave phenomena associated with thin elastic spherical shells with exterior and(or) interior fluid loading, and there has been performed a high-frequency asymptotic reduction of the new rigorous spectral integral forms that quantifies a ray theoretic interpretation and construction of the results [L. B. Felsen and J. M. Ho, J. Acoust. Soc. Am. Suppl. 1 86, S5 (1989)]. By appealing to the rotational symmetry with respect to the polar axis passing through the source and the center of the shell, the problem has been azimuthally independent. For excitation mechanisms without rotational invariance, produced either by direct source configurations or by induced sources generated from truncations or other perturbations of the spherical shell prototype, it is necessary to treat the fully three-dimensional phenomenology. Such general source distributions can be synthesized by contributions from arbitrarily placed point sources in the fixed global spherical coordinate frame. The previous analysis is extended accordingly. It incorporates the full azimuthal, meridional, and radial dependence of the field, formalized most generally by a new double spectral integral representation based on a continuous associated Legendre transform for meridional dependence, and Fourier transform for azimuth. High-frequency asymptotics produce the corresponding generalized forms that describe skewed ray fields with incident, reflected, and shell-guided constituents [J. M. Ho and L. B. Felsen, following abstract]. Special cases include ring source excitation with continuous azimuthal linear phasing, and linearly phased point source ring arrays. [Work supported by ONR and DTRC.]