bluuebunny/crossref_metadata_2025 huggingface dataset:
On reconstruction of acoustic pressure fields using the HELS method
Authors: Wu Sean F.
Published: July 2002

The Helmholtz equation-least squares (HELS) method was recently developed by Wang and Wu [J. Acoust. Soc. Am. 102, 2020–2032 (1997)] to reconstruct the acoustic pressures generated by an arbitrary vibrating structure. In this method the acoustic pressures are expressed in terms of an expansion of ‘‘acoustic modes.’’ The coefficients associated with these acoustic modes are determined by requiring the assumed-form solution to satisfy the pressure boundary condition at measurement points. The errors incurred in this process are minimized by the least-squares method. The advantages of this method are that (1) acoustic pressures can be reconstructed over the entire surface; (2) solutions thus obtained are unique; and (3) efficiency of numerical computation is high, because the number of measurements is determined by that of expansion terms, which is small when a right coordinate system is selected for a particular source geometry under consideration. Such an approach is applicable to both exterior and interior regions. For exterior problems, the reconstructed acoustic pressures can be accurate when the points fall outside the minimum circumscribing spheroidal surface which encloses the vibrating surface, but approximate when they are inside. For interior problems, the accuracy of reconstruction is high because the entire region is inside the minimum circumscribing spheroidal surface. In both cases, the accuracy of reconstruction is limited by excitation frequencies, which is inherent in all expansion theories. [Work supported by NSF.]
A formulation and preliminary validation of an algorithm prescribing the propellers of an aircraft as excitation in an acoustic boundary element analysis
Authors: Vlahopoulos Nickolas , Lyle Karen H. , Burley Casey L.
Published: July 2002

Simulation tools can be utilized in computing and minimizing the interior noise levels in an aircraft subjected to the external acoustic load originating from the propellers. In order to evaluate accurately the interior noise level, and in order to determine the structural changes which will reduce the interior noise, it is important to have an accurate description in terms of magnitude and phase for the external acoustic load exerted on the fuselage. A formulation for modeling the operating propellers of an aircraft as a noise source in a boundary element acoustic analysis was developed, implemented into software, and verified through comparison to test data. It constitutes the initial phase of integrating sophisticated rotorcraft models [D. S. Prichard, D. D. Boyd, and C. L. Burley, ‘‘NASA/Langley’s CFD-Based BVI Rotor Noise Prediction Systems: (ROTORNET/FPRBVI) An Introduction and User’s Guide,’’ NASA Technical Report, TM-109147, November 1994] to a conventional boundary element analysis. The initial validation was performed by comparing numerical results to test data for the external acoustic pressure on the surface of a tilt-rotor aircraft for one flight condition. [Work supported by the NASA, ASEE Faculty Fellowship Program.]
Effect of syllable-initial voicing on temporal characteristics of words
Authors: Allen J. Sean , Miller Joanne L.
Published: July 2002

As part of an ongoing study of the voicing distinction in syllable-initial stop consonants, we measured segmental durations of consonant–vowel–consonant (CVC) words beginning with voiced stop consonants (e.g., ‘‘big,’’ ‘‘duck,’’ ‘‘gap’’) and matched CVC words beginning with voiceless stop consonants (e.g., ‘‘pig,’’ ‘‘tuck,’’ ‘‘cap’’). Target words were produced in randomized lists together with numerous filler words. Results from the four speakers measured to date revealed a consistent pattern. As expected, initial voiceless stops were associated with a longer voice-onset-time (VOT) than initial voiced stops. In addition, initial voiceless stops were associated with a shorter vowel duration (measured from the onset of voicing) than initial voiced stops. Thus, the change from voiced to voiceless stop entailed both an increase in VOT and a decrease in vowel duration. However, the magnitude of the decrease in vowel duration was insufficient to compensate fully for the increase in VOT, resulting in a net increase in the duration of the CV portion of words beginning with voiceless as opposed to voided stops. The results are discussed in terms of implications for models of speech production and syllable planning, as well as implications for studies of speech perception. [Work supported by NIH/NIDCD.]
Initial strengthening and coarticulatory resistance
Authors: Keating Patricia A.
Published: July 2002

In previous work, initial strengthening of lingual articulations has been demonstrated in four languages. One possible interpretation of initial strengthening is that it results from increased coarticulatory resistance: consonants in stronger positions resist the weakening that coarticulation would produce. To test this interpretation, a new study examined consonants in CVCs in which the vowel was varied. If initial strengthening is coarticulatory resistance, then there should be less effect of the vowel on the initial consonant than on the final consonant. Test consonants /t d n l/ and vowels /E a u/ were combined with the nontest consonant /b/ in 24 syllables like /tab/ and /bul/; five subjects produced nine repetitions of each in a frame sentence. Maximum linguopalatal contact, measured by electropalatography, was the measure of consonant strengthening and coarticulation. The result was the opposite from the prediction. Initial consonants showed more vowel-dependent variation than did final consonants (in accord with the traditional coarticulation literature). Yet the initial consonants did show more overall contact than final consonants. Thus initial strengthening cannot be attributed to coarticulatory resistance. Additional experiments, including one which looks at initial strengthening in phrase-initial positions, will be reported. [Work supported by NSF.]
Performance of passive correlation detectors using autocorrelation and energy spectrum inputs
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W.
Published: July 2002

Using the energy spectrum or autocorrelation as a functional input to the cross correlation (energy), bicorrelation, and tricorrelation detectors for unknown transient signals can result in improved detector performance compared to the correlations of the received signals. Test signals with differing autocorrelation and energy spectrum properties are used in computer simulations with Gaussian noise to compare results using the original received signals, the energy spectra of the received signals, and the autocorrelations of the received signals to form the correlations. Detection results are presented for the case when only two channels of input data are available to form the correlations, as well as the case when three and four channels of input data are available to form the higher order correlations. In the former case, it is shown that detection performance can be improved for narrow-band signals by using the energy spectrum and autocorrelation functional inputs rather than the original received signal. In the latter case, it is shown that detection performance can be improved by using the autocorrelation input for a broadband signal and the energy spectrum input for a narrow-band signal, and that for the test signals, the tricorrelation detector performs best. [Research supported by ONR.]
Scattering from buried spheres in a shallow-water laboratory
Authors: Simpson Harry J. , Frederickson Carl K. , Houston Brian H.
Published: July 2002

A series of scattering measurements from buried and proud spheres in the NRL shallow-water laboratory have been conducted in order to understand the scattering of sound from targets at and below the sandy-bottom interface. The water-saturated sandy bottom was a manufactured 212-μm washed and filtered sand. The initial measurements included scattering from two spheres, a solid aluminum sphere with a 15-cm diameter, and a hollow stainless steel sphere with a 60-cm diameter and an h/a of 0.05. For baseline measurements, free-field and proud measurements of both spheres were made. Buried measurements of the spheres ensonified below the critical angle were conducted with a smoothed interface to quantify contributions from the evanescent wave field. Also investigated is the enhancement due to a roughened sand–water interface. The results of these measurements will be discussed and a preliminary analysis will be presented. [Work supported by ONR.]
High-resolution reconstruction of penetrable obstacles at low frequency
Authors: Couchman Luise , Warner Jeremy A. , Ghosh Roy Dilip N.
Published: July 2002

The scattering and inverse scattering of plane acoustic waves from penetrable acoustic targets (including shell-type structures) of arbitrary shapes and compositions are discussed. The scattering problem is solved by combining the technique of shape differentiation of the scattered field with the Padé extrapolation. The solution thus obtained is then used in the inversion recovery of the targets from the far-field data via the Gauss-Newton iterative procedure. Both the shapes and the material parameters of the targets are reconstructed. The advantages of the technique are discussed and numerical results are presented for a number of two-dimensional obstacles. Also presented are some three-dimensional results for Dirichlet objects. As an extension, a random acoustic ambience is considered.
Near-field ultrasonic scattering from a cavity in steel considering the velocity amplitude on the transducer face using an error function model
Authors: Lawu Tjundewo , Tabei Makoto , Ueda Mitsuhiro
Published: July 2002

The influence of nonuniform transducer velocity distribution in the near-field echo formation scattered from a cavity in steel is analyzed. In the present study, the velocity amplitude on the transducer face was modeled using an offset error function. Using this distribution, the echo waveforms scattered from a cylinder cavity in steel were estimated and compared with the echo estimated using uniform distribution and echo observed experimentally. The estimation accuracy of the near-field echo waveforms were improved quantitatively.
The analysis and results of a continuous wave ultrasonic densitometer
Authors: Smit Christian C. J. , Smith Edwin D.
Published: July 2002

This paper investigates an ultrasonic densitometer capable of measuring the densities of liquids. Lynnworth originally proposed an ultrasonic densitometer operating in pulse-echo mode. This instrument makes use of the phase velocity of a torsional elastic wave pulse traveling in a noncircular waveguide immersed in a liquid to indicate the density of the liquid under investigation. In this paper a second mode of operation is proposed by making use of a continuously excited torsional wave to reveal liquid density. An important advantage of this mode of operation is the larger cross-sectional dimensions possible without sacrificing performance degradation which might result from wave dispersion. The theory of this mode of operation is described and used to construct a densitometer. Densities of a few liquids are measured and compared to the theoretical values.
Speech intelligibility assessment in a helium environment. II. The speech intelligibility index
Authors: Lucks Mendel Lisa , Hamill Bruce W. , Hendrix James E. , Crepeau Loring J. , Pelton Jerry D. , Miley Matthew D. , Kadlec Elizabeth E.
Published: July 2002

The Speech Intelligibility Index (SII) was measured for Navy divers participating in two saturation deep dives and for a group of nondivers to test different communication systems and their components. These SIIs were validated using the Speech Perception in Noise (SPIN) test and the Griffiths version of the Modified Rhyme Test (GMRT). Our goal was to determine if either of these assessments was sensitive enough to provide an objective measure of speech intelligibility when speech was processed through different helmets and helium speech unscramblers (HSUs). Results indicated that SII values and percent intelligibility decreased incrementally as background noise level increased. SIIs were very reliable across the different groups of subjects indicating that the SII was a strong measurement for predicting speech intelligibility to compare linear system components such as helmets. The SII was not useful in measuring intelligibility through nonlinear devices such as HSUs. The speech intelligibility scores on the GMRT and SPIN tests were useful when the system component being compared had a large measurable difference, such as in helmet type. However, when the differences were more subtle, such as differences in HSUs, neither the SPIN nor the GMRT appeared sensitive enough to make such distinctions. These results have theoretical as well as practical value for measuring the quality and intelligibility of helium speech enhancement systems.
Response to “Analysis and comparison of recent resonance scattering formulations by M. S. Choi et al. with earlier, traditional RST work” [J. Acoust. Soc. Am. 104, 1720 (1998)]
Authors: Choi Myoung-Seon
Published: July 2002

In the letter by Gaunaurd, there were some comments on recent resonance scattering formulations by the author and his colleagues. Replies to the comments are made here. To clarify the discussion, brief reviews on the recent formulations and more traditional ones are included. It is shown that the recent approaches are based on much more robust physical concepts and approximations than the traditional ones, so that they are sufficient to be presented as novel tools for target identification purposes.
Analytical/numerical matching applied to a finite beam with multiple nonperiodically spaced constraints
Authors: Franzoni Linda P. , Park Christopher D.
Published: July 2002

Analytical/numerical matching (ANM) is used to solve for structural vibrations of a finite beam constrained by multiple, nonperiodic supports. The ANM solution decomposes the stated problem into global, local, and matching problems. The global problem addresses large scale effects, with structural discontinuities replaced by smooth distributed forces. The local problem models the rapidly changing region around a structural discontinuity. These constituent problems are solved independently by the most efficient method available. Here, the local problem is solved numerically using finite element analysis (FEA) and the matching problem is solved analytically. The global problem is modeled using FEA with third-order Bernoulli–Euler beam elements. However, the solution procedure of the FEA model must be modified, in order to be compatible with ANM. Two-dimensional plane elements are required only in the local solution, to resolve the discontinuity. This finite-element order reduction provides significant savings in computation time. Comparison with traditional solution methods shows that the ANM approach accurately solves for local effects at each support, in addition to the overall response of the vibrating structure. The framework of applying ANM to more complex problems is also presented. [Work sponsored by ONR.]
Perceptual assimilation of Japanese vowels by American English listeners: effects of speaking style
Authors: Nishi Kanae , Strange Winifred , Akahane-Yamada Reiko , Trent Sonja A. , Thornton David H.
Published: July 2002

Our previous research on perceptual assimilation of non-native vowels to native categories showed that patterns of spectral and temporal assimilation vary with speaking style (citation vs sentence) and consonantal context. Japanese (J) listeners’ perceptual assimilation of American English (AE) long and short vowels to long (2-mora) and short (1-mora) categories was more consistent when the target syllables were presented in sentences (Strange, et al. ATR Technical Report, TR-H-218, 1997). In the present study, AE listeners categorized 4 speakers’ tokens of 10 J vowels /ii, i, ee, e, aa, a, oo, o, uu, u/ into 11 native AE categories and rated their goodness-of-fit on a 7-point scale (7 = native). Results indicated that patterns of temporal assimilation of the J short vowels /e, a, u/ differed with speaking style. Assimilation of /e/ to mid or high front spectral AE categories also varied with context and individual speakers. Goodness-of-fit ratings suggested that all 10 J vowels were considered relatively ‘‘good’’ instances of AE categories (medians = 5 to 7). In comparison with J listeners’ perception of AE vowels, AE listeners judged cross-language similarities between J and AE vowels more on the basis of their spectral characteristics than on their temporal characteristics.
Ability to perceive non-native contrasts with natural and synthetic speech stimuli
Authors: Gordon Peter C. , Keyes Lisa , Yung Yiu-Fai
Published: July 2002

The perception of the distinction between /r/ and /l/ by native speakers of American English and of Japanese was studied using natural and synthetic speech. The American subjects were all nearly perfect at recognizing the natural speech sounds while there was substantial variation among the Japanese subjects in their accuracy of recognizing naturally produced /r/ and /l/. A logit model, which additively combined the acoustic information conveyed by F1-transition duration and by F3-onset frequency, provided a good fit to the perception of synthetic /r/ and /l/ by the American subjects. There was substantial variation among the Japanese subjects in whether the F1 and F3 cues had a significant effect on their classifications of the synthetic speech; greater use of the F1 and F3 cues in classifying the synthetic speech sounds was positively related to accuracy in recognizing natural /r/ and /l/. These results show that tests using natural and synthetic speech tap into the same variation of ability in perceiving the non-native /r/–/l/ contrast by Japanese speakers. The relation between performance on natural and synthetic speech also provides external validation of the logit model by showing that it predicts performance beyond the data to which it was fit.
A damped sinewave vocoder
Authors: Hillenbrand James M. , Houde Robert A.
Published: July 2002

A speech analysis-synthesis system is described that operates by summing exponentially damped sinusoids at frequencies corresponding to spectral peaks derived from speech signal. The analysis begins with the calculation of a smoothed Fourier spectrum. A running average of spectral amplitudes is then computed for each frame over an 800-Hz window. The running average is subtracted from the smoothed spectrum to produce a ‘‘masked’’ spectrum. The signal is resynthesized by summing exponentially damped sinusoids at frequencies corresponding to peaks in the masked spectra. If an autocorrelation-derived periodicity measure indicates that a given analysis frame is voiced, the damped sinusoids are pulsed at a rate corresponding to the measured fundamental period. For unvoiced intervals, the damped sinusoids are pulsed on and off at random intervals. Results of a perceptual evaluation of the vocoder will be reported.
Long time-base measurements of surf noise
Authors: Deane Grant B.
Published: July 2002

Preliminary results from an experiment conducted over a year to measure surf noise will be presented. In July of 1997 a surf-monitoring sensor array comprised of four broadband hydrophones and a pressure sensor were deployed in 7 m of water, 200 m southwest of Scripps Pier and roughly 200 m from the surf line. Underwater ambient noise over the frequency range of 50 Hz to 22.5 kHz and wave height data from the pressure sensor has been acquired for 9 min every hour almost continuously since deployment. The resulting data set is in excess of 20 000 9-min samples, providing data through a wide range of incident wave fields and weather conditions, including several winter storms. Surf noise predominates on the frequency band of a few hundred Hertz up to 1 kHz. Variations in the surf noise levels can be seen on time scales of seconds, due to individual breaking waves; hours, due to tidal variations; and days, due to variations in the incident wave field amplitude. A preliminary analysis of the correlation between surf noise spectral levels and environmental factors, such as wave height and tidal variations, will be presented. [Work supported by ONR.]
Fine delay estimation in sonar echoes using frequency Prony method
Authors: Palakal Mathew J. , Liang Min
Published: July 2002

Wideband sonar target recognition is becoming important due to the fact that the echo reflected from a target contains more information about the target signatures. In a wide bandwidth sonar system, the echo consists of a sequence of the weighted transmitted signals emanating from the different scattering centers on the target. When a transmitted sonar waveform u(t) is reflected from a stationary or slow moving target, the received echo e(t) is the convolution of the transmitted signal u(t) and the target impulse response h(t), i.e., e(t)=∫−∞∞u(τ)⋅h(t−τ)=∑i=1Ma i⋅u(t−τi), where ai is the reflection strength of the ith scatter on the target, τi is the two-way propagation time delay between the ith scatter and the transmitter/receiver, and M is the total number of point scatters on target. The estimates of the parameters {ai}i=1M are normally chosen as target feature for classification and the difficulty is in estimating these parameters. In this work, the relative differences between time delays {τi}i=1M, i.e., fine delays {Δτi=τi+1−τi}i=1M−1, and the normalized reflection strengths {αi=ai/min(ai)}i=1M are selected as sonar target features. The Prony method is used in frequency domain to estimate parameters {ai}i=1M and {τi}i=1M and hence the target features. The methodology used for deriving the frequency Prony method (FPM) and the results of target feature extraction in noiseless case will be presented. [Work supported in part by NSF.]
Organic Rice—Designing a recital hall for the king of instruments
Authors: Myers Joseph W. A.
Published: July 2002

The Edythe Bates Old Recital Hall at Rice University’s Shepherd School of Music is a purpose-built organ performance hall, seating approximately 200. It houses a 75-stop French-style organ built by C. B. Fisk from tonal design by Manuel Rosales. The bare room was completed in 1991; a wood floor, loose chairs, and retractable acoustic banner system were added in 1995; the organ itself was installed in 1996; and diffusive elements were added to the rear wall in 1997 as voicing was completed. At each of these intermediate conditions reverberation times were measured and the acoustics of the room subjectively evaluated. The gradual fit-up of the room provides an interesting look at the incremental effect of each modification. The extensive adjustable acoustic banner system also provides a dramatic degree of variability inthe room’s acoustic environment. This paper compares the acousticians’ design intent for the room to the completed room and presents data and observations about the effects on the recital hall of the architectural modifications and acoustic banners.
Objective and subjective evaluations of pipe organ sound
Authors: Chaloupka Vladimir
Published: July 2002

Study of correlations between the perceptual and the physical attributes of musical sound is an important part of musical acoustics. This paper will review the status of this field, with particular attention to the pipe organ sound. The pipe organ is an ideal subject for such studies: the sound is simple enough for a study to be feasible, yet complex enough for the study to be interesting. A procedure for systematic measurements and evaluation of many aspects of the organ sound will be described. An interactive, PC-based system enables an efficient yet precise measurement of the fundamental frequencies, spectra of the partials, as well as of the nonharmonic component of all the pipes in an organ, and the transient behavior of selected pipes. Results are presented in a compact and easily understandable form: a ‘‘fingerprint’’ of the instrument. The main room acoustics measurements are also made. The emphasis is on the old but still intriguing question: what imperfections are necessary for achieving the perception of perfection (e.g., small but desirable irregularities in tuning, and in the scaling behavior). If the planned organ concert indeed takes place, measurements of the organ(s) will be made, and the results will be available.
Adaptive classification of ensonified underwater objects
Authors: Helweg David A. , Moore Patrick W. B.
Published: July 2002

The biological sonar system of bottlenose dolphins is adapted for cluttered, high noise, and extremely reverberant shallow-water environments such as bays, estuaries, and near-shore waterways. Echolocation behavior and signals are plastic, modified in-stride during encounters with novel targets and in novel surroundings. Moreover, biosonar target discrimination performance provides an existence proof for biological sonar-based recognition of various kinds of targets. For the dolphin this is accomplished in part by auditory neural computations that are not yet fully understood. A model of adaptive target classification processes was developed using heuristics based on dolphin psychophysics and echolocation behavior. Echoes were recorded while a dolphin ensonified several aspect-dependent targets during a target discrimination task. A computational model of dolphin ear filters was adapted to include filter gain recursively scaled to acoustical characteristics of local ambient noise and reverberation. Stochastic noise was attenuated by multi-ping fusion within an Integrator Gateway processing scheme. Output from the spectral filters served as inputs for a neural net target classifier. The system accommodated changes in local ambient noise and produced classification signficantly better than did traditional classifiers that lacked adaptive filtering processes. [Work funded by ONR 321US.]
An estimation technique of the vector component of blood flow from Doppler information on a plane
Authors: Ohtsuki Shigeo
Published: July 2002

The information of the ultrasonic Doppler effect is the velocity component of ultrasonic scatters in the direction of the ultrasonic beam in fluid. Scanning the ultrasonic beam, a colored Doppler image can be obtained on a plane. Using this data, the velocity component perpendicular to the ultrasonic beam is estimated. In this case, the observation plane is in three-dimensional flow. Considering sources of fluid in the plane, the flow function method [S. Ohtsuki and M. Tanaka, J. Visual. Soc. Jpn. 1869, 40–44 (1998)] is applied. This flow function method was developed for streamlines on a medical ultrasonic colored Doppler image of blood flow in the heart. The flow function without sources is expressed as a single-valued function. The flow function of sources is a multi-valued function named a laminar function. The flow function on an observation plane is the combination of these two functions. The gradient of the flow function on the plane is a flow vector component. The estimation technique introduced here is an application of the flow function method.
Simultaneous measurements of bulk and shear moduli of voided polymers in the 0.5- to 2.5-kHz range
Authors: Willis R. Lance , Wu Lei , Berthelot Yves H.
Published: July 2002

The complex, frequency-dependent, bulk and shear moduli of polymers containing microscopic inclusions can be measured simultaneously [see J. Acoust. Soc. Am. 102, 3549–3555 (1997)]. The method consists in measuring the surface dynamics of the sample under harmonic test by noncontact laser Doppler interferometry and by matching the experimental results with numerical predictions in which the two complex moduli are the adjustable parameters. Results obtained with a sample of known properties (lucite) confirm the validity of the method. Improvements to the system will be discussed. It is more compact and it uses only two miniature fiberoptic probe heads which can be scanned along the surface of the sample. Automated data acquisition with a lock-in amplifier greatly improves the speed of the experiment and enables good frequency resolution (less than 1 Hz) between 0.5 and 2.5 kHz. The measurement errors associated with this technique will be discussed in detail. In particular, measurements made on several samples taken from the same panel will be presented to quantify manufacturing variability. [Work supported by ONR, code 334.]
Calibration of high-intensity pulsed pressure fields
Authors: Madanshetty Sameer I. , Chandran Jogesh B.
Published: July 2002

Meaningful studies in acoustic cavitation require a thorough knowledge of the imposed acoustic fields. Besides knowing the field pattern one needs to know the pressure amplitudes imposed by the transducer. As an alternative to risking a fragile reference transducer like the GEC-Marconi bilaminar PVDF membrane hydrophone to high-intensity pressure fields, a robust method of absolute calibration involving a reflection type, pendulating radiation force balance is presented. In the process of characterizing such radiation force targets, the experiments indicate that the radiation force determined is not independent of the size of the target and one needs to account for an induced mass effect in seeking the radiation force balance. Additionally, using another modified design of the target to allow complete transmission of the sound beam one might be able to resolve the effect of streaming induced deflection and hence measure both the radiation force and the streaming force associated with long duty cycle pressure pulses. At low duty cycles of 1% no streaming force is observed. The fully reflecting radiation force balance for the calibration of high-intensity, low-megahertz frequency, focused acoustic fields has been found satisfactory for general purpose laboratory work.
Directivity of a continuous, uniform strength, circular arc source, phased to its diameter-sensitivity to phasing errors
Authors: Thompson William
Published: July 2002

An expression is presented for the in-plane directivity function of a continuous, uniform strength, circular arc source (or receiver) wherein the output of each element of the arc is phase shifted by a fixed fraction of the wavelength distance from that element to the diameter of the circle which is parallel to the chord joining the end points of the arc. Normally one chooses that fraction to be unity in order to simulate a straight line source, thereby achieving a narrow beamwidth. Some numerical results for various size arcs, for the case where the arc radius measures many wavelengths, are presented to illustrate how the beam pattern deteriorates (the beamwidth broadens and the side lobes increase in level) as that phase shift fraction is varied from the value unity. [Work supported by M. Dembrak, ASTO, through the Naval Sea Systems Command under contract No. N00039-D-0042, delivery order No. 53.]
Computational and experimental comparison of acoustic radiation of micro-loudspeakers
Authors: Shaw Jennifer A. , Burroughs Courtney B.
Published: July 2002

Experimental and computational methods were used to evaluate the acoustic performance of micro-loudspeakers which are utilized by portable communication devices. Experimental microphone measurements were taken in an anechoic chamber to determine the acoustic radiation as a function of frequency. Computational predictions were based on diaphragm surface velocity measurements obtained with a scanning laser doppler vibrometer. The velocity measurements were imported into SYSNOISE, and BEM analysis was used to calculate the acoustic radiation. Directivity patterns plotted in SYSNOISE were compared to those obtained by experimental methods. [Work supported by Motorola, Inc.]
Acoustic gas concentration analyzer
Authors: Florance Jennifer P. , Hoadley Sherwood T. , Zuckerwar Allan J.
Published: July 2002

A free-field acoustical gas purity analyzer/speed-of-sound measurement device has been developed as part of a calibration effort for the NASA Langley Transonic Dynamics Tunnel, an aeroelastic research facility which utilizes either an air or heavy gas testing medium. The device consists of a 40-kHz transmitter, two receivers, and a thermocouple, all housed within a portable anechoic chamber. The transmitter diameter/acoustic wavelength ratio is such that ultrasonic transmission takes place without sidelobes within a narrow illumination zone, precluding the need to correct for boundary layer losses. The time difference between the two received signals and the known distance between the receivers are used to obtain the sound speed. Sound speed, local temperature, and properties of the known pure gases are then used to calculate the gas purity. In wind-off conditions (where temperature corrections due to flow are avoided), the analyzer has achieved sound speed accuracies within approximately 0.11% in air and 0.05% in R134a. Gas purity values (which do not require tunnel-flow-condition matching) within 0.2% average uncertainty, compared to a calibrated infrared purity gauge, have been obtained both wind-on and off.
Validation of sonic boom propagation codes using SR-71 flight test data
Authors: Ivanteeva Lyudmila G. , Kovalenko Victor V. , Pavlyukov Evgeny V. , Teperin Leonid L.
Published: July 2002

Two propagation codes are compared with SR-71 flight test data from 1995. Code ZEPHYRUS (NASA) was developed for level flight in a stratified atmosphere with horizontal winds. Signal propagation marches along ray paths determined by geometrical acoustics, alternating between time and frequency domains. Atmospheric absorption effects are applied in the frequency domain. Propagation continues through caustics (ray focusing). Code BOOM (TsAGI) is based on the Whitham F-function method, without accounting for atmospheric absorption. Ray tracing includes effects of vehicle acceleration and three-component winds. Experimental data include pressure signatures measured by a chase plane (30 to 80 bodylengths away) and a low-flying observation plane (200–300 bodylengths). The observation plane recorded both direct and reflected waves. At distances of about 30 body lengths, predictions show only negligible differences between the codes. Small differences appear in predicted far-field signatures due to atmospheric absorption. Comparison of computed and measured results shows good agreement with peak pressure, duration, and wave shape, thus validating computational codes. [Work supported by the Boeing Company.]
Visual influences on the perception of alveolar/velar place discrimination
Authors: Hampson Michelle , Guenther Frank , Cohen Michael
Published: July 2002

Using ten acoustic stimuli ranging along a /ga/–/da/ continuum, visual influences on the psychophysical boundary between the auditory percepts of /ga/ and /da/ were investigated. A significant shift in the perceptual boundary was found depending on whether syllables were dubbed onto a video of a speaker uttering /da/, or whether they were dubbed onto a video of the same speaker uttering /ga/. The tongue of the speaker was not visible in either video clip, so only subtle cues were available to distinguish place of articulation in the two conditions. The shift in auditory perception was in a direction consistent with the visual information, and indicates that even the subtle visual cues available to discriminate velar stop consonants from alveolar stop consonants can play a role in speech perception. The possibility that other (nonarticulatory) visual cues could be conditioned to play a similar role in speech perception is raised.
Auditory lexical decision in young and older adults: Effects of lexicality and similarity neighborhood structure on spoken word recognition
Authors: Goodman Mara B. , Luce Paul A.
Published: July 2002

Younger and older (70+ yrs) adults made verbal lexicality judgments for words and nonwords presented in the clear. Stimuli included mono- and bi-syllabic items with high and low frequency-weighted similarity neighborhoods. Items were presented auditorily and subjects were asked to respond yes for word and no for nonword as quickly and accurately as possible. Subjects response times were measured from the onset of the auditory stimulus to the onset of the verbal response. Young and older subjects showed markedly different effects of lexicality on accuracy and reaction time. Moreover, differential age effects for similarity neighborhood structure on processing time were observed (independent of the frequency of the target word). Implications of present results for recognition strategies of older adults will be discussed. [This research was supported (in part) by research Grant No. 1 R01 DC 0265801-A1 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]
Diffusion coefficients
Authors: Hargreaves Tristan J. , Cox Trevor J. , Lam Y. W. , D’Antonio Peter
Published: July 2002

For nearly a century, the absorption coefficient has been used as a measure for the amount of energy lost when sound reflects from a surface. There is now a need for a diffusion coefficient which measures the angular distribution of the reflected energy. Diffusion coefficients enable the worth of diffusing surfaces to be evaluated and in the future could help improve the accuracy of geometric room acoustic modeling. A current investigation is looking at forming a diffusion coefficient that is clearly defined, has physical rigor, is usable in a variety of real life applications, and is easy to measure. The problems associated with finding a single parameter to meet all the above criteria will be discussed. A variety of measures for monitoring the diffusion from unbaffled surfaces will be presented, as well as possible solutions for baffled and large surfaces.
Sonic boom acceptability studies at NASA Langley Research Center
Authors: Sullivan Brenda M. , Shepherd Kevin P.
Published: July 2002

As part of the High Speed Research Program at NASA, Langley Research Center conducted a series of studies during the period 1990–1995 to evaluate human responses to sonic boom impact. This work, in combination with aircraft configuration design efforts, was aimed at determining the feasibility of overland supersonic flight. NASA conducted a three part program, comprising laboratory studies, in-home field experiments and community surveys. The laboratory studies used a sonic boom simulator and were designed to quantify relative loudness and annoyance response to a wide range of shaped boom signatures that might be produced by advanced aircraft configurations. The primary conclusion was that several common noise metrics were able to reliably predict judged loudness/annoyance. Field experiments were conducted in people’s homes using a noise simulation system. A controlled sound environment of booms of known level and number was introduced into a realistic home setting and human responses to a variety of boom exposures were assessed. It was found that the ‘‘equal energy’’ hypothesis was applicable to these boom exposures. Community surveys were conducted in two areas routinely impacted by sonic booms from military aircraft. Relationships between boom exposure and residents annoyance were developed for the two survey areas.
Viability of yeast cells in propagating ultrasonic waves
Authors: Radel Stefan , McLoughlin Aiden J. , Benes Ewald
Published: July 2002

In some recent papers the upper limits for the acoustic pressure amplitudes, in standing wave fields, that exert no measurable influence on viability of various biological cells have been reported. However, the pressure amplitude in a standing wave is periodically varying in space in the direction of sound propagation and, because of radiation pressure, the cells are not homogeneously distributed within the sample volume, resulting in effects arising from the dynamic environments created. Thus standing waves are obviously not appropriate to study the direct influence of sound pressure amplitude on viability data. Therefore, both metabolic activity/viability of yeast cells and their ability to replicate as a function of acoustic frequency and sound pressure amplitude have been investigated in propagating waves. The observed effects are compared to those in crossed beam fields and in standing plane wave fields. The results allow a better forecast and interpretation of viability threshold data relevant in predicting the effects of acoustic parameters in standing wave fields. [Work supported in part by the European Commission, Contract No. ERBFMRXCT970156.]
Ultrasonic standing waves to enhance optical particle sizing equipment
Authors: Holwill Ian L. , Martin Andy T.
Published: July 2002

Experiments have been performed using dynamic light scattering (DLS) apparatus to investigate the potential of the use of ultrasonic forces for in situ removal of unwanted particles from the measurement volume. Megahertz frequencies were used to move micron-sized particles from the laser beam focus and leave the submicron particles for measurement. Removal of polystyrene latex (PSL) particles down to a diameter of 2 μm was demonstrated while leaving particles with a diameter below 100 nm unaffected to be accurately measured by the DLS technique. Further experiments have been performed on airborne particles in custom-built single-particle light scattering apparatus. The aim of this study was to direct particles toward a laser focus for sizing by forward light scatter measurements. Sub-100 kHz standing waves were used to direct micron-sized particles to a laser beam focus for analysis. Large particles (of the order of 20 μm) were very successfully moved toward the laser focus, and adjustment of the power to the transducers allowed continuous, real-time control of the concentration of particles delivered to the measurement volume. A concentration range of approximately 100:1 was achieved. For smaller particles below 10 μm, the concentration range was limited to 2:1.
Analysis of the sound emissions of captive bottlenose dolphins (Tursiops truncatus)
Authors: Mello Inês , Brito Cristina , dos Santos Manuel E.
Published: July 2002

Bottlenose dolphins (Tursiops truncatus) produce a great variety of sounds, including whistles, echolocation clicks, and other pulsed sounds. The behavior and the sound emissions of eight bottlenose dolphins were studied in a dolphinarium (Zoomarine, Albufeira, Portugal). Acoustic recordings were made with a B&K 8103 hydrophone and a Sony TCD-D10 Pro DAT recorder. Systematic behavioral observations were conducted (including show behaviors) simultaneously with acoustic recordings. Whistles were the most abundant signal type (n=4238) and several frequency modulation profiles were found to be repeatedly produced. Echolocation click trains and other pulsed signals were also produced. Whistle production throughout the day showed statistical concordance among 4 days of systematic sampling. Highest levels of whistle production occurred in interactions among the dolphins and in interactions between the dolphins and their trainers. The clicks and other pulsed sounds, more frequent in resting and swimming, showed a similar occurrence cycle throughout the day. Performances of conditioned behaviors (during shows) were associated with decreased levels of whistles and increased levels of click trains and other pulsed sounds.
Localization of sounds from a paired source in the dolphin and fur seal
Authors: Zaslavski Gennadi L.
Published: July 2002

There is a notion that the dolphin’s spatial hearing operates similarly to that of humans, even though the dolphin’s ability to localize a source in the vertical plane is practically the same as in the horizontal one. Binaural phenomena are used to explain localization in the dolphin; however, there are no interaural differences in the vertical plane. Given the dolphin’s very short echolocation click and high time resolution, one would find it difficult to describe the dolphin’s hearing in terms of binaural phenomenon. The dolphin’s sonar system performs as a monaural rather than a binaural system [G. Zaslavskiy and V. Ryabov, in Marine Mammal Sensory System (1991)]. In fact, very directional sonar click transmission and reception seem to account well for the dolphin’s spatial hearing. In the present study, the way in which dolphins and fur seals respond to a sum of the signals from two sources will be discussed. There are different hearing phenomena in the human associated with the binaural perception of the sound coming from two different directions. Some of these phenomena were found in the fur seal but none of them was present in the dolphin.
High-frequency acoustic propagation measurements in coastal areas
Authors: Lopes Joseph L. , Paustian Iris C. , Commander Kerry W. , Stroud John S.
Published: July 2002

A measurement was conducted in a very shallow-water (VSW)/surf zone (SZ) region to investigate acoustic propagation and coherence in coastal areas. The measurement utilized several acoustic sources and hydrophones. The sources were mounted onto a stationary sonar deployed in the VSW. The sonar tower was equipped with a horizontal pan and vertical tilt motors. The hydrophones were attached to steel pipes that were water-jetted into the sediment such that the hydrophones were located in the SZ near the midpoint of the water column. The acoustic frequencies varied from approximately 30 to 800 kHz. Data were acquired by directing the acoustic sources (located in the VSW) toward the free-field hydrophones. The data were analyzed using coherence techniques. Results of this acoustic measurement will be reported.
Thermoacoustic research at ETH Zürich in the 1990s
Authors: Bösel J. , Trepp Ch.
Published: July 2002

The linear thermoacoustic theory was developed by N. Rott, formerly Professor at the Institute of Aerodynamics at ETH Zürich, in the late 1960s. Since then a couple of research projects in that field have been carried out under the supervision of Prof. Rott, and more recently at the Institute of Process Engineering. The talk will give a short historical summary of the research activities at ETH Zürich and the latest work undertaken at the Institute of Process Engineering will be presented. This research was aimed at increasing the power density of thermoacoustic engines. Instead of the ‘‘stack,’’ usually consisting of ‘‘long’’ parallel plates, short parallel-plate segments were used, which were randomly oriented to each other. This alternative stack arrangement was expected to benefit from improved heat transfer characteristics and an anisotropic thermal conductivity. The results of a simple numerical model and experiments carried out with a thermoacoustic heat pump confirmed these expectations and will be presented in the talk. a)Former affiliation.
Acoustic boundary layer phenomena near a corrugated surface
Authors: Mehl James B. , Moldover Michael R.
Published: July 2002

Acoustic resonator techniques for measuring thermophysical properties require a quantitative understanding of the viscous and thermal boundary layers. Near smooth solid boundaries, well-known analytic models of boundary layers have been confirmed by careful measurements. Little is known either experimentally or theoretically about the effects of surface roughness on the boundary layers. Roughness effects have been investigated through numerical calculations of the coupled acoustic, thermal, and shear fields near a corrugated interface, i.e., a surface with a profile y=A cos qx. The calculations were carried out in the limit where the acoustic wavelength is much larger than the scale of surface roughness (A,2π/q) or the penetration lengths δt and δv. Boundary layer phenomena cause phase shifts and energy absorption in the reflection of a plane acoustic wave by a smooth surface. These effects are further modified at a corrugated reflecting surface. The calculated reflection coefficients have been applied to the model relating the speed of sound to the frequencies of spherical and cylindrical acoustic cavity resonances, and to the theoretical model of the Greenspan acoustic viscometer. [Research supported in part by the Office of Naval Research.]