bluuebunny/crossref_metadata_2025 huggingface dataset:
A Theory of Excess Jet Noise
Authors: Crighton D. G.
Published: October 2005

Uniform subsonic jet flow issues from a semiinfinite circular duct, and undergoes a spatial instability. The sound field resulting from coupling of the instability to the duct is calculated. It is shown that the intensity of this “lip-noise” varies with speed U and direction θ from the exhaust according to I ∝ U6 sin4θ/2, and that the maximum acoustic efficiency of this process is of order 10−5 M3. The spectrum peaks at a frequency rather higher than that characteristic of jet mixing noise, and the sound power is only slightly reduced by forward motion of the duct at typical aircraft landing speeds. These features offer an explanation of the so-called “excess noise' phenomenon, present in subsonic and supersonic jets alike, and consisting of substantial increases in forward arc noise over the levels predicted by Lighthill's theory of jet mixing noise. [Work supported by NGTE, Pyestock, England.]
Saturn Systems Holddown Acoustic Efficiency and Normalized Acoustic Power Spectrum
Authors: Gilbert D. W.
Published: October 2005

Saturn systems field acoustic data are used to derive mid- and farfield prediction parameters for rocket engine noise. The data were attained during Saturn vehicle launches at the Kennedy Space Flight Center. The data base is a sorted set of acoustic data measured during the period 1961 through 1971 for Saturn system launches SA-1 through AS-509. The model assumes hemispherical radiation from a simple source located at the intersection of the longitudinal axis of each booster and the engine exit plane. The model parameters are evaluated only during vehicle holddown. The acoustic normalized power spectrum and efficiency for each system are isolated as a composite from the data using linear numerical methods. The specific definitions of each allows separation. The resulting power spectra are nondimensionalized as a function of rocket engine parameters. The nondimensional Saturn system acoustic spectrum and efficiencies are compared as a function of Strouhal number with power spectra from other systems. [This analysis has been funded in part under contract under the cognizance of the George C. Marshall Space Flight Center.]
Predicted Acoustic and Aerodynamic Noise Environments for the Reusable Space Shuttle Orbiter
Authors: Himelblau H.
Published: October 2005

Aeroacoustic noise generated by the proposed shuttle vehicle was predicted for various orbiter locations. Over-all SPL of 162–163 dB was calculated for shuttle liftoff, using Saturn V liftoff data and a scaling relationship based on the Eldred method. Over-all SPL of 167 dB was determined for the flow interference region between the mated booster and orbiter during the qmax period of ascent, using wind tunnel data obtained by Coe, Dods, and Robinson and flight data measured on Titan IIIC. Aerodynamic noise of 158 dB was predicted during ascent for regions immediately before and behind the cockpit using wind tunnel data provided by Coe and by Stevens, and for the mid- and aft fuselage using procedures developed by Bies and by Ailman, as well as Saturn V flight data. Maximum entry levels of 139–144 dB were estimated using separate procedures developed by Ailman, Bies, and Heller and Holmes.
Acoustical Modeling of Noise Sources Utilizing Correlation Techniques
Authors: Cook B. D.
Published: October 2005

Acoustical modeling of noise sources is usually performed in the frequency domain. However, there may be advantages in modeling in the time domain using correlation techniques. Examples of the mathematical procedures involved will be illustrated by simple configurations.
Intensity and Frequency Discrimination in One- and Two-Interval Paradigms
Authors: Bilger R. C. , Jesteadt W. H.
Published: October 2005

In an attempt to extend detection theory beyond the intensive domain, both frequency and intensity discrimination data were collected for four subjects using several psychophysical procedures. These included Yes-No, 2IFC, Same-Different with a positive increment, and Same-Different with a negative increment. The two-interval conditions were run with both fixed and random bases. Two increment sizes were used for each condition. The results for intensity discrimination showed the dependencies on method so that the desired intermethod evaluation of frequency discrimination could be effected. Intersubject variability was significantly greater for frequency than for intensity discrimination, but the frequency data for each individual were quite orderly.
Impairment of Pitch Perception by Temporally Contiguous Stimuli
Authors: Holding Dennis H. , Yoder Delmar , Loeb Michel
Published: October 2005

Two experiments were run, combining elements of designs by Elliott (1970) and Massaro (1970), in which noise and pure-tone “masks” bore varying temporal relations to two stimulus tones. The tones, either 20-msec duration (“short”) or 400-msec (“long”) were initiated 4 sec apart; either the first or second was variable, the other fixed (1000 Hz). The mask, an 80-dB white noise or 2193-Hz tone 500 msec long was inserted (position 1) 40 msec after the first tone or (position 2) terminated 40 msec before the second tone, or (position 3) initiated 40 msec after the second tone. In the first experiment, the variable was 1000 or 1050 Hz (“coarse discrimination”); in the second, 1000 or 1025 Hz (“fine”). Discrimination was impaired, especially for short tones, though impairment was minimal in position 2. Impairment was greater by tone than noise in position 1 only and more so for the fine discrimination in position 3 only. One interpretation is that “masking” consists of two kinds of disruption, one associated with storage and one with pitch comparison.
Discrimination of the Silent Gap in Two-Tone Sequences of Different Frequencies
Authors: Divenyi Pierre L. , Hirsh Ira J.
Published: October 2005

Pairs of two-tone sequences were presented in such a way that listeners could adjust the time interval separating the onsets of the two tones in the second pair, so that the gap or rhythmic repetitiveness appeared to be the same in the second as in the first pair. The pairs consisted of two 20-msec tone bursts with 2.5-msec rise time and 10-msec fall time. The time interval separating the onsets of the tones in the first, or standard, pair was 40 msec. Responses were observed as a function of the frequency of the fourth tone, the standard pair being of one frequency (1 kHz), while the variable pair began at the same frequency but ended with a different one. As the frequency difference increases up to 250 Hz, the time interval in the variable pair for apparent equality of gap decreases, as does the variability in judgments. Beyond a difference of 250 Hz, both quantities increase. These results are consistent with those of earlier time discrimination experiments [P. L. Divenyi, J. Acoust. Soc. Amer. 49, 127 (1971)] and may relate to the time required to shift the listening band from one frequency to another.
Latency of the Chinchilla's Response to Auditory Change
Authors: Luz G. A.
Published: October 2005

Chinchillas were tested on auditory pattern discrimination for the set (AA, BB, AB, BA) where A, B stand for two tones and the pattern is 2.25 sec. One of the set was used as a repetitive background signal, which the remaining three were used as signals for instrumental avoidance. Performance was higher when the background was AA or BB than when it was BA or AB. Clear differences between the latency distributions for hits and false alarms were found for the former but not for the latter condition. The data suggest that the chinchilla does not treat a 2.25 sec pattern as a single auditory gestalt.
Detecting Signals of Uncertain Frequency: Analysis by Individual Alternative Signals
Authors: Creelman C. Douglas
Published: October 2005

Gated sinusoids were presented to highly practiced observers for two-alternative detection. Signal frequencies were randomly chosen from populations that were changed from one run of 100 trials to the next. The populations differed in the range of possible signal frequencies and the number of frequencies that could be chosen from within the range. All feasible combinations of ranges (50, 560, 100, 2000, and 4000 Hz) and numbers of alternatives (1, 3, 9, 17, 33, 65, 129, and 257) were run. When one looks at the observers' performance on signals of specific frequencies, it appears that neither the range nor the number of alternatives affected performance. Average performance differed between ranges because the larger populations encompassed more of the audibility curve.
A Computer-Oriented Highway Noise Illustrated by the Rhode Island I-84 Environmental Impact Study
Authors: Copley Lawrence G.
Published: October 2005

A mathematical model of highway noise was developed for use in selecting and evaluating highway corridor locations for minimum adverse noise impact in the adjacent communities. The model is based on the present state of knowledge regarding highway noise, as published by the Highway Research Board and elsewhere. Noise exposure is characterized by L10, the 10-percentile A-weighted sound level. The model includes excess attenuation due to atmospheric absorption, topography, and ground cover. The model has been programmed for computer and is used in conjunction with a comprehensive data bank including land use types and terrain information. These data are geographically coded in grid squares of 15 km side. Noise impact is quantified by the relation between predicted L10 to highway noise exposure and what would be completely acceptable for the land use type. The computer output is in the form of two types of shaded maps. One maps the sensitivity to noise impact and can be used in selecting desirable highway corridors. The other type of map displays the noise impact caused by each highway planning alternative.
Community Sound Levels: A Comparison of Measured and Estimated Data
Authors: Safeer H. B.
Published: October 2005

The Office of Noise Abatement has developed several models of transportation-generated sound levels. These models are useful in studying the magnitude of transportation noise and forecasting the noise reduction of alternative abatement programs. The Community Median Noise Level Model was used to estimate the median sound levels in Medford, Massachusetts. The estimated median sound levels were compared to the measured median sound levels. A total of 18 sets of measured and estimated average median sound levels were obtained, i.e., eight traffic control zones and the total for Medford, for two time periods. The average absolute difference between the measured and estimated average median sound levels was 1.5 dBA. The Community Median Noise Level Model operates on the following parameters: motor vehicle density, mix by type of vehicle, average vehicle speed and shielding due to structures between the noise source and the receiver. Analysis of the Medford data also confirmed the very strong statistical correlation between the median sound level and the decile sound levels. Regression equations were developed and used to generate estimates of the noise pollution level in Medford, Massachusetts.
Model Study of Aircraft Noise Reverberation in a City Street
Authors: Pande L. , Lyon R. H.
Published: October 2005

Experimental studies of sound propagation from a source situated above roof top level in an urban environment have indicated the amplification and shielding effect of buildings. These experiments have been supplemented by diagnostic tests with a spark source which indicate the paths of propagation and their contribution to the received sound. A criterion for reverberation in a city street due to an aircraft is developed in terms of images formed. Charts indicating the amplification or shielding of noise from low flying aircraft are presented.
Predicting Community Response to Blast Noise
Authors: Schomer P. D.
Published: October 2005

A preliminary method is given to predict annoyance levels in the environs of a blasting area. The means are given to scale X pounds of TNT to 1 lb of TNT; buried charges and above ground detonations are also considered. Various ways to predict probable blast overpressure and spectrum as a function of distance on days exhibiting adverse weather conditions are considered. The annoyance of man by blast noise is predicted using the composite noise rating (CNR) and, for this calculation, the impulsive noise startle correction factor suggested by Kryter is added to the perceived noise level. Blast noise case histories are considered for verification of the prediction method, and the prediction method is suitable for computer computation of “equal annoyance” contours.
Diver Auditory Sensitivity: Another Look at Bone Conduction
Authors: Feinstein S. H. , Hollien H. , Hollien P.
Published: October 2005

Support for the hypothesis that divers hear primarily by bone conduction was obtained by Hollien and Brandt [J. Acoust. Soc. Amer. 46, 384–387 (1969)]. In a further test of that hypothesis, the thresholds of seven submerged listeners were obtained (at frequencies of 0.25, 0.50, 1.0, 4.0, and 8.0 kHz) under three different conditions: (1) Wearing a full 316-in. wet suit with no hood; (2) wearing a full 316-in. wet suit with a 316-in. hood; and (3) wearing a full 316-in. wet suit and hood with 14-in. rubber tubes passing through the hood to the meatuses. There were no significant differences between conditions two and three but thresholds were significantly lower in condition one. This finding provides further support for the hypothesis that underwater sound energy is transduced by bone conduction rather than by the normal middle-ear linkage.
Auditory Sensitivity of the Owl Monkey
Authors: Beecher M. D.
Published: October 2005

Pure-tone absolute thresholds for the owl monkey (Aotus trivirgatus) were determined using a tracking procedure. The animal was trained to lick a dry spout; occasional licks produced a tone, following which a lever response (detection) produced food reinforcement. No-tone trials were included to allow an estimate of the animal's false-alarm rate, which for all animals was less than 5%. Threshold testing was conducted in a sound-treated chamber, and tones were presented from a high-fidelity or electrostatic loudpseaker. On threshold sessions, the SPL was decreased 3 dB after each correct detection and increased 3 dB following each miss. The owl monkey audibility curve is characterized by best sensitivity at 8–10 kHz and +40 dB SPL cutoffs at approximately 125 Hz and 42 kHz. The high-frequency slope is very sharp, the +70 dB SPL cutoff occurring at approximately 45 kHz. The audibility curve of this nocturnal monkey is similar to those of other monkeys which have been tested. [Supported by the National Science Foundation and by the National Institute of Neurological Diseases and Stroke.]
Temporal Relations in Low-Frequency Pure-Tone Central Masking
Authors: Billings Bradley L. , Stokinger T. E.
Published: October 2005

Low-frequency contralateral masking was investigated with pulsed (500-msec) 200-Hz pure-tone maskers presented at 10, 30, 50, and 70 dB SL. Brief pure-tone maskers ranging in frequency from 170 to 4000 Hz were located near the onset or at the midpoint of the maskers. Four normal-hearing subjects participated in this experiment; a transformed up-and-down psychophysical method was utilized for the determination of unmasked and masked thresholds. Some existing experimental evidence of an indirect nature suggests that overshoot may be minimal for low-frequency contralateral maskers. The results of the present study, however, indicate that overshoot for low-frequency contralateral maskers appears greater than that which has been determined by other investigators at higher masker frequencies. Selected ipsilateral masking conditions were also investigated. These results will be discussed in relation to the contralateral masking data and to other ipsilateral masking studies.
Changes in the Relative Magnitude of Auditory Adaptation with Additional Measurement Conditions
Authors: Weiler Ernest M. , Blackmond Harry , Hippard Karen
Published: October 2005

For 10 Ss, more adaptation was measured when midplane localization was used before and after asymptotic exposure than when instructions requested midplane localization prior to exposure and loudness balances following, as previously reported by Stokinger and Studebaker (1968). However, when Ss were requested to make a loudness balance before adaptation and the midplane localization afterwards, the greatest amount of adaptation was measured. Analysis of variance revealed significantly more adaptation for conditions requesting preadaptation loudness balances than preadaptation midplane localization. Conversely, significantly more adaptation was measured for postasymptotic measurements requesting midplane localization than for loudness balances. Conclusions suggest the value of testing complete combinations of variables, if possible. A suggestion that learning may influence midplane localization versus loudness balance comparisons seems reinforced by two additional listeners who were self-trained musicians. They reported a 500-Hz tone in one ear and 4000 Hz in the other as a single dissonant chord, localized according to relative intensity of the tones. Milner's (1970) discussion of time-order versus intensity difference localization suggests relationships with learning phenomena.
Interaural Intensity Relations associated with Median Plane
Authors: Vargo Steven W. , Carhart Raymond
Published: October 2005

The interaural intensity relations associated with median plane and left- and right-ear lateralization thresholds were studied in a group of 10 normal-hearing young adults using a method of adjustment. Two tonal stimuli—250 and 2000 Hz—were presented in a counter-balanced order at an SPL of 60 dB to the fixed ear. Subjects were instructed to adjust the intensity to the variable ear in order to (1) position the intracranial sound image at the midsaggital plane following a 30-sec period during which the subject crossed and recrossed his judged median plane; and (2) position the intracranial sound image at the location where he judged the stimulus to be just perceived in the appropriate ear starting from the median plane. Results will be reported with respect to the normal range in intensity present for the lateralization positions as well as intensive magnitude (in decibels) of the ear-bias effect reported in previous studies of lateralization phenomena.
A Redetermination of Binaural Equal-Loudness Contours for Normal Hearing Observers
Authors: Yates James T. , Johnson Robert M. , Starz William J.
Published: October 2005

The relationship of perceived loudness across frequency was investigated with 40 adult subjects. A method of contant stimuli was employed whereby the subjects made equal-loudness judgments to Tones of 125, 250, 500 Hz, and 2, 3, 4, 6, and 8 kHz compared to a 1 kHz reference. Equal-loudness contours were established at 10-dB intervals from 18 to 108 dB SPL. An especially constructed apparatus generated, programmed, and regulated the stimuli and produced reference and comparison pure tones with less than 1% harmonic distortion at all frequencies tested. Some important differences between the present results and those of previous authors were noted. First, the equal-loudness contours were of less severe slope at the lower frequencies than those of previous investigators. Second, the characteristic notch at 8 kHz shown by previous studies was seen, but was shifted to 6 kHz.
Sound Transmission from Deep to Shallow Water
Authors: Urick R. J.
Published: October 2005

The propagation of sound from deep to shallow water was studied by a direct field experiment. Two aircraft were used: one to drop explosive sound signals detonating at 800 and 2000 ft out to 100 miles in two directions off the coast of Delaware, the other to monitor a pair of sonobuoys located in 100 f of water at the break of the continental shelf and at a point 20 miles toward shore in shallow water. The field-recorded data were converted to transmission loss by standard techniques. Surprisingly good transmission was observed. The 100-f receiver showed lower transmission losses for the deep axial shots than it would have if it had been located on the channel axis in deep water. This good transmission is possibly due to two causes: a kind of focusing effect, wherein the continental slope acts to increase the density of rays at its top, plus a near-optimum slope condition enabling axially transmitted sound to take but a single bounce up into shallow water. The 800-ft shots were also well-received in spite of the absence of all-water ray paths, probably as a result of conversion to seismic waves along the slope.
Noise Signature of an Aircraft in Level Flight over a Hydrophone in the Sea
Authors: Urick R. J.
Published: October 2005

An aircraft flying over a hydrophone in the sea produces a noise signature whose magnitude and duration depend on such parameters as hydrophone depth, water depth, and flight altitude. This signature represents sound reaching the hydrophone in four different ways: via a direct refracted path, via one or more bottom reflections, via the so-called lateral wave, and via sea-surface scattering. Of these, the refracted path is the most important and easiest to evaluate. Generalized contours for the nearfield of this component are given; in the farfield it is shown that the source in air can be replaced by an equivalent in-water source having a cosine-squared directivity pattern and a source level 7 dB less than that of the real source. In a field experiment, a Navy P3 Orion turboprop aircraft flew over hydrophones at two depths in deep water. The brief noise signature, lasting but a few seconds, was found to be accounted for satisfactorily by the refracted sound field. However, under conditions not existing in the field experiment, such as in shallow water, in rough seas, or at very shallow depths, it is conceivable that the other contributors to the total underwater sound field may become important.
Lloyd Mirror Effects in Sounds from Aircraft
Authors: Harris B. , Torak S. , Lange G.
Published: October 2005

In the automatic monitoring of environmental noise, it would be useful to use vertical directivity as an aid in discriminating between noise from overflying aircraft and noise from vehicles. However, the benefits of utilizing directivity can be mitigated by the Lloyd mirror effect in which the aircraft noise not only propagates as a direct ray but as ground-reflected ray as well. The purpose of this experiment was to measure the Lloyd mirror signals from actual aircraft moving at reasonable speeds. These signals were broad-band recorded using omnidirectional microphones. Since the Lloyd mirror effect is more apparent in narrow-band signals as consecutive reinforcements and cancellations between the direct and reflected ray, the signals were narrow-band filtered using the fast Fourier transform algorithm. Signal processing was then used to remove the statistical variations of the aircraft noise as well as the variations of the local ambient noise. The final results show amplitude variations of the order of 10 dB at the times predicted by the theoretical models. This means that utilization of sound directivity requires microphones with nulls both at the top and bottom of the microphone pattern.
Sound-Speed Dispersion and Fluctuations in Coastal Ocean Waters
Authors: Rautmann Juergen , Medwin Herman
Published: October 2005

In-situ upper ocean measurements have revealed the existence of significant dependence of the speed of sound on frequency over the range 25–80 kHz. At 4.3-m depth the variation of speed with frequency went through a large resonancelike peak of +6 m/sec and dip of −3 m/sec relative to the predictions for bubble-free water. The behavior is attributed to near surface resonant bubbles with an identifiable population around radius 55 μ at 4.3 m below the surface and a lesser population centered around 125 μ with numbers decreasing with depth to 14.3 m (in 16-m-deep water). The temporal fluctuations of the speed were principally at surface wave orbital frequencies and showed near-Gaussian probability density functions with rms values from 0.27 to 0.52 m/sec. The Gaussian character is disturbed and the rms value is greater at the dispersion center frequencies. [Supported by Naval Ship Systems Command.]
Project Hiawatha Revisited: Application of FFP to Lake Superior Attenuation Experiment
Authors: Browning D. G. , Powers M. R. , Mellen R. H. , DiNapoli F. R.
Published: October 2005

Owing to the pressure dependence of the temperature of maximum density in fresh water, the sound channel in Lake Superior is extremely weak. The fast field program (FFP) is applied to determine if the bottom loss is significant for sound channel propagation in the kilohertz region. The values of attenuation are computed for the frequency range 500–10 000 Hz and compared to values obtained from the Lake Tanganyika experiment.
Effects of Interruption on Noncontextual Speech
Authors: Hopkinson N. T. , Bilger R. C. , Wang M. D.
Published: October 2005

The distortion of speech by interruption and its effects on intelligibility were studied in six listeners with normal hearing. Rates of interruption were varied between 2 and 250 ips, and duty cycles were 50%, 25%, and 12.5%. The signals were a closed message set of 16 CV-nonsense syllables that had been recorded on a drum. The portion of the CV-syllable presented was varied systematically, that is onset of the syllable was delayed parametrically. Random presentation of signals was accomplished by use of a computerized system. In conditions of 50% D. C., at the lowest rate of interruption, transmitted information was highest when there was no delay in onset of interruptions; however, transmitted information dropped significantly when the delay reached a critical time with respect to the period of time the signal was on. At the highest rate of interruption, transmitted information remained high in all conditions of delay in onset of interruption. Duty cycles less than 50% showed lower amounts of transmitted information. Feature analyses in terms of transmitted information will be reported for the various conditions.
Temporal Processing of Speech
Authors: Kuhl Patricia , Speaks Charles
Published: October 2005

Differences between intelligibility of interrupted and compressed speech were examined by holding speech information constant and varying duration of silent intervals between speech segments. We hypothesized that interrupted speech would be more intelligible than compressed speech because silent intervals could be used to “process” the fragmented speech segments. Sentences and words were sampled by computer with a 50% duty cycle. Two discard intervals, 125 and 50 msec, were used. Sample segments were retrieved and arranged with varying silent intervals between segments (3 less than, 1 equal to, and 2 greater than the duration of original discard intervals), producing six experimental conditions. When sample segments for the sentences were abutted with no silent interval (compression), intelligibility deteriorated. When silent intervals were inserted, intelligibility improved regardless of whether the silent interval was less than, equal to (interruption), or greater than the original discard interval. Since intelligibility did not vary significantly with the amount of “processing” time inserted, perhaps the silent interval simply “marked” the place where speech had been removed. Neither the “processing time” or “marking” hypotheses explain the results for word intelligibility.
Perception of Voice Timing in Spanish Stop Consonants
Authors: Abramson Arthur S. , Lisker Leigh
Published: October 2005

In earlier acoustic analysis of Spanish, we showed that speakers differentiate voiced /bdg/ from voiceless /ptk/ in word-initial position by means of voice onset time (VOT), the temporal relation between the onset of glottal pulsing and acoustic features of supraglottal articulation. More recently, we demonstrated the perceptual efficacy of VOT for Thai, a language with three categories along the timing dimension, and English, a language with two categories. The two Spanish categories differ from those of English in their placement of the phonetic boundary. Spanish voiced stops are produced with VOT values that lead the consonant release, while voiceless stops show VOT upon release or immediately thereafter. In the present study, native speakers of Spanish identified randomized recordings of stops synthesized with VOT varying in small steps. Labeling responses showed a fairly good fit between production and perception differing from English in the expected direction. The listeners also discriminated the VOT variants in a psychoacoustic test format. The latter results, along with the earlier ones for English and Thai, indicate that discriminability is primarily determined by specific language experience, although general phonetic categories may have some effect.
How Competing CVs, Vowels, or Synthetic Bleats Affect Dichotic Scores of Temporal Lobectomees, Hemispherectomees, and Normals
Authors: Berlin C. I. , Lowe-Bell S. , Porter R. , Berlin H. , Thompson C. L.
Published: October 2005

Three normals, three hemispherectomees, and three temporal lobectomees were stimulated dichotically with CVs in the contralateral ear (left ear for normals) always at 75 dB SPL; the ipsilateral ear (right ear for normals) received either a different CV, a “bleat,” or an envelope-shaped vowel. The ipsilateral ear was stimulated at intensities ranging in 10-dB steps from SRT to 75 dB SPL. Data show that an ipsilateral “bleat” had suppressive capabilities even with normals, despite little intelligibility of its own. All ipsilateral stimuli suppressed the patients' contralateral ears drastically compared to the normals even if the ipsilateral stimuli were 20–30 dB less intense than the contralateral CVs. The amount of contralateral CV intelligibility loss caused by a simultaneous signal in the ipsilateral ear may be a sign of the latter's “speechlike” qualities.
Temporally Segmented Speech
Authors: Huggins A. W. F.
Published: October 2005

Alternated and interrupted speech both show a minimum of intelligibility when the bursts of speech reaching the listener last about 150 msec. A similar effect occurs with “temporally segmented” speech, which is made by splicing silent intervals into a recording of continuous speech, thus dividing it up into “speech intervals” separated from each other by “silent intervals.” The advantage of this material is that the durations of speech and silent intervals can be independently varied, without discarding any of the speech. An earlier experiment [see MIT Res. Lab. Electron., Quart. Progr. Rep., No. 103 (1971), p. 126.] suggested that the dip in intelligibility is actually due to two separate effects: (1) the probability that a speech interval will be recognized decreases as its duration decreases and (2) the probability that signal parameters can be followed from one speech interval to the next decreases as the duration of the intervening silent interval increases. Experimental support for this view has been obtained using temporally segmented speech (1) by varying the duration of speech intervals with silent intervals held constant and (2) by varying the duration of silient intervals, with speech intervals held constant. [This research was supported by NIH Grant No. NSO4332.]
Reflection of an Elastic Wave from a Free Surface in Quartz
Authors: Jones Gerald L. , Henneke Edmund G.
Published: October 2005

The reflection of a plane, elastic wave in quartz is discussed. Numerical solution has been obtained for quasilongitudinal and quasitransverse waves incident upon the xy, xz, and yz crystal planes for angles less than critical. The angles of the reflected wave vectors, the associated reflection coefficients, and the directions of the energy flux vectors for the reflected waves have been calculated. The numerical results indicate that an incident critical angle occurs when a reflected wave has a Poynting vector parallel to the boundary as suggested in an earlier paper [E. G. Henneke II, J. Acoust. Soc. Amer. 51, 210 (1972)]. In some incidents, the wave vector of the reflected wave may be pointing in a direction in free space, but if its Poynting vector is directed internally, the reflection coefficient is nonzero. In addition, it has been found that for some incident angles greater than critical, three quasitransverse waves may be reflected, and the boundary conditions are satisfied without the necessity of assuming a surface wave. [This work was supported by the National Science Foundation].
Four-Pole Parameters for Hyperbolic Horns
Authors: Molloy Charles T.
Published: October 2005

It is the purpose of this paper to define, outline the derivation of, and show some applications of the four-pole parameters of hyperbolic horns. These horns were first discussed by V. Salmon [J. Acoust. Soc. Amer. 17, 199, 212 (1946)] and include as special cases exponential, catenoidal, conical, and cylindrical horns. Their four-pole equations are a pair of linear equations relating the pressure and volume velocity existing at the throat to the same quantities at the horn mouth. The coefficients in the equations are called the four-pole parameters. The equations may be written in matrix format and are very convenient for analyzing acoustical systems containing hyperbolic horns as elements (as well as combinations of many other acoustical elements). The four-pole parameters for the general hyperbolic horn and its important special cases will be given. Examples of their uses will be given including: throat impedance; insertion loss; horn-type sidebranch filters; horns with arbitrary area functions; loud speaker systems; etc. It is pointed out that, because the fourpole parameter technique involves only 2×2 matrices, it is particularly well adapted for use with high-speed digital computers.
Conical and Sinusoidal Horns as Sound Traps
Authors: Nagarkar B. N. , Dhingra H. C. , Finch R. D.
Published: October 2005

It is shown that the application of Webster's theory to sinusoidal and conical horns leads to the conclusion that such horns, used as receivers and terminating in cusps, should act as sound traps. This result is further discussed in light of three-dimensional conical horn theory. Experimental work to verify the theory is in progress.
Transmission-Line Analogs For Stacked Crystals with Piezoelectric Excitation
Authors: Ballato A. , Bertoni H. L. , Tamir T.
Published: October 2005

A piezoelectrically driven thickness-mode structure containing any number of stacked crystal layers is shown to be rigorously representable by equivalent circuits, which consist of transmission lines and lumped elements. Each crystal stratum is homogeneous but may be arbitrarily anisotropic; the piezoelectric excitation may be applied to a single plate or several plates in combination, its field orientation being either normal or parallel to the layers. The equivalent representation is derived by considering a canonic two-layered element, which is thereafter utilized as a building block for the analysis of general multilayered stacks. In such a configuration, the material in each layer is accounted for by at most three acoustic transmission lines; each layer boundary, on the other hand, is represented by lumped transformer elements that serve to interconnect all of the six transmission lines arriving at that particular boundary. The piezoelectric drive appears as an additional simple network which is also connected to the coupling transformers. This establishes a procedure for a systematic treatment of theoretical and practical problems concerning crystal resonators and filters, delay lines, pulse and code generators, and related applications.
Effect of Initial Stress on the Propagation of Flexural Waves in Elastic Rectangular Bars
Authors: Clark J. A. , Durelli A. J. , Laura P. A.
Published: October 2005

The dynamics of continuous media subjected to initial stress is of great interest in several fields of applied science and technology: geophysics, oceanography, underwater acoustics, and structural design. Pioneering analytical work in this field was done by Biot. Few contributions have been made, however, to the experimental treatment of the problems of determining dynamic stress distributions within statically prestressed continuous media. The present paper deals with an experimental analysis of the propagation of flexural waves in prismatic elastic bars with and without prestressing. A complete, direct, full-field optical determination of dynamic stress distributions associated with the flexural waves is obtained by a combination of photoelastic and interferometric measurements. The effects of prestressing by axial tension, axial compression, and pure bending are illustrated. Comparisons are made with an approximate theory. The results are extended to bars of other materials by scaling laws.
“Clackers” Noise
Authors: Holmes D. G. , Lyon R. H.
Published: October 2005

Impact sounds are normally the result of acoustic radiation from the vibrations of the impacting bodies. The energy pathway is from the preimpact kinetic energy of translation, via the energy of vibration, to the radiated acoustic energy. An alternative mechanism exists, which does not require vibrations of the impacting bodies. The sound radiation is a result of the sudden accelerations of the bodies during impact, and can be said to draw on the kinetic energy, not of the bodies themselves, but of the added mass of the fluid motion. The sound radiated from the impact of two small, hard spheres is a good example. Experiments are described which identify clearly the sound source as the sudden accelerations due to impact; vibrations of the spheres make a negligible contribution to the total energy radiated. The energy spectrum and directivity of the radiation agree very closely with calculated values.
Transient Response Analysis and Experiment on a Transducer with an Intermediate Layer of a Quarter Wavelength for the Generation of Short Ultrasonic Pulses
Authors: Kikushi Yoshimitsu , Okuyama Daitaro , Kasai Chihiro
Published: October 2005

In the field of ultrasonic flaw detection, ultrasonic diagnosis, etc., generation and detection of short ultrasonic pulses are very important for high range resolution. In this paper, the transient characteristics of the transducer with an intermediate layer of a quarter wavelength is analyzed by an impulse response method, and the optimum acoustic impedance of the layer for the generation and detection of the shortest ultrasonic pulses is given as a function of specific impedances of the transducer and an acoustic load. The features of this analysis are that the calculation is much simpler than that in the usual frequency response method, and especially that the pulse length which is the final object of the art can be directly derived. From the calculation, it is found that the transducer with the layer of the optimum impedance can generate fairly short ultrasonic pulses without any acoustic backing, and that consequently the transducer sensitivity is considerably higher than that of the usual transducers with backing. Experiments were carried on in megahertz range with PZT disks using Bakelite or tungsten-resin mixture for the intermediate layer. The results showed fairly good agreement with the theory.
A New Broad-Band Ultrasonic Technique with Biomedical Implications. I. Background and Theoretical Discussion
Authors: Jones Joie Pierce , Wright Hugh A.
Published: October 2005

Ultrasonic techniques presently used for medical diagnosis make use of narrow-band or single-frequency pulse-echo devices. Recent studies at BBN indicate that a new broad-band technique should significantly improve present diagnostic capabilities. This new technique makes use of acoustic impulses, which are short in time but broad in frequency content, and a time domain deconvolution procedure. The result is a temporal waveform which can be related to physical parameters such as specific acoustic impedance and frequency-dependent attenuation. Thus, the new technique allows us to measure quantitatively to a high degree of accuracy the specific acoustic impedance at an arbitrary position within a test object.
A New Broad-Band Ultrasonic Technique with Biomedical Implications. II. Preliminary Experiments Involving Human Skull Bone
Authors: Jones Joie Pierce , Wright Hugh A.
Published: October 2005

A broad-band acoustic pulse, produced by a spark source operating in water, was used to illuminate several test objects. The reflected signal was analyzed using a deconvolution procedure and the specific acoustic impedance obtained as a function of time. In one particular experiment, a series of modest impedance differences were accurately resolved behind a section of human skull bone.
Acoustical Pattern Recognition of Knee Joint Diseases
Authors: Chu M. L. , Gradisar I. A.
Published: October 2005

An improved sound retrieval system and more accurate analysis technique were developed to extract distinguishing acoustical signatures of sound emitted by normal and pathological knee joints during active movements. Background noise was minimized using the principle of “noise cancellation” with a double microphone-differential amplifier setup. Two identical sensitive condenser microphones and an FM recorder with flat responses in the audio range were used. The knee noise was found to be transient in nature and recordings were made on magnetic tape “loops” for “real time” analysis. Waveform, spectral, and statistical (correlation and probability) analyses were performed. Preliminary studies of 30 knee recordings covering normal, rheumatoid arthritic, degenerative knees, and knees with Reiter's syndrome showed that their respective waveforms, spectral patterns, and statistical properties are, on the average, unique and proved to be a promising nondestructive diagnostic tool for early detection of the type and extent of knee joint damage.
Reflection of Acoustic Waves from a Stably Stratified Atmosphere
Authors: Hall F. F. , Neff W. D.
Published: October 2005

Echoes obtained with a monostatic acoustic sounder have to date been attributed largely to random thermal structure in the atmosphere. A dependence of echo strength on the sound beam zenith angle has now been verified for certain highly stable conditions in the planetary boundary layer. Maximum returns are obtained with a vertically pointed beam. The regions of strong return correlate spatially with temperature striations which are essentially horizontal. Measured microthermal structure of such inversion layers can account for the excess or Fresnel acoustic reflection observed. This excess echo may be several times stronger than scattering from random thermal structure. Examples of simultaneous returns at zenith angles of 0° and 45° are presented, and the theory of normal acoustic reflection from realistic temperature inversions discussed.
Gradient Microphone Performance within a Gas Mask
Authors: Morrow Charles T.
Published: October 2005

It has been shown previously that a pressure gradient microphone is so insensitive to standing wave effects in a diving mask that it provides excellent intelligibility, but it does not compensate for detuning of the first formant. Detuning by a gas mask is a more major effect and more complicated—the first two formants are split into a triplet. The uppermost resonance of the triplet, corresponding closely in frequency to the original second formant, is attenuated. The gradient microphone, close to the lips, restores intelligibility by deemphasizing the middle resonance of the triplet and restoring emphasis on the uppermost.
A Wearable Pocket Noise Dosimeter
Authors: Basch M. W.
Published: October 2005

A noise dosimeter that meets the ANSI Type II Sound-Level Meter standard and accumulates the Walsh-Healey percentage is discussed. The dosimeter is composed of two parts—a small pocket unit that accumulates and stores the digital data representing the Walsh-Healey percentage and an indicator unit that provides a digital readout on a light emitting diode display. The indicator unit also has provision for calibrating the pocket unit (including the microphone) and provision for checking batteries. Newest technology has permitted the pocket unit to be made very small and light. It includes a small ceramic microphone, a true rms detector with more than 15-dB crest factor capacity, and an extremely low-power MOS digital counter to store the Walsh-Healey percentage. It weighs but 7 oz and runs for over 300 h on an ordinary 9-V “transistor” battery. Frequency response measurements will show the effects of the proximity of the wearer.
Education by Noise Control Projects
Authors: Haag F. G.
Published: October 2005

Noise control presents many interesting possibilities for student-project-type courses. The projects provide a natural motivation at a low cost to educational benefit ratio. Projects have been successfully conducted with undergraduates in general education, and with undergraduate and graduate engineering students. Among the more recent projects are effect of snowmobile noise on mice, standing wave tube, visible sound apparatus, computer simulation programs, muffler design, wave-tank analogy, noise reduction demonstrator, noise cancellation device, noise reduction of a computer card reader, and the effect of noise on plants. Since most noise control projects involve the student in value judgments, an auxiliary educational benefit results.
Design and Operation of a Continuous, Areawide Aircraft-Noise Monitoring System
Authors: Bricken Gordon , Hilliard John K.
Published: October 2005

A five-station, permanent, 24-h centralized aircraft noise monitoring system has been installed in the community surrounding Orange County Airport, Santa Ana, California. This paper will discuss the design concept, the results obtained from initial tests involving measurement of over 1000 flights, the practical experience gained from the installation, the true value to the community, and the potential for effective noise management programs. In addition, the measurement data will be used to demonstrate the value of the California noise index CNEL.
Implementation of an On-Line Speaker Verification Scheme
Authors: Lummis R. C.
Published: October 2005

The implementation is described of an on-line version of the scheme for speaker verification reported previously. A Honeywell DDP-516 computer is used, with microphone and keyboard input, disk storage, and graphic output. Utterances are converted to pitch and gain contours and compared with similar functions fetched from disk that represent past vocal behavior of the speaker whose identity is claimed. The comparison process includes automatic temporal registration. Special features of the implementation include the ability to update stored reference patterns at will so as to incorporate the features of new utterances, and a graphic display that effectively illustrates which portions of a test utterance are within the programmed limits of acceptability.
On Evaluating Formant Synthesizer Control Signals. II
Authors: Wathen-Dunn W. , Michaels S. B. , Kriger L. V. , Soron H. I.
Published: October 2005

An attempt to evaluate the effectiveness of three sets of formant synthesizer control signals, derived by different means, has utilized VCV utterances in which the C's were one of the six stop consonants and the V's were one of the six vowels, /i, e, a, o, u, Λ/. The stops are the most quickly articulated phonemes and the first five of the vowels are tense and are thus articulated at positions most removed from the central articulatory configuration, which is represented by the last vowel, /Λ/. Use of these utterances is predicated on the idea that the stops and the tense vowels make the greatest demands on synthesizer performance and are hence most suited for evaluation. Two tests have been run: (1) an identification test for each of the consonants and (2) comparisons of the same consonant produced by different means. Results for the labial stops, /b, p/, were presented at the 82nd Meeting of the Society in Denver, and this paper will present the results for the remaining stops, /d, t, g, k/.