bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct Correlation of Fluctuating Lift with Radiated Sound for an Airfoil in Turbulent Flow
Authors: Clark P. J. F. , Ribner H. S.
Published: October 2005

An airfoil in turbulent flow is thought to radiate sound in consequence of its fluctuating lift. The instantaneous sound and lift should be connected by Curle's equation, which describes sound radiation from a rigid surface in contact with a turbulent flow. It follows that the cross correlation of sound and lift should be related in a corresponding way to the lift autocorrelation. Such correlations were measured in the present investigation of an airfoil in a jet flow, and the Curle relationship was verified semiquantitatively. The predicted comparative shapes of the correlation curves were found; the comparative magnitudes showed a 27% (2.7-dB) discrepancy. This small discrepancy is attributed to model vibration that falsely enhanced the lift signal via inertial loading. The work answers in part questions that have been raised as to the applicability of Curle's equation. Further, it confirms that a rigid surface in contact with a turbulent flow need not be inherently passive—a reflector of sound—but can be an active generator of sound.
Response of First-Order Vestibular Afferents to Controlled Angular Accelerations
Authors: Goldberg Jay M. , Fernández César
Published: October 2005

Single-unit activity of the vestibular nerve of the squirrel monkey was recorded with 3M NaCl-filled ultrapipets. Barbiturate-anesthetized animals were fixed on a rotating device controlled by a velocity servo. The plane of any semicircular canal could be made to coincide with the plane of rotation. (1) Most fibers are characterized by a regular and high resting discharge (mean, 80 spikes/sec). (2) The response to angular accelerations is consistent with the established morphological polarization of hair cells. The discharge of all fibers innervating a given canal is increased by accelerations, which bend the hairs towards the kinocillium, and decreased by accelerations in the opposite direction. (3) In their dynamic properties, the fibers may be approximated by a first-order, low-pass linear system with a time constant of about 5 sec. (4) The dc sensitivity of the fibers averages about 2.3 spikes⋅sec−1/deg⋅sec−2 but may vary considerably from one unit to another. [Supported by three NIH grants and an Air Force contract.]
Three-Dimensional Observation of the Inner Ear with the Scanning Electron Microscope
Authors: Lim D. , Lane W.
Published: October 2005

Three-dimensional observation of the surface architecture of the inner ear was made by the use of the scanning electron microscope. A conventional surface preparation of the inner ear was made and then the scanning scope was used to provide a magnification of 20 to 20 000× to view the preparations in three dimensions. Among the more interesting findings are the arrangement of the sensory hair cells, tectorial membrane, the surface arrangement of epithelial cells of the stria vascularis and the spiral limbus, surface architecture of interdental cells and spiral ligament. This presentation shows comparative examples of conventional phase contrast and electron microscopy with scanning electron microscopy and suggests how a three-dimensional surface view of the cochlea may assist in the understanding of the physiology of the inner ear. [Supported in part by the NIH-NINDB research grant and NIH general research grant.]
Microelectrode Recordings of Intracochlear Potentials
Authors: Peake W. T. , Sohmer H. S. , Weiss T. F.
Published: October 2005

Glass micropipets were inserted through the round windows of anesthetized cats. During penetration from scala tympani to scala vestibuli, we continusuly recorded (1) dc potential, (2) magnitude and phase of the fundamental component of responses to tones, (3) resistance of the electrode, (4) position of the electrode drive, and (5) responses from stationary electrodes. At the end of the experiment, electrodes were cemented to the temporal bones where they remained during preparation of the tissue for histological examination. From examination of the sectioned cochlea, we attempted to determine the structures that had been penetrated by the electrode. In 64 cochleas, the average potential of scala media is 100 mV and of scala vestibuli 0 mV re scala tympani. Large negative potentials frequently encountered between scala tympani and scala media were generally held for less than 60 sec. Hence, we find no evidence for an extracellular “Corti potential.” We are not able with this technique to associate recorded electric events with structures as small as individual cells. [Supported by NIH and the Joint Services Electronics Program.]
Discharge Rates of Single Auditory-Nerve Fibers as Functions of Tone Level
Authors: Kiang N. Y. S. , Baer T. , Marr E. M. , Demont D.
Published: October 2005

Plots of firing rate versus stimulus level were obtained for single auditory-nerve fibers in anesthetized cats with cut middle-ear muscles. For tones, the shape of the rate-versus-SPL curve for a given fiber varies considerably with frequency. For some frequencies, the curves are monotonic; for others, there is a rise followed by a dip that may go down to the spontaneous rate. Within a 10-dB range following the dip, the response rate rises to a maximum. Dips have been found for units over a wide range of characteristic frequency (CF). Although dips can be found for frequencies at or above a unit's CF, the lowest SPL at which dips occur is always at frequencies below CF. At high stimulus levels (above 90 dB SPL) where dips occur, responses of units with low CF show large phase changes relative to the stimulus. [Supported by NIH grants and the Joint Services Electronics Program.]
Comparative Analysis of Acoustic Testing Techniques
Authors: Gruner William J. , Saint Lester D.
Published: October 2005

Current progress on research under NASA contract is detailed. Empirical acoustic-vibration energy. transforms are compared to state-of-the-art analytical results for progressive wave and reverberant acoustic excitation. Structural specimens vary from homogenous plane panels to reinforced cylindrical elements. Analytical results and experimental capabilities are briefly reviewed. A comparison of theory and test is performed with analytical assumptions maintained explicit. Emphasis is placed on pressure field coherency, spatial variations, and probable damage potential. Recommendations for subsequent efforts are provided. The culmination of this program of research is to improve design and utilization of acoustic test facilities for environmental testing of advanced space vehicle payloads and equipment and ultimately to optimize component performance relative to weights, volume, and packaging, etc. [This research program supported by NASA, George C. Marshall Space Flight Center.]
Mathematical Aspects of Problems Encountered in Calculating the Response of Structures Excited by Moving Loads
Authors: Criner O. H. , Fleischhaker J. H.
Published: October 2005

Studies of the initial-boundary value problems for singular moving loads on finite cylindrical shells have produced the following results: (1) The problem for supersonic loading is well posed in the sense of Hadamard and has a unique solution that can be calculated by the method of characteristics; (2) the problem for the subsonic loading is ill posed and cannot be calculated by usual methods and therefore requires reformulation; and (3) most of the mathematical methods are inapplicable to this class of transient problems, and therefore the concepts of “resonance” and “normal mode” should be re-examined in this context.
Development of a Multimodal Vibration Test Fixture for Spacecraft Assemblies
Authors: Scharton Terry D. , Yang Thomas M. , Trummel Marc C. , Mansour Momtaz N.
Published: October 2005

This paper presents the results of an experimental research program to develop a novel type of assembly-level vibration test. The design of a multimodal test fixture, which simulates the high-frequency (100–2000 Hz) dynamic characteristics of a MARINER spacecraft structure, is described. Data obtained in research vibration tests with an electronic assembly mounted in the multimodal fixture indicate that the novel testing technique results in a more realistic and more uniform high-frequency vibration environment than conventional tests utilizing rigid fixtures. The paper presents guidelines for designing multimodal fixtures and discusses means of utilizing these fixtures in future spacecraft assembly-level vibration test programs.
Dynamic Shell Theory for Ferroelectric Ceramics
Authors: Drumheller Douglas S. , Kalvins Arturs
Published: October 2005

Plates and shells of ferroelectric ceramics are widely used as electromechanical transducers. The theory of piezoelectricity in which the equations of classical elasticity and electrostatics are coupled with linear constitutive relations can be used to predict the behavior of these materials. In this paper, a shell theory is derived by assuming an orthotropic material in which the principal axes of orthotropy coincide with the two principal directions of the reference surface and its normal. The theory reduces to the piezoelectric theory developed by Tiersten and Mindlin for plates [“Forced Vibrations of Piezoelectric Crystal Plates,” Quart. Appl. Math. 20, No. 2, 107–119 (1962)], and to the shear theory of shells for elastic materials. In addition to the usual elastic boundary conditions of shell theory, the electrical quantities of surface potential, surface charge density, or total charge on an equipotential surface may be prescribed. The free vibration of a shell with complete electrodes on both surfaces, either open or short circuited, and a shell without electrodes is discussed. The equations are solved by a numerical integration technique, and some results for a cylindrical shell are presented.
First-Formant Transitions as a Cue to Place of Articulation
Authors: Delattre Pierre
Published: October 2005

Experiments on the perception of consonants have indicated that the direction of a formant transition may be a cue to the perception of either place of articulation or manner of articulation, and that directions of second- and third-formant transitions are related to place of articulation (labial, dental, velar, etc.), whereas the direction of first-formant transitions is related to manner of articulation (plosive, fricative, nasal, etc.). A study of the five plosive and fricative phrayngeals of Arabic suggests that the direction of first-formant transitions may act as a cue for the perception of consonantal place of articulation.
Distortion of Some “Squarish Pulses” in a Constant Gradient Medium
Authors: Wood D. H.
Published: October 2005

The exact responses to some “squarish pulses” from a point source are found by using an integral representation due to R. R. Goodman. The resulting distortion is shown to depend only on the dimensionless parameter travel time multiplied by the magnitude of the gradient.
Cochlear-Nucleus-Evoked Responses in the Rat
Authors: Crowley David
Published: October 2005

Evoked responses to 118-dB SPL clicks recorded from the rat's dorsal cochlear nucleus (DCN) have a complex waveform with a first biphasic positive-negative component that represents auditory-nerve axon discharge. The second component, which follows the first by 0.8 to 1.3 msec. is a smaller positive-negative wave and may reflect second-order fiber discharge within the DCN, but does not represent N2. In the extreme lateral DCN, a third evoked response component is a large positive-negative biphasic wave that may be related to N2. In the rest of the DCN, the third component is a slow monophasic baseline shift lasting 5–6 msec, upon which the second components may frequently be superimposed. As click intensity is varied between 83 and 108 dB SPL, rarefaction-click DCN responses have shorter latencies and greater amplitude than do condensation-click responses reflecting at the cochlear nucleus level the earlier excitation of auditory-nerve dendrites by upward excursions of the basilar membrane. [Supported by NINDB grant and Middlebury College.]
Cortical Responses of Awake Cat to Narrow-Band FM Noise
Authors: Glaser Edmund M.
Published: October 2005

When a noiselike auditory stimulus is used to study the auditory nervous system, it is difficult to determine the evoked response dependency upon the transitory changes in stimulus intensity and upon its spectrum. This is particularly true when the noise intensity fluctuates, as in filtered white noise, for example. However, if a relatively long tone burst is briefly frequency modulated (FM) by noise, the tone-noise and noise-tone transitions occur with no SPL intensity fluctuation. The responses can then be ascribed solely to the spectral transitions. A series of experiments has been performed on awake cats subjected to such stimuli in which the noise bandwidth was varied. Responses to the tone-noise transitions were obtained from epidural electrodes and were compared with responses to both pure-tone bursts and FM bursts with the same envelope. Of considerable interest is the finding that for relatively large bandwidths, the response is greater to the tone-noise transition than to onset of an FM noise burst with the same bandwidth. [Supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Radiation Patterns for Bat Sonar Cries
Authors: Simmons James A.
Published: October 2005

Specimens of the echolocating, insectivorous bats, Chilonycteris rubiginosa and Eptesicus fuscus, were trained to broadcast their sonar cries in a fixed direction during target-discrimination experiments. An array of condenser microphones measured the peak amplitudes of the sonar signals emitted by the bats at 0° (straight ahead), and at 22.5°, 45°, and 90° to the side in the horizontal plane. The radiation patterns of the cries were directional, with most of the energy directed to the front. Chilonycteris produced somewhat more directional cries than Eptesicus. The Chilonycteris cries were down by 26 dB at 90°, while the Eptesicus cries were 14 dB down. The directionality of the cries was such that, in conjunction with the directional hearing of bats, it might contribute to the reduction of clutter interference from objects to the sides and improve the bat's ability to process echoes from objects at the same distance but different bearings.
Perception of Semivowels and Laterals
Authors: Haggard Mark P.
Published: October 2005

Acoustically, /w, j, r, l/ are more like vowels than other consonants. However, as with other consonants, their chief perceptual cues are formant-frequency transitions, and their articulatory specification omits some parameters, allowing coarticulation of gestures from neighboring phones. If perception reflects the “incomplete” articulatory specification, semivowels and laterals should be perceived similarly to other consonants; for stop consonants, but not vowels, perception is categorical and identifications are more accurate on the right ear than the left. On purely psychoacoustic considerations, /w, j, r, l/ with their vocalic mode of production and slower transitions, than other consonants should produce intermediate results in these experimental situations. Three experiments were performed with /w, j, r, l/. The first showed that the amount of categorical perception is similar to that in the place dimension of voiced stops; the second showed that the right-ear advantage is also similar to that for voiced stops, and a third showed that this advantage is not enhanced if transitions are of a speed more appropriate to stops. These results suggest a single mode for the perception of consonant transition information, possibly related to coarticulation. [Research begun at Haskins Laboratories.]
Vowel Identification in Isolation and in Word Context
Authors: Sachs Ricard M. , Klatt Dennis H.
Published: October 2005

The perception of the vowel pair /ɑ-æ/ was studied both in isolation and in the context /d-dɔl/ (bottle-battle). A set of eight stimuli were created on a speech synthesizer by varying second formant center frequency in equal logarithmic steps, such that Stimulus 1 sounded like / ɑ / or /bɑdɔl/ and Stimulus 8 sounded like /æ/ or /bædɔl/. The method of absolute identification was used to analyze the psychological distance between adjacent stimuli in terms of d′. It was found that the phoneme boundary effect was observed for the vowel pair in word context only; subjects could differentiate between stimuli in the center of the continuum (stimulus Pairs 4 and 5) much easier than between stimuli at the ends of the continuum (Pairs 1 and 2 or 7 and 8). Isolated vowel stimulus pairs (approximately 250 msec in duration) were differentiated equally well over the whole continuum. [This work was supported in part by the National Institutes of Health.]
Sound from Turbulent-Boundary-Layer-Excited Panels
Authors: Davies Huw G.
Published: October 2005

The acoustic power radiated by thin flexible panels excited by turbulent-boundary-layer pressure fluctuations is estimated using a modal analysis, light fluid-loading effects being included. Previous estimates of the modal radiation efficiencies are improved, an extension being made to include the transition region where the acoustic wavelength is comparable to the panel dimensions. The assumption of equipartition of the model energies in a frequency band is used to account for the fluid loading effects. Predictions based on this assumption. and also made by neglecting fluid loading, are compared with experimental results obtained in air. It is shown that where the predictions are not equal they form effective upper and lower bounds, suggesting that some, at least, equipartition of modal energy occurs.
Continuously Swept Technique for Measuring Sound Absorption
Authors: Siekman William
Published: October 2005

A procedure for studying sound absorption has been developed that measured the change in sound-pressure level over a controlled duration instead of the time for a fixed change in level. The procedure permits an ostensibly continuous frequency sweep during the measurement, making it especially applicable to the study of tuned absorbers. Examples of results with various specimens will be presented, with a discussion of current limitations of the technique.
Implementation of the Gas Squeeze-Film Foil Bearing
Authors: Fulton Langdon H.
Published: October 2005

The squeeze-film gas bearing, a recent development in the technology of gas bearings, depends for its operation on the attainment of a relatively high-frequency low-amplitude repetitive normal displacement between the two solid surfaces that comprise a bearing. The frequency and amplitude requirements for this motion are usually such that the piezoelectric transducer constitutes an ideal driving source. The foil bearing, characterized by the low flexural rigidity of one of the mating bearing surfaces, is of particular interest in regard to such envisioned applications as guide bearings for magnetic tape, photographic film, and other foil materials, in high-performance computer-peripheral and electronic-optical recording apparatus. Experiments are described in which squeeze-film bearing action was achieved between various foil materials and a rigid cylindrical surface coupled to a tubular piezoelectric transducer driven in its circumferential mode of resonance. The results are discussed and reconciled to the theory of the squeeze-film gas bearing. Some criteria are established for design application of the foil squeeze-film bearing in this particular configuration.
Manikin Measurements of the Noise Attenuation Provided by Flight Helmets
Authors: Forstal John R.
Published: October 2005

To determine the noise attenuation provided by various flight helmets according to the USASI Standard for the Evaluation of Real-Ear Attenuation at Threshold consumes a considerable amount of time. A manikin head has been developed to serve as a tool for assisting in such evaluations. Its use must be considered in terms of the particular requirements for a given evaluation program. With a manikin head, a helmet can be optimally fitted and reliable data obtained in approximately 3 to 5 min. Variability introduced by human factors is kept at a minimum. High levels of noise can be used as the test stimulus. Visual and auditory monitoring of the attenuated noise provides the experimenter with a precise appraisal of the fit as adjustments are made. The manikin method of measurement also reveals improvements in attenuation resulting from minor modifications. Measurements of attenuation for five flight helmets by the manikin method were very similar to measurements obtained by the real-ear method. In-flight manikin measurements of attenuation will also be discussed. [Work supported by NAVAIRSYSCOM.]
Directivity of the String Instruments and its Influence on the Orchestra Sound in Concert Halls
Authors: Meyer Jurgen
Published: October 2005

The directional characteristics of the string instruments depend not only on the frequency, but on the kind of wood and the thickness of the plates. It is necessary, therefore, to measure several violins, violas, violoncellos, and contrabasses and to evaluate an average characteristic for each instrument group and many frequency ranges. The results of such investigations, made in an anechoic chamber, demonstrate the main directions of the sound radiation and the directions of less sound pressure in dependence on the frequency. These characteristics make it possible to discuss the influence of different seating arrangements of the orchestra on the loudness, the harmonic content and the clearness of the transients in a concert hall. The interaction between the room acoustics and the main directions of the instruments is very important for the ratio between direct and slightly delayed sound and reverberation. It is interesting, too, for the construction of reflectors on the walls near the orchestra and under the ceiling.
Control of Behavior by the Location of an Auditory Stimulus
Authors: Beecher M. D. , Harrison J. M.
Published: October 2005

The control of behavior by the location of tone bursts was investigated in rats and in bats of the species Phyllostomus hastatus. The apparatus consisted of an enclosure with two keys, two loudspeakers (in different locations in the animal's azimuth), and a dipper feeder. On each trial, the animal was exposed to tone bursts from either one or the other of the two speakers and a response on the appropriate key (correct response) was reinforced with food. When tone bursts have a rapid rise time (approximately 0.2 msec), location is a dominant feature of the stimulus: The discrimination is acquired within the first session and the stable-state level is maintained at near 100% correct responses. When the tone bursts do not have prominent transient characteristics (rise time of 1 msec or more) the location discrimination is acquired more slowly (if at all) and the stable state level is low (80%–90% correct responses). [Supported by National Science Foundation.]
Underwater Sound Localization: Preliminary Information
Authors: Hollien Harry
Published: October 2005

A series of studies has been initiated investigating the nature of human sound localization underwater; the research is based in part on the discussions and work of Sivian, Bauer, Torick, and others. The first step in the project was the development of Diver Auditory Localization System (DALS), which consisted of an underwater PVC structure with a series of five 8-ft arms beneath which was slung a subject's chair. DALS allows the diver/subject's head either to be held in a rigidly fixed position or to be moved, with his body fixed. The five arms allow placement—at ear level—of projectors at angles, to the diver, of 0°, 45°, 90°, 270°, and 315°. In this first experiment, six diver/talkers were positioned in DALS, at a depth of 50 ft, with their bodies fixed but their heads mobile; four different experimental signals 250-, 1000-, 6000-Hz sinusoids and thermal noise) were transduced via J-9 projectors. The site of the project was NRL's Underwater Sound Reference Division's Bugg Spring facility. Each signal was presented to the listeners five times randomly from each of the five transducers; each presentation was in the nature of five 1-sec bursts 40 dB re hearing threshold. Listeners responded by means of a specially constructed five-position underwater switch coupled to an IBM keypunch at the surface. Data show unexpected localization ability by subjects (theory would predict no such ability); the mean correct scores for the six subjects were: (1) 250 Hz: 52.7% (2) 1 kHz: 37.3% (3) 6 kHz: 24.0%; and (4) noise: 57.3%. Thus, only the data for 6 kHz approached chance, and it can be concluded that the subjects in this experiment exhibited greater skills at underwater sound localization than was expected. Further studies presently are in progress. [This project was supported by the Physiological Psychology Branch of the Office of Naval Research.]
Front-Back Discrimination in Free-Field Sound Localization
Authors: Toole F. E.
Published: October 2005

When localizing sounds in a free-field environment, listeners frequently confuse front and back. Careful study of these front-back reversals reveals a dependence on factors other than the lack of a reverberant sound field. In the experiments described here, median-plane localizations were produced by single and symmetrically disposed pairs of loudspeakers. Front-back discrimination was examined as a function of source position, head movements, signal type, frequency, and bandwidth. Subjects differed in their sensitivity to each of these factors, but it was clear that source position and signal bandwidth had the most pronounced effects. Some subjects demonstrated front-back localizations that were almost entirely dependent on source position; others exhibited localizations that altered as a function of signal bandwidth but that appeared to be substantially independent of source position. Experiments in which head movements were progressively restricted have shown that small involuntary head movements cannot be of more than slight importance in front-back discrimination.
Inability of Listeners to Trade Completely Interaural Time for Interaural Intensity in a Detection Task
Authors: Hafter Ervin R. , Carrier Sam C.
Published: October 2005

The classical “binaural trading ratio” measures a supposed trade of interaural temporal discrepancies for opposing differences in interaural intensity. Implicit in these measures is the assumption that information is somehow transposed from one dimension, either time or intensity, to the other; if this is so, then the constraint of a time-to-intensity or intensity-to-time conversion must be placed on any viable model of binaural interaction. The information-conversion assumption implies that a tone centered by opposing time with intensity will not be detectably different from a diotic tone. We tested this assertion using 500-Hz, 125-msec tone bursts. For a given value of Δt a subject was tested over a wide range of ΔI's. For all values ΔI, subjects were able to detect differences between the test tones and diotic tones of the same frequency and duration.
Acoustic Navigation as Related to Deep Ocean Search
Authors: Buchanan C. L.
Published: October 2005

Acoustic techniques have a long history of use in the sea. As man becomes more involved in this major portion of his environment, his use of acoustics increases both in quantity and variety. A number of acoustic devices played key rôles in the search for the lost submarines, THRESHER (SSN 593) and SCORPION (SSN 589), as well as in the location and recovery of the nuclear device lost off the coast of Spain. These mishaps have spurred research and development of acoustic and other types of equipment for use on the deep ocean floor and, while considerable progress has been made, there remains much room for improvement. As a result of its successful participation in these search efforts, the Naval Research Laboratory has become deeply involved in man's quest for mastery over this hostile portion of his habitation.
Losses in Cochlear-Microphonic Sensitivity as a Function of Lumped or Spaced Exposure to a 5.0-kHz Tone
Authors: Price G. Richard
Published: October 2005

Previous experiments on the loss of cochlear-microphonic (CM) sensitivity to intense pure-tone stimulation [PRICE, G. R. (1968). J. Acoust. Soc. Amer. 44, 363 (A); PRICE, G. R. (1967). J. Acoust. Soc. Amer. 42, 1156 (A)] have shown that as exposure intensity increases, losses grow slowly up to an intensity 20 dB above that intensity necessary to produce a maximum in CM output (MAX+20) and very rapidly at higher intensities. These patterns of loss have been interpreted as showing that losses in CM are primarily a function of mechanical displacement rather than metabolic factors. In order to provide additional evidence, four groups of ten cat ears were exposed to 5.0-kHz tones at MAX+10 or MAX+30 intensities for 50 min. Exposures were either continuous or on a 1-min on, 4-min off schedule. Losses did not vary significantly as a function of lumping or spacing exposure, thereby reinforcing the contention that losses in CM are a function of mechanical rather than metabolic factors.
Acoustic Measurements for Speaker Recognition
Authors: Wolf Jared J.
Published: October 2005

In a scheme for mechanical recognition of speakers, it is desirable to use acoustic measures that are related in as direct a manner as possible to the voice characteristics of the unknown speaker and that are minimally affected by irrelevant factors. Acoustic attributes that are dependent on anatomical properties of the speaker's vocal mechanism should be particularly effective ones. Certain phonemes or phoneme features are well suited for displaying speaker-dependent characteristics. For example, aspects of the spectra of /∫/ (high frequency shape), /i/ (shape of the F2-F3-F4 peak), and /m/ (pole-zero interplay and nasal ferments) have been found to be effective. This approach suggests that speaker-recognition procedures should utilize a strategy of measuring only significant features of certain segments of an utterance rather than general measurements over the extent of the utterance. Implementation of this approach in automated speaker-recognition schemes is discussed. [Work supported in part by the National Science Foundation, Air Force Cambridge Research Laboratories, and the National Institutes of Health.]
Description of a Completely Automatic Speaker-Verification System
Authors: Luck James E.
Published: October 2005

This paper will discuss the results obtained to date with a real-time speaker-verification system being developed by ARL's Speech Systems Research Department. A speaker wishing to have his identity verified supplies his identity to a computer via a teletype. Reference data previously obtained for that speaker are read into the computer memory from a disk storage unit. The speaker then repeats the test phrase, “My code is _____,” into a microphone whose output is A/D converted and entered into the computer. A comparison is made between the test phrase and the reference data. On the basis of the comparison, the computer either verifies or challenges the purported identity of the speaker. The discussion will describe the “cepstral” measurements made on the test phrase, the nearest-neighbor decision procedure, and the problem of collecting adequate training samples. The system has been trained to recognize four speakers. When tested on new data for both the original speakers and 30 impostors, error rates of from 6% to 13% were obtained.
Subharmonics, Resonant Systems, and Parametric Oscillations
Authors: Adler Laszlo
Published: October 2005

The problem of a fluid-filled cavity caused to resonate by an ultrasonic wave can be described as a parametric phenomenon. Parametric resonance takes place when a parameter of a resonant system undergoes periodic variation. In this example, the cavity length varies with the transducer amplitude, and therefore the resonant frequency of the nth mode it is not constant. The linear wave equation describing this system can be transformed into a Mathieu equation, which is the equation for parametric action. A threshold of parametric resonance is predicted when dissipation is included. This threshold relates the transducer amplitude and frequency with parameters of the liquid. The series solution to Mathieu's equation contains frequency components that agree with those obtained experimentally. [Research sponsored by the U. S. Office of Naval Research.]
Minimum Audible Field Measurements via Békésy Audiometry
Authors: Fisher H. Geoffrey , Freedman Sanford J.
Published: October 2005

A series of auditory localization experiments has been performed with S's listening in a sound field. However, audiometric screening was done with headphones, implying a known relation between these two conditions. There is little in the literature concerning precise relationships between threshold measurements taken with headphones and suprathreshold tasks performed in a sound field. Using Békésy audiometry, we tested 10 college students listening both with headphones and with loud-speakers in a partially balanced experimental design. Statistical analysis of the findings demonstrated significant differences between results produced under the two test conditions with respect both to threshold and to variances.
Principal Component Analysis of Evoked Cortical Potentials from Awake Cat—Narrow-Band Noise Masking
Authors: Suter Charles M. , Glaser Edmund M.
Published: October 2005

A principal component analysis was applied to evoked potentials measured from the primary auditory cortex of awake cats. This analysis uses a linear decomposition of the average evoked response to provide a parsimonious representation of the available information in the form of a few statistically independent scalars. The waveforms corresponding to the eigenvectors are found to be similar to the classically defined evoked response components, and aid in determining where, within the evoked response, masking effects may be observed. The animals were stimulated in free field by a series of tone bursts, some unmasked, and some masked by either AM or FM narrow-band noise. The center frequency or band-width of the noise and the signal-to-noise ratio were experimental parameters. The concomitant changes in the evoked responses will be demonstrated in terms of their principal components and corresponding eigenvectors and discussed in relation to the critical band. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Auditorium Synthesis—A Research Tool
Authors: Veneklasen Paul S. , Ortega Jose C.
Published: October 2005

An array of electroacoustic equipment is designed to present to a listener a series of acoustical events essentially similar to the occurrences in a real auditorium. Direct sound, first side-wall reflections, and the growth and decay of reverberant stored, are independently generated and individually controllable. Thus the ratios of direct/environmental/reverberant sounds can be adjusted by the subject to suit his taste for the program samples. The system and its components are described. It handles either recorded material or live performance, which can be played into the system operating in continuous real time.
Acoustical Modeling of Auditoriums: Correlation with Full Scale—Saratoga Pavilion
Authors: Veneklasen Paul S. , Christoff Jerry P.
Published: October 2005

A detailed comparison is presented between the echograms from the model auditorium during the design period versus the echograms taken in the completed auditorium. In the model, the influence and behavior of separate surfaces can be easily determined. In full scale, the corresponding measurements can be approximated only by using directional source and microphone. Correlation of the physical measurements with musical listener evaluation is complicated by a severe and diffuse language barrier wherein definitive expression is lacking, largely because it has not been possible to isolate and demonstrate the variables that musicians attempt to describe. Nevertheless, certain qualitative auditory observations are helpful and suggest the course for the future.
Theoretical Model for Steady-State Urban Noise
Authors: Shaw E. A. G. , Olson N.
Published: October 2005

A large urban area is treated as a homogeneous incoherent distributed sound source. The source density is calculated from statistical distributions of motor-vehicle noise level measured at a 50-ft distance in open terrain (N. Olson, 1968) and from estimates of vehicle density based on general arguments. Atmospheric absorption data down to 125 Hz have been given by C. M. Harris (1966). The predicted steady-state SPL and spectrum levels for suburban Ottawa are in good agreement with measurements provided that one postulates a constant level reduction of approximately 10 dB, representing the shielding effect of buildings.
Fast Field Program
Authors: DiNapoli F. R.
Published: October 2005

The hydrodynamical field equations yield to three methods of solution. Two of these, the method of characteristics and that of separation of variables, have been widely used for both analytical and numerical investigation, but usually with either physical or mathematical approximations. The third, direct integration of the partial differential equations has always existed in principle but not until the advent of the fast Fourier transform could this approach be exploited in a systematic and economical manner. H. W. Marsh recognized this fact and introduced the concept of the fast field program (FFP). Several examples are presented and discussed which demonstrate that the FFP is not only feasible but a highly efficient algorithm for providing propagation estimations rapidly without undue approximations to the basic field equations. The results are compared with those predicted by both ray theory and normal-mode theory. [This research was supported by the U. S. Underwater Sound Laboratory.]
Modal Response of Cylinders to Various Acoustic Fields
Authors: White Robert W.
Published: October 2005

This paper compares the theoretical response of an idealized aerospace structural cylinder for several types of acoustic loads. Computations were made for an equivalent uniform pinned-end cylindrical shell of the space average acceleration spectral density from 10 to 1000 Hz. The classic modal analysis method employing 570 independent degrees of freedom was used in the computations. The pressure fields were assumed to be homogeneous with rectangular space correlation patterns, and to have uniform acceleration spectra over the shell. The results show basic differences in the modal responses for different acoustic fields at low frequencies, which need to be accounted for in acoustic test simulation.
Comparison of the Aerodynamics of Vocal Fry and Modal Register Phonations
Authors: McGlone Robert E. , Shipp Thomas
Published: October 2005

Airflow and subglottic air-pressure recordings were made as ten adult males sustained phonations in the vocal fry and in the low modal registers. Subglottic pressures were obtained from a tracheal puncture and air flow from a pneumotachograph and face mask placed over the mouth and nose. Fry frequencies were measured from an acoustic trace of the phonation, whereas the modal frequencies were the 10% level of each subject's range. Mean vocal-fry fundamental frequency was 29.8 Hz and mean modal frequency was 101.2 Hz. The latter frequencies were produced at the 25% level of the subject's vocal intensity range. Significant differences were not found when comparing subglottic pressures; however, air-flow values in the modal register were higher than those during vocal-fry production.
Perceptual Differentiation of the Modal and Falsetto Registers
Authors: Colton Raymond H.
Published: October 2005

Experienced and naïve observers heard phonations produced at an identical frequency but in the modal and falsetto registers. These phonations, produced by singers and nonsingers, were arranged into an AX diad and the observers identified the voice qualities of the paired phonation as same or different. In another task, the observers placed an equal number of phonations into each of two undefined voice quality groups. No training in voice quality identification was given in both procedures. There was no difference between the performance of the two observer groups in either task. The observers were able to correctly discriminate between the phonations produced in the modal and falsetto registers 95% of the time. In the categorization procedure, the observers separated the modal and falsetto register phonations into the two voice-quality groups significantly above chance level. However, their general level of performance in this task was considerably below their performance in the discrimination task. The results of both procedures suggest that each register exhibits an identifiable voice quality and observers can utilize this quality characteristic of a phonation to place it into its proper voice-quality group.
Auditory Masking by Many Sinusoids
Authors: Carterette E. C. , Nagel D. C.
Published: October 2005

Following Green [J. Acoust. Soc. Amer. 37, 802–813 (1965)], who derived the response of a simple square-law energy detector in detecting a pulsed sinusoid masked by two continuous sine waves, we derived the equations for the case of n continuous sine waves. Based on statistics of this energy-detection model, experiments were made to determine the masking power of two, four, and six sine waves, of varying frequency separations, upon a pulsed sinusoid located at the central frequency of the set of maskers. In general, the masking curves obtained obeyed the predictions derived from the energy-detection model. However, certain deviations from these predictions indicate that the model is too simple to represent the way in which the human ear works.
Studies on Collapsing Cavities
Authors: Fogler H. Scott
Published: October 2005

A theoretical study has been made on cavities collapsing in liquids when the gases inside the cavities are reacting. It was determined that there can be significant departures from the fluid mechanics of collapse of a cavity containg inert gases. When reacting gases are present, the nonlinear differential equations of motion, energy, and chemical kinetics must be solved simultaneously. Descriptions are presented delineating the behavior of the cavity during the collapse when a gas is reacting within the cavity. In another related study, an analysis is given of the collapse of a spherical cavity in a large body of an incompressible viscoelastic liquid. Proceeding from a linear rheological model for the liquid, one obtains a nonlinear integrodifferential equation for the motion of the cavity. Analytical solutions are derived for certain limiting values of the parameters governing collapse, and some numerical solutions are presented for various other values. As one of the more interesting results of this work, it is found that elasticity in the liquid can significantly retard the collapse of a void.
Experimental Verification of Spinning-Mode Theory
Authors: Gray L.
Published: October 2005

In this paper, fan noise data are presented to show several aspects of spinning mode theory: (1) the presence of a complicated radial pressure distribution near the fan blades; (2) the decay of the sound pressure field; (3) the degeneration of higher-order modes; and (4) the dependence of decay on spinning-mode peripheral speed.
Digital Computer Program for Calculating Noise Exposure Forecast Contours
Authors: Horonjeff Richard D. , Paul Allan P.
Published: October 2005

Recent work in land use planning with respect to aircraft noise has resulted in the concept of the noise exposure forecast (NEF). This concept is an updating of the previously developed composite noise rating and represents a somewhat more sophisticated mathematical model. This paper discusses the digital computer program (written in Fortran IV) that has been developed to generate contours of equal noise exposure about an airport community from given airport and aircraft operational parameters. The flexibility of the program allows the user to vary aircraft noise and performance characteristics, volume of aircraft activity, and other operating parameters in order to determine the effects on the community noise exposure. [Work supported by the Federal Aviation Administration.]
Sound-Absorbing Pad for Minimizing the Acoustical Effect of the Ground on Noise Test Rigs
Authors: Moore C. J.
Published: October 2005

The inaccuracies that occur if acoustical measurements to determine the free-field radiation characteristics of a source are made in the presence of the ground or other partially reflecting surface are first discussed. On test rigs where measurements are made close to the source, interference between direct waves and waves reflected from the surface is the main source of inaccuracy. A correction for this effect cannot easily be calculated for most practical sources. A solution to this problem is to place an acoustically nonreflecting pad on the surface between the source and the microphone. Such a pad has been designed from model tests and constructed for use with an experimental fan used for noise research. Full-scale tests show that the ground interference effect is greatly reduced, giving a maximum error of ±2 dB at 20 ft from a pure-tone source at frequencies between 100 Hz and 20 kHz.
Spectrum of a Reflected Signal from a Time-Varying Stochastic Surface
Authors: Cron Benjamin F. , Nuttall Albert H.
Published: October 2005

The spectrum of a single-frequency wave reflected from a time-varying stochastic homogeneous surface is determined as a function of the statistical parameters of the surface. It is assumed that the surface is stationary in the wide sense in both space and time. For the special case of surface wave heights possessing a narrow-band spectrum at a point, joint Gaussian distribution of heights, and an elliptical spatial field, the integral expression obtained for the reflected acoustic spectrum at the observation point is derived. It is shown that the acoustic spectrum consists of a series of narrow-band spectral lobes, shifted from the incident acoustic frequency by a multiple of the center frequency of the surface variation. The power in each component is evaluated in terms of two parameters: surface roughness and correlation distance of surface wave heights. The computations are made for a Gaussian-modulated sinusoidal and an exponentially modulated sinusoidal autocorrelation function. Curves summarizing the results are presented.
Pulse Excitation of Railway Wheels
Authors: Bray D. E. , Finch R. D.
Published: October 2005

A one-quarter scale model steel railway wheel was excited at a point on the rim using a 350-kHz pulse acting through a 18 in. diam source transducer. A second 18 in. diam transducer was located at points along the periphery and oscillograms of arriving pulses were made with a Polaroid camera. Pulses passing directly through the interior of the wheel were shown to propagate in accordance with Lamb's theory when passing through the plate region. Further, pulses propagating around the interior of the rim were shown to be similar to the thickness and width modes observed by Morse to occur in a rectangular bar. Surface waves propagating around the outer circumference of the rim were also observed.