bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of loss coefficients and phase velocities for optical fibers
Authors: Cuomo F. W. , MacMillan W. W.
Published: October 2005

The standing wave method has been widely used in the determination of the damping properties of viscoelastic solids in the 100–10 000 Hz range and loss coefficients have been obtained either by the experimental observation of the decay modulus or the half-power bandwidth of each resonant peak. This paper investigates by this method the behavior of optical fibers to mechanical vibrations. It is found that for plastic clad fibers the phase velocities are largely dependent on the tension and mass density while for other fibers tested the system behaves as a stiff string whereby the modulus of elasticity takes on a more pronounced role. Experimental data are presented to illustrate the differences in loss factors and phase velocities for several optical fiber configurations. [Work sponsored by NUSC.]
Accessible calibration technique for mechanical impedance measurements
Authors: Corliss Edith L. R.
Published: October 2005

A velocity pickup for stereo disk playback can be calibrated for magnitude of velocity response by using commercially available test records modulated by pure sinusoidal signals. The records may be calibrated independently by using a collimated light beam (sealed beam headlamp) and measuring (with divider and ruler) the extent of the “Christmas Tree” pattern reflected from the grooves. During playback at measured speeds the record becomes a source of calibrated velocity amplitude for each of the pickup channels. Summing and differencing the pickup outputs convert right and left to vertical and horizontal outputs. The phase difference between the stylus velocity and the electrical output of the pickup is calibrated by placing the cartridge tip in a dimple cut into the ground electrode of a piezoelectric force transducer driven electrically well below its resonant frequency. The driving voltage and the pickup output then exhibit the same phase relation as the groove displacement and the pickup output. The force/velocity ratio measuring system is calibrated as a function of frequency by using known masses as loads. For measuring an unknown mechanical impedance, the force pickup is interposed between a driver and the load, with the pickup stylus mounted either in the dimple in the electrode, or on the surface of the load. [This work has been performed using the facilities of the National Bureau of Standards.]
Abbreviation of consonants in clusters: A condition on the temporal structure of syllables
Authors: Walsh Thomas , Parker Frank
Published: October 2005

Consonants in clusters are abbreviated by as much as 30% [Haggard, J. Phon. (1973), Klatt, J. Acoust. Soc. Am. 59, 1208–1221 (1976)]./s/ and /k/, e.g., are shorter in mask than in mass or Mac. Although previous studies have attempted to explain this phenomenon in terms of phonetic context, they leave one basic question unanswered: is shortening an active process? (Earlier investigators considered only two-segment clusters within a single morpheme, which may be frozen forms functioning as single consonants.) In order to address this question, a production experiment was devised in which single consonant morphemes (/t, d, s, z/) were affixed to monosyllables ending in two-segment clusters. The results indicate that the addition of a final segment has the effect of shortening a non-contiguous segment (e.g., the /s/ in masked is shorter than the /s/ in mask). This illustrates two points: (1) shortening is an active process; and (2) it is not simply a function of immediate phonetic context; rather it is controlled on a higher level of organization as a condition on the temporal structure of syllables. There seems to be a tendency to maintain the final consonant portion of a syllable at a fixed ratio to the total duration of the syllable [Port, J. Acoust. Soc. Am. 69, 262 (1981)]. Other processes affecting clusters (e.g., cluster reduction) can also be explained by this principle.
A transport-theoretic analysis of pulse propagation through ocean sediments
Authors: Kohler Werner E. , Besieris Ioannis M. , Freese Herb
Published: October 2005

The reflection of pulsed acoustic plane waves from ocean sedimentary layers is studied using a stochastic transport theory originally introduced by Barabanenkov et al. [lzv. VUZ., Radiofiz. 15, 1852 (1972)] and subsequently extended to the two-frequency context needed for the study of pulse propagation by Besieris and Kohler [Proceedings of the Symposium on Multiple Scattering and Waves in Random Media, edited by P. L. Chow, W. E. Kohler, and G. C. Papanicolaou (North-Holland, Amsterdam, 1981)]. The sediments are assumed to constitute a random medium in which the density and sound speed undergo small, highly laminated (pancake-like) fluctuations. Although the problem is formulated in a general context, the predictions of the theory are fully evaluated only in the special case of normal incidence and no refracting profile. However, even with these approximations, some reasonable qualitative agreement of theoretical predictions with measured data (Hatteras abyssal plains) is achieved. [Work supported by ONR Contract No. N00014-76-C-0056 and NAUSEA Code 63D.]
Mechanical linkage projectors
Authors: Wilcox Howard A.
Published: October 2005

Fundamental constraints pertaining to resonant types of low-frequency underwater projectors explain why a nonresonant approach has permitted the design of a relatively small, efficient, and inexpensive projector whose output frequency, piston motion amplitude, and operating depth are all independently controllable. The resulting unit is inherently a “standard” source not requiring calibration by auxiliary instruments. Overall energetic efficiencies of 1% to 2% have been achieved in operating at 15 Hz and shallow depths (500 ft). Design principles have been worked out for achieving instantaneous switching of output amplitude, frequency, and phase as well as for the simultaneous output of two or three anharmonically related signals. The first unit displaces about 216 lb, uses a 1/12th HP electric motor to generate a 15-Hz signal at a source level of 171 dB re 1 μPa at 1 m, and would cost about $7000 each to manufacture in lots of ten.
A high-power, low-frequency hydroacoustic sound source
Authors: Utterback Max , Nichols Steve
Published: October 2005

A low-frequency sound source of high acoustic output (214 dB re 1 μPa at 1 m) has been developed by Hydroacoustics Inc. The projector has been configured to operate over two distinct frequency bands, with a bandwidth of approximately 40% of each band-center frequency. The conversion between the two bands requires relatively simple hardware changes, principally in the radiating structure. The primary input power to the source is in the form of three-phase electrical power to an electric motor driven hydraulic power supply which is an integral part of the projector structure. Conversion of the input power to acoustic energy is accomplished through a rugged hydroacoustic power amplifier which responds to a low level signal voltage and reproduces this waveform as acoustic pressure/flow acting in a centrally located fluid cavity. Two opposed, edge-supported radiating flexural disks are center driven by drive pistons which communicate with this fluid cavity. The entire structure is very rugged and capable of operation to great depths. Analytical modeling of this projector has been developed by the Naval Ocean Systems Center in conjunction with Hydroacoustics. This model includes the radiation loading, the flexural modes of the radiating disks, the hydraulic power supply, and the two stage hydraulic amplifier—including those nonlinearities associated with large power transduction. In water calibration test results in both bands will be presented, as well as a comparison between these results and the modeling effort. [Work supported by the Naval Electronics System Command.]
A modified AO projector
Authors: Armstrong B. A. , McMahon G. W.
Published: October 2005

The AO projector is a WWII British Admiralty minesweeping source that operated at 230 Hz with a source level of about 198 dB re/μPa at 1 m. Being virtually indestructible, many still exist in operating condition. To improve their utility as research sources, three AO's have been modified to resonate at 110 Hz. A SCUBA pressure compensation system has been installed to extend their operating depth capability. The source level at resonance is displacement limited to 195 dB and a current-limited, broadband source level of at least 182 dB is available above resonance up to the diaphragm breakup at 700 Hz. The modification method will be described and performance predictions given for a modified AO with an 80-Hz resonance.
Measurements of violin vibrato
Authors: Miller Joan E.
Published: October 2005

The periodicity of bowed violin strings has been measured with high resolution by means of a specially designed violin bridge and computer interface. (See ASA Meeting, May 1981, Ottawa, Canada.) The equipment has been used here to examine various characteristics of vibrato. Period lengths are measured with accuracies ranging from 0.5 to 4 cents for a corresponding frequency range of 195 to 1950 Hz, and the four strings are each sampled every 5 ms. Thus, data are gathered in the form of a time series whose probability density and spectrum can be estimated. These measures are examined in the context of actual music as well as sustained notes played on different strings with different fingers and in different positions by different players.
Spectral and perceptual analysis of percussion instruments
Authors: Cohen Elizabeth , Hart Michael S. , Schloss Andrew
Published: October 2005

A series of recordings of percussion family instruments were made in both live and anechoic settings. We examined the response of idiophones (cymbals, gongs, chimes) and membranophones to strokes gauged to produce approximate levels for pp, p, mp, f, etc., which differ by roughly 10 dB. An assortment of strokes, including rim shots, were also included. The sounds were recorded on a Nagra stereo recorder, digitized and analyzed. The results from the three-dimensional spectral plots were compared to subjects data as to pitch and spectral content of instruments. From the study of some members of the idiophone family, we are able to detect certain temporal and spectral characteristics pertinent to the evolution of Chinese gongs. The degree of inharmonicity of the partial sequence for these instruments was also measured.
More on “lucky” equal temperaments
Authors: Hall Donald E.
Published: October 2005

Equal temperaments with N tones per octave can only approximate the small-integer frequency ratios of just tuning. At the Iowa City conference (May 1981) I discussed a probability approach to the question of just how remarkable are the close fits made available by values such as N = 12, 19, 31, and 53. After briefly reviewing that method, I will present an extension of the calculated results up to N = 600, as well as some remarks about ways of predicting which values of N should be “lucky.”
Introduction to the Special Session on innovative fan design
Authors: Brittain Frank H.
Published: October 2005

This paper will serve as an introduction to this special session. The state-of-the-art of prediction of noise from fans and control of that noise will be reviewed. Special problems in predicting fan noise and where normal noise controls are not adequate will be discussed. Also novel methods for controlling fan noise will be identified.
Basic fan noise generation mechanisms and innovative aerodynamic design techniques for their reduction
Authors: Brown Neal A.
Published: October 2005

For low-speed fans, noise radiation results from fluctuating aerodynamic forces on the blades. These may be characterized by their origin as due to vortex shedding or inflow turbulence ingestion. Both of these force and noise mechanisms are nominally broadband in frequency. However, a specialization of the latter considering a standing pattern of inflow velocity distribution yields the familiar discrete frequency spectrum of harmonics of the blade passage rate. Beneficial changes in noise levels and spectral distributions are described and demonstrated for changes in fan blade form such as thickness distribution and sweep. Blade edge sweep is shown to be particularly useful in reducing noise from both aerodynamic phenomena and, with careful design, effective in reducing discrete frequency noise as well. Examples are presented of automotive type fans designed for low noise using these techniques. Not only is noise reduced, but because of the sophisticated aerodynamic considerations required on loading and load distributions, the efficiency is markedly improved.
A signal-detection-theory measure of pitch shifts in sinusoids
Authors: Jesteadt Walt , Neff Donna L.
Published: October 2005

Traditionally, pitch shifts associated with changes in the intensity of sinusoids have been measured using the method of adjustment. The resulting pitch matches often show great variability within listeners and large differences across listeners. To demonstrate an alternative approach, we measured frequency discrimination at 250 and 4000 Hz for three listeners using a 2IFC procedure with intensity differences between intervals and no feedback. Pitch shifts associated with the intensity differences result in better frequency discrimination performance (when the shift adds to the frequency difference), poorer performance (when the shift subtracts from the frequency difference), or a response bias (when both frequencies are shifted and the frequency difference is unchanged). Identical estimates of the pitch shift in Hz can be derived from either the performance or response-bias effect using standard signal-detection theory assumptions and information about the psychometric function. In agreement with the literature, these estimates indicate that pitch increases as a function of intensity at 4000 Hz and is nonmonotonic as a function of intensity at 250 Hz. Pitch matches obtained with the method of adjustment show a similar pattern with smaller pitch shifts. [Work supported by NIH and NSF.]
Free-field measurements on hearing-impaired listeners
Authors: Colburn H. S.
Published: October 2005

Performance of a number of hearing-impaired listeners was measured in a set of free-field tests. The listeners have sensorineural hearing losses with varied histories. The tests included direction-discrimination, direction-identification, and masked detection for several combinations of target and masker directions. The stimuli were noise bursts, either unfiltered or one-third octave bands centered at 0.5 or 4.0 kHz. Results from hearing-impaired subjects are compared with results from normal control subjects and from the literature. Attention is focused on the degree to which the different tests provide independent sources of information about individual abilities. Preliminary analysis of results show that, apart from gross relationships (such as vertical errors in identification corresponding to poor discrimination ability in the vertical median plane), confusions in identification are not directly predictable from measurements of discrimination ability. [Work conducted at MIT Research Laboratory of Electronics and supported by NIH.]
On the calculation of group velocity, attenuations, etc. in a normal mode description
Authors: Penland Cecile , Vidmar Paul J. , Koch Robert A. , Hawker Kenneth E.
Published: October 2005

The fact that a normal mode's group velocity may be calculated, without invoking a finite difference approximation involving a second eigenmode computation, does not appear to be widely recognized. The reciprocity relation is typically employed in the derivation of a group velocity formula in a way analogous to the derivation of normal mode attenuations. This paper obtains these results easily using the adjointness property and inner product appropriate to the problem. The complementarity of the reciprocity and adjoint methods is discussed. [Work sponsored by Naval Ocean Research and Development Activity.]
Precise measurement of frequency disperson and experimental tests of the scaling law for group velocities of different modes
Authors: Yang T. C.
Published: October 2005

The time-frequency structure of wideband pulses propagated to long ranges in the sound channel is investigated experimentally. A method is presented to measure precisely the frequency dispersion with respect to time for each mode. The method is based on a saddle point approximation for the power spectra of a series of segments of the received time series. It is found that if the length of the time segment lies within certain bounds, the spectrum shape can be predicted and should be peaked at the mode frequencies. Results of the analysis for typical shot data in the Arctic Ocean, Shallow Water, and SOFAR Channel will be presented. This method improves the accuracy of the mode frequency measurement by roughly a factor of six over the sonogram method. With the improved precision, one can check experimentally the validity of the scaling law for group velocities of different modes, i.e., Un(ω) = Um(αω) where α is the scaling factor determined partly by the mode number n and m. Some useful implications of the scaling law will be discussed.
Broadband interference patterns in shallow water
Authors: Bachman Richard T. , Bucker Homer P. , Stixrud Thomas E. , Kaye G. Thomas
Published: October 2005

While measuring ship-radiated noise levels in the Inland Sea of Japan, broadband interference patterns were observed for ranges less than 1500 m. The water depth was 42 m with little bottom relief. The water column was well mixed with practically no thermocline. The sea state was nearly calm. For these conditions interference patterns could be observed at acoustic frequencies of 200–2000 Hz, which varied with source-receiver geometry. A ray-tracing program was developed to explain these patterns assuming no acoustic refraction and a simplified bottom loss algorithm. In addition to the Lloyd mirror effect, the patterns were reconstructed from those paths which encountered one bottom reflection. The reconstructed patterns have intensity variations, frequency dependence, and range dependence quite similar to the observed data.
Auditory localization in normal hearing and in high frequency sensorineural hearing impairment
Authors: Ahlstrom Christopher , Humes Larry E. , Grantham D. W.
Published: October 2005

Normal subjects and two age groups of subjects with high-frequency sensorineural heating loss localized white noise in the horizontal and vertical median planes. One hearing-impaired group comprised subjects under 50 years of age; the other comprised subjects over 65 years of age. Thirteen horizontal speakers spanned 180° (±90° from 0° azimuth); four vertical speakers spanned 67.5° (0° to 67.5° elevation). The localization responses were converted to an average magnitude of response error and the preliminary results were analyzed within the framework of the model of auditory localization proposed by Searle et al. [J. Acoust. Soc. Am. 60, 1164–1175 (1976)]. Results were analyzed with regard to the adequacy with which this model described the performance of normal hearers and the modifications of the model required to account for the data obtained from impaired listeners. In addition, the auditory localization abilities of hearing-impaired subjects were compared to those of normal hearers. [Supported, in part, by grant 1-R01-OH00972 from the National Institute of Occupational Safety and Health.]
Lateralization as a measure of suppression
Authors: Weber Daniel L. , Jesteadt Walt
Published: October 2005

A contralateral signal presented at the same time and at the same frequency and intensity as an ipsilateral signal leads to an apparent sound source in the medial plane. The level of the contralateral signal required to produce this effect (the lateralization level) has been used as an estimator of the effective level of the ipsilateral signal in studies of suppression. The apparent contradictions between the properties of suppression measured with lateralization and other techniques are probably attributable to an oversimplified interpretation of the lateralization data. We examined lateralization level as a function of the temporal position of the binaural signal with respect to an ipsilateral masker for several levels of the ipsilateral component of the signal. We found a reduction in lateralization level associated with the introduction of the masker when the masker onset preceded signal onset by about 25 ms or more. We could not obtain an image in the medial plane by presenting a brief ipsilateral signal during an ongoing contralateral signal. The simple interpretation of lateralization as a measure of the effective level of the ipsilateral signal component fails to account for these data, and we argue that the conclusions reached in some earlier lateralization papers should be reconsidered.
Human exposure to vibration: current topics and research methods
Authors: Guignard J. C.
Published: October 2005

Continuing interest in the immediate and long-term effects of human exposure to low-frequency mechanical vibration is reviewed, with particular reference to naval operational and occupational health applications of human whole-body vibration research. The availability of data suitable for incorporation into cognate standards will be touched upon, as will aspects of research methods in human motion and vibration studies. Reference will be made to a recent workshop on the latter topic (to be convened in New Orleans in September 1981).
Cardiovascular responses to low-frequency whole-body acceleration
Authors: Knapp C. , Evans J. , Randall D. , Marquis J. , Bhattacharya A.
Published: October 2005

In one study, sinusoidal whole-body acceleration was used as a noninvasive forcing function to establish the frequency response characteristics of cardiovascular regulation. Unanesthetized (tranquilized), chronically instrumented dogs were exposed to ±2gz acceleration from 0.005 to 0.25 Hz. The participation of neurally mediated cardiac and vascular control mechanisms was examined by comparing the responses of the same animal in a normal (reflexive) state and in a parmacologically blockaded (nonreflexive) state. Integrated neural mechanisms (a) were found to be the most effective in minimizing acceleration-induced, arterial pressure disturbances for frequencies below 0.012 Hz; (b) became progressively out of phase with the disturbances between 0.012 and 0.052 Hz, resulting in decreased effectiveness; and (c) failed to significantly participate for frequencies between 0.052 and 0.25 Hz, where “protection” was provided by the hydraulic and intrinsic biomechanical aspects of the circulatory system. In a second study, whole-body oscillatory acceleration (WBOA) was evaluated as a countermeasure to cardiovascular deconditioning of bed rest. Six adult males were exposed to (a) a control, orthostatic tolerance test (OTT) using 70° head-up tilt for 20 min; (b) an OTT after 6 h of 5° head down bed rest (BR); and (c) an OTT after BR plus 18 min of WBOA (subject supine, 1 and 1.6 gz, 1 Hz, half-sine displacement). Four of the six subjects demonstrated presyncopal episodes during the OTT after BR without WBOA. In all four subjects the presyncopal episodes were either eliminated or the time to occurrence was increased by WBOA. Of the two subjects that did not exhibit presyncopal episodes, one had a reduced orthostatic heart rate response, following WBOA and the other exhibited a higher response. [This research supported by AFOSR Grant 80-0039 and NASA Grant NSF 2318.]
Physical implications of a two-component model for signal fluctuations in the sea
Authors: Urick R. J.
Published: October 2005

An earlier paper [J. Acoust. Soc. Am. 62, 878 (1977)] described a model for the fluctuation of transmitted sound in the sea, wherein the received signal is postulated to have two components: A steady component plus a random component to such causes as multipath interference, microstructure and scattering. The parameter describing the statistics of the fluctuation was called the randomicity, defined as the ratio of random power to the total power in the received signal. The purpose of the present paper is to point out that the model accounts for two fluctuation characteristics in a simple way. One is the observation that, at short ranges, the square of the coefficient of variation, equivalent to randomicity, increases linearly with range, as power is extracted from the steady component and fed into the random component. The other is that, at long ranges, a slowly varying signal, when momentarily strong, fluctuates less than when it is momentarily weak. In the model, this is the result of adding a constant amount of scattered power to the slowly varying power arriving via multipaths. The model thus has physical implications important to an understanding of sound propagation in the sea.
Bounds on performance in acoustic tomography
Authors: New Ronald , Eisler Thomas J. , Calderone Denise
Published: October 2005

The results of a three-dimensional ocean experiment in Acoustic Tomography (AT) are, at this time, being processed and reviewed by the originators in the University Consortium [W. Munk and C. Wunsch, Deep-Sea Res. 26A, 123–161 (1979)]. The hope is that AT will some day soon provide an economical and accurate means to monitor changes in the sound velocity structure over large expanses of the ocean volume. NOAA is attempting to anticipate the engineering implications of operating and maintaining basin-wide and smaller-scale AT systems. We are concerned with the likely bounds on performance and, ultimately, will study the relationships between performance and benefits in the civilian sector—in particular, for climate and fishery studies. Estimates of the sound speed distribution are made by inverting travel time relationships. The accuracy and resolution of these estimates can themselves be estimated and, when combined with field data, used to study the performance of a given AT system versus given design parameters. In our present work, these performance relationships are studied and interpreted by means of a well-known approach of geophysics, the Backus-Gilbert theory. In this approach, the estimate is interpreted as a weighted local average of the unknown function, with statistical error. An averaging kernel is defined which, when integrated with the actual unknown function, produces a local average; this kernel can, therefore, be interpreted as a property of the system. The width of this function defines resolution length. A trade-off relation exists between accuracy and resolution length. Examples will be presented for a two-dimensional problem, a tomographic configuration in a horizontal ocean slice.
Accentuation in reading aloud of news bulletins
Authors: Nooteboom S. G. , Kruyt J. G.
Published: October 2005

Earlier research has led to a “grammar of Dutch intonation,” i.e., a set of rules for generating a suitable pitch contour for any to be synthesized Dutch sentence. However, before these rules can be applied the location of the pitch accents and prosodic boundaries must be specified. As a first step towards accent location rules, the accentuation behavior of Dutch speakers was examined as they read aloud sentences occurring in simulated radio news bulletins. The major independent variables were syntactic form and whether or not a particular referent had been mentioned in the preceding sentence. In all 1296 utterances were transcribed for pitch accents in terms of the grammar of Dutch intonation. The results show that pitch accents occur on a high percentage of the content words. Probability of accentuation is related to word class, lexical meaning, syntactic position, and, to a minor extent, to previous mention of the same referent. [Work supported by the Netherlands Organisation for the Advancement of Pure Research.]
The uses of acoustical scale modeling
Authors: Lyon Richard H.
Published: October 2005

Acoustical scale modeling has evolved in both applications and techniques since the 1930's. This paper reviews the purposes for which modeling has been used, the demands upon instrumentation and materials and the developments in both uses and methods. The uses include scientific study, education, understanding and design of listening spaces, the prediction of noise environments, and design of noise reduction into various situations. Each of these applications place differing demands on instrumentation and methods, and some demands have been met better than have others.
The Hydroshock® water gun
Authors: Bouyoucos John V. , McLaughlin J. K. , Selsam R. L.
Published: October 2005

An impulsive acoustic source has been developed which uses water under high pressure to create a controlled, impulsive signature generally free of bubble pulses or other aftershot clutter. The gun uses high-pressure water to force a piston back against an air spring to a stop position. A trigger signal releases the piston which drives water through ports in the gun housing to form jets at right angles to the axis of piston travel. The piston abruptly closes the ports as it passes by them, terminating the jets and generating cavitation voids. The voids subsequently collapse in synchronism, away from the body of the gun, creating the gun signature. A prototype model, designated HS-56, exhibits a peak-to-peak signature in excess of 8 bar meters (238 dB re 1 μPa@ 1 M) in a 0–2 kHz band, and can be fired at repetition periods of less than 4 s with a 15-hp pump. This model appears useful for high resolution engineering profiling, subbottom investigations, target impulse response studies, and various signaling applications. The gun concept and the results of calibration, reliability and operational tests will be described. A comparison of HS-56 performance with that of competing seismic sources will also be discussed.
Vibrations of and radiation from rib-stiffened water-loaded plates driven by line loads
Authors: Gorman Robert M.
Published: October 2005

The vibrations of and radiated pressure from rib-stiffened water-loaded plates of infinite extent were investigated. By restricting the excitation to sinusoidally varying forces acting along lines parallel to the ribs, the problem is mathematically reduced to an infinite beam with impedance discontinuities representing the ribs. The reaction forces and moments these ribs apply to the plate were calculated and put in terms of force and moment transmissibilities similar to those defined by Snowdon in his work on beams. The cases investigated included two symmetrically spaced ribs excited by a central line force or moment. Both clamped and pinned ribs were evaluated. The effects of inherent plate damping, rib spacing and fluid loading on these transmissibility ratios and resultant acoustic radiation below the critical frequency were calculated.
Acoustical impact of a large outdoor amphitheater on surrounding residences
Authors: McKay Ronald L. , Conant David A.
Published: October 2005

A 3800-seat amphitheater offers amplified popular music concerts within hilly and densely populated terrain. Measured sound levels within the amphitheater and the residential community from 0.5 to 1.25 miles away are presented. Music levels are compared to neighborhood ambient levels and complaint records. Additional attenuation-versus-distance data for rough terrain are offered as well as the noise reduction expected from a fabric enclosure.
Early conceptions and later progress in our understanding of the amphibian ear
Authors: Wever E. Glen
Published: October 2005

In the early investigation of the ear of vertebrates, which had its main advance during the middle of the 19th century, concern for the amphibian ear lagged far behind that for all other types. Under the influence of evolutionary doctrine the early anatomists assumed that this ear must take its place in the series without any significant departure from the general form. Thus they believed that they had identified an auditory papilla like that already known in reptiles and mammals, complete with a basilar membrane on which the hair cells were borne in the usual way. They described and pictured such an organ and its several parts as they perceived them by the only methods then available, which consisted of gross dissection with the aid of relatively simple optical instruments. It remained for later developments of techniques, including proper methods of histological treatment, serial sectioning, differential staining, and the use of high powers of the microscope, to show that the assumption of a progressive relationship for the ear along the vertebrate series is erroneous: that the amphibian ear does not fall into such a pattern but is unique both in structure and mode of performance in response to sounds. Some of these new developments in the character of the amphibian ear emerged during the latter part of the previous century and earlier years of the present one, but many of the details have come to light only recently, and the complete story is still to come. Some of the principal features of the ears of the three existing orders of amphibians will be described and pictured.
Mechanical and electrical mechanisms in the ear: Alligator lizard tales
Authors: Weiss T. F. , Peake W. T. , Leong R. , Holton T. , Rosowski J. J. , White J. R.
Published: October 2005

The ear of the alligator lizard is similar in structure and function to mammalian ears, but somewhat simpler and more accessible to in vivo experimental studies. Our focus has been on signal transmission through the middle ear and the portion of the inner ear having hair cells with free-standing stereocilia. We have measured two-tone distortion products in the sound pressure and the input admittance at the tympanic membrane; velocity of the extrastapes, stapes, and basilar membrane; intracellular receptor potential of hair cells; and spike discharges of cochlear nerve fibers. Many features of these measurements have been represented by a model of the underlying mechanical and electrical mechanisms. Conclusions suggested by the experimental and theoretical work include: (1) Nonlinearities detected in the external and middle ear responses appear to be independent of mechano-electric transduction in the cochlea. (2) The nonlinearities observed in the receptor potential at low-stimulus levels are associated with hair-cell processes. (3) The frequency selectivity of the receptor potential is determined not only by the middle-ear—basilar-membrane mechanical system but also by stereociliary-tuft resonances whose frequencies depend on tuft morphology. [Supported by NIH and the Whitaker Health Sciences Fund.]
Supersaturation of fluctuations of waves propagating in a random medium
Authors: Wenzel Alan R.
Published: October 2005

A theoretical analysis of the incoherent (or fluctuating) component of the wave field radiated by a point source in a one-dimensional random medium is presented. The approach is based on a perturbation technique which is similar to the Rytov method, and which is referred to here as the quasi-Rytov method. The analysis includes both multiple forward-scatter and multiple backscatter effects. An approximate expression for the second moment of the incoherent wave as a function of propagation range is obtained for the case in which the wavelength is much less than the correlation length of the medium. This expression shows that the fluctuations of the wave increase relatively rapidly with propagation range until a maximum value (the supersaturation value) is reached, after which they decrease relatively slowly with further increase in range. These results are in qualitative agreement with observations of intensity fluctuations of optical waves propagating in the lower atmosphere. [Work sponsored by NORDA.]
Incoherence in the propagation of sound near the ground
Authors: Daigle G. A. , Piercy J. E. , Embleton T. F. W.
Published: October 2005

Coherent propagation is normally assumed when predicting levels of community noise. However, atmospheric turbulence reduces both longitudinal (along the propagation path) and lateral coherence (along the wavefront) progressively with distance from the source. We have measured both coherences for pure tones between 500 to 4000 Hz during propagation over ranges up to 100 m from a point source on the ground, with microphone heights up to 6 m. Preliminary analysis of results indicates that: (1) the longitudinal coherence length is similar to the saturation distance for fluctuations of amplitude, (2) the lateral coherence drops asymptotically with increasing distance along the wavefront to the longitudinal value for a given range, and (3) the lateral coherence length for the incoherent wave is approximately 1 m (a figure also representative for the correlation distance of fluctuations of acoustic refractive index), and is relatively independent of frequency, provided the microphone is not too close to the ground. These results are compatible with some theories of propagation in a turbulent medium. The results indicate that the “incoherent wave,” which is commonly ignored, is often a more important carrier of acoustic energy outdoors than the coherent wave to which normal acoustical theory applies.
Analysis of the sensitivity of 2-1000 Hz shallow water acoustic/seismic propagation to geophysical and oceanographic parameters
Authors: McLeroy E. G.
Published: October 2005

An extensive acoustic/seismic propagation experiment has been conducted in shallow water off Panama City, Florida. Using explosives as sources, signals received at hydrophones and geophones were measured. In addition to water column measurements, detailed measurements of the bottom sediments and sub-bottom geology were made using reflection and refraction profiling, cores and grab samples. The experiment provided simultaneously both propagation and environmental data sufficient to permit an analysis of the sensitivity of the propagation to each of those environmental variables and parameters that could be measured either directly or indirectly. This analysis has been carried out, using some 15 environmental variables and parameters, for both the water wave and arrivals traveling in the sea bottom. The sensitivity on these environmental variables is found to be frequency dependent and also to depend on the type of wave constituting a given arrival. Multiple regression model techniques used in the analysis yielded quantitative measures of each variables contribution to the model.
Industrial ultrasonic tomography
Authors: Tsao M. C.
Published: October 2005

Based on applications, ultrasonic tomography can be classified into two categories, reflective tomography and transmissive tomography. Reflective tomography offers the most potential for characterizing the shapes and sizes of cracks, voids, inclusions, corrosion, erosion, detachment of bonds, or imperfections in weldments. The underlying principle of reflective tomography is to use the Time-of-Flight information from sound pulses to determine the location of discontinuities in an otherwise homogeneous material. Transmissive tomography, on the other hand, is most effectively used for determining more general variations in density. In this case, both Time-of-Flight information and variations in sound level attenuation are used to characterize the material properties of concern. Although the end results of displaying the reconstructed images are essentially the same for the two cases, the logic and algorithms are considerably different. The systems and examples of applications of both methods are discussed.
Spectral discontinuities of diffracted waves by periodic corrugated surfaces
Authors: Jungman Alain , Adler Laszlo , Quentin Gerald
Published: October 2005

Anomalies in the spectrum of elastic wave scattering from periodically corrugated structures have been reported (100th ASA Meeting). They are interpreted as mode converted signals along the interface. Measurements are now carried out showing that these sharp minima are not only observed in the normally incident backscattered situation. Spectral discontinuities are also observed under specular non normal reflection from liquid-solid and solid-air periodic interfaces. In addition, the frequency dependence of the minima has been measured as a function of the orientation of the plane of incidence versus the lines of the gratings. Some attempts are made to fit available theories of diffraction with present boundary conditions. The position and the amplitude measurements of the discontinuities can be used to approach some geometrical and physical properties of the interface.
New approach to directional foil electret transducers
Authors: Busch-Vishniac I. J. , West J. E. , Wallace R. L.
Published: October 2005

The overall sensitivity of foil electret microphones has been shown to be independent of area [see G. M. Sessler and J. E. West, J. Acoust. Soc. Am. 40, 1433–1440 (1966)]. However, recent theoretical and experimental investigations have shown that within a single electret transducer, the sensitivity can be varied to affect directional response. Using sensitivity control, arrays of microphones can be replaced by a single transducer. In general, the single transducer is less affected by small errors in construction than its array counterpart.
Comparison of a piezoelectric and an optical technique for determining the frequency content of broadband ultrasonic pulses
Authors: Riley Ward A. , Love L. Alan
Published: October 2005

Polyvinylidene fluoride hydrophones are being used to an increasing extent to study the acoustic pressure waveform and frequency content of broadband ultrasonic pulses. Simple optical techniques have recently been developed which also have the potential for obtaining this information. In this study broadband ultrasonic pulses transmitted by five common medical ultrasound transducers into distilled water were sampled in the transducer focal plane with a commerical piezoelectrical polymer hydrophone (Nuclear Associates model 84-403) and a broadband optical diffraction technique [W. A. Riley, L. A. Love, and D. W. Griffith, J. Acoust. Soc. Am. Suppl. 1 69, S91 (1981)]. Although the hydrophone is an approximate point (0.5-ram-diam) detector and the optical technique a line detector, the temporal waveforms obtained which correspond to the time variation of the acoustic pressure in the focal plane were very similar. The fast Fourier transforms of the digitally sampled waveforms were also obtained and compared. The fiat frequency response of the optical technique over the frequency range from 2.0–10 MHz was used to calibrate the frequency response of the hydrophone which was found to vary by as much as ±3 dB over this range. The results clearly demonstrate that under the experimental conditions studied, consistent estimates of the acoustic pressure waveform can be obtained with either a hydrophone probe or the optical line probe. Since the hydrophone is delicate, easily damaged and susceptible to prolonged immersion in water, the optical technique may be preferable in some applications. [Work supported by NIGMS 27755.]
Sea surface scattering processes applied to low-frequency reverberation estimation
Authors: Franchi E. R.
Published: October 2005

Development of a comprehensive computer model to estimate long-range, low-frequency reverberation must incorporate models of scattering from rough ocean surfaces. This paper reviews ongoing reverberation research, incorporation of developed segments of the scattering process into a prediction model, and identifies additional theoretical studies which would expand reverberation estimation capabilities. At-sea measurements of mean reverberation spectra have shown that surface reverberation is Doppler shifted from the carrier frequency by an amount predictable by treating the sea surface as a moving diffraction grating. Reverberation spectra also show significant spectral spreading about both the doppler-shifted and carrier (bottom reverberation) components. Forward scattering at the sea surface of signals returning from long-range accounts for the carrier spread, but underestimates the spread of the Doppler-shifted component. Scattering models to estimate this additional spread and to compute efficiently backscattered amplitudes will complete the mean reverberation estimation. Recommended analytic developments include extensions down to 50 Hz and to grazing angles below 10°; scattering dependence on the orientation to a directional sea surface; and spatial, temporal coherence and fluctuation estimates.
Automatic word duration rules for demisyllable-based isolated word recognition
Authors: Kahn D. , Rosenberg A. E.
Published: October 2005

It has previously been demonstrated that reliable, speaker-trained, isolated word recognition on a 1109-word Basic English vocabulary can be performed using word templates formed by concatenation of elements from a corpus of demisyllables. Since a dynamic time warping (DTW) algorithm is used to align test and reference patterns, small to moderate differences in duration between test and reference words present no major problem in performing the time alignment. However, improved results (i.e., smaller word distances) are obtained from the DTW algorithm if the syllables of the test and reference words are properly aligned prior to dynamic time warping. In our earlier experiments, each concatenated reference word was linearly prenormalized to the duration of that word in the test set, but this procedure is clearly not applicable for continuous speech recognition. We have now developed a linguistically based set of duration rules which we apply to the demisyllables during the word-creation process (i.e., before DTW), which predict syllable duration as a function of syllable stress level and the position of the syllable within the word. Using the automatic duration rules, we have achieved recognition accuracies comparable to those based on known word durations.
Speaker trained isolated word recognition on a large vocabulary of words
Authors: Keilin W. J. , Rabiner L. R. , Rosenberg A. E. , Wilpon J. G.
Published: October 2005

Most isolated word recognition systems have been tested on small to moderate size vocabularies, e.g., 10 to 200 words. For continuous speech recognition, however, vocabulary sizes of greater than 1000 words are required for a wide variety of tasks. An important baseline performance measure for such systems is the recognition accuracy of the system on isolated words drawn at random from the vocabulary. As such, we have measured the performance of an LPC-based recognizer on an 1109-word vocabulary (Basic English with a set of scientific terms appended) operating in a speaker trained mode. Each of six talkers (three male, three female) trained the system using the robust training procedure of Rabiner and Wilpon. Following training, each talker spoke the entire 1109-word vocabulary four times over the course of a month of testing. Recognition accuracies as a function of talker, vocabulary size, and word position were measured. Results indicate that accuracy is a strong function of both vocabulary size, and choice of vocabulary words from the Basic English vocabulary.
Stress and vowel duration effects on syllable verification
Authors: Marshall Charles W.
Published: October 2005

Recognition system for continuous speech must be able to deal with many sources of acoustic variation, such as variation in stress. We have examined the performance of a speaker-dependent syllable recognition task for a small group of stressed and unstressed syllables. These syllables, some containing the long vowel /æ/ and others the short vowel /I/, were excised from continuous speech and parameterized in terms of mel-scale cepstral coefficients at two levels of precision. From these data, four types of template dictionaries were formed: A contained individual templates for each stressed and unstressed syllable, B contained templates formed by warping stressed and unstressed syllables together, C contained only stressed syllables, and D contained only unstressed syllables. The recognition error rate increased when the template dictionaries were used in the order A, B, C, and D. The results indicate that training data should contain stressed and unstressed tokens, but for most syllables these may be combined into one template. Further results point out conditions for which the inclusion of stress is of importance in dictionary construction. [Work supported by NSF grant MCS-7916177.]