bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring Strategies for Reducing High Intake Temperature Requirements and Allowing Optimal Operational Conditions in a Biogas Fueled HCCI Engine for Power Generation
Authors: Bedoya Iván D. , Saxena Samveg , Cadavid Francisco J. , Dibble Robert W.
Published: May 2012

This paper evaluates strategies for reducing the intake temperature requirement for igniting biogas in homogeneous charge compression ignition (HCCI) engines. The HCCI combustion is a promising technology for stationary power generation using renewable fuels in combustion engines. Combustion of biogas in HCCI engines allows high thermal efficiency similar to diesel engines, with low net CO2 and low NOx emissions. However, in order to ensure the occurrence of autoignition in purely biogas fueled HCCI engines, a high inlet temperature is needed. This paper presents experimental and numerical results. First, the experimental analysis on a 4 cylinder, 1.9 L Volkswagen TDI diesel engine running with biogas in the HCCI mode shows high gross indicated mean effective pressure (close to 8 bar), high gross indicated efficiency (close to 45%) and NOx emissions below the 2010 US limit (0.27 g/kWh). Stable HCCI operation is experimentally demonstrated with a biogas composition of 60% CH4 and 40% CO2 on a volumetric basis, inlet pressures of 2–2.2 bar (absolute), and inlet temperatures of 200–210 °C for equivalence ratios between 0.19–0.29. At lower equivalence ratios, slight changes in the inlet pressure and temperature caused large changes in cycle-to-cycle variations, while at higher equivalence ratios these same small pressure and temperature variations caused large changes to the ringing intensity. Second, numerical simulations have been carried out to evaluate the effectiveness of high boost pressures and high compression ratios for reducing the inlet temperature requirements while attaining safe operation and high power output. The one zone model in Chemkin was used to evaluate the ignition timing and peak cylinder pressures with variations in temperatures at intake valve close (IVC) from 373 to 473 K. In-cylinder temperature profiles between IVC and ignition were computed using Fluent 6.3 and fed into the multizone model in Chemkin to study combustion parameters. According to the numerical results, the use of both higher boost pressures and higher compression ratios permit lower inlet temperatures within the safe limits experimentally observed and allow higher power output. However, the range of inlet temperatures allowing safe and efficient operation using these strategies is very narrow, and precise inlet temperature control is needed to ensure the best results.
Simulation of Vocal Fry
Authors: Titze Ingo R.
Published: May 2012

Some special types of vocal fry have been produced with a multi-mass model of the vocal cords (described at earlier meetings). Special attention is given to the peculiar double-pulse vocal fry. During the first pulse the vocal cords gain only a moderate amount of vibrational energy from the air stream. The glottal width is small, and the successive first closure is brief. Since energy loss occurs primarily during prolonged approximation, most of the energy of the cords is maintained during the first pulse. During the second pulse the cords gain additional kinetic energy from the air stream, resulting in both an increased glottal width and a more rapid closure. Virtually all the energy of the cords is dissipated in this second, rather prolonged, closure. This two-step “pumping” process can be repeated indefinitely. A three-step pumping process is also possible.
Vocal Tract Cavity-Mode Relations Viewed by Spatial Energy Distributions
Authors: Fant Gunnar , Pauli Stefan
Published: May 2012

Although each resonant mode is dependent on the entire vocal tract (VT) system, there exists a smaller or greater dependency of each mode on separate parts of the VT area function. One well-known aspect is the sensitivity of the mode to specific local perturbations. Another aspect is the storage of kinetic and potential energy within the VT. The spatial distribution of the stored energy is chosen as the quantitative basis for defining “formant-cavity” relations. Computer-generated graphs of such functions confirm earlier qualitative statements. Similarly, mode bandwidths may be spatially decomposed according to the distribution of dissipated energy. The first four modes of a few vowels are discussed with respect to VT perturbations, energy storage, and energy dissipation.
Relationship of Intraoral Air Pressure to Tongue Tip-Alveolar Ridge Contact for Lingual Alveolar Stops
Authors: McGlone Robert E. , Brown W. S.
Published: May 2012

Three male speakers were fitted with intraoral air pressure sensing tubes and strain gauge pressure transducers. The transducers were positioned behind the maxillary central incisors. Simultaneous recordings of air pressure and tongue contact were used to determine the relationship between the two during the articulation of /t/ and /d/. The speech samples were VCV utterances constructed using vowels /i/, /a/, and /u/ and words with /t/ and /d/ in the initial, midvocalic, and final positions. Comparison of the resultant curves showed the onset of intraoral air pressure build up coincided temporally with tongue contact with the alveolar ridge. The pressure rise continued until the tongue was withdrawn at which time a rapid pressure drop occurred. This precise relationship was found for all conditions of the study.
Is the Relationship between Acoustic and Articulatory Variables in Speech Intrinsically Linear?
Authors: Atal B. S.
Published: May 2012

The functional relationship between the acoustic parameters of speech and the positions of different articulators was investigated on a computer-simulated model of the vocal tract using nonlinear regression. The area function of the vocal tract in the model was specified by seven articulatory variables, namely, the area and location of the maximum constriction formed by the tongue body, the area and location of the tongue tip constriction, the area of the mouth opening, lip protrusion, and the length of the vocal tract. It was found that any one of the seven articulatory variables could be represented reasonably accurately by a polynomial function of the acoustic parameters of the vocal tract model. Two interesting properties of this relationship were observed. First, in estimating an artic-ulatory variable, knowledge of the other articulatory variables was not required; the articulatory variable was uniquely determined by the acoustic parameters alone. Second, any one of several different acoustic representations—such as predictor coefficients, formant frequencies, and their band widths, or power spectrum—could be used with equal success in determining articulatory variables. The applications of this method for determining positions of the articulators during speech production, for speech recognition, and for control of articulatory models for speech synthesis are discussed.
Lip and Jaw Motor Control during Speech: Motor Reorganization Responses to External Interference
Authors: Folkins J. W. , Abbs J. H.
Published: May 2012

Step function resistive loads were applied selectively to jaw movements during ongoing speech production. These loads were intentionally initiated during the jaw closing movement associated with the production of bilabial stops, resulting in a situation where bilabial closure would be disrupted if ongoing control were open-loop. Three subjects were observed during control and experimental conditions. In almost all utterance where a load was introduced, closure of the lips was achieved and the bilabial stop was adequately produced. To assess the nature of this closed-loop control, displacement of the upper lip, lower lip, and jaw (in the inferior-superior dimension) were recorded along with EMG from the medial pterygoid, anterior tem-poralis, masseter, and orbicularis otis superior muscles. Based on the observation of these variables, it appears that the muscles of the lips as well as those of the jaw were involved in feedback-controlled motor reorganization.
Instrumentation Selection for Correlation Analysis: What Price Versatility?
Authors: Kelly Ronald D.
Published: May 2012

The objective of this paper is to assist the noise control engineer in selecting the most cost-effective correlation analysis system for his requirement. The variew of instrumentation available, different principles of operation, and the important performance characteristics are described. These performance characteristics include signal extraction capability (as limited by inherent electronic noise levels), accuracy, resolution, averaging time, frequency response limitations, time delay capability, and input and output modes. The paper provides guidance to the noise control engineer for matching his specific requirements to the wide range of available hardware and software correlation analysis systems.
Low-Frequency Aspects of High-Frequency Repetition Waveforms
Authors: Pastore R. E. , MacLatchy C. S.
Published: May 2012

Subjects were asked to match a stationary, monaural, “repetition noise” waveform with a sinusoidal waveform presented to the contralateral earphone. The repetition noise waveform was filtered (900–5000 Hz), and had a fixed repetition rate (147, 293, 587 rps). Both the signal and the noiae were maintained at overall levels of approximately 52 dBA. All subjects found strong relationships based upon binaural beats at frequencies corresponding to small integer (1, 2, 3, 4) multiples of the repetition rate. Weaker relationships were found at fractional multiples of the repetition frequency. The perceptibility of frequencies corresponding to certain aspects of the temporal microstructure of the “noise” waveform was also investigated. [This research was supported by a grant from the National Institute of Mental Health.]
Lateralization of Combination Tones
Authors: Zurek P. M. , Leshowitz B. H. , Jenkins G. W.
Published: May 2012

Experiments were performed to compare lateralization of combination tones with that of pure tones under comparable masking conditions. Two primary tones f1 and f2 at 70 dB SPL were employed. The frequency of f1 was 620 Hz, and f2 ranged from 1.1 f1 to 1.5 f1. Phase and amplitude of the cubic difference tone, 2 f1 − f2, were first determined monaurally using an objective forced-choice procedure. These monaural measurements were then used to specify the phase and amplitude of the lateralization tone in the binaural experiment. The two primaries were introduced to one ear and the externally produced lateralization tone of frequency 2 f1 − f2 to the other. Subjects were required to discriminate a change in phase of the lateralization tone in an oddity procedure. In the control condition, in order to simulate the combination tone, an externally generated tone of frequency 2 f1 − f2 was administered in the presence of a 70-dB masking tone of frequency f1. The amplitude of the simulated combination tone was estimated from the initial monaural measurements. Discrimination of changes in phase of the lateralization tone was again observed. Results for both combination and external tone lateralization were very similar. The jnd's for interaural phase ranged from 2° to 20°. [This research was supported by an NIH grant.]
Time-Intensity Trading Functions for Selected Low-,Mid-, and High-Frequency Pure Tones on a Lateralization Task
Authors: Young Lamar
Published: May 2012

Low frequencies are generally considered to be lateralized on the basis of both time and intensity differences between ears, whereas the lateralization of high-frequency sinusolds is sensitive largely to interaural intensity differences. Nevertheless, for pure tones ranging from low to high frequency, quantitative results do not exist that demonstrate the extent to which the intensity of one signal must be reduced to achieve a midline image when a phase lag is present in the contralateral signal. This study, therefore, obtained time-intensity trades using five sinusoidal stimuli: 200, 400, 600, 1000, and 2000 Hz. Phase delays of 0° to 360° in 30° increments were imposed on one of the binaural tones, and the experimenter altered the intensity of the non-delayed signal until the four highly trained subjects reported a midline experience. The experiment (1) yielded the reported tative trading functions for the respective test frequencies; (2) demonstrated that the maximum time-intensity trades for each frequency occurred at 90° and 270° disparity; and (3) revealed that the time-intensity trade was the largest for the 400-Hz pure tone. As the frequency of the test signal was increased above 400 Hz, there was a decrease in the magnitude of the time-intensity trade.
Forced-Choice Procedure for Measurement of Combination Tones
Authors: Jenkins G. W. , Zurek P. M. , Leshowitz B.
Published: May 2012

A three-alternative forced-choice procedure was employed to measure monaurally the phase and amplitude of the cubic combination tone, 2 f1 − f2. To measure phase, two primaries f1 and f2 were presented simultaneously with a third tone at frequency 2 f1 − f2. The third tone had phase θ in two intervals and phase θ + 180° in the third interval. A plot of percent correct discrimination as a function of θ was used to determine the phase of the combination tone. The phase of the combination tone was calculated to be ±90° from the value of θ which resulted in minimum discrimination. A “mirroring” technique was then employed to determine the amplitude of the combination tone. In the odd interval a cancellation tone was added 180° out of phase from the combination tone. Percent correct discrimination was measured as a function of the level of the cancellation tone. It was assumed the minimum in the function occurred at a level 6 dB greater than the combination tone. The results obtained from various objective and adjustment procedures will be compared. [This research was supported by an NIH grant.]
Ultrasonic and Laser Light Scattering Studies in Hydrate Melts
Authors: Borsay Frank , Carpio Ronald , Yeager Ernest
Published: May 2012

Ultrasonic velocity and absorption measurements have been carried out for several hydrate melt systems, including zinc nitrate, zinc chloride, and calcium nitrate, as functions of water content and temperature (extending into the supercooled region). Hypersonic velocity and absorption data have been obtained from Bril1ouin scattering measurements at 5145 Å with an Argon ion laser and a piezoelectric scanning Fabry-Perot interferometer. These data indicate a distribution of relaxation times for all of these hydrates rather than the single relaxation reported in some of the literature. Both the shear and volume viscosities relax. The Brillouin and ultrasonic data do not provide any evidence of temporal relaxation. In the calcium nitrate melts, replacement of protons by deuterium has virtually no effect on the ultrasonic or Brillouin scattering data, which indicate that the breaking of hydrogen bonds is not a critical factor. The viscoelastitc relaxation in these melts involves the disruption of relatively strong ion-ion and ion-water bonds and the reorientation of constituent anisotropic groups. Further information concerning reorientation effects has been obtained from the depolarized Rayleigh component. [Research supported by the Office of Naval Research, NSF, and NATO.]
Determination of the Form Function for Rigid and Elastic Spheres from a Single Ping
Authors: Draconette Louis R. , Vogt Richard H. , Flax Lawrence , Neubauer Werner G.
Published: May 2012

A short acoustic pulse is used to determine significant portions of the form function vs ka curves for rigid and elastic spheres, from a single reflection. Excellent agreement between exact theory and experiment is obtained over limited ranges of ka for aluminum and tungsten carbide spheres measured in water and for metal spheres measured in air.
A New Generation of Hearing Aid Transducers
Authors: Killion M. C. , Carlson E. V.
Published: May 2012

Recent developments in subminiature microphone and receiver technology make possible several new performance options for ear level hearing aids: (1) a smooth response extending to higher frequencies; (2) a drastically reduced vibration sensitivity; and (3) a cardioid directional characteristic, allowing the hearing aid to reject interfering sounds from the rear. These improvements have been brought about by (a) a new wide-band receiver to complement the wide-band piezoelectric ceramic microphone introduced several years ago; (b) the application of the wide-band tailored frequency response of the ceramic microphone to a new electret condenser microphone; and (c) a series of directional microphone configurations using both ceramic and condenser transducers. In the case of the receiver, the well-honed technology on balanced armature magnetic devices was applied to produce a device with an extended high-frequency response. In the case of the electret condenser microphone, separating the electret function from the diaphragm function made possible a device with both exceptionally low-vibration sensitivity and an improved charge storage capability. As with the ceramic microphones, devices with a flat frequency response have been designed in addition to those with a response tailored to the special needs of ear level hearing aids. The directional microphones are realized by using the R-C time constant of the damping resistance and internal air volume compliance to produce a time delay for sounds arriving at one of the two inlet ports. A reasonably accurate analog of such devices requires 25 to 30 discrete elements plus distributed lines, but permits efficient computer optimization of their frequency response and directional characteristics.
Future Implications for Implantable Hearing Aids
Authors: Vernon Jack A.
Published: May 2012

The procedure for testing implantable-type hearing aids has been developed so as to utilize laboratory animals as well as the human. In the case of laboratory animals the test consists of measuring the ac cochlear potentials of the inner ear when that ear is activated by the implantable hearing aid. In the same manner distortion production is evaluated. The same procedure has been utilized to produce tapes of speech discrimination material when the animal in question had known damage to its inner ear. The speech discrimination tapes were recorded when the ear was activated by the best possible acoustical drives and also when the ear was activated by the implantable hearing aid. These tapes were then used to test the speech discrimination ability of young normal hearing adults. The implantable device produced 16% better speech discrimination. The speech discrimination ability of sensory neural impaired adults were tested using both acoustic and the implantable aid deliveries. The possible advantages of the implantable hearing aid are: (1) absence of ringing feedback; (2) possibility of improved speech discrimination in competing background noise; (3) and improved efficiency of delivery.
The Optacon Tactile Stimulator Array
Authors: Brugler J. Stephen
Published: May 2012

The Optacon is a direct-translation reading aid for the blind. In operation, material that has been hand scanned by the small pickup camera is reproduced in vibratory form upon the 144-element vibratory stimulator array. The present array configuration is the result of extensive psychophysical, engineering, and manufacturing effort. The array utilizes piezoelectric “bimorphs,” driven at 250 Hz, for electromechanical energy conversion. Custom integrated circuit driving circuits enable compact packaging. The 24 rows are spaced 45 mils apart and the six columns 90 mils apart, enabling the entire display to be presented on the fingertip of the blind user.
A Transfer Matrix Approach to Elastodynamics of Layered Media
Authors: Bahar Leon Y.
Published: May 2012

In this study, a transfer matrix method is developed in order to solve elastodynamic problems in layered media. Specifically, the dynamic response of composite elastic plates, perfectly joined at their interfaces, when the inner and outer boundaries of the finite medium are simultaneously subjected to arbitrary, time-dependent tractions that exhibit no spatial variation in the longitudinal direction of the layered medium are solved. The Laplace transform is used to remove the time variable, since it does not necessitate the auxiliary step of reducing a problem with time-dependent boundary conditions to one with homogeneous boundary conditions. The transfer matrix approach is suggested, on the other hand, by the fact that the continuity of the stress and the displacement, or equivalently of their transforms across each interface, must be enforced. It thus becomes natural to consider the transformed stress and displacement as the components of a state vector, whoie continuity is maintained as it crosses each interface.
Dispersion of Acoustic Waves by Fiber-Reinforced Viscoelastic Materials
Authors: Sutherland Herbert J.
Published: May 2012

Acoustic waves are dispersed by two distinct mechanisms as they propagate through a fiber-reinforced viscoelastic material. The first mechanism, viscoelastic dispersion is characterized by an increase in phase velocity with an increase in frequency and an exponential attenuation of wave amplitude with propagation distance. The second, geometric dispersion may be characterized as a wave-filtering phenomenon in which periodic waves are selectively transmitted and reflected. Regions of transmission are commonly called “passbands” and regions of reflections have been designated “forbidden bands.” When both mechanisms are present in one material, one or the other may be dominate. In this study, the interplay between these two mechanisms is examined experimentally by determining the dispersion characteristics of two fiber-reinforced viscoelastic materials (viscoelastic dispersion dominating in one and geometric dispersion dominating in the other).
Selective Linear Predictive Spectral Matching
Authors: Makhoul John
Published: May 2012

An optimal and noniterative method is described by which selected portions of any spectrum can be fitted by an all-pole spectrum. The method makes use of the spectral matching properties of the autocorrelation method of linear prediction [J. Makhoul, IEEE AU-21, 140–148 (June 1973); J. Makhoul and J. Wolf, BBN Rep. 2304 (1972)]. The only values needed for the computation of all p parameters of the all-pole spectrum are the first p + 1 autocorrelation coefficients which are computed from the original spectrum by a simple Fourier transform. This selective speclral matching method allows for arbitrary spectral shaping in the frequency domain, thus obviating the need for any special time domain filtering. In addition, different portions of a spectrum can be fitted by different numbers of poles, a property that is useful in speech recognition applications. Since this method operates directly on the spectrum, the manner in which that spectrum is obtained is immaterial. Thus, the spectrum can be obtained either computationally from the time domain signal or straight from a hardware filter bank.
Parametric Analysis of Vowel Duration in Single- and Multi-Syllable Words
Authors: Harris Martin S. , Umeda Noriko
Published: May 2012

Previous investigators have shown that vowel duration decreases as number of syllables in a word increases, when carrier phases constitute the material. Umeda [J. Acoust. Soc. Am. 52, 133(A) (1972;] found that, in many cases, there are no such differences of vowel duration in connected text. This investigation was conducted to provide a more direct comparison of results from connected text with those from carrier phrases. Two subjects, one of whom served in Umeda's study, read lists of monosyllabic and polysyllabic words in carrier phrases. Measurements were taken on duration of one vowel /æ/ in stressed syllables in words of varying duration. Data were further specified as to position of the stressed syllable and class of following consonant. Analyses of variance were computed separately for each subject and each class. Results confirm previous findings of decreased duration, at least up to three syllables. One subject showed statistically significant changes in duration in this study, while exhibiting no differences in the Umeda experiment. Apparently the dependence of vowel duration on a number of syllables is very sensitive to context. Details of this sensitivity will be discussed.
On Coarticulation: Vowel Duration and F2 Transitions in Speech of Deaf and Normally Hearing Children
Authors: Monsen R. B.
Published: May 2012

Two aspects of coarticulation are examined in deaf and normally hearing adolescents: (1) the influence of the final consonant (/t,s,n,d,z/) on the duration of /i/ and /I/, and (2) the influence of initial consonants (/b,d,f/) on the F2 frequency of /i/ and /u/. Whereas in normal speech the tense vowel /i/ is only relatively longer than the lax vowel /i/, in the speech of the deaf subjects these two vowels occupy more restricted durational ranges. The vowel does not appear to coarticulate with the final consonant in the normal manner, and thus does not aid in signaling the consonant. In the speech sample examined, initial F2 transitions appear “reduced”—both the amount of frequency change and the rate of frequency change are less than for normal subjects. Transitions do not appear to result automatically from the mechanical characteristics of the vocal tract. Results are discussed with reference to the possible role of learning in coarticulation effects. [Supported by NINDS Grant NS03856.]
How Does a Mynah Bird Mimic Human Speech?
Authors: Stefanski R. , Klatt D.
Published: May 2012

Broadband spectrograms and computer-generated spectra have been obtained of a trained Indian Hill mynah bird and its trainer each saying seven sentences composed of four to 12 phonetic segments. Comparisons indicate a remarkable ability of the bird to reproduce good approximations to virtually any spectral or temporal detail, although frequencies in the range of the first formant are attenuated by about 10–16 dB relative to human spectra. Fundamental frequency (F0) contours, rapid formant transitions, and turbulent noise spectra for fricatives and plosive bursts are especially well imitated. Contour shapes are better preserved than absolute formant or F0 values. Some vowel spectra have clear formant patterns but many have multiple resonances, formant splitting effects, and formant frequency positions that cannot be accounted for in terms of an acoustic tube model of formant generation. A new description of the behavior of the mynah syrinx is proposed to account for the observed acoustic patterns. One of the paired external labia in the syrinx is implicated as the vibrating source of voicing energy (analogous to the human vocal cords). Some or all of the formant resonances are produced by exciting the mechanical resonant modes of the internal and external membranes in the syrinx. The seven pairs of muscles which are associated with the syrinx are capable of controlling membrane tensions and regulating the positions of the external labia in the syringeal airways during sound production. [Research supported by an N[H grant.]
Pressure Cross Correlations in the Investigation of Aerodynamic Noise from Jets
Authors: Hurdle Patrick M.
Published: May 2012

The employment of pressure cross correlations to investigate the noise-generating regions of jets is described. The use of this technique makes it possible to quantitatively map the noise-generating regions of a jet for a particular farfield angular position. The results of experiments, utilizing this method, on a subsonic free jet are presented. These results indicate that the turbulent volume mainly responsible for the noise generated is confined to a rather limited cylindrical volume centered about the jet axis in the vicinity of the end of the potential core region with a length of approximately six jet diameters. In addition, for the higher farfield angles the shear mixing region becomes an important factor. As the jet velocity was reduced, this volume showed a tendency to contract toward the jet nozzle with the shear mixing region showing increase contribution to the sound pressure at all farfield angles. A comparison of these data is made with the results of a similar experiment conducted on a General Electric T-58 gas generator modified to a turbojet configuration.
Jet Noise Measurements by Means of a Directional Microphone
Authors: Chu W. T. , Kaplan R. E.
Published: May 2012

The noise source characteristics of subsonic jets have been investigated using a directional microphone system in an anechoic chamber. The directional microphone system used is of the reflector type having a diameter of 36 in. and a focal length of 2612 in. As expected, this system is diffraction limited, thereby resulting in a loss of resolution. A special numerical method was used to recover the axial source strength distribution from the diffracted data. Measurements have been performed in the farfield of both a 1- and 2-in. diameter jet operating at exit Mach numbers ranging from 0.6 to 1. Results are presented for both source strength distribution along the jet and spectra of noise radiated from localized regions of the jet. These results were then integrated to obtain the overall noise power and spectrum for comparison with measurements obtained by means of a single nondirectional microphone. [This work has been supported by the Department of Transporation under Grant No. DOT-OS-00002.]
The Directionality Paradox of Jet Noise
Authors: Kaplan R. E.
Published: May 2012

The familiar noise contours for the axisymmetric jet exhibit the rather contradictory nature that at oblique downstream angles (where the noise is most intense) the spectral content is of lower frequency than that normal to the jet axis. The result is paradoxical if one imagines the source of the noise to be converted radiators of sound, Doppler-shifted upwards in frequency in the downstream direction. We postulate (1) that the sonic source region of the jet is bounded and (2) that in some time interval a countable number of independent local radiators are active. If Δt is selected as this time interval measured close to the axis, it is clear that at angles further from the axis one need not listen for as long a period of time to hear these same events. Hence, the frequencies of occurrence increase inversely with the cosine of the angle from the jet axis in the farfield. [This work has been supported by the Department of Transportation under Grant No. DOT-OS-00002.]
Detection of “Mach Wave” Radiation of a Supersonic Jet
Authors: Schlinker R. , Laufer J.
Published: May 2012

Recent measurements carried out in the farfield of a model supersonic jet using a highly directional microphone exhibit pressure signals of rather characteristic shapes. Randomly occurring high-amplitude positive peaks are followed by less intense negative values. Indeed, the measured probability distribution is highly skewed. It is conjectured that these signals are produced by the so-called Mach wave radiation of the jet. [This work has been supported by the Department of Transportation under Grant No. DOT-OS-00002.]
Structure of Supersonic Jet Farfield Pressures
Authors: Kaplan R. E. , Laufer J.
Published: May 2012

Recent measurements in both model and full-scale supersonic jets, at both high and low temperatures, show a marked asymmetry of the amplitude distribution. These positive spikes are taken to be a priori evidence of spherical “blast” wavelets and, as such, are in accord with a model for the noise sources which are locally compact, spatially uncorrelated, and unsteady in the context that their lifetime is of the order of their size divided by their convection velocity. Interpretations of the measurements indicate that there are relatively few of these events existing in the jet column at any given time, and that each event occurs randomly in space and in time. Associated with each event is a relatively coherent fluid mechanical structure. If these conditions are not satisfied, the amplitude probability density of the pressure signal will not be skewed, as is demonstrable by Whitham's theory. [This work has been supported by the Department of Transportation under Grant No. DOT-OS-00002.]
Cylindrical Spoiler Effects on the Sound Power of Subsonic Jets
Authors: Tower T. M. , Plett E. G. , Summerfield M.
Published: May 2012

The degree of coupling between sources of unsteadiness inside a duct and the flow through the duct is studied with regard to the external noise contribution from such internal sources. Flow over cylindrical spoilers inside the duct exhibits several regimes of varying acoustic behavior. Below the (1,0) mode cutoff frequency, the additional noise is due only to fluctuations in the drag component of the strut on the flow, while above the cutoff the lift component of fluctuation, which is in the lateral direction, propagates through the duct, resulting in a strong lateral dipole in the farfield sound. Theoretical predictions of the acoustic power output due to the spoiler were made, accounting for the source convection, the span-wise correlation of the vortex shedding, and the variation in lift coefficient with Reynolds number. These predictions are compared with experimental results. It was found that a spoiler immersed in the duct upstream of the exit generated strong tones, while the same strut placed in the core flow immediately downstream of the nozzle generated broad-band noise of a much lower intensity. In each case, the spoiler markedly increased the noise. [Supported by ONR Contract N00014-67-A-0151-0029].
Monaural and Binaural Masking Phenomena Utilizing Machine-Generated Waveforms. I. The Phase Angle Alpha
Authors: Dolan Terrence R. , Hirsh Richard
Published: May 2012

In an effort to further describe the monaural and binaural processes involved in the detection of a gated tonal signal in a background of gated masking noise, a series of experiments has been initiated utilizing computer-generated, reproducible waveforms. The signal used has been a gated 500-Hz tone and the masker is a gated 400–600-Hz bandpass noise. Our initial effort has been concerned with the influence of the magnitude of the phase angle alpha, the angle at which the tonal signal is added to the noise masker, on the detect-ability of the signal in both homophasic and antiphasic masking conditions. Our results suggest that the magnitude of alpha is extremely important in accounting for performance in the homophasic masking conditions but that the magnitude of alpha does not strongly influence performance in the anti-phasic masking conditions. These results are compared to predictions based on an electrical model described by Jeffress [J. Acoust. Soc. Am. 41, 480–488 (1967)], which consists of a leaky integrator preceded by a narrow bandpass filter and half-wave rectifier.
Pure-Tone Octave Masking in Normal-Hearing Listeners
Authors: Nelson David A. , Bilger Robert C.
Published: May 2012

Octave masking in normal-hearing listeners was investigated at four different primary masker frequencies (250, 500, 1000, and 2000 Hz) as a function of intensity and phase. Slopes of phase-locked octave masking functions were found to increase with frequency of the primary masker, from less than 1.0 dB/dB at 250 Hz to greater than 3.0 dB/dB at 2000 Hz. The monaural octave masking phase effect was considerably larger at low primary frequencies (as large as 30 dB) than at high primary frequencies (no larger than 15 dB), and the phase effect decreased or disappeared entirely at intense primaries. Maximum and minimum masking were found at phase angles of 90° and 270°, respectively, irrespective of frequency and intensity of the primary masker. Implications of these results about distortion in the auditory system are discussed.
Surface Waves of Franz and Stoneley Type on Elastic Cylinders
Authors: Dickey J. W. , Sinay J. , Uberall H.
Published: May 2012

The attenuation and phase velocities of the first four creeping wave modes on a solid elastic cylinder have been calculated numerically as a function of frequency. An additional mode was found which is interpreted as the Stoneley wave. In the high-frequency (or infinite cylinder radius) limit, all the creeping wave phase velocities approach the bulk wave velocity of the external medium, whereas the Stoneley wave approaches a lower velocity. These calculations apply to an elastic cylinder in a liquid medium. The liquid-liquid case, which is similar to the electromagnetic situation, and the air-solid case, approaching the rigid cylinder limit, are derived as special cases. Computer programs were developed to carry out the calculations, which in most cases cover the range 5 ≤ ka ≤ 200.
Visual Sound Patterns as an Aid in Understanding and Applying Acoustic Holography
Authors: Kock Winston E.
Published: May 2012

The scanning technique of the previous paper permits the visual observation, by photographic recording, of the two basic phenomena of holography, namely, wave interference and wave diffraction. Examples are presented and discussed to explain both the hologram concept and the recent medical development in acoustic holography which provides a real-time, x-ray-like visual presentation of bone structures and tumors in the human body. [References: the author's books, Seeing Sound (Wiley, New York, 1971); Lasers and Holography (Doubleday, New York, 1969); and Acoustic Holography, in the forthcoming Vol. 10 of Physical Acoustics (Academic, New York).]
Analysis of the Colored Schlieren for Visualization of Ultrasonic Waves
Authors: Cook Bill D.
Published: May 2012

Using white light in the schlieren technique of visualizing ultrasonic fields produces brilliantly colored images. The color seen depends on the charge of optical path length induced by the sound field. Prediction of the colors is possible by the CIE Tristimulus System. Chromaticity diagrams are presented for some standard cases.
Damping Measurements of a Controlled Composite Material
Authors: Jones E. R. , Sierakowski R. L. , Ross C. A.
Published: May 2012

Increased use of filamentary materials as reinforcements in structural components has necessitated obtaining information on the response of such material systems to a wide variety of loading conditions. One such technically important problem area is that associated with the dynamic response of composite materials to impact-type loading situations. In order to understand the phenomenon of wave trial in material systems, specific knowledge of the damping coefficient and phase velocity as a function of circular frequency is necessary. In the present paper, tests have been conducted on beam-type specimens of a steel-epoxy composite having controlled volume fractions and varying wire sizes. Measurements are reported on the damping coefficient as a function of circular frequency, a(ω), and the real part of the complex modulus, E1. The latter parameter has been further used to calculate the phase velocity, and data are presented on phase velocity, c(ω), as a function of frequency. Detailed tabular and graphical data are presented for the various specimens tested.
Some Results on Segmentation and Segment Classification in Continuous Speech
Authors: Weinstein Clifford J. , Mondshein Lee F.
Published: May 2012

A system for acoustic analysis of continuous speech is being developed as part of Lincoln Laboratory's effort in speech understanding. The acoustic system presently consists of two stages: the first produces a preliminary segmentation of the speech, as well as a gross classification of these segments into several acoustic categories; the second produces a finer classification intended to meet the needs of subsequent linguistic analysis. The current design and performance of the acoustic analysis system is outlined. This description is intended primarily as an interim report, since the system is being actively extended and refined. The first-stage segmentation and segment classification yields the following categories: vowel-like sound; volume dip within vowel-like sound; fricative-like sound; silence or voice bar; and burst. These categories are produced by a decision tree based upon energy measurements in selected frequency bands, derivatives, and ratios of these measurements, a voicing detector, and a few editing rules. Statistics will be presented describing the results of this analysis on a 31-sentence test corpus developed for an ARPA Segmentation Workshop held at Carnegie-Mellon University in July 1973. Second-stage classification includes a fricative identifier, which employs spectral measurements to group the fricative segments into phoneme-like categories. Results of this analysis for the test corpus will be presented. Discussion of additional work, including stop and vowel classification, will be given as time permits. [This work was sponsored by the Advanced Research Project Agency of the Department of Defense.]
An Automatic Algorithm for Locating the Beginning and End of an Utterance Using ADPCM Coded Speech
Authors: Rosenthal L. H. , Schafer R. W. , Rabiner L. R.
Published: May 2012

An automatic algorithm is described for locating the endpoints of an utterance which has been digitized using adaptive, differential coding techniques (ADPCM) [P. Cummiskey, N. S. Jayant, and J. L. Flanagan, Proc. IEEE Int. Coram. Conf., Seattle (June 1973)]. The ADPCM coder operates at a 6-kHz sampling rate, and adaptively quantizes the speech using four-bit samples (the code words). Since the ADPCM coder effectively has an automatic gain compression and expansion or companding feature, it is possible to distinguish between silence and speech by simple measurements on the code words. In the actual implementation of the endpoint location algorithm, a threshold is set on the energy in the code words. The beginning of an utterance is defined as the time at which the code word energy exceeds the threshold for a fixed duration. The end of an utterance is defined as the time at which the code word energy falls below the threshold for another fixed duration. Extensive testing of the algorithm on single words and phrases, spoken in isolation, gave essentially perfect results as determined by both auditory and visual examination of the speech data. For the same corpus of data, other standard measures of the beginning and end of an utterance, such as speech energy, differentiated speech energy, and energy in the quantizer step size, gave far worse results.
Automatic Recognition of Fricatives and Plosives in Continuous Speech Using a Linear Prediction Method
Authors: Molho L.
Published: May 2012

A linear prediction method, the low-coefficient LPC (LCLPC), provides meaningful spectra of fricative and plosive areas of speech. Spectra produced by the LCLPC correspond well both with acoustic phonetic theory and with the experimental results of others. Time resolution is sufficiently narrow to allow independent spectral analysis of the release, frication, and aspiration portions of an unvoiced plosive or to demonstrate spectral change within a consonant cluster, so that clusters such as /ks/ and /ts/ may often be distinguished. For analysis of unvoiced speech, the LCLPC uses the autocorrelation method with eight coefficients and a 6-msec Hamming window, at a sampling rate of 20000 samples/sec. A computer program has been written that uses sequences of LCLPC spectra to perform automatic recognition of fricatives and plosives within an operating continuous speech understanding system. Current results and examples of LCLPC spectra are presented.
Differences between Language-Bound and Stimulus-Bound Subjects in Solving Word Search Puzzles
Authors: Day Ruth S.
Published: May 2012

Studies of dichotic fusion suggest that “language-bound” (LB) subjects perceive speech sounds through the abstract linguistic structure of their language, while “stimulus-bound” (SB) subjects can set aside linguistic rules and make accurate judgments about nonlinguistic events. In the present experiment, subjects of both types were asked to scan a matrix of letters in all directions in order to find words that exemplify a particular theme, e.g., musical instruments. SBs consistently found more words. Perhaps SBs simply have better spatial abilities, since the task requires scanning in eight directions. An alternative view is that the groups have comparable spatial abilities, but that LBs are preoccupied with linguistic operations: given a string of letters, they translate it into “phonetic sense” no matter what direction they happen to scan. For example, the highly pronounceable string TENIPS may obscure the fact that SPINET is spelled out in the reverse direction. Hence the two groups may differ in the relative amount of work performed by the two cerebral hemispheres: SBs are free to rely on right-hemisphere (spatial) operations to conduct an efficient scan, while LBs are more restricted to left-hemisphere (linguistic) operations and hence spend less time in effective scanning.
Optimization Guide for Hartmann Whistle Operation
Authors: Feder E. , McMahon M. P.
Published: May 2012

An essential requirement for developing sound-absorbing liners is to generate the appropriate noise signature for the investigation. For development of aircraft engine duct linings, noise generators having high-intensity tones are often required. The Hartmann whistle provides an efficient means for converting aerodynamic energy into acoustic energy at levels which are characteristic of aircraft engine noise. This paper describes a systematic test program conducted to determine and optimize the noise-generating characteristics of a series of Hartmann whistles. Experiments were conducted with whistles having rods extending through the Hartmann cavity and nozzle for the purpose of studying the effects of varying cavity and nozzle spacing geometry. The frequency of the tones generated was controlled by changing the backing cavity and/or the distance between the nozzle and cavity lip. These two dimensions were varied by remote-controlled traverse mechanisms, with noise spectra being produced for each 12 sec of a traverse. Thus, fairly complete operating characteristics were determined for Hartmann whistles having various combinations of nozzle diameters, cavity diameters, and rod diameters from 14 to 1 in. It was found that a wide range of frequencies could be generated with any whistle by varying the automated dimensions. Curves are presented which will enable an investigator to select spacing geometries for various-sized Hartmann whistles which will provide practically any desired frequency at the maximum power level obtainable with this type of noise-generating system.
Gas Turbine Exhaust Silencer Self-Noise
Authors: Audette Richard R.
Published: May 2012

For two different-size gas turbines, data are presented that show increasing the length of the silencers did not decrease the sound pressure levels measured at the silencer exit.
Equivalent T-Sectiona for Silencer Components at Low Frequencies with Flow Effects
Authors: Wells R. J.
Published: May 2012

A recent paper in the contemporary literature QR. J. Wells and R. B. Tatge, ́Prediction of Silencer Performance Using Transmission Line Theory, Trans. ASME (Oct. 1971), pp. 404–410] shows that, for low frequencies, conventional silencers consisting of various combinations of parallel baffles and expansion chambers may be represented as an equivalent circuit of T-networks in series. This paper shows how it is possible to modify such T-networks to include the effect of gas flow on sound propagation through the silencer sections and hence on the attenuation. (Effects of flow on the impedance of silencing elements must be considered separately.)