bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic characterization of a bubble injected into a fully developed turbulent flow field
Authors: Kolaini Ali R. , Markewicz Ken , Rajendran Veera
Published: October 2005

An experiment was designed to investigate the characteristics of sound produced by the turbulent excitation of bubbles. By injecting a bubble into a fully developed turbulent flow, generated by a submerged axisymmetric horizontal water jet, the excitation of bubbles and shear-induced fission/fusion may occur. In the case of shear-induced bubble distortion by a turbulent jet, nonlinear coupling between volume pulsation and surface oscillations occur at exactly the same frequency as the radial breathing mode of the bubble. Particle tracking velocimetry (PTV) is used to characterize the turbulent flow field. Two high-speed Kodak Ekta-Pro video cameras are used to capture, simultaneously, several 180-×180-×10-mm illuminated regions along the jet. An 8-W argon ion laser is utilized for illumination. The method provides not only a visualization of the various patterns and structures of the turbulent flow, but also yields quantitative instantaneous velocity data of the flow containing the bubble. The role of the turbulent flow characteristics in determining the acoustical bubble response is discussed. [Work supported by ONR.]
An MRI study of the physiological mechanism of F0 lowering
Authors: Hirai Hiroyuki , Honda Kiyoshi , Fujimoto Ichiro , Shimada Yasuhiro
Published: October 2005

The phenomena of F0 lowering in utterances, widely observed in a word accent or near a phrase boundary, is not sufficiently explained by the relaxation of F0 raising musculature, and the physiological mechanism for F0 lowering has been a question to be examined. Morphological observation of laryngeal framework was performed in this study using the magnetic resonance imaging (MRI) during phonation. Midsagittal images near the larynx were taken in different F0 levels in four male speakers. Relative positional changes among laryngeal components were measured to explore the chain of mechanisms that allows vocal fold shortening in low F0. In the results, vertical movements of the larynx were consistently observed to be correlated with F0 levels. Movements of the hyoid bone and changes in laryngeal cavity size were also found. A rotation of the cricoid cartilage was always associated with laryngeal descent towards lower F0. This rotation occurred to the direction of shortening the vocal folds, and its mechanism was confirmed by vertical sliding motion of the posterior plate of the cricoid cartilage along the physiological curvature of the cervical vertebrae. This mechanism can account for the well-known tendencies of laryngeal descent and strap muscle activity in F0 lowering.
Nonlinearities in articulatory/acoustic relations and the evolution of the human vocal tract
Authors: Cohen K. Bretonnel
Published: October 2005

The evolution of the modern human vocal tract is characterized by a progressive increase in the degree of flexion of the base of the skull. The acoustic consequences of this basicranial flexion were analyzed using a transmission line analog model and calculating variations in vocal tract transfer functions as the trailing edge of a constriction is moved anteriorly. The behavior of an unflexed tract was modeled by trading back and front cavity lengths. That of the modern human vocal tract was modeled similarly, except that after the distance of the trailing edge of the constriction tube from the larynx increased past the superior end of the pharynx, the cross-sectional area of the back cavity was increased (instead of its length) as front-cavity length decreased. The modern human vocal tract had a larger area of stability for the second formant frequency for [i]-like constrictions than that produced by the unflexed tract. It appears that the human vocal tract has evolved in the direction of increased size of quantal locations for vowel production.
The quasi-steady approximation, boundary-layer separation, and vibrations in the vocal tract
Authors: McGowan Richard S.
Published: October 2005

Studies of voice and other flow-induced vibratory phenomena in the vocal tract often rely on the quasi-steady approximation based on the smallness of the Strouhal number (a nondimensional frequency measure). However, the relevant parameter do decide the application of the quasi-steady approximation to boundary-layer separation in oscillatory flow situations is a function of both the Strouhal number and the Reynolds number. Boundary-layer separation is important because it helps to determine the pressure distribution on the vibrating solid surface. Thus, unsteadiness in separation could provide a mechanism for energy exchange between the solid and the air to account for self-sustained oscillation. Such a mechanism will be illustrated by a model for tongue-tip trills. [Supported by NIH Grant Nos. DC-00121, DC-00865, and DC-01247 to Haskins Laboratories.]
Foreperiod effects on acoustic laryngeal reaction time
Authors: Watson Ben C.
Published: October 2005

In a simple reaction time task, foreperiod is the preparatory interval between presentation of a warning cue and a respond cue. Two studies examined effects of foreperiod duration, range, and distribution on laryngeal reaction time (LRT) values for production of the isolated vowel /a/. The first study examined foreperiods presented in two series with different durations and ranges (200–1000 ms and 700–2300 ms). Each series had a rectangular distribution. The second study examined the same two foreperiod series presented in nonaging (equi-probable) distributions. Variable inter-stimulus intervals and subject instructions inhibited initiation of preparation prior to presentation of the warning cue. Laryngeal reaction time (LRT) values decreased as foreperiod increased in each series. LRT was longest after the shortest foreperiod in a series, regardless of its absolute length. The same absolute duration foreperiod (i.e., 700–1000 ms) yielded a longer LRT when it was embedded in a wider range of foreperiods. The quadratic relation between foreperiod duration and LRT [K. Izdebski, J. Speech Hear. Res. 23, 485–489 (1978)] was more pronounced when a series was presented as a nonaging distribution versus a rectangular distribution.
Context independence of F3 trajectories in American English /r/’s
Authors: Espy-Wilson Carol Y. , Boyce Suzanne
Published: October 2005

In Boyce and Espy-Wilson [J. Acoust. Soc. Am. 89, 1916(A) (1991)] the coarticulatory effects of American English /r/ on surrounding segments were reviewed, and data were presented to suggest that the articulatory gesture for /r/ is relatively incompressible. Here, data are reported from a larger study that supports the previous claims. Comparing the trajectories through the intervocalic consonant of /wavam/ and /wawam/ with /waram/, we estimate the duration of the /r/ trajectory to be around 150 ms. Further, the trajectory appears to be symmetrical. In addition to /r/’s in clusters with labial consonants, we looked at /r/’s following voiced stops /g/, /b/, and /d/. Given the commonly cited coarticulation hypothesis that (1) articulation will be initiated as soon as possible, and (2) that coarticulation will be more extensive when neighboring segments contain no incompatible gestures [W. Henke, unpublished Ph.D. dissertation, MIT (1966)], it was expected that /r/ trajectories would start earlier in words with labial consonants. However, it was found instead that /r/ trajectories remained the same for each consonant condition. This finding was aided by the fact that for each speaker in every condition at least one token was found where the full symmetrical /r/ trajectory could be observed. Results from 4 male and 4 female speakers of American English will be presented. Implications for coarticulation and speech recognition will be discussed.
Effects of lexical status on children’s and adults’ perception of native and non-native vowels
Authors: Walley A. C. , Flege James E. , Randazza L. A.
Published: October 2005

Monolingual, English-speaking 5-year-olds, 9-year-olds, and adults heard stimuli from two ‘‘native,’’ synthetic continua, in which the vowels ranged from English /i/ to /i/ in the context /b—b/ or /b—p/. Thus the endpoints of the first continuum constituted a word and a nonword (‘‘bib’’ vs *‘‘beeb’’); the reverse held for the second continuum (*‘‘bip’’ vs ‘‘beep’’). Other subjects heard stimuli from two ‘‘foreign’’ continua, where the vowels ranged from English /i/ to a foreign vowel /y/ in the contexts described above. Thus the endpoints of the first continuum corresponded to a word and a nonword (‘‘bib’’ vs *‘‘bYb’’); both endpoints of the second continuum corresponded to nonwords (*‘‘bip’’ vs *‘‘bYp’’). After training on endpoints, subjects’ identifications of the nine stimuli of a given continuum were examined to assess whether: children, like adults, exhibit a ‘‘lexical bias’’ effect for familiar vowels (from the ‘‘native’’ continua); vowel categories not bounded by another native vowel (as in the ‘‘foreign’’ continua) expand outward or become better defined with increasing age and/or lexical status.
Wave-vector filtering and flow noise reduction in finite structures
Authors: Hwang Y. F.
Published: October 2005

It has been shown in the literature that the unwanted noise voltage output from a pressure sensing system due to the pressure fluctuations of a turbulent boundary layer can be minimized by exploiting the wave-number filtering action of finite hydrophones and hydrophone arrays, or by other wave-number filtering techniques. This paper discusses the similar effect in a finite structural panel subjected to the same excitation. However, in this case, the corresponding output is the effective modal force per unit area that excites the structural mode. The wave-number filtering characteristics of structural modes as a function of flow parameters, structural dimensions, mode order numbers, and boundary conditions are presented. The effective modal force per unit area is evaluated as the sum of contributions from three wave-number regions: the low-wave-number region, at and near the modal wave-number (within the major lobe) of a structural mode; the high-wave-number region, at and near the hydrodynamic coincident wave-number; and the intermediate wave-number region that lies between the above two regions. The relative contributions of the three wave-number regions are important criteria upon which further noise reduction strategies are devised. [Work supported by ONR.]
Aerodynamic noise theory—An alternative monopole source term
Authors: Powell Alan
Published: October 2005

Lighthill’s equation for the acoustic pressure perturbation may expressed as ⧠2p=ρ0(1/2ζ2−eii2), where ρ0 is the density of the incompressible inviscid noise generating flow, ζ is its vorticity, and eii is the principal strain rates. In the hydrodynamic field (∇2 vice ⧠2), pressure minima and maxima evidently always tend to occur in regions of vorticity squared and strain rates squared, repectively. For the far field, it is proved that the volume integral over the source region of the two monopole terms cancel exactly: the net monopole strength is always zero. Here the source region is not extensive as for the existing ‘‘simple source’’ theory. This is readily demonstrated in the limiting case, a steady vortex. This supports the gist of Ribner’s 1964 intuitive sketch of turbulent flow eddies having central pressure minima with the maxima in the regions of collision: the notion of the dilatation in the center of a single vortex by itself being the source (Legendre, 1992) is evidently incomplete. Quadrupole radiation may be studied, in principle at least, by taking the second moment of the source strength, or by considering the acceleration of the source field explicitly, say, à la Lowson, 1965.
Localization and wave conversion phenomena in multi-coupled nearly periodic structural systems
Authors: Pierre Christophe , Castanier Matthew P. , Chen Wan J.
Published: October 2005

For disordered mono-coupled systems, wave localization causes an exponential spatial wave amplitude decay, with the associated decay constant known as the localization factor. In multi-coupled structural systems, with multiple wave types, wave conversions complicate the analysis of localization phenomena. In this work, Lyapunov exponents of the system wave transfer matrix are used to analyze localization in multi-coupled disordered systems. Lyapunov exponents are a measure of the exponential growth rate of wave vectors. In a mono-coupled system, the largest Lyapunov exponent is equivalent to the localization factor. Lyapunov exponents are calculated numerically and, for the case of weak disorder, approximated by perturbation techniques. Three examples are presented. First, a representative mono-coupled system is considered. The largest Lyapunov exponent is calculated and compared with localization factors found by Monte Carlo as well as perturbation methods. Then bi-coupled system, a multi-span beam resting on flexible supports, is examined. Lyapunov exponents are calculated and compared with the wave amplitude decay found in a single realization of the disordered system. Finally, a truss beam, which features four types of waves is examined, and the physical significance of the Lyapunov exponents is discussed.
Performance stability of high-resolution matched-field processors to array-element location error in a shallow-water environment
Authors: Chandler Howard A. , Smith George B. , Feuillade C.
Published: October 2005

The effects of array-element location errors on the performance of four matched-field processing algorithms (Bartlett, maximum likelihood, sector focusing, and multiple constraint) have been investigated. The SNAP propagation model was used to generate the replica acoustic pressure field for a shallow-water channel with a depth variable sound-speed profile typical of a mid-latitude summer environment. It was also used to simulate a ‘‘detected’’ field due to an acoustic source in the presence of both uncorrelated and correlated (modal) noise. These were then correlated using the four algorithms for selected degrees of array deformation error. Results will be presented.
Comparisons and sensitivity analyses of numerical predictions of acoustic propagation in shallow-water and surface duct environments
Authors: Bilazarian P. , Kenig N. , Sutton D. , Parish M.
Published: October 2005

Comparisons of commonly used numerical models of acoustic propagation are performed over a wide frequency band in selected shallow-water environments. The models include range-independent propagation loss codes, such as Colossus II and Generic Sonar model (GSM), as well as range-dependent codes, such as SNAP and a wide-angle split-step parabolic equation (PE) model. For both range-independent and range-dependent shallow-water environments, SNAP model predictions typically provide close approximations to measured propagation loss data. Alternatively, large differences and model biases are generally prevalent in comparisons between measured data and Colossus II or PE predictions. Comparisons between the PE and GSM models are presented for sound propagation in surface duct environments. Results pertinent to the sensitivity of shallow-water propagation loss predictions to the amount of range dependence in environmental quantities, such as sound speed, bathymetry, and bottom-interaction parameters, are provided. Advanced 3-D visualizations are shown that illustrate the sensitivity of the optimum frequency of acoustic propagation in shallow water regions to variations in source–receiver geometries and environmental quantities.
Conditions of existing negative components in instantaneous frequency analysis
Authors: Kim Jeung T. , Lim Byungduk
Published: October 2005

An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a simple signal that consists of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The calculation shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria to show the condition of the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.
Relationships between objective measurements and perceptual interpretation: The need for considering spatial emission of sound sources
Authors: Warusfel O. , Kahle E. , Jullien J. P.
Published: October 2005

The room acoustics laboratory at IRCAM has undertaken a series of objective and perceptual measurements in different concerts halls and opera houses throughout Europe. The measurements consisted in recording impulse responses at different seats, using a directive loudspeaker (at different locations on stage) oriented in various directions. The listening tests were undertaken during concerts with subjects seated at the measured locations. The subjects were asked to describe the room acoustic quality with the help of a structured questionnaire, based on the results of former psychoacoustic tests. The links between perception and the criteria based on the time distribution of sound energy, established in laboratory experiments, were confirmed and/or refined. Furthermore the results of this campaign emphasize dependencies of the perceptual factors on the spatial distribution of energy. Subjective description is strongly affected by orchestra size as well as location and directivity of the instruments. Thus a single location, directivity, and orientation of the source used for the measurements will not suffice for properly describing the perceived room acoustic quality. The analysis of the relations of subjective and objective data collected in that campaign, together with additional experiments, gives some hints as to how to define an appropriate measurement protocol.
Recent experiences with binaural measurement techniques in the evaluation of concert hall acoustics
Authors: Jaffe J. Christopher , Burkhard Mahlon D. , Scarbrough Paul H.
Published: October 2005

Binaural recording, measurement, and analysis techniques have been significantly improved over the past decade. The coupling of modern binaural recording heads with advanced computer-based signal processing and analysis equipment offers acoustical designers a valuable tool for use in both subjective and objective evaluation of concert hall acoustics. The authors will describe recent experiences in the use of binaural technology for such evaluations, focusing on specific examples of how the technology can be used to improve our understanding of the acoustical environment of these spaces. The specific halls that were studied include a 2300-seat multiple-use auditorium built in the late 1960’s, an existing theatre that was converted into a 1900-seat symphony concert hall in the mid-1980’s, and a 2700-seat symphony concert hall reconstructed in the mid-1970’s.
Coupled modes in a waveguide with a range-dependent rigid basement
Authors: Gillette Gregory
Published: October 2005

Previous coupled mode approaches to acoustic propagation in ocean waveguides either (1) apply strictly to the case where interfaces other than the (free) ocean surface are range-independent, or else (2) they satisfy the boundary conditions at such interfaces approximately. In this paper coupled mode theory is extended to give a solution that exactly satisfies the boundary condition on a range-varying rigid basement. This is achieved by transforming the coordinate system so that at each range the basement coincides with a coordinate surface, and the partial separation of variables is construed with respect to the coordinate that is normal to that surface. Related work by other researchers is discussed, and the numerical implementation of the theory is described. Results for basements exhibiting both upsloping and downsloping regions are presented, and the exchange of radiated power between the modes is investigated for these cases.
Focusing of fast transverse modes in silicon and slow transverse modes in zinc
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: October 2005

This paper presents focusing of fast transverse (FT) modes in silicon and slow transverse (ST) modes in zinc, both observed at utrasonic frequencies. Using a (001)-oriented silicon disk, the FT modes are generated and detected by two tiny shear PZT transducers, both polarized in the [100] direction. One transducer fixed on the bottom surface acts as a source and the other serves as a detector scanning the top surface along the [100] direction across various points on the [010] axis at some distances away from the epicenter. The observed focusing pattern indicates strong concentration of FT modes on the narrow band about the (100) plane containing the source. For a (001)-oriented zinc crystal, strong focusing of ST or quasi-transverse (QT) modes toward the symmetry direction is observed: first in theoretical and experimental, epicentral Green’s functions; second with very small PZT source and PZT detector; finally with focused pulsed laser excitation and small PZT detector. The focusing patterns observed both in silicon and in zinc are consistent with the results predicted by the theory of phonon focusing. [Work supported by ONR.]
Ultrasonic measurements of excess nonlinearity in polymers
Authors: Adler Laszlo , Nagy Peter B.
Published: October 2005

To obtain nonlinearity parameters of solids one may use either harmonic generation of finite amplitude waves or the stress dependence of the sound velocity, the so-called acoustoelastic effect. In strongly viscoelastic materials, e.g., in polymers, both linear and nonlinear responses are significantly time-dependent and the quasistatic acoustoelastic effect is relatively much stronger than the dynamic harmonic generation effect. In this presentation, several modifications of the acoustoelastic method will be introduced in order to study the effect of excess nonlinearity in polymers due to fatiguing. An experimental system was developed where external bending load was used to degrade polymeric bars through fatigue and simultaneously monitor nonlinearity via the acoustoelastic effect. Due to the symmetry of the applied bending load, only the second-order nonlinearity (combination of second-, third-, and third-order elastic constants) was measured. It was demonstrated that for thin layers, such as adhesive bonds, a different acoustoelastic effect can be observed by measuring the stress dependence of the attenuation coefficient.
An approximate analysis for penetration of spaced foils
Authors: El-Raheb Michael
Published: October 2005

An approximate analysis for penetration of thin-spaced foils is described. When the projectile strikes the first foil, intense pressure ablates projectile and foil materials and a spherical shock forms propagating toward the next foil. As the spherically expanding shock reaches the second foil, it fails when shear stress along the perimeter of the footprint reaches ultimate shear stress. During this stage of impact, propagation has negligible effect on transfer of momentum. When stricken by material from foils above, each foil after the second deforms plastically into a conical shape ending with extensional failure. The cone’s radius grows with time at a rate lower than the speed of propagation of shear waves in the foil’s material. The effective wave front lags the actual front because of reversal in the direction of displacement close to the front. Since the mode of failure relies on maximum extensional strain, penetration will cease when speed of impact is lower than some critical speed that depends on maximum strain of the foil material. At this point, the circle of influence is expanding faster than transverse motion of the foil and maximum extensional strain in the cone of influence is never reached. It is found that weight efficiency of the shield rises inversely with foil thickness asymptotically as a result of mass entrained by propagation. The most efficient shield requires relatively thin layers of foil with material properties that maximize effective speed of propagation and maximum strain in the foil material.
Acoustic signatures: From natural to systems science
Authors: Finch Robert D. , Jansen Ben H.
Published: October 2005

The interest in acoustic signatures began with the problem of detecting cracks in railroad wheels. When a wheel is struck with a hammer it produces a sound like that of a bell. If the wheel is cracked it sounds dissonant and muffled. By comparing sounds from the two members of a wheelset a measure of the difference in their mechanical properties is obtained. A fully automatic system was developed and installed on a Southern Pacific track in the 1980’s. The story of this undertaking is an object lesson in systems science. Recently beams have been used as test objects in an attempt to resolve certain basic questions in the science of the acoustic monitoring method. These questions will be illustrated with results from a test fixture with various beams. The limitation of the vibration monitoring method is that other conditions, such as uncertainties in the geometry of the test object, its surface conditions, and loading can also affect the vibration response, and it is necessary to distinguish the effects due to harmful conditions from those due to harmless ones. The sensitivity of the method is thus determined by the need to make this distinction. [Work supported by NSF Grant No. MSS-9024224.]
Signal analysis techniques for acoustic monitoring
Authors: Robin Pierre Y. , Akerberg Peeter M. , Jansen Ben H. , Finch Robert D.
Published: October 2005

Impacting structures with a hammer and measuring the resonant frequency of the induced vibrations is a commonly used technique in acoustic monitoring. However, the transient and nonstationary characteristics of the vibrations limit the performance of classical spectral analysis. In this paper, a number of alternative techniques specifically designed to deal with the transient nature of impact-induced vibration signals are presented. Among the techniques discussed are the short-time Fourier transform (STFT), the discrete wavelet transform (DWT), and artificial neural networks (ANN). The results obtained with applying these techniques to the acoustic vibrations of intact and slotted beams are presented as an example. It was found with the STFT method, that a relationship exists between slot depth and decay rate. The DWT provided evidence that the decay undulates as a function of time, with a frequency that is related to the integrity of the beam. Early results with ANNs suggest that a net can be trained to differentiate between acoustic vibrations of intact and defective structures. [Work supported by NSF Grant No. MSS-9024224.]
Sonar signal processing and shallow water acoustics
Authors: Baggeroer Arthur B.
Published: October 2005

Sonars operating in shallow water usually encounter what signal processors term a reverberation-limited environment; higher signal levels simply lead to higher reverberation and not to improved performance. Consequently, the principal means of improving sonar performance is to use signals appropriate for the task and environment. This implies that robust environmental models are imperative. In both sonar and radar, reverberation, or scattering, is usually modeled to be a random linear system characterized by a scattering function, or some other second moment such as a two-frequency correlation function. Typically, an active sonar resolves a target or an environmental parameter by either range or time gating (high bandwidth signals) or Doppler gating (long duration signals). The resolution properties of a signal are specified by its ambiguity function and the interaction with the scattering function is the single most important factor in determining system performance. This talk will provide a brief overview of some of the signal processing issues for shallow water sonars.
Forward scatter and signal coherence in shallow water
Authors: Caruthers Jerald W. , Werby Michael F.
Published: October 2005

In shallow water it is difficult to separate the effects of propagation in a waveguide composed of layered media from those of scattering produced by roughness at the layer interfaces. Moreover, to properly account for these combined effects, three-dimensional, fully elastic propagation and scattering models must be used, if a fundamental understanding of shallow water propagation is to be attained. Very few forward propagation studies include scattering effects on forward propagating signal properties such as amplitude and coherence. In shallow water such effects are critical to the condition of the signal when it reaches a target and when it returns to the monostatic receiver. The importance of these effects on the signal properties is magnified for bistatic receivers. Boundary scatter, including out-of-plane scatter, in shallow water significantly affects time and angle (as well as frequency) spreads that lead to degradation of signal coherence. The requirements to deal with scattering in three dimensions and to include full wave field physics in propagation models introduce the need for extensive computer code and computational power. While there are no simple solutions to the problems these requirements impose, the advance of computational technologies and the development of advanced propagation and scattering codes will allow comprehensive and innovative approachs. These issues are addressed and an approach to solving this significant part of the shallow water acoustics problem is discussed.
Fluctuations and predictability of sound propagation at moderate frequencies in bottom-limited sound channels
Authors: DeFerrari Harry A. , Brown Michael G. , Tappert Frederick D. , Monjo Charles , Nghiem-Phu Lan
Published: October 2005

Sound propagation in the moderate frequency range (depth to wavelength ratio, h/λ, between 20 and 100) in shallow water environments with bottom roughness is extremely complicated, variable, and poorly understood. Multipaths are generally neither resolvable (assuming Q≥1) nor stable. Fluctuations are dominated by a combination of continual formation and destruction of multipaths as well as by perturbations to otherwise stable paths—as is the case in deep water. Propagation characteristics observed in the Straits of Florida for several ranges have consistent features. Sound fields are slowly varying and phase coherent. Large fluctuations with periodicities of a few minutes to a few hours can be qualitatively accounted for as a slowly modulated complicated caustic structure. The quantitative description of these phenomena is beyond the domain of validity of existing theories because variables do not separate and rays behave chaotically. Advances in both theory and experiments are required to improve understanding of these propagation issues.
Some features of ambient noise in shallow tropical waters
Authors: Cato Douglas H.
Published: October 2005

This paper discusses the main features of ambient noise in shallow tropical waters near Australia and the implications for shallow water acoustics. Noise from biological sources is usually the dominant component of the ambient, in the absence of high winds and heavy rain. Noise levels fluctuate by more than 30 dB (commonly by about 20 dB) as a result of biological activity. Diurnally varying biological choruses produce the highest noise levels and are evident in the frequency range 40 Hz to 5 kHz. Snapping shrimp noise, extending to frequencies beyond 200 kHz, is the dominant component of ultrasonic noise where habitats are favorable. Biological transients (signals detectable from individual animals, usually fish and whales) are also important. Traffic noise varies from high levels near ports to negligible in areas remote from ports and where propagation is poor.
The issue of time-varying oceanographic conditions as related to acoustics in shallow water
Authors: Stein Peter J. , Lewis James K.
Published: October 2005

Here evidence is shown that time-varying oceanographic conditions are an important consideration in shallow water acoustic propagation. In most shallow water conditions there can be substantial temperature and salinity variations. Coastal jets and freshwater outflows can effect regions out to 40–50 km offshore. Sound-speed profiles, and thus the acoustic propagation conditions, can be highly variable in both space and time. This is shown by looking at a few examples. Oceanographic modeling was conducted using a three-dimensional numerical model for predicting the time- and range-varying conditions. The results from the oceanographic model were input into the Navy standard PE model to predict the acoustic propagation through these model test regions. The results show substantial differences in the transmission loss over time changes on the order of hours. Other issues such as bottom absorption, surface roughness effects, and reflections from a sloping bottom will also be addressed. Further modeling efforts that couple advanced oceanographic models to advanced range-dependent acoustic models are suggested.
A two-wave-number description of shallow water ocean acoustics
Authors: Kennedy Robert M.
Published: October 2005

Wave-number spectrum is a useful measure of the spatial properties of the underwater acoustic field. A basic tenet of the wave-number spectrum approach is the spatial homogeneity of the cross-correlation (or cross-spectrum) function; a property that is frequently satisfied in deep water environments. Shallow water acoustic channels, on the other hand, are basically nonhomogeneous in the depth variable as a result of the addition of numerous normal modes or multipaths. Two-frequency spectrum have been used to analyze (temporal) nonstationary variables and to a lesser extent two-wave-number spectrum have found use investigating the nonhomogeneous noise in hydrophone array structures. For this paper, two-wave-number (vertical) spectrum were found for several canonical underwater acoustic waveguides. The physical significance of the results are identified by comparing them with similar spectrum from structural acoustic analysis. Particular attention is paid to the consequences of the nonhomogeneous structure to hydrophone array design and the channel parameters that emphasize the two-wave-number character of the spectrum. The sensitivity of the results to intermodal correlation suggests a measurement approach for determining this basic component correlation.
Intensity measurement on time-varying signals
Authors: Rasmussen Gunnar
Published: October 2005

Intensity measurements are especially valuable when used for the detection of phenomena of a fast-varying nature. Sound pressure levels are greatly influenced by the character of the environment, the reverberation time, the location of acoustic centers, and other reactive conditions. The intensity data may be largely independent of these conditions especially when obtained in very short periods of time. Some standards require a wide frequency range, which often requires at least two spacings between the microphone acoustic centers and thus two measurements carried out with the same acoustical center for the probe. Many sources are not stationary and will therefore not offer the repeatability required for two measurements to be carried out with the required accuracy. Examples are vehicle passby, explosions, nonlinear structural vibration, reciprocating engines, and measurements during breakdown as well as run up and down. Techniques involving FFT technique may have serious shortcomings under such conditions. They will work extremely well during calibration and laboratory conditions. When there is a need for actual tests, possible errors may be difficult to assess. Spatial transformation will also require steady continuous signals. The response of transducers to very short duration signals, the influence of the transducer size and configuration, as well as ways of assuring a wide frequency range as required for standardized sound power measurement will be reported. The importance of the probe configuration for practical field measurements will be discussed.
The acoustic survey of British auditoria
Authors: Barron Michael
Published: October 2005

By 1980 the understanding of acoustics for concert halls had reached an interesting stage. Two German studies at Göttingen and Berlin with dummy head recordings had gone a long way to determining the important subjective and objective dimensions. However the influence of architectural form on subjective acoustic conditions was much less well established. There were two possible routes: testing acoustic scale models or full-size auditoria. With access to sufficient full-size auditoria, the latter was the obvious choice since it also allowed true subjective assessment. The acoustic survey of British auditoria involved both objective measurements and subjective assessments in over 40 auditoria including concert halls, drama theaters, opera houses, and multi-purpose spaces. The whole exercise has now been published [M. Barron, AuditoriumAcousticsandArchitecturalDesign (Chapman & Hall, London, 1993)]. In concert halls a major conclusion of the subjective exercise was that halls with good reputations score well with regard to several attributes, such as reverberance, envelopment, and intimacy. Several novel observations on the effect of design details will also be discussed.
Comparisons of auditorium acoustics measurements as a function of location in halls
Authors: Bradley John S. , Gade A. C. , Siebein Gary W.
Published: October 2005

In a measurement tour of nine U.S. concert halls measurements were made at 30 or more combinations of source and receiver position in each hall. Each of the three measurement teams (the University of Florida, the Danish Technical University, and the National Research Council of Canada) made parallel measurements of a number of modern room acoustics quantities using different equipment and measurement procedures. These results are compared on a seat-by-seat basis and the differences are explained in terms of earlier systematic studies of the effects of measurement procedure details. The measurement results were also used to examine the influence of different measurement equipment and measurement procedures on the within hall variations of the various acoustical quantities. [Work partially supported by the Concert Hall Research Group.]
Effects of measurement equipment and procedure on IACC measurements
Authors: Siebein Gary W. , Chiang Wei-hwa , Madaras Gary S. , Doddington Harold W. , Schwab Wilhelm K. , Bradley John S.
Published: October 2005

A series of binaural acoustical measurements were taken at several source locations and multiple receiver locations in eight concert halls using the Acoustical Research Instrumentation for Architectural Spaces (ARIAS) system and manikin developed at the University of Florida and the BRAM software system developed at NRC Canada with a B&K dummy head and torso. This paper will compare the results of room average data and several specific seat locations obtained from the two measurement systems with an analysis of the similarities and differences that arose. Correlations among various forms of IACC including IACCearly, IACClate, IACCwith direct sound, and IACCwithout direct sound were studied. A comparison of binaural reflectograms for locations within each room were also made. Summary graphs showing ranges of each measurement within each of the rooms and discussion of similarities and differences among the groups of rooms will be presented. [Work supported by the National Science Foundation and Concert Hall Research Group.]
Comparison of spectral and nonspectral frequency difference limens for human and nonhuman primates
Authors: Pfingst Bryan E.
Published: October 2005

Difference limens for frequency were measured in normal-hearing human and nonhuman-primate (macaque) subjects. Stimuli were 1-kHz pure tones, containing both spectral and temporal cues, and 100-Hz sinusoidally amplitude modulated broadband noise (SAM noise), containing only temporal (nonspectral) cues. Subjects were tested for a minimum of 20 sessions and until difference limens were stable over time for each stimulus at each of several sensation levels. Difference limens for pure-tone stimuli showed almost no overlap between human and nonhuman-primate subjects. Difference limens for SAM-noise stimuli for human and nonhuman-primate subjects overlapped considerably. The correlations between performance for the pure-tone stimuli and performance for the SAM noise stimuli averaged 0.60. These data suggest that at least two factors influence pure-tone frequency discrimination. One factor is dependent on the presence of place mechanisms while the other factor, or group of factors, seems to influence both spectral and nonspectral frequency discrimination.
Adequacy of auditory models to predict human internal representation of speech sounds
Authors: Ghitza Oded
Published: October 2005

A long-standing question that arises when studying a particular auditory model is how to evaluate its performance. More precisely, it is of interest to evaluate to what extent the model representation can describe the actual human internal representation. Here, this question is addressed in the context of speech perception. That is, given a speech representation based on the auditory system, to what extent can it preserve phonetic information that is perceptually relevant? To answer this question, a diagnostic system has been developed that simulates the psychophysical procedure used in the standard Diagnostic-Rhyme Test (DRT). In the psychophysical procedure, the subject has all the cognitive information needed for the discrimination task, a priori. Hence, errors in discrimination are due mainly to inaccuracies in the auditory representation of the stimulus. In the simulation, the human observer is replaced by an array of recognizers, one for each pair of words in the DRT database. The recognizer used [Ghitza and Sondhi, J. Acoust. Soc. Am. Suppl. 1 87, S107 (1990)] was designed to keep errors due to the recognition procedure to a minimum, so that the overall detected errors are due mainly to inaccuracies in the front-end representation. The system provides detailed diagnostics that show the error distributions among six phonetically distinctive features. Results are given for the behavior of two speech analysis methods, a representation based on the auditory system and one based on the Fourier power spectrum, in quiet and in a noisy environment. These results are compared with psychophysical results for the same database.
Electromagnetic acoustic wave transducer for the generation of acoustic evanescent waves on membranes and optical and capacitor wave-number selective detectors
Authors: Matula Thomas J. , Marston Philip L.
Published: October 2005

A novel electromagnetic acoustic wave transducer (EMAT) capable of generating low-frequency tone bursts on metalized membranes is described. The bursts have a phase velocity that is much less than the speed of sound in the surrounding air so that they are accompanied by a plane evanescent wave adjacent to the membrane. Unlike conventional EMATs that rely on an external magnetic field interacting with an eddy current distribution, this system makes use of an applied current pulse through the membrane itself. A spatially and temporally oscillating Lorentz force is generated on the membrane with the application of a tone burst through a meander-line coil configuration simultaneous with a current pulse through the membrane. Studies were carried out on the frequency selectivity of the EMAT, the steady-state buildup of the tone bursts, and the dependence on gap spacing between the meander-line coil and the membrane. Optical and capacitive probes were used to detect the wave train and verify the wave shape characteristics. Wave-number selective differential optical and capacitive transducers are also described. A property of these transducers is their insensitivity to long wavelengths on the membrane.
Remarks on symmetric Lamb waves with dominant longitudinal displacements
Authors: Pilarski Aleksander , Ditri John J. , Rose Joseph L.
Published: October 2005

Proof of the vanishing of the normal component of the particle displacement vector on the free surfaces of an isotropic, homogeneous plate for nonzero-order symmetric Lamb waves is given. Such a conclusion was stated without proof in the book by Viktorov [A. I. Viktorov, Rayleigh and Lamb Waves: Physical Theory and Applications (Plenum, New York, 1967), 1st ed., Chap. II, p. 121]. An expression for the frequency-thickness products where this occurs is also given. This enables practical (e.g., experimental) selection of such modes. Other interesting features of such modes, such as the independence of their group velocity on the mode’s order or its nondispersitivity, are also addressed. The features discussed here are of great practical importance, e.g., in the nondestructive testing (NDT) of plates loaded by liquids and/or in the ultrasonic tensometry of a thin plate.
Multi-frequency transducer assembly for nonlinear ultrasonic measurements
Authors: Wu Jin-Yuan , Shung K. Kirk
Published: October 2005

This letter provides more detail on a multi-frequency transducer assembly used in our nonlinear image enhancement experiments [J. Acoust. Soc. Am. 88, 2852 (1990)]. In these experiments, high-intensity ultrasonic waves were launched into the medium and second harmonic signals or the sum-frequency signals were detected. Therefore, a transducer assembly was needed to operate at two different frequencies separated approximately by an octave. The signals in the lower frequency band were much stronger than the nonlinear signals in the higher band which were the signals of interest. The signals in both bands are coaxial and the much weaker signals in the higher band had to be extracted from the stronger background. The heart of the transducer assembly was an acoustic beam separator. The principle of the beam separator was based on the total transmission of the acoustic waves through a thin isotropic solid layer in a fluid medium. The beam separator served both functions of beam relocation and acoustic filtering. The filtering was accomplished by using both the total transmission phenomenon and the Fabry–Pérot interference phenomenon.
Is Del Grosso’s sound-speed algorithm correct?
Authors: Spiesberger John L.
Published: October 2005

Acoustic tomography data from a 3000-km section in the northeast Pacific are consistent with Del Grosso’s algorithm for the speed of sound in seawater [J. Acoust. Soc. Am. 56, 1084–1091 (1974)] given reasonable assumptions concerning acoustic propagation and thermal variability in the ocean. Because tomographic derivations for the algorithm are sensitive to modeling assumptions, the accuracy of Del Grosso’s algorithm is difficult to test without more data.
Comment on ‘‘Predicting theater chair absorption from reverberation chamber measurements’’ [J. Acoust. Soc. Am. 91, 1514–1524 (1992)]
Authors: Davies W. J. , Lam Y. W. , Orlowski R. J.
Published: October 2005

The relationship between the measured acoustic absorption coefficient of an array of theater chairs and the ratio of the perimeter length to plan area of the array is considered. It is shown that the linear relationship measured by Bradley in a reverberation chamber and reported in ‘‘Predicting theater chair absorption from reverberation chamber measurements’’ [J. Acoust. Soc. Am. 91, 1514–1524 (1992)] is to be expected from simple theory. This means that any nonlinear influence of diffracted energy on the relationship is small. Bradley is also unduly harsh on the usefulness of a chair absorption measurement method involving screens. A sample result is given, showing that this method can predict in-situ theater chair absorption with reasonable accuracy.