bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Feature Analysis of Several Arabic Consonants
Authors: Klatt Dennis H. , Stevens Kenneth N.
Published: October 2005

Several Arabic consonants that are produced with places of articulation that are further back in the vocal tract than the English /k/ have been analyzed. It appears from the formant-frequency data that three contrasting places of articulation are used for these consonants, two of these being in the pharyngeal region and one at the glottis. These places of articulation represent members of a universal set of quantal positions that are predictable on theoretical grounds. The pharyngeal points of articulation differ from other, more anterior, consonantal articulations by the fact that the first formant is higher and is located close to the second formant. Other acoustic features of the Arabic consonants are described and additional evidence from a preliminary speech synthesis experiment is presented. [This work was supported in part by the National Institutes of Health and in part by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research.]
Analysis of Vowels Produced by Spanish and English Speakers
Authors: Stevens K. N. , Klatt Mary M.
Published: October 2005

Measurements of the formant frequencies were made throughout the stressed vowels in a series of monosyllabic and bisyllabic words produced by several Spanish and American-English speakers and the data were displayed in the form of F1−F2 contours. The Spanish speakers generated both Spanish words and English words, whereas the American speakers produced only the English words. Differences between Spanish and English vowels occur not only in target formant frequencies but also in the shape of the F1−F2 contour, i.e., in the dynamics of the vowel. A panel of listeners rated the degree of accent on the vowels for each of the English words. The listener judgments for a given vowel appear to be based on the target formant frequencies, and on the shape and duration of the F1−F2 contour. Implications of the results with regard to the development of automated displays for assisting in second-language learning are discussed. [This work was sponsored by the Advanced Research Projects Agency, Department of Defense, Air Force Office of Scientific Research under contract.]
Intensity Summation of Modes and Images in Shallow Water Sound Transmission
Authors: Urick R. J.
Published: October 2005

An earlier paper [J. Acoust. Soc. Amer. 41, 161 (A) (1967)] gave a simple expression for predicting the transmission loss in shallow water under conditions of downward refraction when incomplete environmental knowledge precludes the use of elaborate theory. The present paper considers the case of near-isovelocity water with parallel lossy boundaries. Summing modes on a computer intensity-wise, assuming random phase between modes, yields a set of prediction curves for the loss in terms of normalized range r/H and normalized water depth H/λ with boundary reflection loss, expressed in decibels per degree grazing angle, as a parameter. The random phase assumption is justifiable, as a practical matter, by the effects of natural environmental irregularities, by the smallness of mode interference effects when many modes are trapped and by the interest of the engineer in only the average sound field at a distance. Summing discrete modes and images in this way, as well as integrating a continuous distribution of modes and images, leads to identical values of loss when H/λ is large. Comparisons of the prediction curves with field data reported in the literature are made.
Cavitation Due to Reflected Shock Pulses
Authors: Wentzell R. A.
Published: October 2005

Cavitation caused by shock pulses reflected from the sea surface is studied. A breaking pressure of zero is assumed and a model based on spalled layers is proposed to determine the prominent characteristics. These characteristics include the extent of cavitation, and return pulse with an initial spike followed by an approximate rectangular pulse, which is longer than the incident pulse by a factor of 103. Experiments using TNT to produce exponential shock pulses of various peak pressure and wavelengths verify the prominent features of the model. The acoustic effects indicate a breaking tension at least a factor of 10 smaller than that indicated by visible effects.
Stimuli Level of Dichotically Presented Tones and Cat Superior Olive S-Segment Cell Discharge
Authors: Boudreau James C. , Tsuchitani Chiyeko
Published: October 2005

Knowledge of the frequency of the stimulus and existing interaural intensity differences are inadequate for predicting S-segment cell discharge rates. The stimulus level, re threshold, of dichotically delivered tones must also be known. At low stimulus levels, the most active population of S-segment cells consists of cells whose CF's are tuned to the frequency of the stimulus tone. As stimulus levels of dichotically delivered tones increase above threshold. cells with CF's not tuned to the stimulus frequency tend to discharge at rates higher than those of the cells initially responsive at low levels. The higher the stimulus level the greater the discrepancy in frequency between the CF's of the most active cell population and the stimulus. Thus, the locus of maximum activity within the S segment is dependent not only on the frequency of the dichotically delivered stimulus tone but also on its stimulus level. [Research supported in part by U. S. Public Health Service.]
Effects of High Frequencies and Intersubject Variability on the Auditory Evoked Cortical Response
Authors: Rothman Howard H.
Published: October 2005

Tone bursts of 2, 4, 6 and 8 kHz, with rise-fall times of 20 msec and durations of 200 msec, were administered to human subjects, through earphones, at sensation levels (SL's) of 10, 30, 50, or 70 dB. The tone bursts were presented once per second in blocks of 60, at a specific frequency and SL. Sixteen combinations of frequency and SL were employed and were presented in a counter-balanced order, with four replications per combination for each subject. Simultaneously with each burst, the slow evoked response (V potential) was recorded between vertex and mastoid. Evoked-response amplitudes (N1−P2) were found to decrease with increasing frequency, particularly at higher SL's. The slopes of the input-output functions also decreased with frequency, though differences between subjects influenced slope even more than frequency. The input-output data, when fitted by straight regression lines, generally showed the same goodness of fit, whether plotted on logarithmic or linear ordinates, versus SL.
Interaural Switching Effects on the Recognition of Consonants
Authors: Rupf John A. , Hughes George W. , House Arthur S.
Published: October 2005

Experiments in which subjects repeated back (that is, “shadowed”) speech that was systematically alternated between their two ears have led to the hypothesis that the place—with respect to certain linguistic boundaries—at which the alternation occurs may affect perception [G. W. Hughes et al., J. Acoust. Soc. Amer. 40, 1283 (A) (1966)]. This hypothesis was investigated in an experiment in which speech samples of the form /hə'CVt/—where C was one of 14 different consonants and V was one of three different vowels—began in one ear and were switched to the other ear at some desginated place in the waveform. Each stimulus item was mixed with noise and presented to 16 subjects who identified the C and the V in a forced-choice test format. The results showed that the place in the waveform where the switching occurred had very little effect on consonant recognition and suggest that any decrement in the shadowing scores when speech is alternated between the ears is better described in terms of syllables than in terms of phonemes. Possible ear-preference effects were investigated and will be discussed. [This research was supported in part by the Air Force Cambridge Research Laboratories under contract.]
Laterality Effects in the Recall of Steady-State and Transient Speech Sounds
Authors: Darwin C. J.
Published: October 2005

The cues for discriminating fricatives are known to lie both in the spectrum of the friction itself and in the formant transitions into adjacent vowels. Although both these cues can vary acoustically with context, only the formant-transition cue is lateralized in dichotic listening. Steady-state fricatives, whether isolated or followed abruptly by a vowel were recalled equally well from either ear; however, when the appropriate transition was added there was an improvement in recall from the right ear, but no improvement from the left. This advantage for the right ear remained when the friction was removed but the transition left intact to give a stoplike sound. The right-ear advantage for recall of dichotically presented initial stops has been confirmed and a similar advantage found for both released and unreleased final stops. This latter effect is influenced by the relative onset times of the preceding vowels within a dichotic pair. By contrast, no preference for either ear could be found for isolated vowels of the same duration as the stop transitions (40 msec). These results indicate that speech sounds only give an advantage for the right ear in a dichotic listening task when they contain formant transitions.
Just-Noticeable Differences for Phoneme Duration in Natural Speech
Authors: Huggins A. W. F.
Published: October 2005

A tracking method [Levitt, J. Acoust. Soc. Amer. 43, 65 (1968)] was used to measure both the incremental and the decremental jND's for the durations of sound segments in naturally spoken sentences. Measurements were made for an unvoiced stop /p/ in word-initial, -medial, and -final positions, in symmetrical vowel context, and the first two also in asymmetric vowel context, and also for a stressed vowel /ɔ/, a fricative /∫/, a nasal /m/, and a lateral /l/. Four subjects served. The results show clearly that psychological time is not homogeneous during the perception of speech, which is equivalent to saying that the input sound wave has been “chunked” by the perceptual processing. [Research supported by the Science Research Council.]
Perceptual Structure of English Vowels
Authors: Singh Sadanand , Lee Ikmo , Woods David
Published: October 2005

Twelve isolated sustained English vowels were magnetically recorded and then presented to English speaking subjects in pairs. The subjects were asked to estimate the perceptual similarity of each pair by drawing a horizontal line. The length of the line corresponded to the degree of similarity. A short line represented a more similar pair; a long line, a less similar pair. The average length of all lines for all auditors was computed for each pair of vowels. These average values were summarized in a matrix and were used in subsequent analysis. Two statistical models were used in the analysis: Multidimensional Scaling (MDS: Shepard, Kruskal) and Hierarchical Clustering Schemes (HCS: Johnson). These models bring out the most prominent dimensions in the set of similarity values and are interpretable generally as phonetic features. Feature strength and feature markedness were also computed. [This work was supported by The National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Use of Acoustical Holography for the Imaging of the Sources of Radiated Sound on a Complex Vibrator
Authors: Greene David C.
Published: October 2005

A demonstration has been made of the application of acoustical holography to the imaging of the sources of radiated sound on a complex vibrator. Demonstration was made in a small water tank using a submerged glass disk as a test object. The disk was driven to flexural vibrations by a force of frequency 2.5 MHz, applied at a point. The radiated sound field was sampled by a mechanically scanned probe hydrophone, the output of which was compared with a synthetic reference “beam” to form a hologram. Optical reconstruction of a hologram provides a picture of the (acoustically) self-luminous disk. Those parts of the disk responsible for the radiated sound may be readily identified and assigned a semiquantitative share of the responsibility for the radiated energy. The principles demonstrated are applicable at lower frequencies and in other media.
Reconstruction of Shapes of Objects from Their Sound-Diffraction Patterns
Authors: Sondhi M. M.
Published: October 2005

A method will be presented for reconstructing the shape of an object from a measurement of the diffraction pattern of the object when placed in the path of a monochromatic sound wave. It will be shown that measurements of amplitude and phase in a plane at a distance from the object enable reconstruction of the wavefront everywhere. It will be further shown that measurements at only a discrete set of points (a square lattice of suitable dimensions) suffice. The results of computer simulation will be presented. An experiment by G. M. Sessler and J. E. West to verify the reconstruction method will also be described.
Transmitted Waves in Sound Scattering from Liquid Cylinders
Authors: Brill Donald , Überall H.
Published: October 2005

In our previous theoretical work [Doolittle, Überall, and Uginc̆ius J. Acoust. Sac. Amer. 43, 1 (1968)], we showed that underwater sound scattering from elastic or liquid cylinders is dominated by “geometric” and “elastic” circumferential waves. Both types of waves were visually demonstrated (using schlieren) by Neubauer [J. Acoust. Soc. Amer. 44, 1150 (1968)]. In this experiment, in addition to the circumferential waves, there appeared waves transmitted through the cylinder. We have shown that in our theory, these transmitted waves (for the simplified case of a liquid cylinder) may be separated out from the geometrically reflected wave by an expansion first utilized by van der Pol and Bremmer, and calculated quantitatively by the saddle-point method. The positions of the saddle points permit a geometrical interpretation in terms of transmitted ray paths containing zero, one, two ⋯ additional internal reflections. [Work supported by the Office of Naval Research.]
Integral Equations for Exterior Scattering That Have a Unique Solution at All Frequencies
Authors: Mitzner K. M.
Published: October 2005

The exterior Dirichlet problem can be formulated in terms of either a first-kind or a second-kind integral equation for the normal velocity at the surface of the scatterer. However, neither of the standard equations has a unique solution at all frequencies. It is shown here that a third formulation, obtained simply by forming a linear combination of the two original equations, does give the correct solution uniquely at all frequencies. Similarly, the exterior Neumann problem can be described by a first- or second-kind equation for the pressure at the surface, neither of which has a unique solution at all frequencies; but a linear combination of the two equations again yields the correct solution uniquely. Numerical results for the analogous problem in electromagnetics indicate that the new formulations should be well suited for practical computation.
Spectra of Interacting Acoustical Waves with a Turbulent Wake
Authors: Izzo A. , Yildiz M.
Published: October 2005

The state of a compressible fluid is completely prescribed by its velocity, density, pressure, and temperature fields. When the compressible fluid is in a turbulent flow, all these quantities fluctuate in a random manner. Space-time Fourier transforms are used to show that these state variables separate into two physically distinct groups, one corresponding to fluctuating longitudinal sound waves, and the other to fluctuating vorticity or turbulence. The corresponding decomposition of the spectral and correlation tensors in a homogeneous isotropic field of turbulence is given. The spectra of interacting acoustical waves with turbulence are evaluated for various practical cases.
Edge Radiation from a Semi-Infinite Fluid-Loaded Plate
Authors: Ranganath P.
Published: October 2005

An infinite, isotropic, elastic plate surrounded by a heavy fluid is analyzed from two types of harmonic loading: (i) a uniform line force, and (ii) a uniform line moment. Approximate expressions for the plate displacements or rotations under the loads are obtained. It is then indicated how these two types of loading may be combined to simulate a clamped or simply supported edge for a semi-infinite fluid-loaded plate, when a harmonic bending wave on the plate approaches the edge at normal incidence. The power radiated by the edge is then estimated from the power radiated by the line force and line moment. It is shown that increased fluid loading has two counteracting effects on the power radiated by the edge: (1) the line force or moment reaction of the edge to a given incident wave increases, and (2) the power radiated by a given line force or moment decreases.
Motion of Underwater One-Dimensional Gas Bubbles
Authors: Epstein David , Keller Joseph B.
Published: October 2005

Investigation of one-dimensional bubble motion presented in an earlier paper [J. Acoust. Soc. Amer. 44, 395(A) (1968)] is continued. Although an oscillating spherical bubble radiates acoustic energy, the bubble motion may be studied with the water incompressible; but, in general, for cylindrical and planar bubbles, the water should be treated as compressible. Nevertheless, an asymptotic-incompressible solution to the cylinder problem yielding expressions analogous to the spherical case may be developed, but certain nonphysical peculiarities temper the applicability of this approximation. The planar bubble problem is solved, and an expression for the bubble expansion time and the pressure radiation field is derived. It is found that no bubble oscillations ensue. Compressible cylindrical equations of motion developed in paper cited above are linearized and solved by Laplace transform; equilibrium bubble motion is found to consist of a super-position of damped oscillations.
Free Oscillations of Acoustical Resonators and Pressure Effects on Damping and Amplification
Authors: Troke Robert W.
Published: October 2005

The effects of sound-pressure amplitude and static pressure are studied, primarily from experimental test results. Oscillograph records of the transient response of both Helmholtz and pipe resonators are analyzed to determine the damping, decay decrement, and relaxation time of the free oscillations. Damping is determined to be inversely proportional to the static pressure. Damping is found to be a function of amplitude and to decrease as the oscillating pressure amplitude decreases, although at a lesser rate. Since the pressure amplification at resonance is proportional to the reciprocal of the damping, very high amplifications are realized for systems with light damping and low pressure inputs. Acoustical resonators such as sea shells are shown to respond, continuously, audibly as pipe resonators to inaudible inputs. Experimental data and theoretical analyses are used to make a plot of amplification at resonance versus input sound-pressure level.
Novel Approach for Obtaining High-Intensity Sound over a Wide Frequency Range in a Large Reverberation Room
Authors: Dendrinos Steve
Published: October 2005

A 120-dB SPL over a frequency range 20–8000 Hz was required for subjective noise evaluation in Wyle's 100 000-ft3 reverberation room. Low frequencies were generated by speakers mounted in a concrete exponential horn connected to the room. Because the sound absorption of the room was large at high frequencies, the acoustic power required to reach high SPL's was extremely large. In order to avoid a large number of high-frequency loudspeakers, a room that acted as an acoustical filter was built within the large reverberation room. A set of high-frequency loudspeakers were mounted inside the inner room. The walls of the inner room were designed to be transparent at low frequencies and reflective at high frequencies, with 500 Hz as the crossover frequency. It is the purpose of this paper to describe some of the results achieved from the design of the inner room. [This work was supported by FA68WA-1971.]
Measuring the Wood Resonances of Treble Viol Plates by Hologram Interferometry
Authors: Ågren Carl-Hugo , Stetson Karl A.
Published: October 2005

Finished top plates for the treble viol were clamped at their edges to a heavy rigid wooden jig, which provided an artificial sound post and an electromagnetic exciter. Excitation was applied first to the back of the bass bar, where the right foot of the bridge would rest, and later to the center of the lower bout. In spite of the sensitivity of the plates to humidity, real-time interferometry permitted a more correct determination of the response peaks than a conventional loudness meter, while giving a picture of the vibration pattern on the plate surface. Time-average holograms were made of the plates at their response peaks and the reconstructions showed surprising details about the vibrations. Many response peaks, for example, were combinations of the basic vibration modes, the eigenfunctions of the plate geometry, some of which had nearly equal natural frequencies. The phase between these combining modes varied with frequency and was sometimes 90°. With a different excitation position, however, it was often possible to excite these modes separately at their own natural frequencies.
Proximity Requirements for Auditory Asynchrony Detection
Authors: Pollack Irwin
Published: October 2005

Gap-interval detection was studied as a function of the relation of the interpulse intervals immediately surrounding the gap region (the “nearfield” region) and of the intervals flanking the surround region (the “farfield” region). The gap threshold is crucially dependent upon the nearfield and is relatively independent of the farfield. Proximity effects are substantially reduced for longer interpulse intervals. The results suggest that the gap threshold is related to the requirements for a local spectral analysis of the gap region. [Research supported by a grant from the National Sciences Foundation.]
Phase versus Power Discrimination for Clicks
Authors: Ronken Don A.
Published: October 2005

Pairs of very brief pulses may be used to generate short duration (less than 10 msec) signals that have spectra that differ only in power, only in phase, or both power and phase. Conventional intensity discrimination for such click pairs is obtained by using the signals that differ only in power. The corresponding signals that differ only in their phase spectra are also readily discriminable. This result raises the question about the relative saliency of power and phase cues. The discriminability of a power difference seems to be reduced when uncorrelated phase differences are also present. [This research was supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, National Science Foundation, and an NIMH postdoctoral fellowship.]
Some Factors Influencing the Release from Masking
Authors: Menzer Judith , Loeb Michel , Smith Richard P.
Published: October 2005

The general purposes of these experiments were to: (1) replicate earlier findings that release from masking could not be obtained using a pure-tone masker, (2) determine whether the release from masking could be obtained for remote masking of low-frequency tones by higher-frequency noise, and (3) determine if there was a relation between the amount of masking and the release from masking. Results indicated that, in confirmation of earlier work, release from masking could not be obtained using a pure-tone masker. Also, the use of high-frequency noise to mask lower-frequency tones did not result in release from masking. Research on the possible relation of the amount of masking to the amount of release from masking is still in progress.
Dependence of Temporal and Spatial Correlation of Forward-Scattered Underwater Sound on the Surface Height Correlation Function
Authors: Medwin H. , Clay C. S.
Published: October 2005

The underwater sound forward scattered from a laboratory model sea surface has been studied to determine the relation between surface height correlation and sound-pressure correlation as a function of temporal and spatial displacements. The wind-driven model sea had a correlation function of the form: C(l)=exp[−(x/a)2]cos qx. The variations of sound-pressure correlation envelope with time lag and hydrophone displacement off specular axis, for different surface roughness through transition, are presented and compared with theory. Support for this research has been received from Naval Ship Systems Command (H.M.) and the Office of Naval Research (C.S.C.).
Time-Varying Spectra of Violin Tones
Authors: Beauchamp James W.
Published: October 2005

Harmonic analyses of several violin tones have been performed by computer. Each sound is represented by a finite series of harmonic-amplitude and phase-spectrum components varying with time. Graphical representations of spectra being explored are: (1) individual plots of fundamental-frequency harmonic amplitudes (both linear and dB), and relative phases as functions of time; (2) line-spectra movies with harmonic amplitude changes slowed 20:1; (3) spectrograms with vertical frequency scale, horizontal time scale, and darkness indicating amplitude. Spectrum analysis can be performed synchronously with the fundamental or asynchronously at a base frequency much lower than the fundamental, with advantages for each method. Completeness of harmonic analysis is demonstrated by examples of tones resynthesized using smoothed versions of harmonic-amplitude and pitch curves. For storage purposes, synthetic tones typically require 500 to 800 parameter-time coordinates per 1 sec of sound. Over all, the violin tones analyzed are characterized by strong resonances in regions 500–700 Hz and 1800–2500 Hz, a strong antiresonance at 1100–1500 Hz, and many peaks and valleys above 2000 Hz. Features of attack, steady-state, and decay will be discussed in terms of spectrum graphs.
Acoustic Orientation by the Rabbit Pinna and External Auditory Meatus
Authors: Fattu J. M.
Published: October 2005

Selected pure-tone pulses (1 to 13.7 kHz) were directed toward a methyl methacrylate replica of the left external ear from a large albino rabbit. Sound-pressure measurements were taken 4 msec after pulse-envelope arrival through a 14-in. calibrated condenser microphone situated within the auditory canal. The signal was amplified, displayed on a CRO, and photographed for analysis. The 12-cm pinna served to diffract directionally sounds of wavelengths smaller than its dimensions. Sensitivity in the horizontal plane 90° to 150° ipsilateral to the pinna opening produced amplifications of 20 dB re 0.0002 dyn/cm2 at the canal base for frequencies 2.2, 5, 8, and 10 kHz. Vertical and horizontal angles displayed marked frequency dependence. Sound-pressure measurements at the base and opening of the auditory canal suggest that cavity resonance interacts with the pinna-diffraction effects and is dependent upon the azimuth of the incident sound. [Supported by a National Science Foundation grant to R. A. Suthers.]
Auditory Localization during Binaural Masking
Authors: Curthoys I. S.
Published: October 2005

Subjects in an echo-deadened chamber judged the direction of a 300-msec burst of thermal noise at 73 dB SPL (T figure). This stimulus was transduced by a loudspeaker that was 3 ft from the subject and could be rotated around him. Another independently rotatable loudspeaker at the same distance transduced a similar but uncorrelated noise at the same intensity (I figure), commencing 500 msec before the T figure but having simultaneous termination. This sequence was presented every 20 sec, and the judged location of the T figure was measured by an adaptive sequential estimation technique (UDTR). The presence of the I figure produced a judged displacement of the T figure away from the I figure: This repulsion was maximal when the I figure was at 30° to the subject's median plane and decreased as the angle increased. An explanation similar to one hypothesized to explain analogous illusions in vision [L. Ganz, Psychol. Rev. 73, 128–150 (1966)] seems consistent with this angular function and the results of related experiments. Such an explanation indicates that the neural coding of auditory space may closely parallel neural coding of space in other sensory modalities.
Optical Investigations of Acoustical Loads on Launch Vehicles
Authors: Wilson L. N. , Krause F. R.
Published: October 2005

An optical cross-correlation technique is being developed to study the character and intensity of the high acoustical and oscillating loads produced in regions of flow separation on rockets and launch vehicles. The technique uses two narrow light beams intersecting in the region of interest, each of which is modulated by turbulent fluctuations in the flow. Cross correlation of the modulation signals then gives area integrals of correlated density fluctuations at the point of intersection. These area integrals are directly related to the integrals of density fluctuation that describe the sound-source intensities comprising the acoustical loads produced by the turbulence. The optical integration of local correlation areas has been confirmed experimentally in jet flows by obtaining the high spatial resolution and three-dimensional spectra expected from the integration. The actual determination of absolute sound-source intensities will be made using a newly constructed infrared system in which beam modulations occur by absorption rather than by scattering from condensation droplets. The signals obtained will then be related directly to the density of the absorbers. Mean convection speeds have been measured successfully in subsonic and supersonic jet shear layers by separating the two beams in the flow direction and depending upon scattering for beam modulation. The statistical description of velocity fluctuations is also theoretically possible, but requires updated eleectronics and new sampling reduction and digital filtering techniques. Theoretical and experimental results are presented and related to launch and flight experience to the extent possible. Emphasis is placed on the potential of the cross-beam technique to further the understanding of the acoustical environment in ways meaningful to the shock and vibration engineer.
Duct Acoustic Lining Technology for Applications to Turbofan Engines
Authors: Atvars J. , Mangiarotty R. A.
Published: October 2005

Fan noise radiated from the inlet and fan discharge during landing of current fan-jet airplanes makes the largest contribution to perceived noise. This noise can be reduced by lining the inlet and duct walls with sound absorbing materials. Because of the paucity of analytical lining design methods, which include duct airflow effects, an experimental program was conducted to investigate the influence of acoustic and geometric duct lining parameters on fan-noise attenuation. The significant parameters were found to be the acoustic impedance, treatment length, depth, core cell dimensions, channel width, number of walls lined, number of layers in the linings, air velocity, and direction of flow with reference to sound propagation. The influence of these parameters is discussed. For simple single-layer linings, a design technology has been developed by means of empirical equations. Experimental results show that this technology is valid, for duct sizes 4–12 in., lining depths of 14–1 in., and duct airflow Mach numbers from −0.4 to 0.4. [Work supported by NASA contract to The Boeing Company.]
Broad-Band Noise Generation in Turbofan Engines
Authors: Gordon Colin G.
Published: October 2005

At the exhaust flow velocities typical of current turbofan engines, a number of source mechanisms for broad-band noise generation can be postulated. These sources exist within the engine and act in addition to the more classical sources of jet noise that arise in the turbulent exhaust stream. Data are presented from laboratory studies that illustrate the importance and identify the mechanisms and parametric dependence of some of these sources. These sources, it is suggested, play a particularly significant rôle in the turbine and fan exhaust ducts of an engine—a rôle that may be augmented rather than diminished by current techniques of engine quieting. There is much to be learned about these sources before their significance in current and projected engine designs can be properly understood. Some suggestions are presented for future studies on real engines and laboratory systems.
Light Scattering from Thermal Fluctuations of a Liquid-Liquid Interface
Authors: Katyl Robert H. , Ingard Uno
Published: October 2005

The thermal fluctuations of a methanol-hexane interface have been studied by means of heterodyne spectroscopy of laser light scattered from the interface. The dispersion relation for high-frequency surface waves has thus been determined, and it is compared with the theoretical dispersion relation obtained from classical hydrodynamic theory. From the results, the interfacial surface tension has been determined as a function of temperature in the region of the critical mixing temperature of the two liquids. [This work was supported by the U. S. Navy (Office of Naval Research) under contract.]
Applications of Variational Principles in Acoustics
Authors: Rentzepis G. M.
Published: October 2005

It has been observed that variational methods, which permit the reduction of the field equations to the equivalent variational problems and subsequently admit direct methods for this solution of these problems, have not been employed in acoustics. In this paper, the field equations are derived by energy methods in a manner that demonstrates the existence of equivalent variational problems. Thus, having shown the admittance of direct methods for solution of acoustics problems, a modified Galerkin procedure is employed in solving a number of acoustics problems and comparing their solution with existing ones.
Some Effects of the Acoustic Reflex Upon TTS
Authors: Mills John H. , Lilly David J.
Published: October 2005

Experiments were conducted to test Ward's hypothesis [(1962). J. Acoust. Soc. Amer. 34, 1610–1619] that low-frequency pure tones produce more TTS than low-frequency noise because of the effects of the acoustic reflex. Sixteen subjects with an acoustic reflex were exposed (10 min at 110-dB SPL) to a 710-Hz pure tone and to a 18 oct-band noise. At 1000 Hz, the pure tone produced about 10 dB more TTS2 than the noise. For 6 subjects without an acoustic reflex (stapedectomized), the TTS produced by the pure tone was not greater than that produced by the noise. These results support Ward's hypothesis. Indirect measures of the acoustic reflex made with a Zwislocki acoustic bridge when the exposure signals were presented for 10 and 30 sec did not reveal differences between the pure tone and the noise in maintaining activity of the acoustic reflex.
Temporary Threshold Shift from Gunshot Noise with Normal and Grazing Incidence
Authors: Fletcher John L. , Loeb Michel
Published: October 2005

Temporary threshold shifts (TTS) were measured following exposure to 4 rounds of gunfire (M-14), at 2-sec intervals, at a distance of 4 ft with incidence grazing or normal. Measured peak level was 168 dB; duration, 200 μsec. TTS was such as to suggest that daily exposure would produce permanent loss at high frequencies and, for normal incidence, possible loss at lower frequencies. Discrepancies between these findings and those of other investigators are discussed.
Pitch Synchronous Vocoder
Authors: Davis Steven J.
Published: October 2005

This paper will present techniques for the implementation of a pitch synchronous vocoder that promises telephone-quality speech at channel vocoder bit rates. The techniques for implementation that will be discussed are a pitch-synchronous FFT and its inverse, and a synchronous detector with a time-domain synthesizer. The inherent advantages and compatibility considerations of the pitch-synchronous vocoder will be presented and compared to the conventional approaches. Computer simulations of the pitch synchronous vocoder will be discussed, and tapes of the simulated system will be presented.
Effect of Glottal Pulse Shape on the Quality of Nattural Vowels
Authors: Rosenberg A. E.
Published: October 2005

An experiment is described that investigates listener preferences for speech samples with varying glottal pulse-shape parameters. A male speaker recorded monosyllabic words and a continuous sentence. A pitch-synchronous analysis was carried out by a digital computer on the vowel portions of these samples. For every pitch period, the analysis provided: formant frequencies, waveform of the glottal excitation function, and an accurate pitch-period measurement. In each vowel, the natural glottal excitation function was replaced by a mathematical function with a shape not unlike that of natural glottal waves. The waveform of the artificial function could be modified by varying two parameters analogous to the “opening” and “closing” times of natural glottal pulses. Four opening times and four closing times (fixed relative to individual pitch-period lengths) were selected for experimentation. The artificial functions were substituted for the natural glottal pulses, and the speech wave was reconstituted period by period. Subjective evaluation of the reconstituted speech was carried out by means of computer-controlled paired-comparison tests. Sequential testing strategies were used to reveal the synthetic samples perceptually most similar to the original. The results indicate that an artificial glottal wave having the same analytical specification in every pitch period can yield reconstituted speech of quality comparable to natural speech.
Potential of High-Intensity Noise Testing
Authors: Morrow C. T.
Published: October 2005

Very nearly all vibration of consequence in missiles and space vehicles is excited by aerodynamic turbulence or noise propagating from turbulence. The presence of noise has stimulated some interest over the past decade or more in supplementing the traditional vibration tests of the flight equipment by some form of acoustic noise test. Recently, interest and activity have focused on the application of such a new technique to major sections of space vehicles. This application is attractive because the noise environment is in principle easier to predict than the vibration environment, the noise test permits simulation of three-dimensional vibration with realistic equipment-to-structure mechanical-impedance relationships, tedious peak notch equalization of the excitation signal is avoided, and the observation of functional interactions between different equipments of the same system during environmental test becomes possible. Such system environmental testing is made possible by the development of high-intensity noise generators, especially in the form of electropneumatic transducers. A typical facility involves a large reverberation chamber of dimensions determined in part by the size of the test item and in part by the low frequency limit of the required excitation. The noise field within the chamber is generated in part by corner-coupled horns and in part by arrays of transducers and horns. The high intensity noise test has its own peculiar limits, which must be considered by the shock and vibration engineer if he is to use it to best advantage. The space-vehicle section must be terminated with care if it is to have a realistic response to the excitation. The reverberant sound field exhibits fluctuations of SPL from point to point, which have been studied extensively for middle and high frequencies but not for low frequencies such that the acoustic modal density is marginally low. Gradients of SPL or turbulence level are difficult to simulate. The most profound limitation on the realism of test is probably the point-to-point correlation of the instantaneous pressures, which, for the reverberant field, is determined primarily by the ratio of separation to wavelength and, for the flight field to be simulated, is determined primarily by time delays associated with the convection of turbluence or the propagation of noise. The reverberant field tends to excite all structural modes simultaneously, whereas the flight fields, varying with air speed, may excite some modes sequentially. However, the high-frequency asymptotic behavior of the reverberant field is not yet completely understood, and no work has been reported on means of controlling it or on low-frequency statistical fluctuations. As with vibration testing, much of the technology of the new test must be learned while it is being used. For the immediate future, the test will be developed as a means of simulating, by fixed SPL's and correlations, a composite condition of flight. In time, it may become possible to introduce realistic and variable times delays in the noise-test field.
Prediction of Shock Motions of a Ship Deck
Authors: Short R. D. , Thornton E. A.
Published: October 2005

Some problems encountered in predicting shock motions on a ship deck are discussed. Several approaches for determining natural frequencies and mode shapes of a bare deck are compared and evaluated against experimental data. A procedure for predicting natural frequencies and mode shapes of a deck with attached masses is developed and evaluated by comparing with the bare hull predictions and experiments on a ship model. Predicted deck motions with and without attached masses in response to a simple boundary motion are compared.
Is the Perceived-Noise-Level Calculation Procedure Better Now Than When It Was First Introduced?
Authors: Little J. W. , Mabry J. E.
Published: October 2005

In 1959, K. D. Kryter published a paper titled “Scaling Human Reaction to the Sound from Aircraft.” Additional studies by Kryter and others since that time have tested and modified the method. The results of several of these studies have been compared and summarized. Analysis of this summary indicates the strange result that noy contour development has tended toward improvement, while the PNL method as a whole has tended toward poorer performance.
Review of the Molecular Absorption Anomaly
Authors: Sutherland Louis C.
Published: October 2005

A deviation between Kneser's theory and experimental data for molecular absorption of low-frequency sound in moist air was first demonstrated by Knudsen in 1933. This anomaly is considered in detail in light of recent experimental data, particularly those of Harris (1963) and Harris and Tempest (1964). The absorption loss measured under normal atmospheric conditions in the laboratory and for air-to-ground field propagation is predicted by the empirical expression: a(dB/ft) = [(a1f)2+(am)2]12+aCL. The new term (a1f) is approximately equal to 0.18 times the maximum molecular absorption in air at the frequency f as predicted by Kneser's theory. am is the theoretical molecular absorption for a given temperature and humidity, and aCL is the classical absorption loss. Possible sources are considered for the added loss term, which varies linearly with frequency.
Loudness Discrimination as a Function of Attenuation Rate and Duration
Authors: Harbert Fred , Paris Deanne , Wenner Claude
Published: October 2005

A monaural suprathreshold test has been developed to study loudness discrimination by assessing the perception of steadily increasing or decreasing stimulus intensity. Pure tones of various durations (0.1 to 10 sec) and gradually changing intensity (growing, declining, or constant) are presented through an earphone at different attenuation rates (1, 2, 4, or 8 dB/sec). Subjects are instructed to judge whether the loudness of the test tone seems to increase, decrease, or remain unchanged from beginning to end. Judgments are made for test tones of 250, 500, 1000, 2000, and 4000 Hz presented at 80 and 100 dB re 0.0002 μbar. Results are tabulated for the duration and attenuation rate yielding the decibel change necessary for differentiating tones of increasing and decreasing loudness. The degree of interaction of the five frequencies, two starting intensity levels, and four attenuation rates in the normal sample is discussed. Comparisons with sensorineural impaired ears on a pilot basis are made.
Pitch Associated with an Irregularity in the Phase Spectrum
Authors: Green David M. , Patterson James
Published: October 2005

Consider a broad-band spectrum produced by periodically repeating a burst of a special noiselike waveform (a Huffman sequence). The noise has essentially a flat power spectrum over the major portion of the audio band. The phase spectrum of the noise is a monotonic function of frequency and is generally increasing at a constant rate except at one frequency region. In listening to this repeated waveform, one hears a low-quency buzz associated with the frequency of repetition. In addition, a clear pitch quality can be heard. This pitch corresponds in frequency to the region of the irregularity in the phase spectrum. This phase pitch is independent of the repetition frequency of the noise burst but can be moved up and down the frequency scale by using different noise waveforms, having irregularities in the phase spectra at different frequency regions. A demonstration of the effect will be presented. [This research was supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Errors in Absolute Judgment as a Measure of Pitch Similarity
Authors: Jesteadt Walter H.
Published: October 2005

Confusion matrices were generated in an absolute judgment task using three overlapping sets of frequencies presented at 75 dB SPL. The first set contained 16 frequencies in the half-octave centered on 1000 Hz. The second and third sets were eight frequency subsets of the first, the second set consistsing of the eight highest frequencies and the third consisting of eight alternate frequencies. A trial consisted of a 500-msec warning interval, a 500-msec tone, unlimited answer time, and 1.5-sec correct-answer feedback. The subject answered by pushing one of 16 buttons in a 4×4 array. A programming device controlled the timing, randomly selected the frequency to be presented, presented feedback, and punched trial-by-trial information on paper tape. This made it possible to consider learning effects in the information and scaling analyses that were performed. [Supported by a grant from NINDB, National Institutes of Health.]
Application of Distribution-Free Tolerance Regions to Automatic Speaker Verification
Authors: Beakley Guy , Tuteur Franz B.
Published: October 2005

The effectiveness of different methods for constructing distribution-free tolerance regions for classification purposes is investigated in a speaker-verification problem. It is assumed that much of the information for the recognition of speakers is contained in the transition between phonemes as well as in the phonemes themselves. For this reason, many short-term spectra of readings of the word my were calculated. These spectra were used to form three different 256-dimensional measurement spaces. The spaces differed in the number of spectra used and the coarseness of each spectrum. Various methods were employed for constructing distribution-free tolerance regions with fixed expected false-alarm probabilities. The recognition capabilities of these methods were tested in the different measurement spaces. Other decision procedures were also tested, and the results were compared. Error rates for several proposed hypersphere tolerance region procedures ranged from 1.99% to 5.3% for 40 main-speaker training samples, 208 impostor training samples, 185 main-speaker test samples, and 439 impostor test samples.