bluuebunny/crossref_metadata_2025 huggingface dataset:
Lateralization of dichotic noise bursts: Effect of onset and offset disparity
Authors: Small Arnold M.
Published: October 2005

Sound image position associated with the interaural onset or offset disparity of a signal was quantified by a scaling procedure in three experiments. Lateralization cues derived from the steady-state portion of the broadband noise signal that would support a specific image position were minimized by the use of independent noise sources for each ear. Onset disparities produced lateralization toward the ear at which the sound was presented first, while offset disparity produced lateralization toward the ear at which the sound remained on longer. Disparity was systematically varied between 0 and 10 ms and for a given disparity, a greater shift in the sound image position was obtained when the disparity was at the onset rather than the offset. The duration of the shorter signal ranged from 2.5–100 ms and for either onset or offset disparity, the image of stimuli of long duration tended to remain near the center of the head, while those of shorter duration could be moved to more extreme positions. In an attempt to rule out dichotic loudness cues as a basis for the lateralization associated with offset disparity, stimuli were presented with equal energy at each ear. Image position for equal energy was virtually identical to that for equal sound pressure, suggesting that loudness differences are not mediating lateralization associated with offset disparity.
An evaluation of three adaptive hearing aid selection strategies
Authors: Neuman Arlene C. , Levitt Harry , Mills Russell , Schwander Teresa
Published: October 2005

Paired-comparison judgments of intelligibility of speech in noise were obtained from eight hearing-impaired subjects on a large number of hearing aids simulated by a digital master hearing aid. The hearing aids which comprised a 5×5 matrix differed systematically in the amount of low-frequency and high-frequency gain provided. A comparison of three adaptive strategies for determining optimum hearing aid frequency-gain characteristics (an iterative round robin, a double elimination tournament, and a modified simplex procedure) revealed convergence on the same or similar hearing aids for most subjects. Analysis revealed that subjects for whom all three procedures converged on the same hearing aid showed a single pronounced peak in the response surface, while a broader peak was evident for the subjects for whom the three procedures identified similar hearing aids. The modified simplex procedure was found to be most efficient and the iterative round robin least efficient.
Responses of auditory-nerve fibers to nasal consonant–vowel syllables
Authors: Deng Li , Geisler C. Daniel
Published: October 2005

Responses of single auditory-nerve fibers in anesthetized cat to spoken nasal consonant–vowel syllables were recorded. Analyses in the form of spectrograms and of three-dimensional spatial-time and spatial-frequency plots were made. Among other features, formant transitions are clearly represented in the fibers’ response synchronization properties. During vocalic segments, especially those in /mu/ and /ma/, at a stimulus level near 75 dB SPL, a strong dominance in the responses by frequencies near the second formant (F2) is found for most fibers whose characteristic frequencies (CFs) are at or above F2. In contrast, at more moderate levels, the same fibers may show response synchrony to frequencies closer to their own CFs. There are significant differences in the response properties of high and low/medium-spontaneous-rate fibers.
A composite auditory model for processing speech sounds
Authors: Deng Li , Geisler C. Daniel
Published: October 2005

A composite inner-ear model, containing the middle ear, basilar membrane (BM), hair cells, and hair-cell/nerve-fiber synapses, is presented. The model incorporates either a linear-BM stage or a nonlinear one. The model with the nonlinear BM generally shows a high degree of success in reproducing the qualitative aspects of experimentally recorded cat auditory-nerve-fiber responses to speech. In modeling fiber population responses to speech and speech in noise, it was found that the BM nonlinearity allows bands of fibers in the model to synchronize strongly to a common spectral peak in the stimulus. A cross-channel correlation algorithm has been devised to further process the model’s population outputs. With output from the nonlinear-BM model, the cross-channel correlation values are appreciably reduced only at those channels whose CFs coincide with the formant frequencies. This observation also holds, to a large extent, for noisy speech.
Explosive source location by relative arrival times of atmospherically and seismically propagating disturbances
Authors: Dowding C. H. , Hryciw R. D. , Garretta J. M.
Published: October 2005

Detonation of explosives during rock excavation in surface mining produces both atmospherically and seismically propagating disturbances. By manipulating the difference in arrival times of the air blast and ground motion, shot-to-recorder distance can be determined with only one recording station. This shot-to-recorder distance is needed for automatic development of ground motion attenuation curves with automatic recording devices and is generally helpful in mine activity detection. With two recording stations, the location of the blast may be determined even if the stations are not time synchronized. Data from production blasting at a coal mine were evaluated to verify the method proposed herein. The blast location as determined by the difference in arrival times of the atmospherically and seismically propagating disturbances showed excellent agreement with the location of blasts as provided by field personnel. The method may be employed to detect any explosive activity that produces both types of disturbances.
Stochastic simulation and first-order multiple scatter solutions for acoustic propagation through oceanic internal waves
Authors: Bates Bruce J. , Bates Susan M.
Published: October 2005

The existing theory of acoustic propagation through an oceanic internal wave field with a Garrett and Munk spectrum is modified and, by numerical computation, is shown to be consistent. The fractional sound speed computation is rederived to satisfy the Garrett and Munk spectrum and used to compute a stochastic simulation of the internal wave sound speed fluctuation field. The Garrett and Munk spectrum in (ω, j) space has been normalized by 4π, and the acoustic scattering is redefined to accommodate scattering from the internal wave phase fronts as in an acoustic phase grating. These modifications are then used to compute the coherent acoustic intensity by two methods: a first-order multiple scatter approximation and a stochastic simulation. Also, the Rytov approximation is shown to be equivalent to the first-order multiple scatter approximation in the form of the stochastic parabolic equation method in the unsaturated region. The computational results show agreement in the weak scattering region using typical deep ocean values. The stochastic simulation method is accurate in the saturated and unsaturated regions; however, the method requires long computer execution times. Phase front fragments propagating along rays with sound speeds reduced by the stochastic internal wave field are used to discuss the computational results.
Geoacoustic parameters in a stratified sea bottom from shallow-water acoustic propagation
Authors: Zhou Ji-xun , Zhang Xue-zhen , Rogers Peter H. , Jarzynski Jacek
Published: October 2005

Due to the difficulty of direct measurement, there is a need to develop inverse techniques for remote sensing bottom geoacoustic parameters in the lowan mode measurements are extended to extract acoustic attenuation and speed in a horizontally stratified bottom in shallow water as a function of frequency and depth. The computational and experimental results show that, for a limited frequency band, we can find an equivalent depth profile of sea-bottom acoustic attenuation with a linear frequency dependence that simulates the effect of nonlinear frequency dependence (without depth structure) on some field characteristics, such as the attenuation rate of individual mode, the frequency response of long-range sound propagation, and the amplitude ratio of mode 2 to mode 1. However, the resultant equivalent negative gradient for the sea-bottom attenuation is too strong to be accepted in light of available data. The conclusion is that nonlinear frequency dependence of the acoustic attenuation in the upper sedimentary layer is required to explain many aspects of shallow-water sound propagation.
High-intensity tone generation by aeroacoustic sources
Authors: Shakkottai P. , Kwack E. Y. , Cho Y. I. , Back L. H.
Published: October 2005

An experimental investigation has been carried out on the production of high-intensity tones by axisymmetric ring cavities. Maximum sound production occurs during an acoustic resonance at Strouhal numbers, which depend only on the local flow velocity independent of cavity location. Values of sound pressure of about 115 dB at 1-m distance can be generated by axisymmetric ring cavities on projectiles moving at a relatively low flight speed equal to 70 m/s. Frequencies in the audible range up to several kilohertz can be generated aeroacoustically. A simple analytical model has been developed to explain the experimental observations.
Measurement of the acoustic nonlinearity parameter in water, methanol, liquid nitrogen, and liquid helium-II by two different methods: A comparison
Authors: Kashkooli H. A. , Dolan Paul J. , Smith Charles W.
Published: October 2005

Light diffraction and finite amplitude loss are used to measure the acoustic nonlinearity parameter for water, methanol, liquid nitrogen, and liquid helium-II. In all cases, the finite amplitude loss technique yielded higher values than the light diffraction technique or thermodynamic estimates from published data.
Acoustic radiation and reflection from a periodically perforated rigid solid
Authors: Norris A. N. , Luo H. A.
Published: October 2005

An exact solution is given for the reflection of a plane wave normally incident on a rigid solid with periodically spaced semi-infinite circular holes. Analytical considerations, verified by numerical calculations, show that the reflection coefficient is unity at the cutoff frequencies defined by the periodicity of the holes. This result is independent of the volume fraction of the holes. It implies that the porous solid acts like a rigid solid at these frequencies. The problem of plane-wave incidence from the holes is also solved. A reflection coefficient of unity is obtained at the same frequencies, again implying a rigid effect. Below the first cutoff frequency, the reflection coefficient can be parametrized by a simple scalar frequency dependent quantity. This simple result can be interpreted in terms of a displaced pressure continuity condition.
Digital waveform generation by fractional addressing
Authors: Hartmann W. M.
Published: October 2005

This article concerns the generation of waveforms by a digital oscillator in which sampled data in a memory buffer are recycled. The buffer contains a fixed waveform and the output sample rate is also fixed. Despite these constraints, the oscillator is capable of arbitrarily high frequency resolution if the technique of fractional addressing is used. However, fractional addressing introduces distortion. This article gives a theory of fractional addressing, resembling the theory of diffraction in crystal lattices with a basis. The theory shows how the spectrum of the distortion components can be calculated and how the distortion can be minimized. Attention is called to numerous symmetries in the distortion spectrum. These symmetries are especially interesting if the purpose of the system is to make use of the distortion components to create inharmonic signals. Of particular importance is the γp symmetry theorem, which makes it possible to derive simple formulas for the level of the largest distortion component and for the total distortion power.
The sound emission pattern and the acoustical role of the noseleaf in the echolocating bat, C
a
r
o
l
l
i
a p
e
r
s
p
i
c
i
l
l
a
t
a
Authors: Hartley David J. , Suthers Roderick A.
Published: October 2005

C a r o l l i a perspicillata (Phyllostomidae) is a frugivorous bat that emits low-intensity, broadband, frequency-modulated echolocation pulses through nostrils surrounded by a noseleaf. The emission pattern of this bat is of interest because the ratio between the nostril spacing and the emitted wavelength varies during the pulse, causing complex interference patterns in the horizontal dimension. Sound pressures around the bat were measured using a movable microphone and were referenced to those at a stationary microphone positioned directly in front of the animal. Interference between the nostrils was confirmed by blocking one nostril, which eliminated sidelobes and minima in the emission pattern, and by comparison of real emission patterns with simple computer models. The positions of minima in the patterns indicate effective nostril spacings of over a half-wavelength. Displacement of the dorsal lancet of the noseleaf demonstrated that this structure directs sound in the vertical dimension.
The 20-Hz signals of finback whales (B
a
l
a
e
n
o
p
t
e
r
a p
h
y
s
a
l
u
s)
Authors: Watkins William A. , Tyack Peter , Moore Karen E. , Bird James E.
Published: October 2005

The 20-Hz signals of finback whales (Balaenoptera physalus) were analyzed from more than 25 years of recordings at a variety of geographic locations on near-surface hydrophones close to whales and on deep hydrophone systems. These signals were composed of 1-s pulses of sinusoidal waveform with downward sweeping frequency from approximately 23 to 18 Hz at variable source levels up to 186 dB (re: 1 μPa at 1 m), usually with slightly lower levels for the pulses at the beginning and end of sequences. These ‘‘20-Hz’’ pulses were produced in signal bouts (separated by more than 2 h) lasting as long as 32.5 h. Bouts were composed of regularly repeated pulses at intervals of 7–26 s (typically), either at one nominal pulse rate or at two alternating (doublet) pulse intervals. Signal bouts were interrupted by rests of 1–20 min at roughly 15-min intervals and by irregular gaps lasting between 20 and 120 min. The distribution of these signals throughout the year and their temporal sequence were analyzed from the continuous drum records of the Bermuda SOFAR Station. Signal bouts occurred during winter, sometimes beginning in September and ending in May. The sound sequences were never exactly replicated. Direct association of the bouts with the reproductive season for this species points to the 20-Hz signals as possible reproductive displays by finback whales.
Piano string excitation IV: The question of missing modes
Authors: Hall Donald E. , Clark Peter
Published: October 2005

It is usually said that a force applied to an extended vibratory system is incapable of exciting any normal mode that has a node at that point. Thus piano hammers positioned to strike the strings at certain fractions of their length should produce spectra with ‘‘missing modes.’’ However, this has been disputed by some observers, and it is sometimes suggested that more careful theoretical treatments would justify a restoration of those modes. Spectra of string motion have been measured as a function of hammer position by moving a piano action frame in small increments along the bed of the case. It is found that there are indeed sharp minima in mode amplitudes (on the order of 20 to 30 dB down) as the striking point passes within a few millimeters of the nodal positions. Possible limitations on the theoretical arguments are discussed, and it is concluded that the small residual strengths in the nearly missing modes can be well accounted for by finite soundboard admittance.
Upper lip, lower lip, and jaw interactions during speech: Comments on evidence from repetition-to-repetition variability
Authors: Folkins John W. , Brown Carl Kice
Published: October 2005

Six studies purporting to demonstrate complementary covariation in lip and jaw activity during speech are reviewed. The statistical procedures used to assess interactions among the upper lip, lower lip, and jaw movements are discussed for four different experiments analyzing repetition-to-repetition movement variation. The findings from two studies analyzing repetition-to-repetition variation for interactions in electromyographic activity recorded from either the jaw musculature or the labial musculature also are evaluated. It is concluded that these studies do not provide convincing evidence of complementary covariation among the articulators or the muscles.
Detection of partially filled gaps in noise and the temporal modulation transfer function
Authors: Forrest T. G. , Green David M.
Published: October 2005

Results of experiments on the detection of silent intervals, or gaps, in broadband noise are reported for normal-hearing listeners. In some preliminary experiments, a gap threshold of about 2 ms was measured. This value was independent of the duration of the noise burst, variation of the noise level on each presentation, or the temporal position of the gap within the noise burst. In the main experiments, the thresholds for partial decrements in the noise waveform as well as brief increments were determined. As predicted by a model that assumes a single fixed peak-to-valley detection ratio, thresholds for increments are slightly higher than thresholds for decrements when the signal is measured as the change in rms noise level. A first-order model describes the temporal properties of the auditory system as a low-pass filter with a 7- to 8-ms time constant. Temporal modulation transfer functions were determined for the same subjects, and the estimated temporal parameters agreed well with those estimated from the gap detection data. More detailed modeling was carried out by simulating Viemeister’s three-stage temporal model. Simulations, using an initial stage bandwidth of 4000 Hz and a 3-ms time constant for the low-pass filter, generate data that are very similar to those obtained from human subjects in both modulation and gap detection.
Transient vibratory response of fluid-loaded shells with axisymmetric excitations
Authors: Stepanishen Peter R. , Ebenezer D. D.
Published: October 2005

A general time domain method is presented to evaluate the transient velocity field of fluid-loaded cylinders of finite length which are excited by axisymmetric, broadband excitations acting in the radial direction. A mechanical pressure which is independent of the acoustic field is used to excite the cylinder. The method is based on the use of time-dependent in vacuo modal expansions of the velocity of the cylinder and the mechanical pressure. As a result of fluid coupling, the time-dependent velocity coefficients are described by a set of coupled, linear, convolution integral equations which can be solved by marching forward in time. Typical numerical results showing the impulse responses of the fluid-loaded modal admittances of the cylinder, the time-dependent coupling coefficients, and the velocity of the cylinder are presented for the case of a cylinder which is simply supported at both ends.
Comparison of the rough surface reflection coefficient with specularly scattered acoustic data
Authors: Miller Allen R. , Vegh Emanuel
Published: October 2005

A comparison is made between a theoretically derived family of rough surface reflection coefficients and specularly scattered acoustic data.
Numerical modeling results for mode propagation in a wedge
Authors: Jensen F. B. , Tindle C. T.
Published: October 2005

A PE (parabolic equation) code is used to study propagation in a shallow water wedge with a penetrable bottom. Particular attention is given to ‘‘wedge modes’’ that have wave fronts that are arcs of circles centered on the wedge apex. For downslope propagation and for upslope propagation before cutoff, the wedge modes propagate independently without coupling. For upslope propagation through cutoff, there is a small amount of coupling to the next lower mode and a trace of coupling to the next higher mode. The wedge modes can be considered the natural modes of the wedge.
Sound waves in a periodic medium containing rigid spheres
Authors: Bai Dov , Keller Joseph B.
Published: October 2005

The effective speed of sound is calculated for a periodic composite medium consisting of a gas or liquid containing immovable rigid spheres arranged in a simple cubic lattice. Long waves propagating along a lattice axis are treated. For such waves, the wave equation for the pressure can be reduced to the Webster horn equation. This is an ordinary differential equation to which Floquet theory is applied. Both perturbation and numerical methods are used to find the effective speed of sound as a function of frequency, and to locate the passbands and the stop bands.
Radiation impedances of interacting acoustic sources expressed in terms of the individual source Green’s functions
Authors: Rudgers Anthony J.
Published: October 2005

A Neumann-series method, previously used to find expressions for the radiation impedance of two interacting acoustic sources in terms of the Green’s functions characterizing the individual sources, is used to find such expressions for the self- and mutual radiation impedances of an arbitrary number of sources that interact via radiation in a fluid. The sources considered may each be of arbitrary shape, may each have arbitrary excitation of its surface, and may each be placed at an arbitrary position in the fluid with respect to the other sources.
Effects of uniform horizontal currents in the parabolic approximation method
Authors: Brent R. I. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

A parabolic approximation to the acoustic propagation equations in a uniformly moving underwater channel is derived, with the intent of investigating current effects. A model is developed from the basic fluid equations for acoustic pressure in the presence of a uniform horizontal current. Sound-speed variations in both range and depth are permitted. Further approximations are applied and justified to yield a two-dimensional parabolic equation like that most widely implemented numerically. It is shown that uniform currents are manifested as a shift in the reference sound speed, which enables current incorporation in already existing algorithms. Boundary conditions and an initial condition are investigated for possible current dependence. For sound-speed profiles with independent depth and range variations, analytic formulas are presented for the ratio of intensity with and without currents. Examination of this ratio for the case when the sound speed is depth independent shows that currents can indeed have substantial effects on intensity. Numerical calculations from an implicit finite difference program illustrate effects on relative intensity of even fairly small uniform currents.
The effect of head-induced interaural time and level differences on speech intelligibility in noise
Authors: Bronkhorst A. W. , Plomp R.
Published: October 2005

A study was made of the effect of interaural time delay (ITD) and acoustic headshadow on binaural speech intelligibility in noise. A free-field condition was simulated by presenting recordings, made with a KEMAR manikin in an anechoic room, through earphones. Recordings were made of speech, reproduced in front of the manikin, and of noise, emanating from seven angles in the azimuthal plane, ranging from 0° (frontal) to 180° in steps of 30°. From this noise, two signals were derived, one containing only ITD, the other containing only interaural level differences (ILD) due to headshadow. Using this material, speech reception thresholds (SRT) for sentences in noise were determined for a group of normal-hearing subjects. Results show that (1) for noise azimuths between 30° and 150°, the gain due to ITD lies between 3.9 and 5.1 dB, while the gain due to ILD ranges from 3.5 to 7.8 dB, and (2) ILD decreases the effectiveness of binaural unmasking due to ITD (on the average, the threshold shift drops from 4.6 to 2.6 dB). In a second experiment, also conducted with normal-hearing subjects, similar stimuli were used, but now presented monaurally or with an overall 20-dB attenuation in one channel, in order to simulate hearing loss. In addition, SRTs were determined for noise with fixed ITDs, for comparison with the results obtained with head-induced (frequency dependent) ITDs. Results show that (1) for noise with only ILD, the gain relies on the ear presented with the most favorable signal-to-noise ratio, but decreases when the noise presented to the other ear becomes relatively loud; (2) the effect of ITD is fairly insensitive to a 20-dB attenuation of either channel, also when ITD is introduced in noise with ILD; and (3) the unmasking caused by a head-induced ITD can be predicted from the delay for low frequencies (250–500 Hz).
The masking-level difference and overall masker level: Restating the internal noise hypothesis
Authors: Yost William A.
Published: October 2005

Recent investigations of the masking-level difference (MLD) have often involved measurement of the MLD as a function of masker level. The results show, as had earlier work, that the size of the MLD decreases as the masker level decreases. These studies have usually not considered an earlier explanation of the dependency of the MLD on masker level, that is, that additive internal noise, which is partially interaurally uncorrelated, leads to decorrelated maskers at low levels of the external masking noise. Because maskers that are decorrelated yield small MLDs, the MLD is likewise small at low masker levels. This review article shows that this explanation provides a good fit to data obtained over the past four decades. It also shows that the MLD depends less on masker level with insert phones than with supraaural phones as would be predicted by the additive internal noise explanation and the observation of lower internal noise with the use of insert phones. It is concluded that the internal noise explanation should be considered when the MLD is measured as a function of masker level.
Cross-sectional tongue shape during the production of vowels
Authors: Stone Maureen , Shawker Thomas H. , Talbot Thomas L. , Rich Alan H.
Published: October 2005

This study used ultrasound imaging to examine the cross-sectional shape of the tongue during the production of the ten English vowels /i,i,e,q,æ,a,v,o,0,u/ in two consonant contexts—/p/ and /s/—and at two scan angles—anterior and posterior. Results were compared with models of sagittal tongue shape. A newly built transducer holder and head restraint maintained the ultrasound transducer in a fixed position inferior to the mandible at a chosen location and angle. The transducer was free to move only in a superior/inferior direction, and demonstrated reliable tracking of the jaw. Since the tongue is anisotrophic along its length, anterior and posterior scan angles were examined to identify differences in tongue shape. Similarly, the coarticulatory effects of the sibilant /s/ versus the bilabial /p/ were examined, to assess variability of intrinsic tongue shape for the vowels. Results showed that the subject’s midsagittal tongue grooving was almost universal for the vowels. Posterior grooves were deeper than anterior grooves. In /s/ context, posterior tongue grooves were shallower than in /p/ context. Anteriorly, /s/ context caused deeper grooves for low vowels. Cross-sectional tongue shape varied with tongue position similarly to sagittal tongue shape.
Auditory constraints on the perception of voice-onset time: The influence of lower tone frequency on judgments of tone-onset simultaneity
Authors: Parker Ellen M.
Published: October 2005

The experiments reported employed nonspeech analogs of speech stimuli to examine the perceptual interaction between first-formant onset frequency and voice-onset time, acoustic cues to the voicing distinction in English initial stop consonants. The nonspeech stimuli comprised two pure tones varying in relative onset time, and listeners were asked to judge the simultaneity of tone onsets. These judgments were affected by the frequency of the lower tone in a manner that parallels the influence of first-formant onset frequency on voicing judgments. This effect was shown to occur regardless of prior learning and to be systematic over a wide range of lower tone frequencies including frequencies beyond the range of possible first-formant frequencies of speech, suggesting that the effect in speech is not attributable to (tacit) knowledge of production constraints, as some current theories suggest.
Learning the hidden structure of speech
Authors: Elman Jeffrey L. , Zipser David
Published: October 2005

In the work described here, the backpropagation neural network learning procedure is applied to the analysis and recognition of speech. This procedure takes a set of input/output pattern pairs and attempts to learn their functional relationship; it develops the necessary representational features during the course of learning. A series of computer simulation studies was carried out to assess the ability of these networks to accurately label sounds, to learn to recognize sounds without labels, and to learn feature representations of continuous speech. These studies demonstrated that the networks can learn to label presegmented test tokens with accuracies of up to 95%. Networks trained on segmented sounds using a strategy that requires no external labels were able to recognize and delineate sounds in continuous speech. These networks developed rich internal representations that included units which corresponded to such traditional distinctions as vowels and consonants, as well as units that were sensitive to novel and nonstandard features. Networks trained on a large corpus of unsegmented, continuous speech without labels also developed interesting feature representations, which may be useful in both segmentation and label learning. The results of these studies, while preliminary, demonstrate that backpropagation learning can be used with complex, natural data to identify a feature structure that can serve as the basis for both analysis and nontrivial pattern recognition.
Application of 30-MHz acoustic scattering to the study of human red blood cells
Authors: Roos Mark S. , Apfel Robert E. , Wardlaw Stephen C.
Published: October 2005

A technique for simultaneously measuring the scattering amplitude of individual particles at two angles is applied to human red blood cells. Using a Rayleigh scattering model, the density and compressibility of the cells may be determined given a priori knowledge of their volume. A calibration method relying on measurements of the bulk properties of particle suspensions is described. Red cell properties in hypotonic and hypertonic hosts are compared with a homogeneous mixture model, and a linear relation between hemoglobin content and scattering amplitude at a 90 deg scattering angle is established.
Nonlinear acoustical sounding system for detection of defects in pipelike objects
Authors: Tohjima Eisuke , Sato Takuso
Published: October 2005

A new method for real-time nondestructive measurement of the distribution of defects in pipelike objects is proposed. In the system two ultrasonic waves, a probing wave with continuous low-pressure amplitude at relatively high frequency and a pumping wave with impulsive high pressure, are used. They are propagated in opposite directions. Then the information on the change of the pumping waveform due to the defects on the inner wall of a pipe is transferred into a phase change of the probing wave; hence, the distribution of defects along the probing beam can be detected by demodulating the phase change of the wave. The principle, physical construction, a number of signal-processing steps to increase the sensitivities, and observed results are presented.
Laser interferometer microscope for the measurement of nanometer vibrational displacements of a light-scattering microscopic object
Authors: van Netten Sietse M.
Published: October 2005

A laser interferometer microscope (LIM) has been developed to measure the amplitude and phase of submicroscopic vibrational displacements. The instrument is based on a combination of differential optical interferometry, optical heterodyning, and high-resolution incident light microscopy. Diffusely backscattered laser light of a vibrating microscopic object (φ≊1 μm) suffices to operate the LIM and to measure vibrational displacements down to fractions of a nanometer for frequencies ranging from 10 Hz to a few kHz. Calibration of the LIM is relatively simple and does not depend on the intensity of the scattered light. Since the instrument is not sensitive to small background motions or drift of the equilibrium position of the object, it is very suitable for measurements on biological objects in vivo. Application of the LIM to the fish lateral line organ enabled the measurement of vibrational displacements of the cupula from below 0.3 nm to about 300 nm.
Ambient noise measurements in open-plan offices
Authors: Moreland J. B.
Published: October 2005

This letter describes our initial efforts toward providing detailed descriptions of the temporal and spectral characteristics of the ambient sound heard by workers in open-plan offices. Using a computer-based system, the ambient sound in seven offices was investigated by sampling the noise in a workstation every 2 min between the hours of 7:00 a.m. and 7:00 p.m. None of the offices had electronic sound masking. It was found that, between the ‘‘core’’ times of 9:00 a.m. and 4:00 p.m., the average A-weighted sound level for the seven offices ranged between 42.9 and 48.4 dB, with the average sound level for the seven offices being 44.9 dB. On the average, the spectra for the office noise generally had most of their energy at the lower frequencies, with the energy falling off at about 12 dB/decade at frequency bands above 100 Hz. Below 100 Hz, the spectra rolled off faster, at about 28 dB/decade.
Obtaining acoustic similarity measures from animals: A method for species comparisons
Authors: Okanoya Kazuo , Dooling Robert J.
Published: October 2005

An efficient procedure has been developed for obtaining similarity measures for complex acoustic signals in small birds. Birds were trained using operant conditioning procedures to detect changes in the repeating background of an ongoing sound. Response latencies for detection were used to construct similarity matrices. Multidimensional scaling procedures were then used to produce spatial maps of these complex sounds reflecting perceptual organization. An example using contact calls from two avian species is described.
Characterization of guided waves propagating in infinite cylinders for oblique insonification
Authors: Molinero I. , de Billy M.
Published: October 2005

The present study confirms that in oblique incidence, leaky guided waves propagate in isotropic elastic cylinders. The various longitudinal and flexural modes of propagation are characterized by phase velocity dispersion curves. From leaking properties and resonance effects, the frequency dependence of phase velocity is experimentally measured in case of an infinite stainless-steel cylinder for values of the dimensionless parameter ka<15. The plots, which are limited to the flexural modes (n=1, m=1–6) and to the longitudinal modes (n=0, m=1–4), are compared to the theoretical calculations based on the Pochhammer–Chree frequency equation.
Spherical-wave scattering by a finite-thickness solid plate of infinite lateral extent, with some implications for panel measurements
Authors: Piquette Jean C.
Published: October 2005

The solution to the problem of the interaction of a spherical wave with a homogeneous and isotropic solid plate of infinite lateral extent, but finite thickness, is considered theoretically. Both the source and the plate are immersed in an infinite, inviscid fluid. Appropriate boundary conditions are imposed on the full three-dimensional elasticity equations. The solution is evaluated numerically for a variety of materials for a 1-kHz incident spherical wave and for a 5-kHz incident spherical wave. For the numerical study, the fluid medium is taken to be water. Under certain conditions, ‘‘overpressures’’ are predicted for both the reflected and transmitted fields (i.e., the amplitude of the reflected pressure and/or the transmitted pressure can exceed the maximum value of the amplitude of the incident pressure on the plate surface). These overpressures are consistent with the law of conservation of energy in the sense that, for a plate composed of lossless material, the total incident power is found to be equal to the sum of the total reflected power plus the total transmitted power. An important conclusion of this research is that the practice of attempting to reduce the influence of edge diffraction in panel tests by using samples of increasingly larger lateral extent may result in measurements that are substantially corrupted by wave-front curvature effects, particularly if the sample panel includes a steel backing plate.
Mathematical model for internal ultrasonic inspection of cylindrically layered structures
Authors: Randall C. J. , Stanke Fred E.
Published: October 2005

An efficient numerical model is described for predicting the pulse-echo response of an ultrasonic transducer insonifying a cylindrically layered medium from the inside. A rigorous 3-D formulation of the problem is first developed. Reduction to an approximate but computationally much more efficient form is accomplished based on several general assumptions regarding the geometrical properties of the transducer and the cylindrically symmetric layered medium. Within these constraints, the model accurately accounts for diffraction, attenuation, and dispersion in the interior immersing fluid and for reflection from the multilayered annular region that may contain strong internal resonances. Calibration of the temporal response of the transducer and associated measurement electronics is an integral part of the model, which is formulated using reciprocity relations for cylindrical coordinates. The principal application for the model is the ultrasonic internal inspection of pipes.
The propagation constant in lossy circular tubes near the cutoff frequencies of higher-order modes
Authors: Hudde Herbert
Published: October 2005

The propagation constants of higher-order modes in lossy circular ducts are investigated with particular interest to the frequency range around the corresponding cutoff frequencies. The analytic expressions for the propagation constants published up to now contain poles at each cutoff frequency. In this article, it is shown that no poles exist. The transition between the frequency range of evanescent and propagating modes is rapid but continuous. An explicit formula for the propagation constant is derived. The theory is experimentally checked with an indirect measuring method that is able to give results in close vicinity to the cutoff frequencies. The measured attenuation due to the transmission line losses is partially somewhat higher than theoretically expected. The deviations are less than about 30%.
Some closed-form solutions of the impedance inverse problem
Authors: Sarwar A. K. M.
Published: October 2005

The time-domain modified Gelfand–Levitan (MGL) integral equation is solved in closed form for the recovery of acoustical impedance logs from a class of reflection seismograms. The MGL method is compared with usual Gelfand–Levitan (GL) inverse scattering method. A relationship between the kernels, considered to be the known data, of the MGL equation and the Gopinath–Sondhi (GS) equation is established.
Near-surface ocean ambient noise measurements at very low frequencies
Authors: Cotaras F. D. , Fraser I. A. , Merklinger H. M.
Published: October 2005

Ambient noise in the frequency range 1–20 Hz was measured for 1-day periods at each of four widely separated sites in the North Atlantic Ocean with freely drifting, surface-suspended hydrophones. The acoustic data were recorded aboard an attending research vessel following transmission over a radio link. Narrow-band spectral analysis was performed at 1-h intervals to form time series of noise spectral level for each site. Statistical analyses of the power-spectral time series included the determination of cumulative probabilities, standard deviation, skew, kurtosis, decorrelation times, and the wind-speed dependence of mean spectral level. Comparisons with data from bottom-mounted hydrophones and studies of inter- and intra-array coherence indicate that the data were, with few exceptions, uncontaminated by self-noise down to 1 Hz. A significant dependence of noise spectrum level upon local wind speed was observed in the 1.5- to 3-Hz frequency band at each site. At 4 Hz, the dependence upon wind speed was much weaker, suggesting that the noise sources at this frequency are more distant. Estimates of noise directionality and tests for normality were also made on the data between 1 and 5 Hz.
The sound fields of an infinite, fluid-loaded plate excited by a point force
Authors: Langley A. J.
Published: October 2005

The acoustic fields of an infinite, fluid-loaded plate that is excited by a source are considered. The plate is modeled exactly as a linear elastic, isotropic, homogeneous layer of constant thickness bounding two different homogeneous fluid half-spaces. First, the complete acoustic field (pressure fluctuations in the fluids and displacements in the plate) of an harmonic monopole source in one of the fluids is derived. Then, by invoking reciprocity, the sound fields in the fluids of an harmonic point force applied somewhere within the plate are found. There are no restrictions upon the frequency or the orientation of the applied force. A standard asymptotic result for the sound fields in the fluids far from a source in the plate is given.
Exact and approximate theories for fluid-loaded, infinite, elastic plates
Authors: Langley A. J.
Published: October 2005

The sound radiated by an infinite, elastic plate excited by a point force is considered. The plate is loaded by two fluid half-spaces that may have different properties, and the force may have an arbitrary orientation. Results derived at low frequency show that the ‘‘exact’’ solution, when the plate is modeled as an elastic layer, concurs with ‘‘thin plate’’ theories. A demonstration of how a thin plate theory fails as frequency is increased is given. Particular attention is paid to the longitudinal wave in the plate (corresponding to the zero-order symmetric Lamb mode), which is shown to be sensitive to the symmetry of the fluid loading. The importance of the position of the driving force within the plate’s thickness, symmetric waves, material absorption, and finite plate size is also studied to see when those factors should be included in the plate model. Results tend to confirm the common view that symmetric waves and the position of the force need not be considered when computing the field of a transverse force, at least at low frequencies and with a typical set of material parameters.
Ultrasonic velocity and absorption in binary solutions of poly(ethylene oxide) with water
Authors: Spickler P. , Ibrahim F. , Fast S. , Tannenbaum D. , Yun S. , Stumpf F. B.
Published: October 2005

Ultrasonic velocity at a frequency of 25.1 MHz was measured as a function of concentration and temperature in binary solutions of poly(ethylene oxide) and water. Absorption measurements at 21 MHz were also carried out for different concentrations and temperatures. In addition, shear viscosity was measured. The poly(ethylene oxide) has an average molecular weight of five million. Values for the velocity increase with both concentration and temperature. Both the absorption and viscosity increase with concentration, but decrease with increasing temperature.
Experimental investigation of the sound field generated by a moving ruby-laser thermoacoustic array
Authors: Berthelot Yves H.
Published: October 2005

A high-power laser is used to produce via thermal expansion a long thermoacoustic broadside array in water by deflecting a ruby-laser beam (optical wavelength 0.6943 μm) off a rotating mirror to a body of water. The rotation of the mirror results in a rectilinear motion of the source over the water surface. Such a source is commonly referred to as a moving thermoacoustic array (MTA) and its penetration depth into the water is inversely proportional to the coefficient of absorption of the laser intensity in water. The sound field radiated by the ruby MTA (long array) is analyzed experimentally for subsonic, sonic, and supersonic source velocities. The results obtained with the long ruby MTA are compared with those obtained with a much shorter glass–neodymium MTA (optical wavelength 1.06 μm). Results reported here include directivity patterns, both in a plane perpendicular to the water surface and in a plane parallel to the water surface, and sound-pressure level (SPL) dependence on distance between the source and the receiver.
The frequency dependence of subjective reaction to vertical and horizontal whole-body vibration at low magnitudes
Authors: Howarth Henrietta V. C. , Griffin Michael J.
Published: October 2005

The assessment of building vibration with respect to human response requires knowledge of the influence of vibration magnitude, frequency, direction, and duration. This article reports an experiment conducted to investigate the effect of three of these factors: frequency, magnitude, and direction. The method of magnitude estimation was employed with a sound reference stimulus (1/3 octave band centered at 1 kHz) so as to determine reaction to vertical (z-axis) and horizontal (y-axis) sinusoidal whole-body vibration. Twenty subjects were exposed to six acceleration magnitudes in the range 0.04–0.4 ms−2 rms at nine frequencies between 4 and 63 Hz. The relation between magnitude estimate ψ and acceleration magnitude φ was determined at each frequency in the psychophysical power form ψ=kφn. The value of the exponent n varied from 1.04 to 1.47 for vertical motion and from 0.68 to 1.99 for horizontal motion. For vertical motion, the effect of frequency was not significant; for horizontal motion, the exponent increased with increasing frequency. Vibration frequency weightings were determined to describe subjective response to whole-body vibration at low magnitudes that might occur in buildings.
A parametric study of acoustical fields of vibrating structures for noise control applications
Authors: Jiang J. K. , Prasad M. G.
Published: October 2005

Machinery noise control effort generally has three aspects: noise control at the source, along the path, and at the receiver. It is known that noise control at the source is usually the most desirable but difficult approach. In machinery, vibration of structural components form one of the major sources of noise. This article reports on theoretical and experimental studies of the acoustical fields due to various types of vibrating structures, with applications to noise control at the design stage. Beam-type vibrating structures are mainly considered in the studies. The theoretical work is based on the boundary element method that can effectively deal with the (exterior) boundary value problems, especially if the domain is infinite. The experiments have been conducted in an anechoic chamber. The studies are aimed at obtaining a better understanding of the influence of structural design parameters on the acoustical nearfield and farfield. The studies have shown that design parameters such as structural geometry, discontinuities, and boundary effects for a given vibration response have considerable influence on the acoustical fields. The studies have yielded some new observations in the application of the boundary element method to noise control at the design stage.