bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of sound by bubble clouds
Authors: Hogan Karin M. , Banta Katherine L. , Korman Murray S.
Published: October 2005

Experimental results are shown for the scattering of ultrasonic pulses by a small volume of air bubbles in water. Two different types of bubblemakers are used to generate the bubble clouds. The first one uses an array of short wires spaced uniformly over a horizontal square area. A transient electronic pulse (of width τ) which has a period T, is simultaneously sent to each individual wire to generate microbubbles through electrolysis. The individual bubble radius generated at each wire is found to depend on the period of the repeated transient pulse. This bubblemaker is used to generate a vertical column of bubbles. The second bubble maker involves the regulation of a transiting volume of air stored in a chamber placed between two solenoid valves. The air escapes through a fine pore fritted disk to produce a transient bubble cloud. Preliminary scattering measurements are presented. Comparisons with theory are made from estimates of the void fraction β, the average bubble radius r0, and other geometrical parameters of the cloud. [Work supported by the Naval Acad. Res. Council.]
Mathematical analysis of machinery noise
Authors: Seybert A. F.
Published: October 2005

As an aid to understanding and controlling machinery noise, mathematical methods may be used. Because of the complex geometry involved, the methods are normally implemented numerically. with solutions obtained on the computer. Two such methods are the finite element method and the boundary element method. This presentation will review and compare these two methods as they are generally applied to machinery noise prediction. The development and practical application of the methods during the past five years will be discussed. Examples illustrating where each method has advantages or disadvantages will be presented. The role of mathematical and computer analysis of machinery noise in the future will be discussed, including the limitations imposed by lack of easy-to-use software and fast computers.
History, progress, and development of a standard for measurement of the noise of new machinery at the operator's position
Authors: Roth Stephen I.
Published: October 2005

An engineer should be able to request reliable and accurate equipment noise level data from a manufacturer to determine equipment acceptance. If analysis of the data indicates excessive noise, the engineer should proceed with an approach to insure an acceptably quiet installation. ANSI Working Group S12/WG20 is writing a standard to assist an engineer in obtaining noise level data of new, stationary equipment. ANSI S12.20 will incorporate the use of existing ANSI, trade association, and professional society noise measurement standards. It will incorporate guidelines to allow the user to interpret equipment noise level data. It is hoped that if users frequently request noise level data using ANSI S12.20, manufacturers will be better prepared to provide noise level data resulting in more accurate, consistent, and timely noise level information for user evaluation.
Scattering by thick cylindrical shells: Ray methods for shell reverberations and experiments
Authors: Marston P. L. , Sun N. H. , Parry S. P. , Hughes D. H.
Published: October 2005

A previous analysis of internal reverberations [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 88, 1114–1122 (1990)] gave the curvature correction to the specular contribution fsp to the form function for backscattering from spherical shells. This was extended to the case of circular cylinders at normal incidence. The result for fsp is R esp(− 2ix) + fcc where the curvature correction is fcc = (rein1 − reiα −  ∑ n 1∞ rneinα(1 + nB)1/2) (1 − r2r) e−i2x with x=ka and the other symbols are as defined for Eq. (8) of the previous analysis for fluid spherical shells. Comparisons with exact partial-wave series computations for fluid shells show good agreement. They exhibit a dip in |fsp| when x is small and when x approaches the thickness resonance. The features are generally similar to those for spheres. The relevance of fsp to the calibration of tank experiments on the scattering of short tone bursts from elastic shells is examined. The experiments separate leaky Lamb wave contributions from specular contributions. [Work supported by ONR.]
Analysis of the acoustic scattering from large aspect ratio, axisymmetric shells
Authors: Hackman Roger H. , Fang T.
Published: October 2005

The development of theoretically sound, “exact” numerical solutions to the scattering from spheroidal shells is important both to establish a nontrivial benchmark and to establish those salient features that may be characteristic of a larger class of more complicated, but related geometries. In previous meetings [J. Acoust. Soc. Am. Suppl. 1 83, S94 (1988); 82, S49 (1987)], the predictions of the spheroidal-coordinate based transition matrix formalism was validated for such targets by a direct comparison with experimental measurements of the backscattered form function of a copper prolate spheroidal shell for general angle of incidence. In these studies, a number of open questions emerged pertaining to the prominent elastic features of the form function of the shell. These questions are revisited here and the elastic response of the shell in terms of the modes of a fluid-loaded, infinite cylindrical shell is analyzed. In this work, it is particularly useful to study the evolution of the scattering as the thick shell limit is approached with reference to the scattering solution (and modes) of a solid elastic target. By examining the evolution of the prominent features of the scattering solution, the evolution of the underlying modes of the system can be inferred. This evolution shows a strong analogy to the evolution of the modes of a spherical shell presented previously.
Determination of material composition from time-domain and frequency-domain resonance echoes of submerged elongated elastic targets
Authors: Dean C. E. , Werby M. F.
Published: October 2005

When scattering from elastic targets backscattered echoes yield interesting information in the resonance region. In particular, resonance scattering theory in the frequency domain along with the circumferential nature of resonances imply that material constituency is a characteristic of resonance location. Moreover, recent discussions of resonance signatures in the time domain [see Uberall's book to be published on resonance scattering] can also yield information concerning resonance widths and average phase velocities which can also be related to material characteristics. By adjusting the orientation of the target over a suitable angular region it is possible to ascertain certain symmetries of the target if they exist, particularly if one varies the frequencies over a suitable range of resonances. If one observes axial symmetry through such a process, then it is possible to obtain both the dimensions of the object and the aspect ratio of the object (ratio of length to width). This is assuming that the target is in a “free” environment; that is, the boundaries of the target are not a factor in calculation. Time-domain responses for specific pulse types also yield information and it is easy to see how a series of questions can form the basis of a scenario that can rule out certain targets or lead to a probability (confidence level) that specific targets are present. To determine the extent that this can be done, targets are examined which are composed of five materials for elastic solid spheroids for aspect ratios of 3 to 1 and 6 to 1 for end-on incidence and for the case of 4 to 1 for all incident angles.
Intelligent ultrasonic signal processing for solving inverse scattering problems
Authors: Sachse Wolfgang , Grabec Igor
Published: October 2005

This paper describes new intelligent or neural-like processing procedures by which the ultrasonic signals scattered by an obstacle can be processed to recover the characteristics of the unknown scatterer. In particular, it focuses on the recently developed automatic modeler by which the characteristics of the scattering phenomenon from a number of scatterers is learned using a set of systematic learning data. It is demonstrated that ultrasonic signals measured in subsequent tests from an unknown scatterer can be processed to optimally recover the characteristics of the unknown obstacle. The solution of the inverse scattering problem that is obtained is thus completely empirical and not based on any elastodynamic theory. [Work supported by the National Science Foundation under Grant MSM-8904384.]
A statistical study of the relation between weather conditions and sonic boom waveforms
Authors: Yao Lixin , Bass Henry E. , Raspet Richard
Published: October 2005

Sonic boom data collected at Edwards Air Force Base in Oklahoma City in the 1960s have been examined to check the validity of some common assumptions concerning the role of turbulence on sonic boom waveforms. A Turner Class was assigned to each flyby based upon reported ground weather conditions. This Turner Class was then used to indicate the presence of convective or mechanical turbulence or stable stratification. The correlation between the Turner Class and the waveform and rise time was then calculated. These results indicate that mechanical turbulence is associated with sonic booms that have more rounded shapes and a greater rise time than common for stable conditions. [Work supported by NASA Langley Research Center.]
Low-frequency long-range sound propagation over impedance discontinuities with the parabolic approximation
Authors: Schlatter P. J. , Robertson J. S. , Siegmann W. L.
Published: October 2005

Previous studies have shown that the parabolic approximation method, widely used in ocean acoustics, can be successfully applied to low-frequency long-range atmospheric sound propagation over a locally reacting boundary, an important problem with many applications. This work models cw acoustic signals as they propagate over horizontal ground surfaces with impedance discontinuities. An implicit finite-difference implementation of the parabolic approximation sound propagation model incorporating locally reacting, variable-impedance ground surfaces is employed to compute estimates of the sound field excess attentuation for a variety of flow resistivities and source frequencies. Both windy and stationary atmospheres are considered. An accuracy benchmark and several example problems in which the sound propagation path includes an idealized lake will be discussed. [Work supported by NASA.]
Acoustics of marine fog: Present standards of transmission, reception, and projection
Authors: Browning David G. , Fitzpatrick Michelle
Published: October 2005

The standards for sound propagation in marine fog have been in service for many years. For example, computations of propagation loss are based on the work of Wiener [F. M. Wiener, J. Acoust. Soc. Am. 33, 1200–1205 (1961)]. Similarly, standards for reception and projection of acoustic signals in marine fog are based on work by Bolt Beranek and Newman Inc. in 1960. A review is made of results that has been published since that time to see if any possible improvements have been suggested.
Array processing for wave vectors and modes in structural acoustics
Authors: Baggeroer Arthur B.
Published: October 2005

Array processing methods have emphasized beamforming and directional spectrum estimation for equally spaced, linear arrays with single component sensors that are in a homogeneous signal field with long duration data. Structural acoustics problems often have just the opposite characteristics with irregular spacing of multicomponent sensors that are in inhomogeneous wave fields with transient data. These eliminate many array processing methods and require generalization of others. Recently, array processing methods such as matched field and matched mode, slowness-time spectra, and singular value decomposition have been advanced and used for structural acoustics. This presentation will give an overview of advanced array processing methods with an emphasis on those applicable to problems in structural acoustics. [Work supported by ONR.]
Theory and experiment of two concentric submerged cylindrical shells coupled by the entrained fluid
Authors: Yoshikawa Shigeru , Williams Earl G. , Washburn Karl B.
Published: October 2005

In this paper theory and experiment for the coupled vibration of two concentric cylindrical shells (double shell) are described; the inner shell contains air, the outer shell is surrounded by water, and water exists in the annular space between them. A point force is applied to the inner shell, whose displacement produces acoustic pressure in the annular space and in turn this pressure wave drives the outer shell. The nature of acoustic field in the annular fluid and its coupling effect on the shells is investigated. Using Flügge's shell equations and the Helmholtz equation, the normal modes of an infinite double shell are calculated. The theory includes the effect of initial prestress (uniform axial compression). The results of these numerical calculations in wave-number space will be compared with the results from generalized near-field acoustical holography (GENAH) experiment on a simply supported finite double shell. The wave-number/frequency representation of this double shell will be also compared with that of a single submerged shell.
Auditory psychophysical performance without a cochlea
Authors: Shannon Robert V.
Published: October 2005

Auditory psychophysical performance has been measured using electrical stimulation of the remaining VIII nerve and of the cochlear nucleus in deaf patients. Psychophysical measures of temporal envelope processing show relatively unimpaired performance in these patients compared to normal hearing, and speech discrimination scores indicate that speech information relating to temporal envelopes can be effectively transmitted and received. This finding also indicates that the cochlea and VIII nerve may play relatively little role in the following tasks: detection of gaps, detection of modulation, recovery from adaptation, nonspectral pitch discrimination, and duration discrimination. Intensity perception is impaired with electrical stimulation: dynamic range of usable loudness is only 10 to 20 dB and intensity discrimination experiments indicate only 10 to 40 discriminable intensity levels. Frequency resolution is completely absent in electrical stimulation and can be only crudely reconstructed by multiple electrodes stimulating discrete neural segments. Psychophysical experiments on multiple electrodes indicate that patients can perceive and discriminate complex dynamic patterns of electrical activity changing in both stimulation frequency and electrode location. The combination of temporal envelope formation and the coarse “frequency” resolution provided by multiple electrodes is adequate to convey a surprising amount of speech information. [Work supported by NIH.]
An analysis of errors in lipreading sentences
Authors: Demorest Marilyn E. , Bernstein Lynne E. , Eberhardt Silvio P. , De Haven Gale P.
Published: October 2005

The long-range goal of this research is to understand the visual phonetic and cognitive/linguistic processes underlying the lipreading of sentences. Bernstein et al. [J. Acoust. Soc. Am. Suppl. 1 85, S59 (1989)] described development of a sequence comparison system that produces a putative alignment of stimulus and response phonemes for lipread sentences. Such alignments permit sentences to be scored at the phonemic level and also permit examination of the types of errors that occur. In this study the sequence comparator was applied to a database containing responses of 139 normal-hearing subjects who viewed the 100 CID everyday sentences [Davis and Silverman, 1970], spoken by a male or a female talker. Analysis of the alignments was made possible by the development of a powerful parsing program that tabulates the frequency of user-specified stimulus or response patterns and generates confusion matrices for selected portions of these patterns. To examine the impact of sentence environment, vowel and consonant confusion matrices derived from the sentences were compared to those obtained from nonsense syllables. To probe for context effects, performance on individual sentences was examined as a function of sentence, word, and syllable characteristics. [Work supported by NIH.]
Lipreading sentences with vibrotactile vocoders: Performance of normal-hearing and profoundly deaf subjects
Authors: Bernstein Lynne E. , Demorest Marilyn E. , Coulter David C. , O'Connell Michael P.
Published: October 2005

Three vibrotactile vocoders were compared in a training study involving aided and unaided lipreading: (1) the Queen's University/Central Institute for the Deaf vocoder, with one-third octave filter spacing and logarithmic output compression (CIDLog) [Engebretson and O'Connell, IEEE Trans. Biomed. Eng. BME-33, 712–716 (1986)]; (2) the same vocoder with linear output equalization (CIDLin); and (3) the Gallaudet University vocoder designed with greater resolution in the second formant region, relative to the CID vocoders, and linear equalization (GULin). Nine normal-hearing and four profoundly hearing-impaired adults participated in the training study. Four of the normal-hearing subjects were assigned to either of two control groups, a group that received no vocoder, and a group that received the previously studied CIDLog vocoder [Brooks and Frost, J. Acoust. Soc. Am. 74, 34–39 (1983); Weisenberger et al., J. Acoust. Soc. Am. 86, 1764–1775 (1989)]. The remaining subjects were assigned to the linear vocoders. GULin was the only vocoder significantly effective in aiding open-set sentence identification, and benefit extended to each subject who received that vocoder. [Research supported by NIH.]
Speech perception ability of adults with multiple-channel cochlear implants, using the spectral maxima sound processor
Authors: McKay Colette M. , McDermott Hugh J.
Published: October 2005

The spectral maxima sound processor (SMSP) was designed at the University of Melbourne for use with the 22-electrode cochlear implant manufactured by Cochlear Pty. Ltd. The processor utilizes a bank of 16 bandpass filters that are assigned to 16 electrode pairs tonotopically. In each stimulation period (typically 4 ms) six electrode pairs are stimulated. The selection of electrodes and stimulation levels are determined by the six filters having the highest amplitude outputs. Speech perception results with a number of adult implantees were obtained and the SMSP's performance compared with that of commercially available speech processors designed for this implant, including the most recent MSP (multi-spectral-peak processor). These results show that, for the subjects investigated, the SMSP improved speech perception ability, in quiet and in noise. This was true both for vowels and for consonants. Speech tests used in this study included open-set sentences, open-set monosyllabic words and closed-set vowel and consonant confusion tests. The tests were administered in the auditory-alone condition.
Use of spectral and temporal cues in vowel identification by normal-hearing and hearing-impaired listeners
Authors: Van Summers W. , Leek Marjorie R.
Published: October 2005

Listeners with sensorineural hearing impairments generally show deficits in frequency resolution accompanying their decreased auditory sensitivity. Poor frequency resolution may make it difficult for these listeners to distinguish among vowels with similar formant frequencies. In English, these vowels tend to form tense/lax pairs (e.g., i/ɪ, æ/ɛ) which differ in duration. The present study examined hearing-impaired and normal-hearing listeners' use of duration and formant frequency information in the labeling of synthetic CVC stimuli forming a /bit-bit/continuum. Durational and F2 frequency cues to vowel identity varied systematically across stimuli. Frequency resolution at 2000 Hz (the F2 region for i/ɪ was measured using a notched-noise masking paradigm. A temporal difference limen for a narrow-band noise centered at 2000 Hz was also measured. Subjects with normal frequency and temporal resolution tended to rely primarily on formant frequency information in the vowel labeling task. However, subjects with abnormal frequency resolution but near-normal temporal difference limens made greater use of vowel duration in vowel identification. [Work supported by NIH.]
A simplified representation of speech for the hearing impaired
Authors: Kates James M.
Published: October 2005

A new approach to improving speech intelligibility in noise is being developed for the hearing impaired. The approach is based on sinusoidal modeling of speech, in which the speech waveform is divided into over-lapping segments, the FFT computed for each segment, and the N-highest peaks are identified. The speech is then resynthesized using sinusoids having the amplitude and phase of the selected peaks, and the remaining spectral information is discarded. Using a small number of sinusoids results in a simplified speech signal; the most intense speech components of any given segment are reproduced, while the less intense speech and noise components are not. The question under consideration is how the speech intelligibility varies as the number of sinusoids is reduced. Normal- and hearing-impaired listeners were asked to judge the intelligibility of sentences in quiet and at a 5-dB speech-to-babble ratio; the results to be presented compare unprocessed speech with speech reproduced using 16, 8, and 4 sinusoids. [Work supported by NIH.]
The role of experiments understanding shallow water coherence and predictability
Authors: De Ferrari Harry A. , Wormser Daniel
Published: October 2005

The combined effect of volume, surface, and bottom scattering and fluctuation in the propagating medium greatly complicates the prediction of fluctuations and coherence for bottom-limited acoustic transmission paths. Of these effects, modeling the bottom is the least well understood and most difficult. Wave fronts interact with the bottom and subbottom, which often have unknown and indeed unknowable range-dependent bathymetries and geoacoustic properties. Exploratory experiments even with limited environmental data, combined with propagation models, provide insight in the sorting out of the relative importance of numerous parameters. After a few bottom bounces, and at intermediate ranges, depending on frequency and other parameters, the sound field is no longer a predictable incoherent detail. Yet average properties such as pulse envelopes after long time incoherent averaging can be predicted and even used in very precise tomographic inversions. At longer ranges, pulse envelopes become unpredictable, even with good average range-dependent sound-speed profiles. And at still longer ranges, signal coherence may be breaking down, resulting in the loss of the 20 to 30 dB of processing gain necessary to see signals above noise. A number of experimental results from the Florida Straits with ray, normal mode, and PE models are examined. Many potentially randomizing factors seem to average out or have little effect, even in the very complicated environment of the Florida Straits. There appears to be an order and simplicity out to usable ranges. Model results raise new questions and suggest new types of experiments. [Work supported by ONR.]
Volume scattering measurements with a 12-kHz multibeam echo sounder
Authors: de Moustier C.
Published: October 2005

Acoustic volume reverberation measurements were made with a 12-kHz sea beam multibeam echo sounder by recording quadrature samples of the echoes received on each of the system's sixteen 2.66° beams. For initial inspection, the signal amplitudes from three channels (a center channel and outer channels on either side) were displayed as a function of depth and along-track distance in a grey level image quantized to 4 bits. Deep scattering layers identifiable in these images were analyzed by integrating the echoes received on each beam over a 50-m depth slice containing a layer or set of layers and by correcting for beam pattern and time spread effects as a function of angular direction. Results from data recorded during night time periods in the Northern Pacific show a fairly consistent volume scattering picture with variations averaging about 10 dB over 4-km segments along the ship's track, and 2 to 3 dB over a few hundred meters across track. The centroid of the returns in the 50-m window was also calculated for each beam and showed an along-track wavy pattern with an amplitude of about 10 m and a “period” of roughly 120 to 140 m. These results are discussed along with applications for 3-D mapping of volume scattering and patchiness distribution. [Research sponsored by ONR.]
Seismo-acoustic effect of trapped air pockets underneath a floating ice plate
Authors: Chamuel Jacques R.
Published: October 2005

Little is known about the characteristics, distribution, and role of trapped air pockets present underneath the Arctic ice cover. Laboratory ultrasonic modeling results are presented demonstrating striking effects of small trapped air pockets underneath a floating plate on broadband pulsed flexural waves. The thickness of the trapped air pocket is small compared to a wavelength. The experimental studies were conducted on ice, Plexiglas, and glass plates floating on water. The air pockets increase the flexural wave velocity causing horizontal refraction and shadow zones in the plane of the floating plate. A variety of air pocket sizes and cluster configurations have been investigated. The presence of a shallow-water pool on the top surface of the floating plate has a negligible effect on the flexural wave compared to an air pocket of the same dimensions located underneath the plate. A number of different phenomena occur causing the amplitude of the detected flexural wave to be attenuated or simplified. The new findings indicate that trapped air below the Arctic ice cover may play a significant role in Arctic acoustics. [Work sponsored by ONR.]
A comparative experiment on under-ice acoustic scattering in the marginal ice zone
Authors: Buckingham Michael J.
Published: October 2005

For several years a series of ambient noise experiments has been conducted in the marginal ice zone (MIZ) off the east coast of Greenland from a fixed-wing airborne platform. In the spring of 1991, in addition to ambient noise measurements, a propagation experiment will also be attempted, aimed at establishing the effect of scattering due to the under surface of the ice cover. Parallel to the ice edge, two lines of omnidirectional sonobuoys will be deployed over a distance of about 100 km, one line about 1 km out in the open ocean and the other 1 km within the ice field. Explosive shots will be detonated at both ends of the dual line. Being so close, the primary difference between the propagation conditions down the two lines is in the scattering from the ice cover relative to that from the open-sea surface—bathymetry and sound-speed profiles being essentially the same. To support this experiment AXBTs will be deployed along both lines of buoys, although, in view of salinity variations in the vicinity of the ice, airborne expendable sound velocimeters would be preferable. These are planned for future Arctic experiments. An airborne technique for measuring the under-ice profile would also be highly desirable.
Focused beamforming for vertical line arrays in near-field bottom scattering experiments
Authors: Caruthers Jerald W. , Chandler Howard A.
Published: October 2005

A fine-scale acoustic bottom scattering experiment is planned for the summer of 1993 on the Mid-Atlantic Ridge flank just north of the Kane Fracture Zone as a part of the Acoustic Reverberation Special Research Program (ARSRP). The site (or sites) of the detailed experiment will be about 5 × 5 km. The experimental design includes the use of four vertical line arrays moored near the bottom within the site. Several factors complicate the geometry of the experiment, one of which is that the scattering patch will be in the near field of the arrays. This will require the use of focused beamforming for viewing a scattering patch within the experimental site. Added difficulties arise in the fact that, within the experimental specifications, the arrays may not be straight and vertical and the bottom may not be horizontal. An algorithm has been formulated for the phase shifts required at elements along a distorted vertical line for focusing on points on a sloped flat plane for use in processing the data to arrive at a valid value for scattering strength. Presented are calculations that show effective “beam patterns” in the experimental geometry and other geometric considerations affecting the experiment and the calculation of scattering strength. [Work supported by ONR.]
Courtship communication and hearing in an African electric fish
Authors: Crawford John D.
Published: October 2005

Among sound-producing fishes, Pollimyrus isidori is of particular interest because of its unusually large repertoire of sounds (5), and because its ears (sacculi) are specialized for sound pressure detection. Males use temporally patterned sounds for courting females, and the male's sonic behavior is elicited by electric signals from the female. The courtship sounds are composed of trains of clicks, and inter-click interval (ICI) distinguishes the different sounds. The processing of these temporal features is being explored in the brain (mesencephalon) with single unit electrophysiology. The P. isidori auditory system is most sensitive to sounds in the region where amplitude spectrum for the communication sounds peaks (235 Hz), and at a distance of a meter from a sound-producing male (i.e., about 20 body lengths) many neurons would be at least 20–30 dB above threshold. Most neurons are broadly tuned (Q10dB⩽2), and precisely represent temporal periodicities in their phase-locked activity. A subpopulation of neurons shows an increased probability of response when the ICI is close to that of one of the courtship sounds. These neurons probably play an important role in the brain's analysis of temporal features of communication sounds. [Work supported by NIH NRSA DC00020-02 and CDR P50 DC00293-06.]
Structure-function relationships in the auditory system of the mustache bat
Authors: Park Thomas J.
Published: October 2005

The mustache bat depends on interaural intensity differences (IIDs) for localizing returning sonar signals. The inferior colliculus (IC) contains many neurons that are excited by sound at one ear and inhibited by sound at the other and are thus sensitive to IIDs. These neurons were studied to determine how their response properties and spatial receptive fields are shaped by the convergence of inhibitory inputs from lower centers. Inhibitory pathways (GABA-ergic and glycinergic) to the IC were identified by colocalizing a retrograde tracer injected in the IC and antibodies against putative transmitters. Glycinergic projections to the IC arise from the superior olive and GABA-ergic projections from the lateral lemniscus and IC interneurons. The effects of GABA and glycine were then assessed by iontophoresing agonists and antagonists of the transmitters onto individual IC neurons while recording acoustically evoked responses. Application of GABA and glycine inhibited responding, while application of GABA and glycine receptor blockers increased responding. Furthermore, both blockers were capable of expanding the neuron's receptive field. This result suggests that inhibition in the IC functions to “fine tune” IID-sensitive neurons by narrowing their receptive fields. [Work supported by NIH.]
Baleen whale vocal behavior: A synthesis of what we have and have not learned
Authors: Edds Peggy L.
Published: October 2005

The earliest attempt to record the sounds of a baleen whale was by Schevill and Lawrence [Science 109, 143–144 ( 1949)]. Since that time, a growing body of literature has revealed that sound production by baleen whales is quite variable, including relatively narrow-band or tonal calls, and broadband, pulsed series with variable repetition rates or complex amplitude/frequency modulations, as well as flipper slaps, tail slaps, and “noisy” underwater exhalations that appear to be communicative. Although interest in the songs of hump-back whales once dominated the field, numerous studies have documented the behavior and vocalizations of other baleen whale species. A brief review and synthesis of those studies will be provided, and the concepts of “contact” calls, “song,” “social sounds,” and individual variation will be considered. In addition, the limitations of acoustical censusing will be discussed. [Original research by the author was supported by ONR, AAUW, and the Cetacean Society.]
Acoustic response times (RTs) for Tursiops truncatus
Authors: Ridgway S. H. , Carder D. A. , Kamolnick P. L. , Skaar D. J. , Root W. A.
Published: October 2005

Seven dolphins (4 males and 3 females age 5–30 +) were trained to make underwater acoustic responses (ARs = whistles or pulse trains) to tonal or click train (10-ms interclick interval) stimuli (St). After first training, St delivery and AR and RT recording was computer controlled. St duration varied from 60–450 ms. St were 120 dB (re:1 μ Pascal peak to peak at 1 m) ±24 dB in 6-dB steps. With the dolphin at 1-m depth and 1 m from St hydrophone, the trainer started a randomly variable 3- to 20-St block. The computer selected St from a file in random sequence and interval (1.1–2.1 s in 0.1-s steps) and offered St via a St generator. ARs were received by another hydrophone, digitized, and stored. Each AR file with 20–200 St was edited on a CRT display of a 700-ms St window. No-Ar trials, noisy trials, and wrong ARs were identified. RT varied with individual, and with amplitude and duration of St. Median RT typically was less than mean by 1%–5%. Median simple RT (1 St, 1 AR) ranged from 145 ms to just over 300 ms. Median choice RT (2 unlike random St, 2 unlike ARs) ranged from 170–448 ms.
Chaos in a bioacoustic signal
Authors: Buchler Edward R. , Alapati Nanda K. , Mack Gregory A.
Published: October 2005

Zebra finches (Poephila guttata) emit sexually dimorphic, multiharmonic distance calls. These calls exhibit deterministic chaos. This was demonstrated by first digitizing the time series of the calls of five adult birds of each sex, then embedding a stationary portion of each, selecting an appropriate time delay (tau) value, and generating three-dimensional phase plots. From these plots, strange attractors were reconstructed. The morphology of these attractors is different for each bird and highly repeatable across calls for a given individual. Correlation dimension and local intrinsic dimension values were also calculated and support the conclusion that the signals are chaotic. The avian vocal tract has been modeled as a nonlinear system [J. H. Brackenbury, J. Theor. Biol. 81, 341–349 (1979); N. H. Fletcher, J. Theor. Biol. 135, 455–481 (1988)]. Its nonlinear dynamics are the probable cause of the chaotic properties of the signals. It is suggested that chaos may be a common property of bioacoustic signals produced by systems which utilize fluid forces to generate sound. It has not yet been determined if the birds can distinguish between sounds based on their chaotic properties.
Minimization of radiated sound power from structures using shape techniques
Authors: Koopmann G. H. , Lamancusa J. S.
Published: October 2005

A strategy for the optimal design of quiet structures will be presented and applied to some simple examples to illustrate the approach. One study involves the radiation of a baffled, rectangular, isotropic, flat plate of nonuniform thickness distribution. The plate's mode shapes and vibration response to a prescribed loading are calculated using finite element analysis. The radiated sound power is determined via a Rayleigh integral formulation. The optimal thickness distribution of the plate that produces a minimum radiated power condition is determined with shape optimization techniques. Four different optimization strategies are compared: (a) the minimization of radiated sound power at a single frequency, (b) the minimization of radiated sound power over a broad frequency band, (c) the minimization of the sum of modal radiation efficiencies, and (d) forcing the plate to vibrate as a “weak radiator.”
Mechanisms of noise generation in semihermetic, twin-screw compressors
Authors: Jones J. D. , Andrews R. W.
Published: October 2005

The noise radiation characteristics of a 70-ton semihermetic, twin-screw compressor are examined under controlled laboratory conditions to identify the mechanisms of noise generation. Results indicate that a majority of the acoustic radiation occurs at the first six harmonics of the fundamental screw frequency of refrigerant gas compression and discharge. Compressor sensitivity studies are performed to correlate changes in the noise radiation characteristics and internal gas pulsations with variations in select operating parameters of the compressor. Sensitivity tests suggest that the primary mechanisms of noise generation are discharge gas pulsations, rotor chatter, and flow noise. Discharge gas pulsations, which are created by a mismatch between the chamber pressure and discharge pressure, are significant at all capacities. At low capacities, the reduced refrigerant flow rates and oil circulation decreases the gas cushion between the twin rotors, consequently promoting rotor chatter. Conversely, at high capacities the increased refrigerant flow rate and oil circulation reduces the rotor chatter effect but introduces flow noise. [Work supported by United Technologies Carrier.]
Acoustic diagnostics of a HVAC system
Authors: Lauchle G. C. , Brungart T. A. , Tichy J.
Published: October 2005

The heating ventilation, and air conditioning (HVAC) system of an automobile can be a source of acoustic annoyance, particularly when it is operated under maximum airflow conditions. In order to suggest possible design changes for the purpose of noise control, a systematic characterization of the acoustic sources and mechanisms must be conducted initially. This presentation addresses such a characterization for a typical system. The approach is based on acoustic intensity measurements of the stand-alone HVAC system operating under maximum airflow conditions in a flow-through anechoic chamber. The experimental data indicate that the centrifugal blower is the dominant low-frequency source of noise, while separation zones and the flow over sharp edges within the HVAC system ducting are secondary sources of noise that become increasingly dominant as the frequency increases into the kHz range. Qualification of these identified sources of sound is aided by detailed flow visualizations of the subject system. [Work supported by Ford Motor Co.]
Axial fan noise reduction by improved inlet conditions
Authors: Hoover K. Anthony
Published: October 2005

Low-frequency noise levels in occupiable space near an axial supply-air fan were significantly higher than expected, even though massive and correctly installed ductwork lagging was in place. It was discovered that opening a small access panel in the fan-intake plenum clearly reduced low-frequency noise. A baffle was constructed and adjusted within the plenum to distribute air more evenly across the fan inlet, thereby reducing noise levels by 10 dB in the 31-Hz octave band. Related experiences highlight the importance of proper fan-intake conditions to minimize fan-generated noise.
Measuring the frequency-dependent ultrasonic attenuation of liquids with a pulse transmission method
Authors: Jiang Peng , Apfel Robert E.
Published: October 2005

To measure the ultrasonic attenuation of a lossy liquid or liquid mixture, an experiment setup using a pulse transmission method has been developed. The setup consists of a focused transmitting transducer, a measurement cell, which is used to hold the liquid, a PVDF receiver, a preamplifier, and a digital scope. It has several advantages over other methods usually employed in attenuation measurement. Compared with α = 0.109f2 measured by ultrasonic interferometer [G. S. Verma, J. Chem. Phys. 18, 1352–1354 (1950)], the attenuation of olive oil is found to be fitted by either α = 0.103f2.013 or α = 0.111f1.953, where α is the attenuation in dB/cm and f the frequency in MHz. The error sources in the method are analyzed both theoretically and experimentally. The attenuation of some liquids and liquid mixtures is given. The potential use of the setup in industry and medicine is discussed. [Work supported by the National Institutes of Health through Grant No. 5R01CA39374.]
On the liquid-wedge technique to generate Scholte-Stoneley waves
Authors: Luppé F. , Doucet J. , de Billy M.
Published: October 2005

The liquid-wedge technique is described in the case of the generation of a Scholte-Stoneley wave on a water-aluminum interface with the use of an alcohol wedge. The exact conditions under which the desired Scholte-Stoneley wave is actually generated are reviewed. In particular, special attention has to be given to the selection of the incidence angle given by the Snell-Descartes laws, the relative position of the transducer with respect to the wedge, and the hydrostatic condition relating the alcohol height to the one of water, which ensures a good coupling. Measurements are presented, and the damping of a 2-MHz Scholte-Stoneley wave propagating over a 400-mm distance on a water-aluminum interface is investigated and compared to theoretical calculations. Results of a theoretical study, done by L. Sebbag, of the reflection coefficient of an either homogeneous or evanescent plane wave on an alcohol-aluminum-water interface are also presented. They confirm the actual generation of the Scholte-Stoneley wave at the water-aluminum interface. [This work has been done at Paris 7 University and supported by French D.R.E.T.]
Directions of degenerate plane-wave propagation in orthorhombic media
Authors: Schoenberg Michael , Helbig Klaus
Published: October 2005

At each direction of propagation in an anisotropic elastic medium, there are three possible plane waves, each with its characteristic phase slowness. Points at which one or more of the sheets of the slowness surface are in contact are “degenerate” and specify directions for which the characteristic equation has repeated roots. For an orthorhomic medium, one with three mutually orthogonal mirror symmetry planes (and no further symmetry, for the purposes of this discussion), the degenerate directions are isolated. For degenerate directions that lie in any of the symmetry planes, the characteristic cubic equation in three variables, i.e., the squares of the three components of the slowness vector, is factorable, and the problem reduces to solving for the intersection of a straight line and a conic. The problem is much more complicated out of the symmetry planes as the characteristic equation is not factorable. However, from the fact that in a degenerate direction, the Christoffel equations' 3 × 3 matrix of coefficients, whose eigenvalues and eigenvectors give the slownesses and polarizations of the three waves, is rank one or less, one finds three linear equations on the squares of the three components of the repeated slowness vector. If the squares of the components are all positive, there is a single degenerate direction, not lying in any symmetry plane, in each symmetric octant, and explicit expressions for all relevant quantities are readily derived; if not, there is no degenerate direction that does not lie in a symmetry plane.
Acoustic wave propagation in a temporal and spatially varying tube
Authors: Thompson Charles , Le Tam
Published: October 2005

Acoustic wave propagation in a temporal and spatially varying tube is investigated. The method of multiple scales is used to determine the dispersion of wave packets. This primary objective is to ascertain the effect of variations in tube shape on the state transition probabilities used in hidden Markov models of speech.
Application of direct integral-equation method in acoustic-wave diffraction
Authors: Huang L. C. , Huang C. I. , Chwang A. T.
Published: October 2005

The direct integral-equation method (DIEM) is applied to study the diffracted acoustic field of a point source at an arbitrary location relative to a ring aperture in a soft baffle. The velocity potential at an arbitrary field point is expressed in terms of a surface-source distribution with complex densities. A set of eight real Fredholm integral equations of the second kind is used to determine the surface-source densities. These equations are transformed into discrete forms by applying the Gauss-Legendre quadrature formula in the radial direction and the best possible numerical integration formula in the angular direction. In comparison to the boundary-element method, the DIEM is more efficient, accurate, and flexible. The advantages of DIEM become apparent, especially when the parameters in a given problem vary within a large range. The numerical result of source strengths on the baffle surface in the far field agrees very well with the asymptotic solution. The effect of different parameters on the diffracted acoustic field is systematically studied and compared. These parameters include the location of the acoustic source, the wave number, the size of the ring aperture, as well as the thickness of the baffle. The numerical results show that the baffle thickness and the size of the ring aperture have relatively little influence on the diffracted acoustic field within the tested range. However, the wave number has a significant effect on the diffracted pressure field.
Loudness matching for compressed speech signals
Authors: Bakke Matthew H. , Neuman Arlene C. , Levitt Harry
Published: October 2005

The purpose of this experiment was to determine a rule for matching the loudness of uncompressed and compressed speech samples. Eight normal hearing and 16 sensorineural hearing-impaired subjects (divided into four groups of differing severity and configuration) listened to two continuous speech samples (male and female talkers) under conditions of linear and compression amplification. Compression conditions consisted of 12 selected combinations of varying compression ratio, threshold, and release time (compression ratio = 2:1, 4:1, 8:1; knee point = 5, 10, 15, and 20 dB below the highest speech peak; release time = 20, 200 ms). Subjects matched the loudness of the compressed signals to a reference uncompressed signal using an adaptive procedure. Overall levels and cumulative distributions of the processed speech signals were obtained. Estimates of equal loudness based upon rms level and 90th percentile of the cumulative distribution were both found to closely match the gain selected by subjects. [Work supported by NIH Grant No. 2PO1 DC00178.]