bluuebunny/crossref_metadata_2025 huggingface dataset:
An eigenvalue problem relating to reactive acoustic power and acoustic radiation
Authors: Chen Pei-Tai , Ginsberg Jerry H.
Published: October 2005

The acoustic power radiated for mono-frequency vibrations from submerged bodies can be calculated by evaluating one half of surface integral of surface pressure multiplying the complex conjugate of normal velocity. The real part of the integral is the radiated power from bodies, whereas the imaginary part, or the reactive power, is seldom used in the study of surface acoustics. The present study is to explore the reactive power in the connection of dynamic characteristics for surface pressure and normal velocity. This problem is considered by investigating the quadratic expressions of complex surface acoustic power as discretizations are introduced on the surface. A reciprocal principle for acoustic medium is employed to assert the symmetry of the matrices associated with the quadratic forms. Correspondingly, the investigation of surface acoustics turns into the examination of symmetrical eigenvalue problems associated with the matrices. Eigenvalues are identified as the indication of phase differences between surface pressure and normal velocity in the corresponding eigenvectors. These eigenvalues are then used to classify the modes for strong or poor radiations. The triple quantities, which are eigenvalues, modal modes for surface pressure, and normal velocity, provide a full description of dynamic characteristics for submerged bodies. [Work supported by Chinese National Science Foundation, NSC 82-0209-E-019-063 and United States Office of Naval Research, Code 1132-SM.]
Modal radiation from a nonbaffled rotating circular plate in light fluid medium
Authors: Beslin Olivier , Nicolas Jean
Published: October 2005

A circular plate vibrating on resonance and rotating with a uniform angular speed is considered. In a moving frame (rotating with the plate), the plate motion can be expressed as the superposition of two propagating circular waves, traveling in opposite angular directions and having the same angular wave number and angular frequency. In a fixed frame (relative to the surrounding medium), the plate motion is still seen as two propagating circular waves, having the same angular wave number as in the moving frame. However they have two different angular frequencies, depending on the rotating speed. The modal radiation of a rotating plate can then be expressed in terms of radiation from propagating circular waves that allow a better understanding of the physical phenomena induced by the rotation. Radiation from propagating circular wave is computed using an integral formulation: The acoustical velocity is imposed on the plate area. The jump of pressure across the plate area is computed using a discretization method based on an approach proposed by Filipi [J. Sound Vib. 54(4), 473–500]. The influence of the rotating speed of the plate and the angular wave number of the mode on the radiation factor is discussed.
Interpretation of the reactive instantaneous acoustic intensity, and its relationship to energy transfer in the time domain
Authors: Burns Thomas H. , Thompson William , Burroughs Courtney B.
Published: October 2005

The instantaneous acoustic intensity is a spatially dependent vector that describes the power flow through a point in space as a function of time. It consists of both active and reactive components. For time harmonic sources, both components oscillate in time. In the past, multiple reactive intensity vectors have been simultaneously displayed in the form of vector fields. Each vector represented the maximum value the reactive intensity obtained at that point in space; it did not represent a time average since the reactive intensity, unlike the active intensity, time-averages to zero. Although plots of the amplitude of the reactive intensity are useful for localization and field characterization, they do not contribute to an understanding of energy transfer in the time domain. A vector field suggests that each vector obtains its maximum value at the same time instant, which is not true. The purpose of this presentation is to clarify conventional interpretations of the reactive intensity. This will be accomplished by analyzing the expression for the instantaneous acoustic intensity, interpreting traditional reactive intensity vector field plots, and using this information to make conclusions concerning energy transfer in the time domain. [Work supported by International Jensen, Inc.]
Far-field sound radiation study of a steel beam with a T bar by k-space filtering
Authors: Wei Ruey-Chang , Mann J. Adin
Published: October 2005

By using the concept of the radiation circle, simulations were done to investigate the contributions to the far-field radiated sound from different waves in the structure. The far-field radiated sound is from the waves with wave numbers inside of the radiation circle, which include evanescent and propagating waves. The simulations show the important role of the evanescent wave in the sound radiation. K-space filtering involves removing energy in spatial wave numbers that are outside the radiation circle, leaving only the energy that radiates to the acoustic far field. The application of the k-space filter can be used to locate the area of a structure that radiates sound to the far field. The experimental results for the steel beam with a welded T bar shows that the T bar radiates significant sound to the acoustic far field, even though the size of the T bar is small. The k-space filtering is proved to be very useful in the study of sound radiation for a structure with discontinuities or inhomogeneities. [Work supported by ONR, Grant No. N00014-93-1-0493.]
Measured phase-speed variation in a steel beam with a T bar
Authors: Wei Ruey-Chang , Mann J. Adin
Published: October 2005

Residual stress is produced by the welding process that attaches a T bar to a steel beam. A spatially distributed residual stress was built into the plate equation, and the modified wave numbers are solved for. The simulated data show that the residual stress has significant effects on the wave numbers and amplitudes of the waves in the structure. Experimental investigations were conducted on a HY-80 steel beam with a welded T bar. Using a wave-speed tracking technique, the phase speed and arrival time of propagating waves can be computed, and the reflection coefficient at a boundary can be calculated. The phase-speed change over the distance traveled by the wave is detected by this technique as an indication of inhomogeneities in the measured structure. Clear phase-speed decreases were observed near the T bar. The decrease of phase speed around the T bar is a% to 7%, and the reflection coefficient of the T bar is around 0.16. [Work supported by ONR, Grant No. N00014-93-1-0493.]
The radiation modes of baffled finite plates
Authors: Currey Noelle , Cunefare Kenneth A.
Published: October 2005

The modal-style approach for representing the exterior radiation characteristics of structures generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator in the exterior domain of the structure. The choice of basis functions for the modal representation is arbitrary, though use of the natural modes of structural vibration tends to provide some physical insight. The acoustic modes are found through an eigen analysis or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. The dependency of the radiation efficiencies and mode shapes on the number of degrees of freedom permitted in the derivation of the radiation operator is investigated for a baffled finite rectangular plate. The accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator, with the least efficient modes converging slowest. Further, the rate of convergence is dependent on the particular basis function selection. The convergence behavior has significant impact on those applications of the exterior acoustic modal approach that seek to exploit the least efficient modes. [Work supported by NASA GSRP program.]
Acoustic applications of fiber optic Bragg gratings
Authors: Brown David A. , Zhang Qin , Reinhart L. J. , Morse T. F.
Published: October 2005

Optical fiber Bragg gratings are made using an Excimer KrF laser and a phase mask to induce a periodic variation of the index of refraction of the core of the optical fiber. This narrow-band reflector can be used as an absolute acoustic or static pressure sensor by monitoring the wavelength of the light reflected in the fiber. Also, fiber optic Bragg gratings written at different wavelengths provides a new method for multiplexing of optical fiber based acoustic and nonacoustic sensors. This talk will present results on the fabrication of optical fiber Bragg gratings, sensors based on gratings, and interrogation schemes. [Work supported by the DoN—Program Executive Office—ASTO, NSF, and AFOSR.]
Acoustic intensity and structural power flow methods for scientific visualization
Authors: McDowell Donald J.
Published: October 2005

Interpreting large data sets that result from the application of high-resolution computational and experimental methods to the solution of structural acoustics problems is a difficult, time-consuming task. The use of scientific visualization techniques expedites the process of data interpretation by condensing these large quantities of data into small packets of visual information. As generally applied, scientific visualization techniques are used to produce color coded plots of the acoustic pressure magnitude and of the structural motion. The focus of this paper is to show that the vector quantities, acoustic intensity and structural power flow, are very useful for the visualization of the complex phenomena that result when a vibrating structure interacts with its surrounding acoustic fluid. Results will be shown for applications to both two- and three-dimensional data sets resulting from the analysis of acoustic radiation from a submerged elastic shell. Algorithms for the required computations will also be given.
Animation of the transient motion and radiation of a fluid-loaded membrane
Authors: Rollow Douglas , Swanson David C.
Published: October 2005

A fluid-loaded membrane, excited on the surface with an impulsive force, is modeled and animated to visualize the surface motion and resulting radiated field. The system is represented by a linear model of structural modes coupled to an unbounded light fluid, typical of a thin baffled Mylar membrane in air. The effects of fluid loading are found by analytical methods and a boundary element application program, and the field is found by direct use of the Rayleigh integral and FFT methods. The structural motion is also shown in the wave-number domain for an understanding of the coupling of power to the far field. [Work supported by the Exploratory and Foundational Fund, Applied Research Laboratory.]
Experiences in three-dimensional visualization of near-field acoustical holography data sets
Authors: Washburn Karl B. , Williams Earl G.
Published: October 2005

Data collected and processed in near-field acoustical holography are inherently multi-dimensional. The data span two spatial dimensions (or their transform-space counterparts) and a dimension in either time or frequency, and the quantities of interest within those spaces also represent dimensions. Various processes, such as multiple projections or time-frequency transforms, can increase the dimensionality even further. When powerful, inexpensive graphics display systems became available, they brought the capability for viewing at least four dimensions simultaneously (two in the screen space, one implicit in space via depth cues, and one in color). A public domain package called ‘‘BoB’’ (for ‘‘Brick-of-Bytes’’), provided by the Army High Performance Computing Research Center (AHPCRC), was used to view large blocks of holographic data in four dimensions. This work examines our experiences in trying to explore holographic data using this form of visualization. It was found to be inferior in comparison to currently used forms of visualizing data, in particular, mosaics of false-color plots. Reasons for this apparent lack of success will be discussed.
Solutions of coupled-mode equations with a large dimension in underwater acoustics
Authors: Stotts S. A. , Knobles D. P. , Levinson S. J. , Mitchell S. K.
Published: October 2005

A new fast and efficient acoustic propagation model is introduced which solves the coupled-mode differential equations in underwater acoustics for range-dependent, fluid-layered, ocean environments. The coupled range equations are first modified and then solved using the Lanczos method, an approach recently introduced in nuclear theory. This method has been successfully applied to the description of the nuclear response of heavy atomic nuclei in the giant resonance region of the energy excitation spectrum [T. Udagawa and B. T. Kim, Phys. Rev. C 40, 2271–2275 (1989)], as well as, other physical processes in low to medium energy in nuclear theory. The efficiency of this method permits the solution of coupled mode equations with large dimensions. The eigenvalues and depth-dependent mode functions are quickly obtained using an Airy function approach, which allows the range-dependent mode-coupling matrices to be evaluated analytically. The validity of the model is demonstrated, and example calculations are presented. [This work is supported by the Office of Naval Research (ONR 4530) Project RO35K01.]
Parametric study and sensitivity analysis of plane-wave reflection from poroelastic seafloor
Authors: Badiey Mohsen , Cheng Alexander , Jaya Indra
Published: October 2005

Acoustic wave reflection from seafloor is very sensitive to the sediment properties. Assuming a plane wave reflected from an homogeneous but anisotropic seafloor, a parametric study is conducted for seabed properties such as shear and bulk modulus, permeability, porosity, etc. It is demonstrated from the numerical solution by the propagator matrix method that the porosity is the most sensitive parameters that affects the reflection coefficient and bottom loss. The effect is most pronounced at low grazing angles. The numerical evidence is further supported by an asymptotic analysis of the analytical expressions of sediment wave velocity and the reflection coefficient at the water–sediment interface, for homogeneous, isotropic material. The numerical study is then extended to inhomogeneous sediment and the sensitivity to different layering patterns is examined. a)Present address: Office of Naval Res., Ocean Acoust. Prog. Code 324 OA, 800 N. Quincy St., Arlington, VA 22217.
Time reversal transformation in linear acoustics and application in a cross borehole prospect
Authors: Yu Shoumian , Yu Tian , Liu Yinbin
Published: October 2005

A time reversal transformation transforms a process into its inverse, and is stated mathematically by the transformation of time t→t′=−t. The velocity potential Φ(r,t) and its Fourier transform φ(r,ω) are transformed into Φ′(r,t′)=−φ(r,−t) and φ′(r,ω)=−φ*(r,ω), respectively. It is proved that the time reversal of a source is a receiver and vise versa. The signal received by a receiver at r2 in the field φ(r,r1;ω) produced by a source at r1 is defined by φ̄(r2,r1;ω)=ℱds⋅φ(r,r,ω)∇φ′(r, r2ω), where the surface integral is taken around the receiver. Here, φ̄ is proportional to the power absorbed by the receiver. This theory leads to an important assertion that for a reducible transducer, if the frequency spectrum is f(ω) and the directional factor is D(θ,φ) when it is used as a source, then the frequency response and directional factor when it is used as a receiver must be f*(ω) and D*(θ,φ), respectively. The theory is applied to a cross borehole prospect. The radiation pattern produced by a source borehole and that received by a distant receiving borehole are obtained and plotted for comparison. [Work supported by NSFC.]
Hot topics in engineering acoustics: New acoustic products and processes
Authors: Busch-Vishniac Ilene J.
Published: October 2005

Engineering acoustics is the study of products and processes that are directly related to sound or that use sound as a tool. This talk discusses some of the exciting advances in acoustic products and processes in the last few years. New acoustic products which are discussed include solid-state acoustic sensors and actuators, improved hearing aids, and thermoacoustic refrigerators and engines. Solid-state acoustic transducers are miniature sound sensors and sources which are made using silicon (or another semiconductor) and fabricated using VLSI technology. Such transducers offer the opportunity for mass production and extreme miniaturization. Hearing aids are devices intended to present amplified sound to hearing impaired individuals. Recent advances in their signal processing have made dramatic improvements in the quality of sound being presented to the wearer. Thermoacoustic refrigerators and engines are devices which use sound waves to achieve ‘‘pumping.’’ They offer the advantages of making it possible to eliminate moving parts, and to eliminate use of environmentally unfriendly chemicals. There have also been exciting advances in acoustic processes in recent years. This section of the talk will focus on ultrasonic machining, in which ultrasonic vibration of a machine tool is used to achieve precise and relatively rapid material removal.
Hot topics in bioresponse to vibration and ultrasound
Authors: Weisenberger Janet M.
Published: October 2005

New developments in a number of research areas have led to significant advances in bioresponse to vibration and ultrasound. The present paper will focus on work in three of these areas. First, a number of researchers have investigated changes in functioning of tactile mechanoreceptors as a function of the aging process. This work has come from a variety of approaches, including physiological measurements, psychophysical studies, and perceptual experiments. The convergence of these areas of study has led to a substantial increase in our understanding of the effects of aging in the tactile system. Second, recent technological advances in the development of tactile displays for basic science and virtual sensing applications have led to the construction of displays that permit the presentation of stimuli for differential stimulation of mechanoreceptive populations and investigation of spatial resolution abilities. Other displays have been designed to provide feedback about object shape, contact force, and surface texture for operators in telerobotics and virtual environments. These displays attempt to provide a veridical experience for the operator, and current research focuses on determining optimal strategies for encoding stimulus parameters. Finally, recent work in biological response to ultrasound has yielded exciting progress in lithotripsy, the destruction of kidney stones via ultrasonic radiation, in hyperthermic applications of ultrasound, and in the development of medical criteria for appropriate administration of ultrasound in medical applications.
Hot topics in musical acoustics: Wind-instrument response in the time domain
Authors: Keefe Douglas H.
Published: October 2005

Physical modeling of sound production in the time domain has recently emerged as a useful tool for the study of musical wind instruments, with applications to instrument design and computer music synthesis. The air column response is described by a reflection function (or impulse response), defined at the location of sound regeneration in the mouthpiece or double reed. Thus experimental measurements of instrument response directly in the time domain are of great interest. One approach uses a single source and single microphone mounted in a long cylindrical tube coupled at one end to the air column. Singular value deconvolution is first used to generate an optimal band-limited impulse, and again used to calculate the reflection function from the incident and reflected pulses [J. Agulló etal., SMAC, Stockholm (1993)]. A second approach allows insertion of the source/microphone directly into the mouthpiece, thereby eliminating the need for the long tube. This may be advantageous for measurements on instruments and in applying the technique in hearing. A calibration step is added that involves measurements on a single cylindrical tube of known dimensions. Results on various wind instruments will be presented. [Work supported by NIH.]
A study on radiation pattern and radiation efficiency of an upright piano soundboard
Authors: Dérogis Philippe , Caussé René
Published: October 2005

In this study, a modal analysis of the soundboard of an upright piano with strings mounted was performed. The measurements of the frequency response functions and the use of modal testing software have allowed us to find the eigenfrequencies and the mode shapes. The results agree for the most part with earlier measurements [I. Nakamura, ‘‘The vibrational character of the piano soundboard,’’ Proc. 11th ICA Paris, 385–388 (1983)]. Indeed, below 300 Hz the mode shapes are almost the same for an isotropic rectangular plate. However above 300 Hz, they become more complicated. These results were used to compute the acoustic field resulting from the vibrations of the soundboard by calculating numerically the Helmholtz Huygens integral. Then the radiation pattern curves obtained were compared with measurements and with two simple models (isotropic baffle plate and isotropic plate radiating on one side). The integration of the calculated acoustic field was performed in order to determine the radiation efficiency of the soundboard. Finally, the radiation efficiency as a function of the plate characteristics (size, stiffness) was computed using the models above.
Time-domain simulation of sound production in brass instruments
Authors: Adachi Seiji
Published: October 2005

Sound production in brass instruments has been formulated physically, including two different models of lip vibration; the perpendicular model, where lips strike laterally to the direction of the air flow, and the ‘‘swinging door’’ model, where lips execute outwardly rolling motion. The above formulation was used to carry out time-domain simulation. As a result, self-excitation of the brass instrument was found to be possible with both of these lip models. By changing the lip eigenfrequency, sustained oscillations near at least the first through the eighth resonant impedance peaks of the instrument were realized. The simulated sound was shown to have variety in the harmonic structure accompanied with pitch and loudness variations as is seen in sound the natural brass instruments produce. Unusual regimes of oscillation were also obtained; the pedal tone, whose fundamental does not participate in its sound production, a tone octave below the third impedance peak, whose odd harmonics do not contribute to the regime of oscillation, and a multiphonic, which is an oscillation perceived having two fundamentals simultaneously.
A history of hearing protection in the United States
Authors: Moritz C. T. , Bruce R. D.
Published: October 2005

During the late 1800s it was known that exposure to high sound levels could lead to permanent hearing loss. Although several U.S. patents were awarded for hearing protective devices in the 1800s, hearing protectors were not generally available until the 1920s. These devices were marketed to help people cope with the high sound levels of the ‘‘big city,’’ not to protect against hearing loss. It was not until World War II that hearing-protective devices became generally available for industrial workers. This paper will present an overview of the major developments in hearing protection in the United States from the 1920s to the present and discuss the forces behind their development. Emphasis will be placed on the availability of different types of hearing-protective products to industrial workers and consumers.
Protection of the ear from noise: Limiting factors
Authors: VonGierke Henning E.
Published: October 2005

A theoretical and experimental study with this title was undertaken in the 1952–1953 period and published in the Benox Report [‘‘An Exploratory Study of the Biological Effects of Noise,’’ Univ. of Chicago (1 Dec. 1953) also Am. Indust. Hygiene Assoc. Q. 15(1) (March 1954)] to support protection from increasing noise levels in aviation and industry. The factors explored, quantified, and analyzed by means of an analog circuit of the head-ear-protector system appear to be still the limiting factors in light of subsequent, more detailed investigations. This historical review will also mention later experiments in our laboratory on the bone conduction threshold in a free sound field (1959), on the development of extra large and extra small sizes for the V-51R earplug (1956), on improving ear protector effectiveness beyond the passive limits by static pressure changes [U.S. patent 2,719,523 (4 Oct. 1955)], and early experiments on active noise cancellation.
Binaural interference and grouping
Authors: Shackleton Trevor M.
Published: October 2005

The threshold interaural time difference (ITD) of a target tone increases in the presence of spectrally remote distractor tones [e.g., R. H. Dye, J. Acoust. Soc. Am. 88, 2159–2170 (1990)]. It has been suggested that this is because ITD information is grouped across both target and distractor components [e.g., T. N. Buell and E. R. Hafter, J. Acoust. Soc. Am. 90, 1894–1900 (1991)]. If this is so, then the lateralization of the target should be shifted towards the lateralization of the distractor. Alternatively, the presence of a distractor could introduce extra discrimination noise, causing threshold ITDs to rise, but without affecting the target lateralization. Subjects reported whether a target tone presented with a variety of ITDs was perceived to the left or right of midline when a distractor tone was either not present, presented diotically, or presented with a supra-threshold ITD. The slope of the function relating the percentage of leftward responses to the ITD of the target decreased when a distractor was present (indicating a higher threshold). The functions were also shifted horizontally towards the ITD of the distractor. These results suggest that binaural interference results from grouping target and distractor components together. [Work supported by The Wellcome Trust.]
Binaural segregation of concurrent sounds involves within-channel rather than across-channel processes
Authors: Culling John F. , Summerfield Quentin
Published: October 2005

Four 150-Hz-wide noise bands, centered on (1) 225, (2) 625, (3) 975, and (4) 1925 Hz, represented the formants of whispered vowels. Presented simultaneously, the four bands formed a competing perceptual organization, interpretable as /i/+/open aye/ (bands 1 and 4 vs 2 and 3) or /u/+/backward eh/ (bands 1 and 3 vs 2 and 4). Listeners were encouraged to perceive a particular organization by presenting pairs of bands with different interaural delays (±700 μs) or with different interaural level differences (dichotically, one vowel to each ear). In control conditions, the four bands were presented with the same interaural delay (−700 μs) and monotically (left ear). Listeners were instructed to identify the vowel heard on the left. The nominal target vowel was presented at different gain levels relative to the competing vowel. Listeners identified the target more accurately than chance only when the vowels were presented dichotically or with a positive target gain. Thus listeners were unable to group the formants of concurrent, whispered speech sounds by common interaural delay. In contrast, a similar experiment found that identification was facilitated when the noise bands representing the target vowel were interaurally uncorrelated, while the competing vowel was diotic. This result is consistent with a within-channel mechanism for segregation, such as interaural cancellation.
Divided auditory attention with up to three sound sources: A cocktail party
Authors: Yost William A. , Sheft Stanley , Dye Raymond (Toby)
Published: October 2005

This study investigated listeners’ performance in a divided attention task involving up to three simultaneously occurring messages presented in a sound field and monaurally over headphones. Either NU-6 words or spoken numbers and letters were delivered over seven loudspeakers placed equidistance along the azimuth plane, 1 m in front of the listener. Each listener performed two tasks: a message recognition task in which the listener indicated all of the messages that he/she heard, and a message location task in which they indicated the spatial location of each message. In the sound field study, the messages were presented over either one, two, or three loudspeakers simultaneously. In the monaural study, a single microphone was placed at the location of the listener in the sound field and its output was fed to the right headphone of the subject seated in a sound proof room at a remote location. Both message recognition and location measures were compared for one versus two versus three simultaneous message presentations, and for sound field versus monaural presentations. The results will be discussed in terms of binaural processing and the cocktail party problem. [Work supported by AFOSR.]
Animated visualization of structural dynamics and acoustic radiation associated with immersed hull structures
Authors: Sartori Michael A. , Clark Joseph A.
Published: October 2005

It is important to develop visualization methods for comparing numerical predictions of large hull dynamics with whole scan experimental determinations because large quantities of detailed data must be examined in order to verify the consistency of the two results or to characterize significant differences. In this talk a variety of animated visualization methods based on the Explorer software package running on a visual processing computer will be described. Procedures followed to develop typical visualization programs will be explained. The methods will be illustrated with animated visualizations of hull dynamics data obtained both numerically and experimentally which show and compare surface pressures, velocities and intensities, slice views of the acoustic nearfield and 3-D radiation patterns. Examples of animation with respect to time, frequency and viewing aspect will be given. [Work sponsored by NAVSEA.]
Psychophysical results from electrical stimulation of hearing: Implications for understanding auditory processing
Authors: Shannon Robert V. , Zeng Fan-Gang
Published: October 2005

Psychophysical results in gap detection, forward masking, temporal integration, and modulation detection have been obtained in electrically stimulated listeners (both cochlear implant and brain-stem implant) as a function of stimulus intensity. The results indicate that temporal processing is similar in normal-hearing and implant listeners when the intensity scale is normalized. Recent loudness balancing and intensity discrimination experiments have demonstrated that loudness is coded by dual mechanisms depending on stimulus frequency. The loudness of low-frequency (<300 Hz) electrical stimuli is a power-law function of electrical amplitude and the mechanism is inferred to reside in the cochlear nucleus. In contrast, loudness of high-frequency stimuli is an exponential function of electrical amplitude with a more peripheral mechanism. By comparing temporal processing at low and high frequencies the processing order of loudness and timing information in the auditory system can be inferred. [Supported by NIH/NIDCD.]
Forward masking during intracochlear electrical stimulation: Models, physiology, and psychophysics
Authors: Eddington Donald K. , Rubinstein Jay T. , Dynes Scott B. C.
Published: October 2005

Interactions between nonsimultaneous stimuli presented on the same or different electrodes may affect the performance of cochlear implant systems. Single-unit models based on nonlinear nodes of Ranvier include three mechanisms whereby a subthreshold masker (STM) could affect the spike threshold of a following probe pulse: (1) stored charge, (2) sodium channel activation, and (3) sodium channel inactivation. Physiological (single-unit) recordings in cat show that the threshold for a single, monophasic cathodic probe is decreased with cathodic STMs and increased with anodic STMs. This anodic/cathodic asymmetry is qualitatively consistent with the model’s linear mechanism of stored charge. However, nonlinear sodium channel activation/inactivation are required to predict the effects quantitatively. Model, physiological and human psychophysical studies using biphasic (charge-balanced) stimuli also show asymmetries in the maskers’ effect on probe threshold. In human, (a) the maximum effect of a cathodic-phase-last masker is stronger than that of an anodic-phase-last (APL) masker, (b) the APL masker decreases probe threshold (in contrast to the model’s prediction), and (c) the APL masker’s effect remains significant after 3 ms while the model and physiological results show effects lasting less than 0.5 ms. Taken together, these studies suggest that the human psychophysical results cannot be explained solely by response characteristics of the auditory nerve. [Work supported by NIDCD.]
Speech perception and production results in children with multichannel cochlear implants
Authors: Osberger Mary Joe
Published: October 2005

The results from a number of studies in our laboratory will be presented to demonstrate the benefits that children with profound hearing impairments derive from multichannel cochlear implants. The performance of children with cochlear implants has been evaluated over time and compared to that of children who used conventional hearing aids, grouped according to unaided thresholds. Results showed that speech perception and production skills developed over a time course as long as 5 years in children with prelingual deafness who received multichannel cochlear implants. After roughly 3 years, the scores of prelingually deafened children with multichannel implants were higher than those of children with hearing aids with unaided thresholds of 101–110 dB HL and similar to those of children with unaided thresholds of 90–100 dB HL. New research directions involve examination of lexical effects on word recognition in multichannel implant users. Data suggest that pediatric cochlear implant users are sensitive to the acoustic-phonetic similarities among words, that they organize words into similarity neighborhoods in long-term lexical memory, and that they use this structural information in recognizing isolated words. [Work supported by NIH.]
Mathematical modeling of vowel perception by users of the Ineraid cochlear implant: Temporal and place-of-stimulation cues
Authors: Svirsky Mario A.
Published: October 2005

The Ineraid cochlear implant filters the speech spectrum into four frequency bands and delivers each signal to one of four electrodes in the cochlea. Higher frequency bands stimulate more basally placed electrodes. Ineraid users may recognize vowels using temporal cues, place-of-stimulation cues (such as amount of energy sent to each electrode) or a combination of place and temporal cues. A mathematical model is proposed to account for vowel perception by users of the Ineraid cochlear implant. The model is computationally similar to the one that was proposed for users of pulsatile cochlear implants [M. A. Svirsky and S. H. Svirsky, J. Acoust. Soc. Am. 92(4), 2415–6 (1992)], but the perceptual dimensions involved are different in the two cases. To test the model vowel identification data obtained with ‘‘conflicting cue’’ vowels was used [Dorman etal., J. Acoust. Soc. Am. 92(6), 3428–31 (1992)]. The model was run under three different assumptions: Ineraid users only employ temporal cues for vowel perception, they only employ place cues, or they combine temporal and place cues. Model output fit the data well only under the temporal/place assumption. This suggests that Ineraid users combine information from temporal and place cues in order to recognize vowels. [Work supported by NIH Grant No. R03-DC01721 and Contract No. N01-DC-2-2402.]
Electrode discrimination measures: Relationship with speech perception and clinical applicability of results
Authors: Collins Leslie M. , Zwolan Teresa A. , Wakefield Gregory H.
Published: October 2005

Results from previous experiments with multichannel cochlear implant subjects [Collins etal., Midwinter Research Meeting, Association for Research in Otolaryngology, February, 1994] have shown that removal of indiscriminable electrodes from subjects’ maps resulted in significant improvements in speech perception scores in some of the better subjects. The procedure used to evaluate electrode discrimination in this previous study lacked clinical applicability due to the amount of time required for data collection. In the present paper several measures of electrode discrimination, including an adaptive discrimination procedure, a pitch ranking procedure, and a paired comparison procedure are evaluated and compared. The clinical applicability of each procedure will be discussed as it relates to both efficiency and impact on mapping for improved speech perception, as measured by both open and closed set tests. In order to evaluate the effect of remapping on speech perception, information transmission analyses were performed on vowel and consonant confusion data from each subject. These data were obtained while subjects used a standard map employing all active electrodes, and while they used maps based on the results of each electrode discrimination procedure. [Research supported by NIH.]
Lexical influences on speech perception by children with multichannel cochlear implants
Authors: Kirk Karen I. , Osberger Mary Joe , Todd Susan L. , Robbins Amy M. , Riley Allyson I.
Published: October 2005

This study examined lexical effects on word recognition by children with multichannel cochlear implants. Based on computational analyses, word lists were constructed to allow systematic examination of the effects of word frequency, lexical density (i.e., the number of phonemically similar words, or neighbors), mean neighborhood word frequency, and word length. The percent of words correctly identified was significantly higher for lexically ‘‘easy’’ words (high frequency words with few neighbors) than for ‘‘hard’’ words (low frequency words with many neighbors). The percent of phonemes correctly identified did not differ between the ‘‘easy’’ and ‘‘hard’’ words, suggesting that phoneme scores do not accurately reflect word recognition. Word recognition scores were also better for multisyllabic than for monosyllabic words. These results demonstrate that children with multichannel cochlear implants systematically organize words in long-term lexical memory using processes similar to listeners with normal hearing. Lexical effects will also be examined on a longitudinal basis to determine if performance increases with implant use. [Work supported by NIH.]
Acoustic propagation in waveguides of variable thickness
Authors: Coury R. A. , Siegmann W. L. , Collins Michael D.
Published: October 2005

The parabolic equation (PE) method is an efficient approach for solving range-dependent ocean acoustics problems. Many types of range dependence have been considered previously, including variable sound speed, ocean depth, density, and other sediment parameters. Recently, interest has increased in problems involving waveguides with variable depths, for example, the case of a sloping ocean bottom that continues onto a beach. A new PE that allows for variations in the size of the waveguide has been formulated using energy conserving techniques. In addition, environments where this PE has validity are identified and discussed. Numerical results obtained using the new PE will be presented. [Work supported by ONR.]
Comparison of various parabolic equation methods in a shallow water environment
Authors: Ryan F. J.
Published: October 2005

The parabolic wave equation (PE) is a powerful numerical method for computing the full-wave complex acoustic pressure field in range-dependent environments. Various PE implementations have been proposed including those based on finite element Pade (FEPE) and split-step Fourier PE (SSFPE) algorithms. Numerical results from these algorithms will be presented for a range-dependent bottom-limited shallow water environment off San Diego, CA. These simulations will be compared to experimental data collected during the SWellEX-1 experiment in August 1993. Among the issues to be discussed are (1) computational efficiency versus model accuracy, (2) effects of environmental (water column and bottom properties) spatial sampling on model output, (3) treatment of PE grid boundary conditions, and (4) reciprocity. [Work supported by NRaD IR program.]
A fast Green’s function method for one-way sound propagation in the ocean
Authors: Korte Rodney R. , Gilbert Kenneth E.
Published: October 2005

A Green’s function method recently developed for atmospheric sound propagation [K. E. Gilbert and X. Di, J. Acoust. Soc. Am. 94, 2343–2352 (1993)] is used to derive a fast, general algorithm for one-way sound propagation in the ocean. In this paper the method is applied to sound propagation in an ocean with angle-dependent surface loss. The results provide a rigorous solution to the problem treated heuristically by M. E. Moore-Head etal. [J. Acoust. Soc. Am. 86, 247–251 (1989)]. Within the context of an effective reflection coefficient for specular reflection from a rough surface, the present method is exact and can be applied without regard to the water depth or the frequency. Selected numerical examples are presented to demonstrate the effect of angle-dependent surface loss on shallow-water propagation.
A perturbative Lanczos solution method for alternative wide-angle parabolic equations
Authors: Yevick David
Published: October 2005

In this talk, the Lanczos procedure is applied to the high-order alternative wide-angle propagation operator. This operator is obtained by approximating √1+ε+μ, where ε=n2(Z)−1 and μ=k−20∂/∂z2, by the expression √1+ε+μ= −1+√1+ε+√1+μ−1/8(εμ+με)bf+ 1/16[(ε+μ)3−ε3−μ3+... . The exponential of the first three terms on the right-hand side of the above expression correspond to the Thomson–Chapman propagator and can be evaluated with the standard split-step Fourier algorithm. The remaining correction terms can be implemented either through standard Padé approximants or with the Lanczos procedure. Unlike the Padé formalism, the perturbative Lanczos scheme can be implemented equally efficiently in both two and three spatial dimensions. The procedure further does not suffer from the previously documented convergence difficulties associated with the Lanczos evaluation of the full square-root operator [Hermansson etal., IEEE J. Light. Technol. 10, 772–776 (1992)] and is therefore highly computationally efficient. Finally, it is verified that the Lanczos method yields highly accurate results for a leaky surface duct test case.
Propagation of acoustic waves near an ocean surface with mean flow inhomogeneities
Authors: Li Kai Ming
Published: October 2005

There is considerable interest in the model of underwater sound propagation in a moving-stratified ocean as it has long been established that variations in current speed have significant effects on the propagation of acoustic waves. This is due to the fact that these variations modify the sound-speed structure. This paper describes a mathematically rigorous method to study the propagation of acoustic waves in a vertically stratified ocean with a mean flow. Much of the significant theoretical work in this field makes use of a high frequency approximation and the so-called plane-wave ansatz. In this classical method, one substitutes the ansatz into the governing wave equation in order to determine an approximate solution. The first-order approximation leads to an eikonal equation that defines the ‘‘rays’’ and the second-order approximation leads to a transport equation that gives the wave amplitude. However, a different approach is used in this paper. It is demonstrated that the acoustic pressure can be represented by a twofold Fourier integral. The sound pressure is then estimated asymptotically by the method of stationary phase. The solution is particularly useful to provide a better physical understanding of the problem at much reduced computational cost.
Marching out the parabolic equation model: A graphical approach
Authors: Paz Nils , Mohseni Laleh , Townsen Ronald
Published: October 2005

The parabolic equation (PE) acoustic model uses a Fourier spectral method of solving a second-order differential equation. The solution is ‘‘evolved’’ by solving a series of fast Fourier transforms whereby the source is convolved with the environment of the propagating energy. Each convolution marks a step of the march until the solution is marched out to the final range. This evolution has been described mathematically many times in previous published papers [Hardin and Tappert, SIAM Rev. 15, 423 (1973), Thomson and Chapman, J. Acoust. Soc. Am. 74, 1848–1854 (1983)]. A graphical evolution of the convolution of the source with the environment is important in providing a fresh perpective and further insight into the refinement and the understanding of the source function and the sensitivity to the reference sound speed. In addition, the observation of the geometry as it marches the propagation forward in wave space is an important graphic tool for understanding the analytical description of the Tappert split step PE approach.
An efficient and robust method for underwater acoustic normal mode computations
Authors: Levinson Scott J. , Koch Robert A. , Westwood Evan K. , Mitchell Stephen K. , Sheppard Carol V.
Published: October 2005

An efficient, numerically robust algorithm for calculating acoustic depth-dependent normal modes for stratified fluid, multichannel ocean environments is described. An Airy-layered solution is used, and eigenvalues are found by a process which avoids the numerical instabilities associated with evanescent (nonoscillatory) depth dependence. Eigenfunction solutions are valid for multichannel environments. Computation time increases only linearly with frequency or number of modes. This algorithm (called ModeLab), is compared with KRAKEN [M. B. Porter and E. L. Reiss, J. Acoust. Soc. Am. 77, 1760–1767 (1985)] and with a model designed for fast cw calculations [K. J. McCann and F. Lee-McCann, J. Acoust. Soc. Am. 89, 2670–2676 (1991)]. ModeLab achieves the fastest computational speeds by more than an order of magnitude, and simultaneously provides eigenvalue accuracies comparable to the best available from KRAKEN. [Work supported by the Advanced Surveillance and Prediction System (ASAPS) Program of the Space and Naval Warfare Systems Command (SPAWAR, PMW 183-32).]
Sudden changes in simulated room acoustics influence echo suppression
Authors: Freyman Richard L. , Clifton Rachel K. , McCall Daniel D.
Published: October 2005

Listeners seated in an anechoic chamber discriminated the direction of the lag noise burst within a lead-lag pair. The lead loudspeakers were 42° or 48° left of midline, and the lag loudspeakers were 35° or 55° right. A train of noise bursts, during which the lag was always 45° right, preceded the test noise in some conditions. In the first experiment the lead was broadband (‘‘B’’) and lag was either high-(‘‘H’’) or low-pass (‘‘L’’) filtered. Discrimination of the test noise location was poorer when the B-L (lead-lag) test was preceded by a B-L train than when the test noise was presented in isolation, suggesting that echo suppression built up during the repetitious train. By comparison, discrimination of the B-L test was unaffected by a B-H train, indicating that any buildup of suppression during the train was broken when the lag’s frequency shifted from H to L, which simulated a change in absorption of echoes by room surfaces. A second experiment in which the intensity of the lag varied between train and test produced similar results. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners’ built-up expectations about room acoustics are violated. [Work supported by NIH DC01625.]