bluuebunny/crossref_metadata_2025 huggingface dataset:
Plates with regular stiffening in acoustic media: Vibration and radiation
Authors: Mead Denys J.
Published: October 2005

Flat plates and cylindrical shells with regular and identical stiffening constitute spatially periodic structures. Specially convenient methods of vibration analysis are available for these, some of which are suitable for the inclusion of the effects of fluid loading from adjacent acoustic media. This paper outlines the nature of free wave motion in periodic structures stiffened either in one direction or in two orthogonal directions. The structural response to distributed harmonic pressure fields is analyzed by using displacement functions consisting of a series of space harmonics. The sound radiated or transmitted by the vibrating structure is also found. The method of space harmonics is next combined with the method of phased array receptance functions to yield equations for the propagation constants of fluid-loaded periodic plates, stiffened in just one direction. Some calculated propagation constants are presented. Recent developments in the application of the hierarchical finite-element method to periodic structures are described. Computed results are presented for the propagation constants of an orthogonally stiffened plate, without fluid loading. Consideration is given to those frequency ranges and wave motions that could radiate into an adjacent medium.
From touch to string vibrations. I: Timing in the grand piano action
Authors: Askenfelt Anders , Jansson Erik V.
Published: October 2005

This article describes an experimental study of the timing in the grand piano action. The function of the action is described by timetables for the motions of the moving parts. Important timing properties included are the relation between key bottom contact and hammer–string contact, the interval of free hammer motion before the impact on the string, and the hammer–string contact duration. The influence of the regulation and dynamic level on these timing properties is analyzed. The results of the measurements are discussed, with a focus on the implications for piano playing, regulation, and design.
On the dispersion of Scholte wave propagating on a layered medium
Authors: de Billy M. , Quentin G.
Published: October 2005

The phase velocity of the Scholte wave is experimentally studied in the case of plane multilayered systems immersed in water. The ‘‘liquid wedge’’ technique is used for its generation and the investigation is limited to the case where the layers have a high density and a high shear wave velocity with respect to the fluid (water). The variations of the difference between the phase velocity of the Scholte wave and the sound velocity in water is obtained by recording the ‘‘penetration factor’’ of the investigated wave into the liquid, the amplitude of which decays exponentially as exp(−k″z) from the surface; z measures the coordinate perpendicular to the interface and k″ designates the ‘‘penetration factor.’’ The agreement between theoretical and experimental results is reasonably good. The method of investigation limits our study on the dispersion of the Scholte wave to the ke values>1.8 (k designates the wave vector in the water and e the thickness of the layer).
The localization of low- and high-frequency vibrotactile stimuli
Authors: Sherrick Carl E. , Cholewiak Roger W. , Collins Amy A.
Published: October 2005

Four experiments were conducted to determine whether spatial localization on the skin varied in acuity as a function of frequency of vibratory stimulation. The glabrous skin of the palm over the hypothenar eminence was selected as the site for stimulation by two frequencies, one at 25 Hz to stimulate non-Pacinian receptors, and one at 250 Hz to excite Pacinian receptors. Because the Pacinian receptors have larger receptive fields than the non-Pacinians, it was thought that the subjects’ ability to localize would be poorer when the Pacinians were the class of receptor stimulated. In addition to frequency of vibration, the presence of a surround, the site of stimulation, the separation of the stimulator pair used in the 2AFC method, and the use of an impulse stimulus were all conditions varied to determine whether a simple direct correlation exists between receptor category and spatial acuity for vibratory stimuli. A significant difference in acuity was found as a function of vibration frequency at a proximal locus on the palm, but this vanished at a distal locus. The results have been interpreted to suggest that receptor density and its gradient across the skin areas involved may be as important as receptor type in the determination of spatial acuity.
Electrophysiological evidence for the critical band in humans: Middle-latency responses
Authors: Burrows Dennis L. , Barry S. Joseph
Published: October 2005

Electrophysiological evidence for the critical band phenomenon in humans using event-related potentials has been sought for many years with conflicting results. Components Na and Pa of the middle-latency response (MLR) and wave V of the auditory brain-stem response (ABR) were simultaneously recorded in response to a two-tone complex varying in bandwidth from 76 Hz to 1012 Hz, centered at 2 kHz, and presented at an overall level of 85 dB SPL, in ten normal female subjects. Only the amplitude of Na showed an abrupt increase as bandwidth changed from 268 to 330 Hz, yielding an estimate of critical bandwidth in good agreement with previous behavioral estimates.
Analysis of high-frequency multitone transmissions propagated in the marginal ice zone
Authors: Catipovic Josko A. , Baggeroer Arthur B.
Published: October 2005

This work presents estimates of frequency and time coherence functions of acoustic transmissions centered at 50 kHz over a 1-km horizontal underice path in the marginal ice zone (MIZ). The data were collected during the MIZEX ’84 experiment as part of a feasibility study for an underwater acoustic telemetry link. It is shown that the acoustic fluctuations are dominated by a 10-Hz process conjectured due to the turbulent under-ice boundary layer. Significant fluctuation energy in the 0.1-Hz band was also observed. The two processes differ in frequency coherence characteristics. An underwater telemetry system designed for this channel will be dominated by the high-frequency fluctuations, but the slower process is capable of causing disastrous data losses unless its effects are anticipated.
Driving-point impedance measurements of a clamped circular plate driven by a noncentral force
Authors: Delaplane Neil C. , Kerlin Roger L.
Published: October 2005

The driving-point impedance of a thin, clamped circular plate driven first at the center and subsequently off-center by a point force was measured and compared with the prediction of theory. Tests were performed on an aluminum plate loaded by a concentrated mass at the driving point, and comparisons have been made with an equation for driving-point impedance. The measurements show excellent agreement with the theoretical computations, which were based on the thin plate equation extended to account for the internal damping of the plate material. Two different masses were used to investigate the effect of mass loading. Additionally, attempts to cancel certain symmetric modes proved successful by applying the vibratory force at a point on the corresponding nodal circle.
Transients in piezoelectric transducers of finite dimensions
Authors: Kaz̆ys Rymantas J. , Maz̆eika Liudas
Published: October 2005

Transients in piezoelectric transducers using spatial impulse responses and a finite-element method have been studied. The developed calculation procedure makes it possible to obtain two-dimensional nonstationary electroacoustic fields inside a transducer as well as spatial distributions on its surfaces under various driving conditions. Numerical simulations of plane and concave transducers have been carried out. The edges of the piezoelectric elements in both cases are sources of strong spurious impulsive waves propagating to the center of a transducer. Some methods to improve the uniformity of the spatial distributions and reduce the amplitude of spurious waves have been proposed. The results obtained may be of particular interest for calculating more accurately pulsed ultrasonic fields radiated by piezoelectric transducers of finite dimensions.
Auditory filter shapes at low center frequencies
Authors: Moore Brian C. J. , Peters Robert W. , Glasberg Brian R.
Published: October 2005

Auditory-filter shapes were estimated in normally hearing subjects for signal frequencies (fs ) of 100, 200, 400, and 800 Hz using the notched-noise method [R. D. Patterson and I. Nimmo-Smith, J. Acoust. Soc. Am. 67, 229–245 (1980)]. Two noise bands, each 0.4fs wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter shape and asymmetry. Two overall noise levels were used: 77 and 87 dB SPL. In deriving the shapes of the auditory filters, account was taken of the nonflat frequency response of the Sennheiser HD424 earphone, and also of the frequency-dependent attenuation produced by the middle ear. The auditory filters were asymmetric; the upper skirt was steeper than the lower skirt. The asymmetry tended to be greater at the higher noise level. The equivalent rectangular bandwidths (ERBs) of the filters at the lower noise level had average values of 36, 47, 87, and 147 Hz for values of fs of 100, 200, 400, and 800 Hz, respectively. The standard deviations of the ERBs across subjects were typically about 10% of the ERB values. The signal-to-masker ratio at the output of the auditory filter required to achieve threshold increased markedly with decreasing fs .
Auditory filter shapes at 8 and 10 kHz
Authors: Shailer Michael J. , Moore Brian C. J. , Glasberg Brian R. , Watson Nick , Harris Susan
Published: October 2005

Auditory filter shapes were derived from notched-noise masking data at center frequencies of 8 kHz (for three spectrum levels, N0 =20, 35, and 50 dB) and 10 kHz (N0 =50 dB). In order to minimize variability due to earphone placement, insert earphones (Etymotic Research ER2) were used and individual earmolds were made for each subject. These earphones were designed to give a flat frequency response at the eardrum for frequencies up to 14 kHz. The filter shapes were derived under the assumption that a frequency-dependent attenuation was applied to all stimuli before reaching the filter; this attenuation function was estimated from the variation of absolute threshold with frequency for the three youngest normally hearing subjects in our experiments. At 8 kHz, the mean equivalent rectangular bandwidths (ERBs) of the filters derived from the individual data for three subjects were 677, 637, and 1011 Hz for N0 =20, 35, and 50 dB, respectively. The filters at N0 =50 dB were roughly symmetrical, while, at the lower spectrum levels, the low-frequency skirt was steeper than the high-frequency skirt. The mean ERB at 10 kHz was 957 Hz. At this frequency, the filters for two subjects were steeper on the high-frequency side than the low-frequency side, while the third subject showed a slight asymmetry in the opposite direction.
Bacterial luminescence: A new tool for investigating the effects of acoustic energy and cavitation
Authors: McInnes Christopher , Engel David , Martin Roy W.
Published: October 2005

An assay utilizing luminescent bacteria, Photobacterium phosphoreum, was adapted to assess the antibacterial effects of acoustic energy. Acoustic pressures up to 67 kPa in the 100- to 800-Hz frequency range were applied to bacteria freely suspended in a liquid medium. Bacterial luminescence decreased after sonication, thus showing sensitivity to the effects of acoustic energy. This decreased luminescence was linearly related to exposure duration, appeared independent of acoustic frequency in this range, and was significantly heightened by the presence of cavitation. High-frequency components of the acoustic emission were recorded from the sonicated fluid, and it was found that the decrease in luminescence due to sonication was directly related to the logarithm of the acoustic emission. Viability studies on exposed bacteria indicated a diminution of luminescence without bacterial death. The potential use of luminescent bacteria in assessing the biological effects of acoustic energy-generating systems is discussed.
Signal detection in the presence of inaccurate multipath time delay modeling
Authors: Lourtie Isabel M. G. , Carter G. Clifford
Published: October 2005

In this paper, a new class of signal detectors is considered whose structure is similar to the log-likelihood detector developed under low signal-to-noise ratio conditions, but with different choices to the sensor filters. In the presence of incorrect delay assumptions, the performance of the log-likelihood processor is analyzed and interpreted. Based on this study, ad hoc detectors are proposed, and their performance compared to that of the log-likelihood structure. It is shown that, for increasing misadjustment in the delay assumptions, the performance of the proposed ad hoc detectors is superior.
Sharpness applied to the adaptive beamforming of acoustic data from a towed array of unknown shape
Authors: Ferguson Brian G.
Published: October 2005

When a vessel towing a horizontal line array of underwater acoustic sensors changes course, the array responds by changing its shape so that the sensors no longer lie along a straight line. However, the spatial processing of the acoustic data still proceeds on the assumption that the array is straight with the positions of the sensors being known and invariant. When the array adopts a nonlinear shape so that the actual locations of the sensors no longer coincide with the assumed positions, the performance of the beamformer is observed to deteriorate. This degradation is most marked when an adaptive beamformer is used to optimize the array gain. The adaptive beamformer considered here is a constrained optimum beamformer that is based on the inversion of the observed (signal-plus-noise) cross-spectral matrix of the sensor outputs. The adaptive beamformer responds to any deviation of the sensors from their nominal positions by suppressing the received signals so that the output signal-to-noise ratio of the beamformer, and hence the array gain, decrease in the direction of each signal. One method of overcoming the array shape problem is to monitor the geometrical configuration of the array’s sensors by instrumenting the length of the array with compasses and depth sensors. This paper examines an alternate method whereby data from the acoustic sensors themselves are used to infer the shape of the array. This narrow-band acoustic technique, which relies on at least one acoustic source being present in the far field, evaluates a sharpness function for a variety of possible array shapes. The sharpness is calculated by summing the product of the beam output power squared and the sine of the beamsteer angle over all beamsteer directions from forward endfire to aft endfire. Using simulated data, it is shown that the estimated array shape matches the actual shape when the sharpness attains its maximum value. Also shown is the dramatic reduction in signal suppression when this acoustic technique is applied to the adaptive beamforming of real acoustic data.
Application of integral equation technique to nonlinear stochastic response of rectangular plates
Authors: Srinivasan R. S. , Krishnan P. A.
Published: October 2005

The present paper is an illustration of the application of the integral equation technique to a nonlinear random response problem. This method relies heavily on the effective use of matrices ab initio and appropriate matrix manipulation to get the equivalent linear stiffness matrix which is the crux of the equivalent linearization technique used here. Rectangular isotropic plates clamped laterally and free of in-plane stresses at the edges are subjected to random excitation. The analysis is done using Von Karman equations and numerical results have been presented.
Light diffraction by ultrasonic pulses: Analytical and numerical solutions of the extended Raman–Nath equations
Authors: Van Den Abeele K. , Leroy O.
Published: October 2005

Light diffraction by ultrasonic pulses at normal incidence is studied as well in the Raman–Nath region (low frequencies) as in the Bragg region (high frequencies). Based on a generating function method, an analytical expression for the Raman–Nath-like diffraction has been derived and compared with earlier work. Only small corrections within its validity region were observed. In order to extend these existing theories toward higher frequencies, numerical expressions for the intensity of the diffracted light waves are obtained by means of the Laplace transform theory. This powerful method leads to the same results for Raman–Nath-like diffraction and can easily be applied for much higher frequencies, too. Examples are provided showing the frequency dependence of the ultrasound, the influence of the Raman–Nath parameter v, and the spectral composition of the pulse on the diffraction pattern. When the pulse approaches a continuous wave, both theories converge to known results. A general condition concerning the symmetry properties of the diffraction spectrum has been derived.
Adiabatic normal-mode theory of sound propagation including shear waves in a range-dependent ocean floor
Authors: Arvelo Juan I. , Überall Herbert
Published: October 2005

A normal-mode model, including absorptive effects and elastic waves in the ocean floor, is presented for a source in the water column and a receiver in the water or the elastic medium. The appropriate boundary conditions between all liquid and solid layers are taken into account, and an absorptive semi-infinite basement is assumed, which causes the radiating wave-number spectrum to be discrete. The adiabatic approach has been adopted for the case where the acoustic properties or the boundaries vary slowly with range. Results of these calculations display the importance of even a slight range dependence, and of bottom elasticity in shallow-center sound propagation.
Correlations among the modal components of the field of a moving source: Low-frequency Doppler effects in shallow water
Authors: Gragg Robert F.
Published: October 2005

Beginning with the normal mode expansion for the acoustic field at a fixed receiver due to a source that moves at constant depth on a straight-line course (not necessarily a radial from the receiver) [K. E. Hawker, J. Acoust. Soc. Am. 65, 675–681 (1979)] while emitting a time-harmonic signal, an expression is derived for the correlations among the modal components of the field generated by such a source whose emission is a statistically stationary random process with nonzero bandwidth. This expression is used to identify the degradation suffered by the modal components of the received signal autocorrelation due to experimental time integration. An illustrative example of a low-frequency narrow-band source in a shallow water environment is examined. There, the motion of the source results in Doppler splitting of the single source emission line into a group of modal spectral lines at the receiver. Recently it has been experimentally verified [Glattetre et al., J. Acoust. Soc. Am. 86, 680–690 (1989)] that for a ‘‘collision course’’ (one that passes directly over the receiver) these lines are stable, resolvable features of the received spectrum. The source in the example, however, is on a ‘‘near miss’’ heading that passes the receiver at a range of 2 km. This produces a time dependence in the frequencies of the Doppler lines that makes their experimental resolution problematic. It is concluded, however, that some of the structure of this line group should still be experimentally resolvable.
Sound scattering by live zooplankton and micronekton: Empirical studies with a dual-beam acoustical system
Authors: Wiebe Peter H. , Greene Charles H. , Stanton Timothy K. , Burczynski Janusz
Published: October 2005

Measurements and analyses are presented of the backscattering of 420-kHz sound by 43 individual animals of representative zooplanktonic and micronektonic taxa. Direct measurements of an individual’s target strength were made with a commercial dual-beam sonar system in an enclosure filled with filtered seawater deployed off a dock at Friday Harbor, Washington. The dependence of target stengths upon individual length, wet weight, and dry weight was investigated. In addition, the ‘‘target strength’’ and statistical variations of echo amplitude due to variations in shape and orientation of the organism were compared with acoustic scattering models involving different shapes (the general shapes of the sphere, and straight and uniformly bent finite cylinders were used along with attempts to take into account roughness). It was found that: (1) backscattering cross sections are proportional to volume of the organisms rather than area as would be predicted by a sphere scattering model, (2) mean target strength based on average backscattering crossection is best described by the bent cylinder model whose modal series solution is truncated, and (3) the fluctuations of the echo amplitudes are well described by the Rice probability density function whose shape parameter is related to the randomly rough straight cylinder model. These extensive studies showed conclusively that the elongated animals scattered sound more like elongated targets than spherical ones, thus demonstrating the need for models more sophisticated than the spherical ones routinely used to date. The data and model analyses provide a basis for devising future acoustical data acquisition and processing techniques for bioacoustical field studies.
Nonconventional traveling wave formulations and ray-acoustic reductions for source-excited fluid-loaded thin elastic spherical shells
Authors: Ho J. M. , Felsen L. B.
Published: October 2005

A continuous Legendre transform spanning the polar angle (θ) domain −∞<θ<∞ embodies the essence of a nonconventional integral representation derived here for source-excited time-harmonic pressure fields in the presence of a thin elastic spherical shell immersed in different interior and exterior fluids. Avoiding the conventional Sommerfeld–Watson transform route, the formulation identifies directly the traveling waves with their multiple encirclements of the shell by extending the θ domain from its conventional 0≤θ≤π range with periodicity constraints into the unbounded (multi-sheeted) domain without these constraints. Periodicity for the closed shell is recovered by summing contributions from an infinite array of image sources located in the ‘‘nonphysical’’ portion θ<0 and θ>π of the angular space. The rigorous solution is obtained by synthesis over a complex spectral continuum. Various alternative representations are derived from it, with special attention given to those that lend themselves to ray-acoustic asymptotics. The rigorously derived ray acoustic constituents include incident and geometrically reflected ray fields as well as surface guided ray fields. The latter are excited by phase matching of the incident ray field to the traveling wave modes in the shell, and they reach the observer by phase-matched detachment [see also P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. The phase matching applies to directly excited leaky waves as well as to waves that decay initially into the fluid; the latter are excited from an exterior source by evanescent tunneling. Transitional effects, where simple ray theory fails, are discussed as well, as is the special case of far-field plane wave scattering. The ray parametrization for the canonical closed spherical shell will play an essential role in subsequent treatment of deformed and truncated shell geometries [cf. L. B. Felsen and I. T. Lu, J. Acoust. Soc. Am. 86, 360–374 (1989)].
Generation of a nondiffracting beam with frequency- independent beamwidth
Authors: Campbell James A. , Soloway Sidney
Published: October 2005

A method is presented for generating a beam with a beam shape that is independent of distance and frequency over large axial and frequency ranges. The half-width of the beam can be less than a wavelength at the low end of the frequency range and can hold this narrow waist for hundreds of wavelengths, giving a large depth of field. The phase fronts of this beam are planar and perpendicular to the beam axis over the depth of field. By virtue of the flat phase fronts and the frequency independence of the beam, a pulsed beam with flat pulse fronts and an unchanging time response can be created. This beam is shown to share some of the properties of an axicon. A numerical simulation is done to demonstrate the feasibility of generating such a beam with an annular array.
Thresholds for transient cavitation produced by pulsed ultrasound in a controlled nuclei environment
Authors: Holland Christy K. , Apfel Robert E.
Published: October 2005

Transient cavitation is a discrete phenomenon that relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1-μm polystyrene spheres, microbubbles in the 1- to 10-μm range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. These experimental measurements of cavitation thresholds elucidate the importance of ultrasound, host fluid, and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate analytical theory for the prediction of the onset of cavitation.
The loudness of sounds that increase and decrease continuously in level
Authors: Canévet Georges , Scharf Bertram
Published: October 2005

A sound at a low level is heard as much softer after having decreased continuously from higher levels than if presented after a period of silence at that same low level. Canévet [Acustica 61, 256–264 (1986)] demonstrated this phenomenon for a tone that (1) decreased from 65 to 20 dB in 180 s; he also presented a tone that (2) increased from 20 dB, or (3) was presented as pairs of bursts at various levels in random order. Below about 40 dB, loudness changed most rapidly in the decreasing condition so that, at 20 dB, the tone was judged ten times softer than in conditions (2) and (3). In the present experiments, magnitude estimation was used to examine the possible role of judgmental biases and adaptation in this rapid loudness decline, which we call decruitment. Results show that decruitment did not come about because subjects made many successive loudness judgments; loudness declined as much when a tone was judged only twice, at the beginning and end of its 180-s decrease. In contrast, interrupting the decreasing tone so that it was heard only at 70 dB and 160 s later at 30 dB greatly diminshed the decruitment. Similarly, pairs of 500-ms tone bursts presented at successively lower levels instead of continously decreasing did not show decruitment, suggesting that sequential biases are irrelevant. The likely cause of decruitment is sensory adaptation.
Effects of stimulus level on forward-masked psychophysical tuning curves in quiet and in noise
Authors: Nelson David A. , Chargo Steven J. , Kopun Judy G. , Freyman Richard L.
Published: October 2005

Forward-masked psychophysical tuning curves were obtained from normal-hearing listeners at different probe levels in quiet and in a broadband background noise. In quiet, tuning-curve shape changed with probe level. For six listeners, tuning curves became broader with increasing probe level, primarily due to a decrease in the low-frequency slopes. For one listener, tuning curves became narrower with increasing probe level. The addition of a background noise, which was presented continuously at a level 10 dB below the noise level required to mask the probe tone, reduced the masker levels required to mask the probe tone. The reduction was greater near the tip of the tuning curve than on the tail, so that tuning curves in background noise were narrower than those obtained in quiet. Tuning curves with comparable masker levels near the tip of the tuning curve (Lmtip) were similar in shape, regardless of probe level or whether tuning curves were obtained in quiet or noise. Comparisons of tuning-curve characteristics derived by fitting tuning curves with least-squares procedures, indicated that low-frequency slopes decreased with Lmtip. As a consequence, Q10 dB values decreased with Lmtip. These results are consistent with the interpretation that tuning-curve shapes are determined by the intensities of the maskers required to mask the probe tone. The addition of a background noise restricted (partially masked) the excitation pattern of the probe so that lower masker intensities were required to ‘‘forward mask’’ the probe tone, and narrower tuning curves resulted from less intense maskers. The results are well described by a two-process model of auditory excitation patterns.
The combination of interaural information across frequencies: Lateralization on the basis of interaural delay
Authors: Dye Raymond H.
Published: October 2005

Three experiments were carried out that employed low-frequency tone complexes with interaural delays that varied across the frequency domain. In the first experiment, threshold interaural delays were measured for three-tone complexes for which one, two, or all three components were delayed. The center frequency was 750 Hz and the frequency spacing (Δf ) between components was 20, 50, 100, 250, or 450 Hz. For all Δf’s, the presence of two diotic components elevated the threshold interaural delays obtained for the third component relative to that obtained for a pure tone of the same frequency. In the second experiment, observers made left–right judgments regarding the direction of movement of signals for which two components were delayed by 25 μs to the left ear during one interval and to the right ear during the other interval, while a third component of a variable time difference was delayed to the opposite side as the tone pair. Subjects reported single intracranial images during each interval, and the data showed that interaural delays of one component to one ear could be offset by interaural delays of the other two components to the other ear. In the final experiment, threshold interaural delays were measured for five-tone complexes in which one, two, three, four, or five components were delayed. The center frequency was 750 Hz and Δf was fixed at 100 Hz. Thresholds decreased in a linear fashion as the number of delayed components increased, falling by about a factor of 5 as the number of delayed components went from one to five. These results are consistent with spectrally synthetic binaural processing, with the lateral position of intracranial images determined by a combination of interaural information across the spectrum. These effects could be brought about by a linear combination of the outputs of frequency-specific cross-correlation networks or by a wideband cross correlation of the signals at the two ears.
The auditory periphery of the ferret. I: Directional response properties and the pattern of interaural level differences
Authors: Carlile Simon
Published: October 2005

The transformations of sound by the auditory periphery of the ferret have been investigated using an impulse response technique for a large number of sound locations surrounding the animal. Individual frequencies were extracted from the detailed spectral transformation functions (STFs) obtained for each stimulus location and, using sophisticated spatial interpolation routines, were used to calculate the directional response of the periphery at that frequency. The strength of the directional response was directly related to the analysis frequency. Furthermore, as the analysis frequency was increased to 20 kHz, the orientation of the directional response increased in elevation from the horizon (E0°) to about E30°, while the azimuthal location remained fairly constant at 30° to 40° from the midline. For analysis frequencies above 20 kHz, the response became increasingly directional toward the ipsilateral interaural axis. The interaural level differences (ILDs) were also calculated for all animals studied. ILDs increased from around 5 to 25 dB over the range of frequencies from 3–24 kHz. The two-dimensional patterns of iso-ILD contours were roughly concentric and centered on the interaural axis for frequencies below 16 kHz. For higher frequencies, there was a tendency for the ILD contours to be centered on more anterior and inferior locations. The increased directionality of the auditory periphery with increasing analysis frequency, together with the presence of sharp nulls in the response at high analysis frequencies, is consistent with a diffractive effect produced by the aperture of the pinna. However, this simple model does not predict the directional responses over the low to middle frequency range.
Response of auditory-nerve fibers to intensity increments in a multitone complex: Neural correlates of profile analysis
Authors: Shivapuja Bhagyalakshmi G. , Salvi Richard J. , Saunders Samuel S.
Published: October 2005

Recent psychophysical studies have shown that the detection of an intensity increment superimposed on the center component (1 kHz) of a multitone complex (1,3,7, or 11 components) improves as more components are added outside of the critical band. It has been suggested that this form of intensity discrimination is based on a change in the neural profile. To test this hypothesis, neural profiles were constructed by plotting the degree of phase locking to the 1-kHz tone as a function of each unit’s characteristic frequency (CF). Neural phase-locking profile to the 1-component signal at 1 kHz had a broad peak; however, the neural profile became narrower as the number of components in the signal increased. The just detectable increment for the 1-component condition was −5 dB re: 1000-Hz component level (3.86-dB increment plus component level re: component level), whereas, for the 3-, 7-, and 11-component conditions, it was −15 dB re: component level (1.42 dB). The neural and psychophysical IDL for the chinchilla were similar for the 1-component condition. However, the overall trends in the psychophysical and neural data are different. In the psychophysical studies IDL is typically poorest in the 3-component condition and improves when more components are added. By contrast, the neural IDL was poorest in the 1-component condition and improved when more components were added. In the multicomponent conditions, units with CFs in 492–1380 Hz were found to be most sensitive in detecting the intensity increment to the 1000-Hz component.
Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). III: Additivity of click level and rate with noise level
Authors: Burkard Robert , Voigt Herbert F.
Published: October 2005

Two experiments were performed that evaluated the effects of ipsilateral-direct broadband noise maskers on the gerbil brain-stem auditory-evoked response (BAER) to click stimuli. In experiment 1, clicks were presented at 27 Hz at levels including 70, 80, 90, and 100 dB pSPL. Noise conditions included a no-noise control, and included noise levels varying in 10-dB increments from 20 dB SPL to a maximum noise level of 50, 60, 70, and 80 dB SPL for click levels of 70, 80, 90, and 100 dB pSPL, respectively. Gerbil BAER peaks were labeled with small roman numerals to distinguish them from human BAER peaks. The dependent variables included waves i and v latencies and amplitudes. Peak latencies increased and peak amplitudes decreased with decreasing click level and increasing noise level. To a first approximation, peak latencies and amplitudes showed changes with increasing noise level that were similar across click level. With increasing click level, there was little or no effect on the i–v interval. There was an increase in the i–v interval with increasing noise level. In experiment 2, click level was held constant at 90 dB pSPL, and click rates included 15, 40, 65, and 90 Hz. For each click rate, noise conditions included a no-noise control, and noise levels included 20, 30, 40, 50, 60, and 70 dB SPL. With increasing click rate and noise level, there was an increase in peak latencies, an increase in the i–v interval, and a decrease in peak amplitudes. The magnitude of peak latency and amplitude shifts with increasing click rate was dependent on noise level. Specifically, the magnitude of rate-dependent changes decreased with increasing level of broadband noise. These data are compared to human BAER experiments, and are found to be in fundamental agreement.
A note on hidden factors in vowel perception experiments
Authors: Traunmüller Hartmut
Published: October 2005

The article ‘‘Static, dynamic, and relational properties in vowel perception,’’ by Terrance M. Nearey [J. Acoust. Soc. Am. 85, 2088–2113 (1989)], contains a report on a vowel perception experiment that reproduces the previous finding that the perceptual identification of vowels is influenced by both extrinsic, contextual factors and by intrinsic factors such as F0. The effect of F0 is, however, interpreted to be smaller than claimed in previous research. This appears to be due to an incorrect analysis of the role of context. It is shown how the results are to be interpreted taking into account how the listener’s expectations are affected by a preceding context. The results are compatible with predictions on the basis of a relational theory of speech perception for cases in which intrinsic and extrinsic factors do not counteract each other.
Reflection and scatter of acoustic waves from a thin, rough elastic plate on the surface of a fluid: Theory and experiment
Authors: Tolstoy Ivan , Diachok Orest I.
Published: October 2005

When the wavelength of an incident plane wave is greater than the plate thickness h and the scale a of the roughness (kh<1, ka<1), one may combine the generalized smoothed boundary condition technique with the classic Germain thin plate equation to obtain a simple and compact theory of scatter. The predictions of the theory are in substantial agreement with recently reported model experiments.
Remarks on ‘‘On the coefficient of nonlinearity β in nonlinear acoustics’’ [J. Acoust. Soc. Am. 8
3, 74–77 (1988)]
Authors: Tarkenton Grey M.
Published: October 2005

Through an alternate analysis, the results of Hamilton and Blackstock [J. Acoust. Soc. Am. 83, 74–77 (1988)] are reviewed and a new interpretation is presented. In this view, the nonlinearity of the momentum equation is examined, and its effect on the coefficient of nonlinearity is revealed.
Comments on the relationships between linear systems theory and the free-space solution of the inhomogeneous linear wave equation
Authors: Ziomek Lawrence J.
Published: October 2005

Using the principles of linear, time-variant, space-variant, filter theory, and time-domain and spatial-domain Fourier transforms, derivations of the solutions of the linear, three-dimensional, inhomogeneous wave equation for (1) an unbounded isospeed fluid medium and (2) an unbounded fluid medium with speed of sound an arbitrary function of a single variable are presented.
Optimal time-domain beamforming with simulated annealing including application of a p
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Authors: Kuperman W. A. , Collins Michael D. , Perkins John S. , Davis N. R.
Published: October 2005

A fast simulated annealing algorithm is developed for an optimal time-domain beamformer. The optimal beamformer has greater resolution than the standard frequency-domain beamformers, which discard information by averaging the data to form a correlation matrix and remove degrees of freedom by collapsing the number of unknown parameters. The optimal ambiguity function uses the data in raw form and depends on all of the unknown source parameters. This approach is practical with simulated annealing. A specialized simulated annealing algorithm is required to search for the source bearings and time series because the parameters are analogous to a mixture of substances with different freezing points. Examples are presented to demonstrate that the optimal beamformer can be enhanced significantly with a priori information and to illustrate the effects of source level and bandwidth, noise level, array size, and number of sources.
Observation of optoacoustic amplitude in CS2 at high-input energies
Authors: Cheyne Stanley A. , Bass Henry E.
Published: October 2005

The optoacoustic amplitude as a function of laser pulse energy has been measured. A nitrogen laser emitting UV (337 nm) pulses 800 ps in duration was used to excite liquid carbon disulfide (CS2), which strongly absorbs the UV radiation. Measurements indicate an optical absorption coefficient of 370 cm−1 implying an optical penetration depth of 27 μm. The spatial profile of the pulse was an ellipse at the focal point with dimensions of 330×90 μm. The energy coupled with the short penetration depth resulted in a high energy density (532 J/cm3). This was varied by placing glass microslides in the beampath. The optoacoustic amplitude as a function of energy exhibited changes in slope as the liquid in the focal volume underwent vaporization. The experimental observations were explained in terms of an energy-dependent coefficient of thermal expansion and optical absorption.
Numerical simulation of the second-order Kirchhoff approximation from very rough surfaces and a study of backscattering enhancement
Authors: Chen Jei S. , Ishimaru Akira
Published: October 2005

A Monte Carlo simulation is used to study the second-order Kirchhoff scattering and backscattering enhancement of a scalar wave from one-dimensional soft Gaussian rough surfaces. The surfaces are very rough with the rms height σ/λ=0.707, 0.5, and 0.3, and the correlation distance l/λ=1. Numerical results of the scattered intensity using the Kirchhoff approximation and second-order scattering are compared with the exact calculations of the integral equation. With the corrections of incident and scattering shadowing and the propagation shadowing for the second-order scattering, good agreement between approximate and exact results is obtained. The results also show that the backscattering enhancement may be explained by the second-order Kirchhoff scattering including shadowing effects. The law of energy conservation and the problem of convergence in the simulation are also investigated. The results of numerical simulation may be useful for the development of an analytical model for very rough scattering.
A very-wide-angle acoustic model for underwater sound propagation
Authors: Dalrymple Robert A. , Munasinghe Levsiri C. , Wood David H. , Kirby James T.
Published: October 2005

A parabolic model, valid for wide angles (out to 90° from the assumed propagation direction for a homogeneous environment), is presented. Numerical computations for the model are done almost entirely in the Fourier domain, and the model can be shown to be theoretically exact for a homogeneous ocean. In addition, the model can implicitly handle range-dependent sound-speed profiles. An error analysis indicates that the model is more accurate than the standard parabolic equation (SPE) and the modified-wide-angle parabolic equation (MWAPE) for constant perturbations of the index of refraction. The accuracy of the model is examined by comparison of computed solutions with exact solutions for range independent cases. Several idealized range-dependent cases are also examined.
Scattering from very rough surfaces based on the modified second-order Kirchhoff approximation with angular and propagation shadowing
Authors: Ishimaru Akira , Chen Jei S.
Published: October 2005

A theory of scattering from very rough surfaces is presented. Both the surface rms height and the correlation distance are close to a wavelength and the rms slope is close to unity. The theory is based on the first-order and modified second-order Kirchhoff approximations. The second-order scattering includes the incident and scattering shadowing and the angular and propagation tapering shadowing. The angular shadowing limits the angular spectrum of the second-order scattering within those intercepted by the surface, while the propagation shadowing limits the propagation distance within those intercepted by the surface. The calculations are made for the rms height σ/λ=1.5, 1.0, and 0.5 and the correlation distance l/λ=1.8, and show close agreement with the Monte Carlo simulation of the exact integral equation. The results show that the first-order Kirchhoff scattering is dominant for σ/λ=0.5, but for σ/λ=1.0 and 1.5, the second-order scattering becomes comparable to the first-order and produces the enhanced backscattering. Therefore, this theory provides a possible physical explanation for the enhancement.
Standing wave apparatus for measuring fundamental properties of acoustic materials in air
Authors: McIntosh Jason D. , Zuroski Michael T. , Lambert Robert F.
Published: October 2005

A standing wave apparatus employing multiple microphones for measuring fundamental properties of acoustic materials is analyzed. The apparatus is basically a tube with a compression driver at one end with a rigid plug at the other and a finite length sample of acoustic material strategically located in between. A microphone array is then used in obtaining the pressure and velocity boundary conditions of the sample from which basic acoustic properties can be calculated. Such properties as internal propagation constant, characteristic admittance (inverse impedance), and bulk modulus are measured and data for a 100-pore-per-inch (ppi) open-cell acoustic foam is presented. A relatively new parameter called the complex flow impedance is measured under low- and high-intensity levels and is shown to exhibit finite amplitude properties. Of particular concern is how finite sample lengths effect the accuracy of the measurements. It is shown that in general a long sample length (on the order of a wavelength or more) is required for the accurate measurement of propagation constant, characteristic admittance, and bulk modulus measurements while a short length (much less than a wavelength) is required for good finite amplitude flow impedance measurements. Previous studies of flow impedance have been carried out using a similar but not identical apparatus [W. E. Zorumski and T. L. Parrott, ‘‘Nonlinear Acoustic Theory for Rigid Porous Materials,’’ U.S. NASA TN-6196, 1971; K. U. Ingard and T. A. Dear, ‘‘Measurements of the Acoustic Flow Resistance,’’ J. Sound Vib. 103, 567–572 (1985)]. However, the previous studies have lacked an analysis of the possible errors in the measurement methods that can be very significant for these types of flow impedance measurements.