bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind- and wave-induced acoustic noise at very low frequencies
Authors: Kibblewhite A. C. , Ewans K. C. , Coup D. C.
Published: January 2006

Underwater ambient noise is known to be dependent on the wind. Several mechanisms have been proposed to explain the nature of the transfer of energy from the wind field to the acoustic noise field. Examples include wind and wave turbulence and nonlinear interactions between surface waves, which given rise to many phonemena not present in linear theory. This study examines these wind-related mechanisms from the low end of the acoustic spectrum. Data from a long-term study of ocean waves and the associated microseismic field recorded ashore has produced evidence helpful to the identification of processes active in the acoustic field at somewhat higher frequencies. The unique environment under which these recordings were made in New Zealand has contributed to the success of the study. Correlations with ambient noise recorded by a shallow water hydrophone were also made.
High-frequency acoustic sea surface scatter correlated with wind and wave measurements
Authors: McConnell Steven O. , Atakturk Serhad , Katsaros Kristina B.
Published: January 2006

Backscatter and forward-scatter measurements were made at frequencies ranging from 20 to 50 kHz (principally 21 and 40 kHz) in Lake Washington. Simultaneous measurements were made of the wind speed, stress, and direction, and of the large and small scale wave height up to frequencies of 30 Hz. The wave height sensors penetrated the water surface at the approximate center of the area of ensonification, allowing a spatially as well as temporally simultaneous comparison of scattering levels with wave height. Preliminary results show the backscatter level to be about 10 dB less than in the open ocean for a given wind speed. This result may be due to differences in near-surface bubble size density distributions between salt and fresh water [Scott, Deep-Sea Res. 22, 653–657 (1975)].
Measurements of wind-generated noise levels in the Eastern Indian Ocean
Authors: Kewley D. J. , Burgess A. S.
Published: January 2006

Recordings of ambient sea noise made with a vertical linear hydrophone array (VLA) at five sites in the Eastern Indian Ocean have been analyzed for wind-speed dependence. Use is made of the vertical directional discrimination of the VLA to resolve noise generated at a distance and locally generated wind noise. The results are compared with data from similar experiments off the east coast of Australia [A. S. Burgess and D. J. Kewley, J. Acoust. Soc. Am. 73, 201–210 (1983)].
Recent trends in practical applications of macrosonics
Authors: Neppiras E. A.
Published: January 2006

Macrosonics includes the area of technology where treatment by sound or ultrasound produces permanent and useful changes in the treated medium. To date, two types of application have achieved major importance as viable commercial techniques. These—cleaning and plastics welding—are still expanding in scope and importance. Recent progress has been mainly in the direction of a greater degree of automation and control. Apart from these two established areas there are several applications that have already been more-or-less fully developed but which, for one reason or another, have a much more limited scope. Examples are: ultrasonic machining, metal-welding, tinning, and various metal deformation processes. A third category consists of applications and ideas that appear very promising but which have not yet been fully explored or developed. Examples are: some aspects of chemical processing and various gas-load applications, including the production of aerosols (atomization). After briefly reviewing the latest progress in the established areas, this paper will concentrate on new ideas and applications that show signs of developing into valuable practical techniques.
TDS measurement of the second harmonic emission from ensonified bubbles
Authors: Heyser Richard C. , Rooney James A.
Published: January 2006

The second harmonic spectrum of backscattered sound from air bubbles in water has been measured by TDS methods. Using the technique of Miller and Nyborg [D. L. Miller and W. L. Nyborg, J. Acoust. Soc. Am. 73, 1537–1544)], air was trapped in the pores of immersed hydrophobic Nuclepore filter membranes to produce stable bubbles whose diameters lay in the 3–4 μ range. The membrane was insonified with a wideband transmitting crystal driven from a linear amplifier, and the backscattered sound was received by a second wideband ultrasound crystal. Transmission in the 0.5-to 10-MHz range was accomplished by a digitally controlled sweeping generator operating at a rate of 500 MHz/s. Second harmonic reflection of energy was detected by a tracking receiver whose sweep program was driven synchronously with the transmitting program, but with a tracking rate of 1 GHz/s and a delay offset corresponding to the arrival time of backscattered sound from the membrane. Selected combinations of transmission and reception sweep rate established that the observed second harmonic signal was due to resonance of bubbles and not due to incidental transmitter or receiver distortion components. The measured frequency spectrum of second harmonic backscatter from bubbles corresponds closely to the predicted spectrum shape, showing a dominant peak at twice the frequency at which a strong absorption dip occurs for sound passing through the bubble-filled membrane.
Application of advanced excitation and analysis techniques to the Galileo Spacecraft modal survey program
Authors: Hunt David L.
Published: January 2006

A modal test of the Galileo Spacecraft will be used to tune a finite element model that will serve in a subsequent loads analysis. A part of the test is being devoted to applying new techniques for performing modal tests. Testing efforts will be applied in the areas of multi-shaker broadband (MSB) excitation, time domain calculation of rational frequency response functions, and polyreference estimation of modal parameters. These three techniques, having been developed and implemented, are being examined as a means to perform modal tests in a fraction of the time previously required, with a resulting data quality which meets or exceeds current standards. The presentation will detail the techniques, their application to the specific Galileo program, and highlight and interpret the results achieved.
Using holographic interferometry in vibration measurements
Authors: Page R.
Published: January 2006

This paper will review principles of holographic interferometry and provide examples of current applications in vibration analysis. Specific techniques discussed will include double exposure (frozen fringe), real time, and stroboscopic and time-average holographic interferometry.
Recognition of a small vocabulary spoken by two dialect groups
Authors: Bossemeyer R. W. , Laferriere M.
Published: January 2006

A major difference among American English dialects lies in the variety of phonetic characteristics of vowels (H. Kurath, Studies in Area Linguistics, 1972). Since LPC-based speech recognition systems depend heavily on the vowel portion of an utterance, dialect differences not represented in a template inventory could affect recognition accuracy in a speaker-independent, LPC-based isolated word recognition system. Eighty-five speakers from each of two dialect groups, Eastern New England and Southeastern, recorded the digits and two command words. Word recognition scores for speakers in each dialect group were compared when reference templates were from (1) the other dialect group; (2) the same dialect group; and (3) a combination of the two groups. Comparisons are made on a word-by-word basis to determine what types of phonetic dialect variation affect recognition accuracy.
Digital sound synthesis for underwater music perception
Authors: Redolfi Michel , Ray Lee
Published: January 2006

A piece of original electro-acoustic music, Sonic Waters II, was created. Software “instruments” and “note lists,” descriptions of the behavior of those instruments in the musical time of a sequence, were specified for the cmusic synthesis program to produce, by frequency modulation, amplitude modulation, and localization and motion within a synthesized space, morphological transformations of several harp recordings. Means of (1) transduction of this wide-band musical work (20 Hz to 16 kHz) for human listeners immersed in water and compensating for changes of such musically significant psychoacoustic cues as depth perception and relative amplitudes of overtones occasioned by the prominence of bone conduction in underwater listening were investigated. One pressure-loaded diaphragm and four piezoelectric transducers were positioned to broadcast the computer-processed sound. The wavelength of some bass notes exceeded the dimensions of the pool, limiting musically useful propagation of low frequencies due to cancellation and reinforcement of standing waves. [Work supported by the CME, System Development Foundation and the French government.]
Bottom-interacting acoustic signals in the Arctic channel: Long-range propagation
Authors: Kutschale Henry W. , Lee Tai
Published: January 2006

Hydroacoustic signals from underwater explosions that have propagated over the Arctic abyssal plains commonly display marked frequency dispersion in pulses that are bottom-interacting and that arrive after the SOFAR signal. In the infrasonic band of 2 to 20 Hz, the temporal dispersion for each pulse that has interacted with the flat bottom of the plain can be nearly as strong as that observed in the SOFAR signal for the first mode. However, the bottom-interacting pulses correspond to a coherent summation of many higher-order normal modes in a channel bounded above by the ocean surface and below by the upper 400 m of the bottom sediments, where the velocity increases with depth. Using normal-mode theory and the Multiple Scattering Pulse Fast Field Program (MSPFFP), we have analyzed the dispersion and pulse shapes and have derived the acoustic properties of the bottom in the Pole, Barents, and Mendeleyev Abyssal Plains. The principal properties of the bottom controlling the propagation are compressional velocity, density, and attenuation. In contrast, the ice layer has a negligible effect on the dispersion of the observed waves. The effect on pulse compression of this frequency dispersion of the bottom-interacting signals was simulated numerically, using predistorted waveforms matched to the dispersion of the SOFAR channel at specified ranges.
Ambient noise in the central Arctic Ocean
Authors: Dyer Ira
Published: January 2006

Underwater ambient noise has been measured in the central Arctic Ocean on three separate occasions with the use of a horizontal and a vertical array. These data help to identify various noise mechanisms. Of principal interest is noise caused by various ice cracking events which depend upon stress levels in the ice and which seem to have varying temporal and spectral characteristics. I review these mechanisms and show how the data relate to them. While spatial analyses have been carried out only at very low frequencies, spectral analyses cover the range from 1 to 10 000 Hz. In this frequency range noise mechanisms other than pack ice are sometimes important, such as wind-generated noise and earthquake noise. [Work supported by ONR.]
Seismic/acoustic propagation in the Arctic Ocean
Authors: Baggeroer Arthur H. , Duckworth Gregory L.
Published: January 2006

During the FRAM II and FRAM IV experiments in the Pole Abyssal Plain and the Barents Abyssal Plain of the Arctic Ocean 24 channel hydrophone arrays approximately 1 km × 1 km in extent were used to record digitally both seismic refraction and long-range acoustic propagation data. From these data the velocity versus depth function for the seismic structure along the FRAM II and FRAM IV drift tracks were estimated by high-resolution velocity spectral analysis and tau-slowness migration methods. These indicate oceanic layers 2 and 3, but they are relatively thin. These techniques were also used to identify internal and surface-reflected multipaths as well as converted shear paths to obtain a detailed characterization of the seismic propagation. The long-range acoustic signals contained strong modal components and bottom interacting ones. Velocity spectra and autoregressive algorithms resolved the dispersive properties of the phase and group velocity of each mode. These were used to estimate the water column sound velocity profile with an inversion algorithm. During FRAM II the bottom interactions lasted up to 80s long and contained as much energy as the low-order modes at low frequencies. These signals were used to estimate the shallow velocity versus depth structure. During FRAM IV the dispersion characteristics of the low-order modes changed slightly. In contrast, virtually no bottom-interacting energy was observed suggesting strong scattering of the deep paths by an intervening midoceanic ridge. [Work supported by ONR Arctic Program Office.]
Law-frequency acoustic propagation in Canadian Arctic waters
Authors: Brooke Gary H.
Published: January 2006

Underwater acoustic propagation within, and surrounding, the Canadian Arctic Archipelago is typical of shallow Arctic water. That is, the propagation is strongly dependent on bottom properties at lower frequencies (<40 Hz) but is increasingly influenced by the surface at higher frequencies due to the characteristic upward refracting velocity profile in the water column. Water depths are generally less than 600 m and are typically 200–400 m. DREP has made propagation measurements in several locations and, hence, under a variety of propagation conditions. In this paper the salient features and trends in the data are discussed.
Some ambient noise measurements in spring ice, Pt. Barrow, Alaska
Authors: Cummings W. C. , Holliday D. V.
Published: January 2006

Spring ice conditions off North Alaska are confounded by dynamic changes resulting from lead openings and closings, rapid changes in degrees and kinds of ice cover, rapidly changing wind conditions, and drifting floes. The measurements were taken in the spring of 1982 using a 9-nmi telemetering link. [Work supported by the North Slope Borough.]
TRISTEN/FRAM IV Arctic ambient noise measurements
Authors: Nielsen R. , DiNapoli F. R. , Fecher M. , Potter D. , Stocklin P. L.
Published: January 2006

Approximately 250 h of multichannel ice camp ambient noise data were recorded by NUSC during the TRISTEN/FRAM IV experiment in the Barents Abyssal Plain, Arctic Ocean during April 1982. Single hydrophone data were recorded from various elements of both the Massachusetts Institute of Technology/Woods Hole Oceanographic Institute horizontal array and the Naval Research Laboratory vertical array. This paper characterizes the average ambient noise level, and its variance as a function of frequency (to 2500 Hz), depth, and time. [This work is funded by ONR Code 425-AR, Program Manager, R. Obracta.]
The tuning of Harry Partch's 43 tones-to-the-octave just intonation scale, and it's musical endowments and consequences
Authors: Mitchell Danlee
Published: January 2006

Harry Partch (1901–1974) is the American composer noted for his bold and unique departure away from 20th century tuning and performance practices of our present day European influenced music monolith. During the 1920's Partch formulated the theoretical parameters of his tuning system, based on an interlocking harmonic and subharmonic grid extended to the 11th partial. This system features a “micro” tuned scale of 43 tones-to-the-octave, and just harmonic relationships in ratios of successive integers 4-5-6-7-9-11 that surpass the resources of 12-tone Equal Temperament. Not content with a mere theoretical victory, Partch then devoted his entire life to the building of sculpturally beautiful musical instruments, and the employment of these many instruments in his theatrically oriented musical works. Mr. Mitchell, Partch's close associate for the last 20 years of his life, will present an intimate view of Partch's world.
Perception of melodic and harmonic intonation of two-part musical fragments
Authors: Rasch Rudolf A.
Published: January 2006

Short musical fragments consisting of a melody part and a bass part were mistuned in various ways and to various degrees. They were presented to a group of subjects for a judgment of the quality of intonation and for an identification of the mistuned part. Mistuning was applied to the melodic frequency intervals of the melody part and/or the bass part (melodic mistuning) as well as to the frequency intervals of simultaneous tones in melody and bass (harmonic mistuning). Results indicate that the melodic mistuning of the melody part has the largest influence on the perception of the intonation, followed by the harmonic mistuning, while the melodic mistuning of the bass is less important. When mistuning is present in both melody and bass part, mostly the melody is considered to be the mistuned part. When the sound-pressure levels of the two parts are unequal, there is a tendency to consider the louder part as the mistuned part. In the perception of harmonic mistuning, the deviating interval size is probably of more importance than the presence of beats. Small amounts of mistuning go unnoticed or may even cause an increase of the intonation quality.
Phantom beats in mistuned chords
Authors: Hall J. L. , Mathews M. V. , Roberts L. A.
Published: January 2006

Beats are heard in slightly mistuned musical intervals. For example, a mistuned fifth with frequencies f1 = 804 Hz and f2 = 1204 Hz will produce 4 beats per second. These beats have been attributed to interaction between the 3rd harmonic of f1 at 2412 Hz and the 2nd harmonic of f2 at 2408 Hz. However, 4 beats per second can be heard when the mistuned fifth is played with pure sinusoids which have no harmonics. A second hypothesis attributes these phantom beats to interaction between combination tones f2 − f1 at 400 Hz and 2f1 − f2 at 404 Hz. Experimental results supporting the second hypothesis are presented. If one combination tone is removed by a cancellation tone of appropriate amplitude and phase, the beats can no longer be heard. If tones are added to a perfectly tuned fifth so as to approximate the combination tones produced by a mistuned fifth, the resulting stimulus is difficult to distinguish from the mistuned interval. Similar results were obtained for mistuned fourths, attributable to interaction between combination tones f2 − f1 and 3f1 − 2f2.
Surface intensity and radiation loading on cylindrical surfaces via FFT methods
Authors: Stepanishen P. , Chen H. W.
Published: January 2006

A numerical approach is presented to evaluate the surface intensity and radiation loading on a finite cylindrical surface with a known harmonic radial velocity distribution. The approach is based on a combined FFT and Green's function method [P. Stepanishen and H. W. Chen, J. Acoust. Soc. Am. Suppl. 1 73, S22 (1983)]. Surface pressure, intensity, and radiation loading are rapidly obtained via the use of standard FFT methods. The spatial fluctuations of the surface pressure and intensity for a known velocity distribution can thus be readily investigated. Numerical results are presented to illustrate the spatial variation of surface pressure and intensity as a function of axial mode shape, circumferential mode number, and frequency. Negative intensity regions and edge effects are clearly observed in the results at low frequencies.
A temperature correlation for the radiation resistance of a thick-walled circular duct exhausting a hot gas
Authors: Mahan J. R. , Cline J. G. , Jones J. D.
Published: January 2006

It is often useful to know the radiation impedance of an unflanged but thick-walled circular duct exhausting a hot gas into a relatively cold surroundings. Results based on data available in the literature [N. Fricker and C. A. Roberts, Acustica 38, 124–130 (1977); A. Cummings, J. Sound Vib. 52, 299–304 (1977)] and a new experimental study confirm that the reactive component is insensitive to temperature, while the resistive component increases with the temperature difference between the gas flowing from the duct and the surrounding air. A temperature correlation is developed permitting prediction of the radiation resistance from a knowledge of this temperature difference. The effect of wall thickness is shown to be unimportant compared to other geometrical and acoustic factors for a range of thickness of practical interest. A physical basis is presented for the observed variation of the radiation resistance with temperature. [Work supported by NASA.]
Transition from the nonlinear King integral to spherical propagation for a finite amplitude sound beam
Authors: Ginsberg Jerry H.
Published: January 2006

The propagation of finite amplitude waves radiating from a baffled piston has been described in terms of directional spherical waves [J. C. Lockwood, T. G. Muir, and D. T. Blackstock, J. Acoost. Soc. Am. 53, 1148–1153 (1973)]. That analysis predicts waveforms at large distances, provided that comparable information is known at a reference location in the farfield. Lockwood et al. used this approach based on assuming that linear theory is accurate at the reference location. Such an assumption is inaccurate when the source pressure level is sufficient to generate significant nonlinear effects (growth of higher harmonics and depletion of the fundamental) within the near field. The present work describes the interfacing of the spherical propagation theory and the nonlinear King integral [J. H. Ginsberg, J. Acoust. Soc. Am. Suppl. 1 71, S30 (1982)]. The latter theory is used in this approach to evaluate the nonlinear waveform at the reference location. Comparing the results of interfacing, and of direct propagation according the nonlinear integral formulation, with experimental data provides a strong validation for both theories. The advantage of using directive spherical wave theory lies in its superior computational efficiency and its ability to describe shock formation. [Work supported by ONR, Code 425-UA, and NSF, Grant MEA-8101106.]
Distribution of resonance frequencies of coupled dynamic systems
Authors: Maidanik G. , Maga L. J.
Published: January 2006

Finite, uncoupled dynamic systems have response maxima at specific frequencies, the resonance frequencies, the distribution of which can be ascertained. When the dynamic systms are coupled and, therefore, interact with each other, the coupling affects the distribution of the resonance frequencies. In this paper the dynamic systems are modeled as one-dimensional wave-bearing systems and the coupling is effected via the transmission coefficients of the junctions between the systems. The nature of the change in the distribution of the resonance frequencies is examined in some simple cases.
Reciprocity calibration of “second sound” transducers in superfluid helium
Authors: Garrett S. L.
Published: January 2006

The reciprocity theorem has been used for over 40 years to facilitate absolute calibrations of electroacoustic transducers from purely electrical measurements, without reference to a primary acoustical standard. A generalization of this calibration procedure to reversible second sound transducers in He II will be described. The symmetry of two-fluid hydrodynamics is used to derive an expression for the second sound specific acoustic transfer admittance, thus permitting absolute mechanical measurement of temperature oscillations in superfluid helium. In the temperature range from 1.15° to 1.9 °K, the Tisza approximation and the thermodynamics of an ideal Baste-Einstein gas [F. London, Superfluids, Vol. II, Sec. 7] lead to a transfer admittance which is quadratic in temperature. This generates a calibration constant that has the experimentally convenient feature of being a linear function of absolute temperature [f(T) = 21.31T − 17.01 ± 0.17 g1/2 °K−1 s−3/2]. Applications to nonlinear hydrodynamics, photoacoustic spectroscopy, and the characterization of porous diaphram second sound transducers will be suggested. [Work supported by the NPS Foundation Research Program.]
An experimental test of acoustical reciprocity calibration applied to thermal transducers in superfluid helium
Authors: Valdivia J. , Ogg B. R. , Yarber R. K. , Garrett S. L.
Published: January 2006

An experiment will be described which has verified an extension of the reciprocity calibration technique to reversible thermal transducers in superfluid helium. A plane-wave resonator of circular cross section was capped at both ends by reversible teflon electret diaphrams which contained many razor slits to generate or detect thermal waves (second sound). The resonator also incorporated a thermophone and a dc biased carbon resistance thermometer to set independent upper and lower limits on the amplitude of the temperature oscillations within the resonator. The acoustical resonance data was acquired and analyzed by a computer controlled system described previously [D. V. Conte and S. L. Garrett, J. Acoust. Soc. Am. Suppl. 1 72, S82 (1982)]. The temperature excursions measured by the reciprocity method fell between the upper and lower limits which, for lower modes, were separated by only a few percent. At higher modes the lower limit departed from the upper limit due to the thermal inertia of the resistance thermometer. Temperature excursions smaller than 10−8 °K/[(Hz)1/2] were detectable using the electret transducers and a pre-amplifier with a noise floor of 10−8 V/[(Hz)1/2]. [Work supported by the NPS Foundation Research Program.]
Ultrasonic evidence for structural relaxation in large unilamellar liposomes
Authors: Strom-Jensen Philip R. , Magin Richard L. , Dunn Floyd
Published: January 2006

The ultrasonic absorption of large unilamellar vesicles (average diameter 0.2 μm) was determined in the frequency range 0.5–5 MHz. The liposomes were composed of a 4:1 mixture by weight of dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylglycerol. A large increase in absorption occurs at the solid to liquid-crystalline phase transition temperature (42 °C) of the pure lipid vesicles. This increase in absorption is interpreted as a structural relaxation of the “melting” fatty acid chains occurring with an average relaxation time of 76 ns. The liposomes were also found to be extremely permeable near the transition temperature, releasing encapsulated cytosine arabinoside. Addition of cholesterol or gramicidin to the liposome bilayer broadened the ultrasonic absorption and reduced the efflux of cytosine arabinoside at the transition. Gramicidin, in addition to broadening the transition, slows the isomerization of bonds in the hydrocarbon chains of the lipids. A concentration of 5 mole percent gramicidin increased the average relaxation time to 210 ns. [Work supported in part by grants from the National Cancer Institute, National Institutes of Health, and the American Cancer Society.]
Sound absorption in aqueous mixtures of MgSO4 and HCl
Authors: Hsu C. C. , Fisher F. H.
Published: January 2006

Sound absorption measurements were made at 25 °C over the frequency range of 30–300 kHz for aqueous mixture of 0.02 M MgSO4 and HCl, using a spherical resonator method. At 1 atm, the excess sound absorption measured for a mixture of 0.1 M HCl is negligible while that of 0.05 M HCl showed a maximum absorption, (agr;λ)max × 106, of 9.49 ± 0.21 at 214 kHz and that of 0.01 M HCl, 68.90 ± 0.71 at 161 kHz. AT 307 atm the mixture of 0.05 M HCl showed a maximum absorption of 5.78 ± 0.14 at 205 kHz. These results will be discussed in terms of normal mode coupling Of HSO4− and MgSO4 dissociation reactions. The observed decrease in absorption as HCl is added cannot be explained by ion-pairing concepts alone.
Acoustic force potential on a sphere in rectangular, cylindrical, and spherical resonators
Authors: Barmatz M. , Collas P.
Published: January 2006

Generalized expressions of the acoustic force potential on a sphere in rectangular, cylindrical, and spherical geometry have been developed. The method of Gor'kov [L. P. Gor'kov, Sov. Phys. Dokl. 6, 773 (1962)], valid for arbitrary sound fields was used to derive these expressions in the limit of small sample radius (kR < 1). The critical points of the force potential, where all the force components are zero, were investigated. General expressions for the coordinates of the potential minima for various modes were determined from theoretical considerations and an analysis of computer generated potential contour graphs. Besides isolated minima points, nonisolated minima were found consisting of lines, circles, and plane, cylindrical and spherical surfaces. The behavior of the acoustic pressure, potential, and forces for selected modes from each geometry is presented. The application of these modes to the field of acoustic levitation is also discussed. [Work supported by NASA.]
Propagation of standing waves in axisymmetric cavities enclosing an inhomogeneous medium
Authors: El-Raheb M. , Wagner P.
Published: January 2006

This paper studies how gradients in speed of sound c and density ρ influence standing waves in an axisymmetric cavity. The c and ρ gradients are assumed independent of radial and circumferential coordinates of the cavity and to vary only along its axis. The effects on propagation of the c and ρ gradients are studied separately. First, the problem with a step function as c gradient in a cylindrical cavity is treated in detail since it is amenable to analytical solution. A smooth c gradient described by exponential functions is considered. In this case, a transfer matrix coupled to a numerical integration procedure is adapted to the solution of the differential equation governing the axial dependence. The quasilinear c2 gradient follows and it also yields to analysis. The poor energy transmission characteristics of transverse standing waves in cylindrical cavities with c gradient prompted consideration of a geometry that includes two cylindrical segments with different cross sections joined by a conical connector. The transfer matrix method couples the acoustics of various segments of cavities. The radial dependence in the conical segment is determined by the method of shooting while the axial dependence follows from numerical integration. The analysis is then extended to cavities with concentric center bodies. An approximation considers piecewise conical frustra and leads to discontinuous pressure gradients at the junction of conjoined segments. The approximate analysis is tested against numerical results from an accurate simulation that invokes a Green's function and surface elements with account made for medium inhomogeneity.
Normal mode and ray equivalence in the Arctic sound channel
Authors: Mellen Robert H.
Published: January 2006

Effects of upward refraction combined with scattering by the rough ice interface result in a dispersive sound channel capable of propagating only very low frequencies to long range. Because only a few modes are involved, normal mode theory is appropriate. However, surface-scatter models are usually based on plane-wave approximations for which ray theory is most useful. The two approaches are simply combined in the impulse-response method. Application of this method to the propagation of transients and continuous wave signals is discussed. Removal of dispersive effects by deconvolution to increase data rate is also considered in view of the extreme temporal stability of the channel. [Work supported by ONR and NUSC.]
Sonar receiver performance models for the arctic channel in the presence of ridge scattering
Authors: Jacyna Garry M. , Friedman Alan J.
Published: January 2006

A generic class of sonar receivers are modeled in an attempt to describe average receiver performance in the Arctic channel. A ray-theoretic model, discussed in a companion paper, describes the average reverberation intensities within an Arctic channel in the presence of pressure ridge scattering. Receiver performance is evaluated in terms of signal detectability as a function of range, ridge location, and source/receiver depth. The models are extremely general in that arbitrary pulse shapes and sensor locations are allowed. As an illustration, two pulse shapes are considered—a transient and a CTFM pulse. Their effect on receiver performance is dependent on the source/receiver geometry as well as ridge location. In general, however, the longer CTFM pulse often leads to a reverberation-limited condition as a result of surface as well as pressure ridge scattering. [Work supported by ONR.]
Evaluation of a signal-averaging method for the measurement of signal-to-noise ratios in speech
Authors: Hillenbrand James
Published: January 2006

Many abnormal voice qualities are characterized by unusually large amounts of noise. Although the presence of noise is easy to identify, precise quantification of signal-to-noise (S/N) ratios is a difficult problem. Yumoto, Gould and Baer [J. Acoust. Soc. Am. 71, 1544–1550 (1982)] developed a technique based on signal averaging. Using a sustained vowel segmented into pitch periods, the signal component of the S/N calculation is defined as the average of the individual pitch periods. The noise component is estimated by successive subtractions of the average signal from individual pitch periods of the original vowel. In the present study, the accuracy of this technique was evaluated in a series of computer simulations. A synthesized vowel was mixed with varying amounts of synthesized noise. S/N ratios varied over a 36-dB range. Known S/N ratios were compared with S/N ratios calculated by the Yumoto et al. technique. The correlation between calculated and actual S/N ratios was nearly perfect (r = 0.99) and the mean absolute error was only 0.1 dB. Results are also reported for tests involving naturally produced vowels mixed with synthesized noise. [Work supported by NIH.]
Neural representation of bisonar information in the auditory cortex of the mustached bat
Authors: Suga Nobuo
Published: January 2006

For echolocation, the mustached bat (Pteronotus parnellii rubiginosus) emits orientation sounds containing up to four harmonics, each of which consists of a long constant-frequency (CF) component followed by a short frequency-modulated (FM) component. The auditory system of this species extracts different types of bisonar information from complex orientation sound and echo pairs and represents these systematically in the separate areas of the cerebral cortex. Nine clusters of combination-sensitive neurons have thus far been found in the auditory cortex. Two of these clusters making up the CF/CF area consist of CF1/CF2 and CF1/CF3 facilitation neurons which are tuned to particular Doppler shifts, i.e., target velocities from 8 to −2 m/s. The remaining seven clusters consist of different types of FM-FM neurons which are tuned to particular echo delays, i.e., target distances. Three of these clusters, making up the FM-FM area, consist of FM1-FM2, FM1-FM3, and FM1-FM4 facilitation neurons. The FM-FM area projects bilaterally to the dorsal fringe (DF) and ventrolateral (VL) areas of the nonprimary auditory cortex. The DF area consists of three clusters of FM-FM facilitation neurons. The VL area contains a small cluster of facilitation neurons that are tuned only to the FM1-FM2 combination. The FM-FM area represents target distances from 7 to 310 era, while the DF area represents these from 14 to 140 cm. [Work supported by 1-R01-NS 17333.]
Echolocation and foraging behavior of Hipposideros ruber (Chiroptera)
Authors: Bell G. P. , Fenton M. B.
Published: January 2006

Although a great deal of recent literature deals with the neurological and anatomical aspects of Doppler-shift compensation (DSC) by some bats, there are a few data on the foraging behavior of these species. We studied the foraging of Hipposideros ruber in Zimbabwe, and conclude from its behavior and echolocation calls that it is capable of DSC. These bats selected moths which were fluttering their wings whether the prey were flying or sitting on the substrate. If, during an attack, the moth stopped fluttering its wings, the bat terminated its approach. Pursuits of flying and sitting targets were equally successful, with the bats capturing the targets 40% of the time. Control experiments indicated that the bats did not use vision or the sound of fluttering to locate their prey. DSC appears to be a means of rejecting clutter. [Work supported by NSERC, Canada.]
Mechanisms of sonar pulse production by oilbirds
Authors: Suthers Roderick A. , Hector Dwight
Published: January 2006

The echolocating clicks of oilbirds (Steatornis caripensis) are generated in two bronchial semisyringes. Each click has a duration of 20 to 60 ms and may consist of a continuous broadband sound or be divided by a short silent interval into two shorter sounds. Electromyograms, together with measurements of subsyringeal pressure, tracheal pressure, and the rate of tracheal airflow, show that clicks are preceded by contraction of the sternotrachealis muscles which move the syrinx caudad, causing adduction of the syringeal membranes during expiratory airflow and initiating phonation. Subsequent contraction of a previously undescribed syringeal muscle terminates the click by rotating a syringeal cartilage and abducting the external tympaniform membranes. This syringeal muscle does not contract during longer duration vocalizations. It is thus specialized for the production of clicklike sounds. Simultaneous measurement of the rate of airflow through each semisyrinx indicates that during some clicks one semisyrinx closes while the other remains open. This is the first evidence that airflow through each side of the syrinx can be independently controlled during pronation. [Work supported by NSF.]
Acuity of echolocation in the oilbird, Steatornis caripensis
Authors: Thompson David B. , Suthers Roderick A.
Published: January 2006

The neotropical oilbird echolocates in totally dark caves with a click which has most of its energy between 0.5 and 3.0 kHz. The acuity of echolocation was measured with an array of stationary cylindrical obstacles (diameter 8.9, 3.2, or 0.5 cm) which were shifted between trials to prevent the birds from learning their position. Birds were tested in a dark room and observed with an infrared viewer. Flights through the row of obstacles were scored as hits, light touches, or misses. The birds' ability to negotiate the 3.2-cm array was significantly better than with 0.5-cm obstacles, indicating that oilbirds can acoustically detect 3.2-cm-diam obstacles. This is considerably smaller than the 20-cm threshold of previous studies [M. Konishi and E. I. Knudsen, Science 204, 425–427 (1979)]. Like echolocating swiftlets [D. R. Griffin and D. Thompson, Behav. Ecol. Sociobiol. 10, 119–123 (1982)] and bats, oilbirds can detect obstacles whose diameter is a fraction of the wavelength of their echolocating pulses. [Work supported by NSF.]
A new method for measuring head aim in echolocating bats
Authors: Masters W. Mitch , Simmons James A.
Published: January 2006

A new method has been developed for continuously monitoring the direction in which an echolocating bat is pointing its head. Two light emitting diodes are mounted on the bat's head and their positions read sequentially, under microprocessor control, using an x-y position sensing photodiode. The microprocessor calculates the angle of the line between the two light emitting diodes with respect to an initial direction, and the location of the midpoint of this line. Readings can be made over a 360° range with an accuracy of ±1°, at a rate of 100/s. This device has been used to determine the bat's head aim in measurements of horizontal angular resolution. Simultaneous monitoring of the bat's sonar emissions provides data on how information is integrated over time by the bat. Results of these studies will be discussed. [Work supported by NIH and NSF.]
Spectrogram processing in echolocation
Authors: Altes Richard A.
Published: January 2006

Echolocation behavior and neuronal representations of sound suggest that animal sonar can be modeled in terms of a spectrogram correlation process. Recent experimental results, however, indicate that bats may be sensitive to the fine structure of the signal-echo cross-correlation function (J. A. Simmons, Science 204, 1336). This sensitivity cannot be explained by cross correlation of spectrograms. Spectrogram deconvolution or an analysis-by-synthesis procedure can be used to reconstruct a signal from its spectrogram, aside from an arbitrary phase shift. Cross correlation of two such reconstructed signals, with the same arbitrary phase shift assigned to both, yields the required sensitivity to cross-correlation fine structure. The waveform reconstruction procedure is accurate only if spectrogram filters are not smooth window functions as in man-made processors, but have large time-bandwidth product, e.g., sharp rise and slow decay in the frequency domain, as in critical band models of hearing. This filter property insures that the filter ambiguity function has the same or larger support in the range-Doppler plane as the signal ambiguity function, a necessary condition for spectrogram deconvolution.
Stimulus parameters governing confusion effects in forward masking
Authors: Neff Donna L. , Weber Daniel L.
Published: January 2006

Confusion effects in forward masking occur when the listener has difficulty discriminating a suprathreshold signal from the preceding masker. Confusion effects were examined for “pulsing” forward maskers composed of repeated bursts of a sinusoid followed by a sinusoidal signal. Differences between the level, frequency, and duration of the signal and an individual masker pulse, as well as offset—onset delay were varied to determine the change necessary to resolve confusion. For maskers composed of 20-ms pulses, changes in signal level of 1–5 dB or in signal frequency or 20–30 Hz resolved confusion. For maskers composed of 10-, 20-, or 40-ms pulses, the signal delay necessary to resolve confusion increased with masker-pulse duration but was typically less than 10 ms. For these three pulsing maskers, signal durations less than one half or greater than twice the masker-pulse duration were necessary to resolve confusion. [Work supported by NSF, NIH, and the University of Nebraska.]
The occlusion-impedance of the ear canal and its influence on the occlusion effect and external physiological masking
Authors: Pösselt Christoph
Published: January 2006

Bone conduction (BC) as the limiting factor for the sound protection rate of earplugs and earmuffs can be calculated by models. A model of this kind is part of a dummy head system, recently developed in our laboratory for objective sound attenuation measurement of sound protection devices. Based on the separation of BC into external-, middle-, and inner-ear components, the model allows determination of BC according to the actual type of occlusion. BC is mainly affected by the acoustic impedance, seen outwards from the entrance to the ear canal. We have measured this “occlusion-impedance” for different occluding devices. Sample results will be presented. The occlusion effect is, then, determined by the occlusion impedance and, also, by the relative vibrations between skull and earmuff, the latter depending on the mechanical impedance of earmuff and underlying skin as well as on the vibration modes of the skull. Further, the physiological noise spectrum, as generated in the external ear, is affected by the occlusion impedance too, thus leading to a characteristic external physiological masking, former known as the “missing 6-dB effect.” [Work partly supported by Minister für Wissenschaft und Forschung, NRW.]
Detection cues in forward masking and their relationship to off-frequency listening
Authors: Yacullo William S. , Abbas Paul J.
Published: January 2006

Previous studies [D. Johnson-Davies and R. D. Patterson, J. Acoust. Soc. Am. 65, 765–770 (1979) and B. J. O'Loughlin and B.C. J. Moore, J. Acoust. Soc. Am. 69, 1119–1125 (1981)] suggest that off-frequency listening is a major factor contributing to sharpness of psychophysical tuning curves. The present study is designed to evaluate the contribution of off-frequency listening to the sharpness of psychophysical tuning curves as a function of temporal characteristics of both the variable masker and stationary masker used to restrict listening to a narrow region surrounding the probe using the restricted-listening tuning curve paradigm first employed by Johnson-Davies and Patterson (1979). Conventional forward-masked psychophysicai tuning curves initially were generated using stimuli of varying temporal characteristics (sinusoids, AM and QFM tones, and AM noise) as the variable masker. Restricted-listening tuning curves subsequently were obtained utilizing fixed-level stationary maskers 100 Hz wide of differing temporal characteristics (QFM tone, AM noise, and synthetic noise comprised of sinusoids of equal amplitude, random phase relation, and spaced 1 Hz apart) which were gated with the variable masker. Results suggest that the off-frequency listening effect observed utilizing a tuning curve paradigm is largely dependent on the temporal characteristics of both variable and stationary maskers. Assuming differing detection mechanisms for maskers of varying temporal characteristics, it appears that the different detection cues are not equally dependent on off-frequency listening.
Masking ability of forward maskers of varying temporal characteristics
Authors: Yacullo William S. , Abbas Paul J.
Published: January 2006

It has been suggested that the detection cues for simultaneously presented sinusoidal and noise maskers are different [D. Green, J. Acoust. Soc. Am. 41, 1517–1525 (1967) and D. Weber and R. Patterson, J. Acoust. Soc. Am. Suppl. 1 68, S37 (1980)]. The present study was designed to evaluate masking ability of forward maskers of varying temporal characteristics. Conventional forward-masked tuning curves were generated utilizing a sinusoidal probe and four types of stimuli for the masker: a sinusoid, quasi-frequency-modulated (QFM) tones, AM tones, and AM narrow-band noise 100 Hz wide. These maskers were selected as their envelopes possess a wide range of amplitude fluctuation. The AM and QFM tones (50 Hz wide) had identical spectral structures, yet distinctly different temporal characteristics. Differences in masker effectiveness were evaluated by comparing the tuning curves generated using the various types of maskers. Results indicate that stimuli with amplitude fluctuations that are large and random in nature (AM noise) exhibit greater forward masking ability that stimuli with either minimal or no envelope variation (QFM tone and sinusoid) or large, yet periodic, amplitude perturbations (AM tone). This difference in masking ability is exhibited on the high-frequency branch and within the tip region of the tuning curve. it is suggested that differences in masking ability may reflect the use of different signal detection cues.
Changes in differential sensitivity for frequency modulation in noise-exposed chinchillas
Authors: Clark William W. , Bohne Barbara A. , Long Glenis R.
Published: January 2006

Frequency modulation discrimination thresholds were obtained for two chinchillas before, during, and after exposure to an octave band of noise centered at 0.5 kHz, 95 dB SPL, for 54 days. During exposure, when the animals had threshold shifts of 35–45 dB, difference limens for frequency modulation (DLs) were impaired by ten-fold for center frequencies below 2.3 kHz; at 2.3 kHz and above they were completely unaffected. Thirty days after exposure, when threshold shifts had recovered to about 25 dB, DLs recovered about halfway (fivefold reduction) for the low-frequency stimuli; high-frequency DLs remained normal. Histological evaluation of the cochlea from these two animals showed losses of outer hair cells in the apical turn averaging 30%, and a basal-turn lesion in one animal at a point 60% of the distance from the apex. The results of this study extend our previous observation that the base and the apex of the cochlea are affected differently by exposure to noise. [Work supported by NINCDS.]