bluuebunny/crossref_metadata_2025 huggingface dataset:
The air/sea interface as a wave source
Authors: Ffowcs-Williams J. E.
Published: October 2005

The surface waves on the ocean are coupled to the underwater sound field, the coupling arising either because the one generated the other, or because they were both created coherently by a common source. This paper discusses the various mechanisms of sound generation at and near the ocean surface and identifies parameters controlling the regimes where the various sources are dominant. Reference will be made to the results of some exact model problems involving aerial turbulence-induced surface waves and their associated sound field in an infinitely deep ocean. These model problems utilize the techniques of aero-acoustics on the ocean sound problem and indicate that some aspects have not previously been adequately modeled when the surface is vigorously disturbed in the main noise-producing conditions.
On the wind-wave interaction mechanism
Authors: Mellen R. H. , Middleton D.
Published: October 2005

Sonar and radar backscattering measurements indicate that the wind-driven sea surface does not behave acccording to linear theory at high wavenumbers. Backscatter strengths at small grazing angles are much greater than expected and the scatterers appear to move without the usual dispersion associated with “capillary” waves. Theory shows that nonlinear effects of surface-drift and wind-wave interactions can account for the shocklike properties. Nonlinear wind-wave effects have been observed in wave-flume measurements by spectral analysis of wave-gauge data. Initially periodic ripples develop coherent harmonics with increasing fetch; however, subharmonic growth leads to rapid degeneration and a continuous spectrum. The mechanism appears to involve intermodulation between wind and wave leading to chaotic behavior and redirecting the energy cascade to lower wavenumbers. In the equilibrium stage, further development of longer gravity waves ceases as they outrun the source, incoming energy being balanced by high-wavenumber dissipation. Unstable disturbances generated on the surface should degenerate into ensembles of solitons, explaining the Doppler spreads and backscatter cross sections observed at high frequencies.
Infrasonic ambient ocean noise: Northeast Pacific Ocean
Authors: Nichols Rudolph H.
Published: October 2005

Measurements of ocean ambient noise were made at three widely separated deep-water bottom locations in the N. E. Pacific, at eight frequencies in the range from 2.5–20.0 Hz, for 40 consecutive days. Concurrent data on wind speed and wave height were collected. Analysis indicates that the spectrum level of infrasonic noise is linearly related to the log of the wind speed above a threshold level. There is evidence that the noise can be directly associated with the wind, rather than through the surface waves it produces. [Work supported by ONR.]
Underwater noise caused by precipitation
Authors: Scrimger Joseph A.
Published: October 2005

The characteristics of underwater noise in the ocean generated by precipitation are important to weather forecasters and oceanographers since they permit the detection and measurement of rain over the ocean by remote (i.e., buoyed or bottom-mounted) acoustic sensors. We have recently observed the character of the underwater noise generated by rain, hail, and snow. The spectrum of rain noise, for wind speeds below 1.5 m/s, shows a peak of 13.5 kHz with a sharp cutoff on the low-frequency side and a gradual falloff (7 dB per octave) on the high-frequency side. Stronger winds smear the peak. Hail spectra show a peak at 3.0 kHz with a gradual (roughly 11 dB per octave) falloff on both sides. The spectrum of snow noise is unique. Our instrumentation permitted the measurement of the drop (or stone) size distributions in the precipitation. These findings will enhance the art of remote acoustic sensing in oceanograpy. [Work supported by: Supply & Services Canada; Institute of Ocean Sciences, Sidney, BC, Canada; Atmospheric Environment Service, Toronto, Canada; and Department of National Defence, Canada.]
Coherence versus time delay for spatially separated receivers in deep water using a z-transform method
Authors: Feuillade C. , Kinney Wayne A.
Published: October 2005

Broadband coherence values versus time delay for two horizontally separated receivers and for different source azimuth angles (from broadside to endfire) are presented for (a) a surface-bottom (SB) path, (b) a bottom-surface (BS) path, and (c) a combination of SB and bottom-reflected (B) paths. The water depth and range are both 5 km. The source and receivers are all at 200-m depth. The ocean bottom is assumed to be rigid and flat. Scattering from the ocean surface is modeled with the facet-ensemble method [H. Medwin, J. Acoust. Soc. Am. 69, 1060–1064 (1981), W. A. Kinney and C. S. Clay, J. Acoust. Soc. Am. (submitted)] applied to a long-crested wave model of the ocean surface using actual wave-height measurements with an rms value of 1 m. A z-transform algorithm [suggested by C. S. Clay (private communication)] has been used to perform broadband filtering and to compute coherence. Results demonstrate how signals propagating via the SB path possess greater coherence (with values near 0.8) than signals propagating via the BS path (values near zero). [Work supported by NAVELEX 612.]
Active and passive imaging of features on a rough seafloor
Authors: Clay C. S. , Daneshvar M. R.
Published: October 2005

We are exploring array design and signal processing techniques for imaging features on the seafloor. In our numerical studies, rough features are modeled as diffracting wedges. Active imaging uses known sources. Passive imaging uses natural sources such as storms, earthquakes, etc. Natural sources are modeled as occurring at random times and random locations. We use delay and sum array processing to focus the array on diffraction sources. The results are displayed as two-dimensional vertical and horizontal pictures of diffraction sources. We also compare two methods of processing, squaring the array output and split array cross correlation. The diffractograms show that a wedge can be identified for active and passive sources. [Work supported by Weeks Bequest, Wisconsin Alumni Research Foundation, National Science Foundation, and NORDA.]
Effects of convergence zone multipath on cross correlation
Authors: Hauck Walter S. , Robinson E. Richard , Quazi Azizul H.
Published: October 2005

Recent work by Hauck [NUSC TD 7409] indicates autocorrelation processing may be adversely affected by the large number of acoustic rays from a source within a convergence zone. The object of the current study is to examine the effect of CZ multipath on cross correlation of frequency hopped pulses. The sensitivity of the correlation to source or receiver depth, and the location of the source within a convergence zone is examined using the generic sonar model [H. Weinberg, NUSC TD 5971C]. Results for both first and second CZs will be presented.
Multipath effects in a nonisospeed medium on a wave front curvature ranging system
Authors: Bilazarian P.
Published: October 2005

The influence of multiple ray arrivals on the localization performance of the wave front curvature ranging (WCR) system is investigated. The novelty of this work is that this influence is analyzed for a nonisospeed medium and for a system which performs time-delay measurements with limited resolution capabilities. The WCR system consists of three sensors located on a horizontal line. Source location parameters are determined from estimates (via cross correlation) of time delays associated with the aggregate of ray arrivals at each sensor. Conditions are defined where localization accuracy is affected by multipath arrivals. Formulas are developed which predict localization errors in terms of multipath time-delay differences between various sensor pair. These formulas incorporate the system discrimination capabilities and contain multipath parameters, such as amplitude and arrival-angle differences. The effect of multipath on system performance is demonstrated for a variety of sound-speed profiles and multipath environments.
Low-frequeney noise problems and psychological and physiological influences of low-frequency noise
Authors: Yamada Shinji , Watanabe Toshio , Kosaka Toshifumi
Published: October 2005

In Japan infrasound or low-frequency noises are emitted from highway bridges, large compressors, boilers, and diesel engines etc. Windows or doors of wooden houses are vibrated by infrasound and emit rattling noises. Low-frequency noises are sometimes heard directly and annoy people. These complaints and low-frequency noises were investigated. Psychological and physiological influences on university students and low-frequency noise sufferers were investigated in a laboratory. University students were not influenced as much by low-frequency noise. The results clearly indicated that the heart and respiration rates of several low-frequency noise sufferers increased. Many low-frequency noise sufferers were influenced psychologically or physiologically.
Community response to low-frequency noise from large wind turbine generators
Authors: Shepherd Kevin P.
Published: October 2005

The introduction of large wind turbine generators in the United States and Europe has, in some instances, resulted in adverse community reaction to noise and noise-induced building vibrations. In particular, this has been associated with horizontal axis wind turbines for which the rotor blade is mounted downwind of the supporting tower. Such an arrangement results in the generation of low-frequency impulsive noise due to the passage of the rotor blades through the tower wake. This paper will review the available literature on community reaction to low-frequency wind turbine noise. In particular, levels of noise and noise-induced building vibrations will be estimated by using available measured data and a recently developed low-frequency sound propagation model. Estimated levels will be compared with known perception thresholds of low-frequency noise and building vibrations. [Work supported by NASA Langley Research Center.]
Comparison of advanced turboprop and conventional jet and propeller aircraft flyover noise annoyance
Authors: McCurdy David A.
Published: October 2005

A laboratory experiment was conducted to compare the annoyance to advanced turboprop aircraft flyover noise with the annoyance to conventional turboprop and jet aircraft flyover noise. The effects of fundamental frequency and tone-to-broadband noise ratio on advanced turboprop annoyance were also examined. A computer synthesis system was used to generate 18 realistic, time varying simulations of propeller aircraft takeoff noise in which the harmonic content was systematically varied to represent the factorial combinations of six fundamental frequencies ranging from 67.5–292.5 Hz and three tone-to-broadband noise ratios of 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 32 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in harmonic content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.
Reduction of tank main gun noise with a muffler
Authors: Atack Rodney M. , Bales Joel D. , Wrobel John G. , Lewis Nelson D.
Published: October 2005

With the continuing encroachment of residential communities on military installations and the noise complaints received from these residents, it is necessary to reduce the noise levels propagating from these facilities. At stationary 105-mm tank gun firing locations, such as those used for weapon testing, the noise from the firing can be significantly reduced by firing through a large muffler. The muffler used at one installation to reduce the noise impact is approximately 2.3 m in diameter, 6.3 m long, and weighs approximately 20 metric tons. During a test of this muffler, the noise level in the adjacent community was reduced by approximately 7 dBA from levels that caused a moderate risk of complaints to levels which are barely audible. The significant noise reduction produced through utilizing a noise muffler presents an avenue through which research can be directed towards reducing noise impact from certain types of weapons testing.
A noise monitoring and warning system for intermittent large-amplitude impulsive sounds (blasts and sonic booms)
Authors: Schomer Paul D. , Averbuch Aaron , Lendrum Lester
Published: October 2005

The noise generated by large weapons (artillery, tanks, demolition) is a source of considerable problems for many Army installations. As a part of the Army's program to mitigate noise problems, the U.S. Army Construction Engineering Research Laboratory (USA-CERL) has designed and installed a blast noise monitoring and warning system at several installations. Each system consists of a base station and several remote, smart sensors. Each smart sensor actually contains two microprocessors and a large memory. When sounds that are “too loud” are detected, the sensor uses a “smart” modem to call the base station computer and warn operations personnel of the high levels. Alternatively, the sensor can buffer (monitor) these data in its memory and read out these data on command (by telephone) to a distant base station. Each sensor, designed for unattended long-term operation, includes such features as self calibration, an uninterruptable power supply, and a −40° to +85°C operating temperature range. Early indications are that the desired reliability and user friendly ease of operation have been attained.
Identifying prominent discrete tones in noise emissions
Authors: Nobile Matthew A.
Published: October 2005

Research has shown that broadband noise containing one or several discrete tones is usually judged more annoying than the same noise without the tones. In view of this, new noise emission standards are requiring that the presence or absence of prominent tones be reported along with the measured data. Therefore, it is imperative that a reliable accurate, and repeatable measurement method be available to identify and evaluate tones in noise. The methods described in current standards are based on the rather outdated, analog procedure that appeared in ANSI S 1.13 Appendix A (1971), but as a result of the growing use and affordability of modern digital signal processing instruments, new methods are now being proposed. One method [Noblie et al., Proceedings of NOISE-CON 85, Columbus, OH (June 1985)] is based on FFT measurements, while another is based on 1/12-octave-band analysis. This paper will review the concept of a prominent discrete tone, review the proposed new methods, and present comparisons of results from the different methods applied to actual machine noise.
Comparison of new and “dead” nylon guitar strings
Authors: Hanson Roger J. , Munns Gordon O.
Published: October 2005

Classical guitarists are troubled by nylon strings becoming “dead” after a short period (days or weeks) of intensive use. The problem is most severe for the lower three strings which are normally wire wound. New and “dead” strings have been studied under a variety of conditions in an attempt to determine the most evident measurable differences. The time decays of the different partials of the sound radiated from a guitar have been measured, but the interaction of the vibrating string with the guitar body and the difficulty of standardizing plucking and detecting conditions complicate the interpretation. To simplify and standardize the test conditions, the string is mounted on a steel beam with rigid supports. The vibrating motion of the mechanically plucked string is detected optically with a system similar to that used by Gough [C. E. Gough, J. Acoust. Soc. Am. 75, 1770–1776 (1984)]. Measurements of vibration amplitude for different spectral regions as a function of time after the pluck and of the inharmonicity of the partials will be discussed.
Digital recording techniques involving vocal and percussion ensembles: The Gyuto Tantric Monks
Authors: Cohen Elizabeth A. , Hart Michael S. , Smith Huston
Published: October 2005

The Gyuto Tantric Monks use handbells, cymbals, damaru (skull drums), rejong (double-membrane wood drums), horns, and long trumpets to summon their deities. Their chants consist of slowly recited Sanskrit texts. They are able to produce and sustain harmonic chords over long periods of time [Smith et al., J. Acoust. Soc. Am. 41, 5 (1967)]. They produce a music of unparalleled dynamic range. The disparity between the voices and the drums offers a unique challenge to the recording engineer. The Monks were recorded on several occasions in May of 1985. We developed techniques for both live stereo and studio multitrack digital recording. Individual and ambience miking techniques will be discussed. Shared, dynamic, fastomiking techniques for live recordings will be explored. Methods for balancing recording requirements with PA demands will also be discussed. The results of spectral analysis of the recordings confirm the level of fidelity obtained.
Surface wave velocity measurements at fluid-porous solid interface
Authors: Mayes Michael J. , Nagy Peter B. , Adler Laszlo
Published: October 2005

The presence of ultrasonic surface waves of various modes on a fluid-porous solid interface is demonstrated and their velocities are measured. The experimental technique developed earlier [A. Jungroan et al., J. Appl. Phys. 53, 4672 (1982)] for a fluid-isotropic solid interface utilizes reflected broadband spectra from periodic surfaces. Three sharp minima corresponding to mode coupling of incident waves into surface waves at the fluid-porous solid interface are observed. The velocities of these surface waves are in qualitative agreement with theoretical predictions [S. Feng and D. L. Johnson, J. Acoust. Soc. Am. 74, 906 (1983)] and are identified as pseudo-Rayleigh, pseudo-Stoneley, and true Stoneley waves. [This work is supported by the U.S. Department of Energy through Lawrence Livermore National Laboratory.]
Scattering problems involving fluid-porous interfaces
Authors: Thompson C. , Sen R.
Published: October 2005

The problem of plane-wave scattering by a rigid planar obstacle between a fluid and a fluid-filled porous medium is investigated. Porous materials are used extensively in industry as sound-absorbing liners, and their effect on the incumbent pressure field has traditionally been accounted for by postulating a point-reacting boundary condition at the fluid-porous medium interface. It is shown that such an assumption leads to a considerable misrepresentation of the physical situation. A fluid-porous interface is characterized by a rapid local variation in the mass reactance and flow resistance, and the length scale associated with this variation is fundamental to the scattering analysis. It is shown that local velocity fields at the interface determine important features of the solution, such as the nature of the edge singularity. Pressure and velocity jump conditions at the interface are rigorously derived using the local mass and momentum equations and the method of matched asymptotic expansions. We also compare our result to a solution of the problem that employs the locally reacting boundary condition.
Biorthonormalization technique in scattering
Authors: Dallas I. Allan G. , Gaumond Charles F. , Sarkissian Angie
Published: October 2005

The problem of scattering of time-harmonic acoustic waves by a smooth rigid obstacle is considered. A formalism is developed for the construction of the farfield pattern. The method involves the biorthonormalization of two complete families in the Hilbert space of square-integrable functions on the surface of the scatterer. The procedure is more attractive than the orthonormalization technique for the solution of the same problem. [C. F. Gaumond and A. G. Dallas, J. Acoust. Soc. Am. Suppl 1 75, S53 (1984)], since fewer computations are required in applications.
Biorthonormalization technique in acoustic scattering, II
Authors: Sarkissian Angie , Gaumond Charles F. , Dallas Allan O.
Published: October 2005

Results obtained by applying the biorthonormalization method, in the particular case of a rigid prelate ellipsoidal scatterer, are presented for farfield backscattering at axial incidence. Computations based on two forms of the solution are described and compared with the available separation-of-variables calculations [T. B. A. Senior, Can. J. Phys. 44, 655 (1966)], for the ratios a/b = 2, 5, and 10, and over the ka range of 0–10 (a = semimajor axis, b = semiminor axis, and k = wavenumber).
Scattering of elastic waves by an anisotropic inclusion
Authors: Varadan Vasundara V. , Jeng Jen-Hua , Varadan Vijay K.
Published: October 2005

Form invariant stress-strain relationships are presented for anisotropic media. The case of transversely isotropic media is then considered and the five elastic constants needed to describe such a medium are obtained in terms of the elements of the stiffness tensor. The dispersion equation is solved and approximate basis functions are constructed to expand the displacement fields inside such an anisotropic inclusion. The scattering of elastic waves by spherical or nonspherical inclusions is studied as a function of frequency and geometry and compared with the isotropic case.
Scattering of ultrasonic pulses by a turbulent water jet
Authors: Korman Murray S. , Corsaro Robert D.
Published: October 2005

Experimental results are presented for the scattering of an acoustic pulse from a region of turbulent flow. The investigation was performed in the 7-m-deep section of the USNA Hydrodynamics TOW Tank facility. Turbulent flow is produced by a submerged nozzle of 4.8cm-diam and 100-cm/s exit velocity. Flow is directed perpendicular to the water's surface. The 1.9-MHz acoustic pulse is generated from a 2.54-cm-diam ultrasonic transducer located 18-nozzle diameters downstream from the jet exit and at a perpendicular distance of 84 cm from the jet axis. An identical transducer receiver located at the depth of the sender is positioned 217 cm from the jet axis. Angular scattering measurements are made in a plane parallel with the water's surface. Scattering results are presented for the temporal broadening, the spectral broadening, and the energy distribution of the incident pulse using a digital data collection and analysis system. Results are compared with theoretical predictions. [Work supported by NRL (Physical Acoustics Branch) and USNA.]
Spontaneous versus prepared speech
Authors: Bernstein Jared , Baldwin Gay
Published: October 2005

Some speakers use different forms when training a speech recognizer than when speaking spontaneously to the device—this could be called “enrollment diglossia.” As a preliminary study of this phenomenon, we compared selected phonological and prosodic features of spontaneous speech to read and recited versions of the same sentences and paragraphs. Three subjects were interviewed and were later asked to read or memorize and recite, at various nominal rates, portions of the material that they had originally spoken spontaneously. We made detailed measurements of /t/ allophonics, speech rate, and the forms of certain words. For some speakers, there are considerable differences between spontaneous and prepared renditions; e.g., one speaker produced 45% vs 18% of /t/s as flaps, another speaker varies local speech rate and produces more nonsyntactic pauses in spontaneous paragraphs, and one speaker invokes “fast speech” forms at slower speech rates for spontaneous speech than for prepared speech. [Work supported by DARPA.]
Statistical treatment of the acoustic effects of vocal effort
Authors: Li Kung-Pu , Benson Peter
Published: October 2005

Speech recognition performs best when trained and operated in the same environment. Such training is often impractical, especially in military applications. Apart from the difference in the noise environment, talkers change their speech habits when speaking over poor quality channels. The acoustic changes due to increased vocal effort reduce the performance of speech recognizers. While the acoustic effects of vocal effort are varied, it is possible to deal with a bulk of the differences using a statistical approach. A database of two talkers was collected under conditions which produced a variety of degrees of vocal effort. These conditions included both loud sidetone and noise which, when delivered over headphones, change stress and vocal effort. The talkers differed in their reaction to the extreme level in that one shouted and the other did not. Read materials consisted of lists of digits, randomized but the same across talkers. Acoustical parameters such as pitch, amplitude, and word duration were measured and compared across conditions. Using standard statistical procedures, transforms were computed to map the speech from several conditions into a common transformed space. Recognition experiments demonstrated that significant increases in automatic speech recognition performance can be achieved when templates from one condition are matched against unknown speech, when both have been transformed into the common space. An analysis of the recognition errors was made in light of the acoustic differences between vocal effort conditions.
Evaluation of a vowel shadowing task
Authors: Montgomery Allen A.
Published: October 2005

This study was concerned with preliminary steps in the development and evaluation of a shadowing task designed to yield quantitative information on the perceptual-motor processing of speechlike stimuli. In this task, the subject was required to shadow (reproduce vocally as quickly and accurately as possible) a synthetic vowel stimulus (target) which is presented to one ear. The stimuli vary in difficulty from steady-state vowels for calibration, normalization, and training, to continuously varying series of vowels used to test the subject's ability to perform rapid vowel transitions and produce a variety of tense and lax vowel targets. The subject's performance is evaluated by comparing F2 curves of the produced vowels with those of the targets using cross-correlation and coherence techniques. Results of training and testing ten normal speaking subjects will be presented, and further refinements necessary for developing the tracking procedure into a research/clinical tool will be discussed. [Work supported by the Department of Clinical Investigation, Walter Reed Army Medical Center.]
Acoustic-phonetic properties of vowels produced in noise
Authors: Pisoni David B. , Yuchtman Moshe
Published: October 2005

It is well known that speech produced in noise has higher intensity, longer duration, and higher fundamental frequency than speech produced in quiet. However, recent studies in our laboratory have indicated that changes in the acoustic properties of speech produced in noise are not limited to changes in the glottal source but may also include significant changes in the acoustic-phonetic structure of speech reflected in the characteristics of vocal tract transfer function. We investigated the effects of wideband noise on the acoustic properties of vowels. Talkers produced ten American-English vowels in /hvd/ context. Ten tokens of each vowel were produced in quiet and in the presence of masking noise (90 dB SPL). The results indicate a rather complex pattern of changes in formant frequencies. First, with the exception of the vowels /æ̈ɑ, ɔ/, whenever a significant change in F1 was observed. F1 frequency was higher in the noise condition. Second, F2 frequencies decreased in front vowels and increased in back vowels. The net results of these changes is a more compact vowel space.
A dynamic analysis of reiterant speech production in Japanese
Authors: -Bateson Eric V. , Kelso J. A. S.
Published: October 2005

Previously, we have modeled supralaryngeal articulatory motion in the production of English reiterant speech in terms of underlying dynamical constraints on movement gestures [Kelso et al., J. Acoust. Soc. Am. 77, 266–280 (1985)]. Here, we extend the model to Japanese, a language whose temporal structure is believed to be based on the “mora” and thus very different from English. Preliminary analysis of acoustic lip and jaw movement, and electroglottographic data from three Japanese talkers reveal production differences between the reiterant renditions of multimora and single mora syllables. Multimora CVC syllables are characterized by a glottally truncated vowel followed by a lengthened silent period prior to voicing onset for the following syllable, e.g., a word like 〈motte〉 is realized reiterantly as [ba?ba]. Thus the timing of the glottal gesture appears specific to the mora structure of Japanese, while upper articulator motion, which does not differ for the two syllable types, can be shown to adhere to dynamic constraints hypothesized for movement gestures in general. [Work supported by NINCDS and ONR.]
Phase-dependent sensitivity to perturbation reveals the nature of speech coordinative structures
Authors: Munhall K. G. , Kelso J. A. S.
Published: October 2005

The detailed workings of hypothesized speech coordinative structures-functionally specific articulator ensembles—can be explored by varying the phase of an unexpected perturbation during ongoing speech. The present research examined the characteristics of remote (nonmechanically linked) and autogenic compensation when the lower lip was perturbed in either the opening or closing phase of the motion for the utterance /bæb/. Preliminary results indicate that the relative contribution of remote and autogenic responses to the perturbation varies with the phase of perturbation; remote compensation plays a greater role when the lower lip is perturbed during the closing phase of motion for a bilabial consonant. Analysis of trials immediately following perturbed trials reveals a hysteresis in the articulator configuration due to the preceding loaded trials. The articulators tend to overcompensate in these trials in a manner that reflects the phase sensitivity of the immediate compensation pattern. These phase-sensitive compensation patterns provide strong support for the notion that the articulators in speech are flexibly assembled as coordinative structures for accomplishing specific phonetic goals. [Work supported by NINCDS and NSERC.]
Articulatory contact patterns in /t/ and /s/ produced with and without a bite block
Authors: Flege J. E. , Fletcher S. G.
Published: October 2005

Dynamic palatometry was used to examine linguapalatal contact during consonant production. The subjects (two native English, three native Arabic) produced /s/ and /t/ in two normal speech samples immediately after insertion of a bite block and, again, after 10 min of practice with the bite block. One English subject contacted more sensors when producing /s/ with the bite block, the other contacted fewer sensors. Two Arabic subjects showed an increase in the width of the /s/ groove, along with a decrease in the number of sensors contacted; the other Arabic subject showed a decrease in groove width and an increase in the number of sensors contacted. Only one of the Arabic subjects showed significant adaptation, producing /s/ with a narrower (more normal) groove width in bb2 than bb1. Inserting the bite block did not affect the width of A-P constriction used by the English subjects to form /t/ but did lead to an increase in the number of sensors contacted. On the other hand, all three Arabic subjects contacted fewer sensors when producing /t/ with a bite block. The Arabic subjects all formed a /t/ with narrower constriction in the bite-block samples, but only two showed significant adaptation from bb1 to bb2. The intersubject differences will be discussed in terms of cross-language phonetic and individual morphological differences.
The new nationally shared x-ray microbeam facility: Status report
Authors: Nadler R. , Abbs J. H. , Thompson M. , Fujimura Osamu
Published: October 2005

A 600-kV x-ray microbeam system for studying tongue movements and other articulatory gestures has been constructed to serve as the core instrument of a nationally shared speed production research facility at the Weisman Center, University of Wisconsin. Preliminary speech movement data have been obtained and this system currently is capable of tracking multiple articulatory pellets (up to 12) at aggregate sampling rates of about 1000 per second and simultaneous A/D sampling of multiple EMG and acoustic signals. The facility includes parallel capability for data display and analysis for multiple experimenters. It is expected that this system will be used by many U.S. research groups. The administrative structure, as well as technical specifications of the facility will be described, and proposals for its use will be invited. [Support for this facility is provided by NINCDS (NS-16373).]
A coefficient of nonlinearity for noncollinear plane-wave interaction
Authors: Hamilton Mark F. , TenCate James A.
Published: October 2005

An inhomogeneous wave equation, exact to second order in the field variables, is derived for the sum and difference frequency pressure generated by two plane waves, of angular frequencies ω1 and ω2, which intersect at an angle θ in a lossless fluid. The coefficient of nonlinearity pertaining to the sum or difference frequency wave (ω± = ω1 ± ω2) is shown to be β± (θ) = B/2A + cosθ ± 4(ω1/ω±2)sin4(θ/2), where B/A is the parameter of nonlinearity. The same result may be deduced from the work of Zverev and Kalachev [Soy. Phys. Acoust. 15, 322 (1970)]. The first term of β± is due to the isentropic equation of state, the second term represents convection, and the third term comes from the momentum equation. Alternative formulations of the inhomogeneous wave equation are presented, and comparisons are made with the analyses of others. An experiment designed to measure the angular dependence of β± was conducted with noncollinear waves in an airfilled waveguide. Results are reported. [Work supported by ONR.]
Wave steepening in Van der Waals gases
Authors: Cramer M. S. , Sen R.
Published: October 2005

Van der Waals gases having sufficiently large specific heats are known to possess regions of negative nonlinearity, i.e., regions where the nonlinearity parameter 1 + B/2A < 0. When the amplitude of a pulse or wavetrain is sufficiently large, different parts of the wave may correspond to positive and negative values of the nonlinearity parameter, and the resultant propagation will be qualitatively different than that observed in ideal gases. A complete finite amplitude theory of the steepening of both pulses and wavetrains will be presented. Although monosigned pulses in ideal gases and many liquids form no more than one shock wave, it will be shown that, under the same conditions, Van der Waals gases may form as many as three shock waves.
Fourier series representation of finite amplitude sound beams
Authors: Miao Hsu-Chiang , Ginsberg Jerry H.
Published: October 2005

An earlier analysis of finite amplitude sound beams derived general expressions from the behavior in the off-axis region [J. H. Ginsberg, J. Acoust. Soc. Am. 76, 1201–1214 (1984)]. An asymptotic analysis of the region very close to the beam axis confirms the earlier result for the velocity potential. The signal is rewritten in a form that makes the contribution of each wavenumber in a continuous spectrum appear to be the sum of two waves traveling transversely, as well as axially. The coordinate transformations required to renormalize this form lead to a temporal Fourier series that is reminiscent of the Fubini solution for finite amplitude planar waves. The complex amplitude of each harmonic is obtained from an integration over the transverse wavenumber. The computational efficiency of this representation permits extensive evaluation of propagation properties. An example compares the signal derived from a piston to that obtained from the one-dimensional assumption that p = ρcvn, on the boundary, which has been employed in prior investigations using approximate parabolic equations. [Work supported by ONR, Code 425-UA.]
Finite amplitude acoustic waves generated by a baffled dual frequency transducer
Authors: Foda Mosaad A. , Ginsberg Jerry H.
Published: October 2005

In a previous presentation [J. Acoust. Soc. Am. Suppl. 1 75, S92 (1984)], a nonuniformly accurate expression for the velocity potential was derived using a singular perturbation procedure. The linearized signal was represented by a dual King integral, and the cumulative growth was evaluated asymptotically. In this paper, the renormalization version of the method of strained coordinates is employed to annihilate the secular terms. The result is a uniformly valid expression for the acoustic pressure at all locations preceding the formation of a shock. Additional discussion is devoted to a simpler model that interfaces the dual frequency King integral in the nearfield with nonlinear spherical distortion in the farfield. The results obtained from both descriptions in the case of a parametric array (proximate primary frequencies) agree better than earlier theories with previous measurements performed for a wide range of parameters. [Work supported by ONR, Code 425-UA.]
Theoretical description of a focused Gaussian beam
Authors: Du Gonghuan , Breazeale M. A.
Published: October 2005

The nonlinear equation in nondimensional form used by S. I. Aanonsen et al. [J. Acoust. Soc. Am. 75, 749 (1984)] is solved to obtain an expression for the sound-pressure distribution produced by a plane Gaussian radiator with a concave solid lens in an absorbing fluid medium. Analysis of the solutions shows that the sound field of a focusing lens still maintains a Gaussian distribution across the beam without maxima and minima in the nearfield as well as without sidelobes in the farfield. The theory also shows that the focal distance is not equal to that predicted by geometrical acoustics, but is always shorter because of diffraction. The second harmonic pressure also exhibits Gaussian behavior throughout the beam, even in the focal plane, where the second harmonic is observed to be more narrow than the fundamental. The growth of total energy in the second harmonic also is evaluated. The results indicate that the second harmonic initially increases quite rapidly up to the focus. Beyond the focus, the rate of growth of the second harmonic is found to decrease, and, at a certain distance, the second harmonic is found to have an even smaller magnitude than would be the case without focusing. A set of curves is presented which helps to describe the features of a focused Gaussian beam. [Research supported by the Office of Naval Research.]
Computer simulation of the vertical structure of mid-ocean ambient noise
Authors: Murphy Donald A. , Del Balzo Donald R. , Wagstaff Ronald A.
Published: October 2005

The acoustic field for a realistic distribution of noise sources was calculated at a deep-water location in the Northeast Pacific corresponding to the CONTRAK VI measurement site [M. Z. Laurence and D. J. Ramsdale, J. Acoust. Soc. Am. Suppl. 1 77, S70 (1985)]. The calculations were made with the NORDA Parabolic Equation programs along four horizontal directions representing distinctly different environments and historical shipping distributions. The calculated field at the CONTRACK VI site was sampled by vertical line arrays to determine the vertical arrival angles of the noise. This vertical structure was studied as a function of array depth, array length, and frequency for each horizontal direction and compared with the CONTRACK VI measurements. The shape and depths of the resulting vertical noise notch are heavily affected by arrivals from sources over continental slopes and in cold water. [Work supported by DARPA.]
Arctic Ocean basin theory
Authors: Dyer Ira
Published: October 2005

Low-frequency ambient noise sources observed in the Arctic are discretely located in space and time. With a large number of events per unit area per unit time, the total number of contributions to any one observation grows with horizontal range but also shrinks in intensity inversely with range. This standoff therefore suggests that limits on observed ambient noise are set by basin bathymetry and/or by sound absorption. In one useful model we find the source spectral density typical of low-frequency events is changed via the basin by an f2 shaping at frequencies below, and by an f−1 shaping at frequencies above a characteristic frequency. [Work supported by ONR.]
A tribute to James H. Botsgord (1925–1984) and a historical review of impulse noise measurement in the steel industry
Authors: Toothman Edwin H.
Published: October 2005

A tribute to Jim Botsford who passed away on 18 May 1984 will be presented. A historical review of noise measurement in the steel industry, including impulse noise, highlighting Jim's endeavors will be given. The instrumentation and methods used for noise measurements along with rating information will be discussed. Problems associated with impulse noise measurement will be reviewed and questions regarding proper instrumentation, analysis, and rating for impulse noise will be raised.
Noncollinear interaction of two sound beams from displaced Gaussian sources
Authors: Hamilton Mark F. , Naze Tjøtta Jacqueline , Tjøtta Sigve
Published: October 2005

We consider the noncollinear interaction of two sound beams in a nondissipative fluid, one formed by a high-frequency (pump) wave and the other by a low-frequency (source) wave. It is assumed that both waves are generated by Gaussian shaded sources. However, the sources may possess linear phase shading, different spot sizes, and their centers may be displaced by a small distance relative to each other. The analysis is based on the fundamental theory developed in earlier papers [G. S. Garrett et al., J. Acoust. Soc. Am. 75, 769 (1984) and M. F. Hamilton, J. Acoust. Soc. Am. 76, 1493 (1984)], and it is valid throughout the paraxial field. Numerical results are presented, and asymptotic formulas which explain the development of the parametric field along the axis of the pump wave are given. The analysis may be applied to a parametric receiving array located in the nearfield of the sound source. [Work supported by ARL: UT IR&D funds.]
Excitation of underwater wall-flex oscillation under static conditons
Authors: Elder S. A.
Published: October 2005

In a previous paper, resonant acoustical oscillations of a free-flooding cavity were described. These take place when the mouth of the cavity is located along the side of a towed model with flexible walls. It has been the working hypothesis that oscillation amplitude for this case is limited by the nonlinear acoustical impedance of the cavity mouth, in a fashion analogous to self-excited Helmholtz resonance in air cavities. In order to investigate the nonlinear response characteristic of the cavity mouth, tests have been made, under static conditions, using an array of J9 projectors to stimulate wall vibration. Detailed mapping of wall motions has been performed by means of accelerometers. Although the complexity of the wall vibrational modes makes it difficult to reproduce the exact conditions of towed-model cavity tones, it has been possible to associate large fluctuations of internal sound pressure with certain normal modes that periodically alter the cavity cross section. The search for nonlinear mouth flow effects has been complicated by the presence of amplitude-dependent vibrational states of the walls. At this writing, it appears that the present feedback model of wall-flex oscillation may have to be modified to allow for nonlinear wall behavior.
Hearing-aid microphone systems with increased directionality
Authors: Rabinowitz William M. , Frost Daniel A. , Peterson Patrick M.
Published: October 2005

Under some conditions of background noise and/or reverberation, increasing the directionality of hearing-aid microphone systems can lead to gains in speech intelligibility. Conceptually, directional microphone systems are realized by combining the outputs of multiple, spatially distributed omnidirectional sensors. Two approaches to obtaining increased directivity D derive from the classical antenna theory: (1) With uniform or tapered sensor weightings, increasing the spatial extent L of the sensor array increases D. The maximum D is limited to 2Lf/c, where f is frequency and c is the speed of sound. (2) With arbitrarily small arrays, broadband “superdirectivity” can be achieved whereby the maximum D is independent of frequency and equals the square of the number of sensors in the array. A conventional hearing-aid directional microphone exploits suboptimum superdirectivity; two closely spaced sensors attain D = 4.5 dB up to about 4 kHz. We shall review the basic principles and limitations of such microphone systems and report on our effort to develop a four-sensor array (using two conventional directional microphones) that achieves D = 8.5 dB and a 3-dB beamwidth of ± 37° for f < 4 kHz with an array length L = 4.1 cm that is practical for hearing-aid applications. [Work supported by NIH.]
Spectral profile analysis in the hearing impaired
Authors: Wightman F. L. , Perkins M. E. , Allen P.
Published: October 2005

We tested the hypothesis that hearing-impaired listeners with reduced frequency selectivity have abnormal difficulty discriminating spectral patterns, especially when degraded by background noise. Both normal and hearing-impaired listeners were asked to discriminate a stimulus with a flat spectrum from one with a rippled spectrum. A two-interval forced-choice paradigm was used, in which overall stimulus level was randomized from interval to interval. The stimuli consisted of random-phase sinusoidal components spaced at half-normal critical band intervals. The spectral ripples were sinusoidal on dB versus critical-band coordinates. The depth of the ripple was fixed (e.g., at 6 dB or at 10 dB) for a block of trails, and a wide-band Gaussian noise was added, with its level varied adaptively from trial to trial to track the signal-to-noise ratio required for 71% correct discrimination. Normally hearing listeners show large individual differences, both in discrimination and in duration of practice effects. However, the effect of noise was the same across all normal listeners: once the stimuli were a few (5 or less) dB above masked threshold, discrimination was asymptotic. Hearing-impaired listeners have much greater difficulty discriminating spectral profiles, particularly in a noise background.
Critical bands in the perception of speech signals. Part 2: SNHL data
Authors: Bienvenue Gordon R. , Celmer Robert D.
Published: October 2005

The critical band is essentially a filtering process of the auditory system whereby sound is categorized according to its frequency content. While some empirical evidence suggests that the critical band may serve in the analysis of speech, this has only been indirectly demonstrated. The authors have developed digital signal processing techniques for altering available recorded speech materials so that the frequency resolution may be controlled. Tapes have been produced wherein the frequency resolution is limited to narrower than, equal to, and wider than one critical band. In a previous paper [Celmer et al., J. Acoust. Soc. Am. Suppl. 1 76, S14 (1984)], it was reported that these tapes were used in intelligibility testing with normal listeners. Evidence of distorted critical bands in some sensorineural hearing impaired listeners has been reported in the literature. In the present study, the tapes described above were used in intelligibility testing of listeners with confirmed cases of sensorineural hearing loss. The critical bandwidths of the subjects were also measured by a two-tone masking technique, and were shown to correlate highly with the results of the bandwidth-resolution-limited speech test.