bluuebunny/crossref_metadata_2025 huggingface dataset:
Laryngeal activity in Swedish obstruent clusters
Authors: Löfqvist Anders , Yoshioka Hirohide
Published: October 2005

Laryngeal articulatory movements and their coordination with supralaryngeal events have proved to be important for control of voicing and pre- and post-aspiration in obstruents. A reciprocal pattern of activity generally has been observed among laryngeal abductor and adductor muscles in the control of glottal opening in voiceless obstruent production. Current notions about laryngeal articulatory control rest, however, mainly on studies using simple linguistic materials, where voiced and unvoiced segments alternate in a regular manner. The present study examines laryngeal activity in voiceless obstruent clusters using the combined techniques of electromyography, fiberoptic filming, and transillumination of the larynx. The results indicate that laryngeal articulatory movements are precisely coordinated with the oral articulations of clusters to meet the aerodynamic requirements of speech production. Several laryngeal movements may occur in a cluster. Comparison of temporal patterns of glottal area variations obtained by fiberoptic filming and by transillumination of the larynx, showed them to be practically identical.
Effect of element failure and random errors in amplitude and phase on the sidelobe level attainable with a linear array
Authors: Ramsdale Dan J. , Howerton Roger A.
Published: October 2005

In experiments with linear arrays at sea, one frequently operates with an array which has not only errors in amplitude and phase between channels but also inoperative elements. Previous calculations have shown that in the presence of random errors in amplitude and phase, the sidelobe level of the mean beam pattern is the sum of that of the error-free pattern plus an angle-independent background level due to the random errors. If the time constant of the random process is much larger than the integration time of the beamformer (as is most often the case), then a more relevant statistic is the mean value of the peak sidelobe due to a single realization of the random process. Our numerical calculations show that this value can be substantially larger (approximately 6 dB) than the peak sidelobe of the mean beam pattern. When the error-related sidelobes are predominant, appreciably greater sidelobe suppression cannot be achieved by using a set of amplitude weights which yield an error-free sidelobe level less than that of the error-related level. Element failure also produces an elevated sidelobe level whose peak value can be estimated and in many cases bounded above by the ratio of the sum of the amplitude weights of the faulty elements to the sum of the amplitude weights of the functioning elements. This ratio is nearly linearly related to the rms amplitude and phase errors in the way in which each affects the peak sidelobe level. This allows one to construct a characteristic curve for the peak sidelobe level in the presence of all these degrading factors, given an array of N elements and a set of amplitude weights. Processing techniques are available which may allow one to regain the sidelobe suppression lost due to inoperative elements. Among such techniques are algorithms for adjusting the amplitude weights, cross-sensor beamforming, subaperture processing and a procedure for estimating the signal at inoperative elements by using those from neighboring elements.
Transfer function method of measuring in-duct acoustic properties. I. Theory
Authors: Chung J. Y. , Blaser D. A.
Published: October 2005

The theory of a transfer function method of measuring normal incident in-duct acoustic properties is presented. In this method, a broadband stationary random acoustic wave in a tube is mathematically decomposed into its incident and reflected components using a simple transfer-function relation between the acoustic pressure at two locations on the tube wall. The wave decomposition leads to the determination of the complex reflection coefficient from which the complex acoustic impedance and the sound absorption coefficient of a material and the transmission loss of a silencer element can be determined. Also presented are the theories of two techniques for improving transfer function estimates: a sensor-switching technique for automatic system calibration and a coherence function technique for signal enhancement.
Low-frequency wind-generated noise produced by the impact of spray with the ocean’s surface
Authors: Wilson James H.
Published: October 2005

Ambient noise measurements for frequencies from 50 to 1000 Hz indicate that wind-generated noise is a significant source of the total ambient noise field during high-wind/sea-state conditions. The acoustic source spectrum levels for the physical mechanism involving the impact of water droplets from ocean spray, streaks, and white caps were derived as a function of wind speed. An empirical approach using the results of Franz and measurements of Morris were used in this analysis. A full analytical derivation of the wind-generated source level using Franz’s results was not possible because knowlege of certain parameters such as size and impact velocity of ocean spray as a function of wind speed is currently unknown. Recent measurements of the ’’white capping index’’ as a function of wind speed were used in conjunction with Morris measurements and Franz’s results to derive the source spectrum levels for wind-generated noise in this frequency interval. The acoustic noise from bubble oscillation in white caps was not addressed in detail in this paper since bubble size distributions and the results of Strasberg indicate that this source is significant only above 1000 Hz. Rain noise was also not included in this paper because knowledge of raindrop size distribution as a function of wind speed and geographical extent of rain within the storm area is currently not known or predictable enough to model. The wind-generated source levels from 5 to 50 Hz from a previous analysis by the author were combined with the results of this paper to yield an estimate of wind-generated source spectrum levels as a function of wind speed for 5 to 1000 Hz. A definite change of wind-speed dependence from 5- to 50-Hz interval to the 150- to 1000-Hz interval is predicted by these results since the dominant physical mechanisms are different in these two intervals. Noise measurements by Perrone, Piggott, and Morris seem to substantiate this prediction, but more measurements are needed to prove this conclusively.
Resonating fields inside elastic scattering objects
Authors: Flax L. , Raju P. K. , George J. , Überall H.
Published: October 2005

The resonance theory of acoustic scattering from elastic objects predicts the field exterior to the scattering object to consist of resonance terms, superimposed on a nonresonant background which corresponds to the scattering amplitude for an impenetrable object. In contrast, the interior field is predicted to consist of resonant amplitudes only, so that a substantial amount of penetration of the incident field into the scatterer occurs only at and near the resonance frequencies of the body. We have made quantitative numerical studies of the interior fields in glass cylinders imbedded in water, and subject to incident acoustic fields from far distant or nearby line sources. The results are compared to, and agree with, experimentally measured fields inside glass cylinders as visualized by the method of optic-elastic birefringence. The study of resonances in the separate partial wave amplitudes will additionally lead to the interpretation of resonances in terms of circumferential waves, whose dispersion curves are obtained here as a function of the Poisson ratio of the cylinder.
Acoustic scattering and transmission of wide-band plane waves by fluid loaded plates
Authors: Stepanishen Peter , Guigli John
Published: October 2005

Acoustic scattering and transmission of wide-band plane waves by fluid loaded plates is addressed using Timoshenko–Mindlin plate theory. The solution for the case of an impulsive excitation is first developed via the use of a double Fourier transform method. This solution is then used to develop the solutions for the scattered and transmitted fields corresponding to an arbitrary pulsed excitation via convolution integral relationships. The characteristics of the impulsive solutions are investigated as a function of incident angle. Precursors, which are due to the dispersive nature of flexural waves in the plate, are noted to occur in certain angular ranges. The nature of the precursors, and hence the impulse responses, are discussed.
Comments on ’’Application of the Fourier series method to the detection and localization of signals embedded in a noise background [J. Acoust. Soc. Am. 64, 1064–1069 (1978)]
Authors: Cooper W. W.
Published: October 2005

Several claims given in the above-cited paper are discussed and found to be incorrect.
The design of Tonpilz piezoelectric transducers using nonlinear goal programming
Authors: McCammon Diana F. , Thompson William
Published: October 2005

The design of Tonpilz piezoelectric transducers often involves the satisfaction of multiple, conflicting design specifications. To arrive at an optimal compromise solution to a specific design formulation, nonlinear goal programming techniques can be applied. For this optimization technique, a mathematical model of the transducer and its associated housing is constructed and the values of the desired transducer responses and attributes—the design objectives—are computed. The nonlinear goal programming formulation minimizes the differences between the objectives and their specifications. The use of priorities and weights in this minimization process is the key to the great utility of the technique. An example of the application of nonlinear goal programming in a simple hypothetical transducer design is presented to demonstrate the value of the optimal compromise approach for this or more complex systems.
On the anatomy of the retard: A study of timing in music
Authors: Sundberg Johan , Verrillo Violet
Published: October 2005

The timing of the last tones constituting the final retard is studied in performances of motor music, i.e., music dominated by long sequences of short and equal note values frequently accompanied by similar series of twice as long note values. The results suggest that the retard length is related to the length of the final cadence and that the retards are divided into two phases, the first of which is variable while the second is more regular; its length and decrease in tempo depends on the length of the last conceptual unit (motive) of the piece and, as regards the decrease in tempo, also the preretard mean tempo, with which the piece is played. The same preretard mean tempo also determines the duration of the note preceding the final chord. These observations are expressed in a set of equations by means of which retards are computed for a set of compositions. The musical quality of such rule generated retards is assessed by a jury of experienced musicians and music listeners.
Asymmetric Doppler amplitudes in the surface scatter channel for crosswind transmitter–receiver geometry
Authors: Tuteur F. B. , Tung H. , Zornig J. G.
Published: October 2005

Doppler asymmetries have been observed in model tank experiments in the signal received after being scattered from a wind-driven surface. A distinct spectral shift was observed when the plane containing the transmitter and receiver was perpendicular to the wind direction. This paper examines the conjecture that this shift arises from the fundamental asymmetry observed in a wind-driven surface, i.e., from the fact that the upwind slopes tend to be shallower than the downwind slopes. Three different situations are considered: (1) a deterministic surface, (2) a random surface with large Rayleigh parameter, (3) a random surface with small Rayleigh parameter. All three models show that the slope asymmetry results in Doppler asymmetry; however, the amount of this asymmetry corresponding to realistic values of surface parameters is very small. Hence the slope asymmetry does not completely explain the occasionally observed larger spectral shifts, and other mechanisms must be considered.
On source radiation
Authors: Levine Harold
Published: October 2005

The power output from given sources is usually ascertained via an energy flux integral over the normal directions to a remote (farfield) surface; an alternative procedure, which utilizes an integral that specifies the direct rate of working by the source on the resultant field, is described and illustrated for both point and continuous source distributions. A comparison between the respective procedures is made in the analysis of sound radiated from a periodic dipole source whose axis rotates in a plane, on a full or partial angular range, with prescribed frequency. Thus, adopting a conventional approach, Sretenskii [Sov. Phys. Acoust. 2, 89(1956)] characterizes the rotating dipole in terms of an infinite number of stationary ones along a pair of orthogonal directions in the plane and, through the farfield representation of the latter, arrives at a series development for the instantaneous radiated power, whereas the local manner of power calculation dispenses with the equivalent infinite aggregate of sources and yields a compact analytical result.
Influence of direct sound on the fluctuations of the room spectral response
Authors: Ebeling K. J.
Published: October 2005

Fluctuations of the room spectral response are theoretically studied taking direct sound into consideration. An exact, simple, analytical formula is derived which describes the dependence of the intensity fluctuations upon the direct-to-reverberant acoustic energy ratio. In much the same way an exact integral representation is obtained for the fluctuations of the sound intensity level (measured in decibels). The derived relations are useful for determining reverberation distances.
Directional characteristics of the acoustic receiver of the leopard frog (R
a
n
a p
i
p
i
e
n
s): A study of eighth nerve auditory responses
Authors: Feng Albert S.
Published: October 2005

The directional characteristics of the peripheral auditory system were assessed from studying the effects of sound direction on the responses of single auditory fibers in the eighth nerve of leopard frogs (Rana pipiens). Two types of directional response characteristics were observed which are correlated with the best excitatory frequency of the afferent fiber. Low-frequency sensitive neurons possessed V-shaped directional-response curves with a null at the frontal sound field. High-frequency sensitive neurons, on the other hand, showed a strong response to sound coming from the ipsilateral field with a progressively weaker response as the sound source was rotated to the frontal and contralateral field. Two directional cues were revealed: pressure variation at the eardrum and the directionality of the acoustic receiver system. The relative weight contributed by each factor also varies with frequency.
The relationship between spike rate and synchrony in responses of auditory-nerve fibers to single tones
Authors: Johnson Don H.
Published: October 2005

Discharge patterns of single auditory-nerve fibers in the cat responding to single tones were recorded and analyzed. Synchronization of the discharges to the stimulus tone was measured for frequencies below 6-kHz. The synchronized response and the average discharge rate each varied with stimulus level over 20–30-dB ranges. However, these ranges overlapped only over a 10-dB range. Under certain conditions the average rate of response varied without accompanying variation in the synchronized response. The physiological implications of these observations are discussed.
The air gun impulsive underwater transducer
Authors: Barger James E. , Hamblen William R.
Published: October 2005

We are reporting our experience with the use of high-pressure guns at many depths to generate impulsive underwater sound in the fundamental frequency range from 10 to 200 Hz. Air guns are not often used outside of seismic exploration, but they have potential as cheap, energetic, impulsive sources of low-frequency sound. A simple analysis shows that the fundamental frequency of waveforms increases faster with increasing depth than predicted by the Rayleigh–Willis equation. In addition, the acoustical efficiency of air gun sources is found to decrease with increasing depth, falling sharply as the ambient pressure becomes a significant fraction of the initial gun pressure. Experimental waveform and energy source level data verify these analytical results. Finally, data obtained from arrays of air guns are presented. These data demonstrate that air guns may be successfully arrayed and that the internal impedance of the air gun source is high enough that each air gun resembles a constant source strength (volume velocity) source, resulting in more radiated energy than expected from constant energy sources for some spacings.
Optical interferometric visualization and computerized reconstruction of ultrasonic fields
Authors: Higgins F. P. , Norton S. J. , Linzer M.
Published: October 2005

A unique scanning Michelson interferometric system has been implemented with decided advantages over previous schemes for accurate measurement of the complex components of ultrasonic fields over wide apertures. Amplitude and phase information from transducers and scattering objects was acquired over 100 mm×100 mm planes using both narrowband (gated cw) and wideband (pulse) insonification. Ultrasonic wavefronts at other planes and reconstructions of the test objects were computed by means of a fast Fourier transform technique based on the angular spectrum of plane-waves approach. A critical review of wavefront reconstruction methods was also carried out.
Porpoise echo-recognition: An analysis of controlling target characteristics
Authors: Hammer Clifford E. , Au Whitlow W. L.
Published: October 2005

A baseline-probe technique was used to investigate target echo recognition by an echolocating Atlantic bottlenose porpoise (Tursiops truncatus). Baseline performance was established using a two-alternative, forced-choice method, with two hollow aluminum and two coral rock cylinders (standard targets) presented successively in a random sequence. After a near errorless performance was achieved with the standard targets, probe targets were used to investigate the animal’s target echo recognition capability. The probe target results suggested that the animal learned to recognize the characteristics of echoes from the aluminum standards and differentiated other targets on that basis. All of the targets were subsequently examined by using a broadband porpoise-like acoustic signal. Analysis of the echoes suggested a strong correlation between the behavioral results and measured characteristics of the envelopes of the matched filter responses to the echoes.
The directional nature of attenuation of sound due to scattering at a rough ocean surface
Authors: Chapman D. M. F.
Published: October 2005

The coherent component of sound propagating in a shallow water acoustic environment suffers attenuation with range due to the irreversible scattering of energy into the incoherent component by a rough ocean surface. Using a ’’frozen surface’’ approximation, the relevant description of the surface roughness for this problem is the Fourier transform of the spatial autocorrelation of the surface, which is the symmetric part of the wave spectra reported in the literature. The attenuation coefficients of the normal modes are calculated using a boundary perturbation method, and the directional dependence of these are deduced analytically from the anisotropy of the surface wave spectrum. An anisotropy of the form cos2φ gives a directional dependence of the form an+bn cos2ϑ for the nth normal mode. The parameters an and bn are calculated from the radial portion of the spectrum, and from the eigenfunction and eigenvalue of the normal mode. The direction of propagation ϑ of the acoustic wave is measured from the wind direction. Calculations are performed for a Pekeris model of the ocean acoustic environment.
Propagation of sound above a porous half-space
Authors: Attenborough Keith , Hayek Sabih I. , Lawther James M.
Published: October 2005

An exact solution for the field due to a point source above a homogeneous and isotropic porous ground has been derived in terms of a single branch line integral and a pole residue. The expected properties of the porous ground lead to a less complex solution than that usual to geophysics or underwater acoustics. The method of steepest descents modified by subtraction of the pole enables the derivation of an approximate solution for an externally reacting boundary. The precise nature of the further approximations that follow the assumption of a locally reacting (or impedance) boundary is made explicit and the role of the surface wave pole is clarified. Finally, the existing solutions for a locally reacting boundary are compared, and with one exception they are shown to be identical.
Time dependency of whole-body vibration discomfort
Authors: Griffin Michael J. , Whitham Eleri M.
Published: October 2005

The current International Standard (ISO 2631, 1978) on whole-body vibration defines a complex relation between discomfort and duration of vibration exposure. There are doubts concerning the accuracy of this relation and there are difficulties and dangers in its application to some non-steady-state conditions. This paper compares the ISO time-dependency with those based on root mean square (rms) and root mean quad (rmq) averaging of levels over time. [The rmq averaging procedure is based on experimental studies reported by Griffin and Whitham (1980) J. Acoust. Soc. Am. 68, 1277–1284.] It is shown that although the rmq procedure was developed from studies involving only short duration vibration, it defines a time dependency which may be acceptable for much longer periods.
A two-hydrophone method of eliminating the effects of nonacoustic noise interference in measurements of infrasonic ambient noise levels
Authors: Buck Beaumont M. , Greene Charles R.
Published: October 2005

Water flow around hydrophones and their cables can induce turbulence, flutter, and bounce noises that interfere with measurements of ambient noise at frequencies of 10 Hz or less. Assuming these noises to be uncorrelated at independently suspended hydrophones and with the ocean ambient noise of interest, it is possible to remove their influence from the result of the ambient noise measurement. Two hydrophones can be suspended independently but closely compared to the wavelength of interest, thereby assuring that the ambient noise is highly correlated. The desired ambient noise level will then be given by the covariance of the two hydrophone signals.
Acoustic environment of the Hatteras and Nares Abyssal Plains, western North Atlantic Ocean, determined from velocities and physical properties of sediment cores
Authors: Tucholke Brian E.
Published: October 2005

Seventeen piston cores up to 13 m long were recovered from representative acoustic and lithologic environments of the Hatteras and Nares Abyssal Plains in the western North Atlantic. Compressional-wave velocities (corrected to in situ conditions) and bulk physical properties measured on the cores are used to characterize the acoustic framework of these areas. For correlation with conventional seismic data, whole-core averages of properties are a better index to the acoustic nature of abyssal plain sediments than properties of the upper few centimeters of the seafloor because (1) strong changes in lithofacies (and acoustic properties) occur over depth scales of tens of centimeters to meters in the sediment column, and (2) conventional seismic frequencies of 3.5 kHz or less sample these variations to subbottom depths of tens of meters and more. Whole-core properties are a function of the thickness and distribution of high-velocity silt and sand layers in the core; they vary in a complex fashion with proximity to the source of turbidity currents, distance from axial paths of turbidity-current flows, local and regional basin geometry, and seafloor slope. Thus strongly reflective seabed regions with numerous high-velocity layers are not restricted simply to near-source areas nor are weakly reflective seabed regions (clay sediments only) limited to ’’distal’’ areas. Whole-core properties show a good qualitative correlation to variations in 3.5-kHz reflection profiles, and 3.5-kHz echo character therefore provides a useful means of mapping general acoustic properties over large regions of abyssal plains.
Acoustic attributes of preadolescent voices
Authors: Hasek Carol S. , Singh Sadanand , Murry Thomas
Published: October 2005

The purpose of this study was to investigate acoustic attributes of the voices of preadolescent children as a function of sex and age. Voice samples of the sustained vowel /a/ were obtained from 180 children, 15 males and 15 females at ages five, six, seven, eight, nine, and ten years. Measurement of fundamental frequency was obtained to determine sex-related differences and age-related trends. This acoustic analysis revealed that a male/female difference in fundamental frequency emerged by age seven, and that fundamental frequency decreased significantly in male children only, between age five and age ten.
Wave propagation in a duct with boundary scattering (with application to a surface duct)
Authors: Bucker Homer P.
Published: October 2005

Scattering integrals are derived that represent the contribution of boundary scattering in a sound channel. These integrals are added to the normal mode sum which represents the coherent field in the channel. A comparison is made between experimental and calculated sound levels in a surface duct. For the case examined, it is clear that (except for short ranges) surface scattered energy is a significant source of sound at a below duct receiver.
Wave motion generated by a time-harmonic buried line force in a solid with a stress-free, periodic boundary
Authors: Fokkema J. T. , van den Berg P. M.
Published: October 2005

The wave motion generated by a time-harmonic buried line force in a solid with a stress-free, periodic surface is investigated. The problem is formulated in terms of a spectral type of representation for the total particle displacement on the boundary. Numerical results are presented for the sinusoidal boundary. The computations have been carried out for four different heights of the periodic profile (the plane boundary included), a single value of the Poisson ratio, a single frequency of operation, two different orientations of the line force and two different locations of it.
Sound radiation from a finite length unflanged circular duct with uniform axial flow. I. Theoretical analysis
Authors: Johnston G. W. , Ogimoto K.
Published: October 2005

An analysis has been carried out to evaluate the sound radiation from a finite length unflanged, hard walled circular duct with uniform axial flow, both inside and outside the duct, using the Wiener–Hopf technique (in particular, Jones’ method). The theory developed includes many of the earlier results for the semi-infinite length duct carried out by other authors, in particular, Lansing, Carrier, and Vajnstejn, in the appropriate limit. The acoustic model employed simulates the noise radiation from a turbojet aircraft engine, in flight, at low to medium specific thrust levels such as landing or steady cruise flight. It therefore includes the diffraction of sound at both duct ends and the mean convection of sound by the axial duct and external flow fields. However, the refraction effects due to nonuniform exterior flow fields which are encountered near the inlet and exhaust under conditions of high thrust (i.e., takeoff) are excluded. This study is presented in two parts. The first part deals with the theoretical development of the model utilizing the Wiener–Hopf techniques. The second part presents some computed radiation characteristics for typical duct configurations.
Psychophysical tuning curves in the parakeet: A comparison between simultaneous and forward masking procedures
Authors: Kuhn Angelika , Saunders James C.
Published: October 2005

Forward and simultaneous masking were used to measure psychophysical tuning curves (PTCs) in four parakeets at three probe frequencies. The sharpness of tuning varied drastically with procedure; the forward masking curves had Q10-dB values that were more than double those obtained from the simultaneous masking procedure. Generally, the PTCs from both methods remained fairly symmetrical on the high- and low-frequency side of the probe signal. The results are discussed with respect to two-tone suppression and pitch discrimination cues.
How to choose a square root in calculating the reflection coefficient for a lossy liquid–lossless isotropic solid interface
Authors: Claeys J. M. , Leroy O.
Published: October 2005

To calculate the reflection coefficient for an ultrasonic wave at a lossy liquid–lossless solid interface, we need a uniquely defined square root. This is made possible by noting that the wave is not absorbed in the direction of propagation into the solid. Using this right square root, we find a reflection coefficient which is always smaller than unity.
Interaural time differences: Implications regarding the neurophysiology of sound localization
Authors: Roth G. Linn , Kochhar Ravindra K. , Hind Joseph E.
Published: October 2005

Interaural time differences (ITDs) were measured from 400–7000 Hz on cats in order to provide quantitative data for use in physiological/behavioral studies on sound localization. ITDs derived from clicks and the initial portion of tone bursts showed a pronounced roughness and frequency dependence. This frequency dependence is most evident at higher angles of incidence and indicates that a single ITD will not always represent a single position on the azimuth. Controls demonstrate that most of the roughness in these functions was due to reflections off the surface supporting the animal and that the measured ITDs corresponded to predictions made by steady-state theory. Measurements made with and without the pinnae in position indicate that they have relatively little effect on these ITD functions, particularly for frequencies below 2500 Hz and for small angles of incidence. In spite of acoustic limitations exemplified by the roughness and frequency dependence of these functions, ITDs generated by sound sources situated close to the midline provide reliable localization cues that are much better than those derived from sources well out on the azimuth. Finally it is noted that another ITD, the group ITD, can be ascribed to an acoustic signal. Calculations based on the measured steady-state ITDs show differences between the group and steady-state ITDs over a given range of frequencies. Differences between the group and steady-state ITD can be significant, and it is argued that: (1) the group ITD can provide a localization cue to the auditory system that is distinct from the steady-state ITD; and (2) it is possible these group ITDs are used by the nervous system to localize sound sources in realistic situations.
A multi-parametric study of impact noise-induced TTS
Authors: Trémolières Claude , Hétu Raymond
Published: October 2005

A series of three experiments with 15 normal-hearing listeners measured temporary threshold shifts (TTS) as a function of various parameters of impact noise exposure. A criterion of 15 dB TTS at 4, 6, and 8 kHz, measured 3 min after exposure was adopted. Results indicated that; (1) the growth of TTS is a power function of the peak level of impact noises, (2) recovery from TTS appears to proceed linearly with the logarithm of the time in quiet, (3) the amounts of TTS3 are exponentially related to the logarithm of the decay time (or e duration: te) of the impact sound pressure envelope, (4) with constant total amounts of energy and a constant repetition rate, increasing the number from 60 to 1000 increases the final amount of TTS; the derived trading relationship involves a 12.7-dB level change for a tenfold change in the number of impacts, (5) repetition rates ranging between 0.5 and 1 pps (pulse per second) are the most harmful to hearing and, (6) daily exposure to 100 impacts (te: 200 ms; repetition rate: 0.5 pps) should be limited to a 130-dB peak level, in order to protect 90% of the exposed people. Results are discussed in terms of the possible use of the equivalent continuous noise level as an index in setting safe limits of occupational impact noise exposure.
On using pressure and pressure gradient sensor pairs in linear acoustic arrays
Authors: MacPhie Robert H.
Published: October 2005

This paper investigates the mapping capabilities of a linear receiving array of acoustic sensor pairs that measure both the pressure and pressure gradient along the array axis. It is demonstrated that unambiguous pressure maps of remote sources can be obtained even if the separation between sensor pairs is one wavelength (twice the spatial Nyquist sampling interval). The effect of additive noise—both correlated and uncorrelated at each sensor pair, but uncorrelated between sensor pairs, is studied and found not to be a major problem. In the second half of the paper an analysis of the cross correlations of the output voltages from the various sensor pairs reveals that each pair provides three distinct cross correlations. Accordingly from data obtained from an array with sensor pairs spaced three half-wavelengths apart an unambiguous map of the source intensity distribution can be formed. Examples of such maps are provided.
Task variables in the study of vowel perception
Authors: Strange Winifred , Gottfried Terry L.
Published: October 2005

Vowels produced in isolation by six speakers were identified less accurately than vowels coarticulated in /k/-vowel-/k/ syllables, whether tested by a key word task or by a rhyming task. Performance by naive listeners in the two tasks was highly correlated.
Noise-equivalent pressure of a single-fiber interferometric acoustic sensor
Authors: Stanton T. K.
Published: October 2005

An expression has been derived for the limiting noise-equivalent pressure of a single-fiber optical hydrophone. The expression is compared to that of the two-beam optical hydrophone. It is shown that under similar conditions, the noise-equivalent pressure of the single-fiber hydrophone is 6–18 dB greater than the noise in the two-beam hydrophone.
Digital filter models for media having linear with frequency loss characteristics
Authors: Kuc Roman
Published: October 2005

Linear with frequency acoustic loss characteristics have been observed for soft biological tissue when probed with diagnostic ultrasound and for Plexiglas when used for underwater applications. Two digital filter models are described that exhibit this linear characteristic. The first filter model, designed using a frequency sampling technique, produces a symmetric unit sample response and a linear with frequency phase characteristic. Several features of this linear phase model, however, are found to be incompatible with the physical mechanisms producing the loss. Upon resolving these incompatibilities, a second filter model is obtained which has a minimum phase transfer function. Experimental verification, using Plexiglas as an acoustic propagation medium, demonstrates the superiority of the minimum phase model for describing the physical mechanisms which produce a linear with frequency loss characteristic.
Sound radiation from convex and concave domes in an infinite baffle
Authors: Suzuki Hideo , Tichy Jiri
Published: October 2005

The sound radiation from convex and concave rigid diaphragms represented by portions of a spherical surface was investigated for the purpose of modeling a direct radiator loudspeaker. Pressure responses, radiation impedances, directivity patterns, and some other characteristics were obtained and compared with those of a circular flat diaphragm of the same radius. While the on axis pressure response of the rigid flat piston remains constant, the response of the convex dome decreases for about ka?1.0 as the height of the dome increases. The concave dome has a wide smooth peak around ka=1.5 and several peaks and dips for larger values of ka. The radiation resistance of the convex dome increases by the rate of 12 dB/oct or less up to ka=2.0 and remains constant in the higher frequency regions. On the other hand, the radiation resistance of the concave dome has its largest peak at the frequency corresponding to the peak of sound pressure response. The directivity patterns of either the convex or concave dome do not have minima with zero sound pressure and their radiation patterns are generally wider than those of the circular plate. All these results are well explained by the energy flow and pressure distribution near the radiator.
Weak and short waves in one-dimensional inhomogeneous nonlinear elastic materials
Authors: Tokuoka Tatsuo
Published: October 2005

In this paper, wave propagation in a deformed elastic material is investigated theoretically. The material is assumed to be one-dimensional and inhomogeneous and to have a nonlinear stress–strain relation. The amplitude is assumed to be small with respect to the wavelength, and the wavelength is assumed to be small with respect to distances over which wave quantities, the predeformed state, and the inhomogeneity are subject to considerable change. Order of magnitude estimations are made via the equation of motion. By equating first-order terms, the propagation velocity is determined. Likewise, by equating second-order terms, a differential equation which governs the variation of amplitude is obtained. The waveform becomes flatter or steeper according to the material, the predeformed state and the waveform.
Low-frequency surface interference effects in long-range sound propagation
Authors: Bannister R. W. , Pedersen M. A.
Published: October 2005

Characteristics of surface decoupling loss are discussed for acoustic frequencies below 250 Hz. It is shown that large losses will occur at frequencies below 100 Hz and for source or receiver depths less than 25 m. A significant dependence of decoupling loss on the average angle of surface-incident energy is indicated. It is this property which gives rise to two major effects in long-range propagation. Firstly, experimental data are presented from a selection of bottom-limited enviroments, which show a range dependence in decoupling loss for 18-m source depths. At 25 Hz these losses correspond to a loss coefficient of 0.013 dB/km and at 50 Hz to 0.008 dB/km. At these frequencies this is greater than the water column attenuation coefficient. The effect is caused by successive bottom interactions reducing the average angle of incidence at the surface consequently increasing surface decoupling loss. A second effect described is also due to bottom interactions. In this case, encounters with an upward-sloping bottom increase the average angle and reduce the decoupling loss. An apparent level enhancement results. Both experimental data and models are used to describe and interpret these effects.
Optimization of discrete arrays of arbitrary geometry
Authors: Streit Roy L.
Published: October 2005

The concept of Directivity Index with Beamwidth Control (DIBC) leads to a practical method for the optimization of element excitations to control the tradeoff between beamwidth and sidelobe level in a discrete array of arbitrary configuration. This optimization procedure depends on the design frequency, specified element positions, individual element field patterns, and ambient noise field. Each of these factors can be specified in a completely general manner. In addition, the optimization procedure can be adapted to computers of modest memory size by using subarrays of the full array. Examples are included to show the versatility of this approach to the optimization problem, as well as its limitations. One of these examples is a 105-element cylindrical array.
Measurement of the 2f1–f2 cubic difference tone with the binaural masking-level difference
Authors: Lutfi Robert A. , Yost William A.
Published: October 2005

Stimulus-like properties of the 2f1–f2 cubic difference tone (CDT) were examined by determining whether a binaural masking-level difference (BMLD) could be obtained for a 500-Hz physical tone to one ear and a CDT of the same frequency to the other ear. Masked thresholds for the physical tone (signal) were obtained as the phase of this tone varied through 360° relative to harmonically related primaries (f1=625 Hz, f2=750 Hz). A continuous low-pass (2000 Hz) diotic noise comprised the masking stimulus. The level of this noise was varied to establish thresholds in a two-interval same–different adaptive procedure with the primaries occurring in both observation intervals. In keeping with other stimulus-like properties of the CDT, the results show BMLDs of 10–13 dB. Additional BMLDs were obtained with a method of adjustment to derive phase and level estimates of the CDT as a function of primary level. These estimates are compared to cancellation estimates obtained from the same subjects. Both BMLD and cancellation estimates of CDT level show a 10-dB growth in the CDT with each 10-dB increase in primary level. However, cancellation-level estimates are consistently above corresponding BMLD-level estimates, greater by an average of 4–14 dB, depending on the subject. BMLD and cancellation estimates of CDT phase show a near-identical dependence on primary level, decreasing by an average of 5°/dB. The agreement between the two procedures argues against the notion that the phase dependence is the result of confounding peripheral interactions between the cancellation tone and the primaries in the cancellation procedure.
Perceiving vowels in isolation and in consonantal context
Authors: Diehl Randy L. , McCusker Susan Buchwald , Chapman Laura S.
Published: October 2005

Recent studies have shown that vowels tend to be identified more accurately in consonantal context than in isolation. This contextual advantage is often explained perceptually, e.g., by assuming that the formant transitions associated with the consonants convey significant vowel information. In two experiments with stylized synthetic speech patterns, we were unable to replicate the contextual advantage. These negative results were probably due to certain unnatural stimulus characteristics. In another experiment we used natural speech stimuli to assess whether nonperceptual factors associated with the identification task contribute to the contextual advantage. Subjects responded to the test items either by (a) circling written CVC syllables, (b) circling written isolated vowels, or (c) vocally mimicking the items (a task that we assume imposes minimal memory load on subjects). Of these response conditions, only the first yielded an advantage for vowels in context, suggesting that the effect depends on two factors: Stimulus–response compatibility and memory load.
Effects of vocalic formant transitions and vowel quality on the English [s]–[š] boundary
Authors: Whalen D. H.
Published: October 2005

The effects of the vocalic portion of fricative–vowel syllables on the perception of alveolar and palatal fricatives were examined. The fricative noises were synthesized to represent a continuum from [s] to [?]; the vowels ranged from [u] to [i] through [ï] and [ü]. The vocalic formant transitions were of two types, those appropriate to [s] and those to [?]. All stimuli were presented in forced-choice labeling tests. The boundary between [s] and [?] for English-speaking listeners was found to vary as a function both of transitions and of vowel. The effect of the transitions was clear and straightforward: An ambiguous fricative noise was heard more often as [s] before [s] transitions, and as [?] before [?] transitions. The quality of the vowel clearly had an effect, but the interpretation of the effect in terms of the perception of coarticulation was not clear. The responses of listeners who were unfamiliar with languages which use [ü] and/or [ï] distinctively were not significantly different from those of listeners who were familiar with such languages.
Dependence of the ultrasonic scatter coefficient on collagen concentration in mammalian tissues
Authors: Pohlhammer J. , O’Brien W. D.
Published: October 2005

The difference between literature values of ultrasonic attenuation and absorption coefficients, defined as the scatter coefficient, was related to percent wet weight collagen concentration for brain, heart, liver, kidney, and tendon, in the range of 0.7 to 7 MHz. The comparison shows that as the ultrasonic frequency increases, the scatter coefficient increases, and the dependence of scattering upon collagen concentration decreases.
Acoustic reflex thresholds in young and elderly subjects with normal hearing
Authors: Gelfand Stanley A. , Piper Neil
Published: October 2005

This study replicated Silman’s [J. Acoust. Soc. Am. 66 (1979a)] experiment comparing acoustic reflex thresholds in normal hearing young and elderly subjects. The original study was modified so that the criterion for normal hearing was extended through 8000 Hz, and the range of auditory thresholds among the younger group was selected to approximate those of the elderly subjects as closely as possible. The data confirmed those reported by Silman, showing an elevation of the ART for broadband noise, but not for tonal activators in the elderly group.
Backscattering strength and the range dependence of sound scattered from the ocean surface
Authors: Medwin H. , Novarini J. C.
Published: October 2005

The wind-driven ocean surface has been modeled as a conjoint assemblage of finite wedges such that the ocean statistics are correctly represented as a function of wind speed alone. The impulse response due to wedge diffractions and facet reflections from this surface has been calculated by the Biot–Tolstoy theory [J. Acoust. Soc. Am. 29, 381–391 (1957)]. After transformation to frequency space, the range dependence of the scattered intensity is found to vary from R−2 to R−4 depending on range, percentage of reflecting facets, and ratio of surface height correlation length to sound wavelength. It is proposed that the concept of backscattering strength be redefined as BSS=10 log10(IBS/I0)[(RN+2)/RN0A], where I0 is source intensity at R0=1 m; A, scattering area; R, range in meters; and IBS, backscattered intensity. The exponent 0?N?2 may be determined experimentally, at sea, or as shown in these calculations.
Absorption of sound by air: High temperature predictions
Authors: Bass Henry E.
Published: October 2005

The literature has been examined to determine the temperature dependence of the various energy transfer rates important in the calculation of the absorption of sound in still air. The experimental data are reviewed and analytical expressions are developed for the temperature dependence of the important energy transfer rates. The temperature dependence of absorption due to rotational relaxation, viscosity, and thermal conduction are discussed briefly. Then all the relationships are combined to predict the absorption of sound in air at elevated temperatures.
Effect of water vapor on sound absorption in nitrogen at low frequency/pressure ratios
Authors: Zuckerwar Allan J. , Griffin William A.
Published: October 2005

Sound absorption measurements were conducted in N2-H2O binary mixtures at 297°K, over a range of frequency/pressure (f/P) from 0.1–2500 Hz/atm, to study the vibrational relaxation peak of N2 and its location on the f/P axis as a function of humidity. At low humidities the best fit of the reported data to a linear relationship between (f/P)max and humidity yields an intercept of 0.013 Hz/atm and a slope of 2.00×104 Hz/atm⋅mole fraction. The slope is lower than the value of 2.6×104 reported by Chang, Shields, and Bass at higher humidities [J. Acoust. Soc. Am. 62, 577–581 (1977)], but the two sets of data are shown to be mutually consistent by means of a model in which V–V transfer is assumed to provide the dominant relaxation path. The best fit to both sets of data is expressed by the relationship (f/P)max=0.013 +2.0×104 [(1+173h)/(1+133h)]h Hz/atm, h in mole fraction. The reaction rate constants derived from this model are lower than those obtained from extrapolation of previous high-temperature data.