bluuebunny/crossref_metadata_2025 huggingface dataset:
Active structural acoustic control with broadband disturbances and real time structural wave-number sensing
Authors: Maillard Julien P. , Fuller Chris R.
Published: October 2005

The present work gives further developments and experimental testing of a new time domain structural sensing technique for predicting wave-number information and acoustic radiation from vibrating structures. Most structure-borne active sound control approaches now tend to eliminate the use of microphones located in the far field by developing sensors directly mounted on the structure. In order to reduce the control authority and complexity required to minimize sound radiation, these sensors should be designed to provide error information that is solely related to the radiating part of the structural vibrations, i.e., the supersonic wave-number components. The approach discussed in this paper is based on estimating supersonic wave-number components coupled to acoustic radiation in prescribed directions. The spatial wave-number transform is performed in real time using a set of point structural sensors with an array of filters and associated signal processing. Experimental results on planar radiators show that only a few point sensors are required to provide accurate radiation information over a broad frequency range. The use of the sensing approach is then experimentally demonstrated in the time domain LMS active control of broadband sound radiated from a vibrating plate. [Work supported by ONR.]
Design of feedforward ASAC systems by eigenfunction assignment
Authors: Burdisso Ricardo A. , Fuller Chris R.
Published: October 2005

The traditional design approach of feedforward control systems involves the selection of number and location of the actuators and sensors based on some physical understanding of the system. This empirical methodology yields satisfactory results for simple structures and sinusoidal inputs. However, such an heuristic approach can easily result in an inefficient control system with unnecessary large number of control channels for complex structures and more realistic disturbances. In this wok an efficient formulation is presented for the optimum design of actuators and sensors for structurally radiated sound reduction. The technique is based on the modification of the eigenstructure such that the system responds with the weakest set of modal radiators. The technique is applicable to both narrowband and broadband excitations. The formulation is demonstrated for controlling the odd–odd modes of a simply supported plate driven by a point force located at the center of the plate. The radiation due to the first three odd–odd modes is reduced with a single -input, single-output (SISO) controller. The control actuator and error sensor are implemented with piezoelectric (PZT) ceramics and polyvinylidene fluoride (PVDF) films, respectively. It is shown that the optimum actuator and sensor configuration yields excellent global sound reduction. [Work supported by ONR.]
Design of auditory prostheses to aid speech communication
Authors: Soli Sigfrid D. , Shannon Robert V.
Published: October 2005

Research on the treatment of hearing impairment and deafness has, in recent years, increasingly focused on auditory prostheses that can aid speech communication in both quiet and noise. For these prostheses to be most effective, several research goals must be achieved. First, the residual capacity of the impaired auditory system must be determined. Next, the essential acoustic information for speech recognition must be characterized and re-coded to exploit the residual auditory capacity. Finally, algorithms and circuits that can extract and process this information are required. Efforts toward these goals in hearing aids and in cochlear and brainstem implants will be described. The binaural directional hearing capacity of individuals with sensorineural hearing impairment has defined the main focus of this hearing aid research because of its potential to improve speech communication in noise. In this implant research, the channel capacity and channel interactions of the electrically stimulated auditory system have received major attention because of the effects of these interactions on speech coding for multi-electrode implants. Methods for characterizing the residual capacity of an individual, techniques for using residual capacity to aid speech communication, and results from perceptual tests obtained with real-time, laboratory-based processors will be discussed.
Tracking the gliding tongue and lips: Articulatory undershoot or perceptual overshoot or ...?
Authors: Lisker Leigh
Published: October 2005

At the last ASA meeting it was shown that for a set of synthetic vowel–glide–vowel sequences varying in F2 trajectories a range of frequencies can equally well serve as mid segments in patterns identified as English /iwi/ and /uyu/. Many of these mid segments, when lengthed and presented in isolation, resemble the high front rounded vowel [y], so that when short and intervocalic one might expect them to be heard as the glide [inverted h], at least by phonetically trained listeners. However, perceptual data suggest that intended [inverted h] in /i/—/i/ is heard as /w/, while in /u/—/u/ it is /y/. Assuming the syllabifications /i$wi/ and /u$yu/, one might then expect an initial [inverted h] to be heard as /w/ in [inverted hi] and as /y/ in [inverted hu]. Test data indicate otherwise. Unlike /iwi/ and /uyu/, /wi/ and /yu/ show no overlap of F2 values in their initial steady-state segments—there is instead a range of F2 values for which listeners report both not-/wi/ and not-/yu/. Thus for English /w,y/ the steady-state and transitional intervals have different perceptual weights initially and medially. [Work supported by NIH Grant No. HD-01994 to Haskins Laboratories.]
The stability of a temporal distinction: Vowel length in Thai
Authors: Abramson Arthur S.
Published: October 2005

This is part of a larger effort to test the robustness over speaking styles of acoustic properties that underlie phonological contrasts. So much of the knowledge comes from the study of citation forms that one might wonder whether in running speech the presence of much top-down information and other contextual cues does not lead to the impoverishment of some of the bottom-up phonetic information. A good candidate for possible instability is relative duration as a means of distinguishing phonemes. The Thai language, in both production and perception, uses relative duration to distinguish its ‘‘short’’ and ‘‘long’’ vowels. In this study vowel durations were measured under three conditions. (1) Eight minimal pairs of words were recorded in carrier sentences by four native speakers at two rates, normal and fast. (2) Casual unrehearsed conversations were recorded by two couples. (3) Many words and short expressions taken from each person’s part of a conversation were read aloud by that person. The data show that the quantity distinction in Thai is rather stable. The overlap in the pooled data from running speech largely disappears once certain contextual factors are taken into account. [Work supported by NIH Grant HD-01994 to Haskins Labs.]
Shallow-water noise—A review
Authors: Urick Robert J.
Published: October 2005

Like most aspects of underwater sound, the noise in the sea received its first quantitative attention during World War II, when a team under the venerable acoustician V. O. Knudsen made measurements in the shallow coastal waters off Southern California and Florida—ostensibly for the purposes of acoustic mines and harbor protection sonars. At that time too, the pernicious snapping shrimp of the warm shallow tropic waters of the Pacific were investigated. One of the principal features of shallow water noise is its variability—from place to place and time to time. Yet it may be said that there are only three major noise sources in shallow water: ships and other man-made activities at moderately close ranges, biologics, and the wind or waves. Strangely, when the first two of these are absent, the noise levels in shallow water at frequencies above 1 kHz or so are the same as in deep water; the so-called ‘‘Knudsen’’ curves have long been used in deep water. At lower frequencies, many shallow locations are often more quiet than deep water because of the absence of deep-going favorable transmission paths. When environmental conditions can be estimated, one’s knowledge of shallow-water noise should be good enough to permit a prediction of the expectable noise level at an arbitrary location—at least as good as one’s prediction capability of transmission loss out to useful ranges. [Work supported by the Applied Research Laboratory, The Pennsylvania State University, and the Office of Naval Research.]
Biological sources of noise in coastal waters
Authors: Tyack Peter L. , Howald Terrance
Published: October 2005

Underwater biological sounds are transient events. Durations range from microseconds to tens of seconds, frequencies from ≤10 Hz to ≥100 kHz, and source pressure levels up to ≥220 dB re : 1 μPa at 1 m. While each sound is produced by one individual, many sounds occur in choruses that may involve thousands of simultaneous sources. Some crustaceans produce loud impulsive noise in the 2–20 kHz range. These animals are common enough in many shallow areas to dominate the ambient near 10 kHz. Evening fish choruses seasonally dominate the ambient in many shallow waters in the 100–1000 Hz frequency range. While whales and dolphins are less numerous than the animals listed above, many species produce sounds of sufficient intensity to affect the ambient. For example, during their winter breeding season fin whales produce series of 20-Hz pulses lasting 1 s at source levels of 180 dB re : 1 μPa at 1 m. Dolphin echolocation clicks may reach source pressure levels ≥220 dB with spectral peaks 50–150 kHz. Dolphins are also skilled mimics of manmade sounds, which may lead to unpredicted interference.
Acoustic radiation from breaking waves
Authors: Ding Li , Farmer David M.
Published: October 2005

Observations of the sound from breaking surface waves using a small hydrophone array illustrate the temporal and spatial characteristics of this sound source and its dependence on the surface wave field. Such observations provide a source description that might have application in ambient noise model development. By tracking the propagation speed of the breaking event its wave scale is inferred; other measured properties include breaking length, duration, and spatial separation. Analysis indicates that the dependence of breaking probability on the fourth moment of the wave spectrum is consistent with a linear model. The measured speeds of breaking events imply that their scale is less than the dominant wind-wave scale. Group structure of wave breaking, in which there is a tendency for waves to break repetitively at twice the wave period and spaced one wavelength apart, also occurs but is more readily identifiable at lower wind speeds.
Application of the Wiener–Hopf technique to the scattering of structural acoustic waves from discontinuities in fluid-loaded cylindrical shells
Authors: Means Steven L.
Published: October 2005

Several types of structural acoustic waves are known to propagate on fluid-loaded cylindrical shells. When propagating in the axial direction they can be described by a dispersion relation D(kx,ω)=0. When these waves are incident on a shell discontinuity, here considered larger than the radius and smaller than the wavelength, energy is scattered back along the cylinder axis and into the surrounding medium. To characterize this phenomenon, the shell is considered to be locally reactive from −∞ to 0, and rigid from 0 to ∞ along the x axis. A wave of known type is incident from x=−∞ and excites a reflected wave and acoustic waves originating from the vicinity x=0. Pertinent asymptotic results are obtained including the reflection coefficient of the reflected wave and the far-field acoustic radiation pattern of the scattered wave. [Work supported by ONR and by the William E. Leonhard endowment to Pennsylvania State University.]
Evolution of the scanning microscopes both for imaging and lithography
Authors: Quate C. F.
Published: October 2005

In recent times the atomic force microscope and other scanning probes have emerged as formidable instruments for imaging insulating surfaces. They can be operated in air, in liquid, and in vacuum and they have had an impact in the fields of electrochemistry and in cellular biology. Here, focus will be on solid surfaces where the AFM has been successfully used to image a variety of surfaces that are difficult to study with the optical and electron microscopes. Topography and microroughness of silicon wafers will be used to illustrate the utility of this instrument. Surface modification on the atomic scale has been demonstrated for a variety of systems. In a second application the force microscope has been combined with other forms of microscopes. The combination provides the operation with a simple means of controlling the spacing between tip and sample throughout the scanning cycle. This principle is illustrated with a description of the near-field optical microscope as combined with the force microscope. This combination allows one to scan with the tip space 5 nm from the sample.
Some light emission features of single bubble sonoluminescence
Authors: Cordry Sean M. , Crum Lawrence A. , Roy Ronald A.
Published: October 2005

Bubbles created via electrolysis were allowed to rise though water in a quiet acoustic levitation vessel. The sound field was then activated, forcing several bubbles to converge and coalesce near a pressure antinode. Light emission measurements were then taken with a Hamamatsu photomultiplier tube and single photon counter as a state of single bubble sonoluminescence (SBSL) evolved. The measurements reveal brief periods fluctuations in light emission intensity followed by long periods of stable (i.e., nonfluctuating) emission. The time scales for the fluctuations are on the order of half a second. Previous measurements of light emission have indicated that SBSL exhibits remarkably long-lived, stable behavior [Gaitan etal., J. Acoust. Soc. Am. 91, 3166 (1992); B. P. Barber and S. J. Putterman, Nature 352, 318 (1991)]. These measurements, however, imply a transient regime that the bubble must pass through while seeking a final position of stability. The highest light emission intensities are seen in the transient regime. These transient light emission should provide important information concerning the mechanisms through which SBSL develops its remarkable stability. Further, acoustic emissions from SBSL were observed to evolve from broadband to narrow-band noise during the transient period. These light emissions and acoustic emissions will be presented and possible correlation discussed. [Work supported by ONR.]
Similitude in thermoacoustics
Authors: Olson Jeffrey R. , Swift Gregory W.
Published: October 2005

The principle of similitude has been applied to thermoacoustics. Using similitude reduces the number of variables necessary to describe an experiment, which can greatly reduce experimentation time. In addition, it provides insight into the building of models with identical performance characteristics. Such models would duplicate even unanticipated nonlinear behavior. This allows one to build test prototypes that operate at conditions which are more easily accessible than the desired final product. For example, a prototype that operates at modest pressures using heavy gas such as argon could model equipment that is intended to operate at high pressure using light gas such as helium. Similitude has been verified using a large thermoacoustic engine operating with helium, neon, and argon, and has been found to be obeyed almost perfectly, even for nonlinear effects whose origin is not understood. Therefore it is believed this principle can be applied to make meaningful predictions using simpler, cheaper test models.
Intracellular transfer functions in the apical cochlear turn: Implications for the pitch code
Authors: Chatterjee Monita , Zwislocki Jozef J.
Published: October 2005

Intra- and extracellular ac transfer functions were recorded in the 500-Hz to 1-kHz region of the Mongolian gerbil cochlea. In agreement with previous results obtained in the 2-kHz location, the best frequency decreased with increasing SPL, the shift ranging from 1/2 to 1 oct. The phase transfer function also exhibited a shift from low to high SPLs amounting to about 180 deg. Damage to the preparation resulted in smaller responses, lowered EP, a reduction in the peak shift, as well as a disappearance of the phase shift at high SPLs. The normal transfer functions demonstrate a conspicuous high-frequency notch and secondary maximum at moderate and higher intensities. The finding that, in the range between 500 Hz and 2.5 kHz, the BF is intensity-dependent, indicates that the place of maximum excitation cannot be an adequate code for pitch. It has been suggested previously with respect to the 2-kHz location, that the one intensity-independent feature of the transfer functions is the high-frequency cutoff. This seems to be approximately true for the apical turn of the gerbil also. [Work supported by NIDCD.]
Stream segregation in normal-hearing and cochlear-impaired listeners
Authors: Grose J. H. , Hall J. W. , Mendoza L.
Published: October 2005

Cochlear-impaired and normal-hearing listeners were compared on two tasks intended to assess auditory stream segregation. One task measured gap discrimination between two tones that were presented either in isolation or were embedded into a sequential stream of tones. For tone pairs distally spaced in frequency, performance was poor when the tones were presented in isolation but improved when they were drawn into separate auditory streams, presumably because temporal judgments could now be made within a stream. Both groups of listeners gave similar patterns of results although some differences were apparent. The second task was a melody recognition procedure [J. A. P. M. de Laat and R. Plomp, J. Acoust. Soc. Am. 78, 1574–1577 (1985)] and involved identifying a 4-note target melody embedded between two competing melodies as a function of the proximity and temporal synchrony of the competing melodies. In both groups, marked individual differences were observed. Results from both tasks will be discussed in terms of the effects of cochlear impairment on auditory grouping skills. [Work supported by the NIDCD R01-DC01507.]
Localization of sound sources in the median sagittal plane by listeners with high-frequency hearing loss
Authors: Vander Velde Timothy J. , Rakerd Brad , Hartmann William Morris
Published: October 2005

Sources in the median sagittal plane are localized on the basis of spectral cues. The elevation of sources toward the front is determined from cues at high frequency (7 kHz and above). The distinction between front, overhead, and back (FOB) potentially involves broadband cues. One therefore expects that individuals with high-frequency hearing loss will fail at elevation tasks, though they might succeed at FOB tasks. Listeners with bilateral sensorineural hearing loss, moderate in the speech range and severe at high frequencies, were given source identification tasks in both elevation (three sources spanning 30 deg) and FOB geometries. The stimuli were white noise bursts, ranging in level from 42 to 90 dB SPL. A control experiment showed that the listeners could successfully identify sources in the left-overhead-right plane. Results for the sagittal plane showed that all listeners performed significantly less well than normal controls. In the FOB task, performance was well above chance, though listeners characteristically lacked either a front sensation or else a back sensation. In the elevation task, performance was, with a few exceptions, near chance for all listeners and all levels. [Work supported by the NIDCD, DC00181.]
Effects of vigilance on cortical processing
Authors: Daly D. M.
Published: October 2005

Normal persons significantly deprived of sleep show impaired vigilance with slowing of motor responses, errors in cognitive processing, and defects in recall. Pupillometry measures autonomic correlates of vigilance. Effects of sustained and of fluctuating vigilance on cortical processing using standard sets of synthetic acoustic stimuli are reported. [Daly etal., J. Neurophysiol. 44(1), 200–222 (1980)]. A 60-yr-old woman had lifelong difficulty awakening, and if not awakened might sleep 14 h continuously. A single 7 am 30-mg dose of methylphenidate aided arousal; once awake she could remain alert. In 2-h sessions of unmedicated continuous testing she classified stimuli consistently [p(χ2≳G2)0.0001] and appropriately (p0.001, re: 32 normal adults). Her performance after 1 1/2 h was as consistent as the best controls. A 54-yr-old man had since adolescence slept less than 3 h per night (typically 2–5 pm). Unlike other reported philagrypniacs, for 30 yr he has also napped for an hour in late morning. Despite diminished sleep requirements, he does not remain alert while awake. Performance with FM transients in CVs fluctuated widely (p<0.01 to p<0.0001), but remained consistent with relatively CF vowels (p<0.0001). His performance improved temporarily with caffeinated (but not decaffeinated) coffee. These results are consistent with evidence that vigilance modulates cortical auditory processing; they suggest that like capacity for sleep, individual capacity to remain alert may also vary in a Gaussian distribution.
Reciprocity theorem for oscillations of inhomogeneous elastic structures in a liquid—Modified reciprocity theorem and applications
Authors: Lyamshev Leonid M.
Published: October 2005

The oscillatory vibrations of inhomogeneous elastic structures are considered. In particular, two problems involving plates and shells with attached ribs excited by forces and moments are discussed. The formulation uses the Green’s function for the wave equation of sound propagation in a liquid, and the equations of motion of plates and shells coupled with those of flexural and torsional vibrations of ribs. An integral relationship connecting the solutions of two self-conjugated boundary problems of inhomogeneous plates and shells oscillations theory is obtained. This relationship is the reciprocity theorem that is a precise mathematical formulation of the well-known Rayleigh reciprocity principle for oscillating mechanical systems. If a liquid is moving and there is a shear flow outside or inside of a shell (plate) then this relationship is the modified reciprocity theorem for inhomogeneous elastic structures oscillations in a flow that is the generalization of the Rayleigh principle. Applications of the reciprocity theorems are discussed. Flexural waves reflection, scattering, and radiation by elastic ribs in plates are considered. Nonspecular reflections and resonance phenomena are observed. These are similar to nonspecular reflection, sound scattering, and radiation by elastic bodies in a liquid and are connected with interactions of flexural waves in a plate with flexural and rotational waves in ribs.
The new City of Houston sound regulation ordinance
Authors: Moritz C. , Huey H.
Published: October 2005

In January of 1993, the City of Houston adopted a new sound regulation ordinance. Previous ordinances did not specify allowable sound levels, only that it was unlawful to make loud or excessive noises. The city health department had used values of 75 dBA (daytime) and 65 dBA (nighttime) to determine if noises were excessive. The new ordinance established allowable A-weighted sound levels of 65 dBA (daytime) and 58 dBA (nighttime) on residential property and 68 dBA (day or nighttime) on nonresidential property. Enforcement under this ordinance is now shared between the city health and police departments. Because there is no zoning in the City of Houston, this ordinance poses some unique challenges; manufacturing facilities, bars, and nightclubs are often located in residential areas. The motivation for this new ordinance and recent experiences with its enforcement will be discussed.
Thermoacoustic engines
Authors: Swift Gregory W.
Published: October 2005

Thermoacoustic engines are energy-conversion devices that achieve simplicity and reliability by use of acoustics. Their efficiency can be a substantial fraction of the Carnot efficiency. In thermoacoustic prime movers, heat flow from a high-temperature source to a low-temperature sink generates acoustic power. In thermoacoustic refrigerators, acoustic power is used to pump heat from a low-temperature source to a high-temperature sink. Applications of thermoacoustics under development at several institutions will be shown, possibility including refrigeration, sonar, cryogen liquefaction, and electric-power generation. Fundamental principles of thermoacoustics will be reviewed, and assumptions underlying our present (linear) understanding will be discussed. Limitations of our present understanding will be outlined, and their implications for design of practical devices will be discussed.
Helioseismology: Listening to the inside of the sun
Authors: Toomre Jurl
Published: October 2005

The sun is oscillating in an intricate though gentle manner. The patterns of motion observed in the solar atmosphere are complicated, for they result from interference between about 107 resonant modes of oscillation of the interior. The sun possesses both acoustic p modes, for which pressure is the restoring force, and gravity g modes, for which buoyancy is the dominant force. Each resonant mode resides in a cavity beneath the solar surface, the depth of which depends both on the type of mode and on its geometry. Some cavities are quite shallow, whereas others extend to the very center of the star. Since the frequencies of the modes are determined by the stratification and dynamics of the portion of the sun where their amplitudes are appreciable, accurate determination of the frequencies by observations affords remarkable ways of probing the inside of the star. During the past decade there has been significant progress in both observation and theory. The unravelling of information from many modes forms the basis of the subject called helioseismology. It promises study of the inside of the sun in sufficient detail to test the premises of stellar structure theory, and thus has implications for much of astrophysics. It can also provide crucial information about the temperature and mass distribution within the sun for testing issues in particle physics and theories of gravitation.
Physical acoustics at 500 GHz: 31 octaves above middle C
Authors: Maris Humphrey J.
Published: October 2005

Experiments are described in which the techniques of picosecond optics are used to generate and detect ultrasonic waves at frequencies as high as 500 GHz. The method also provides exceptionally good spatial and temporal resolution, thereby making possible pulse-echo acoustic measurements on a broad range of nanostructures of current technical interest. Examples will be given of results that have been obtained by this approach, and possible future developments will be discussed.
Synchronous picosecond sonoluminescence
Authors: Barber Bradley P. , Hiller Robert , Lofstedt Ritva , Putterman Seth
Published: October 2005

A strong sound field can (1) trap a bubble of gas at a velocity node, (2) maintain the bubble against diffusion, and (3) at sufficient intensity cause it to emit flashes of light that have intensities over 30 mW and widths less than 50 ps. The flashes are emitted in a clocklike fashion with a jitter that is also less than 50 ps. The spectral intensity of the sonoluminescence (SL) increases into the ultraviolet. The mechanism for this effect is still unknown but light scattering experiments have resolved the bubble motion—radius versus time—on a scale of nanoseconds and indicate that the light is emitted by a supersonic collapse. The emitted intensity is a strong function of ambient temperature and varies by a factor of 200 between 1 and 40 C. Light scattering measurements of temperature-dependent SL therefore provide data that can critically test any proposed theory such as imploding shock waves [C. C. Wu and P. H. Roberts, Phys. Rev. Lett. (May 1993)]. [Work supported by the US DOE Division of Advanced Energy Projects, R. L. is supported by an AT&T fellowship.]
The effect of vehicle exhaust system components on performance and noise in firing spark-ignition engines—An experimental study
Authors: Selamet A. , Croy M. S. , Kach R. A. , Novak J. M.
Published: October 2005

In vehicle exhaust systems, the sound attenuation and the reduction of flow losses are often competing demands. The present experimental study considers a full vehicle exhaust system and investigates both the sound attenuation and the flow performance of production configurations including the catalyst, the resonator, and the muffler. Dynamometer experiments have been conducted with a firing Ford 1.9-Liter I4 Escort engine with speeds ranging from 1000 to 5500 rpm. Measurements including the flow rates, the temperatures, and the absolute dynamic pressures of the hot exhaust gases at key locations (upstream and downstream of every component) with fast-response, water-cooled piezoresistive transducers facilitate the calculation of acoustic performance of each component, as well as the determination of flow losses caused by these elements and their influence on the engine performance. The present study describes the experimental aspects of an extensive effort toward employing nonlinear fluid dynamic models in the time domain for the prediction of the acoustic and power performance of firing internal combustion engines with full production exhaust system.
The physics of normal modes
Authors: Weinreich Gabriel
Published: October 2005

This is primarily a tutorial paper to organize and clarify various concepts whose understanding is required for work with linear systems. Among the questions to be addressed are: What is the difference between a resonance and a normal mode? What about an antiresonance? How do normal modes relate to free motion? To forced motion? Are there ‘‘strong’’ and ‘‘weak’’ modes? Are resonance denominators quadratic in frequency, or linear? What does it mean for modes to be ‘‘coupled’’? In a measured frequency characteristic, when are normal modes represented by peaks, by dips, by both? What information is carried by the phase? In searching for normal modes, what is the difference between pulse excitation, white noise excitation, and sinusoidal excitation? Are there other options of interest? Do dissipative systems have normal modes? [Work supported by NSF.]
Mechanical vibrations and radiation fields of guitars
Authors: Brooke Matthew , Richardson Bernard
Published: October 2005

Some of the research undertaken by the Cardiff group to try to establish relationships between the classical guitar’s construction and its acoustical output are reviewed. Real instruments have been studied using techniques such as holographic interferometry, and the structural vibrations and associated radiation fields have been modeled using finite-element analysis and boundary-element methods. Primitive psychoacoustical tests have established that radiated frequency components of plucked notes are important in recognizing individual instruments. Large amounts of data, collected over the years, have clearly demonstrated that there are no simple relationships between the modal properties of instruments and their estimated ‘‘quality.’’ Similar conclusions have, of course, been drawn by other workers in this field. Recently, the authors have concentrated more on determining the precise role played by individual modes in coupling the strings to the body and in radiating energy to the surrounding air; it is felt that this sort of detail is more indicative of the instrument’s final acoustical action. These investigations emphasize the importance of the precise shapes of modes, particularly in the vicinity of the bridge. A discussion of the ways in which the luthier can fine-tune mode shapes and hence maintain control during instrument manufacture is included.
Current status of sleep disturbance research and development of a criterion for aircraft noise exposure
Authors: Finegold Lawrence S.
Published: October 2005

There currently exists no generally accepted criterion for an acceptable level of nighttime sleep disturbance from aircraft noise. Indeed, there is little agreement concerning the appropriate scientific definition of sleep disturbance, the appropriate noise exposure metric for this environmental effect, or the circumstances under which such predictions need to be included in environmental impact analyses. However, with the large body of scientific evidence on sleep disturbance due to environmental noise that has accumulated over the past 20 yr, it is now possible to promote an interim sleep disturbance curve for use in the federal environmental impact analysis process. This presentation focuses on the results of recent research and the implications for environmental policy decisions. Both laboratory and field research, including research in the United States and Europe, are addressed. Development of the sleep disturbance curve incorporated into the 1992 report of the Federal Interagency Committee on Noise (FICON) is also reviewed.
Assessment of speech interference from aircraft flyover noise in schools and other communication critical environments
Authors: Pearsons Karl
Published: October 2005

Although most assessments of the effects of community noise impacts on people concentrate on annoyance, it is important in some speech-critical settings to assess the degree to which noise interferes with communication as well. Speech intelligibility metrics are helpful in such situations, even though they require more detailed information about noise exposure than is captured by cumulative metrics such as the day–night average sound level (DNL). Alternate metrics for assessing speech intelligibility and their uses and limitations will be described. Comparisons will be made between such metrics and those commonly used to assess environmental noise effects on a long-term average basis.
The present aircraft noise evaluation process
Authors: Maillett Louise
Published: October 2005

The legal background and policy decisions underlying present U.S. Government noise impact assessment procedures are outlined. Collaboration and review processes to satisfy the mandates of the various agencies are discussed, with emphasis on the FAA’s mission and plans regarding aircraft noise abatement.
Global acoustic mapping of ocean temperatures (GAMOT)
Authors: Speisberger John L. , Frye Dan , Hurlburt Harley , McCaffrey Joe , Johnson Mark , O’Brien James
Published: October 2005

Successful feasibility experiments for mapping global ocean warming and climate variability with sound have been conducted since 1983 [J. L. Spiesberger etal., J. Acoust. Soc. Am. 92, 384–396 (1992)]. The GAMOT group is developing two new high-technology instruments for making these same measurements in near-real time at one-eighth the cost of our previous measurements taken from sources and receivers connected to shore with cables. One instrument is a surface suspended acoustic receiver (SSAR), which dangles a hydrophone array beneath a freely drifting surface unit. The other instrument is a subsurface autonomous mooring equipped with an acoustic source and a new telemetry scheme for removing travel time changes due to mooring wander in real time. Climatic temperature variability from past and present experiments is studied with state-of-the-art ocean models. A program update will be presented. [Work is supported by the Advanced Research Projects Agency.]
High-fidelity displacement sensors for acoustic emission source characterization
Authors: Fortunko C. M. , Hamstad M. A. , Fitting D. W.
Published: October 2005

Acoustic emission (AE) source characterization requires the use of broadband, typically 20 kHz–2 MHz, ‘‘point-contact’’ sensors. Generally, AE sensors based on the NIST ‘‘conical’’ transducer approach can meet this requirement. However, because naturally occurring AE events are considerably less energetic than those produced by artificial AE sources, optimization of the sensor signal-to-noise performance is of critical importance. Using a computer model, a variety of sensor-design approaches have been studied, with particular emphasis on transducer/preamplifier/specimen compatibility issues. In this paper, computer-model predictions are compared with the results of experiments. The use of different piezoelectric transducer materials—PZT-5A, lead metaniobate, LiNbO3, X-cut quartz, and PVDF—is considered. It is shown that ceramic materials exhibiting the highest dielectric constants, ε33S, are best suited for most high-performance AE sensor applications. In addition, the impact of preamplifier input capacitance, including the Miller effect, and specimen mechanical impedance on the performance of a ‘‘point-contact’’ sensor is discussed. In particular, using the computer model, the limitations of sensors that use piezoelectric ceramics and single-crystal materials are examined. It is shown that in certain situations, such as very thin metal plates and materials that exhibit very low characteristic impedances, sensors that use piezoelectric ceramic and single-crystal transducers may not be the best choice. Therefore, to address such cases, alternative sensor approaches are needed.
Artificial neural nets for acoustic nondestructive evaluation
Authors: Akerberg Peeter , Jansen Ben H. , Pandya Shail R. , Wang Zhijing , Finch Robert D.
Published: October 2005

Artificial neural networks (ANNs) are being used for the detection of cracks in metal and concrete beams and structures. Vibration signals are obtained from these structure by impacting with a small hammer and recording the activity of an accelerometer attached to the structure. These vibration signals are digitized, and the samples are input to an ANN. Detection of cracks proceeds in two different ways. For both methods, the networks are trained on data obtained from intact structures, but in the case of the first method, training is halted once the ANN can accurately predict future samples of the vibration signal from present and past observations. These ANNs are then fed with data obtained from structures with varying degrees of defects, and the prediction error is noted. In the second method, training continues after a small defect has been made to the structure, and the weights of the nets are compared. With both methods, we can detect cracks as small as 0.1 in. Examples of the results obtained for metal and concrete beams will be shown. [Work supported by NSF Grant no. MSS-9024224.]
Application of nonlinear dynamics for noise reduction in measured signatures containing broadband information
Authors: Hughes Ronald
Published: October 2005

Nonlinear dynamics has been of great academic interest in recent years. Its concepts have been employed as a foundation for modeling nonlinear processes in diverse fields extending from economic trends to medical dysfunctions. Although the developments of nonlinear dynamics concepts in acoustics are sparse, their application in acoustics has advantages over linear techniques in extending broadband signatures in high-noise environments. Linear signal analysis approaches are significantly limited when the noise environment is nonstationary or when the signal duration is short. Furthermore, the application of filters alters the information content of the original broadband signals. Nonlinear dynamics methods do not suffer these limitations. Two such methods will be described for effecting noise reduction where the signal-to-noise ratio is zero or negative and where there is no apriori knowledge of either the signal or the noise. Signals used for demonstration include sinusoids and chaotic sequences; additive noise includes uniform and Gaussian random noise and noise that produces a power spectrum equivalent to that of the ‘‘clean’’ sequences. Noise reduction of 15–18 dB using nonlinear dynamics will be shown, and fidelity reproduction of the original signal will be demonstrated.
Low-frequency acoustic transmission at a shallow water site in the Gulf of Mexico
Authors: Cable Peter G.
Published: October 2005

During Area Characterization Test I (ACT I), conducted in September 1992 in 100-fathom water on the West Florida Shelf, acoustic transmission measurements were made covering the band 50 Hz to 1 kHz using explosive charges detonated at 90-m depth. The test site had a sand–silt–clay bottom with a gentle slope of 0.135°, and up, down, and cross-slope transmission data to ranges of 40 km were collected on collocated 25-element vertical and horizontal hydrophone line arrays. The low sea states and downward refracting acoustic conditions prevalent during ACT I ensured that transmission loss was controlled by geometric spreading and bottom interactions. Transmission loss as a function of range, frequency, and receiver depth has been determined and compared favorably with predictions for both the flat and sloping bottom cases. In addition, the multipath temporal structure and the vertical arrival structure of the received signals have been analyzed and have indicated the role of bottom and subbottom characteristics to the properties of the received signal. These analyses of the signal structure have highlighted transmission mechanisms not readily apparent in transmission loss data and have emphasized the importance of knowing subbottom structure to a detailed understanding of shallow water transmission over sand bottoms. [Work supported by the ARPA Adverse Environments Program.]
Complex effective depth and mode eigenvalues for a layered elastic waveguide
Authors: Tindle C. T. , Chapman N. R.
Published: October 2005

The complex effective depth [Z. Y. Zhang and C. T. Tindle, J. Acoust. Soc. Am. 93, 205–213 (1993)] has been investigated for a shallow water waveguide with a layered elastic bottom. For multiple layers, both the complex effective depth and the reflection coefficient for the bottom have oscillatory structure as a result of resonant effects in the layers of the sediment. Under these conditions and for elastic layers, some of the normal mode eigenvalues can be difficult to find, as a simple mode counting procedure is not available. The complex effective depth leads to a formulation of a eigenvalue problem in terms of a phase integral. The phase integral is a function of complex wave number and a normal mode exists whenever it is a multiple of π. A path exists in the complex plane along which the phase integral is real and monotonic. The path passes through all eigenvalues for both trapped and leaky modes and these can be found systematically. [Work supported by DND.]
Parabolic equation average propagation in the presence of rapid range variation in a sediment layer
Authors: Oba Roger M.
Published: October 2005

The routine for computing the average solution to the generalized parabolic equation [R. M. Oba, J. Acoust. Soc. Am. 90, 2300(A) (1991)] in the water works for propagation with sediments modeled by fluid layers. It can be used in a ‘‘marching algorithm’’ from one range step to another, especially if they are statistically independent. Because the algorithm relies upon analytic forms of matrices for horizontal propagation of vertical modes, a natural limit exists when (a) the sediment variation is rapid compared with wavelength and depth, (b) the sediment variation is statistically independent in each range step, and (c) the probability distribution over the velocity profile ensemble in each range step is identical. Its application to the case where the probability distribution can be parametrized by one variable is demonstrated. This approach has advantages over averages of multiple runs of deterministic models over realizations of sediment velocities. Features of the average solution transmission loss and phase change, preserved by this algorithm, will be discussed. [Work supported by ONR/NRL-SSC and ONR Young Navy Scientist Program.]
Estimating vertical and horizontal wave-number temperature spectra of a buoyant thermal plume
Authors: Oeschger John , Goodman Louis
Published: October 2005

Acoustic scattering from a buoyant thermal plume described by the far-field Born approximation results in a simple relationship between the scattered pressure field and the scattering field; namely, the two are Fourier transform pairs. For media variability, such as the buoyant plume where the spatial variability is larger than the Fresnel radius, wave-front curvature must be included to describe experimental results adequately. Under conditions where Taylor’s hypothesis is satisfied (the time variability is entirely due to the advection at a constant velocity of spatial variability), the effects of wave-front curvature on the scattering process can be removed. Data are collected for simultaneous multiple bistatic scattering experiments in common and antiparallel scattering directions for the unstable and turbulent plume. Results include an estimation of the vertical and horizontal wave-number temperature spectra of the buoyant plume.
Determining elastic seafloor parameters in shallow water using ambient noise
Authors: Deane Grant B. , Carbone Nicholas M. , Buckingham Michael J.
Published: October 2005

The ambient noise field in shallow water contains information about the seafloor. Measurements of the coherence of ambient noise have been used successfully [M. J. Buckingham and S. A. S. Jones, J. Acoust. Soc. Am. 81, 938–946 (1987)] to infer the critical angle of a variety of fluid basements. This technique has been extended to include the case of a shear-supporting bottom. A theoretical model of the ambient noise in an isovelocity, shallow water channel overlying an elastic basement with independent, randomly distributed surface sources will be presented. The model shows that elastic basements with shear speed greater than 650 m/s have sufficient effect on the noise field to enable the geoacoustic parameters of the bottom to be determined. The two main effects observed are an asymmetry in the vertical directionality and the arrival of energy at angles greater than the critical. [Work supported by ONR.]
Effects of perturbations on long-range propagation
Authors: Kuperman William A. , Collins Michael D. , McDonald B. Edward , Heaney Kevin D.
Published: October 2005

Results of numerical modeling of long-range (greater than 500-km) low-frequency acoustic propagation in the ocean have been presented previously. These results were in qualitative agreement with measurements for the Heard Island Feasibility Test and the SLICE89 experiments. To quantify the differences between experimental and parabolic equation (PE) results, time-dependent modal decomposition was applied to the received signals. This modal tomography gives us an indication of the depth-dependent differences between the actual and assumed sound-speed profiles. This work is extended to look at the effects of small perturbations in the sound-speed field (i.e., internal waves) on the arrival pattern. Internal waves were modeled using a statistical realization of the Garrett–Munk spectrum. Results of the effects of internal waves on specific deep ocean mode functions and model group velocities are presented. a)Present address: Marine Physical Labs., Scripps Inst. of Oceanogr., UCSD, La Jolla, CA 92093.