bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration and decay characteristics of electrical basses
Authors: Ebbitt Gordon , Suzuki Hideo
Published: October 2005

One of the assets of electric musical instruments such as guitars and basses is that they posess very long sustain. Since no acoustic radiation is required from the body of the instrument, very rigid and massive elements may be used in its construction. This will generally ensure that the sustain is long and constant from note to note. Structural resonances, however, occur in all structures with finite stiffnesses and masses and these resonances will influence the sustain of the instrument. Since the resonances occur at discrete frequencies, certain notes may have a more rapid decay than others and this may cause “dead spots” at certain notes. The relation among the structural resonances, the decay rates, and the input inertances at the ends of the speaking lengths of the strings of an electric bass will be discussed. The modal shapes will be shown and their shapes relative to the speaking length of the string will also be considered.
A finite element analysis of the violin body
Authors: Knott George
Published: October 2005

The normal modes of a violin body were studied using finite element methods. The NASTRAN finite-element analysis package and PATRAN-G pre/post-processor graphics software were the workhorses for this “computer laboratory” investigation. Free finite-element top and back plates were first “tuned” to generally accepted parameters and were then assembled into a complete body consisting of the plates, bassbar, sound post, and end blocks. The normal modes of the finite-element body compare favorably with those obtained from an impact hammer modal test on a real violin. Animated graphics of the normal modes, which provide significant insight into the physics of the violin structure, will be presented.
Finite amplitude distortion and dispersion in a hard-walled waveguide
Authors: Ginsberg J. H. , Miao H. C.
Published: October 2005

The fundamental symmetric two-dimensional mode in a hard-walled rectangular waveguide is decomposed into a pair of obliquely propagating planar waves, in order to treat the effect of nonlinearity. A perturbation analysis of the nonlinear wave equation for the velocity potential identifies amplitude dispersion as one source of singularity. The only interaction between the oblique waves attributable to this effect is a change in the distance parameter affecting the magnitude of the higher harmonics. Another singularity arises when the frequency ω or width L is large. The oblique waves are then closely aligned with the axis, resulting in resonant interaction with the true planar mode. Harmonic generation in this case has the appearance of a spatial beating pattern. A set of coordinate transformations make the representation uniformly valid. Analyses of limiting forms are confirmed by quantitative examples. Small values of ωL are well described by an earlier general solution in terms of groups of nondispersive modes [J. H. Ginsberg, J. Acoust. Soc. Am. 65, 1127–1133 (1979)], while large ωL yields a quasiplanar signal. The transition at moderate ωL is characterized by frequency, as well as amplitude, dispersion. The distortion of waveforms then is very close to that obtained in the nearfield of sound beams. [Work supported by ONR.]
Production of skewness by coupling of nonlinearity and frequency dispersion
Authors: Crighton D. G.
Published: October 2005

In full scale jet noise experiments it has been observed that the skewness factor S = 〈p3〉/〈p2〉3/2 of the pressure fluctuations increases from near zero values near the source to positive values as high as 0.8 in the farfield, with a distinctive change in the typical waveform to one containing high, spiky positive pressure rises followed by more gradual and smaller negative pressure excursions. Further, the value of S at a fixed range and identical running conditions is highly sensitive to meteorological conditions. This paper presents a simple model—based on coupling between nonlinear acoustic distortion and linear frequency dispersion—capable of explaining these observations. Such coupling will be shown to always produce positive skewness, increasing with range, and extremely sensitive to the difference between frozen and equilibrium sound speeds, and hence to atmospheric humidity levels.
Hydrodynamic attenuation of weak shock waves
Authors: Curtis W. D. , Rosenkilde C. E.
Published: October 2005

A pair of ordinary differential equations is derived, giving the shock amplitude and pressure gradient at the front as functions of range, for a weak shock propagating in a homogeneous medium. These equations enable us to complete a discussion originally given by G. I. Taylor in his work on the decay of blast waves. It is shown that the equations can be solved asymptotically at large ranges to give the well-known results for amplitude decay and pulse spreading for plane, cylindrical, and spherical week shocks. [This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.]
Nonlinear stability analysis of a Stokes boundary layer
Authors: Thompson Charles , Burke Shawn
Published: October 2005

The stability of the Stokes boundary layer generated by an acoustic disturbance in a two-dimensional waveguide having a slowly varying height is examined. It is shown that the stability of the Stokes layer to three-dimensional disturbances is governed by the value of three small parameters ε, 1/R, and 1/S, where ε is the wall slope, 1/R is the ratio of the oscillatory boundary layer thickness to the typical duct height, and 1/S is the ratio of the oscillatory particle displacement to the duct height. A stability analysis is presented for the amplitude range ε2R/S2 = O(R). It is shown that instability to infinitesimal disturbances occurs when h″ε2R/S2 is greater than 49.3. As the disturbance amplitude becomes finite in value the solution bifurcates from that obtained using linear stability theory. We will show that the first bifurcation satisfies the equation d2A/dx2 + (γ1x + T1γ2)A = γ3A3, where A is the disturbance amplitude and, γ1, γ2, and γ3 are parameters dependent on the local behavior of acoustic wave as well as the duct geometry. [Work supported by the National Science Foundation.]
Nonlinearity parameters from measurement of acoustic radiation-induced static strains in silicon
Authors: Yost W. T. , Cantrell John H. , Li Peter
Published: October 2005

The radiation stress associated with a finite amplitude acoustic wave propagating in a solid generates a static strain having an amplitude directly proportional to the energy density of the propagating wave. The coupling coefficient in the static strain-energy density equation is the acoustic nonlinearity parameter. We have determined the nonlinearity parameters in single crystal silicon along the pure mode propagation directions from acoustic radiation stress measurements. We obtain the values 2.12 ± 0.36 along (100), 4.3 ± 0.72 along (110), and 3.87 ± 0.58 along(111). These values are in good agreement with independent measurements obtained from harmonic generation as well as from stress derivative experiments.
Place synchrony and the masking-level difference
Authors: Cohen Marion F. , Schubert Earl D.
Published: October 2005

Detection threshold of a masked signal can be lowered in two ways: First, by varying the interaural configuration of the signal and masker, the MLD, and second, by a noise masker which has the same envelope at different frequencies, place synchrony. This experiment was performed to determine if these two processes are independent. The signal was a tone burst. The masker, a continuous 100-Hz-wide noise band centered at the signal frequency, was created by modulating a tone with a 50-Hz low-pass noise. A second noise band, centered at a different frequency, had either the same envelope as the first noise or a different envelope. The MLD was measured for two conditions; when the two noise bands in the homophasic condition were synchronous, and when they were not. MLDs measured in the synchronous noise were substantially smaller than those in the independent noise or in the 700-Hz noise alone. It is probable that the detection threshold shifts which are due to the MLD and those due to place synchrony are not independent. The MLD may be a manifestation of place synchrony. [Work supported by NIH.]
Some observations on BMLDs
Authors: Henning G. B. , Zwicker E.
Published: October 2005

A simple extension of the Webster-Jeffress model of the BMLD is presented with its predictions for (1) the effects of various stimulus parameters on the size of the BMLD, (2) the relative size of the BMLD in simultaneous and post-masking, and (3) the dependence of the BMLD on differences in frequency between the signal and masker. Data illustrate the high correlation between observers' sensitivity to level differences and their sensitivity to interaural delay. The attentuation characteristic of the interaural-delay-tuned mechanisms responsible for the BMLD is also illustrated.
Lateralization of clicks based on interaural time: Additivity of information across frequency II
Authors: Wenzel Elizabeth M. , Hafter Ervin R.
Published: October 2005

Sensitivity to interaural differences of time (IDT) was measured for single clicks composed of Gaussian envelopes centered on high-frequency carriers. In one study, performance was measured for clicks with fixed carriers of 4, 5.2, 6, or 7.2 kHz, both alone and combined with a second click whose carrier ranged from 3.5–8.5 kHz. The IDT was constant across sets of carrier combinations. In a second study, sensitivity was measured as a function of the IDT in clicks with carriers of 5.2, 6, or 7.2 kHz, both alone and combined with a 4-kHz click with a fixed IDT. For two subjects, performance improved as the separation between the simultaneous carriers increased, regardless of any difference in IDTS, until the limit predicted by additivity of independent information from each frequency band was reached at a 1- to 2-kHz separation. A third subject only showed consistent additivity when the IDTs carried by the two bands were similar.
On Lamb wave conversion effect of nondestructive evaluation of spot welds
Authors: Rokhlin S. I. , Adler Laszlo
Published: October 2005

The interaction between ultrasonic Lamb waves and the region of rigid contact between two elastic layers is discussed. This problem is a model of two sheets welded in this region. The transmission of Lamb waves through such regions is estimated. The conversion of Lamb modes plays a major role. The effect of the temperature change in the welded region is also discussed. The effect of phase transformation in metal, metal melting, and solidification on wave transmission are described. Permanent address: Materials Engineering Department, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
Controlling plate radiation with Anderson localization
Authors: Maynard J. D.
Published: October 2005

When a plate is stiffened with a periodic array of ribs, the normal modes of the system are extended and structural vibrations may travel long distances with little scattering. If the rib array is made random, then structural vibrations become localized within a distance inversely related to the degree of randomness. This effect, analogous to a phenomenon in solid state physics, is referred to as Anderson localization. At the present time we are using nearfield acoustic holography to study the possibility of controlling sound radiation from ribbed plates through the effects of Anderson localization. Results from a one-dimensional system will be reported. [Work supported by ONR and NASA.]
Auditory spatial resolution under static and dynamic conditions
Authors: Grantham D. Wesley
Published: October 2005

The minimum audible movement angle (MAMA) is the minimum angle a horizontally moving sound source must traverse to be just discriminable from a stationary source [Perrott and Musicant, J. Acoust. Soc. Am. 62. 1463–1466 (1977)]. To further explore the relationship between the MAMA and the traditional minimum audible angle determined with stationary sources (MAA), we examined auditory spatial resolution of 500-Hz tones under both dynamic and static conditions: (1) In the static (MAA) condition subjects had to respond whether the second of a pair of stationary 20-ms tone bursts was to the left or the right of the first; (2) In the dynamic (MAMA) condition subjects had to respond whether a single moving stimulus moved left or right. The independent variable was the duration of the interstimulus interval (ISI) in condition 1, or of the moving stimulus in condition 2. While the MAA increased from 1°–2° as ISI decreased from 500 to 50 ms, the MAMA increased from 3°–10° as stimulus duration decreased over this range. These results suggest that the severe degradation of the MAMA as duration decreases, originally reported by Perrott and Musicant, is primarily a consequence of the dynamic nature of the stimulus and not of the brief duration per se. [Work supported by NSF.]
The vibrotactile periphery: Receptor potentials and neural impulses in the Pacinian corpuscle
Authors: Bolanowski S. J.
Published: October 2005

Understanding of mechanotransduction within the cutaneous sensory system is limited by the complex nature of the skin matrix in which the receptors are embedded. At least one of these receptor types, the Pacinian corpuscle, is more easily accessible in cat mesenteric tissue and as such has become prototypical for describing many peripheral physiological processes probably common to the other skin mechanoreceptors. For example, the receptor potential of the Pacinian corpuscle has an asymmetric, full-wave rectified intensity characteristic possessing a saturating nonlinearity and a time-dependent hysteresis. Receptor potentials of sufficient amplitude and rate of change generate action potentials on adjacent membranes, the characteristics relating firing rate to stimulus intensity containing plateaus at multiples of the stimulus frequency. For the frequency domain, three filters in cascade can account for the U-shaped characteristics obtained under iso-rate criteria. These filters are (a) mechanical, located at the receptor's accessory capsule which surrounds the transductive membrane, (b) electrochemical, located in the receptive membrane, and (c) electrochemical, involved in the spike firing threshold.
The organization and connections of somatosensory cortex in primates
Authors: Kaas Jon H.
Published: October 2005

The use of microelectrode mapping methods, in conjunction with studies of cortical architecture, patterns of connections, and the response properties of single neurons, has led to a greatly increased understanding of the functional organization of somatosensory cortex in mammals. All mammals appear to have the traditionally defined first and second somatosensory representations, SI and SII, but at least some mammals have additional body representations as well. Furthermore, the area traditionally regarded as “SI” in monkeys actually includes four functionally distinct representations. Within “SI,” four striplike architectonic fields, areas 3a, 3b, 1, and 2 have long been recognized. It is now clear that areas 3b and 1 form separate parallel and largely mirror-image representations of the body surface, each with major inputs from a single representation of the body surface in the ventroposterior nucleus (VP) of the thalamus. VP appears to relay information from both slowly and rapidly adapting peripheral neurons to area 3b, while information from rapidly adapting neurons is relayed to area 1. Neurons with properties that could reflect Pacinian receptor influences are found in area 1, but not area 3b. The anatomical pathways mediating Pacinian-like responses are unknown. Area 3a contains a representation of largely deep receptors, probably muscle spindle afferents, relayed from part of the thalamus dorsal to VP. Area 2 forms a representation of both deep and cutaneous body receptors. The somatosensory cortex receives input from other regions as well, including the anterior pulvinar and ventroposterior inferior nucleus of the thalamus. Other portions of the somatosensory cortex are less well understood.
A triplex model of cutaneous mechanoreception
Authors: Van Doren Clayton L. , Verrillo Ronald T. , Gescheider George A. , Sklar Bradley F.
Published: October 2005

The technique of heterofrequency forward masking was used to determine thresholds of three cutaneous receptor systems at the thenar eminence of the hand. A 50-ms sinusoidal test stimulus was presented 25 ms after the termination of a 700-ms sinusoidal masking stimulus. Both test and masking stimuli were varied over the frequency range of 15–300 Hz. The stimuli were delivered through a 0.01 cm2 contactor eliminating the influence of the Pacinian receptor system and exposing the threshold characteristics of two non-Pacinian systems, designated as NPI and NPII. The low-frequency slopes of the NPI and NPII tuning curves are similar to those measured physiologically from SA and RA receptors, respectively.
Acoustic behavior of a vibration-sensitive frog
Authors: Narins Peter M. , Lewis Edwin R. , Lopez Pamela T. , Moore Steven W.
Published: October 2005

The white-lipped frog, Leptodactylus albilabris inhabits the Luquillo Mountains in eastern Puerto Rico. Males have been shown to produce seismic “thumps” concomitant with both of their common calls: the “chirp,” a presumptive advertisement call, and the “chuckle,” emitted during male-male vocal interactions. We have investigated the calling behavior of this species, specifically its vocal response to natural and synthetic acoustic stimuli. Results of our preliminary acoustic playback experiments suggest that in response to a 20-dB increase in chirp playback intensity, some individuals increase the intensity of their chirps as much as 5 dB. When presented with a chuckle call however, males increase their vocal output immediately to the highest observed levels. The incidence of chuckle calls is positively correlated with the intensity of the stimulus, so that as intensity “following” proceeds to higher intensities, the chirp is replaced by the chuckle. The relationship between the call and thump amplitudes is under investigation. [Work supported by NIH (PMN) and NSF (ERL).]
The effects of speaking rate on the isochrony of monosyllables
Authors: Smith M. R. , Fowler C. A.
Published: October 2005

Phonetic segmental manipulations of the onset, vocalic nucleus, and coda have been shown to affect the observed onset-onset intervals in perceptually isochronous productions of monosyllables [M. Smith and C. Fowler, J. Acoust. Soc. Am. Suppl. 1 76, S81 (1984) and references therein]. Lengthening of the onset-onset interval accompanies segmental differences that naturally increase prevocalic, vocalic, and post-vocalic acoustic intervals. In this study we examine the effects of another factor in natural differences in production, speaking rate. The productions of two talkers made under a self-paced and two different metronome-timed conditions were measured. The effects due to speaking rate are compared to the segmental effects. The asymmetries previously found for the segmental effects and the previously reported context effects with metronome-timed productions are re-examined in the data from the self-paced condition. [Work supported by NICHHD.]
The effect of speech rate on the application of low-level phonological rules in American English
Authors: Moore Kimberly C. , Zue Victor W.
Published: October 2005

The acoustic characteristics of speech sounds are often affected by the speaking rate. The purpose of our study was to investigate the extent to which the application of certain low-level phonological rules are correlated with the speech rate. The corpus consisted of a short paragraph made up of 77 syllables, 47 words, and 4 sentences. The paragraph was constructed such that the application of a low-level phonological rule, such as gemination, palatalization, and flapping, was permissible, at many of the word boundaries. The paragraph was read several times by 4 speakers, 2 male and 2 female, at their normal speaking rate, as well as twice and half of their normal rates. The sentences were then digitized using the SPIRE facility and the corresponding spectrograms were made. At each word boundary, the experimenters separately determined whether a particular rule had been applied through critical listening and careful examination of the spectrograms and other interactive displays. The results were tabulated as a function of the speaking rates. Our results suggest that: (1) For most low-level phonological rules, their relative frequency of occurrence increases when the speaking rate is increased from the speaker's nominal rate; (2) Speakers often adopt different strategies for slowing down their speech, including the insertion of pauses and the releases of work-final stops, such that the frequency of occurrence of the rules varies from speaker to speaker. Detailed descriptions of our findings, including the acoustic measurements within words and across word boundaries, will be presented.
Coordination of fingers and speech
Authors: Borden Gloria J. , Armson Joy
Published: October 2005

Contact between fingers and thumb on a task of counting on one's fingers was related to lip/jaw and laryngeal movements while simultaneously counting aloud. Finger contacts were measured from the onset of a voltage produced as the contact completed a circuit. Speech movements were inferred from the deflections of a LED attached to the lower lip of the speaker and from the slow and fast (filtered) impedance changes recorded by an electroglottograph. Subjects counted 20 four-digit number series composed of the numbers 2, 3, 4, and 5. They were instructed to simultaneously count aloud and on their fingers, the second task providing more uncertainty than the first. Results showed that subjects timed finger contacts most closely with the movements of lip/jaw lowering and vocal fold adduction preparatory to voicing, rather than with voicing itself. These results add physiological evidence to acoustic data previously reported by G. Allen [Lang. Speech 15, 72–100 (1972)], K. Rapp [Pap. Linguist., Univ. Stockholm 8, 14–19 (1971)], and C. A. Fowler and L. G. Tassinary [Attention and Performance IX, edited by Long and Baddeley (Erlbaum, Hillsdale, NJ, 1981), pp. 521–535] indicating that the systems may be coordinated on the basis of the most dynamic parts of the utterance rather than the relatively steady state portions. [Work supported by NIH.]
Sound durations in Italian vowel sequences
Authors: Salza Pier Luigi
Published: October 2005

The duration of Italian vowels in monosyllabic and bisyllabic sequences was investigated. The corpus consisted of about 120 PVPAPA nonsense samples, uttered five times in frame sentences by a professional speaker. The test syllable was always the first, containing vowel sequences actually produced in the Italian lexicon. The duration data were taken on digital spectrograms by applying broadly accepted rules for sound boundary identification [G. Peterson and I. Lehiste, J. Acoust. Soc. Am. 32, 693–703 (1960)]. The resulting durational patterns seem to be correlated with both the vowel type and the sound position in the sequence. The shortest values have been measured for asyllabic vowels in diphthongs, in first and in second position as well. Stress and syllable-per-word factors were also analyzed by employing specific control lists. The overall results were compared with earlier acoustical data on single vowels [F. Ferrero et al., J. Ital. Linguist. 3, 87–96 (1978)]. These results will be particularly useful in the generation of prosodic rules for text-to-speech synthesis.
Predictive model of segmental durations in French
Authors: Bartkova Katarina , Sorin Christel
Published: October 2005

A set of rules was established in order to assign to each phoneme of a sentence a duration matching the observed duration for a given French speaker reading paragraph-length texts. The model, which presents some analogy with Klatt's model for segmental durations in English [in Frontiers of Speech Communication Research, edited by B. Lindblom and S. Ohman (1979), pp. 287–299], is summarized by the following formula: DUR (vowels) = DI×Vi×mc and DUR (consonants = DI×Cj, where DI is the intrinsic duration of a segment in ms (as observed in nonsense CVC and VCV sequences spoken in short carrier sentences), Vi and Cj are the percentage of shortening or lengthening depending on the position of the segment in the word and in the sentence, and mc is the percentage of shortening or lengthening of the vowels due to the influence of the following consonant. The input to the model is a string of phonemes and markers. These seven markers indicate content and function words, the location of predicted short and long pauses, the prosodic word boundaries, and the degree of cohesion between prosodic words. Two sets of values of the coefficients Vi, Cj, and mc were defined in order to account for the individual segmental durations observed for two speakers differing essentially in articulation rate. The model predicts segmental durations that differ from measured durations by a σ smaller than 15 ms for both speakers. The predicted durations are also in good agreement with French segmental durations reported in the literature.
Stutterers' durational control of syllabic stress
Authors: Hoffman Paul R. , Daniloff Raymond G. , Guitar Barry E.
Published: October 2005

Six adult stutterers and age-matched nonstutterers produced 15 randomly presented syllable trains of differing stress patterns. Each stimulus train consisted of six repetitions of [pa]. Stress patterns were equistressed [ˈpaˈpaˈpaˈpaˈpaˈpa], bistressed [ˈpapaˈpapaˈpapa] and tristressed [ˈpapapaˈpapapa]. Lip closure for [p] was transduced via lower lip strain gauge. Durations between lip closures were measured from the recorded waveforms. In the equistressed condition, nonstutterers produced syllables of equal duration. Stutterers produced significantly longer first syllables, indicative of slower speech initiation even for these fluently spoken utterances. In the bistress condition, both stutterers and nonstutterers produced longer stressed than unstressed syllables; however, the stutterers produced significantly longer syllables overall. In the tristressed condition, stutterers again produced patterns similar in shape but longer in duration when compared to the nonstutterers' productions. Results suggest that the fluent productions of stress patterns by stutterers differ from normal in their overall rate and in time of utterance initiation.
Probability density measurements for cw propagation in the Arctic ocean
Authors: Giellis George R.
Published: October 2005

An experimental investigation of signal amplitude and phase fluctuations under Arctic conditions has been conducted. The data were sampled from low-frequency cw transmissions during the FRAM IV experiment in April 1982. The signals were generated at the Tristen ice camp and received at the FRAM IV ice camp located north of Spitzbergen. The average water depth along the propagation paths was 3000 m. The range was approximately 275 km. The 28 receivers were positioned along a vertical array at depths from 30 to 960 m. The single hydrophone data exhibited a high signal-to-noise ratio (⩾10 dB) and a high phase stability. The measured phase was modified by means of a frequency shift to compensate for relative platform motion. Histograms of the single hydrophone amplitude and phase were examined for goodness of fit to hypothetical density functions. Amplitude and phase distributions were consistent with a multipath fluctuation model, at the 0.05 level of significance. These densities are associated with a partially saturated process. They were first theoretically derived by P. N. Mikhalevsky [J. Acoust. Soc. Am. 72, 151–158 (1982)].
An analysis of acoustic propagation across the East Greenland Frontal Zone
Authors: Mellberg Leonard E. , Connors Donald N. , Johannessen Ola M. , Browning David G. , Botseas George
Published: October 2005

Oceanographic data (CTD and XBT profiles) were obtained in the summer of 1983 on a transect from within the marginal sea ice zone (at about 76° 30′ N Lat) across the northern Greenland and Norwegian Seas to Tromsø, Norway. The initial 150-km section embraces the complex frontal zone between waters of polar origins in the upper layer of the East Greenland Current and Arctic waters of the Greenland Sea gyre. Interposed between these two water types is a warmer, more saline water of Atlantic origin. The data from this 150-km section have been used as input for an environmental range-dependent sound propagation model (GRASS). By independently limiting the number of bottom bounces and refractive turning points, insight is gained into the contribution of each principal propagation mode: bottom bounce, surface duct, and convergence zone for various source and receiver depths. The relative importance of each propagation mode to the total propagation loss is presented as a function of range from the East Greenland Current end of the section. [Work supported by ONR and NUSC.]
A simulation model for high-frequency under-ice acoustic backscattering
Authors: Bishop Garner C. , Mellberg Leonard E. , Albanese Carl J. , Overdeep Suzanne E. , Ellison William T.
Published: October 2005

A model has been developed to evaluate the backscattering of a high-frequency acoustic pulse from the pack ice regions characteristic of the interior Arctic. The model utilizes measured two-dimensional under-ice profile data and several empirical results that relate the morphological parameters of the large under-ice scattering features called ice keels, to construct a three-dimensional bimodal under-ice canopy consisting of first-year ice keels and flat ice regions. A first-year ice keel is modeled as an ensemble of randomly oriented ice blocks on a planar surface inclined at some slope angle with respect to the plane of the ice-sea water interface. The keel is further characterized by length, draft, width, ice thickness, and aspect angle. A region of flat ice is modeled as a smooth planar surface whose slope angle is less than some critical angle that serves to distinguish a flat ice region from an ice keel. The Kirchoff approximation is used to evaluate the scattering strength of an individual ice block. The scattering strength of a keel is calculated in range increments and is synthesized by moving the pulse down the track and summing coherently the scattering strengths within one-half the pulse length projected onto the keel. The reverberation within each range bin along the track is then calculated. Model results are compared with measured reverberation data and excellent agreement is obtained.
A ray theory for ice keels
Authors: Gordon David F.
Published: October 2005

A ray theory computer program has been developed to simulate the effect of ice keels on underwater sound in the depth-range plane. Keels are modeled with linear and parabolic sections. Reflected and refracted rays are traced. Interface waves can be included. The program has been used to separate the different components of the acoustic field and to investigate the combined reflectivity of a set of keels. Some finite wavelength effects are considered.
Arctic tomography feasibility experiment in MIZEX 84
Authors: Spindel R. C. , Lynch J. F. , Jones M. , Birdsall T.
Published: October 2005

In order to assess the possibility of performing ocean acoustic tomography in the marginal ice zone (MIZ), a 224-Hz center frequency, phase-encoded acoustic source was deployed in the Greenland Sea as part of MIZEX 84. The source was moored in the near-surface sound channel at a depth of 175 m. It transmitted hourly signals designed to test acoustic path stability and decorrelation times. Receptions were recorded on an array of hydrophones suspended 100 m beneath the ice at a range of about 175 km. The data were processed to remove the effects of source-receiver relative motion (due to ice drift), and were coherently averaged to determine coherence times and achievable processing gains. Results on coherence, arrival structure, path stability, and other acoustic experimental qualities relevant to MIZ and Arctic tomography will be presented.
A two-hydrophone technique for measuring the complex reflectivity of materials in water-filled impedance tubes
Authors: Corbett Scott S. , Stuart Alan D.
Published: October 2005

This paper describes the in-water extension of the two-microphone technique used for measuring the complex acoustic reflectivity factor of surface materials. Unlike the more common air-filled standing-wave or Kundt tubes, there is a potential for greater coupling of energy between the vibration field in the steel walls of the water-filled tubes and the acoustic field in the water. This coupling required several significant modifications to the original in-air techniques; primarily, the need to design and develop a suitable two-hydrophone system that would neither perturb the acoustic field in front of the material sample, nor be sensitive to the structure-borne noise propagated in the tube wall. In addition, elaborate signal processing procedures had to be derived in order to apply the required processing techniques to pulses of incident sound. Pulses, rather than continuous sound fields, are commonly used with water-filled tubes to separate the fluid-borne and structure-borne sound. (Subsequent measurements indicated that both pulsed and continuous sound fields are acceptable for water-filled tubes.) This paper presents the measured complex reflection factor, and the corresponding calculated complex surface impedance, of three different simple terminations (air, steel, rubber). Excellent agreement was found between the results obtained with the two-hydrophone technique and those obtained with the more conventional standing wave ratio procedure.
Wave propagation in a waveguide with discontinuous wall impedance
Authors: Thompson C. , Sen R.
Published: October 2005

Nonlocally reacting porous liners are used extensively in ducts to achieve sound absorption. We consider wave propagation in a duct in which the boundary condition on one wall jumps from the impermeability condition to one exhibiting bulk reaction. The bulk-reacting boundary condition of Bliss [J. Acoust. Soc. Am. 71, 533–545 (1982)] is used to model the behavior of the liner. There are three regions in the duct in which the fluid exhibits different overall behavior; two “outer” regions and one “inner” region in which a fast transition occurs in wave character. The method of matched asymptotic expansions will be used to obtain a solution that is uniformly valid throughout the three regions. [Work supported by the National Science Foundation.]
One-dimensional wave propagation in relatively stiff, partially reticulated acoustical foam
Authors: Bolton J. S. , Gold E.
Published: October 2005

Recently the authors have conducted measurements of the acoustic properties of a relatively stiff (in vacuo bulk modulus of elasticity greater than air) partially reticulated (i.e., some of the cell membranes remained intact) polyurethane foam of the type often used in noise control applications. The results were interpreted by using a theory governing one-dimensional wave propagation in elastic porous materials [G. S. Rosin, Sov. Phys. Acoust. 19, 60–64 (1973)] which was extended to account for frequency-dependent viscous and thermal effects. The parameters of the theoretical model (flow resistance, structure factor, frame bulk modulus of elasticity, and loss factor, etc.) were determined by matching the predicted and measured impulse response of a 25-mm-thick layer of unfaced foam. Reasonable agreement was obtained between the measured and theoretical impulse reponses, reflection coefficients and surface normal impedances of the foam in two configurations (faced and unfaced). The theoretical work has indicated that the frame wave (associated with the bulk mechanical properties of the foam) plays an important role in determining the acoustical properties of relatively stiff, partially reticulated foam.
On the effective size of a point acoustic multipole
Authors: Roebuck Ian
Published: October 2005

The Green function approach has been of great benefit in linear acoustics. But there are occasions when an uncritical use of this conceptual picture of the source distribution as a collection of elementary point sources can lead to paradoxical and misleading conclusions, especially when the physical problem takes account of nearby boundary surfaces. Further, with the Lighthill acoustic analogy, in the vicinity of the point source the nonlinear terms may dominate. In this paper we determine the neighborhood of the point source within which, even in linear problems, the existence of boundaries and/or other sources will preclude the use of unmodified “point source” ideas. The derivation relies on the rigorous utilization of the mutual impedance concept, and gives an effective size which is multipole-order and radiation wavelength dependent. For radiators at low frequency this may exceed the classical “nearfield limit.” Some of the problems referred to earlier—in particular for turbulent flow noise over rough boundaries—are shown to lie in domains where moderating influences exist in the “farfield” of a source but within its effective dimensions.
Edge diffraction of transient nondispersive wave—theory and experiment
Authors: Brown Michael G. , Emmett Brian K.
Published: October 2005

Edge diffraction of transient nondispersive waves in two dimensions is considered. The characteristic single-edge diffraction pattern for time-harmonic waves is described by the Fresnel function. The time domain counterpart of the Fresnel function is derived. We argue that the time domain wavefield representation is more insightful than its frequency domain counterpart. It shows, for example, that the diffracted pulse which originates at the shadow casting edge is of opposite polarity in the illuminated and shadow regions. Theoretical and experimental results are compared. [Work supported by ONR.]
Some work on hearing at Goettingen
Authors: Schroeder Manfred R.
Published: October 2005

The audibility of short tone pulses (5–10 ms) in a periodic masker (typical period 20 ms) depends critically on the presence of well-formed gaps in the envelope of the masker. Furthermore, for best detection, these temporal gaps in the masker must be constant in shape for a long time (>100 ms) both before and after the tone pulse. This suggests that higher centers in the auditory pathway are able to detect and store long-time patterns in the masker envelope against which they can test the presence of a test tone. In another study, detection thresholds of tones in chirped maskers were found to vary sensitively with the direction of the chirp (“up” or “down”). Up-chirps whose “delay distortion” is opposite to that of the basilar membrane were found to lead to 20-dB lower thresholds than identical down-chirps. In binaural masking experiments we investigated the question of how fast the ear can switch binaural processing strategies and whether the binaural system can process different binaural configurations simultaneously. For sufficiently long durations of the masker (>50 ms) we found that different strategies for different signal/masker configurations are not only possible at widely separated frequency regions, but that even within the same critical band the binaural system can employ different strategies simultaneously.
Hearing thresholds at high frequencies: Results obtained using a new measurement technique
Authors: Kidd Gerald , Berkovitz R. , Stevens K. N. , Green David M.
Published: October 2005

The hearing thresholds for 40 young adults (18–26 years) were measured at 13 frequencies (8, 9,…,20 kHz) using a newly developed high-frequency audiometer. All subjects were screened at 15-dB hearing level at the low audiometric frequencies, had tympanometry within normal limits, and had no history of significant hearing problems. The audiometer delivered sound to the ear canal through a tube and earpiece in which a small calibrated microphone was located. For each ear, a calibration function relating sound pressure at the inner end of the ear canal to voltage at the acoustic source was calculated from an impulse recorded at the microphone. Calibration functions for different ears extended over a range of 15 dB at some frequencies. For some subjects cross modes in the ear canal prevented accurate calibration at the highest frequencies. Most high-frequency audiograms exhibited a sharply sloping increase in threshold. The location in frequency of this abrupt increase in threshold differed considerably among different subjects and appeared to provide the best characterization of an individuals's high-frequency hearing. [Supported by a contract from NINCDS.]
Adaptation to low-level tonal stimuli
Authors: Bilger R. C. , Matthies M. L. , Carney A. E.
Published: October 2005

Adaptation to low-level, continuous tones has been measured via magnitude estimation, loudness balancing, and subjective report with varying degrees of success. We needed an efficient procedure for measuring adaptation in subjects with tinnitus because of our use of long-duration signals in the study of tinnitus. A double-staircase procedure was used to obtain bifrequency loudness matches between a 1000-Hz reference and a 4000-Hz exposure (adaptation) tone for normal-hearing young adults at 10–50 dB SL. Loudness matches were made twice before, during, and after a continuous 10-min exposure. Data blocks where the sound pressure level of the exposure was instrumentally increased or decreased were used for training and as a check on the procedure. The means of the 70% and 30% positions on the psychometric functions were used to estimate the loudness of the 1000-Hz standard. Approximately 2 1/2 min were needed to collect 84 trials for this calculation. Pilot data indicated that the procedure was sensitive to sound pressure level changes and to loudness adaptation of the 4000-Hz tone. [Work supported by grant NS-17273.]
Effect of number of components and spectral uncertainty on masking by multicomponent maskers
Authors: Neff Donna L. , Hanna Thomas E. , Green David M.
Published: October 2005

Thresholds for sinusoidal signals at 250, 1000, or 4000 Hz were measured in the presence of multicomponent maskers for three listeners with normal hearing. Masker and signal were 200 ms, presented simultaneously. Within a block of trials, the number of sinusoidal components in the masker was fixed, but the frequencies of the components were drawn at random from a range of 1–5000 Hz (excluding the signal frequency). Different drawings were used for each of the two listening intervals. The spectral content of the maskers therefore varied both within and between trials. Phase and amplitude of each masker component was randomized. Maskers with small numbers of components (10 or less) often produced larger amounts of masking than maskers with up to 100 components or broadband noise. Consistent with previous work by Watson and by Spiegel, masker uncertainty influenced performance in a way not easily explained by peripheral theories of masking. [Work supported by NIH.]
Off-frequency masking for monaural and binaural detection
Authors: Cokely Jeffrey A. , Hall Joseph W.
Published: October 2005

Measures of critical bands reveal larger binaural than monaural critical bands [J. C. Sever, Jr., and A. M. Small, Jr., J. Acoust. Soc. Am. 66, 1343–1349 (1979)]. To date, the largest binaural critical band reported for a 500-Hz pure tone signal is 220 Hz [J. W. Hall, R. S. Tyler, and M. A. Fernandes, J. Acoust. Soc. Am. 73, 894–898 (1983)]. Our study suggests an appreciably larger binaural critical band when a procedure other than the traditional bandlimiting approach is used. We determined So and Sπ thresholds for a 500-Hz pure tone masked by an No 50-Hz narrow band of noise centered at 500 Hz. Then, to the 50-Hz masker, we added a 30-Hz narrow band of noise centered at one of 11 different frequencies from 200–2000 Hz. The 50-Hz band was always No whereas the 30-Hz band was No or Nπ. We observed increases in binaural thresholds when 30-Hz narrow bands of noise as far as 500 Hz from the signal were added. These results suggest that a masking noise spectrum as wide as 1000 Hz influences binaural threshold for a 500-Hz pure tone; a value almost five times larger than previously reported estimates.
Loudness functions and temporal resolution for hearing impaired listeners
Authors: Cudahy Edward A. , Mikami Karen A.
Published: October 2005

Loudness perception was measured using a magnitude production procedure. Temporal resolution was measured in the same listeners using a tuning curve masking paradigm and a two-interval forced-choice adaptive procedure. Loudness functions were measured for pure tone signals at 500, 1000, and 3000 Hz with durations of 20 and 500 ms. The signal and masker for the temporal masking experiment were 20-ms sinusoids in phase at 500, 1000, or 3000 Hz. Quiet and 80-dB SPL broadband noise backgrounds were employed for both experiments. There were four primary findings. First, the loudness scaling data agrees with previous literature employing other techniques. Second, the hearing impaired listeners have broader than normal temporal masking functions in the quiet. Third, in the noise conditions, the two groups have broader functions than in quiet. Fourth, the temporal masking functions for the normal and hearing impaired listeners in a noise background are virtually parallel. Interrelations between the loudness and temporal masking data will be discussed. [Work supported by Hoover Foundation.]
Effects of notched noise on the rate of growth of loudness of tones in normal and recruiting ears
Authors: Moore Brian C. J. , Glasberg Brian R. , Hess Robert F. , Birchall John P.
Published: October 2005

Five subjects with unilateral cochlear hearing impairments and three normally hearing subjects made loudness matches between tones presented alternately to the two ears, as a function of the intensity of the tone in the impaired ear (or the left ear of the normal subjects). The impaired ears showed recruitment; the rate of growth of loudness with increasing intensity was more rapid in the impaired ear than the normal ear. Presenting the tone in the impaired ear with a notched noise centered on the tone frequency, at a fixed signal-to-noise ratio, did not abolish the recruitment. This suggests that recruitment is not caused by an abnormally rapid spread of excitation in the peripheral auditory system. The noise had a greater effect on the loudness of the tone in normal ears than in impaired ears. It is possible that the loudness reduction of the tone in noise is mediated by suppression; suppression is weak or absent in impaired ears, and so the loudness reduction is smaller. [Work supported by the Medical Research Council, U. K. and the Wellcome Foundation.]
The jnd's of sound intensity depend on loudness, not on its gradient
Authors: Zwislocki Josef J. , Jordan Herbert N.
Published: October 2005

Fechner's law implies that jnd's of sound intensity depend on how fast loudness grows with the intensity. We show that this is incorrect, and that jnd's depend on loudness rather than on its gradient. The jnd's were measured at 0.25, 1, and 4 kHz on two populations of listeners—normal and those with unilateral hearing loss of 30–75 dB accompanied by loudness recruitment. By means of dichotic loudness balancing, sensation levels were determined for the pathological ears, which produced, respectively, the same loudness as did sensation levels of 10, 20, 40, 60, 80, and 90 dB in normal ears. The jnd's determined in the normal and pathological ears at sensation levels producing loudness equality were equal in spite of slope inequality of the loudness functions. One exception to this rule occurred at 10 dB where the increased slope of pathological loudness functions was accompanied by a larger jnd, the opposite of what Fechner's law would predict. [Work supported by NIH.]