bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic and Articulatory Properties of Linguistic Boundaries
Authors: Umeda N. , Coker C. H.
Published: October 2005

The linguistic concept of “juncture” has existed for decades but without consistent definitions in terms of objective physical quantities. Since 1969, we have proposed lengthened terminal consonants as physical correlates of word prominence [J. Acoust. Soc. Amer. 47, 94(A) (1970)]. Last year we asserted that English has consistent allophone selection at certain linguistic boundaries [J. Acoust Soc. Amer. 52, 132(A) (1972)]. Here we support those assertions with additional data on intensity and some spectral variations of fricatives, and data on nasal opening and glottal opening in consonant clusters. Using also the previous data on stops and fricatives and some inferences from speech synthesis, we attempt to give a complete picture of junctural effects in American English. We observe two extremes of “junctural” allophones: one in word-final positions, and the other in word-initial or stress-syllable-initial positions. Word-medial unstressed consonants have characteristics intermediate between these extremes. In words with differing stress or prominence, there is a continuous distribution from medial to the most extreme prominant-word-initial stressed consonants; distributions of final consonants are more disjoint. Boundaries between affixes and very common stems are sometimes clearly marked by initial or final allophones. Except for this and the stress effect, syllable and morpheme boundaries are not marked.
Acoustic Measurements of the “Fake” Vowel Length and the Three Degrees of Vowel Length in Yupik Eskimo
Authors: Koo Jang H. , Badten Linda
Published: October 2005

One peculiarity of Yupik Eskimo is the “fake” vowel length which is triggered by a schwa ə in a conditioned environment. The degree of the fake vowel length has never been seriously questioned nor recognized by Eskimologists as being distinct, phonetically or phonemically, from the intrinsically long or short vowel. It has thus been ignored in the phonemic analysis. Based on acoustic evidence, the present paper argues that there are three distinct degrees of vowel length in Yupik Eskimo, hence recognizing the degree of the fake vowel length as being significant. It also discusses the perceptual difficulties in identifying the fake vowel length which are primarily due to its unsubstantial contrast with the other degrees of vowel length. Measurements to these vowel lengths were made on spectrographic displays to determine their degrees and to find the acoustic attributes of their perceptual abstruseness.
The Intelligibility of Speech Processed by Delayed Long-Time-Averaged Compression Amplification
Authors: Robinson Charles E. , Huntington Dorothy A.
Published: October 2005

Conventional compression amplification introduces undesirable distortion when brief (several milliseconds or less) time constants are utilized, and reacts too sluggishly for longer time constants. We have devised a method of processing speech in which the average power of the waveform over intervals of several tens of milliseconds is measured continuously and is used to determine the gain to be applied to the waveform at the center of each interval. The resulting amplitude-compressed signal is delayed by one-half the length of the averaging interval. Tape-recorded monosyllabic word lists are processed by a digital computer and the resulting tapes are compared with originals for intelligibility, in quiet and in noise, by hearing-impaired and by normal subjects. Preliminary results show that the intelligibility of the processed tapes is selectively superior under some conditions to that of the original tapes. [This study was supported by a grant from the Research Development Fund and by the cooperation of the Artificial Intelligence Laboratory, Stanford University.]
Signal Processing to Improve Speech Intelligibility in Perceptive Deafness
Authors: Villchur E.
Published: October 2005

Many deaf persons with recruitment cannot use enough hearing-aid gain to bring weak consonants into the useful dynamic range of their hearing, because this amount of gain would make lower-frequency, high-amplitude vowels intolerably loud. Whether or not from this cause, such subjects commonly find amplified speech to have poor intelligibility. In the present experiments, speech is processed by a two-channel amplitude compressor whose frequency-dependent compression ratio is adjusted to compensate the frequency-dependent recruitment of the individual subject, and the compressed speech is subjected to frequency equalization similarly adapted to the subject. The aim is to amplify each acoustical element of speech, at each frequency-amplitude coordinate of the speech band, to a relative loudness for the deaf subject corresponding to the relative loudness of that speech element perceived by normals, This processing improved speech recognition, both in quiet and in the presence of competing speech introduced before processing, for six perceptively deaf subjects. Each subject showed an improvement in either initial- or terminal-consonant recognition of at least 22% and as much as 160% at optimum levels in quiet, and from 10% to 229% with speech interference 10 dB below the pre-processed signal.
Comparison of Two Visual Display Devices in Speech-Training of Deaf Adolescents
Authors: Stark R. E.
Published: October 2005

Two groups of 10 deaf adolescents were taught to produce the word “see.” One group used the Bell Telephone Visible Speech Translator, the other the Lucia Spectrum Indicator—devices which differ mainly in their mode of representing time. Effects of training were assessed by means of listener judgments and duration measurements. Both measures were analyzed for the word, and for vowel and consonant, separately. The judgment scores indicated that for both groups of subjects word production improved with training; both vowel and consonant production improved; however, vowels were more often correct than consonants before and after training. Word duration for the deaf subjects was greater than for normal-hearing subjects. It increased with training for both deaf groups. Vowel duration was greater than consonant duration, before and after training. However, both groups showed a decrease in vowel duration and an increase in consonant duration with training. It was concluded that responses of deaf subjects to the two training devices did not differ with respect to the measures employed. [Research supported by NINDS.]
Speech Cue Discrimination and Sensorineural Hearing Impairment: Masking of F2 Frequency Transitions
Authors: Danaher E. Martin , Pickett J. M.
Published: October 2005

Our general purpose is to define specific aspects of the speech-discrimination deficit often found in cases of sensorineural hearing impairment. This paper describes measurements of discrimination acuity for detecting the presence of an initial transition in F2 of a synthetic vowel-like sound, depending on certain “masking” conditions of F1. The masking conditions were: F1 absent, F1 present in the same ear as F2, F1 present in the opposite ear, and F1 delayed in onset by varying amounts. In some of the tests F1 had a transition; in others there was no F1 transition. Transitions were 100 msec in duration, followed by a steady-state of 150 msec. The data indicate that F1 in the same ear produces upward spread of masking which is considerably released when the two formants are in opposite ears. In addition, F1 transitions produce a different sort of masking which further reduces discrimination. In most subjects, F1 masks discrimination of F2 transitions even when the F2 transition is complete before the onset of F1. In subjects with sloping hearing losses, some F1 masking is present when F1 is cut back by 200 msec. There was considerable variability among subjects. These data indicate that F1 produces a type of backward masking which can reduce discrimination of frequency transitions which precede F1 voicing in vowels. Findings are related to discrimination of voiced versus voiceless initial consonants.
Speech Production Errors as Related to Speech Intelligibility in Deaf Children
Authors: Smith C. R.
Published: October 2005

The mean intelligibility of the recorded speech of 40 deaf children was 18.7% to untrained listeners, with a range from zero to 76%. Segmental and suprasegmental errors in the speech were compared with the intelligibility scores. Errors of place of articulation and voicing remained in essentially the same proportion for all speakers, regardless of intelligibility. Errors of manner of articulation and combined place-and-manner showed a slight systematic decrease from the poorest to the best speakers. Omissions decreased sharply but not quite systematically. Vowel and diphthong errors showed the most marked and systematic decrease as intelligibility improved. The correlation of segmental errors with intelligibility was −0.80. The dispersion of the data was related in part to poor pitch control and excessive variability of intonation. Children of deaf parents generally showed a greater proportion of segmental errors, poorer control of intonation and rate of speech, and poorer speech intelligibility than children of hearing parents. [This research was partially supported by Grant No. 09252 from the National Institute of Neurological Diseases and Stroke.]
A Similarity Scale to Evaluate the “Sub-Intelligible” Speech Patterns of Young Deaf Children
Authors: Asp Carl W. , Keller James , Stewart Andrew , Felknor Karen
Published: October 2005

The speech of young deaf children is usually unintelligible and difficult to evaluate with standardized speech tests. The observer will usually have difficulty assigning conventional phonetic symbols to the unintelligible response of the child. However, with the appropriate speech training, some deaf children improve and develop speech that is intelligible. Thus, it is desirable to have one procedure that can evaluate the entire continuum from subintelligible to intelligible levels. To accomplish this, a similarity scale was used to evaluate improvement as a function of therapy time. Deaf children were tested with 27 words in four stimulus—response conditions. The teacher provided the oral stimulus (word) and the child responded by attempting to immitate the stimulus. Normal-hearing listeners used a nine-point similarity scale to judge the response as it related to the stimulus. A score of 1 indicated that the response was similar to the stimulus and a score of 9 indicated that it was dissimilar. A group of deaf children demonstrated a significant improvement over testing time. Then, the responses that represented different points on the similarity scale were judged for intelligibility. It appears that changes in similarity values between 9 and 5 represent the subintelligible range and can be partially attributed to changes in segmental features. From 2.5 to 1 there is a rapid improvement in intelligibility. Perceptual changes on the similarity scale will be related to corresponding changes in spectrograms. [Work supplemented by U. S. Office of Education.]
Perceived Order of Tone Pulses
Authors: Peters R. W. , Wood T. J.
Published: October 2005

Several variables including pulse duration, pulse interval, pulse frequency, and pulse order were examined relative to judgments of temporal order for successive tone pulses. The tone pulses were 500-, 1000-, and 2000-Hz tones presented at various durations and with various intervals between pulses. Observers either judged the order for all three pulses or identified the position of a single pulse. The results indicated that pulse interval durations are more important for correct order judgments than are pulse durations. Position and frequency of pulses were also found to affect order judgments. [This research was supported, in part, by the University Research Council of the University of North Carolina.]
Identification of the Temporal Order of Three Tones
Authors: Divenyi Pierre L. , Hirsh Ira J.
Published: October 2005

Monaural listeners were asked to identify permutations of a given set of three tones which differed only with respect to their frquency. In one set of experiments the duration of each tone was fixed at 10 msec, the frequency of the middle tone remained constant at 1 kHz, and the frequency difference, Δf, between the lowest and the highest tones was varied from 100 to 1500 Hz, symmetrically (log) around 1 kHz. Overall identification performance, poor at the smallest Δf value, improved when Δf was increased to 227 Hz but was unaffected by further increase in Δf. In another set of experiments the duration per tone was variable (2 to 20 msec) while the tonal frequencies were held constant (Δf=227 Hz, symmetrical around 1 kHz). From the resulting psychometric functions, one could determine tone durations necessary for identification thresholds. Across all patterns this threshold was found to be between 7 and 13 msec, depending on the observer. A feature analysis of the data shows that the terminal frequency is the dominant identification cue in almost all conditions. [Supported by NINDS Grant No. NS03856.]
Discrimination of the Silent Gap in Two-Tone Sequences of Different Frequencies. II Dichotic Case
Authors: Divenyi Pierre L.
Published: October 2005

Two tone bursts, one to each ear, were separated by an interval, t1. Observers had to adjust the time interval, t2, between two subsequent tone bursts so as to match that interval. Each 86-dB-SPL burst was 20 msec long and was shaped with a 2.5-msec rise time and a 10-msec fall time. The leading edges of the standard tone burst pair were 40 msec apart. The frequency of the first three bursts, f1, was the same whereas that of the forth burst was f1−Δf. The geometric mean of the two frequencies was held constant at 1 kHz. As in the monaural case [Divenyi and Hirsh, J. Acoust. Soc. Amer. 52, 166(A) (1972)], the adjusted duration of t2 becomes 3–8 msec shorter than t1 as Δf increases to the third octave. This discrepancy is all but eliminated when the intensity of the fourth tone burst is lowered by 30–40 dB. [Supported by NINDS Grant No. NS03856.]
Simultaneous Adaptive Threshold Estimation with Frequency Uncertainty
Authors: Creelman C. Douglas
Published: October 2005

An adaptive threshold tracking procedure (PEST) was used to adjust the amplitude of each of an ensemble of possible sinusoidal signals. The data were thresholds for each alternative in the context of the ensemble. This procedure avoids some of the problems in strategy for the observer and other problems in theoretical interpretation for the experimenter. Separate conditions involved variation in the number of alternative signals in the ensemble (3–33) and the spacing between lowest and highest member of the ensemble (50 Hz–5000 Hz). Within limits, prior findings are confirmed; loss in sensitivity due to uncertainty reaches a maximum of 3–5 dB with all but very narrow ranges of frequency, compared to detection of a fixed, known frequency.
Multi-Dimensional Encoding within the Temporal Microstructure of Auditory Displays
Authors: Pollack Irwin
Published: October 2005

Four variables—direction, polarity, amplitude, and interpulse interval—were binary coded within auditory pulse trains. Listeners heard four pulse trains, one of which was constrained in terms of the individual variables or in terms of their combination. Their task was to determine the constrained pulse train. For a constant informational constraint across the entire display, discrimination suffers with the number of variables entering the constraint: a constraint reflecting the combination of n variables is more poorly detected than the same constraint reflecting the combination of (n − 1) variables. For a constant informational constraint per variable, discrimination improves with the number of variables entering the constraint: the same constraint imposed upon each of n variables is more easily detected than when imposed upon (n − 1) variables. In the latter case, performance is at least as good as that predicted by the resultant of the component signal detectability indexes.
Audibility of Harmonics in Periodic “White Noise”
Authors: Duifhuis H.
Published: October 2005

The finding that spectrally suppressed high harmonics (n>16) in a periodic pulse are perceptible has been related [H. Duifhuis, J. Acoust. Soc. Amer. 48, 888–893 (1970); 49, 1155–1163 (1971)] to the ear's limited resolving power in peripheral frequency analysis. The limited frequency resolution provides the possibility for an analysis in time. In order to verify the proposed explanation, we examined the audibility of harmonics in periodic “white noise,” which had the same amplitude spectrum as a periodic pulse, but a very different time structure. The audibility of low harmonics was similar in periodic pulse and noise, but for high harmonics significant differences were observed, as expected. Not expected, however, was the finding of relatively low thresholds of individual high harmonics, which seems to suggest that in the given listening condition (stimulus preceded by a conditioning tone in which the harmonic under consideration is suppressed), almost any harmonic is perceptible.
Perceived Roughness of Amplitude-Modulated Pure Tones
Authors: Guirao Miguelina , Garavilla J. M.
Published: October 2005

Two studies were conducted to determine the perceived auditory roughness of pure tones modulated in amplitude. AM signals were 500- and 2000-Hz tones at 70-dB sound-pressure level. Auditory roughness was measured by the psychophysical methods of magnitude estimation and magnitude production. The averages of the numerical estimates given by ten subjects were plotted versus the degree of modulation m = Δp/p of the SPL. Initial results indicate that the perceived auditory roughness functions can be described by a power function with an exponent of about 1.0. The exponent remained the same for the two tones at different relative amplitude fluctuations.
Intracochlear Electrical Stimulation: Results of Psychoacoustic Studies in Man and Physiological Studies in Cats
Authors: Merzenich M. M. , Pettit C. R. , Schindler R. A. , Reid M. , Knight P.
Published: October 2005

A series of simple psychoacoustic experiments has been conducted on subjects previously implanted with an intracochlear bipolar electrode. With use of simple ac electrical stimulation, subjects heard sounds described as “tones” over a frequency range from about 100 to at least several thousand Hz. The apparent pitch rose rapidly up to 400–600 Hz; at higher frequencies, it changed slowly if at all over a broad range of frequency. The dF was about 1–3 Hz at 100 Hz, 5–10 Hz at 500 Hz, and 50–100 Hz at 1 kHz. Physiological experiments were conducted to determine how sensation heard by these subjects is generated and encoded in the auditory nervous system. Study of single units of the inferior colliculus in cats using standard microelectrode techniques has revealed: (1) Tuning curves of colliculus neurons excited by electrical stimuli were flat, and all were roughly parallel. The normal “place” representation of stimulus frequency is obscured. (2) The period of the stimulus is represented in the time order of discharge of colliculus neurons at frequencies up to 500–600 Hz. (3) With the stimulus electrode employed, the threshold of the acoustic nerve at the cochlear base was 30–40 dB lower than at the cochlear apex. Psychoacoustic and physiological evidence strongly suggests that hearing in these subjects is akin to the described sensation of “periodicity pitch.”
Dynamic Control of a Computer Model of the Vocal Cords
Authors: Flanagan J. L. , Ishizaka K. , Shipley K.
Published: October 2005

Dynamic, time-varying controls are implemented for a vocal-cord model described earlier [Bell System Tech. J. 51, 1233–1268 (1912)]. A speech synthesis system is formulated from the cord-model, a programmed vocal tract, and a control mechanism. Time-varying controls in the simulation include subglottal pressure, cord tension, glottal area at rest, and vocal-tract shape. Previously reported physiological data on muscle electromyography, air flow, and lung pressure are used to estimate control correlates in the computer model. For voicing at constant subglottal pressure and with an unoccluded vocal tract, the rest-area of cord opening is found to be the dominant factor in voiced/voiceless control. Asymmetry in onset and cessation of voicing is found to relate to direct observations of cord motion. Cord tension is dominant in pitch control. Time variations in lung pressure and in tract occlusion modify these control factors. A computer movie is presented to illustrate the dynamic control and behavior of the model.
Response Time of Laryngeal Muscles in Controlling F: Results of a Correlation Analysis
Authors: Atkinson James E.
Published: October 2005

Many electromyographic (EMG) studies have investigated the function of the laryngeal muscles in controlling the fundamental frequency of vibration of the vocal folds (F0). It is a well-known fact that muscles physically take a finite amount of time to contract due to the mass involved. When studying the correlation between EMG data and F0 in speech, it is necessary to correct for this time lag. No data are available, however, for contraction time of human laryngeal muscles. Using a discrete form of cross-correlation analysis, a related measure which we call “mean response time” was measured for several laryngeal muscles in one (human) speaker. The technique is described and the results are compared with available data from other species. Although not truly a measure of contraction time as it is usually defined, the mean response time agrees very well with the best data available for contraction times (measured in cat and dog), and offers a useful tool for EMG studies.
Physiological Factors Controlling F: Results of a Correlation Analysis
Authors: Atkinson James E.
Published: October 2005

Many electromyographic (EMG) and aerodynamic studies have attempted to determine the physiological factors controlling the fundamental frequency of vibration of the vocal folds (F0). All of the EMG and most of the aerodynamic studies have been analyzed in a very subjective way (e.g., looking for peaks in physiological data that correspond to peaks in acoustic data). In the present study, an objective measure of correlation was obtained, for a single speaker, between EMG activity of various laryngeal muscles, subglottal pressure, and F0. The results show that the dominant factors controlling F0 depend upon the utterance type and the nature of the acoustic signal required, and suggest a model of F0 control in terms of shifts in laryngeal mode, within what is commonly considered the “chest register.” In the “low F0” mode, the larynx is quite sensitive to subglottal pressure and it is the strongest physiological correlate, while in the “high F0” mode laryngeal tension is the primary correlate. The sternohyoid muscle appears to be involved in shifting between these “modes.” Based on these promising results, further studies on more speakers are planned.
Identification of Vocal Register Shift in a Helium-Rich Atmosphere
Authors: McGlone Robert E. , Brown W. S. , Hazen Barry
Published: October 2005

Three methods were used to identify where subjects changed from model to falsetto register while breathing either air or a helium-oxygen mixture. Six male subjects sustained phonations in discrete semitone steps up and down the scale twice each way under both gas conditions. They notified the investigators when a shift in registers occurred. Recordings were made, randomized, and played to judges instructed to locate the shift. The recordings also were subjected to spectrographic analysis. Results showed subjects were slightly more constant at place of shift when breathing HeO2 than air. Judges also agreed with the subjects more frequently for phonations under the helium condition. No systematic differences except frequency could be found on the spectrograms of the phonations around the shift. Implications, from these results, of how registers are produced will be presented.
Perceptual and Acoustical Effects of Oral Anesthetization on the Speech of Young Children
Authors: Bishop M. E. , Daniloff R. G. , Ringel R. L. , Wu B. C.
Published: October 2005

Speech samples of four normal-hearing and -speaking children aged 2.6, 3.7, 5.0, and 9.3 were recorded prior to and during oral anesthetization. Phonetic and acoustical analysis of the speech samples were made. The speech of all the children remained intelligible; however, anesthetization produced slightly more perceptual disruption of the younger children's speech than the older. The nature of disruptions were for the most part consistent with those reported for adults by Scott and Ringel [J. Speech Hearing Res. 14 (1971)]. Acoustical analysis revealed temporal as well as spectral changes in the speech signals of all children during anesthetization. The acoustical changes which occured, however, were more variable for the younger children than for the older children. These results are discussed in terms of open- and closed-loop models for the acquisition and subsequent control of the articulatory gestures of speech.
Forward Coarticulation of Velar Movement at Marked Junctural Boundaries
Authors: McClean M.
Published: October 2005

Using high-speed cinefluorographic techniques, the effects of marked junctural boundaries on the onset of forward velar coarticulation were studied. Three speakers were filmed while producing a constant CVVN sequence with a variety of prosodically marked boundaries falling between the two vowels. Frame-by-frame tracings made of the velum and associated reference structures yielded plots of velar movement over the CVVN sequence. It was found that the onset of forward coarticulation to the nasal consonant was consistently delayed in those cases where marked junctural boundaries were present. Also, two distinct patterns of velar movement were observed, and previous data on velar coarticulation at unmarked boundaries were corroborated. The above findings are discussed in relation to a general model of speech production.
Aircraft Flyover Noise—Spectral Analysis of Sounds and Sound Intensity Fluctuations
Authors: Gonter Robert H.
Published: October 2005

Tape-recorded sounds from aircraft flyovers were digitized 2000 times per second and spectral analysis performed. These spectra show peaks about 400 Hz with a decrease of 40 dB by 1000 Hz. Intensity fluctuations of the sounds were obtained with a peak detector and digitized 100 times per second. The spectra of intensity fluctuations show 10 dB drop up to 5 Hz, then variability or gradual decrease up to 50 Hz. For simultaneous recordings with microphones spaced 33 m, cross spectra of the fluctuations have very low coherence, indicating that the scale of the fluctuations is considerably less than 33 m. One case of a high-flying jet aircraft shows regular change in the phase with increasing frequency, which would occur with fluctuations reaching the microphone array with a constant angle of incidence.
Sideline Measurement of Aircraft Noise: Is It Necessary?
Authors: Vogel James W.
Published: October 2005

Recent testing has shown that difficulties may be encountered in determining the so-called sideline noise of modern aircraft. Present national requirements and recommendations of international organizations stipulate that measurements be made on either 0.25- or 0.35-NM symmetrical sidelines. This translates into distances between microphone and aircraft of, typically, 1800 ft or greater. These large distances, together with the inherent quiteness of the newer aircraft, are at the root of the problems alluded to above. This paper discusses some of the problems encountered with sideline measurements, whether or not such measurements are actually needed, and offers several possible solutions to the problems.
Fuselage Pressure Fields caused by the 20-mm, M-61-A1 Rapid Fire Gun
Authors: Soffel A. R. , Hancock R. N. , Hutchinson J. A.
Published: October 2005

Acoustic pressure fields generated by large-caliber rapid-fire weapons are sufficiently intense to constitute sources of concern to airplane designers. The operation of such weapons could result in greatly increased equipment and structure vibration and danger of hearing damage to flight personnel. Acoustic pressures from both fuselage and wing-mounted M-61-A1 guns have been measured on the fuselage and wing of an A-7 airplane. The measurements covered an area extending several feet fore and aft of the gun muzzles. Both static and flight firings were measured. Recordings of acoustic pressure were analyzed for waveform, instantaneous amplitude distributions, spectra, and spacial distribution. The waveform for a burst of fire is approximately a series of decaying sinusoids at the gunfire repetition rate. Peak-to-rms ratios as high as 5 to 6 are not uncommon. On the fuselage near the gun muzzle, peak pressures can reach 2 to 3 psi (177–181 dB SPL). The possible effect of these high-pressure fields on airplane design and operation is discussed in relation to structure and equipment vibration and personnel safety.
Experimental Investigation of Radiated Acoustic Power of an Externally Blown Flap
Authors: Reddy N. N. , Yu J. C.
Published: October 2005

Radiated acoustic power generated by a model subsonic cold-air jet with a blown flap was measured. The experiments were conducted in the NASA Langley Research Center 55-ft vacuum cylinder (reverberation room) by inducing the flow from the atmosphere to the cylinder through the contoured converging nozzles. Since there were no controlling valves, the upstream noise sources in the flow were not present. The nozzles used for basic jets were the 2-in.-diam circular nozzle with a contraction ratio of 16 and the slot nozzle with an exit area of 3.14 in.2 and an aspect ratio of 10. The acoustic power generated by the model jets without flap was measured and correlated with the existing theories of subsonic jet noise. The flap was slotless and bent to form a 45° angle with the jet axis. The distance between the nozzle exit plane and the impingement point on the flap was varied. The jet velocity was varied from 500 to 950 ft/sec. The results are presented in the form of 12-oct spectra, normalized power spectra, and the variation of total power with jet velocity. These results are compared with the other results available in the open literature. It is found that the total acoustic power is increased by about 5 dB due to the introduction of the flap in the jet stream. This increase in power is primarily in the low- and mid-frequency range.
Acoustic Correlation Analysis in the Atmosphere
Authors: Constantine J. G. , Dickinson M. D.
Published: October 2005

Correlation analysis on radiated acoustic signals has been made. The analysis was performed as a function of (a) the base line between the elements of a two-sensor array, (b) the nature of the acoustic source, and (c) the dynamics of the acoustic source relative to the array. The results of the analysis for a maximum base line length of 1000 m show: (1) Cross-correlation techniques over 1-km base line are applicable for acoustic sources whose sound-pressure level (SPL) is about 100 dB re 0.0002 μbar. (2) The correlation coefficient is independent of the base line but strongly dependent on the terrain. (3) The correlation coefficient and the envelope of the correlation decrease as the correlation time window is increased. For most of the targets examined, window sizes of several seconds are required to obtain discernible correlation maxima. (4) The multipath in a jungle environment has a strong effect only on signals of frequencies above 150 Hz. (5) The accuracy of locating and tracking an acoustic source is optimum when the target is between the orthogonal extremes of the base lines. Errors in accuracy less than 10 m are possible. (6) In most cases, signal prewhitening is necessary because prominent spectral lines lead to periodic structures in the correlation function which obscure the features of interest. (7) In the case of moving acoustic sources, Doppler correction is required because the Doppler difference between signals received at separated microphones imposes a limit on the bandwidth over which the signals can be cross-correlated.
A Theoretical and Experimental Study of the Exhaust Noise Environment of a Proposed High Reynolds Number Tunnel
Authors: Robertson J. E. , Starr R. F.
Published: October 2005

The growing interest in noise pollution has presented designers of modern aerodynamic test facilities with new problems and interesting and complex challenges. Due to the sheer magnitude of their power output, many existing aerodynamic facilities and some of those designed for the future are enormous sources of sound. As part of a feasibility and preliminary design study of a High Reynolds Number Tunnel (HIRT) currently being performed by ARO, Inc., at the Arnold Engineering Development Center (AEDC), an investigation has been conducted to (a) predict the acoustic environments which may be anticipated from the operation of HIRT and (b) perform a comprehensive experimental study using a scale-model facility in order to obtain acoustic data over the anticipated range of operational variables for HIRT. One important feature of the facility which necessitated this study is the open-circuit blowdown design which causes the starting shock wave and high-speed jet flow to exhaust into the atmosphere. A comprehensive analysis of the noise-generating mechanisms associated with the facility has been conducted, although based in some cases on engineering approximations and acoustic models of the flow environment. These data were used to define those design features of the facility which would produce predominant noise source mechanisms. Based on the analytical findings, a one-thirteenth-scale model of HIRT was designed using precise scaling of the important features of HIRT to retain, within practical limits, those design features which contribute to the noise characteristics of the facility. Utilizing the model facility, acoustic tests were performed over a broad range of operational variables representative of the operational range of the full-scale facility. Free-field acoustic measurements were taken along various polar rays around the exhaust stack of the facility to define the noise levels and spectra, directivity patterns, and propagational characteristics. Comparisons are made between the acoustic predictions and the experimental measurements and show the applicability of current noise prediction methods (which are based on jet and rocket exhaust flow) to noise problems associated with aerodynamic test facilities.
Community Noise Impact Planning for a Very Large Wind Tunnel
Authors: Plotkin Kenneth J.
Published: October 2005

A study was conducted to determine community impact of noise from a large intermittent wind tunnel to be located in a predominantly rural area near several small cities. Acoustic power output will be up to 208 dB, with each run lasting 3 sec. Because run schedule and acoustic power for each run will be variable, noise impact was expressed in terms of the Noise Exposure Forecast (NEF) scale. An important part of this study was to determine noise standards whereby genuine good relations may be maintained with surrounding residents. The generally accepted NEF = 30 used near busy urban airports could not be automatically assumed for the rural community under consideration. It was therefore necessary to examine noise impact and establish limits appropriate to a quiet rural community. Data on the interference of residential activities by noise were reviewed. Based primarily on sleep disturbance and speech interference, nominal limits of NEF = 15 for residences and NEF = 5 for hospitals were determined. It was found that these limits will be generally met for average anticipated facility utilization. However, certain marginal areas exist and unacceptable levels can result under adverse meteorological conditions. Alleviation of these problem areas can be achieved by careful scheduling of facility usage. It was noted that NEF contours for an arbitrary run schedule can be related to NEF for a reference schedule through a factor representing run frequency and intensity. A nomogram was devised so that facility operating personnel can obtain this factor easily for any planned schedule. [This work was performed under Contract No. F 40600-72-C-0007.]
Cavitation Dynamics
Authors: Flynn H. G.
Published: October 2005

A program of research in acoustic cavitation that was started at the suggestion of F. V. Hunt and continued through his cooperation has resulted in an extensive study of the motions of small bubbles under the influence of acoustic pressure fields. The principal tool in this investigation has been a mathematical formulation made up of a set of integral equations, differential equations, and algebraic equations. Solutions of this formulation obtained through use of a digital computer have so far given considerable insight into the free pulsations of cavities, the thresholds for generation of transient cavities, and the temperatures and pressures that might be reached in the collapse of transient cavities. A brief survey of these results will be given. [This work was supported by Acoustics Programs, Office of Naval Research.]
Acoustic Cavitation: Film Sequences and Threshold Measurements
Authors: Apfel R. E. , Harbison J. P.
Published: October 2005

A novel technique for measuring the tensile strength of liquids was recently reported [R. E. Apfel, J. Acoust. Soc. Amer. 49, 145 (1971); Nature (Phys. Sci.) 233, 119 (11 Oct. 1971)]. In this technique a droplet of the sample rises slowly in a column of another liquid, the “host,” in which it is nearly insoluble. When the droplet reaches a certain position in the host, an acoustic standing-wave field at about 50 kHz is established in the column, serving two purposes: (1) to balance the buoyancy force on the droplet and thus levitate it and (2) to rend the sample apart by raising the acoustic pressure to a great enough amplitude. If the droplet is simultaneously superheated, the cavitation event takes the form of an irreversible explosion of the sample into its vapor. Taking advantage of the levitation scheme, this explosion has been filmed with both diffuse and shadow lighting at about 3500 frames/sec and shows resonant oscillations and what appears to be jet formation during the collapse of the vapor bubble. New results for the tensile strength of superheated n-pentane as a function of temperature have been measured and appear, like previous results for ether and n-hexane, to be in reasonable agreement with the theory of homogeneous nucleation. [Work supported by the U. S. Office of Naval Research, Acoustics Program.]
Bjerknes Forces Between Two Pulsating Air Bubbles in a Liquid
Authors: Crum L. A. , Nordling D. A.
Published: October 2005

Air bubbles present in an acoustic stationary wave have often been observed to behave in enigmatic ways. They can be trapped by the sound field, and will sometimes dart about in erratic fashion and whirl rapidly in circles; often many small bubbles will coalesce into larger ones. These effects have commonly been attributed to the action of “Bjerknes forces” between the air bubbles. An experiment will be described that separates the forces (and effects) into two general types: a long-range, pressure-gradient force that causes individual bubbles to move through the sound field, and a short-range, attractive force that causes nearby bubbles pulsating in phase to be attracted toward each other. In this experiment, the two types of motion can be analyzed independently of each other. A short movie will be shown which shows coalescence of bubbles due to the Bjerknes force as well as motion of the individual bubbles through the sound field. The bubble pulsations, which are rather large in amplitude, can be seen easily in the movie. Data taken from similar films were analyzed directly to obtain a measure of the magnitude of the Bjerknes force.
Effects of Diffusion on Gaseous Cavitation Bubbles
Authors: Eller Anthony I.
Published: October 2005

Rectified diffusion is a mechanism whereby a gas bubble, set into pulsation by a sound field, can grow in size because of an effective gating action by the bubble surface area. Bubbles that might otherwise dissolve can grow instead if the sound-pressure amplitude exceeds a threshold that depends on the bubble size. A theory of rectified diffusion is used to determine the threshold conditions for bubble growth and to calculate the rates of growth for conditions above threshold. Implications of the results are then examined with regard to the problems of the nucleation of gaseous cavitation and the shifting size distribution of a bubble population. Although calculated thresholds for growth have been found to agree with observed thresholds, calculated growth rates are often much lower than observed rates. Reasons for the partial failure of the theory are suggested, and recent attempts to improve the theory are indicated.
Cavitation Apparatus and Thresholds for Water at 14 kHz
Authors: Morgan John S. C.
Published: October 2005

Cavitation thresholds of distilled water have been measured over a narrow range of dissolved-gas content near saturation. The sample was continuously filtered and entirely isolated from the atmosphere. Cavitation was produced in a large spherical glass tank with 12 driving transducers. The measured thresholds were repeatable, and were much lower than the observations of Greenspan and Tschiegg [J. Res. Nat. Bur. Std. 71C, 299–312 (1967)], but the reduction of the dissolved gas content by only 14% resulted in a transition from gaseous to vaporous cavitation and in a marked increase in the threshold. It appears that the influence of dissolved-gas content on the threshold near saturation increases with filtering, in contrast to published expectations and observations for undersaturated water. The sample was degassed without being subjected to reduced hydrostatic pressure. [Work supported in part by the Office of Naval Research].
The Status and Future of Nonlinear Acoustics
Authors: Westervelt Peter J.
Published: October 2005

In addition to serving as an ideal discipline for introducing the concepts of quantum field theory and general relativity, nonlinear acoustics provides new means for absorbing and generating sound. The many applications of this exciting subject are based in part on the fact that, in common with vector (electromagnetic and shear) and tensor (gravitational) waves, the scalar sound wave transports energy, angular momentum, linear momentum and, incidentally, information. The methods of nonlinear acoustic can account for such disparate phenomena as the parametric array and the radar time delay in a gravitational field, the absorption of sound in superfluid helium and shock wave attenuation in a gas, radiation pressure and sonic boom, the scattering of sound by sound, and the generation of gravitational waves. Based on the ability of nonlinear acoustics to subsume within its methodology, and hence to unify, different physical processes as well as its demonstrated ability to contribute solutions to practical problems, it seems reasonable to expect that this subject will become a part of the curriculum in more colleges and universities than is the case at present. [This work was supported by the U. S. Office of Naval Research].
An Experimental Investigation of Subharmonic Generation in an Acoustic Interferometer
Authors: Yen Nai-Chyuan
Published: October 2005

In our previous study [J. Acoust. Soc. Amer. 49, 119(A) (1971)], we showed that the nonlinear properties of the medium can induce coupling among the modes in a multiresonant system and the theory is able to predict the threshold and the steady-state response of subharmonic components. Such a mechanism is further illustrated by observing the subharmonic generation phenomenon in an acoustic interferometer. The experimental investigation was conducted with a 1.5-mHz driving signal and used filtered and degassed water as the medium. Data concerned with the actual modes of the interferometer, the loss factor associated with the subharmonic modes, and the threshold of subharmonic generation, with length of the interferometer and the driving frequency varying, are consistent with the analytic results provided that cavitation is carefully avoided. [The work was carried out at Harvard University and supported by the Office of Naval Research.]
Effective Length of Horns
Authors: Pyle R. W.
Published: October 2005

Some authors, writing about brass musical instruments, have loosely used the term “effective length,” usually meaning the length of a cylindrical tube with the same resonance frequencies as a given horn, but possibly with different end conditions. In this paper, an attempt is made to define effective length in a precise way that is still consistent with the intent of previous workers who have used the term. Within the framework of plane-wave horn theory, a nonlinear first-order differential equation is derived that yields effective length as a function of frequency and horn contour. This formulation appears well suited to calculating the effect of small changes in the bore of a brass instrument by using a perturbation technique. The differential equation has been solved for some horn contours resembling brass instruments. The solutions display good qualitative agreement with the effective lengths of actual instruments, determined from measured resonance frequencies.
Seeding the Field of Acoustical Signal Processing
Authors: Anderson Victor C.
Published: October 2005

This is an historical look at the contributions to the field of acoustical signal processing which originated under the nurture of F. V. Hunt at the Harvard Acoustics Research Laboratory. The early research is highlighted by the work of Faran and Hills on the use of correlators for space-time processing. This early work was followed by research in the use of multiple element arrays and by the development of real-time processors for correlation and beamforming applications. The impact of these contributions can be seen in the expanding field of signal-processing research today. Upon retirement, Hunt transferred the pursuit of his last research interest, “Sic Transit Sonitus”—a ship transit detector, to the Marine Physical Laboratory, where a real ocean investigation of the technique is currently underway.
Solitons and “Synacetics”
Authors: Zabusky Norman J.
Published: October 2005

The soliton, a localized wave entity, has successfully described long-wave propagation in a a class of one-dimensional, nonlinear, dispersive, continuous, and discrete systems. We demonstrate how “synacetics” (synergetic amalgam of analysis, computation, and experiment) has led to new insights and interpretations. The relationship of the Korteweg-deVries equation to nonlinear lattices (discrete media) and shallow water waves is given and properties of solutions are discussed, including “envelope” (E-) solitons and “lattice” (L-) solitons. Quantitative comparisons to shallow water wave experiments are made and applications of L-solitons to the lattice thermal conductivity problem are advanced. Computer-generated films will give a cogent demonstration of the new phenomena.
Nonlinear Interactions in Dispersive Media
Authors: Westervelt Peter J.
Published: October 2005

The exact solution for first-order nonlinear scattering of two plane sound waves in a nondispersive medium [P. J. Westervelt, J. Acoust. Soc. Amer. 53, 384(A) (1973)] is here extended so as to be valid for a dispersive medium. This solution is applied to a discussion of the absorption of sound by sound and the absorption of sound in superfluid helium. The influence dispersion has on degrading the performance of the Acoustic Parametric Array is demonstrated. The Electromagnetic Parametric Array will be briefly discussed in order to point out the effects of dispersion in its performance. [This work was supported by the U. S. Office of Naval Research].