bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound Velocity and Absorption in Low-Pressure Gases Confined to Tubes of Circular Cross Section
Authors: Shields F. Douglas
Published: October 2005

The propagation constant for sound waves propagated through gases confined to tubes is shown to be a function of the specific heat of the gas, a “Reynolds” number, a “Knudsen” number, and the momentum and energy accommodation coefficients of the surface. A numerical solution for the propagation constant agrees with room-temperature velocity and absorption measurements in Ar and N2 assuming a momentum accommodation coefficient of 1 and an energy accommodation coefficient of 0.9. No effort was made to clean the tube-wall surface, and no difference could be detected in a stainless steel and a brass tube. The method offers considerable promise for measuring energy-accommodation coefficients. [Work supported by the Office of Naval Research.]
Effects of Direction of Frequency Sweep on Békésy Audiometry
Authors: Young I. M. , Harbert F.
Published: October 2005

Continuously variable Békésy threshold tracings for pulsed and continuous tones were compared for forward sweep (low frequency to high) and backward sweep (high frequency to low) in normal and pathological cars. In normal ears, direction of sweep made no difference for either pulsed or continuous tone. Thresholds for a given frequency were similar for fixed- and variable-frequency tracings for both pulsed and continuous tones in normal ears. In pathological ears, pulsed tones showed no significant threshold difference between forward and backward tracings except in ears with marked abnormal adaptation. In certain pathological ears, for a given continuous tone, comparison of fixed-frequency tracings with variable-frequency tracings often showed considerable differences. This difference, furthermore, was greater for one direction of sweep than for the reverse, but there was no consistent pattern resulting from the direction of sweep. Comparisons were made on the basis of intensity and amount of adaption at adjacent frequencies. The latter seemed more important in predicting discrepancies between forward and backward tracings.
Reconsideration of Loudness Adaptation
Authors: Petty J. , Elliott D. , Fraser W.
Published: October 2005

Six S's were tested with three procedures. In all of the studies the adapting stimulus was a 1-kHz tone delivered to the S's right ear. The comparison stimuli used during the various studies were, with respect to the adapting stimuli, either homophonic (same frequency, in phase), π (same frequency, 180° out of phase), or heterophonic (different frequency, 1.2 kHz). The results may be summarized as follows: (1) Auditory adaptation as measured with a homophonic simultaneous dichotic loudness-balance (SDLB) procedure increased as a function of the adapting ear exposure duration. (2) With heterophonic and homophonic methods of delayed balance procedures, the loudness of the adapting stimulus did not decrease as a function of AE exposure. (3) The balance levels obtained during the homophonic and heterophonic modified SDLB studies remained at a constant level irrespective of AE exposure duration. (4) When the CE stimuli were of a type that minimized lateralization cues (heterophonic and π) the unadapted loudness balances were made at a lower intensity level during SDLB's than when the homophonic CE stimulus was used. The major conclusion of the present study was that the loudness of a moderate acoustic signal does not decrease as a function of the duration of the presentation.
Pitch Control and Pitch Paradoxes Demonstrated with Computer-Synthesized Sounds
Authors: Risset J. C.
Published: October 2005

Using computer-generated sounds, R. N. Shepard has demonstrated circularity in judgments of relative pitch [J. Acoust. Soc. Amer. 36, 2346–2353 (1964)]. Other unusual sounds will be presented, including endlessly descending glissandi; a succession of periodic tones that are perceived as going down in pitch although the final pitch is perceived as higher than the original pitch; successions of periodic tones that are perceived as going both up and down in pitch. Most of these sounds consist of octave components; the fundamental frequency can be varied and the spectral envelope can be shifted, independently of the fundamental frequency, along the frequency axis. The way some of these sounds are perceived supports the view that pitch perception cannot always be adequately represented by a linear scale, but rather implies a circular component (“tonality”) and a linear component (“tone height”), which can vary independently for specially contrived stimuli. [Work supported by the Délégation Générale à la Recherche Scientifique et Technique.]
Perceived Rate of Dichotically Alternated Clicks
Authors: Huggins A. W. F.
Published: October 2005

A train of pulses in which successive pulses are presented alternately to the left and right ears can be perceived only as a series of discrete pulses when the repetition rate is low. At faster rates, two identical but nonsynchronized pulse trains are perceived, one at each ear. The switch from one percept to the other is quite sharp. Subjects adjusted a binaural train until its repetition rate sounded most like the total rate of an alternated train, for 16 rates log-spaced between 1.5 and 48 pps. Each subject made 16 matches of each rate. When pulses in the alternated train were separated by less than about 70 msec (i.e., 140 msec for successive pulses in one ear), subjects matched the rate of the train in each ear. When pulses were separated by more than about 120 msec, subjects matched the total rate, in pulses-into-the-head per second. The results are discussed in relation to results on the perception of alternated and interrupted speech. [Supported in part by National Institutes of Health.]
Frequency Discrimination in the Adapted Ear
Authors: Nielsen D. W. , Elliott D. N. , Fraser W. D.
Published: October 2005

The reported loss of tonal quality of a pure tone with increased duration of an adapting stimulus raised the possibility of a change in frequency discrimination limen (DLf) or a shift in pitch. This study investigated the effects of adaptation on the monotic and dichotic DLf and determined the amount of pitch shift for the adapting frequency. DLf's were obtained under normal and adapted conditions for two frequencies (1 kHz, 250 Hz), at two intensities (40 dB SL, 60 dB SL) and for two modes of presentation (monotic, dichotic). These DLf measures were calculated by the constant stimulus method using the least-squares solution; CE's were also obtained. The DLf analysis showed significant results for the main effects of frequency, adaptation, and mode of presentation. Results of the CE analysis showed no statistical significance. An increase in DLf due to adaptation was predicted on the basis of previous reports, but the effect was a group phenomenon. Thus, generalizations concerning the individual functional characteristics of the auditory system could not be made. [Research supported by the National Institutes of Health.]
Computer Recognition of Single-Syllable English Words
Authors: Medress Mark
Published: October 2005

Recognition of single-syllable words is attempted by estimating element values of the distinctive features matrices defining their phoneme strings. These values are determined by making measurements on a filter bank representation of the short time spectrum of the unknown utterance. The first properties estimated are those least influenced by the phonetic environment, such as the presence and location of stops and fricatives, and whether the vowel is front or back. Other more dependent features are determined by phonological rules and additional measurements that depend on the estimates of the first set of properties. These include place of articulation for the stops and fricatives, other vowel features, and detection and identification of nasals, liquids, and glides. For three speakers' recordings of 60 words containing five vowels and initial and final liquids, this procedure correctly identified all but three of the vowels, and identified without error the liquids in all words with front vowels. Preliminary work indicates that similar success can be expected for a more heterogeneous word list. [This work was supported in part by grants from the National Institutes of Health.]
Acoustics of Open Plan Spaces—Some Case Histories
Authors: Hirtle P. W. , Watters B. G. , Cavanaugh W. J.
Published: October 2005

Open planning in office buildings and in schools has presented a new range of problems in the control of the acoustical environment. Several case histories are described, including objective measurements and subjective reactions of the occupants. A preliminary scheme for the systematic analysis and evaluation of privacy and communication problems in these types of spaces is presented. The analysis technique utilizes the widely known AI concept in developing an objective rating for privacy (or communication) and corresponds reasonably well with observed subjective reactions in field situations.
Reduction of the Time Average of the Spatial Variations of the Sound Pressure in a Small Reverberant Room with a Rotating Diffuser
Authors: Vér István L. , Kurze Ulrich
Published: October 2005

In small rooms, the spatial variation of the sound pressure at low frequencies is very large. In order to reduce the time-average spatial variations in a designated test section within the reverberant room, in the region below the frequency of modal overlap, a rotating vane diffuser is employed. Effects of the rotating vane, such as changing the character of the acoustical space from a time-invariant into a time-variant system, which in turn introduces new frequencies, is considered. Some experimental findings are presented. [This research was supported by the Naval Applied Science Laboratory, Brooklyn, N. Y.]
Present Status in the Design of Flextensional Underwater Acoustic Transducers
Authors: Brigham Gerald A. , Royster Larry H.
Published: October 2005

The history of the flextensional transducer development is briefly outlined from the original designs developed by W. J. Toulis to its present status. Then the present designs are classified in five different categories. The state of the art with respect to the development of mathematical models for each classification is presented. Experimental data are discussed where applicable and permissible. [The development of the flextensional transducer has been partially supported by the Office of Naval Research, Acoustics Programs, and the Naval Underwater Sound Laboratory.]
Measurement of the Phase of Vibrational Displacement by a Laser Interferometer
Authors: Serbyn M. R. , Andrews F. A.
Published: October 2005

A method of measuring the phase of vibrational displacement, utilizing a Michelson interferometer with a laser source, has been developed and applied to the study of underwater-sound transducers. The technique makes possible direct determination of transducer mechanical impedance and electromechanical coupling factor as functions of frequency, and permits point-by-point measurements of phase throughout the vibrating surface. It is a sensitive indicator of the effect of radiation loading and the degree of nonlinearity. Examples of these measurements are presented and discussed.
Rôle of Impurities in Cavitation Threshold Determination
Authors: Apfel Robert E.
Published: October 2005

Galloway, Strasberg, Barger, and others have observed that vaporous cavitation thresholds for unfiltered water at frequencies below 100 kHz depend strongly upon the air content of the water sample; and Strasberg has offered theoretical arguments that are consistent with these observations. Greenspan, on the other hand, has observed little dependence on air content at 30–60 kHz for carefully filtered water and for liquids that readily wet solids. Strasberg's theory has been re-examined and extended to include the size of solid impurities (i.e., motes) in the liquid sample and the degree to which the liquid wets them. The results appear to explain the above observations, as well as some temperature and frequency effects, and are entirely consistent with Harvey's basic hypothesis that gas cavities trapped in surface crevices of motes are the primary source of cavitation nuclei. It is concluded that, at sufficiently low frequencies (i.e., below 100 kHz for water), the observed vaporous cavitation threshold depends primarily upon the initial growth of a vapor cavity in an imperfectly wetted crevice. [This work is supported by the Office of Naval Research.]
Triggering of Hydrodynamic Instabilities by Acoustic Pulses
Authors: Friedland Allan B. , Pierce Allan D.
Published: October 2005

It was demonstrated by Landau in 1944 that a vortex sheet between two compressible fluids in relative motion is absolutely instable if the relative Mach number is less than 2√. The present paper investigates the triggering of such an instability by an incident acoustic pulse generated by a line source located a distance d below an interface separating the nominally quiescent lower half-space from a half-space in which the ambient fluid velocity is constant and parallel to the interface. The hypothetical transient linear problem is solved exactly by Cagniard's method using the Ribner-Miles internal boundary conditions. Although various wave categories are predicted, the most interesting feature is that of an instability wave that is excited only if M<2√ and that appears in the solution as a moving triangular-shaped region below the interface within which the solution is a formally singular rapidly oscillating function. This may possibly represent the prediction of the spatial extent of a turbulent region arising from the acoustic triggering of the instability, although the linear equations clearly cannot describe the nature of the turblent flow.
Developments in Transducers for Studying Linguo-Palatal Contacts
Authors: Paterson R. L. , Proffit W. R. , McGlone R. E.
Published: October 2005

Several investigators have recently used strain-gauge pressure transducers to study linguo-palatal contacts during speech. The transducers offer a new and more accurate way to study tongue placement during production of an acoustic signal. Physical deformation of strain-gauge transducers causes changes in gauge resistance that are proportional to the deforming pressure. Strain gauges are also temperature sensitive. Base-line deviations due to thermal changes are particularly troublesome when automated data processing is desired. A successful lingual pressure transducer must be small, sensitive, highly temperature compensated, and capable of being packaged to withstand the intraoral environment. We describe two improved types of lingual pressure transducers, one using semiconductor strain gauges, the other employing film strain gauges. Despite their high inherent sensitivity, semiconductor transducers have performed poorly in the mouth because of temperature-compensation problems and fragility. Transducers based on film strain gauges can offer a highly stable base line with excellent sensitivity, acceptable size characteristics, and reduced cost.
Vocal-Tract Limitations on the Vowel Repertoires of Rhesus Monkey and other Nonhuman Primates
Authors: Lieberman Philip I. , Klatt Dennis H. , Wilson William A.
Published: October 2005

The vowel repertoire of a rhesus monkey (Macaca mulatta) was explored by means of a computer program that calculated formant frequencies from the area function of the animal's supralaryngeal vocal tract, which was systematically varied within the limits imposed by anatomical constraints. The resulting vowels were compared with human vowels and the vocalizations of nonhuman primates previously analyzed by Lieberman [“Primate Vocalizations and Human Linguistic Ability,” J. Acoust. Sac. Amer. 44, 1574–1584 (1968)]. The results are in accord with the previous study. The computer model indicates that the acoustic “vowel space” of a rhesus monkey is quite restricted as compared to the human range. This limitation is due to an anatomical feature of nonhuman primates, the lack of a pharyngeal region that can change its cross-sectional area. These animals thus lack the output mechanism that is necessary for the production of human speech. Man's speech-output mechanism is apparently species specific.
Derivative Synthesis of Musical Instrument Tones
Authors: Gschwandtner Eric
Published: October 2005

Spectral variances, typical for musical instrument tones, occur with changes in loudness level. Nonlinear electronic circuit elements, having appropriately chosen transfer characteristics, can produce spectra, variant with the level of their input signals. Based on this, a system of musical tone synthesis has been developed and a synthesizer was built. Parameters that characterize musical sounds can be programmed into the synthesizer. Such parameters—the major ones being the attack and decay time constants, the nonlinear transfer characteristic, and the formant filter—to be determined through measurements or experimentation. Synthesized sounds of some conventional musical instruments will be demonstrated.
Practical Engineering Approach to Surface Marine Acoustics
Authors: Bell Lewis H.
Published: October 2005

It is not the intention of this article to add to the already voluminous technology of underwater acoustics, but rather to outline a systematic technical approach to reducing the noise (unwanted sound) endured by people who must or choose to live aboard a boat. The clang of a diesel-powered generator can hardly be described as a lull when operating next to a stateroom, or, worse yet, to the neighboring boats at a quiet anchorage in the tropics. Attention will be focused on the over-all control of noise generated by internal-combustion engines utilized for propulsion or in conjunction with generators for production of electricity. In particular the major noise sources are identified, characterized, and treated analytically. With these results, experimental procedures and design methods are presented in a systems-type approach. Finally, the acoustical properties and installation methods of recently developed new materials are discussed.
Noise Radiation from Hermetic Reciprocating Compressors
Authors: Ingalls Douglas J.
Published: October 2005

Noise radiated from a hermetic reciprocating compressor consists of harmonics of the rotational frequency. At low frequencies, the noise radiation is due to solid body motion and exhibits a dipole pattern. At higher frequencies, the noise radiation is due to shell deformations and the corresponding noise pattern is that of quadrupole or higher-order radiation.
Acoustical Modeling of Reverberation Chambers
Authors: Ortega Jose C. , Hyde Jerald R. , Christoff Jerry P.
Published: October 2005

Critical listening tests conducted in full-scale reverberation chambers utilized in the recording industry reveal that there are often two major faults present in the decay of sound in the frequency range below 1000 Hz: (1) prolonged decay of certain axial modes resulting in a characteristic tone imparted to program materials; (2) beating between the modes resulting in a modulation of program material. Scale-model measurements allow the physical factors behind these faults to be isolated quickly. In addition, the model measurements provide a means of minimizing these faults through the optimal selection of room proportions and shape. The experimental technique is described and some preliminary tape-recorded results comparing the decay of pulsed and steady-state sources are presented for scale-model and full-scale chambers.
Modified Ray Theory for the Two-Turning-Point Problem
Authors: Murphy E. L.
Published: October 2005

A wavelength-dependent modified ray theory is developed to represent the reflected and transmitted fields for a harmonic point source located in an inhomogeneous medium giving rise to the two-turning-point, or split-beam, type of sound field. A generalization of the WKB procedure based on Weber's functions is used to construct approximate solutions that, unlike the ordinary WKB approximations, are valid throughout the two-turning-point region. These solutions are used for the construction of a contour-integral representation for the sound field of the point source. A stationary phase condition is invoked to develop, formally, a modified ray theory. For example, in a symmetric parabolic index of refraction n(z), the ordinary ray scheme is modified such that a ray with turning point at level z = z1 is reflected instead at some level z = zc. The cutoff level zc has the approximate value −(12)D[1+(z1/D)2], where the parameter D is wavelength dependent. The level z = zc can be interpreted as a reflection plane; there is some transmission from such rays, and it can be represented in the transmission region, beyond the second turning-point level, as originating from a transmission plane at level z = −zc.
Experimental Digital System for the Prediction of Underwater Sound Propagation
Authors: Tate D. C.
Published: October 2005

An experimental digital system to measure a depth-temperature profile of an area of water and utilize this data for the calculation of sound transmission paths and isointensity loss contours has been designed using commercially available hardware including temperature measuring equipment, digital computer, and output display unit. Computer software programs were developed to handle the temperature sampling of the ocean water, all calculations to determine the desired results, and the output of the resultant data. Numerous field tests were conducted, and the experimental data were compared with the predicted data to verify the accuracy of the system.
Time-Smear and Frequency-Smear Studies on the BIFI Range
Authors: Sussman Bernard , Kanabis William G.
Published: October 2005

The BIFI range is a shallow-water acoustic range in Long Island Sound, about 19 miles long and 120 ft deep. Results of the time and frequency-smear studies made on this range are presented. It is shown how these results may be used to predict signal fluctuation. In time-smear studies, the received signal is divided into a front, main arrival, and tail. The relative energies of the three sections of the signal are computed, and these results are used to predict the range of signal fluctuations. The above analysis and computations are easily carried out on a digital computer using as input data automatically punched on IBM cards. Frequency smear is the Doppler shift undergone by a signal as a result of being reflected from a moving surface. Many frequency-smear spectra were obtained for varying sea states, and, from these, dispersion as a function of sea state was calculated. The dispersion increased with sea state, in agreement with theory.
Model for Low-Frequency Sound Propagation in Deep Water
Authors: Franklin J. B. , Mohammed A. , Jordan R. J.
Published: October 2005

Low-frequency sound-propagation loss in deep water between near-surface sound sources and hydrophones exhibits short- and long-term fluctuations with range. A model of the sound field based on a product relationship between the two types of fluctuations is discussed. Long-term fluctuations are described by a deterministic range function obtained from the application of simple ray-tracing techniques. A random variable is used to describe the short-term fluctuations. The effect of multipath interference on both types of fluctuations is considered. The deterministic range function, and the probability density functions and spectra describing the short-term fluctuations are discussed using experimental results. The experimental work was carried out using source and hydrophone depths of 25 and 400 ft, respectively. Source signals were provided by TNT charges and a 230-Hz CW projector.
Computer Solution of the Response of Complex Structures to Random Excitation
Authors: Rommel Bruce A. , Racker George F.
Published: October 2005

The major problem in the computer solution to the response of complex linear systems to Gaussian random excitation is core and peripheral storage capacity. This problem is solved in various ways by using known general relationships and computing selected results. Two response equations, compatible with finite element modeling of structures, are discussed. Their formulation, suitable for programming, is in matrix form and all forcing-function spectra enter the response equations in a simple two-dimensional matrix form. The first of these response equations ignores the modal cross products and computes the response at all points simultaneously. The second response equation does not ignore the modal cross products and computes the response one point at a time. The second response equation has a “source-tracking capability” that may be used to ascertain which exciting forces or pairs of forces contribute most to the response at a given point. Computer results are used to evaluate statistically the effects of the modal cross products on the response. Other topics discussed briefly are: (1) the use of covariants to reduce computer stores requirements; (2) computer run times and eigenvalue extraction; (3) truncation of the modal spectra; (4) the modal viscous-damping assumption; (5) the mode-acceleration method applied to the random-response problem; (6) correlation lengths and the coalescing of pressure in the force; and (7) the planning of wind-tunnel tests and the extrapolation of data to provide input data for random-response calculation
Internal-Force and Moment-Response Equations for Structures Exposed to Aeroacoustic Excitation
Authors: Himelblau Harry
Published: October 2005

Relationships between the internal stresses of a structure and the vibratory displacements in applied loading are reviewed and extended to the case of distributed random loading. Two methods of calculating the internal force and moment spectra, and hence the internal stress spectra, are described. The first method relates the internal forces and moments to the modal displacements and their spatial derivatives. The second method utilizes influence coefficients between the internal stresses and the applied and inertial loadings, which are obtained statically, and is therefore an extension of the classical mode displacement and mode acceleration methods. The advantages and limitations of each method are discussed.
What Good is Statistical Energy Analysis Anyway?
Authors: Lyon Richard H.
Published: October 2005

It is now seven years since papers first appeared that were said to use statistical energy analysis (SEA) in solving problems of sound structural interactions. SEA has been described as a point of view in dealing with vibration of complex structures and, as such, it employs a series of analytical and experimental “methods,” most of which predate the identification of SEA. This viewpoint is statistical because the systems under analysis are presumed drawn from populations with random parameters; energy is the independent dynamical variable chosen because distinctions between acoustical and mechanical systems disappear; analysis emphasizes that there is an approach to a problem rather than a set of techniques, as such. At present, there are at least 10 university groups and a similar number of industrial and government groups that identify themselves as working on SEA problems. Workers in these groups are generally intrigued by the apparent power of some of the techniques, but they also ask searching questions concerning the basis of SEA and about its applicability for real engineering problems. The purpose of this paper is to discuss these questions and at least offer some tentative answers as to what one can reasonably expect to gain by adopting (part time, at least) this viewpoint.
Lingual and Intraoral Air-Pressure Variations as a Function of Vocal Intensity
Authors: Brown W. S. , McGlone Robert E. , Proffit William R.
Published: October 2005

The relationship between tongue pressure and intraoral air pressure during variations in vocal intensity was investigated. Simultaneous recordings of the two intraoral pressures were collected during the phonations of nine young adult males repeating syllables at three distinct vocal intensity levels. Both intraoral pressures were shown to increase as the subjects increased their vocal level from low to medium to high. These results demonstrate that an interaction between tongue activity and respiratory air flow occurs, which accounts for variations in intraoral air pressure during changes in vocal intensity. These data when combined with previously reported data for consonants demonstrates the relationship between air pressure and tongue pressure.
Subglottal Pressure Variations and Glottal Frequency
Authors: Ohala John , Ladefoged Peter
Published: October 2005

Most investigators agree that variations in subglottal pressure (ΔPs) and variations is vocal-cord frequency (Δf0) are related, such that Δf0/ΔPs in usually less than 10 Hz/cm aq. in normal speech. Theoretical work by Flanagan indicates that this ratio may vary according to vowel quality. Lieberman's theory, however, predicts a much greater range for the ratio (although his data for normal speech do not). This paper reports data from two more subjects. Ps was recorded directly via a tracheal puncture or by a small transducer inserted through the glottis into the trachea. Transglottal pressure changes were induced by pressing the subject's chest or by obstructing outgoing air at the lips. Electromyographic activity of the laryngeal muscles was monitored in one subject, ensuring the absence of muscular changes that might affect f0. Variations in vowel quality could not be shown to affect Δf0/Ps as suggested by Flanagan's predictions; however, the ratio remained below 10 Hz/cm aq., refuting Lieberman's claims. [Research supported by USPHS and ONR.]
Motion Pictures of the Vocal Folds in Speech
Authors: Sawashima Masayuki , Abramson Arthur S. , Cooper Franklin S. , Lisker Leigh
Published: October 2005

During the past decade, several techniques have been developed by which the opening and closing of the glottis during running speech may be observed indirectly. The techniques involve transillumination, measurement of electrical impedance across the glottis, ultrasonic echo ranging, and x-ray motion pictures. In earlier work at Haskins Laboratories, the transillumination technique was used. Certain questions raised by our transillumination data called for direct visual observation of the glottis. With a technique developed at the University of Tokyo by one of the authors, we have begun using a coherent fiber-optics bundle to provide an image of the larynx that might be examined visually and recorded photographically without interfering with running speech. Transillumination data are collected at the same time. A series of short sentences produced by several speakers of English was recorded, with special attention paid to voiced and voiceless consonants in different contexts. For almost all productions of voiceless stops and fricatives, an opening of the glottis was clearly observable. A demonstration film is presented with the paper. [This research was supported by the National Institute of Dental Research and the Office of Naval Research.]
Vocal Intensity in the Modal and Falsetto Registers
Authors: Colton Raymond H.
Published: October 2005

The minimum, most comfortable and maximum sustainable vocal intensity levels were measured at three frequencies produced in the modal and falsetto registers. Singers and nonsingers produced the phonations at an identical frequency in the two registers. At all frequencies, singers tended to produce larger ranges of intensity in the two registers than did nonsingers. For both subject groups, the minimum intensity levels were very similar in the modal and falsetto registers. The largest difference of intensity occurred at the maximum intensity condition, where falsetto phonations were generally about 15 dB less intense than modal register phonations. Consequently, the range of intensity measured for falsetto-register phonations is smaller than modal-register phonations. Both vocal-intensity level and range varied as a function of the fundamental frequency at which the phonations were produced. The differences of vocal intensity between the modal and falsetto registers may be one physical criterion for identification of each register.
Masking of Low-Frequency Tones by High-Frequency Bands of Noise and Frequency-Modulated Tones
Authors: Bilger R. C. , Hopkinson N. T.
Published: October 2005

The masking of a low-frequency test signal (245 Hz) by a FM tone of much higher frequency (fc = 1200 Hz; Δf = ±100 Hz; and fm = 25-Hz sawtooth) was described earlier by one of us (NTH). An attempt has been made to understand further this FM masking by looking at the effect (1) throughout the frequency region below the masker, (2) at selected frequencies in a sample of 60 hard-of-hearing listeners, and (3) in relationship to remote masking as seen in both normal and hard-of-hearing listeners. The most striking result, so far, is that among hard-of-hearing listeners the magnitude of these masking effects depends as much upon the origin of their loss as upon the magnitude of their loss of hearing.
Masking, Combination Tones, and Critical Bandwidth
Authors: Greenwood D. D.
Published: October 2005

In experiments mapping pure-tone masked audiograms, in which the signal is either a pure tone or a narrow band of noise, a notch appears on the high-frequency side of the masker with a low point at a frequency one critical bandwidth from the masker frequency. This notch has been shown to be caused by the detection, on the lower-frequency side of the masker, of the combination tones that are produced by the addition of masker and signal. The same results are obtained when a very narrow band of noise masks a pure-tone signal. The implication that the same process that creates combination tones creates combination bands further supports other evidence as to the mechanical nature of combination tones. The immediate further implication bands or tones should therefore produce low-frequency masking effects in the same way that external stimuli do has been tested and confirmed over a wide range of intensities and frequency separations of the masking primaries. The latter have consisted of pairs of tones, tones plus narrow bands of noise, and pairs of narrow bands of noise. Some of the implications of these results for cochlear physics and critical bandwidth are outlined.
Theory of Sonic Boom Rise Times
Authors: Pierce Allan D.
Published: October 2005

A previous interpretation of anomalously large rise times as being caused by multiple ray arrivals associated with wavefront folding leads to an estimated mean rise time of the order of the rms ray-travel-time deviate, in reasonable agreement with the experimentally observed value of 5 msec. To place this theory on a firmer mathematical basis, the deterministic solution of the problem of an initially planar step function of overpressure Δ advancing through a weakly inhomogeneous medium is obtained for early arrivals (by a generalization of the Kirchhoff approximation) as [Δ/(2πcz)]dA/dt. Here A(t) is the area of the initial wavefront comprising all points rs whose net ray travel time τ(rs) to an observer at distance z is less than t. Travel times are computed to first order in the inhomogeneities by approximating rays as straight lines. Statistical properties of τ(rs), indicating an extremely small correlation length, are derived. Jumps in pressure are associated with points at which ∇τ(rs) vanishes. The number of such points is enormous (100 or greater) when z is of the order of several kilometers; this result supports the multiple-ray arrival theory of the rise times.
Specular Scattering of Underwater Sound from Anisotropic Sea and Swell Surfaces
Authors: Mayo Ned , Medwin Herman , Wright Wayne M.
Published: October 2005

The surface of a large, anechoic tank was excited by centrifugal fans and a mechanical swell maker to produce several different anisotropic “sea” and “swell” surfaces characterized by “typical” but distinctive frequency spectra, non-Gaussian height correlation functions, and wave-height probability densities. Surface roughness, g(=4k2σ2 sin2θ), was varied from zero to five by a wide selection of sound propagation constants: k, rms wave heights, σ, and grazing angles of specular scatter, θ. Using scattering surfaces that were, variously, swell alone, wind waves alone, and a combination of the two (producing a dual-peaked spectrum), continuous, simultaneous analog data were recorded, displayed, and analyzed for instantaneous wave height, instantaneous scattered pressure, and 20-sec integrations of the squared wave height, the total scattered squared sound pressure, and the variance of the scattered pressure. The steady component of the forward scattered squared pressure for both low-roughness swell and wind-driven surfaces is found to vary as e−g. However, compared with a broad spectrum sea, the swell surface produces a larger time-varying component (at the swell frequency). Results obtained are compared with theories by Parkins, which ignores shadowing, and Wagner, which overcorrects for shadowing. [Work supported by Naval Ship Systems Command.]
Fluctuations in the Reflections of Low-Frequency Acoustic Pulses from the Ocean Surface
Authors: Brown M. Vertner , Saenger Alfred
Published: October 2005

Thirteen-msec pulses of acoustic energy at 200, 300, 400, 500, 600 and 700 Hz were reflected from the ocean surface at normal incidence. Both the source and the receiver were fixed upon the bottom. The ocean surface was measured by a surface float, and power spectra of the surface displacements and slopes were calculated. The reflections were investigated for both arrival time and intensity fluctuations. These were arranged in a time sequence and analyzed for their power spectra. Curves will be presented to show that: (1) both the arrival time and the intensity spectra resemble the surface spectra, (2) both the arrival time and intensity spectra tend to broaden and become more sensitive to the surface slopes and/or shorter surface wave lengths as the insonifying energy spreads over the ocean surface.
Statistical Studies of Back-Scattered Sound near 28 kHz
Authors: Moose Paul H. , Swarts R. L.
Published: October 2005

A relatively simple but sufficiently general expression for the autocorrelation function of the complex modulation envelope of back-scattered underwater sound has been derived under certain geometrical and environmental limitations from the model for acoustic reverberation proposed by Middleton. [“Statistical Theory of Reverberation and Similar First-Order Scattered Fields,” IEEE Trans. Information Theory, IT-13 3 (July 1967)]. The parameters of that expression are estimated for some conditions from the first- and second-order statistics of narrow-band reverberation data collected at 28.2 kHz in the Strait of Juan de Fuca. In particular, the sample means, variances, and normalized auto-covariances have been computed as a function of range from the transceiver. From the sample variances, average acoustic back-scattering strengths have been obtained. Comparative examples are given for short-, long-, and burst-pulse transmissions. The estimation problems caused by inhomogeneities in the scattering medium are clearly indicated. The necessity for environmental stationarity and the resulting statistical homogeneity is discussed.
Empirical Determination of Air-Water Impedance Differences in Small Tanks
Authors: Weiss Burton A.
Published: October 2005

Airborne sonic pressure in an open or sealed housing enclosing an aquarium was measured in the air and in the water. Effective impedance differences were 9.1 dB with the housing open and 4.5 dB with the housing sealed. Both conditions indicated an effective impedance difference considerably less than the 35.5 dB impedance difference between air and the open ocean. Prevalent use of sonic fields in small aquariums thus require detailed calibration of sonic fields in tanks where the air-water interface is tranversed. The middle ear apparently functions primarily to transduce airborne sonic pressure into displacement in the cochlear fluids, rather than to match sonic pressure impedance.
Volume Back Scattering in the Coral Sea
Authors: Hall Marshall
Published: October 2005

Volume back-scattering strengths S averaged over three depth intervals are presented for a number of deep water stations in the Coral Sea at frequencies between 2.5–12.5 kHz in 13-oct steps. At daytime stations, mean values for the 1-m S ranged from −95 dB at the low frequencies to −77 dB at 12.5 kHz. On the average in the depth interval 0–1500 m, S was a maximum in the interval 0–450 m at the lower frequencies, but at the higher frequencies S was a maximum in the interval 450–750 m. Deep scattering layers were found at three stations, where significant negative correlations were observed between S and water temperature at a depth of 200 m. At evening stations 1 h before sunset, S was a maximum in the interval 0–750 m and increased with frequency at an average rate of 9 dB/oct. At 1 h after sunset, S was a maximum in the interval 0–450 m and increased with frequency at an average rate of 6 dB/oct. The main temporal increases in S ranged from a maximum of 14 dB at 3.2 and 4 kHz to 4 dB at 12.5 kHz. The increases obtained are consistent with the hypothesis that volume scattering is geared to swimbladders of fish that migrate toward the surface over the sunset.
Response of a Plate to Noise in a Supporting Elastic Medium
Authors: Remington Paul J.
Published: October 2005

The steady-state response of in infinite Bernoulli-Euler plate placed on the surface of a vibrating viscoelastic half-space is studied both theoretically and experimentally. The surface displacements of the half-space before the plate is added are assumed to be stationary homogeneous random functions on position and time. Given the wavenumber frequency spectra of these displacements, the frequency spectra of the displacements of the plate-half-space interface are calculated. Two boundary conditions at the plate-half-space interface are considered, no shear stress and no relative motion in the plane of the interface. A test of the shear-stress free interface case was performed in which several plexiglass plates of varying thickness were place on the vibrating surface of an “experimental half-space,” a tub filled with Plasticine, a modeling clay. Wavenumber spectra transformed from correlation measurements, made on the surface of the clay, were used in the theory to obtain response predictions that agreed to within 3 dB of measured response levels. [Support for this work was provided by the National Aeronautics and Space Administrations and the National Science Foundation.]
Response of a Thin-Walled Cylindrical Duct to a Random Pressure Field
Authors: Khosrovani H. , Cohen R. , Chanaud R. C.
Published: October 2005

The vibration of a thin-walled cylindrical duct, which results from an internal random pressure field was studied both experimentally and theoretically. The Green's function for the duct [M. G. Cottis, J. Acoust. Soc. Amer. 37, 31–42 (1965)] was convolved with a simplified model of the internal pressure cross correlations to predict the displacement cross correlations. These were then compared with measured displacement cross correlations. The Reynolds number range for the experiments was near 105 and the Mach number was below 0.1, typical of air handling applications. A muffler between the fan and test duct (112 long×7 diam×0.008 thick) was used to simulate a long duct length and it was found that the pressure spectra were dominated by the fan sound at low audio frequencies. The duct responded primarily to this sound because of the large correlation areas; the turbulence appeared to have little effect. Although the actual pressure fluctuations did not have similar spectra to that used in the calculations (white noise), the experimental and predicted displacement cross correlations were in reasonably good agreement.
Fatigue Evaluation of Noise Suppression Materials
Authors: Scott David H.
Published: October 2005

In conjunction with acoustical tests now in progress on engine duct liners intended to reduce noise levels in jet aircraft, a separate study is being conducted regarding the mechanical properties of these materials, in particular their behavior in relation to acoustical fatigue. In order to investigate these properties a three-phase test program was initiated. The first phase was a flexural fatigue test of the porous sheet materials to establish basic “S-N” data. The second phase of the program was established to analyze accurately the fatigue characteristics of the porous sheet material in a panel facing configuration. Several small panels were constructed and tested as clamped cantilever beams using an electromechanical shaker with a random excitation. The third phase necessitates using the progressive wave test chamber of the sonic fatigue test facility, where we have the capability to test a full-scale model at various sound-pressure levels until failure. This paper summarizes the progress of and the information obtained from the investigation, and discusses some of the test procedures and problems encountered.
Interpretations of Cross-Correlation and Cross-Spectra Measurements of Boundary Layer Turbulence and Panel Response
Authors: White P. H.
Published: October 2005

The random pressure field of boundary layer turbulence, or the response of a panel to this pressure field may be described by the space-time correlation or the cross spectrum. Measurements of these quantities are used to determine system response or to investigate the physics of the turbulence. Many past measurements of correlation area, convection velocity, and wavenumber spectra are in disagreement because of incorrect or incomplete interpretation of the data. Proper interpretation of the measured data can lead to increased understanding of the phenomena and to improved instrumentation techniques for new measurements.
Separation of Dispersive and Nondispersive Energy through Correlation Techniques
Authors: DuBack Earl , Weiss Robert
Published: October 2005

The purpose of this paper is to illustrate a method for separating dispersive energy from nondispersive energy through correlation techniques. A white noise “nondispersive” signal was added to two accelerometer “dispersive” signals. This information was digitized and processed using the Univac 1107 computer. The cross correlation between the accelerometers produces an energy peak for the nondispersive signal and a distributed “peak” for the dispersive signal. The section of the correlogram containing the nondispersive peak is zeroed out and the cross spectrum determined. The cross spectrum is transformed in terms of Tf (where T is the time lag and f is the frequency). A new correlation function is obtained that has analogous properties to the standard cross correlation function. In this manner, the nondispersive energy is eliminated and an energy peak due to the dispersive signal can be determined.
Spatial Averaging in a Diffuse Sound Field
Authors: Lubman David
Published: October 2005

Estimation of mean pressure-squared in a reverberation room embodies averages over time, frequency, and space. The benefits of space averaging may be expressed by a number Neq—the equivalent number of uncorrelated samples (degrees of freedom) resulting from space averaging. A method for finding Neq is presented that is based upon knowledge of the spatial covariance function for pressure squared. Results are given for the cases of sampling at discrete locations, and for continuous integration over a straight line traverse. These results are based upon a covariance function that is intended for pure-tone or extremely narrow-band noise excitation. It is shown that Neq for continuous integration along a straight-line traverse of length L is approximately equivalent to that for discrete sampling at half-wavelength intervals on the same line.