bluuebunny/crossref_metadata_2025 huggingface dataset:
The importance of including the direct field contribution in transmission loss field testing
Authors: Long Marshall
Published: October 2005

The contribution of the direct field has been traditionally ignored in transmission loss testing. For field testing where there is a moderate amount of absorption in the receiving room, this practice results in an underestimate of the actual transmission loss of the partition. Part of the ancient 5 dB difference between lab tested and field tested results may be attributable to this phenomena.
An alternate set of hypotheses for the concert hall problem
Authors: Lee James B.
Published: October 2005

Wallace Clement Sabine proposed, upon founding the theory of reverberation, that large rooms ought to be considered as “energy problems,” because the time between reflections is, on the average, short compared to the reverberation time. The mean time between reflections is not, however, short compared with the time constant; moreover, the time constant and the reverberation time decrease rapidly as absorption is added to the room, a fact not considered by Sabine with respect to his “energy” hypothesis. The alternate possibility is a set of hypotheses based on detailed interactions, taken discretely, of sound with the several surfaces of the room. Two such interactions worthy of study are the “image-impedance effect,” which can multiply the power radiated by bass viols placed close to a stage shell, and the well-known phenomenon of diffuse reflections in the body of a concert hall. Deductions from these hypotheses agree well with the experimental facts of built concert halls. Extensions of these hypotheses poinl to a comprehensive theory of room acoustics using information theory and holography [J. B. Lee, Acustica 30, 196–200 (1974)].
Privacy and communication in an open-plan office: A case study
Authors: Picasso Gere , Sundstrom Eric , Herbert Kring
Published: October 2005

As two departments moved from conventional offices at corporate headquarters to a nearby open plan office, 70 employees at five job levels completed a questionnaire before and after the move. The lowest levels (secretaries) moved from free-standing desks to partially enclosed work spaces; those at middle level II left double offices for single, doorless enclosures. The highest levels (III & IV) left private offices for individual enclosures in open plan. Acoustical tests were also performed at both facilities in Basking Ridge, NJ. They were made in the open office areas at Mt. Airy Rd. and between enclosed offices at North Maple Ave. As predicted, the index of satisfaction with privacy was highest for those at level III and IV before the move. Afterward, it declined, despite the fact that under normal operating conditions, the Mt. Airy open office environment had significantly less distracting noise and better speech privacy then comparable offices at North Maple Ave. Those employees at secretarial and lower management levels (11), whose physical enclosure had improved, were more satisfied.
Frequency resolution and temporal resolution in sensorineural hearing-impaired listeners
Authors: Nelson D. A.
Published: October 2005

Temporal masking patterns and frequency tuning curves were obtained from normal-hearing and hearing-impaired listeners by measuring masker levels that just forward masked a probe tone of constant intensity and constant frequency. Time constants calculated from the temporal masking functions were larger for hearing-impaired listeners than for normal-hearing listeners. Comparisons of time constants and tuning bandwidths, both obtained from the same listeners, demonstrated a high correlation. Those listeners with the longest time constants exhibited the broadest tuning; they also demonstrated the greatest amount of hearing loss. [This research supported by grants from NINCDS.]
Auditory filter shape and age
Authors: Patterson Roy D. , Webber Daniel L.
Published: October 2005

Auditory filter shapes were estimated at three center frequencies (0.5, 2.0, and 4.0 kHz) for 16 listeners from 23 to 75 years old. Estimates were derived for both ears of each listener from the function relating signal threshold to the width of the “notch” in a bandstop noise masker [e.g., Patterson, R. D. and Nimmo-Smith, I. J. Acoust. Soc. Am. 67, 229–245 (1980)]. There is little variation in filter shape across ears, individuals, or age for listeners below 60 years old. However, above 60 years, variability increases. Whereas tuning in some ears remains sharp up to age 75, in other ears the filter is quite broad before age 70. These relations are represented in a calculation of the filter shape which separates the filter characteristic and processing efficiency. [D.L.W. supported by NIH.]
Finite-amplitude behavior of N-shaped pulses from sparks
Authors: Blackstock D. T. , Wright W. M. , Davy B. A. , Lockwood J. C. , Cornet E. P. , Anderson M. O. , Kleeman D. R. , Cobb W. N. , Essert R. D.
Published: October 2005

This paper is a review of experiments done in our laboratory on airborne N waves generated by electric sparks. The purpose of the experiments has been to investigate the effects of finite amplitude on a variety of classical wave phenomena. The N waves used have duration 10-70 μsec, amplitude 0.1 – 100 mbar, and risetime frequently less than 1 μsec. Experiments have been done on simple propagation in an open medium; refraction and diffraction by an acoustic lens (a gas-filled soap bubble); diffraction by a circular aperture, by a disk, and by a slit; focusing by a spherical mirror; and propagation in waveguides (parallel plates and circular tube). All nonlinear effects observed may be traced to modification of the propagation speed by the acoustic field itself. The modification causes elongation and extra decay of simple propagating N waves, unusual interference effects in diffraction, and self-refraction. Self-refraction, which is bending of rays due to a variation of particle velocity (and therefore propagation speed) from ray to ray, sometimes prevents converging rays from actually focusing. [Work supported by ONR, AFOSR, and NASA.]
Acoustic effects and bubble dynamics during the explosive boiling of droplets at the superheat limit
Authors: Sturtevant B. , Shepherd J. E.
Published: October 2005

A droplet of volatile liquid immersed in a different heated but nonvolatile liquid can be heated to very high degrees of superheat before it boils explosively by spontaneous initiation. A series of experiments have been carried out to examine the rapid processes that occur during the early stages of the vapor explosion when departures from equilibrium are very large. The radiated acoustic field has an unexpectedly complex structure which, though not yet fully understood, appears to be related to other unexpected effects observed in the experiments. During the first few microseconds of the explosion, a previously unobserved instability develops at the liquid-vapor interface, resulting in a rather more complex flow field than that envisioned by classical cavitation theory. The nature of this instability is described and some speculations about its consequences are presented. A series of high speed photographs are presented showing the complete development of the explosion from initiation, including the processes occurring on a microsecond time scale thereafter, to the final bubble oscillations which occur on a millisecond scale.
A symmetry based Lagrangian formulation of the acoustic properties of a multi-component medium including boundary conditions at planar interfaces
Authors: Linton David
Published: October 2005

A generalized and simple Lagrangian formulation of the acoustic properties of a microscopically homogeneous and isotropic medium consisting of two or more interpenetrating solid or fluid constituents is presented in terms of a set of phenomenological bulk parameters. The isotropy severely limits the kinds of terms (the number of parameters) that can appear. Biot's theory for the fluid-solid system and Tiersten and Jahanmir's theory for the solid-solid system are shown to be special cases. The approach is extended to interfacial properties of two such systems where boundary conditions are derived in terms of phenomenological surface parameters; again, isotropy and positive definiteness of the strain energy severely limit the number of different parameters. The model dependent boundary conditions of Rosenbaum, Tiersten and Jahanmir, Geerstsma and Smit, and others are shown to be special cases of the general formulation.
Biot's theory of elastic waves in fluid-saturated porous media
Authors: Berryman James G.
Published: October 2005

A new method of identifying the coefficients of the strain energy functional in Biot's theory is presented. Two types of porous media are distinguished: (1) with the granular constituents fully consolidated so the porous frame acts at a cohesive unit and (2) with the granular constituents only partially consolidated so the porous frame consists of a fraction of the solid particles while the remaining particles are (essentially) suspended in the saturating fluid. For complete consolidation, an exact identification of the coefficients is found. This identification differs from the standard identification of Geertsma and of Biot and Willis for frames whose effective elastic moduli are not related to the grain moduli by the Voigt average. For partial consolidation, an exact identification of the coefficients is not known but the standard identification is a good approximation. The predictions of the theory for a fully consolidated frame are compared to Plona's recent measurements on a water-saturated porous structure of sintered glass beads. Measured fast and slow compressional wave speeds and shear wave speeds agree with the theoretical predictions within experimental error (3%) in all cases.
Elastic wave propagation in sediments induced by surface water waves
Authors: Yamamoto Tokuo
Published: October 2005

The time harmonic problem of the propagation and damping of the elastic waves in marine sediments induced by the surface ocean waves are treated analytically based on the M. A. Biot's theory on the acoustic wave propagation in porous elastic media and a linearized stress-strain relation of a slightly inelastic porous media. Through the boundary conditions at the sea-seabed interface, the velocity and the damping of the three elastic waves in sediments are coupled with the phase velocity and the damping of surface water waves. In the horizontal direction, the three elastic waves have the same velocity and damping as the surface water waves. In the vertical direction, the three elastic waves have three different velocities and dampings which are functions of the velocity and damping of the surface water wave and the velocity and damping of each of the three elastic waves in unbounded porous media. [Work supported by NSF.]
A nonlinear oscillator model for an acoustic resonance chamber
Authors: Jacobi N. , Barmatz M. , Lucero M.
Published: October 2005

The exact nonlinear acoustic wave equation, derived from conservation of momentum, mass, and the equation of state, was used to average out the spatial dependence and obtain a forced anharmonic oscillator equation for the time-dependent part. The non-linearity is expressed by a resistive-restoring coupling term ɑxẋ, rather than the restoring term αx2 + βx3 in the modified Duffing equation. A solution is sought in the form of a Fourier series, including all harmonics, and the equation is solved by a perturbation technique, retaining the dominant term in each harmonic. This results in an infinite system of coupled, nonlinear algebraic equations and leads to non-Lorentzian response curves for a sinusoidally driven resonator. These response curves are evaluated numerically and compared with predictions of the Duffing equation and with recent measurements of response curves and harmonic generation in an acoustic resonance chamber (M. Barmatz, N. Jacobi, and J. Stoneburner, 10th International Congress on Acoustics, Sydney, 1980). [Work supported by NASA.]
Drop breakup induced by modulated acoustic radiation pressure: Photographs
Authors: Goosby S. G. , Marston P. L.
Published: October 2005

Shape oscillations of liquid drops acoustically levitated in water have been driven by modulated acoustic radiation pressure [P. L. Marston and R. E. Apfel, J. Colloid Interface Sci. 68, 280–286 (1979); J. Acoust. Soc. Am. 67, 27–37 (1980)]. The splitting of drops into two or more drops had been observed as the amplitude of the modulated acoustic wave was increased. In the present research, motion picture photographs have recorded the oscillation and splitting of drops with initial radii of 1 to 2 mm. The drops (a dyed dimethyl siloxane polymer liquid) were acoustically levitated in a 55-kHz standing wave in water. Breakup was induced by a 170-kHz standing wave modulated at a low frequency. After breakup, the new drops often remained distinct even after removal of the modulated wave. [Work supported in part by ONR and by an M. J. Murdock Charitable Trust Grant of Research Corporation. P. Marston is an Alfred P. Sloan Research Fellow.]
Articulatory compensation in the production of vowels with bite blocks
Authors: Wright James T. , Riordan Carol J.
Published: October 2005

Studies of vowels produced using bite blocks have shown that speakers compensate for unusual degrees of jaw opening thereby preserving acoustic vowel targets. Lindblom and Sundberg [B. Lindblom and J. Sundberg, J. Acoust. Soc. Am. 50, 1166–1179 (1971)] suggest that articulatory compensation is accomplished by preserving the relevant aspects of a vowel's area function with tongue “supershapes.” We investigated this hypothesis by measuring sagittal tongue-palate distances with an infrared sensing system during the production of the vowels in “hid,” “head,” and “had” with and without bite blocks. Simultaneous audio signals were recorded and analyzed for formant frequencies. Possible articulatory strategies for compensation were investigated using a vocal tract simulation model defined by articulatory parameters [P. Ladefoged and J. T. Wright, J. Acoust. Soc. Am. 66, S12 (1979)]. Our data suggest that speakers invoke a set of strategies, more complex than simply attempting to maintain the area function, in order to achieve an acoustic target. [Work supported by NIH.]
Anticipatory and carryover coarticulation in some simple word sequences
Authors: Hilt Gary , Harris Katherine S. , Bell-Berti Fredericka
Published: October 2005

Previous results suggest that anticipatory lip rounding appears to precede the onset of a rounded vowel by a constant temporal duration and hence, that the effect of rounding on preceding alveolar consonant strings may be better described in terms of temporal proximity to the vowel than in terms of the spreading of temporal features. An extension of this general principle suggests the hypothesis that consonant strings should be acoustically less affected by the identity of preceding or following vowel segments as the duration of the string increases. In order to test the hypothesis, production of semantically anomalous sentences containing words with either the vowel /i/ or /u/, and with /s/, /st/, or /st-st/ between the two vowels (e.g., “leased stool,” etc.) were measured, using a spectral display program. Preliminary measurements suggest effects of surrounding vowels on /s/ friction in all these consonant string types, but differences in the magnitude of the effect depending on consonant string duration. [Work supported by NINCDS and BRSG.]
Some biomechanical correlates of jaw movements
Authors: Sorokin Victor N. , Gay Thomas , Ewan William G.
Published: October 2005

The relative contributions of jaw mass and supporting muscle system stiffness to jaw movements were studied to a first approximation. The amplitude-frequency characteristics of jaw movements were measured in both the normal state and under conditions of increased mass (externally applied weights) and stiffness (spring loading). Vertical jaw movements were produced and controlled by muscle stimulation through wire electrodes implanted directly into the masseter muscle of a single subject. The stimulation signal (2-ms pulse width, 200 pps) was modulated through a function generator to produce oscillatory jaw movements varying from 1 to 15 Hz. Jaw movement was tracked in the vertical dimension using a photoelectric sensing device. It was found that increases in both load and stiffness reduced the amplitude-frequency characteristics of the jaw and that the bandwidth of the amplitude-frequency characteristics of the jaw corresponded to the calculated Eigen frequency of the jaw. These findings suggest that the bandwidth of the amplitude-frequency characteristics of the jaw is determined primarily by the mechanical properties of the controlling muscle. The experimental data were also compared to real speech jaw movement data. [Work supported by NIH Research Grant, NS-10424.]
“Intelligent” (statistically-guided) algorithms for vowel normalization
Authors: Harshman Richard A. , Lundy Margaret E. , Disner Sandra Ferrari
Published: October 2005

New normalization methods are presented which alter a speaker's acoustic space in only “natural” ways, corresponding to identified patterns of naturally occurring speaker variation. These “intelligent” algorithms (i.e., which incorporate statistical-linguistic knowledge) may stretch or shift some regions of a speaker's vowel space more than others, and may do so in directions not parallel to any formant axis. Quantitative descriptions of patterns of speaker variation are obtained by an improved application of PARAFAC three-way factor analysis. Then the investigator selects those factors of variation he wishes to remove and inputs them into the program, along with the data set to be normalized. The program uses regression methods to remove the identifiable aspects of unwanted variation from each speaker's data. Three-factor normalization reduces within-cluster variance in the Peterson-Barney English data by more than 70%, without causing any shifts of vowel cluster centroids. Thus the method seems to be both more powerful and more selective than previously proposed methods.
Hierarchies of affrication of palatalized dental stops
Authors: McCoy Priscilla
Published: October 2005

In this paper, the affrication of palatalized dental stops in Russian is presented as an ongoing sound change. The environment investigated was word initial position in disyllabic words. Three different factors were tested for their influence in this change: (1) the placement of the stress; (2) the height of the following vowel; and (3) the voicing of the dental stop. Fourteen words, five tokens of each word, were recorded by native speakers from Moscow and Leningrad. Spectrograms up to 16 kHz were measured for the highest frequency and the duration of the frication noise following the stop segments. Hierarchies were then established from data based on the average of these measurements for the two criteria. The results show that stress has an effect on the likelihood to affricate. High vowels are more conducive to affrication than low vowels, and the voiceless variant affricates before the voiced variant.
The array gain of a planar array against two-dimensionally isotropic noise fields in the plane of the array
Authors: Martin N. C. , Berkman E. F.
Published: October 2005

In certain cases of practical interest, the noise field seen by a planar array can be modeled as two-dimensionally isotropic in the plane of the array. That is, arrival angles for the noise are confined to a plane containing the array, and equal noise power arrives from all directions within the plane. Example situations include a well baffled array where the residual noise field is dominated by diffraction around the edges of the baffle and an unbaffled array near a plate where the noise field is dominated by the evanescent nearfield pressures associated with a diffuse flexural vibration field in the plate. For a separably shaded planar array, simple approximate expressions are developed to estimate the array gain for such noise fields. At very low frequencies the array reception can be dominated by main lobe response, but at higher frequencies reception is dominated by the principal axis side lobes. Computations show that array gains for such noise fields typically exceed the directivity index of the array.
Electrical determination of the electrical and acoustic mutual admittances of an array
Authors: Thompson Stephen C.
Published: October 2005

An experiment has been conducted to determine the electrical mutual admittances of a fifty-two element underwater acoustic array. In taking the data, a single element is driven with a broadband voltage signal, and the current signals in each of the fifty-two elements are measured. Using a dual-channel FFT analyzer, the mutual admittance spectrum YijE(f) is calculated as the ratio of the ith measured current spectrum to the jth drive voltage spectrum. The number of admittance spectra required was reduced to 676 by using the quadrantal symmetry of the array. These spectra were acquired in about one day by the use of a computer controlled FFT analyzer. Using the YijE(f) and the array element electroacoustic transfer matrices, it is possible to calculate the acoustic mutual admittances between the element radiating faces. These calculations are underway, and at least preliminary results will be presented.
Taylor shading conformal arrays
Authors: Miller Max K. , Futterman John A. Hardt , Lockhart Clayton M.
Published: October 2005

Sidelobe suppression for conformal arrays was analyzed using extended Taylor shading for a line array. The goal of this study was to maximize sidelobe suppression while maintaining a narrow major lobe. An array geometry defined by a quartic was used. Three types of shading techniques were applied. First, theoretical beam patterns were computed using unit amplitude weighting for the array elements, dropping “shadowed” elements. Then, Taylor shading for a line array was used. Finally, geometrical density corrected (GDC) Taylor shading for a line array [M. K. Miller and C. M. Lockhart, J. Acoust. Soc. Am. Suppl. 1 67, S81 (1980)] was used for element weights. Theoretical beam patterns were compared for several steering angles. Results show that the GDC shading technique enhances sidelobe suppression by as much as 12 dB relative to unit weighting, and by 2–3 dB relative to ordinary Taylor shading for a line array. The GDC shading technique gives best results for angles 20°–40°, relative to the apex of the quartic. [Work supported by NAVSEA 63X5B under N00024-79-C-6358.]
A scannable ultrasound transducer for producing torsional waves in metallic wires
Authors: Prout James H. , Frost Harold M.
Published: October 2005

The use of noncontracting—and thus scannable—ultrasound transducers for sending and receiving “pulsed” torsional waves along the lengths of stationary or moving wire was described in a paper presented at the 99th meeting of the Acoustical Society of America (H. M. Frost and J. H. Prout, “Velocity and attenuation measurements in metal waveguides,” Paper XII). That paper focused on measurement of attenuation-related quantities and therefore dealt only briefly with the design, construction, and testing of the transducers themselves. In this paper we describe the development of these “Lorentz force” transducers. A detailed description will be included of the coil configuration, permanent magnet structures, and the wire “guides” used to insure optimum, noncontacting alignment of the test wire within the coils and magnet polefaces. We present evidence that these transducers generate and receive the lowest order torsional wave mode. For peak electrical current amplitudes of about 500 A and pulse durations of about 1 μs, signal-to-noise levels are typically 40 dB on aluminum wire 1 mm or less in diameter, for a sender-receiver pair with a typical coil-wire cumulative gap of 0.36 mm. Excellent results have also been obtained for other types and sizes of wires including metal matrix composites. A three-transducer arrangement is described for obtaining velocity and attenuation data that are relatively insensitive to transducer-wire gap. [Work supported by the Naval Sea Systems Command SEA-62R4.]
Reaction time adaptation at lower frequencies and possible implications
Authors: Goldman Thomas , Weiler Ernest , Davis James M.
Published: October 2005

Davis and Weiler (1975) found that significant decreases in reaction time could be measured as a function of exposure to an adapting tone. Following Davis' procedure in the present study, change in reaction time for 22 normal hearing individuals was measured with a 50-dB SPL, 400-Hz test tone and a 50-dB SPL, 500-Hz adapting tone presented for seven minutes. In counterbalanced fashion, a 500-Hz test tone with a 400-Hz adapting tone was tested to determine the possibility of contrasting effects as a function of tonotopic position of the two frequencies. A significant increase in reaction time was found using the 400-Hz test tone (p < 0.01) while no significant time increase was found using the 500-Hz test condition. The significantly increased reaction time could be partially attributed to the effects of passage of the traveling wave through the 500-Hz adapted region whereas the 500-Hz test tone does not completely overlap with the 400-Hz adapting tone. The significant increase in reaction time contrasts with Eggermont's (1979) decrease in AP latency in recruiting ears.
The microstructure of quiet and masked thresholds
Authors: Long Glenis R.
Published: October 2005

Kemp [Scand. Audiol. Suppl. 9, 35–47 (1979)] showed that local maxima and minima in auditory thresholds are reflected in low level suprathreshold measurementsuch as loudness and frequency discrimination. While studying masking with tones and broad-band noise, the author found that these maxima and minima (in earphone voltage) also affect masked thresholds. As masking levels and masked thresholds increase, the threshold differences decrease until the masked thresholds reach 40–50 dB SPL where no maxima and minima can be seen. The shape of psychophysical tuning curves can also be influenced by these maxima and minima leading to curves with more than one best frequency, with a flat tip or with the best frequency displaced away from the probe to the frequency of an adjacent minimum. [Work supported by NINCDS Grant NS 03856.]
Morphological influences in speech perception
Authors: O'Connor-Dukes Kathleen D. , Nakatani Lloyd H.
Published: October 2005

We investigated the role of English morphology in the perception of nonsense phrases embedded in English sentences. Each nonsense phrase consisted of two roots and an English affix occurring either word-initially, as in “morkel proklaided”, or word-finally, as in “morkelpro klaided.” In a discrimination task, listeners indicated the order in which they heard two sentences that were identical except for the position of the affix in the nonsense phrase. In a mispronunciation task, listeners saw the text of a sentence and judged whether the utterance they heard was a good or bad production of the sentence. For half the trials the position of the affix in the text did not correspond to its position in the utterance. For example, the text contained the phrase “morkel proklaided” but listeners heard “morkelpro klaided.” On half the trials, spoken and written sentences were identical. Results from these experiments support our earlier findings [O'Connor-Dukes and L. H. Nakatani, J. Acoust. Soc. Am. Suppl 1, 66, (1979)] that listeners use their knowledge of available prefix and suffix forms when parsing nonsense phrases. The mispronunciation task raises the related question of how morphological knowledge influences speech production.
The feasibility of measurement of transport and heat flux of the Florida current by acoustic methods
Authors: Nghiem-Phu Lan , DeFerrari Harry A.
Published: October 2005

We consider the feasibility of measuring the mass transport and heat flux in the Florida current by acoustic methods. A significant fraction of the net poleward mass transport is known to pass through the Florida Straits and then contributes to the origin of the Gulf Stream. Peak currents of 4 to 5 knots across the 50 nmi span make measurements difficult with conventional oceanographic moorings. However, acoustic transmission is by Refracted Bottom-Reflected (RBR) rays, and therefore bottom-mounted sources and receivers can be used to sample the entire water column. The concept of reciprocal (two-way) transmission [Worcester, J. Acoust. Soc. Am. 62, 895–905 (1977)] allows for separation of transport and integrated temperature along a ray. The results of model studies show that the concept is feasible with existing hardware and signal-processing technique. [Work supported by ONR.]
An integral equation formulation of the impedance bottom boundary condition for the parabolic wave equation
Authors: Papadakis John S. , Lee Ding , Botseas George
Published: October 2005

A numerical algorithm dealing with the parabolic wave equation is introduced for handling the impedance formulation of the bottom boundary condition. The impedance condition for the parabolic wave equation is in the form of an integral equation along the bottom boundary and includes the characteristics of the subbottom region as: sound speed, density and absorption coefficients. This integral equation is solved numerically by an approximate sum, using finite differences. Preliminary test comparisons show good agreement with the FFP.
The effect of seamounts on SOFAR propagation: Louisville Ridge II
Authors: Guthrie K. M. , Denham R. N. , Bannister R. W. , Browning D. G.
Published: October 2005

A previous paper [R. Bannister et al., J. Acoust. Soc. Am. 55, 417 (A) (1974)] described SOFAR Propagation across a Seamount in the recently discovered Louisville Ridge to the east of New Zealand. This paper reports a more extensive follow-on experiment across two separate peaks in this chain which are located in a water depth of 5000 m. For one Seamount (490 m from the surface) rising considerably above the sound-channel axis (depth 1200 m), SOFAR Propagation from shots at both axis depth and relatively shallow depth (244 m) suffered a 20-dB drop when crossing the peak. This was independent of frequency for 13 octave bands at 63, 125, and 250 Hz. The second Seamount (1100 m from the surface) rose only marginally above the sound-channel axis. SOFAR propagation from axis-depth shots suffered a 10-dB drop independent of frequency when crossing the peak with a rapid recovery to nearly normal propagation conditions during the next 200 knots. Similar behavior was observed for the relatively shallow shots (244 m) except that the initial drop was 20 dB. Comparison is made with results obtained across the South Tasman Rise and another example where surface decoupling effects are also present.
Long range sound-pulse propagation in an underwater surface channel
Authors: Topuz E. , Felsen L. B.
Published: October 2005

Sound-pulse propagation for short horizontal ranges in an underwater surface channel can be analyzed conveniently in terms of ray acoustics. At long ranges, the multiple reflected rays from caustics pile up at receiver depths approximately equal to the source depth. When, at a particular frequency, ray caustics are separated by less than the distance between the (parallel) caustics of two adjacent normal surface modes, even the Airy function corrections for isolated ray caustics are inadequate to validate a ray-caustic calculation. It is then necessary to employ a sound-field representation either in terms of normal surface modes alone or in terms of a recently developed hybrid ray-mode expansion [L. B. Felsen and T. Ishihara, J. Acoust. Soc. Am, 65, 595–607 (1979)]. These alternatives are studied in detail for a high-frequency Gaussian pulse transmitted into a surface duct with exponentially increasing velocity profile. Special attention is given to working criteria which validate or delimit ray acoustics as the receiver at a fixed long range moves from the ocean surface to large depths through the multiple-caustic transition layer. The hybrid formulation is shown to provide an efficient correction scheme, wherein well-determined ray-mode combinations overcome the deficiencies of the ray method. [Work supported by ONR Ocean Acoustics Branch.]
An accurate numerical solution for the scattering properties of abrupt discontinuities in acoustic waveguides
Authors: Brooke Gary H.
Published: October 2005

A numerical mode-matching technique is used to accurately determine the scattering properties of abrupt discontinuities in acoustic waveguides representative of shallow-water channels under sea ice. A simple two-dimensional planar waveguide model consisting of three isovelocity fluid layers is considered. The discontinuities are formed by abrupt changes in the ice or water-layer thicknesses. It is shown that by introducing a fictitious rigid boundary in the bottom layer, the continuous spectrum is accurately represented by a small number of corresponding discrete modes. The scattering properties for various discontinuity heights over the frequency range of 10–50 Hz are presented.
The influence of sediment rigidity on interface wave excitation
Authors: Vidmar P. J.
Published: October 2005

Stoneley waves traveling along the interface between a fluid sediment and a solid substrate are a loss mechanism affecting low-frequency sound propagation in the oceans [K. E. Hawker, J. Acoust. Soc. Am. 64, 548–555 (1978); 65, 682–686 (1979)]. Here we report a study of the effect of sediment rigidity (shear wave propagation) on the excitation of Stoneley waves. A numerical model [P. J. Vidmar, T. L. Foreman, J. Acoust. Soc. Am. 66, 1830–1835 (1979)] of the plane-wave reflection coefficient, R, of the ocean bottom was used to study the effects of a finite sediment shear speed, Cs, and attenuation on the characteristic Stoneley wave peak in the bottom reflection loss, RL = -20 log 10 (|R|). For a 100-m-thick sediment layer with a shear wave attenuation of 15 dB/m/kHz, shear speeds of 100, 200, and 400 m/s were investigated. At 25, Hz Cs = 0 (fluid sediment) had the expected peak in RL; Cs = 100 m/s increased the height of the peak; Cs = 200 ms broadened the peak and shifted it to a higher grazing angle; and at Cs = 400 m/s (a reasonable value for Cs at the substrate interface) the peak is no longer visible in the generally increased RL. Frequencies of 50 and 100 Hz were also investigated. These results show that sediment rigidity greatly modifies the Stoneley wave-loss process. [This work was sponsored by Naval Electronic Systems Command and Naval Ocean Research and Development Activity.]
Effects of turbulence on the attenuation of noise by barriers
Authors: Daigle G. A. , Embleton T. F. W. , Piercy J. E.
Published: October 2005

Although atmospheric turbulence influences many aspects of sound propagation outdoors, its effects have not previously been considered when predicting the attenuation of sound by barriers. We have measured traffic noise attenuated by a barrier alongside a highway with microphones positioned above an asphalt surface 15 and 30 m behind the barrier. The sound levels were analyzed to obtain the average sound levels per 13-octave band. To obtain a better test of the influence of turbulence on diffraction an idealised experiment was also performed. A barrier 2.5 m high and 17 m long was erected on a flat asphalt surface. Sound levels from a point source were measured for various source and receiver positions. The two series of measurements are compared with simple diffraction theory currently used and show that sound levels behind the barrier are often greater than predicted at higher frequencies. [Work supported by NSERC grant to Carleton University.]
A comprehensive model for the straight-edge noise barrier: Theory and experiment
Authors: Nobile M. A. , Hayek S. I. , Lawther J. M.
Published: October 2005

A mathematical model has been developed which describes the acoustic diffraction from a point source to a point receiver over a straight edge located on an impedance-covered ground plane. Appropriate frequency summations and integrations over an incoherent line of point sources yield values of excess attenuation that may be expected from real-world highway noise barriers with car or truck traffic flow. The model accounts for such factors as the ground reflections (“ground effects”) on both sides of the barrier, arbitrary impedance cover on each face of the barrier, “tilt angles” for the barrier itself, transmission loss through the barrier, as well as the double-diffraction effect due to a ground-plane impedance discontinuity on the source side of the barrier. This paper addresses the rigid perpendicular barrier on various ground surfaces and compares the predictions to 15-scale model experimental results. [Work supported by FHWA.]
Digital noise correction
Authors: Long Marshall
Published: October 2005

By subtracting the internal noise produced by the preamplifier and amplifier the noise threshold of a digital sound level meter may be considerably improved. Side-by-side measurements using a GenRad 1962-9610 12-in. electret microphone and 1972-9600 preamplifier with a Digital Acoustics DA 607 P V.03 Environmental Noise Monitor and a B&K 4145 1-in. condenser microphone with a B&K 2209 Precision Sound Level Meter indicate a 19-dB improvement in the noise floor of the Digital Acoustics device with digital correction. The noise threshold achieved was on the order of 13 dBA.
Noise masking as a factor in fatal accidents involving railroad trains and pedestrians
Authors: Lane Sam R.
Published: October 2005

During the past five years, there have been several newspaper accounts in the Los Angeles area of children, adults, and dogs who were killed by trains while walking on railroad tracks. One question that immediately arises is—“Why didn't the victim(s) hear the train and warning signals. and move out of the way?” In a preliminary study, the circumstances of a few of these accidents were examined to determine if poor hearing or deafness was involved, and the accident sites were visited to investigate the possibility of masking by local nonrailroad sources as a contributing factor.
Aural discrimination of target echoes in white noise by human observers using broadband sonar pulses
Authors: Martin Douglas W. , Au Whitlow W. L.
Published: October 2005

Sonar echo-discrimination performances were measured as a function of S/N with three human observers. Targets included hollow cylinders of aluminum and glass having diameters of 3.81 and 7.62 cm, and a solid 7.62-cm aluminum cylinder. The subjects were required to discriminate between the 7.62-cm solid and hollow aluminum cylinders, and between the hollow aluminum and glass cylinders. Digital recordings of target echoes were obtained using dolphin-like echolocation signals, and played back to the subjects at 150 of the original sample rate. The slope of the psychometric function for the solid-hollow discrimination was approximately 2.2% correct/dB, and between 0.7 and 1.3% correct/dB for the hollow aluminum-glass discrimination. The average 75% correct response threshold occurred at a S/N of 22 dB for the solid-hollow discrimination, and at 42 dB for the 7.62-cm hollow aluminum-glass discrimination. The S/N for 75% detection of the 7.62-cm hollow aluminum cylinder was 11 dB for one of the subjects, indicating that the above discriminations required considerably higher S/N than detection.
Predicting effects of spectral shaping on speech recognition of hearing-impaired listeners
Authors: Kamm Candace A. , Dirks Donald D. , Carterette Edward C.
Published: October 2005

The effects of spectral modification on speech recognition were investigated for sensorineural listeners: One group with flat audiometric configuration and a second group with sharply-sloping high-frequency hearing loss. Three spectral shapes were tested: Uniform frequency gain, high-pass filtering, and a response shaped relative to loudness discomfort levels. Performance-intensity functions were measured at four levels (from 80–95 dB SPL) using the CUNY Nonsense Syllable Test (NST) and the Synthetic Sentence Identification task (SSI), both presented monaurally under earphones against a background of multitalker babble. No significant differences in performance on the NST were observed between the two subject groups across all spectral shapes and presentation levels. On the SSI, performance of subjects with flat audiometric configuration was highest using the uniform frequency response, while performance of listeners with sloping hearing loss was poorest for the uniform spectral shape. The recognition data were compared with predictions of relative performance using a modification of the Articulation Index. The AI provided accurate estimates of relative performance across spectral shapes, but were not consistent with relative performance as a function of presentation level. [Work supported by NIH.]
Development of a model for generating synthetic animated lip shapes
Authors: Montgomery Allen A.
Published: October 2005

Progress is reported on a project aimed at developing the capability to synthesize realistic animations of the visible aspects of speech for the purpose of studying lip reading. An intelligent graphics system's CRT is programmed to display animated images through presenting sequences of static lip shapes. Previously it had been demonstrated that hand-copied, frame-by-frame tracings of talkers on videotape were intelligible to lip readers when redisplayed as sequences of 130-vector frames at 30 fps, and further that linear interpolation between initial and final tracings produced smoother and equally intelligible stimuli. The current model for synthesizing CVCVC stimuli from a limited set of primative shapes is described, and includes an approximation to forward and backward coarticulation and nonlinear interpolation between derived shapes. The results of lip-reading intelligibility testing are presented, the strengths and weaknesses of the model are discussed and comparisons to other possible generation stratatgies are made. [Work-supported by Clinical Investigation Service, WRAMC.]
Extraction of spectral pitch information from auditory patterns as a function of pattern duration
Authors: Gilliom J. D. , Wollverton V. , Wall S. M.
Published: October 2005

The ability to extract specific pitch information from one tone part of a musical chord might reasonably be expected to depend on the duration of that chord. The purpose of the current study was to explore this relationship. The observer was required to perform a mortaural detection task where the frequency of a signal event was randomly varied from trial to trial. On each trial, a cue matching the frequency of the signal event was presented in the contralateral earphone channel prior to the detection interval. Previous studies in this series have established the observer's ability to use the pitch information from this cue to reinstate detection performance to normal levels. In this study, two variables were manipulated. The first variable was (1) whether the duration of the cue was randomly varied across trims or (2) whether cue duration was varied across blocks of trials but fixed in duration within a block. The second variable was whether the cue was one tone part of a three-element musical chord or presented alone. A comparison of performance in the resulting four experimental conditions suggests that pitch extraction from auditory patterns is most demanding for pattern durations under 100 ms. However, if an observer knows what pattern duration to expect, extraction of relevant pitch information from the embedded cue can reach the levels realized with the cue presented in isolation, even for short pattern durations.
Played-again SAM
Authors: Burns Edwards M. , Garton Bradford , Viemeister Neal F.
Published: October 2005

The weak pitch-like sensation elicited by sinusoidally amplitude-modulated (SAM) wideband noise remains a controversial phenomenon. The controversy centers on two major points: (1) whether this sensation is “really” pitch rather than, e.g., roughness or intermittency, and (2) the possibility that any pitch sensation is mediated by short-term spectral information rather than temporal information—thus nullifying the interesting aspect of the phenomenon. We will report on the results of a number of studies employing SAM wideband noise, SAM wideband noise bandpass-filtered after modulation, and a SAM 10-kHz pure tone, including: Open-set melody identification, melodic dictation, and musical-interval adjustment. These experiments extend our earlier study [Burns and Viemeister, J. Acoust. Soc. Am. 60, 863 (1976)]. The results provide further evidence that SAM wideband noise can, at suitable modulation frequencies, elicit a sensation of pitch (as defined by the ability to carry melodic information) and that this pitch represents a purely temporal phenomenon. [Research supported by NINCDS.]
Effects of signal phase on the detection of tonal signals in the presence of repeatable noise maskers
Authors: Gilkey R. H. , Hanna T. E. , Robinson D. E.
Published: October 2005

Detection of a 500-Hz tonal signal masked by 25 samples of reproducible Gaussian noise was investigated. The starting-phase angle of the signal was varied systematically. For diotic (N0S0) presentations and fixed signal phase, large differences in hit and false-alarm rates were found across samples. The false-alarm rates for individual samples remained relatively constant when the starting phase of the signal was varied. Hit rates for individual samples were found to be a cyclic function of the signal phase. Although the magnitude of this effect varies across samples, in some cases the hit rate changes from near zero to near unity when the signal phase is shifted by 180°. These changes in hit rate correlate well with changes in the stimulus energy near Ire signal frequency. However, similar spectral analyses have thus far proven unsuccessful in predicting false alarm rates. These diotic results will be compared to results obtained under equivalent dichotic (NOS π) conditions. The importance of these results for various models of monaural and binaural detection will be discussed.
Lateralization of click trains having opposing interaural differences of time for the initial and succeeding clicks
Authors: Wenzel Elizabeth M. , Dye Raymond H.
Published: October 2005

Subjects lateralized trains of dichotic clicks presented in a configuration where the interaural difference of time contained in the first dichotic pair (IDT1) was in opposition to the differences of time in the remaining clicks (IDTR). The clicks were bandpass filtered at 5 kHz and presented at a rate of 200 Hz. The number of clicks in the trains was 2, 4, 8, or 16. The percentage of responses consistent with IDT [P(c)ONSET] was plotted as a function of IDTR for IDT1 = 100, 200, and 400 μs. As IDTR was increased to approximately 400 μs, the P(c)ONSET fell to some minimum dependent upon the value of IDT1. As IDTR was increased further, P(c)ONSET rose again until it reached a level equivalent to that achieved with IDTR = 0. With longer click trains (8 and 16) the minimum P(c)ONSET reached 0, often for several values of IDTR. These functions can be thought of as mapping out the salience of onset cues as the ongoing information is strengthened, either by increasing the size of IDTR or adding additional samples.