bluuebunny/crossref_metadata_2025 huggingface dataset:
A perceptual representation of sound for source separation.
Authors: Ellis Daniel P. W. , Vercoe Barry L.
Published: October 2005

Building machines that emulate the kinds of acoustic information processing that human beings perform effortlessly has proved unexpectedly difficult. The irresistible conclusion is that the human auditory system is extremely sophisticated in its adaptation to real-world sounds and uses an impressive array of features as cues to organization and interpretation. As more of these cues become known through psychoacoustical experiment, it becomes feasible to program computers functionally to mimic human perception of sound. Since the processing is so integrated and the roles of different features only partly understood, the best approach to simulating real listeners (including susceptibility to illusions) is to build as direct an analog of the actual processing chain as can be devised. Concentrating on the task of distinguishing and separating individual superimposed sonic sources, such as a singer and accompaniment, a perceptually sufficient invertible representation has been built that analyzes sound down to a relatively small number of ‘‘atoms.’’ Psychoacoustic rules of stream formation can then be applied to these atoms to simulate many aspects of human source separation. Examples will be shown and played.
Aeroacoustics of transitional and separated boundary layers.
Authors: Lauchle Gerald C.
Published: October 2005

Experimental and theoretical research related to the acoustic emissions from nonsteady laminar and turbulent boundary-layer flows is described. Transition of a laminar boundary layer into a turbulent one is characterized by the formation and growth of turbulent spots. The spots are interspersed with laminar regimes (thus causing the laminar boundary layer to be nonsteady) and they create local wall pressure fields and acoustic radiation that are notably different from those generated by a full turbulent layer. The current research in this arena is concerned with refining the theoretical bases for predicting the acoustic radiation and on the performance of experiments to help verify these models. Other research deals with the radiation and structural response due to the separated turbulent flow over forward and rearward facing steps on flat panels. This effort is experimental with some new analytical techniques being developed for the signal processing of pressure and intensity probe signals that permit identification of coherence areas and source strengths for the reattaching flow. The research projects discussed here are forming the dissertations of R. C. Marboe and W. A. Kargus, Ph.D. candidates in the Graduate Program in Acoustics at Penn State. [Work supported by ONR and Ford Motor Co.]
Subsea vehicle pump pulsation measurements.
Authors: Simon Murray M.
Published: October 2005

The use of seawater ballast pumps for small undersea vehicles has increased demands for noise reduction in such subsystems. With severe constraints on volume, weight, and efficiency and the need to operate at high head pressure, the usual noise reduction techniques used on large submarines are not feasible. There are stringent requirements on a measuring system to evaluate such subsystems. To prevent biased results due to the differing spectral content of various subsystems, nonreactive acoustic termination is required. Also, care must be taken to ensure that the hydraulic load providing the required back pressure does not contaminate the results with its own noise. This paper describes an easily assembled system meeting the requirements for testing in a laboratory environment. Data were taken on two styles of water pumps to evaluate the system. Two in-line acoustic filters (mufflers) of the commercially available ‘‘three pipe’’ configuration were tested with one of the pumps and compared to analytical results using a transmission matrix model. The results indicate significant insertion loss over a broad frequency range. [Work supported by Alliant Techsystems internal IR and D funding.]
Quantitative schlieren analysis of acoustic interaction with submerged plates.
Authors: Richards Roger T.
Published: October 2005

Transmission and radiation of sound from submerged plates were investigated by means of a quantitative schlieren method that produced accurate visual representations of sound fields. The method was shown to be significantly faster than the usual point-by-point scans of acoustic fields with no loss of accuracy. The low-frequency resolution of the classical schlieren system was improved by nearly two orders of magnitude; sound waves with frequencies as low as 27 kHz were easily visualized. These improvements were demonstrated with a thorough investigation of sound transmission through submerged plates over a frequency range from well below to over one hundred times the classical coincidence frequency. Beam shifting caused by Lamb waves and a previously unknown cancellation with increasing frequency of modal pairs of Lamb waves were both observed.
Performance capabilities of the adaptive filtered-x algorithm for active control of broadband excitation.
Authors: Sommerfeldt Scott D. , Nashif Peter J.
Published: October 2005

Applications of the adaptive filtered-x algorithm to active noise and vibration control problems involving broadband excitation of the system have been reported previously in the literature. For these different applications, varying degrees of control effectiveness have been reported, sometimes for the same class of active control problem. This paper will address the issue of using the filtered-x algorithm for broadband control applications to establish the performance that can be expected based upon the parameters associated with the system to be controlled. In particular, issues such as causality of the control system, the characteristics of the broadband excitation, and the amount of damping in the physical system will be addressed to determine how such parameters can be expected to influence the control achieved.
Passive adaptive control of plate vibration and acoustic radiation.
Authors: Gruenhagen Deborah A. , Burroughs Courtney B. , Sommerfeldt Scott D.
Published: October 2005

The frequencies of resonance of the lower-order modes in a plate are sensitive to boundary conditions. By adaptively controlling the clamping pressures on the edges of a vibrating plate, the frequencies of resonance can be continuously detuned from the frequency of a pure-tone source. Results from laboratory demonstrations of the passive adaptive control of the vibration and acoustic radiation from a plate excited by pure-tone sources with varying source frequencies are presented and discussed.
An automated focusing and scanning system for measuring fast waves on elastic structures by laser Doppler interferometry.
Authors: Kil H.-G. , Jarzynski Jacek , Berthelot Yves H.
Published: October 2005

A laser Doppler vibrometer has been designed, built, and tested for specific applications to structural acoustics. It is capable of measuring small in-plane displacements associated with the propagation of fast waves (shear or longitudinal) on the surface of a structure. The probe head is compact, rugged, and can operate underwater. The system has been automated so that extensive data can be collected over the structure and analyzed in the K-space as is done in acoustical holography. The motion of the probe head is controlled by two stepping motors. The first one controls the focusing action (laser spot size on the structure) and the second one controls the position of the whole probe over the structure. The laser Doppler signal measured by the probe head is detected by a photodiode, demodulated by a phase-lock loop, digitized, and sent to a computer that acquires the data and controls the stepping motors. Automated focusing action is achieved by an iterative process. Automated scanning over a given structure is also achieved digitally by computer control of the second stepping motor. Results obtained with the system collecting data over a vibrating surface will be presented. [Work supported by ONR.]
Phonological representation affects phonetic perception.
Authors: Jongman Allard , Sereno Joan , Lahiri Aditi , Raaijmakers Marianne
Published: October 2005

This study examines to what extent phonological representations affect word identification in Dutch. Dutch has an underlying contrast in voicing that is neutralized word-finally. Also, vowels are lengthened approximately 20 ms when preceding medial voiced consonants. Vowel length can therefore be a cue to voicing. The present study investigates whether the vowel length cue influences listeners when hearing stimuli with ambiguous vowel duration in an identical, neutralized, consonantal context but where the underlying representation of the consonant differs in voicing. A vowel length continuum ([at] to [a:t]) was made by shortening a long vowel in 12 steps. To this continuum, initial consonants were added to create four phonetic endpoints with opposite underlying voicing patterns: /zat/, /zaad/, /stad/, /staat/. Results of a vowel categorization task showed that, using an identical vowel length continuum, the crossover boundary in the zat–zaad continuum occurs at a significantly shorter vowel length than that in the stad–staat continuum. These results provide evidence that listeners use the underlying phonological representation in the perception and identification of words.
A mechanism for the rapid quenching of sonoluminescence pulses.
Authors: Prosperetti Andrea , Og̃uz Hasan
Published: October 2005

It has recently been found that the duration of sonoluminescent light emission from stably oscillating bubbles is of the order of 200 ps or shorter [Barber and Putterman, Nature 352, 318 (1991)]. This result is very surprising because, according to the best available estimates, temperatures high enough to cause luminescence from excited OH radicals persist for times 3–4 orders of magnitude longer [Egolfopoulos etal., J. Acoust. Soc. Am. (submitted)]. A possible mechanism to explain the observed premature quenching of the light emission is as follows. Near the time of minimum radius a very strong acceleration exists directed from the gas into the liquid. This situation is Rayleigh–Taylor unstable and may cause the shedding of minute liquid droplets from the bubble surface into the gas. These drops may cool the gas sufficiently to prevent further light emission. To investigate this mechanism a boundary element calculation of the evolution of the surface shape of a collapsing bubble is performed. [Work supported by NSF.]
Detection of mistuning in the presence of an interfering sound.
Authors: Carlyon Robert P.
Published: October 2005

Mistuning is an important cue for the perceptual segregation of concurrent sounds. Although it often has to be detected when more than one sound is present, the effect of extraneous sounds on sensitivity to mistuning remains unknown. This was investigated using a 2AFC task, where the standard consisted of the first seven harmonics of 500 Hz, all frequency modulated coherently (5-Hz rate, 200-ms duration) by the same percentage of their starting frequencies. The initial modulation phase was randomized across presentations. The signal was identical, except that the fourth harmonic was modulated in antiphase re: the other components, causing it to become mistuned by an amount proportional to the FM depth (the dependent variable). Stimuli were presented at 45 dB SPL per component in a continuous pink noise. The threshold FM depth necessary for the detection of mistuning was measured as a function of the level of a 2000-Hz unmodulated sinusoid. When this ‘‘interferer’’ was gated on and off with the complex, it had only a small effect on thresholds provided that its level was lower than about 42 dB SPL. However, when it was gated on 400 ms before, and off 100 ms after, the complex, thresholds were higher than with a synchronous interferer, and were elevated even at low interferer levels. Continuous interferers produced thresholds intermediate between the two conditions. The effect of interferer asynchrony persisted when the interfering sinusoid was replaced by narrow-band noise and is interpreted in terms of auditory streaming.
Auditory stream segregation by musical timbre.
Authors: Iverson Paul
Published: October 2005

A series of experiments examined the acoustic attributes of timbre that most contribute to auditory stream segregation. In the first experiment, listeners heard short sequences of repeated pairs of tones from orchestral instruments, and were asked to rate how strongly the tones formed different streams. These ratings were used as difference measures, and were fit to a two-dimensional space using multidimensional scaling. One dimension corresponded to average spectral frequency, and the other to multiple dynamic factors. These ratings were highly correlated with similarity judgments from a previous study. A second experiment assessed if the dynamic factors indirectly contributed to streaming by influencing perceptual attack time. The perceptual attack time of each tone was measured, and new sequences were recorded with the perceptual attacks isochronous. The results were highly correlated with the first experiment, and the effect of the dynamic factors was not diminished. These experiments indicate that streaming and similarity judgments are based on the same acoustic attributes. Implications for the segregation of melodic lines in music will be discussed.
Theory of iterative time reversal acoustic mirrors.
Authors: Prada C. , Thomas J. L. , Fink M.
Published: October 2005

A new ultrasonic focusing method for reflective target has been demonstrated in the laboratory. This method is interesting for nondestructive testing and lithotripsy. It uses an ultrasonic time reversal mirror made of a 2-D array of transmit and receive transducers each connected to a programmable generator. The array first transmits a wave that is reflected by the target. The reflected wave is received by the same array and then the corresponding signals are stored, time reversed, and re-emitted. The resulting wave focuses on the target even when the propagating medium is inhomogeneous. This process can be iterated and when the medium contains several reflectors that are well resolved, this allows one to focus on the strongest one. These self-focusing properties have been demonstrated theoretically and experimentally [C. Prada etal., J. Acoust. Soc. Am. 90, 1119–1129 (1990)]. In the general case, the convergence of the iterative process is not obvious. A matrix theory, valid for an inhomogeneous propagating medium and reflectors of complex scattering properties, shows that the process converges but may yield to different limits for odd and even numbers of iterations. This analysis is illustrated by several numerical and experimental examples.
A new design for ultrasonic wedge transducer.
Authors: Shen Zhi Hua , Huang Dehua
Published: October 2005

The ultrasonic wedge transducer has attracted much interest in recent years in the fields of microscopy, medical ultrasonic, and nondestructive testing evaluation. The new design gives a better particle velocity distribution on the surface of the wedge transducer. When the Gaussian transducer technique is involved in the design, a Gaussian wedge transducer is achieved. The theory behind the design is also presented.
Federal review of the aircraft noise assessment process.
Authors: Dickerson William D.
Published: October 2005

The Federal Interagency Committee on Noise (FICON) was formed in December 1990 as an outgrowth of airport noise analysis concerns raised by the Environmental Protection Agency. The committee’s function is to review the Federal approach for airport noise assessment used in Environmental Impact Statements (EIS). The committee has made preliminary recommendations for improving the airport noise assessment process and has circulated their report for public comment. The recommendations cover the continued use of the DNL metric, use of supplemental metrics, how these metrics are described in documents available to the affected public, the scope of analysis in EISs, mitigation options used in EISs, and the need for continued systematic public input to improving the process. After public review, final recommendations will be made to Federal Agency decision makers for their consideration.
U. S. Navy shipboard noise criteria.
Authors: Herstein Louis A. , Bernhard David D.
Published: October 2005

Steady state airborne noise criteria for communication and habitability within shipboard spaces have evolved from simple qualitative statements, through octave-band limits, to A-weighted levels. It is now recommended that A-weighted criteria supplemented by C-weighted minus A-weighted criteria be used to avoid the occurrence of low frequency (less than 200 Hz) problems. The recommended levels, while still somewhat higher than those considered acceptable for shore based environments because of ship cost, weight, and space restraints, should result in improved shipboard concentration and habitability. Octave band criteria related to the A-weighted and C-weighted minus A-weighted criteria would continue to be used for engineering design purposes. This paper will briefly describe the development of the criteria. [Work supported by Naval Sea Systems Command.]
Acoustics of a high rise residential project.
Authors: George Ballard W.
Published: October 2005

This paper describes acoustical elements of an urban residential project from design stage through construction. The project consists of nine stories of residential units over commercial space and occupies a city block in San Francisco. Design objectives included achieving consistency with, and in some cases bettering, California Title 24 Noise Insulation Standards. These standards are concerned with control of exterior to interior noise and the sound insulation afforded by common partitions. Other topics addressed included: mechanical equipment; plumbing systems; ceiling treatment; elevators; trash chutes; fire safing material; fire alarm horns; interconnecting ducting; duct attachments to structure; garage door mechanism; sprinkler pipe; and unit entry doors near commercial space. Fire safing effectiveness for acoustics depends on both resiliency and transmission loss; sometimes tradeoffs are needed. An investigation was made of the feasibility of placing fire alarm horns in the corridors; however, in the final design fire alarms were located in each dwelling unit for best audibility. Comments were received from a neighbor concerning an audible tone from rooftop equipment; an investigation was made to locate the specific source, and findings are reported.
Finite amplitude standing waves in harmonic and anharmonic closed tubes.
Authors: Gaitan D. Felipe , Atchley Anthony A.
Published: October 2005

Recent developments in thermoacoustic devices have generated a renewed interest in finite amplitude standing waves in resonant cavities. Such devices can generate standing waves with acoustic pressure amplitudes on the order of 10% of ambient pressure. The similarity between previously observed finite amplitude waveforms in closed tubes and those in prime movers could be modeled as anharmonic resonating cavities. Measurements of the energy transfer into the harmonics and the resonant modes of both harmonic and anharmonic closed tubes driven at resonance (∼200 Hz) will be presented. These measurements were compared with calculations using Coppens and Sanders’ formulation [A. B. Coppens and J. V. Sanders, ‘‘Finite-amplitude standing waves within real cavities,’’ J. Acoust. Soc. Am. 58, 1133–1140 (1975)], which requires the measured quality factors and resonance frequencies. [Work supported by ONR and the NPS Research Program.]
Turbulent energy spectrum predictions by nonlinear acoustic scattering.
Authors: Parker James E. , Korman Murray S.
Published: October 2005

An underwater nonlinear experiment is performed involving the propagation of finite-amplitude sound waves through a turbulent flow. The experimental geometry involves the interaction of two mutually perpendicular crossed ultrasonic beams that are generated by individual focused transducer units (with frequencies of 2.0 and 2.1 MHz, respectively). The alignment positions the center of the interaction at the overlapping focal regions. A mechanical apparatus allows the crossed beams to rotate in a horizontal plane containing the submerged circular water jet. The beam axes always remain perpendicular. In the presence of turbulence, a radiated nonlinear sum frequency component (f+=4.1 MHz) is scattered and detected by a receiving transducer unit located outside the interaction region. In the absence of turbulence, there is virtually no nonlinear scattering. Measurements of the broadened intensity spectrum versus angle contain statistical information about the turbulent velocity components. Further analysis shows that focused crossed beam scattering exhibits good spatial resolution. From theory [Korman and Beyer, J. Acoust. Soc. Am. 85, 611–620 (1989)] the energy spectrum of turbulence E(k,r) (where k is the wave number of the turbulent eddies) is predicted by performing angular measurements at several scan positions r across the jet. [Work supported by the Naval Academy Research Council.]
Observation of single-point excitation and shocking of rotating acoustic waves.
Authors: Ceperley Peter H. , Koren Alon
Published: October 2005

In a cylindrically symmetric resonator or a ring resonator, the proper combination of standing wave modes results in a rotating wave field. Such a field has the appearance of a traveling wave chasing its tail, a constant field profile rotating in space. However, unlike traveling waves, rotating waves are limited to distinct modes. Rotating waves offer the clearest insight into angular momentum and rotary motion in wave fields. The following observations will be reported: (1) rotating acoustic waves in a concentric ring resonator and in a cylindrical resonator; (2) single-point excitation of these waves [P. H. Ceperley, ‘‘Split mode traveling wave ring resonator,’’ U.S. Patent 4,686,407 (1987)]; and (3) weak shocking of the wave fronts at acoustic amplitudes near 1 kPa. These all relate to one atmosphere, air-filled resonators. [Work supported by ONR.]
Further investigation of a single, stable, sonoluminescing bubble using Mie scattering.
Authors: Gaitan D. Felipe , Lentz W. Jerry , Atchley Anthony A.
Published: October 2005

A year after its discovery, a single sonoluminescing bubble is far from being understood. The role of the various physical parameters such as vapor pressure, ambient temperature and pressure, etc., are yet to be determined. To this end, we have varied these parameters while monitoring the dynamic radius of the bubble using Mie scattering. Furthermore, the nature of the sonoluminescence emissions has been investigated by measuring the overall intensity as well as spectra as a function of these parameters. [Work supported by ONR and the NPS Research Program.]
Near-field array with constant focal area.
Authors: Adorno Noel A. , Hixson Elmer L.
Published: October 2005

A microphone array to be placed in the headliner of an automobile was designed for Cellular telephone application. The design goal was to provide a focal area of 20×20 cm centered at the driver’s mouth to be held constant from 300 to 3000 Hz. Digital filtering-delay techniques were used to control focal area. Array size limitations and a limited number of elements produced focal area sizes of 19×19 to 24×24 cm from 450 to 3000 Hz.
Nonlinear wind-wave effects in backscatter.
Authors: Mellen R. H. , Leykin I. A.
Published: October 2005

In backscatter experiments, nonlinear wind-wave effects have been observed in Doppler spectra and azimuthal asymmetry of scattering strength. Both effects have been ascribed to spatial skewness associated with nonlinear steepening of the wavefronts. Bicoherence analysis of wavegauge measurements in a laboratory flume supports this mechanism. However, standard statistical methods reveal only average properties. In a recent paper [N. E. Huang, Nonlinear Water Waves Workshop, Bristol, U. K. (1991)], Huang reported on the use of phase/time analysis of the analytic wave function to obtain additional information on local properties and analyzed wave-buoy data by this method. His results showed evidence of ‘‘wave groups’’ in addition to possible fractal properties, the spectra of the phase fluctuations being consistent with a self-similar process of fractal dimension ≊1.4. Phase/time analysis of the laboratory flume data is reported here with similar results and this appears to support fractal behavior of the ‘‘wave groups.’’ Some of the implications for backscatter are considered.
Digital audio.
Authors: Stockham Thomas G.
Published: October 2005

This tutorial addresses an audience with no background in digital audio and builds a basic and fundamental understanding of the subject. The presentation covers a set of topics that define a digital audio chain from input to output. The topics are signal preparation, sampling, digitization, recording/correction, signal processing, editing, playback, error detection/correction, decoding, and signal reconstruction. This set of concepts provides substantial insight into digital audio across a broad spectrum of applications from the lowest quality voice to the highest quality music.
Temporal evolution of the bubble plumes generated by breaking waves: Acoustical implications.
Authors: Monahan Edward C. , Wang Qin
Published: October 2005

Via a series of ‘‘tipping bucket’’ experiments in UConn’s Whitecap Simulation Tank IV, the temporal evolution of the bubble plumes that result from spilling breaking waves in fresh water and sea water has been investigated. The saltwater bubble plume in its early stages is characterized by many more bubbles than are encountered in a freshwater plume in the same stages. The peak in the early salt-water bubble population spectrum, ∂N/∂R, has an amplitude approximately 24 times the amplitude of the comparable freshwater spectral peak. The spectra obtained at various times after a ‘‘breaking wave event’’ have been used to estimate the temporal variation of the void fraction at the top of the plume, and from this estimate the speed of sound through the portion of a plume just below its associated whitecap, as a function of time, was ascertained, for both the freshwater and seawater cases.
A laboratory experiment on nonlinear coupling between surface and volume modes of a bubble.
Authors: Mao Yi , Crum Lawrence A. , Roy Ronald A.
Published: October 2005

M. S. Longuet-Higgins has predicted [J. Fluid Mech. 201, 525–541 (1989)] that the distortion modes of a bubble can produce, through nonlinear coupling, a monopole radiation of sound. Here, some preliminary results are presented of an experiment designed to investigate this phenomenon. A hydrophone and needle are submerged in water in a small (6.5×6.5×7.0 cm3) sealed cell that is connected to a regulated evacuation system for pressure control. The sound radiation produced by releasing a bubble from the needle is monitored by a hydrophone and displayed on a digital oscilloscope. Two high-speed video cameras simultaneously record the motion of the bubble and the sound radiation trace as displayed on an analog oscilloscope. At low pressures (i.e., a few cm Hg), it is seen that after the pinch-off sound dies out, there follows a sound of the same frequency but with a lower and relatively constant magnitude, which we believe is evidence of the coupling between surface and volume modes. Observation of the phase between the surface oscillation and the radiated sound indicates a causal relationship. [Work supported by ONR.]
A dual frequency ultrasonic probe for medical application.
Authors: Saitoh Shiroh , Izumi Mamoru
Published: October 2005

A dual frequency probe employing two ceramic layers for medical ultrasonic diagnostic equipment has been developed for simultaneously obtaining both a high-resolution tomogram and a high S/N Doppler mode image. This ceramic vibrator, which has opposite poling directions and different individual thicknesses, has enabled the excitement of a second harmonic in addition to the fundamental resonance. Therefore, only a pair of electrical terminals are enough to excite dual frequencies. Ultrasonic attenuation in a human body is reduced, since the Doppler reference frequency can be set below the tomogram center frequency. Moreover, the two relative resonant levels are widely controllable by changing the thickness ratio of the two layers. An optimum thickness ratio of 1:0.7 has been obtained by computer simulation under Mason’s model. A cofiring multilayer method has been developed to achieve a multilayer ceramic with a large adhesive strength. As a result, the S/N of the Doppler mode has been improved as much as 5 dB over that of a conventional probe at an artery located 5 cm deep from the surface.
A prototype cylindrical wave-number calibration array.
Authors: Luker L. D.
Published: October 2005

There has been considerable interest in recent years in the acoustic interference of the turbulent boundary layer (TBL) produced on the surface of a vehicle moving through water. The ‘‘flow noise’’ produced by the TBL is generally characterized by pressure waves that are transported along the surface at speeds much less than the sound speed in water and are, therefore, evanescent. Planar array devices have been constructed previously that generate evanescent waves with desired spatial wave numbers in a region near the front surface of the array. This paper describes a prototype cylindrical wave-number calibrator array designed to generate the desired evanescent waves inside the free-flooded calibrator. This geometry is suitable for the evaluation of line acoustic sensors such as in towed sonar arrays. The prototype calibrator consists of a cylindrical tube of PVDF with an electrode pattern along the tube length that allows the PVDF to be operated as 40 independent bands each of which can be driven at a specified amplitude and phase. The required drive voltages are calculated by measuring the electroacoustic transfer matrix of the calibrator at the desired drive frequency. Measured evanescent pressure fields inside the calibrator are compared with desired and predicted fields at selected spatial wave numbers for frequencies of 800 and 1600 Hz. [Work jointly supported by ONR and ONT.]
The effect of the rough air–sea interface on scattering from tenuous bubble clouds.
Authors: Thorsos Eric I.
Published: October 2005

Henyey has developed a theory for low-frequency scattering from tenuous bubble clouds [F. S. Henyey, J. Acoust. Soc. Am. 90, 399–405 (1990)]. The bubbly water is treated as an effective medium, described with a spatially varying index of refraction, and the scattering is found using a perturbation theory approach. This model applies to bubble clouds with sufficiently low air volume fraction that buoyancy forces are negligible; the bubble clouds are thus referred to as tenuous. Henyey simplified his analysis by assuming that the air–sea interface is flat. Here the effect of including surface roughness is examined for the 2-D problem (1-D surface roughness), but otherwise Henyey’s approach is followed. The integral equation method is used to obtain the exact acoustic fields near the rough surface, which are then employed in the bubble scattering calculations using perturbation theory. Results comparing bubble scattering with rough and flat sea surfaces show that the average scattered intensity is not much affected by surface roughness, but the statistical distribution of intensities can be significantly affected, leading in some cases to a hightailed intensity distribution (spikes) when the surface is rough. Implications for the time dependence of the scattering and for the Doppler spectrum will also be discussed. [Work supported by ONR.]
Acoustic daylight: Imaging the ocean with ambient noise.
Authors: Buckingham Michael J. , Berkhout Broderick V. , Glegg Stewart A. L.
Published: October 2005

For many years the principal means of probing the ocean using sound has been through the use of either ‘‘active’’ or ‘‘passive’’ techniques. With an active system, an object is illuminated by a pulse of sound and its presence inferred from the echo it produces, whereas the passive approach involves simply listening for the sound that the object itself emits. Here a new method of employing sound in the ocean is reported, which is neither passive nor active. It relies on the naturally occurring, incoherent ambient noise field in the ocean as the sole source of acoustic illumination. By analogy with daylight in the atmosphere, ambient noise scattered from an object in the ocean can be focused onto an image plane, and from this acoustic image, with appropriate signal processing, a visual image can be produced on a television-type monitor of the object space in the ocean. To test this concept, several simple experiments have been conducted in the ocean off Scripps pier, with a single parabolic reflector acting as an acoustic lens, which confirm that objects illuminated only by ambient noise can indeed be ‘‘seen’’ over a frequency band between 5 and 50 kHz. [Work supported by ONR.]
Acoustic radiation due to surface wave breaking.
Authors: Kennedy Robert M. , Glegg Stewart A. L.
Published: October 2005

While wave breaking is continually occurring at the sea surface, its transient and sporadic nature makes it difficult to measure. Experimental results are presented that show how acoustic methods can be used as a remote sensor of this fundamental process. Sea surface-generated acoustic radiation (40 to 4000 Hz) is directly related to a quantitative measure of the boundary dynamics; i.e., the Toba variable. The frequency spectrum of the radiation remains remarkably unchanged over a wide range of environmental conditions but the correlation between the sound pressure level and the Toba variable undergoes an abrupt change when spilling breakers start to occur. Results support the use of acoustics to remotely measure the rate of energy being dissipated by wave breaking and the wavelength of the dominant gravity wave component. Theoretical studies have related the field measurements to analytical and laboratory results cited in the literature indicating that remote monitoring of the rate of occurrence and size distribution of ‘‘infant’’ (freshly entrained) bubbles may be possible if splashes on the surface do not radiate significant sound. Signal processing algorithms for the remote measurements discussed above are enhanced by eigenstructure analysis of the measured cross-spectral density matrix. [Work sponsored by ONR and NUSC.]
Laboratory experiments on bubble-cloud oscillations.
Authors: Crum Lawrence A. , Nicholas Michael , Kolaini Ali , Roy Ronald A.
Published: October 2005

A variety of experiments that have been undertaken to investigate the acoustic characteristics of bubble clouds will be described. These experiments have involved both passive acoustic emission, in which the radiated noise is measured from a bubble cloud that is being produced, and active acoustic scattering, in which sound waves are scattered from a similarly produced bubble cloud after it has ceased to radiate emissions. It appears that the dominant acoustic characteristic of these clouds is that they readily emit, and can easily be stimulated into emitting, low-frequency sound by the collective oscillations of the bubbles within the cloud. This mode of oscillation [see papers by Prosperetti and by Carey and Browning in SeaSurfaceSound, edited by B. R. Kerman (Kluwer Academic, Dordrecht, 1988)] appears to provide a physical mechanism for a broad range of ambient noise emissions in the ocean and may play an important role in low-frequency active scattering from the ocean surface. [Work supported by ONR and ONT.]
Fractal characterization of the near-surface oceanic bubble layer from deep-ocean reverberation measurements.
Authors: Gilbert Kenneth E. , Wang Lintao
Published: October 2005

At high sea states and low grazing angles, it has been hypothesized that surface reverberation is dominated by backscatter from the bubble layer beneath the sea surface. Assuming the hypothesis is true, a simple stochastic bubble-layer backscatter model has been used to analyze surface reverberation data from four different deep-ocean areas. In every area, the inferred wave-number spectrum for the horizontal structure of the bubble layer is an inverse power law of the form P(K)=AK−β, where A is a constant, K is the horizontal wave number of the structure, and 3≲β≲4. The existence of power-law wave-number spectra indicates that the horizontal structure of the bubble layer is fractal. Using D=4−β/2 for the fractal dimension, 2≲D≲2.5 is obtained for measurements analyzed so far. Fractal structure in the bubble layer implies that horizontal inhomogeneities exist on a wide range of scales and possess scale invariance. Hence, on the average, the medium looks the same at all scales between some ‘‘inner scale’’ and ‘‘outer scale.’’ (Presently, the inner and outer scales are not known.) In this paper some physical processes are considered that could generate fractal structure in the bubble layer and some experimental means are suggested for identifying the processes. [Work supported by ONR.]
On using coherence to measure distortion in hearing aids
Authors: Kates James M.
Published: October 2005

Coherence is a frequency-domain measure of the degree to which the output of a system is linearly related to the system input. The signal-to-distortion ratio (SDR), where the distortion term includes all nonlinear effects and noise in the system, can be computed from the coherence. The coherence estimate, however, is subject to sources of variance and bias that reduce the accuracy of the measured SDR. The origins of the variance and bias and their effects on distortion measurements are presented. New procedures for reducing the variance and bias effects are described, and the processing effectiveness is demonstrated for a simulated hearing-aid response.
Rectangular parallelepiped resonance—A technique of resonance ultrasound and its applications to the determination of elasticity at high temperatures
Authors: Anderson Orson L.
Published: October 2005

The experimental work on resonance ultrasound, especially using the technique called rectangular parallelepiped resonance (RPR) is reviewed and summarized. The work on high-temperature (at temperatures beyond the Debye temperature) measurements of elastic constants is emphasized. Several applications of this high temperature work are described, including thermal equations of state, the determination of thermodynamic functions, and the determination of the bulk modulus at temperatures beyond experimental capability.
Direct measurement of the temperature-dependent piezoelectric coefficients of composite materials by laser Doppler vibrometry
Authors: Rittenmyer Kurt M. , Dubbelday Pieter S.
Published: October 2005

The longitudinal (d33) and transverse (d31) piezoelectric coefficients of a piezoelectric composite material (NTK PR-306) are determined as functions of frequency and temperature by using laser Doppler vibrometry to measure the strain induced in the sample by an electric field. Measurements are performed over the temperature range from −50 °C to 50 °C and over a frequency range from 0.1–10 kHz. Some measurements were made at frequencies up to 100 kHz in order to demonstrate the ability of the technique at frequencies in the vicinity of an electromechanical resonance. The results show that the viscoelastic relaxation affects the piezoelectric response of the composite material primarily through the dielectric stiffness rather than the elastic stiffness. The d33 coefficient is observed to relax in a normal fashion near the glass transition of the polymer phase whereas the relaxation in the d31 coefficient varies over the entire measured range of temperature.
Optimal design of an electret microphone metal-oxide-semiconductor field-effect transistor preamplifier
Authors: van der Donk Armand G. H. , Bergveld Piet , Voorthuyzen Johannes A.
Published: October 2005

A theoretical noise analysis of the combination of a capacitive microphone and a preamplifier containing a metal oxide semiconductor field-effect transistor (MOSFET) and a high-value resistive bias element is given. It is found that the output signal-to-noise ratio for a source follower and for a common-source circuit is almost the same. It is also shown that the output noise can be reduced by making the microphone capacitance as well as the bias resistor as large as possible, and furthermore by keeping the parasitic gate capacitances as low as possible and finally by using an optimum value for the gate area of the MOSFET. The main noise source is the thermal noise of the gate leakage resistance of the MOSFET. It is also shown that short-channel MOSFETs produce more thermal channel noise than longer channel devices.
An acoustical study of Korean monophthongs produced by male and female speakers
Authors: Yang Byunggon
Published: October 2005

The first three formants of the ten Korean monophthongs were studied. The vowels were produced by 20 male and female speakers in an ‖hVda‖ (V=vowel) context. Then the male–female variations in the Korean formant data were examined. The uniform scaling method resulted in less than a 6% difference between the scaled and reference data. A regression analysis showed that the slope of a regression equation with a small intercept near the origin could be used for the uniform scale factor.
Speech pattern hearing aids for the profoundly hearing impaired: Speech perception and auditory abilities
Authors: Faulkner Andrew , Ball Virginia , Rosen Stuart , Moore Brian C. J. , Fourcin Adrian
Published: October 2005

A family of prototype speech pattern hearing aids for the profoundly hearing impaired has been compared to amplification. These aids are designed to extract acoustic speech patterns that convey essential phonetic contrasts, and to match this information to residual receptive abilities. In the first study, the presentation of voice fundamental frequency information from a wearable SiVo (Sinusoidal Voice) aid was compared to amplification in 11 profoundly deafened adults. Intonation reception was often better, and never worse, with fundamental frequency information. Four subjects scored more highly in audio–visual consonant identification with fundamental frequency information, five performed better with amplified speech, and two performed similarly under these two conditions. Five of the 11 subjects continued use of the SiVo aid after the tests were complete. A second study examined a laboratory prototype compound speech pattern aid, which encoded voice fundamental frequency, amplitude envelope, and the presence of voiceless excitation. In five profoundly deafened adults, performance was better in consonant identification when additional speech patterns were present than with fundamental frequency alone; the main advantage was derived from amplitude information. In both consonant identification and connected discourse tracking, performance with appropriately matched compound speech pattern signals was better than with amplified speech in three subjects, and similar to performance with amplified speech in the other two. In nine subjects, frequency discrimination, gap detection, and frequency selectivity were measured, and were compared to speech receptive abilities with both amplification and fundamental frequency presentation. The subjects who showed the greatest advantage from fundamental frequency presentation showed the greatest average hearing losses, and the least degree of frequency selectivity. Compound speech pattern aids appear to be more effective for some profoundly hearing-impaired listeners than conventional amplifying aids, and may be a valuable alternative to cochlear implants.
Ray chaos in underwater acoustics
Authors: Smith Kevin B. , Brown Michael G. , Tappert Frederick D.
Published: October 2005

Generically, in range-dependent environments, the acoustic wave equation cannot be solved by techniques which require that variables be separated. Under such conditions, the acoustic ray equations, which have Hamiltonian form, are nonintegrable. At least some ray trajectories are expected to exhibit chaotic motion, i.e., extreme sensitivity to initial and environmental conditions. These ideas are illustrated numerically using simple models of the ocean sound channel with weak periodic range dependence. The use of Poincaré sections, power spectra, and Lyapunov exponents to investigate and characterize ray chaos are discussed. The practical importance of chaotic ray trajectories—a limitation on one’s ability to make deterministic predictions using ray theory—is emphasized.
Sea surface dipole sound source dependence on wave-breaking variables
Authors: Kennedy Robert M.
Published: October 2005

Estimates of the surface dipole sound source spectrum per unit water surface area were obtained from 40–4000 Hz and related to environmental parameters characterizing the wind and wave fields. The results give additional credence to the role of entrapped air bubbles and bubble clouds in the generation of acoustic ambient and indicate a change in the entrainment mechanism when the water surface transitions from aerodynamically ‘‘smooth’’ to ‘‘rough.’’ The measured dipole sound source spectrum, when scaled by the gravity wave equilibrium range wave-breaking rate of energy dissipation appears to be a self-similar function dependent only on the acoustic frequency nondimensionalized by the frequency of peak acoustic spectral level.
Effects of higher-order harmonics on phase determination in an ultrasonic interferometer
Authors: Jhung Kwang Hwa Chung , Hong Seung S. , Lee Chul R. , Kim Young H.
Published: October 2005

The effect of higher-order harmonic components on phase determination were analyzed to improve the accuracy of transient time measurement in an ultrasonic interferometer with a quadrature detector system. Under ideal conditions the locus of output signals of the phase sensitive detector forms a circle on the phase plane as the frequency changes and any nonideal factor would distort the circle, leading to erratic phase determination. This analysis has shown that the nth-order contribution to the phase is mostly determined by the product of the amplitudes of corresponding components of the reference and echo signals fed to the phase detector. The distortion parameters were obtained by least-squares fitting of the data to the distorted circle in the phase plane, and compared with those roughly estimated from the frequency components of the reference and echo signals. The exemplary numerical phase corrections for the third-order harmonics were carried out, so as to illustrate the improvement in the accuracy of the ultrasonic interferometer.
A computer simulation of sound power determination using two-microphone sound intensity measurements
Authors: Laville Frédéric , Nicolas Jean
Published: October 2005

A computer simulation of sound power determination using intensity measurements has been developed to reach a better understanding of the accuracy issue as well as help with the development of standards and the training of practitioners. Previous computer simulations have been limited in scope to only one kind of error, the sampling error (since only the exact intensity was computed) and only the source field (the background noise field was not simulated). This simulation has a broader scope: since the intensity estimated with two microphones is computed in addition to the exact intensity, instrumentation error is evaluated in addition to the sampling error; also, the background noise field is included. Several monopoles with variable phase and coherence between them are used to model point or extended noise sources. This simulation is used together with theoretical considerations to investigate the accuracy of sound power determination and the use of indicators to assess this accuracy. Special emphasis is put on sampling and phase mismatch errors and the validity of their evaluation using indicators proposed in the ANSI and ISO draft standards.