bluuebunny/crossref_metadata_2025 huggingface dataset:
Modal impulse response and wave vector–time domain methods to evaluate transient radiation from axisymmetric planar radiators
Authors: Sun Jie , Stepanishen Peter R.
Published: July 2002

The modal impulse response method and the wave vector–time domain method are two of the existing methods to evaluate the transient acoustic field from an axisymmetric planar radiator. Representations of the transient acoustic field in the space-time domain and the wave vector–time domain are linked through the Fourier/Hankel transform relationships, and the wave vector–time domain method is used to derive the modal impulse response for a space-time separable normal velocity distribution of an axisymmetric source. The classical uniformly shaded piston is first addressed as a benchmark case, and a Bessel shaded aperture is then addressed as a result of its importance in addressing more general source distributions. Numerical results are presented for both cases to illustrate the procedures in using the modal impulse response and the wave vector–time domain methods. [Work supported by URI/Ocean Technology Center.]
Convolution integral methods of evaluating the transient response of fluid-loaded plates and shells with attached structures
Authors: Stepanishen Peter R.
Published: July 2002

A general time-domain approach is presented to address the transient vibratory response of fluid-loaded plates or shells of arbitrary shape with attached substructures when subjected to specified mechanical and/or acoustical excitations. The approach is based on utilizing an in vacuo eigenvector expansion with time-dependent coefficients to describe the velocity field of the basic structure. Fluid loading and the effect of the substructures on the basic structure are described via the use of convolution integrals involving the modal velocity coefficients and impulse responses. A universal set of coupled convolution integral equations for the time-dependent modal velocity coefficients of the basic structure are developed using a time-domain method of analysis. Special cases, which include a finite plate and a general shell of revolution, are addressed. A reduced set of the coupled convolution integral equations for the time-dependent modal velocity coefficients is obtained for the plate, and sets of similar equations are also obtained for the shell. Numerical results are presented and discussed for some simple beam, plate, and shell problems involving transient excitations.
Closed-loop finite-element modeling of active/passive structural vibration damping in the time domain
Authors: Lim Young-Hun , Varadan Vasundara V. , Varadan Vijay K.
Published: July 2002

Finite-element modeling is used for the study of structures with piezoelectric actuators and sensors augmented by viscoelastic passive dampers. The structure is excited by a transient force; the response of the structure as determined by the computed voltage response of the sensor is used to construct a feedback loop that excites the actuator. A constant gain P–D (proportional and derivative) controller is used. The controller changes the effective stiffness of the structure and the derivative feedback also introduces the desired damping. The increased stiffness also lowers the vibration amplitude. Active vibration damping is compared and contrasted with passive damping provided by a viscoelastic dampers. A BMG model is used for the viscoelastic phase. A hybrid approach using modal superposition in conjunction with time integration is used for solving the matrix equations in space and time in an efficient manner. A parametric set of results is presented showing the contribution of active and passive damping for the transient response of a clamped plate structure.
Comparisons of measures of speech intelligibility in rooms
Authors: Bradley J. S.
Published: July 2002

The speech transmission index, useful-to-detrimental ratios, and percent articulation losses are three quite different types of measures of speech intelligibility in rooms. They each combine a measure of the speech-to-noise ratio and a room acoustics measure to better relate to speech intelligibility. Variations of all three types of measures were calculated from 91 impulse responses obtained from a wide range of acoustical conditions, and for different speech-to-noise ratios. Several broadband forms of these measures are shown to be reasonably well related to each other. The results are used to derive conversion equations between the three types of measures.
Review of speech intelligibility indicators: Their relationship and applications
Authors: Barnett P. W.
Published: July 2002

This paper will review selected speech intelligibility indicators including word scores. %ALcons, and speech transmission index. The implied relationship between indicators will also be deduced based on work and experiments by others. These relationships will be presented on a new scale known as the ‘‘Common Intelligibility Scale,’’ which is currently under consideration for incorporation into measurement standards in the United Kingdom. Finally, the use and applicability of various indicators will be discussed, including sensitivity, ease of prediction, and measurement.
Predicted and actual intelligibility-rating values produced by a unique church speech reinforcement system
Authors: Clayton Dan , Marshall L. Gerald
Published: July 2002

A new speech-reinforcement system was included in the 1996–97 reconstruction of historic St. James’s Church in Richmond, VA, following a major fire in 1994. Intelligibility of the spoken word was of primary importance to the congregation, yet they also wished to improve the already lively sanctuary acoustics for enhancement of the choral and organ music so integral to traditional Anglican worship. Considerations of superior electro-acoustic performance and sensitivity to appearance in this architecturally significant and reverberant room overcame the usual client preoccupation with cost, and led to the selection of a system incorporating digitally controlled, steerable-pattern, vertical-line-source loudspeakers. Evaluations of system performance during design were based on both ‘‘drawing-board’’ calculations and computer modeling with a sound system design program, and involved three speech-intelligibility predictors: C50, STI (RASTI), and %Alcons. Comparisons of the predicted intelligibility ratings are made with post-completion measured ratings. Results of effective-directivity (Qds) and frequency-response measurements are included.
Application of a novel algorithm for calculating a brass instrument’s impulse response to sound simulation
Authors: Adachi Seiji , Ayers R. Dean
Published: July 2002

A novel algorithm for calculating a brass instrument’s acoustic pressure response to an impulsive volume flow at the input end [R. D. Ayers, J. Acoust. Soc. Am. 100, 1190–1198 (1996)] is applied to sound simulation. The algorithm employs several impulse responses that have no multiple reflections and that decay very rapidly. These are convolved with the mouthpiece pressure and volume flow in the past to give the pressure at the present. The impulse responses calculated from the measured dimensions of an actual B■ trumpet can be considered for simulation purposes as being confined in a period of 13 ms, which is four times shorter than the nonzero period of the reflection function used in the conventional algorithm. Due to the shorter convolution time, the new algorithm, incorporated with a nonlinear driver model of lip vibration and airflow, can run about 4.5 times faster than the method using the reflection function. Simulations with the two algorithms indicate the same behavior for the transition among the air-column resonance modes. Individual waveforms synthesized with the new algorithm are in very good agreement with their counterparts synthesized with the conventional algorithm.
Computer analysis of the resonant scattering of sound by a bubbly fluid encapsulated by a submerged spherical shell
Authors: Korman Murray S. , Swain Scott R. , Crum Lawrence A.
Published: July 2002

The theoretical results for the resonant backscattering form factor f (θ=π,k) versus wave number k for scattering from a submerged elastic shell filled with a bubbly fluid are presented using MATHEMATICA 2.2. The elastic shell is a castable urethane known as Smooth-On 775 which has a density of ρ=1.03 g/cm3 and longitudinal and shear speeds of cd∼1450 m/s, cs∼70 m/s, respectively. The bubbly fluid is taken to be air bubbles of uniform radius (50 μm) and spacing, suspended in a host liquid of castor oil, instead of water, due to its greater viscosity. Resonant scattering is compared over a range of volume void fractions 0<β<0.01 for the frequency range 0–20 kHz. Shell inner radius b and thickness t are varied. Results are compared with an ‘‘ideal’’ spherical cloud of bubbly water. Comparisons are virtually identical for shells where b=5.08 cm and t=0.635 cm. The scattering theory by Ayres et al. [Int. J. Solids Struct. 23, 937–946 (1987)] is used, along with the theoretical model by K. W. Commander and A. Prosperetti [J. Acoust. Soc. Am. 85, 732–746 (1989)] for the complex sound speed and density in a bubbly medium.
Frequency response of a cantilever beam attached to a plate with varying boundary conditions
Authors: Bouws Robert C. , DeJong Richard G.
Published: July 2002

The frequency response function at the free end of a cantilever beam attached to an irregularly shaped flat plate has been measured experimentally. Variations in the drive point accelerance due to changes in the boundary conditions of the plate are presented. The ensemble of frequency response functions shows some deterministic features (due to the modes of the beam) and some statistical features (due to the varying boundary conditions of the plate). A numerical model using a beam impedance element and a simply supported rectangular plate with the same area and thickness as the test plate gives results that are similar to the ensemble of test results.
Two-dimensional wave-number descriptions of flexural vibration in ribbed plates
Authors: Brown Richard N.
Published: July 2002

Regularly ribbed plate constructions are common in marine, aircraft, and other structures, and their vibrational response has been a subject of many theoretical studies. Most studies have been concerned with propagating waves in one-dimensional structures. In order to understand two-dimensional structural vibration, radiation, and near fields due to point-force excitation, it is helpful to study the distribution of surface velocity in two-dimensional wave-number space. This presentation is intended to clarify the physics of the complex response of such a periodic structure. An exact solution for the surface velocity response of a fluid-loaded ribbed plate subjected to a point-force load is solved for the distribution in wave number of the surface velocity. The result is graphically presented as a ‘‘movie’’ of color images of the velocity distribution where time is proportional to frequency. Overlaid indicators delineating the acoustic response region, Bloch-wave dispersion contours, and rib response filtering actions help to clarify the complex response patterns and their interactions.
Vibroacoustic behavior with total or partial layer of constrained viscoelastic
Authors: Nicolas Jean , Foin Olivier , Atalla Noureddine , Mercier Bertrand
Published: July 2002

The actual efficiency of constrained viscoelastics layers is sometimes misunderstood. To study in depth this configuration, a theoretical approach has been developed by generalizing Ungar’s formulation [E. E. Ungar, J. Acoust. Soc. Am. 34, 1082–1089 (1962)]. The shear effect, ‘‘in-plane’’ motion, and flexion are taken in account into the viscoelastic layer while only flexion is considered for the metallic layer. By expressing ‘‘in-plane’’ and shear displacements in terms of transverse displacements, a linear system is obtained. Radiation impedances are calculated via Nelisse’s model [H. Nelisse et al., J. Sound Vib. 198(4), 485–506 (1996)]. The theoretical results have been systematically validated experimentally with a dedicated setup. Basic configurations of interest are: basic plate, basic plate and constrained viscoelastic layer with total or partial covering under or not under the excitation forces. A case of nonmetallic (fiber resin) material is also studied, leading to very interesting results. Finally, an optimization study brings new meaningful design possibilities.
The rebirth of a ribbon loudspeaker
Authors: Butler Alexander L. , Butler John L.
Published: July 2002

Although the ribbon driver has been around for many decades, it is still quite unknown to many people. A particular ribbon driver, which acts as a tweeter/midrange, was developed by Image Acoustics, Inc. The driver evolved from a multiple ribbon with substrate to a single corrugated ribbon design with a transformer. Throughout the development and testing the goal was a flat response, broad bandwidth (650 Hz to 20 kHz), wide beamwidth, and high sensitivity. This was not easy to achieve. A low-loss and low-inductive electric system as well as a strong magnetic field were required. The reduction of the inductance played a large part in achieving a flat response in the 15- to 20-kHz band. The approach and techniques used to achieve the desired results will be presented.
Acoustics of Eastern and Western bells, old and new
Authors: Rossing Thomas D.
Published: July 2002

Bells have been a part of nearly every culture in history. The acoustical properties of many different types of bells are compared, including church bells, carillon bells, handbells, ancient Chinese two-tone bells, and temple bells from several countries. Special attention is paid to modes of vibration and sound radiation.
Implementation of a ‘‘buy quiet’’ policy for equipment purchases at the NASA Lewis Research Center
Authors: Cooper Beth A. , Nelson David A.
Published: July 2002

At the NASA Lewis Research Center, more than 1100 civil servant and contractor employees are included in a hearing conservation program that incorporates the requirements of the Occupational Safety and Health Administration standard on occupational noise exposure, as well as NASA’s policy, which prohibits unprotected exposure to A-weighted noise levels above 85 dB. In many work areas, multiple, complex, or distributed noise sources require emphasis on hearing protection and personnel enclosures as the primary means of noise exposure management. Gradual, yet cost-effective, reductions in area noise levels are expected over time as equipment is replaced by selecting low-noise equipment whenever possible. To achieve maximum results from each equipment purchase, a ‘‘Guide to Specifying Equipment Noise Emission Levels’’ assists engineers and designers with identifying appropriate equipment noise emission requirements and incorporating those requirements into comprehensive specifications. The guide covers noise emission from a broad variety of fixed and portable equipment expected to produce A-weighted noise levels approaching 80 dB and higher. Developed to support hearing conservation program goals, the guide also addresses relevant community noise and speech communication issues. [See NOISE-Con Proceedings for full paper.]
Modulation instability of wave packets in media with resonant dispersion
Authors: Zozulya Oleg M.
Published: July 2002

In this work the modulation instability of quasimonochromatic wave packets propagating in conservative media with quadratic nonlinearity and linear nondamped oscillators attached to each point of a continuum is analyzed. Various density distributions of oscillators on natural frequencies are considered and carrier frequency ranges of unstable wave packet propagation are determined. It is shown that instability is closely related to the fact that the resonant dispersion relation can have many branches and thus permit phase-group synchronism between long and short waves. A wave packet propagating under the synchronism condition generates long-wave disturbances (with wavelengths near envelope width) and transmits up to one-half of its initial energy to them. The possible application of this effect for evaluation of microcavities size distribution in imperfect solids is considered.
Aircraft damage detection from acoustic and noise impressed signals found by a cockpit voice recorder
Authors: Stearman Ronald O. , Schulze Glen H. , Rohre Stuart M.
Published: July 2002

Currently, research is being conducted to detect damage through structural acoustics, signal processing, and transducer designs. The present study illustrates that damage detection may be carried out with an existing system acting as a latent signal transducer. One example involved a reliability problem in a commuter liner aircraft engine mount design where undetected crack growth created a critical whirl flutter condition destroying the aircraft. This reliability problem prompted the need for an in-place damage detection system to identify critical engine mount conditions. Signal analysis of data acquired by a cockpit voice recorder prior to and during the catastrophic aircraft whirl flutter event provided insight into critical signals that indicated the failure onset. Although regularly scheduled inspections failed to detect the problem, cockpit voice recorder signals contained a dynamic signature of this damage feature throughout the duration of the tape. It is highly probable that this damage signature existed for a much longer period of time, but due to the endless loop configuration of the cockpit voice recorder the earlier data were erased. The study indicated that even in the case of an unused cockpit voice recorder track, careful signal processing can extract surprising details about detecting potential damage. [See NOISE-CON Proceedings for full paper.]
Measurements and modeling of signal spread in the Barents Sea using time-forward and time-reversed signals
Authors: Gauss Roger C. , Preston John R.
Published: July 2002

Low-frequency (350-450 Hz), shallow-water propagation measurements were made in several sites in the southern Barents Sea in June 1991 using combinations of broadband signals. The experiment used a two-element vertical source array to transmit the signals, and an omnidirectional source/receiver echo-repeater system to retransmit the signals back to a horizontal line array near the original source location. (All platforms moved at 3 kt.) Measures of two-way signal spreads were collected over a variety of ranges (5 to 50 km) and environmental conditions. Considerable time spreads (up to 1 s) were observed with a characteristic constancy of peak values over the length of the spreads, while analysis of PRN and CW data showed that spectral spreads were confined to very low Dopplers. Furthermore, selected sets of signals were time reversed prior to echo repeating to measure the ability of this highly-spread environment to refocus acoustic energy back to the original source location. Simulations of two-way temporal signal dispersion using the OASES and ORCA models for both time-forward and time-reversed retransmissions are presented and compared to data results for several representative cases. [Work supported by ONR and NAWC.]
A review of parallel traffic noise barrier literature
Authors: Martel Nicole L. , Busch-Vishniac Ilene J.
Published: July 2002

It is widely accepted that a single noise barrier beside a highway will provide a degree of noise reduction for neighboring homes. An interesting issue arises when residential areas line both sides of the highway, requiring two parallel barriers, one on each side of the highway. An abundance of research has been carried out to examine this situation. The research suggests that this configuration allows for multiple reflections to occur between the two barriers, unfortunately resulting in less noise reduction for both residential areas. Researchers attacking this problem have uncovered many relevant issues. This paper will summarize these issues and will class them into those in which there is consensus and those in which there is no consensus. Researchers agree that multiple reflections exist in a parallel wall situation, that these reflections cause an insertion loss degradation, that the insertion loss degradation can be controlled, and that making barriers absorptive or tilting them is effective in reducing the degradation. They do not agree on the extent of insertion loss degradation, the significance of environmental variables such as ground cover, or the limits to improvements from absorptive or tilting barriers.
On the use of pavement surfaces to attenuate traffic noise
Authors: Calamia Paul T. , Busch-Vishniac Ilene J. , Turen Tracy A. , McNerney Michael T.
Published: July 2002

Efforts to limit the propagation of traffic noise tend to focus on the use of noise barriers and their associated insertion loss. Bearing in mind that the source which contributes most to roadside automobile noise at highway speeds is tire/pavement interaction, an investigation into the use of ‘‘quiet’’ pavements to reduce tire/pavement interaction noise, and thus attenuate traffic noise at the source, has been undertaken. Using the trailer method, onboard and roadside measurements have been made of tire/pavement interaction noise on various pavements currently in use in the state of Texas, as well as in the Western Cape and Gauteng provinces, South Africa. Preliminary results obtained with a test-vehicle speed of 60 mph show that reductions in roadside noise levels from 4 to 15 dB can be achieved with ‘‘quiet’’ pavements. [Work supported by the Texas Department of Transportation.]
1-3 piezoelectric composite materials for ultrasonic transducer applications—A comprehensive theoretical and experimental study
Authors: Geng Xuecang , Zhang Q. M.
Published: July 2002

1-3 piezoelectric composites are widely used as the transduction materials for underwater and ultrasonic transducers. In order to guide the design of the composite material and the devices based on it, a dynamic model is developed to precisely predict the dependence of the thickness drive on various parameters. For example, the velocity of the longitudinal wave, the dispersion curves of the wave propagation in 1-3 piezoelectric composite, and the antiresonance frequency, as well as the electromechanical coupling coefficient of the fundamental thickness mode, can be exactly predicted. The effect of the loss of the polymer phase on the properties of the 1-3 piezoelectric composite is also included in this theory; as a consequence, the quality factor of the 1-3 piezoelectric composite and its dispersion can be described. The origin of the lateral modes in the 1-3 composite plate can also be elucidated from this model, which shows quite different behavior from the early models such as the stop-band edge resonance model. Parallel to the analytic model, a systematic experimental study was also conducted to examine the mode coupling and the mode evolution with the thickness of a 1-3 composite plate.
Design and development of PC-IMAT: Teaching strategies for acoustical oceanography
Authors: Foret Jacob A. , Korman Murray S. , Schuler John W. , Holmes Eleanor
Published: July 2002

PC-IMAT (Interactive Multisensor Analysis Training) was developed in 1994 by NPRDC as a set of software tools to satisfy the initial need — to enhance the training of aviation ASW operators. While Navy training opportunities have decreased (reductions in deployments, encounters, and shore-based training facilities), training requirements have increased. The PC-IMAT project is proving to be a flexible and effectively evolving computer based training/educational platform needed to help tackle ASW and other tasks which require extensive analysis, classification, and interpretational skills. Students taking SP411 (Underwater Acoustics and Sonar) are currently using PC-IMAT to help investigate what are the effective instructional strategies which convey understanding of a complex multivariate domain (like ray trace or propagation loss models). Recent research on ‘‘scientific visualization’’ (to enhance comprehension and retention) and modeling from student feedback will be used to help develop and evaluate existing training materials. Questions arise naturally. What are the issues of the educational platforms to successful learning? What is the best computer utilization so that there is efficient evolution in the distributed training, whose contents have been reviewed, overhauled, and accepted by experts in the field? Finally, shipboard training is limited by the senior person’s knowledge.
Automated reverberation time experiments employing artificially generated noise
Authors: Lancey Timothy W. , Marine Jon
Published: July 2002

Using an IBM compatible PC, an inexpensive and simple method was developed to conduct acoustic absorption measurements in a reverberant chamber. The technique provided random noise distributed around 1/3 octave band center frequencies from 200 to 1000 Hz, through a D/A converter, to speakers within the chamber. Turbo-Pascal software was written to create a random noise file for each of the 1/3 octave bands. As a consequence, while a random noise signal was sent by the computer, that signal was identical for each experiment, for a specific 1/3 octave band. The noise signal, of 3-s duration, was programmed to increase to maximum intensity, and decrease to zero over a period of 25 μs, eliminating a steplike transient to the dynamic system at termination. The decaying noise was sampled 1000 times per second using an A/D converter, and the decay rate calculated. This technique was initiated with a keystroke and produced a sound-pressure level versus time plot file, allowing determination of the reverberation time and absorption coefficient of the chamber.
The effects of virtual pitch cues on the detection of coherent and incoherent frequency modulation
Authors: Carlyon Robert P.
Published: July 2002

Recent experiments [S. Furukawa and B. C. J. Moore, J. Acoust. Soc. Am. 101, 1632–1643 (1997)] indicate that listeners are better at detecting coherent than incoherent FM imposed on two widely separated frequency components. Experiment 1 repeated one of these experiments using carrier frequencies of 1100 Hz and 1925 Hz, modulated by one cycle of a 2.5-Hz sinusoid, in a noise background. Four out of eight listeners showed superior detection for coherent than for incoherent FM. Experiment 2 investigated whether this superiority was due to coherent FM producing larger changes in virtual pitch than does incoherent FM, despite the inharmonic ratio between the two components. In the signal interval of a 3I,2AFC task, the carrier frequencies of 1100 and 1925 Hz were shifted in either the same or in opposite directions, without disrupting the pattern of FM, which was either coherent, incoherent, or absent. Whatever the pattern of modulation, sensitivity was better for ‘‘same direction’’ than for ‘‘opposite direction’’ shifts, a result consistent with sensitivity to changes in virtual pitch. It is concluded that virtual phase sensitivity may account for the superior detection of coherently modulated tones, without recourse to an across-frequency mechanism specific to FM coherence.
Modulation gap detection in multicomponent stimuli
Authors: Grose John H. , Hall Joseph W.
Published: July 2002

The auditory system does not appear to adopt an efficient wideband temporal analysis if the temporal event to be detected traverses frequency with concomitant spectral discontinuity across the temporal event. In order to determine whether spectral continuity across the temporal event is a prerequisite for wideband temporal analysis, a novel paradigm was implemented in which the temporal event to be detected was a gap in the modulator of a sinusoidal carrier (the carrier was present throughout the modulation gap). The two markers of the modulation gap could be carried either by the same carrier frequency or by different frequencies across the modulation gap. In the latter case, the multiple carrier frequencies were continuously present whether they were carrying the modulation or not. Modulation gap detection was measured for an 8-Hz modulator carried by multicomponent stimuli whose standard duration was 625 ms. For all listeners, modulation gap detection deteriorated when the modulation gap traversed carrier frequency relative to when it was carried by a single frequency. Results will be discussed in terms of the conditions necessary for wideband temporal analysis. [Work supported by NIH NIDCD R01-DC01507.]
The influence of two-source noise on echo suppression
Authors: Silk Megan L. , Freyman Richard L. , McCall Daniel D.
Published: July 2002

When listeners are presented with lead and lag pairs of clicks from two loudspeakers in an anechoic room, they hear a single image near the location of the lead loudspeaker, provided that the delay of the lag is only a few ms. However, Thurlow and Parks [Perceptual and Motor Skills 13, 7–12 (1961)] reported that the addition of a continuous background of noise from a single loudspeaker causes the lag click to become audible as a separate auditory event. The current experiment investigated whether this apparent breakdown of echo suppression would also occur if the background noise was presented from two loudspeakers with one delayed relative to the other. The signal was a pair of brief white-noise bursts presented from loudspeakers located at 45 deg right and 45 deg left in an anechoic chamber, with delays ranging from 2 to 14 ms. A continuous background white noise presented from the same two loudspeakers disrupted echo suppression only when the direction of its time delay was inconsistent with the signal delay. One interpretation is that echo suppression was broken because stimulus and noise provided conflicting information about the acoustics of the room. [Work supported by NIH DC01625.]
Binaural sluggishness in the masked discrimination of signals with different patterns of frequency change
Authors: Culling John F.
Published: July 2002

The binaural system helps listeners to understand speech at low signal-to-noise ratios, presumably via time-varying binaural cues. However, the binaural system is often described as sluggish, because listeners cannot follow rapidly changing binaural cues. The speech in such experiments may have been articulated slowly enough for the binaural system to temporally resolve critical formant transitions. Alternatively, changing signal spectra may be analyzed by a nonsluggish aspect of the binaural system. In the former case, binaural unmasking of speech will depend upon speech rate. In a preliminary study, listeners’ discrimination of changing signals in noise was measured as a function of the rate of frequency change. Masked discrimination thresholds were taken for NoSo and NoSπ using a 2I-2AFC task. The signals consisted of ascending or descending three-tone glissandos (400, 500, and 625 Hz), presented repeatedly and continuously during a 1.6-s broadband white noise burst. Rate of frequency change was controlled by altering the duration of each individual tone (32 to 100 ms). The difference between NoSo and NoSπ was smaller for rapidly changing signals. Thus the binaural unmasking of speech should be dependent upon speech rate. However, the rate of articulation sufficient to abolish masking release is not known.
A comparison of spectral correlation and local feature-matching models of pinna cue processing
Authors: Macpherson Ewan A.
Published: July 2002

Two models of spectral cue processing were compared to determine how the auditory system might extract directional information from pinna filtering. Previous experiments [E. Macpherson, J. Acoust. Soc. Am. 99, 2515 (1996)] suggest that the processing is robust to irregularity in source spectra, making effective use of pinna cues without utilizing prior knowledge of the source. The two candidate models attempt to achieve this by different means. The first uses correlation to find the best match between eardrum spectra (or their derivatives) and a set of stored templates associated with particular directions. The second makes the match based on prominent local spectral features such as peaks and notches. The models’ predictions were compared to listeners’ responses in localization experiments involving free-field presentation of stimuli with a variety of nonflat spectra. Correlational matching of the spectral gradient gave the best agreement overall, while feature-matching proved unrealistically sensitive to spectral irregularities. Neither model consistently predicted specific mislocalizations or stereotypical front–back confusions. Despite serious shortcomings, the correlational model demonstrates that a simple, physiologically plausible process can exhibit the required general robustness. The results do not support the hypothesis that local features are the spectral cues for sound direction. [Work supported by NIDCD.]
Sound localization in the presence of multiple distracters
Authors: Wightman Frederic L. , Kistler Doris J.
Published: July 2002

Listeners gave verbal apparent position estimates in response to a frozen 250 ms wideband noise burst presented from one of 36 locations in virtual free-field. A click train and a modulated harmonic complex, both presented simultaneously with the noise target, served as distracters. On each trial, the distracters were presented in one of six randomly chosen configurations in virtual space. All virtual sources were synthesized from the listeners’ own HRTFs. The impact of the distracters on the apparent position of the target varied considerably across listeners. For all listeners, when the distracters were presented on the horizontal plane at +90 degrees and −90 degrees (directly opposite the two ears), the apparent elevation and front-back position of the target were disrupted. For some listeners, this was the only effect of the distracters. In a separate condition, the stimuli were presented ten times in succession and listeners were encouraged to move their heads during stimulus presentation. Synthesis of the virtual sources was coupled to head position in order to simulate stationary virtual sources. In this condition the distracters had no effect on the apparent position of the target. [Work supported by ONR.]
Time reversal array focal zone predictions using simulations in the time domain
Authors: Hallaj Ibrahim M. , Kargl Steven G. , Roy Ronald A.
Published: July 2002

The use of finite-difference time-domain (FDTD) computer simulations for wave equation calculations has deep roots in the electromagnetic pulse propagation literature, where many of the modern techniques were developed. Results are presented from high-resolution simulations of the linear acoustic wave equation in inhomogeneous media with absorbing boundary conditions. The results address the focusing behavior of sparse ultrasonic arrays under various propagation conditions. Focal spot attributes and size are investigated in the presence of inhomogeneities, time-varying media, and multiple scatterers. Comparison with known benchmarks, such as the diffraction limit, show that useful results can be obtained using FDTD calculations in medical applications, for example, where the frequencies and scales allow full-sized simulations in major organs. [Work supported by the Office of Naval Research.]
Three-dimensional modeling of a time reversal mirror to image objects buried in an inhomogeneous seabed
Authors: Turgut Altan
Published: July 2002

The time reversal mirror (TRM) imaging and self-focusing concept was tested numerically by using a newly developed 3-D full-wave propagation model and a stochastic model of bottom heterogeneity. The 3-D propagation model was used to calculate pulse scattering from an attenuating inhomogeneous seabed and buried objects. Two-dimensional seabed roughness and three-dimensional sediment volume inhomogeneities were modeled by using the Von Karman type of spectra with proper statistical parameters which were obtained from stereo photography, sediment tomography, and chirp sonar measurements. A parametrical study was performed to identify proper choice of pulse shape, time gating, phase-screen backpropagation, and amplitude correction for selected distributions of multiple scatterers, burial depths, sediment layering, and statistical properties. Numerical simulations indicated that the TRM should perform well for detection of 3-D objects buried in the seabed. Finally, based on the results of the parametrical study, design criteria of a TRM field experiment are also discussed.
The effect of masking and filtering of envelope modulations on the recognition of consonants
Authors: van der Horst René
Published: July 2002

Consonant identification scores were obtained for 18 Dutch consonant phonemes in VCV context, in two experiments in which the narrow-band envelopes of the speech stimuli were manipulated by masking or filtering. For this purpose, the speech stimuli were split up into 26 frequency bands, each one critical band wide. The amplitude envelope of each band, as obtained with a Hilbert transform, was disturbed in two ways: (1) by a narrow-band envelope masker around 4, 8, and 12 Hz, and (2) by notch-band filtering around the same frequencies. Next the speech stimuli were synthesized by using narrow-band noise carriers, each a critical band wide, which were modulated by the aforementioned envelopes. Ten normal-hearing subjects participated in the experiments. The confusion matrices were analyzed by means of multidimensional scaling techniques and compared between the two manipulation methods. The results of the filtering experiment show that consonant recognition scores behave like a low-pass function of notch-width when expressed in octaves. The differences with the results of modulation masking will be discussed, especially with respect to modulation transfer function and consonant recognition cues.
The spectral difference of different vowels: Toward a new acoustical concept
Authors: Maurer Dieter , Klinkert Andreas
Published: July 2002

When isolated vowels were produced beyond F0 of speech (F0>150 Hz for men, F0>300 Hz for women and children), the related formant patterns were found to deviate substantially from the values of formant statistics, and the formant frequency variations proved to be nonsystematic (for details, see poster Klinkert and Maurer). Moreover, formant frequency estimation for vocalizations with F0>400 Hz is highly problematical, although many vocalizations remain unambiguous in the vowel identity up to F0=700 Hz and even above. The nonsystematic formant variations and the methodological problem of formant frequency estimation hardly allow for a normalization of formant patterns. Dynamic spectral properties do often not appear in isolated vowels. Thus, for the acoustic theory of vowel sounds, the question arises as to whether there is a concept to determine the physical correlates of the sounds apart from formants. A first approach toward such a concept is described for voiced vowels: A hypothesis is presented which predicts characteristic differences in the harmonic spectra of different vowels. Implications for vowel perception are discussed.
Visual and auditory factors in vowel perception
Authors: Strand Elizabeth A. , Johnson Keith
Published: July 2002

This study investigated four factors in vowel perception. Two of these factors are linguistic in nature: the F1 value and the identity of the visual word. The other two factors are speaker-related: the F0 value and the visual gender of the speaker. The auditory stimuli used in this experiment were tokens in continua ranging from ‘‘hood’’ to ‘‘hud’’ for both a male and a female voice which were produced using LPC resynthesis, maintaining the original male or female voice source and altering the formant values. These continua were then matched with movies of male and female speakers saying either ‘‘hood’’ or ‘‘hud,’’ to create four series of stimuli. From identification judgments made by 20 listeners, we calculated 50 crossover points on the F1 ‘‘hood’’–‘‘hud’’ continuum. The boundaries were analyzed with a three-factor ANOVA (visual gender, visual word, and original voice). There were three main effects and no interactions. The visual word effect shows that visual and auditory cues are integrated in determining vowel quality. The original voice effect is essentially an F0 normalization effect. The visual face effect shows auditory-visual integration in the perception of speaker identity which, we hypothesize, has an impact on perceived vowel quality.
Optimal use of spatial bandwidth in underwater acoustic communications to enhance bandwidth efficiency
Authors: Kilfoyle Daniel , Priesig James , Catipovic Josko
Published: July 2002

The operation of underwater acoustic communication systems is often directly or indirectly limited by the available temporal bandwidth with performance measures, such as range and information rate, closely tied to the system bandwidth efficiency. Spatial diversity has typically been viewed as a secondary channel feature, either introducing undesirable intersymbol interference or, more favorably, offering a mechanism to offset fading. It is proposed to treat spatial diversity as spatial bandwidth and demonstrate higher bandwidth efficiency with existing power and temporal bandwidth constraints. Several spatial modulation algorithms are explored, including time variant transmitter beamforming where both waveform and choice of projector weights denote information, a spatial analog to multi-carrier modulation where each propagation path corresponds to a carrier, and a coordinated multi-user scenario where each projector emits independent information. Performance of each algorithm is shown to be superior to conventional phase-coherent modulation techniques that make no explicit use of spatial bandwidth. Results of a small-scale field experiment will also be given.
Pharmacological intervention with noise-induced hearing loss
Authors: Henderson Donald , Hu Bo-Hua
Published: July 2002

High-level noise has the capability of damaging the cochlea via several mechanisms, including the generation of reactive oxygen intermediaries with their capacity of cytotoxicity. Several laboratories have reported that prior exposure to conditioning noise (moderate levels of noise for several days) can render the cochlea more resistant to future traumatic exposures. This lab in collaboration with the Albert Einstein College of Medicine, reported that antioxidant enzymes: catalase, glutathione reductase, and γ-glutamyl cysteine synthtase, are upregulated with noise exposure—the greatest increase being found in animals exposed to a traumatic noise with previous conditioning noise exposure. This increase, with conditioning noise, suggests the antioxidant system may be involved in protection from noise exposures. To better understand the role of antioxidants, a second set of experiments was conducted that manipulated their level. The applications of R-N6-phenylisopropyladenoisine (R-PIA) (a drug that upregulates the antioxidant system) decreases the effects of noise; and conversely, applications of buthione-sulfoximine (a drug that suppresses the antioxidant system) increases the effects of noise. These results will be discussed in terms of the balance of free radicals/antioxidants as a common factor in noise and other ototoxic reactions. Also, the R-PIA studies will be discussed in terms of potential therapeutic value.
Atmospheric multipath resolution using spread spectrum acoustic signals
Authors: Swanson David C. , Mast T. Douglas , Mahon Mark P. , Norris David
Published: July 2002

An investigation into multipath resolution for outdoor sound propagation is done using spread spectrum acoustic signals. A low-frequency sinusoid is bi-phase modulated using a pseudorandom sequence with period 2M−1. The ‘‘chip rate’’ fc in Hz is the number of bits per second used in the bi-phase modulation. The shape of the spread spectrum sinusoid is in the form of sin(x)/x, where the peak is at the sinusoid frequency and the adjacent nulls are at ±fc in Hz. Faster chip rates result in broader spectra. Cross correlating the received acoustic signals with the transmitted signals provides a time delay and amplitude estimate for each path in the propagation channel. A field experiment in a strong 15-kn wind revealed a clear direct path and ground reflection appropriate for the profile conditions and confirmed by ray tracing. [Work supported by DARPA.]
Atmospheric boundary layer sound velocity profile model for wind and temperature
Authors: Swanson David C. , Reichard Karl M. , McClintic Kathy T. , Norris David
Published: July 2002

Effective outdoor sound propagation modeling requires an accurate knowledge of the wind and temperature profiles to elevations at least on the order of 1/10th the propagation distance of interest. Using similarity theory and ground-based wind and temperature sensors, the profile near the ground is modeled. However, extending a similarity-based profile above the surface layer is not physical and leads to large errors. This work presents a new profile model which fits very closely to similarity theory within the surface layer, and smoothly transitions to fit upper elevation atmospheric data available worldwide through aviation weather resources. Field experiments confirm the new profile’s validity in stable atmospheres, both from SODAR and RASS measurements, as well as very long-range acoustic detection and parabolic equation modeling for low-frequency sinusoids. [Work supported by DARPA and U.S. Army CE-COM.]
Sonic boom scattering from anisotropic turbules
Authors: Kelly Mark , Raspet Richard , Bass Henry E.
Published: July 2002

The single-scatter first Born approximation has previously been used to describe sonic boom scattering from spherically shaped turbules. Boulanger et al. [J. Acoust. Soc. Am. 98, 3412–3417 (1995)] used it to model the turbulent atmosphere (assuming isotropic turbulence) with reasonable success. An adaptation of this method to calculate the scattered wave from an ellipsoidally shaped turbule, using a Cartesian coordinate system centered at the turbule, gives more realistic results than those obtained from a spherical scatterer. The ellipsoidal method produces directionally dependent rise times, allowing better description of turbulence with mean wind flow, or anisotropic turbulence. This new approximation was applied to simulated booms from a T-38 flying at an altitude of 10 000 m, with a collection of turbules located in the planetary boundary layer (PBL). The size distribution and number of turbules used to simulate the atmosphere in the PBL were calculated using recorded meteorological data and Monte Carlo routines. This method of simulating the turbulent atmosphere has produced rise time distributions in good agreement with data empirically obtained from the Joint Acoustic Propagation Experiments performed at White Sands in 1991.
Using musical acoustics to teach digital signal processing, scientific computing, and human–computer interface technology
Authors: Cook Perry
Published: July 2002

This talk discusses the role of musical acoustics in teaching engineering courses offered at the Stanford Center for Computer Research in Music and Acoustics, and in the Princeton University Department of Computer Science. For digital signal processing, musical acoustics is used to motivate and demonstrate mathematical concepts such as zeroes (multi-path cancellations in rooms), poles (resonant modes in a guitar), nonlinearity, and instability (what happens when one turns up the guitar amp). Simultaneous real-time visual and auditory displays build intuition and interest. For scientific computing, the pendulum provides a simple but meaningful first experience in numerical methods. By setting up differential equations from a physical description, noting the possibility of linearizing assumptions, and solving the system discretely on a computer, students discover how parameter values affect accuracy and stability. By solving both with and without the linearizing assumption, then placing a soundfile header on the output data, differences in frequency and waveform can be easily detected. Techniques are extended in plucked string and vibrating membrane simulations. For human–computer interface technology, musical instruments are perfect examples of effective human-artifact interfaces. Labs using computer sound synthesis clarify basic interaction concepts such as latency and cross-modal perception.