bluuebunny/crossref_metadata_2025 huggingface dataset:
SOFAR propagation paths from Australia to Bermuda: Comparison of signal speed algorithms and experiments
Authors: Shockley Richard C. , Northrop John , Hansen Palle G. , Hartdegen Carl
Published: October 2005

Signal speeds (average horizontal ray velocities) are calculated on the basis of bathymetry and nine sound speed profiles (SSPs) for three great circle paths from shot detonation sites off Perth, Australia to receivers near Fernando de Noronha (14 552 km) and Bermuda (19 766 and 19 810 km). We use two signal speed algorithms, one a long-range ray-tracing code and the other an adiabatic invariant approximation (AIA) method, which assumes J = ∮ c−1 sin ϑ dz is constant for a given ray (where ∮ dz is an integral over one-ray cycle, c the local depth-dependent sound speed, ϑ the ray angle, and z the depth coordinate). Comparison with field measurements made 21 years ago shows that the ray-tracing and AIA methods, when applied to the same eigenrays, yield values averaging, respectively, 5.9±2.3 and 4.5±2.4 m/s below the observed values. The AIA method, however, yields values only 2.0±1.6 m/s below measurements when applied to rays vertexing just above the chief bathymetric obstructions near the Crozet and Kerguelen Islands. The specific reason for the offset is unclear, but this study shows AIA methods can be accurate for very general range-dependent SSPs.
Acoustical measurements of vibrational relaxation in moist N2 at elevated temperatures
Authors: Zuckerwar Allan J. , Meredith Roger W.
Published: October 2005

Sound absorption measurements were conducted by the resonant tube technique to study vibrational relaxation in moist N2 at 301°, 343°, and 387 °K. Analysis of the data yields the following results: (1) The improved measurement accuracy at the higher temperatures establishes vibrational–vibrational (V–V) energy transfer as the operative relaxation path for the de-excitation of N2* by H2O beyond the uncertainty of experimental error. (2) The best-fitted temperature dependence of the V–V rate constant is k30 = 5.41×106 exp(−25.3/T1/3 )(atm⋅s)−1, an expression which is consistent with seven independent sets of both acoustical and nonacoustical data. (3) The measured humidity and temperature dependence of the relaxation frequency of N2 in air differs substantially from that specified by the recent ANSI Standard S1.26/ASA23–1978. The N2 contribution causes error, up to a few dB/1000 ft, in the total sound absorption coefficient predicted by both the ANSI Standard and ARP866A.
A two-stage version of the Kassam–Thomas nonparametric dead-zone limiter detection system
Authors: Tantaratana Sawasd , Poor H. Vincent
Published: October 2005

A useful modification of the Kassam–Thomas nonparametric dead-zone limiter detection system is proposed. The modified detector is based on a recently established procedure for multistage hypothesis testing which offers improved efficiency over fixed-sample-size tests while retaining the implementational and mismatch advantages that fixed-sample-size tests have over strictly sequential tests. The proposed detector operates as follows: A group of observations is taken and the Kassam–Thomas procedure is applied to decide whether or not a signal is present. If it is decided that no signal is present the procedure stops; otherwise a second group of observations is taken and the test is reperformed in order to double-check the results of the first test. Thus the presence of a signal is announced only when this decision has been double-checked. Two versions of this detector are proposed, one of which discards the first group of observations when double-checking and the other of which performs the double-check on the combined first and second groups. Both detectors are strictly nonparametric. Improvement in performance, in terms of the average number of samples, over the Kassam–Thomas detector is observed. With proper choices of data group sizes and of the significance level for testing the first group of observations, significant improvement can be obtained. These modified detectors are particularly attractive when the prior probability of the signal being absent is very much larger than the prior probability of the signal being present. Under this condition, the asymptotic performance of the proposed detector is better even than that of the linear detector under Gaussian noise in most cases considered. However, these new procedures are strictly nonparametric whereas the linear detector is parametric.
On the detection of a tone masked by two tones
Authors: Hartmann W. M.
Published: October 2005

We reopen the question of an appropriate representation to describe the masking of a sine tone midway in frequency between two sine maskers. We suggest that when the maskers are closely spaced in frequency signal detection is mediated by differences in the the stimulus envelope caused by the target signal. We show that in previous two-masker experiments detection threshold was limited by stimulus duration. Our experiments for long stimulus durations find thresholds that are approximately independent of the phase angle between the target and the maskers. Because the different phase angles correspond to very different stimulus envelopes the observed invariance is not easy to understand. For a general phase angle the presence of the signal causes both periodic changes in the envelope and periodic frequency modulation. The experimental detection data do not allow one to distinguish between these two effects.
Change in the pitch of a complex tone following its association with a second complex tone
Authors: Hall Joseph W. , Peters Robert W.
Published: October 2005

The pitch of a high-frequency complex stimulus was changed and maintained in the direction of the pitch of a low-frequency complex stimulus with which it was associated. Six observers made pitch matches for a pitch-shift stimulus (1250–1450–1650 Hz) before and after simultaneous presentation of this stimulus with the first through fifth harmonics of 200 Hz (200–400–600–800–1000 Hz). Data were collected for each observer on five consecutive days and one week following the fifth day. The experimental phases each day were (1) ten matches, (2) simultaneous stimuli followed by ten matches, and (3) simultaneous stimuli followed by ten matches. Association periods for simultaneous stimuli were 5 min in duration and a 5-min rest period separated the association and matching periods. The results indicated that the pitch of the pitch-shift stimulus continued to change significantly for days one through four, from an initial pitch match near 210 Hz to a final match near 205 Hz. The post one-week pitch match was also significantly lower than the initial pitch match. The pitch changes are discussed in terms of a pitch learning hypothesis.
Short-term release cues to stop-consonant place of articulation in child speech
Authors: Chapin Carol , Tseng Chiu-yu , Lieberman Philip
Published: October 2005

In recent work Blumstein and Stevens [J. Acoust. Soc. Am. 66, 1001–1017 (1979); 67, 648–662 (1980)] have proposed that the short-term onset spectra at stop-consonant releases provide invariant cues for the perception of place of articulation, and that the salient acoustic characteristics of these cues can be characterized by a set of templates. The present study investigated the suitability of these templates for characterizing place of articulation in utterance-initial voiced stop consonants produced by two children 71–75 weeks old in spontaneous discourse. The overall correct categorization rate for the templates was 65%, with 70% correct categorizations for the bilabial template, 85% for the alveolar template, and 40% for the velar template. The results of a perceptual study in which listeners were asked to identify place of articulation for computer-edited 15-, 25-, 40-, and 135-ms samples of the initial parts of these utterances were compared with the results of the template matching study. Although listeners’ identification of place of articulation was at well above chance level on even the 15-ms tokens, there was no correlation between the results of the template-matching study and the perceptual data. The perceptual data thus indicate that short-term onset cues exist in the spontaneous speech of children at an early stage of language development, however, these cues do not appear to be adequately characterized by the Blumstein–Stevens templates.
Finite impulse response ultrasonic transducers
Authors: Hazony D. , Kocher T.
Published: October 2005

The conventional thickness mode equivalent circuit of the piezoelectric transducer is analyzed when one face is perfectly well terminated. It is shown that the impulse response of the transducer can be made ideally time limited by inserting a linear network in the electrical circuit. This ideal solution is achieved without the need for severe electrical or mechanical damping and applies even when the transducer is used in both the transmit and receive mode. Consequently it is also shown that in the ’’transmit’’ mode the transducer’s impulse response is independent of k, the electromechanical coupling coefficient.
Tapered circular beam as dynamic vibration absorber
Authors: Davidson Phillip B. , Vance Ollie L.
Published: October 2005

The study of vibration absorption is extended by developing the theory for a continuous, uniformly tapered, circular beam. The free- and steady-state forced vibration solutions are developed for the beam supported by a central mass. The condition which results in vibration absorption is discussed. An expression is given relating beam parameters to the frequency of the input force which is to be absorbed. Also, the beam deflection amplitude during absorption is discussed.
Comparison of aircraft and ground vehicle noise levels in front and backyards of residences
Authors: Ortega Jose C. , Kryter Karl D.
Published: October 2005

Investigation of aircraft overflight and ground vehicle noise around a general aviation airport provided the opportunity to measure the frontyard to backyard noise reduction afforded by residential structures for these two types of noise sources. The measured average noise reduction for two residences using passing street vehicles as noise sources was found to be 17 and 21 dBA. For aircraft overflights using identical measurement instrumentation and microphone locations, as were used for the street traffic noise, the average measured noise reduction (i.e., difference between frontyard and backyard noise levels) was found to be 0.2 and 0.4 dBA. The results of the measurements show that acoustical factors around residences are such as to generally cause substantial frontyard to backyard noise reduction for street traffic noise, but not for the noise from aircraft overflights.
Location ambiguity in a multistatic sonar system with range only information
Authors: Dommermuth F.
Published: October 2005

In a planar multistatic sonar system employing omnidirectional source and receivers, two receivers generally do not suffice to permit localizing a target unambiguously. Whether three receivers are sufficient depends on the geometrical configuration of source and receivers. This note provides a necessary and sufficient condition for unambiguous localization.
Underwater sounds recorded from migrating bowhead whales, B
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Authors: Ljungblad Donald K. , Thompson Paul O. , Moore Sue E.
Published: October 2005

Bowhead whale sounds were recorded from sonobuoys in the course of conducting aerial surveys of the Beaufort Sea during spring and fall migrations in 1979. Sounds were recorded over 28 day (spring) and 12 day (fall) investigations. Most bowhead sounds in both spring and fall samples were low-frequency (below 800 Hz) moans of two classes: simple and complex. Repetitive moan sequences were found in the spring sample and are regarded as simple songs. No such repetitive sequences were found in fall recordings. High-frequency (to 4 kHz) trumpeting calls were recorded in the fall. No particular behavior, nor environmental condition, could be associated with bowhead sound production.
High-level impulsive noise source
Authors: Kenna L. C.
Published: October 2005

To assist in the development of hearing protection and communication systems for use by crews of artillery weapons, a source of high-level impulsive noise has been produced which has operating characteristics allowing its use within the laboratory. Generating peak sound pressure levels in excess of 180 dB and amenable to automatic operation, the source produces no fumes or high temperatures. Its basic principle of operation is the sudden release of compressed air to the atmosphere from a pressure chamber. The physical characteristics and acoustical performance of the source are described.
Fluid loading of plates under tension
Authors: Busch-Vishniac I. J.
Published: October 2005

Below the critical frequency, fluid loading of a plate causes an increase in the flexural wavenumber. If the plate is under tension, this wavenumber increase is enhanced, particularly at low frequencies.
Vibrations of a clamped rectangular plate of generalized orthotropy with a free, straight corner cutout
Authors: Laura P. A. A. , Verniere de Irassar P. L. , Ficcadenti G. M.
Published: October 2005

An exact solution of the title problem is probably out of the question. It is shown in the present study that a very simple solution can be obtained using simple polynomials and the Ritz method. The displacement amplitude is approximated in terms of a polynomial which identically satisfies the prescribed boundary conditions along the orthogonal edges but not along the corner cutout.
Placement equalization of microphones in small rooms
Authors: Terts Pearu
Published: October 2005

A method is described whereby a fairly flat frequency response was obtained without electronic or architectural intervention for the special case of a sound source occupying a fixed location in a small room. A sound pressure contour plot through a section of the room was made of a dominant low-frequency (LF) standing wave which shows as a peak of X dB on an initial transmission characteristic. A contour having a value of approximately −X dB was chosen and a position on it was selected to give an inverse shaped frequency response at the LF end. A final frequency response flatter than the original and its LF inverse was obtained for a microphone position located by a process of iteration.
Is non-Gaussian noise preferred over Gaussian noise in signal detection?
Authors: Church Curtis K.
Published: October 2005

The generalized Gaussian class of noise densities is considered relative to detection probabilities for a recently proposed locally optimum discrete-time stochastic signal detector [H. V. Poor and J. B. Thomas, J. Acoust. Soc. Am. 63, 75–80 (1978)]. It is shown that for a noise density with a slower rate of decay in the tails than the Gaussian distribution that a non-Gaussian noise environment results in higher detection probabilities.
Side-lobe behavior of conformal arrays
Authors: Sullivan Edmund J.
Published: October 2005

The side-lobe pattern of an array that is generated by projecting the elements of a conformal array onto a plane is shown to be generally lower in level than the expected value of the side-lobe pattern of the original conformal array. It is shown that the discrepancy between the two patterns increases with the angle from the main response axis for all side lobes of the planar array that are lower than a particular value. This is taken as a demonstration that, in this sense, the side-lobe behavior of conformal arrays is expected to be inferior to that of planar arrays.
Suppression effects for complex stimuli
Authors: Stelmachowicz Patricia G. , Small Arnold M. , Abbas Paul J.
Published: October 2005

A pulsation-threshold paradigm was used to evaluate suppression effects within complex stimuli. Stimuli were chosen to represent a continuum of spectral complexity ranging from sinusoids to complexes with one and two suppressors. Results indicate that suppression effects exist between the response to components of complex stimuli. For frequencies above a single suppressor, the suppression region is broad whereas below a suppressor, the region is relatively narrow. With two suppressors, little additivity of suppression is seen. When they are spaced closely, the response to the higher-frequency suppressor is reduced, presumably due to the low-frequency suppressor; this tends to diminish spectral contrasts despite considerable suppression at frequencies between the two suppressors. Enhancement of contrasts is greatest when suppressors are widely spaced and when both are presented at moderate levels (?60 dB SPL). These data suggest that suppression may not play a simple role of ’’peak enhancement’’ in the peripheral coding of steady-state vowels.
A method for analyzing wave propagation in random media
Authors: Wenzel Alan R.
Published: October 2005

A method for analyzing wave propagation in random media is proposed. The method, which is referred to as the quasi-Rytov method, is similar to the Rytov method, but is shown to be more convenient for the calculation of statistics of the wave field. The main advantages of the quasi-Rytov method, as compared to the ordinary Rytov method, are that it involves no heuristic assumptions and that it generally leads to simpler analytical expressions for field statistics.
Asymptotic analysis of the modes of wave propagation in a piezoelectric solid cylinder
Authors: Paul H. S. , Raju D. P.
Published: October 2005

An asymptotic method due to ’’Achenbach’’ is used to analyze the longitudinal and circumferential modes of wave propagation in a piezoelectric solid circular cylinder of crystal class (6 mm) or ceramics (∞m). Information obtained in this method is useful for the frequency spectrum at long wavelengths. In this method the displacement components, electric potential, and the frequency are expressed as power series of the dimensionless wavenumber, ε = 2π× radius/wavelength. Substituting these expansions in the field equations and the boundary conditions, a system of coupled second-order inhomogeneous ordinary differential equations with radial coordinate as the independent variable is obtained by collecting the terms of same order εm. Integration of such systems of differential equations yields the various terms in the series expansions for the above modes and for the whole range of frequencies, when the real valued dimensionless wavenumber is less than unity (0<ε<1). To test the correctness of the present scheme, the roots of the exact frequency equation are computed and the results thus obtained are compared with the results obtained in the present analysis.
Elastic wave scattering from elliptical shells
Authors: Simon Murray M. , Radlinski Ronald P.
Published: October 2005

The extended boundary condition approach to elastic wave scattering is reformulated for inclusions obeying thin shell theory. Results are presented for the scattering of plane p and sv waves from infinite cylinders of elliptical cross section for ratios of minor to major axis varying from 0.5 to 1.0 (circular). Calculations were made for cylinders of plastic and steel and for elastomers having three different shear moduli.
Longitudinal study of hearing in children II: Cross-sectional studies of noise exposure as measured by dosimetry
Authors: Siervogel R. M. , Roche A. F. , Johnson D. L. , Fairman T.
Published: October 2005

General Radio and Metrosonics brand portable noise dosimeters were used to record daily average 24-h log equivalent sound levels [Leq(24)] in 127 children and youths aged 7.0 to 20.0 years (?±S.D. = 14.2±3.5 years). These children were a subset of those participating in a long-term serial study of hearing in children at the Fels Research Institute. Seventy-five children had multiple 24-h recordings; 234 measurements were made in all. The mean Leq(24) was substantial, between 76.7 and 83.8 dB and several children had levels dangerously high, above 90 dB. There were no significant age trends or racial differences for Leq(24) and no significant differences in Leq(24) occurred between tests recorded during the school year (September–May) and those recorded during the summer (June–August). There were, however, small, but significant sex differences; boys had a mean Leq(24) about 2 dB higher than girls. Hearing threshold levels were positively correlated with Leq(24) in girls, but a similar trend was not present in boys. The mean Leq(24) (±1 S.D.) for data collected with Metrosonics dosimeters was 76.7±5.7 dB (n = 58) and 83.8±5.1 (n = 109) for data collected with the General Radio dosimeters. These significantly different means may be explained by the properties of the two dosimeter types arising from differences in the design philosophy of the instruments. These design differences result in systematic measurement errors in the two dosimeter types; the GR dosimeters systematically overestimate actual noise in certain situations while Metrosonics dosimeters underestimate it in different situations. While there are differences between the instruments as to how noise is measured, the data from either instrument provide a reasonable estimate of noise exposure in children, data that are not otherwise available. Furthermore, they provide strong evidence that the noise exposure in children is substantial.
Robust adaptive array antennas
Authors: Evans Robin J. , Ahmed Kazi M.
Published: October 2005

In this paper we present a new type of adaptive array antenna. The array optimizes well-known cost functionals such as mean-square error or output power, subject to strict inequality constraints on any part; or all the antenna pattern shape, e.g., controlling side-lobe levels, null placement, directional control, etc. Moreover, the adaptive algorithm determines array gains which are ’’robust’’ in the sense that the antenna pattern will satisfy the pattern shape constraints even if the array weights are implemented with error, as might occur with digitally controlled weights, for example. The antenna pattern also exhibits a robustness property against wavefront distortion, mutual coupling uncertainties, and array geometry errors. Finally, by appropriate choice of constraints the array can have a broadband capability.
Quadrature receivers connected in parallel to improve detection performance in a multipath environment
Authors: Higgins Robert C.
Published: October 2005

In active sonar applications, a quadrature receiver is a conventional processor used to detect sinusoidal signals reflected from an underwater object. In an adverse underwater environment, the incoherent combination of multipath returns reduces the coherence of the received signal when the transmit pulse is a cw pulse with a time duration long enough to produce overlapping returns (i.e., nonresolvable multipath). This causes a degradation in the receiver’s performance. For this analysis, the received signal model is assumed to be piecewise constant with Rayleigh amplitude fluctuations and uniform phase fluctuations. The background noise is white Gaussian with zero mean. In this paper, the probability of detection formulas along with the corresponding receiver operating characteristic curves are derived for a parallel quadrature receiver structure where the integration times of the component receivers correspond to successive coherence intervals within the signal duration. For tractability, the signal duration is divided into two equal time intervals with signal correlation characteristics between intervals specified by the correlation coefficient, ρ. The results are compared with a single quadrature receiver structure where the integration is performed once over the signal duration. The performance curves of the two receivers are compared for ρ = 0 and ρ = 1. The results demonstrate that when the two signal parts are not correlated (ρ = 0), the parallel quadrature receiver structure provides a substantial improvement in detection performance; however, when the two signal parts are completely correlated (i.e., coherent signal), this receiver suffers only a slight loss in performance compared with the conventional quadrature receiver.
On the development of acoustically transparent structural plastics
Authors: Montgomery Robert E. , Weber Fred J. , White David F. , Thompson Corley M.
Published: October 2005

The acoustic, mechanical, and physical properties of two types of diamine cured epoxy resins were investigated, and the feasibility of density reductions and impedance matching through the addition of microballoon fillers was demonstrated. A filled resin system based on a polyether diepoxide oligomer was shown to possess a mass density near 1.0 g/cm3 and to propagate acoustic waves at speeds comparable to those of water. The mechanical properties of these resins, however, were shown to be more elastomeric than plastic. A resin system based on a diglycidyl ether of bisphenol A was found to possess a high level of stiffness, with sound speeds and specific acoustic impedances about twice those of water. Incorporating microballoon fillers in the resin formulations resulted in densities closely matching that of water. Although sound speeds increased slightly, a net decrease in specific acoustic impedance was observed in all samples.
A solution to the symmetric bistatic volume
Authors: Jilling Adam
Published: October 2005

A closed solution for the intersection volume formed by two identical elliptical cones is given. This quantity is of interest in the bistatic scattering problem. The solution is limited to the case where the central axes of the cones intersect and where there is both left–right symmetry and symmetry around the plane formed by the intersecting central axes. The solution, however, may be generalized to the case of unequal beamwidths and beam angles using an approach similar to what is presented.
Large scale model measurements of airframe noise using cross-correlation techniques
Authors: Miller Wendell R. , Meecham William C. , Ahtye Warren F.
Published: October 2005

Cross-correlation techniques are used to measure the sound radiated by wing/flap airfoil configurations in the NASA–Ames 40- by 80- foot wind tunnel using a 6.7-m semispan model with three deployed flaps. The sound from the flap side edges exceeds other airframe noise sources by more than 10 dB, with the noise from the side edges of the leading flaps the strongest. The radiated sound is estimated using two formulas based on the standard aeroacoustic theory and one method using only the near and farfield cross correlation. The last method is essentially independent of such theory. The classic dipole angular distribution pattern is modified by wing diffraction effects to yield stronger radiation in the forward direction. The radiated intensity increases at slightly higher than the fifth power of the mean flow speed U0. The location of the flap track fairings is found to have a substantial effect on the radiated intensity: placing the fairings at or near the lateral edges of the flaps substantially reduces the radiated noise.
Criterion for quantitative rating and optimum design of concert halls
Authors: Hulbert G. M. , Baxa D. E. , Seireg A.
Published: October 2005

The study reported in this paper investigates the feasibility of developing a quantitative merit function for rating the acoustical quality of concert halls. The ray tracing (method of images) modeling procedure developed by Baxa and Seireg is utilized in this study to calculate the basic parameters that quantify the different criteria used for rating the concert halls. Although the calculated parameters are obtained by limiting the ray tracing in the model to three surface reflections, experimental measurements taken in several halls showed that the parameters can be used as a relative measure of the physical quantities they represent. Expressions are developed to correlate the calculated parameters with subjective evaluations of six concert halls. The criteria represented by these expressions are weighted according to the generally accepted judgments of their relative contributions to the total merit of a concert hall. The final merit function produces figures of merit that are in good agreement with generally accepted subjective ratings of the six considered concert halls. Use of the developed merit function to evaluate the acoustic quality of the remodeled New York Avery Fisher Hall resulted in considerable improvement of its computed figure of merit over that calculated for the original hall design.
Comparison of frequency selectivity for the monaural and binaural hearing systems: Evidence from a probe-frequency procedure
Authors: Yama Mark F. , Robinson Donald E.
Published: October 2005

Frequency selectivity was measured for one monaural system condition (NOSO) and two binaural system conditions (NOSπ and NOSM) using the probe-frequency method originated by Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. Subjects were first trained to detect a 500-Hz tone in noise for each condition of the experiment. Following training, the usual detection paradigm was altered such that on 25% of the trials a second signal of a different frequency was substituted for the 500-Hz signal. Performance at each of these secondary or probe-frequencies was transformed into equivalent decibels of attenuation by means of psychometric functions obtained at 500 Hz. A correction was then applied to these data which compensated for the relationship between frequency and the size of the MLD. The transformed and corrected data were interpreted as describing attenuation characteristics of an internal auditory filter. No systematic difference was found between attenuation characteristics for the two binaural system conditions. However, the attenuation characteristics for the binaural system conditions were approximately twice as wide as those for the NOSO condition.
Acoustically induced shear stresses in the vicinity of microbubbles in tissue
Authors: Lewin Peter A. , Bjo/rno/ Leif
Published: October 2005

The shear stresses in the vicinity of gaseous microbubbles in tissue irradiated by continuous and transient ultrasonic fields typical of those used in diagnostic practice have been calculated from a solution of the equation of motion of the bubble. The assumptions and limitations of the model have been considered, and within these limits, it appears that the steady stresses produced may lie above reported thresholds for biological effects. It would appear from the data in the literature that not all the biological effects reported may be caused by stresses resulting from acoustic streaming.
Effect of finite bandwidth on measured reverberation times
Authors: Sisler Peter , Bass H. E.
Published: October 2005

The effect of finite bandwidth filters on measured reverberation times of enclosures has been numerically simulated. The reverberation time measured with a real filter will differ significantly from that of a pure tone with a frequency at the geometric center of the band if air absorption is larger than wall absorption or if the wall attenuation is a very strong function of frequency.
Low-frequency ambient ocean noise and sound transmission over a thinly sedimented rock bottom
Authors: Worley R. D. , Walker R. A.
Published: October 2005

Measurements of ambient sea noise and sound transmission loss were made at a coastal site with a hard rock bottom, in 20 fathoms of water. A bottomed hydrophone was used; data were taken in the range from 50 to 800 Hz. A series of intermittent measurements over a period of 18 months showed the noise levels to be unusually low; spectrum levels of 40 to 78 dB re 1 μPa at 100 Hz were observed. Close correlation of noise level with wind velocity was found over the entire frequency band. CW transmission measurements at 97, 360, and 580 Hz disclosed exceptionally high loss in the area; between 1 yd and 2 mi the loss was about 100 dB. A combination of sparsity of shipping and poor transmission is believed responsible for the low noise levels. An exploratory test with a vibration sensor on the bottom indicated results similar to those of the water-borne sound experiments.
Is periodicity detection central?
Authors: Huggins A. W. F.
Published: October 2005

What periodicity is perceived when two different segments of noise, E and F, are alternated dichotically between the ears (Left: EFEFE..; Right: FEFEF..)? Earlier work has suggested that for nonfusible signals, preliminary auditory processing is performed separately for the two ears before the results are combined. If so, the perceived period should correspond to the combined lengths of the two segments, since this is the signal that iterates in one ear, EF. But if periodicity is detected centrally, the perceived period should be equal to the length of one of the alternated segments (E, F), since each segment presented to one ear is immediately repeated in the other. Subjects compared an alternated sequence with two dichotic iterated sequences (Left: CCC...; Right: DDD...) in an AXB paradigm, and segment duration was varied between 25 and 400 ms. In one comparison sequence, the iterated segments were equal in duration to the alternated segments (C = D = E = F), and in the other they were twice as long (C = D = E+F). The results show that periodicity is detected separately for the two ears at the shorter durations (nonfusible signals), but becomes central when the segments become long enough for structure to be heard within each segment (i.e., longer than 140–200 ms).
The simultaneous study of light emissions and shock waves produced by cavitation bubbles
Authors: Gimenez G.
Published: October 2005

Light pulses (sonoluminescence) and pressure pulses produced by the collapse of cavitation bubbles are investigated simultaneously by means of an optical cable connected to a photomultiplier (PM) and a miniature piezoelectric probe. All collapses do not systematically lead to the occurrence of a pulse on the PM anode. The maximum occurrence is one anodic pulse per 4.6 ultrasonic periods. Pulse height analysis of anodic pulses indicates that the most probable pulse is the one producing the emission of one photoelectron by the photocathode of the PM. Simultaneous pulse height analysis shows that no correlation exists between the pulse heights of the two types of pulse. Numerical resolution based on the Kirkwood–Bethe–Gilmore equation and on the ’’hot spot’’ theory of Noltingk and Neppiras [Proc. Phys. Soc. (London) B63, 674 (1950); B64, 1032 (1951)] indicates that collapsing bubbles subjected to analysis display the same initial radius (?1 μm) and that they collapse at varying distances from the probe.
Scattering of a cw plane wave by a pulse
Authors: Trivett D. H. , Rogers Peter H.
Published: October 2005

An examination of the scattering of sound by sound indicates that the boundary of the interaction region is very important in determining not only the level of the scattered sound but also the frequency of the scattered sound. In the case of a pulse propagating through a cw plane wave (where the boundary of the interaction region is propagating at the sound speed) the frequency of the farfield scattered sound at a fixed angle is the cw frequency, Doppler shifted i.e., fs(ϑ, φ) = fl(1−cos ϑ)/(1−cos φ), where fl is the frequency of the plane wave, ϑ is the angle between the cw wave vector and the pulse wave vector, and φ is the observation angle with respect to the pulse wave vector in the interaction plane. The scattered signal has a strong maximum at the Doppler angle φd, where the frequency of the scattered signal is equal to the sum frequency. The scattered signal at φd observed at a finite distance from the interaction region thus appears as a pulse whose frequency sweeps from a value somewhat above the sum frequency to a value somewhat below the sum frequency. Previous detection of sum frequency in a cw crossed-beam experiment has been attributed to nonlinear processes other than scattering from the interaction region. Positive results from this type of experiment would unambiguously demonstrate the existence of scattered sound by the angular dependence of the scattered signal.
Three-port two-microphone cavity for acoustical calibrations
Authors: Wong G. S. K. , Embleton T. F. W.
Published: October 2005

The performance of a three-port two-microphone cavity for acoustical calibrations is investigated theoretically and is verified experimentally. The calibration procedure described has overcome some of the limitations in conventional coupler calibration methods, and made it possible to calibrate acoustical measuring systems by means of comparison to a reference system.
Effect of filter shape on measured spectrum
Authors: Bass Henry E.
Published: October 2005

Atmospheric absorption acts as a distance and frequency-dependent low-pass filter for an acoustic source. This effect can be accurately predicted if the atmospheric absorption, source spectrum, and filter function are known [Sutherland and Bass, J. Acoust. Soc. Am. 66, 885–894 (1979)]. The purpose of this letter is to report a rather simple experimental verification of this effect.
A method of obtaining C-scan images by use of interdigital transducers
Authors: Toda Kohji , Hayama Masaru , Moriizumi Toyosaka , Yasuda Tsutomu
Published: October 2005

An ultrasonic technique is described for nondestructive testing. According to this method, a sound beam is radiated and detected at a liquid–solid interface by arched interdigital transducers, under the condition of no contact of interdigital electrodes with a liquid. Tests on C-scan imaging had satisfactory results.
Attenuation parameters from normal mode measurements
Authors: Tindle C. T.
Published: October 2005

A new method of determining the bottom attenuation coefficient in shallow water is described. Normal mode amplitudes are measured relative to the lowest mode at a single location. These relative mode amplitudes are compared with theoretical results to obtain the bottom attenuation coefficient. The method does not require source level calibration nor measurements at different ranges. Increased attenuation as modes approach cutoff is in good agreement with theory.
Observation of Raman–Nath optical diffraction in the phase grating plane
Authors: Riley Ward A. , Love L. Alan , Griffith David W.
Published: October 2005

Previous studies of Raman–Nath optical diffraction have emphasized the characteristics of the light distribution in either the nearfield or the farfield of the optical phase grating produced by an acoustic beam. The plane in which this grating is located can be imaged outside of the acoustic medium and experimentally studied with a photodetector. This paper describes measurements of the light intensity variations which occur in the image plane containing the optical phase grating after spatial filtering is performed. Theoretical results are presented for values of the Raman–Nath phase parameter v?6 when the negative optical diffraction orders are removed by a spatial filter. Experimental results are also presented from a 2.5-MHz transducer radiating into distilled water which confirm the theoretical predictions. It is possible to use this technique to assess the frequency response of an optical system over a large frequency range since frequencies as high as four times the fundamental are generated in the optical intensity variation. For small values of the phase parameter, the approach should be useful for observing the temporal waveforms of broadband ultrasonic pulses of the type frequently encountered in medical diagnostic systems.
Acoustical holography with an annular aperture
Authors: Norton Stephen J.
Published: October 2005

A synthetic-aperture imaging system using an annular array of transducer elements is analyzed. The aperture is assumed to consist of N elements, where each element serves both as a source and receiver of sound, giving rise to N2 amplitude and phase measurements around the annular circumference. Because of source–receiver reciprocity, however, (1/2)N(N−1) of these measurements [where (1/2)N(N−1) is the number of element pairs on the annulus] are redundant, giving a total of N2−(1/2)N(N−1) = (1/2)N(N+1) independent measurements. It is shown how suitable processing of these measurements can yield a high-resolution image of a reflecting object in a plane parallel to the annulus and located within its Fresnel region. Moreover, the resultant resolution is shown to be equivalent to that of a full circular aperture twice the diameter of the annulus. This approach differs from the J2 synthesis of Wild [Proc. R. Soc. London Ser. A 286, 449–509 (1965)] in that the annular array acts as a source as well as a receiver and that no assumptions regarding the spatial coherence of the reflecting object are required. Numerical reconstructions based on simulated data are presented. Possible areas of application of the annular imaging system include medical ultrasonic imaging, underwater acoustic imaging, and microwave imaging.
Implications of causality, time-translation invariance, linearity, and minimum-phase behavior for basilar-membrane response functions
Authors: Koshigoe Shozo , Tubis Arnold
Published: October 2005

Several implications of the assumptions of causality (C), time-translation invariance (TTI), linearity (L), and minimum phase behavior (MPB) for basilar membrane (BM) frequency-response functions are derived. They are then used to: (1) test the consistency of calculated results for a two-dimensional cochlear model [S. T. Neely, J. Acoust. Soc. Am. 69, 1386–1393 (1981)] and (2) check experimental data on the BM displacement/malleus displacement [W. S. Rhode, J. Acoust. Soc. Am. 67, 1696–1703 (1980)] for approximate consistency with these assumptions. Both the theoretical model results and experimental cochlear-partition response data are in fairly good accord with these assumptions.
Signal and masker uncertainty with noise maskers of varying duration, bandwidth, and center frequency
Authors: Spiegel Murray F. , Green David M.
Published: October 2005

The detectability of sinusoidal signals added to repeatable noise bursts was measured under conditions of signal-frequency uncertainty and masker-waveform uncertainty. Either source of uncertainty raised thresholds by 2–5 dB over those measured in a fixed-signal, fixed-masker condition, while the combination of both types of uncertainty raised thresholds by 8–12 dB. The magnitude of these elevations are similar to those found in a previous study, which employed maskers composed of random sets of equal-amplitude tones [Spiegel et al., J. Acoust. Soc. Am. 70, 1015–1019 (1981)]. When masker level varied by up to 40 dB between the two intervals of a forced-choice trial, the signal thresholds were elevated by only 2.5 dB. The results support a form of profile analysis in which listeners detect signals by noticing a relative change in the masker spectrum.
Some effects of spectral shaping on recognition of speech by hearing-impaired listeners
Authors: Kamm Candace A. , Dirks Donald D. , Carterette Edward C.
Published: October 2005

The effects of spectral shaping on speech recognition were investigated for hearing-impaired listeners with flat and steep audiometric configuration. Three frequency responses were tested: uniform frequency gain, high-pass filtering, and a response shaped relative to each subject’s loudness discomfort level curve. Speech-recognition performance was measured at four levels (from 80 to 95 dB SPL) using nonsense syllable (NST) and synthetic sentence (SSI) tests, presented against a background of ’’cafeteria noise.’’ No significant differences in performance on the NST were observed between the two subject groups across all spectral shapes (frequency responses) 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 steep configuration was poorest for the uniform response. The recognition data were compared with predictions of relative performance using a modification of the Articulation Index (AI). The AIs provided accurate estimates of relative performance across spectral shapes but were not consistent with relative performance as a function of presentation level. The results indicate that the selection of spectral shape for optimal performance is influenced by the particular speech task used to test recognition and also suggest that, with further validation, the AI may provide an objective technique for selecting optimal spectral shape.
Acoustical characterization of flute head joints
Authors: Fletcher N. H. , Strong W. J. , Silk R. K.
Published: October 2005

A method is described for characterizing the acoustical properties of flute head joints by measurement of the quantities Fn = fn/(2n−1), where fn is the frequency of the nth impedance maximum of the head joint as viewed from the end of a short cylindrical tube simulating a part of the flute body and with the embouchure hole completely unobscured. The tube length is chosen to make f1≊170 Hz. It is shown that the pattern of this ’’resonance signature’’ curve Fn in the frequency range fn up to 5 kHz is sensitive to the precise geometry of the head joint so that it may serve as a convenient correlate for playing behavior, even though its shape is only indirectly related to conditions in a blown flute. A simple and inexpensive apparatus for determining this resonance signature is described.
Stress and rate: Differential transformations of articulation
Authors: Tuller Betty , Harris Katherine S. , Kelso J. A. Scott
Published: October 2005

Early theorizing in speech production considered variations in syllable stress and speaking rate to be identical transformations of motor activity [e.g., Lindblom, J. Acoust. Soc. Am. 35, 1773–1781 (1963)]. More recent work, however, suggests that modulation of stress and rate have different acoustic and perceptual effects, and thus may have independent ’’signatures’’ in production. The experiments reported here examined these hypotheses. In the first experiment, electromyographic activity from two muscles, one primarily related to vowel production and the other to consonant production, was examined during utterances whose stress and rate characteristics were systematically varied. The results support the hypothesis that stress and rate modulations have differential effects on muscle activity. The second experiment addressed the same basic question but examined a broader set of muscles. In all cases, the changes in duration and peak amplitude of muscle activity for altered stress were not equivalent to the changes for altered rate. Decreases in stress produced decreases in peak amplitude and duration of vowel-related muscle activity that were consistent across speakers. In contrast, activity patterns associated with rate contrasts varied considerably across muscles and speakers.
Correlation measurements of surface-reflected underwater acoustic signals at several sea states
Authors: Olson J. R. , Nichols R. H.
Published: October 2005

A coherent wavefront which strikes the rough and moving surface of the ocean is expected to suffer some degree of decorrelation. Two exploratory experiments were performed to investigate the effect of sea state on decorrelation for acoustical wavelengths of the order of the ocean wave heights and signal durations comparable to the ocean wave periods. In the first, 10-s pulses of random noise signal of 300-Hz bandwidth centered at 750 Hz were generated by a bottomed omnidirectional sound source, reflected once from the surface at a grazing angle of 31° and received on two bottomed omnidirectional hydrophones spaced 500 ft apart, approximately broadside to the sound path. Cross-correlation coefficients for the last 5 s of each pulse were measured at several sea states. In the second experiment, the output of one hydrophone was cross correlated with a replica of the pseudo-random signal which drove the sound source. Cross-correlation coefficients between the two receivers decreased with increasing sea state to a value of about 0.4 at 20-ft wave height. Replica-correlation coefficients with a single receiver also decreased, but to only about 0.8 at 20-ft wave height. These values are higher than values presented in other publications of theoretical and experimental results obtained under other conditions. One reason for the difference may lie in the shorter duration of our signals relative to the ocean wave periods.