bluuebunny/crossref_metadata_2025 huggingface dataset:
Modal Analysis of Sound Propagation in a Circular Duct and Application to In-Duct Sound Measurements
Authors: Bolleter U. , Chanaud R. C.
Published: October 2005

The work of Dyer [J. Acoust. Soc. Amer. 30, 833–841 (1958)] was extended to derive expressions for the sound pressure cross spectrum and cross correlation within a hard circular duct and with arbitrary boundary conditions. Results are expressed either in terms of a source plane pressure cross spectrum or in terms of a modal spectral distribution. An internal impedance concept was used to account for the source end boundary condition. Reflected waves are included, the termination being specified by a local impedance. In order to estimate sound power from pressure cross-correlation measurements in the cross-mode region, programs were written to compute the exact sound power and the error of the estimate by use of the plane-wave formula for given measuring positions, given modal spectra, and given modal correlation. Depending on the type of source, optimum measuring positions were determined. Methods to measure modal spectra of a certain source were developed. [Essential support of this work was given by Air Conditioning and Refrigeration Institute.]
A Comparison of the Sound Fields Observed near a Triplane, a Spherical Shell, and a Helium Balloon
Authors: Delsasso L. P. , Knudsen V. O. , Walker B. E.
Published: October 2005

Continuous and pulsed sounds from a point source were recorded as a microphone moved with constant velocity a distance of 22 ft along the length of an anechoic room. From the sound fields observed when a triplane, a spherical shell, and a helium balloon were successively introduced between the source and the microphone, the reflection, refraction, and interference characteristics can be estimated. The reflection and interference patterns for the triplane and the spherical shell agree with previously published results. The helium balloon records show that the sound level has been reduced in the “shadow” by 5–8 dB and that the reflection coefficient normal to the surface at 4000 Hz is 0.2. A short motion picture showing the interference refraction details will be shown. The change in reverberation provided by introducing twenty 40-in. helium balloons in a 19×30×24 ft reverberation room will be demonstrated by recorded speech and music.
Radiological Findings in the Study of Vocal Registers
Authors: Appleman D. Ralph
Published: October 2005

Radiological techniques were used in the kinesiological analysis of the structures of articulation and the phonatory tract during the register changes at the primary points of passage in three male and three females voices. Vowels used were /ɛ/, /ɑ/, /ô/. Register changes were examined by means of radiology, tomography, and cinefluoroscopy. The radiology and tomography variation in the movement of the physical structures are determined by superimposition of negatives. In cinefluoroscopy, analysis was made by perceptoscope projection. All phonation was synchronized with recorded sound. Analysis of the data reveals that direction of the variation of physical-structure displacement is constant but that the degree of displacement is inconstant. For each register change, the velum and uvula move to the pharyngeal wall but vary in length, tension, and thickness. Relaxation of the point stricture at the inner orifice makes the system more tightly coupled. The vestibule increases its dimension anterioposterially, laterally, and vertically. The increase in the vertical dimension is caused by a lowering of the vocal folds. The vestibular entrance is altered by proximity of the epiglottis to the pharyngeal wall. The laryngeal movement is always one of lowering accompanied by a forward tilt.
Binaural Signal Detection: Analysis of Decision Spaces
Authors: Pastore R. E. , Sorkin R. D.
Published: October 2005

This paper is an extension of the binaural signal-detection study reported by the authors at the Philadelphia meeting [J. Acoust. Soc. Amer. 46, 125–126(A) (1969)]. The task was a two-interval, four-alternative task. In the first interval, a standard tone, V0, was presented simultaneously to each ear. During the second interval, one of four events occurred: (1) V0 was presented to both ears; (2) V0 presented to the left ear, V0+ΔV to the right; (3) V0+ΔV left, V0 right; and (4) V0+ΔV presented to both ears. In addition to this four-choice task, individual paired comparison experiments were conducted in which each of the four events was compared with every other event, e.g., lateralization tasks, detection tasks, etc. Decision spaces for the complex task were constructed by use of multidimensional scaling techniques and were highly similar to the decision spaces based on the d's of the individual paired-comparison experiments. For several levels of continuous noise, decision spaces were developed for the Nu−S0, Nu−Sπ, and Nu+0−S0 stimulus conditions. The data were also analyzed in terms of the estimated between-channel correlation, and the facilitative-inhibitory interactions between channels. The decision spaces that resulted have two interpretable dimensions: a lateralization dimension and a net signal-level dimension.
Talker Recognition on Large Populations
Authors: Wachter Kenneth W.
Published: October 2005

Automatic talker recognition based on single-word utterances has been investigated for two populations of 172 talkers each. Five replicates of the words “one,” “two,” “three,” “four,” and “nine” were fed through a 40-channel frequency analysis covering a 20- to 2900-Hz range. The output was digitized and summed over utterance duration. Thus one vector in 40-space represents an utterance. Statistical discriminant analysis determines a set of linear combinations of these 40 coordinates that maximally separate talker centroids relative to the variation of the replicate utterances around the centroids. The first few of these new “CRIM-coordinates” may be used to restrict the set of talker centroids with which an unknown utterance need be compared. Centroids not thus excluded are ranked in order of their likelihood to match the unknown, on the basis of weighted Euclidean distances in CRIM-coordinate space. Efficient recognition strategies utilizing these methods have reduced running time of the algorithm per unknown to 0.18 sec (costing $0.02) on a GE 635 computer. On word “one,” for 82% of the unknowns the first most likely match was correct; for 92% either the first or second; for 95%, one of the first five. Combining information from different words can improve results still further.
Hearing in the Monkey (Macaca) : Absolute and Differential Sensitivity
Authors: Stebbins William C. , Pearson Richard D. , Moody David B.
Published: October 2005

Monkeys were trained to make an observing response that was occasionally followed by a pure tone or by a change in the frequency or intensity of a continuously pulsed pure tone. A correct report of the stimulus or stimulus change was reinforced with food. Failure to report had no consequences, but an incorrect report produced a brief time-out from the experiment. Thresholds were determined by both tracking and constant-stimulus methods. The monkey's hearing is similar to man's at the lower frequencies (below 8 kHz) but extends to 45 kHz or an octave above the upper limit of human hearing. For tones below 8 kHz at 40 dB and 60 dB above threshold, the monkey's differential acuity for both frequency and intensity is slightly less than that of man. Differential sensitivity (ΔI and ΔF) for the monkey was found as high as 30 kHz at 40 dB above absolute threshold. [Research supported by PHS grants.]
New Hybrid Real-Time Spectrum Analysis System
Authors: Winkler Joerg H. , Blaesser H.
Published: October 2005

This contiguous-band analyzer for the frequency range of 1.8 Hz to 45 kHz combines in its detector stage a number of analog short-term averagers with one central digital long-term integrator. This allows a significant decrease in sampling rate while maintaining the same accuracy. Running integration can be performed. Integration times up to several hours can be selected without changing the sampling rate. Over-all detector accuracy is 0.5 dB over a dynamic display range of up to 60 dB with a digital resolution of 0.1 dB.
Significance of Osmotic Pressure Gradients During Cochlear Perfusion
Authors: Moscovitch D. H. , Gannon R. P.
Published: October 2005

The effects of ions and drugs on cochlear function can be studied by perfusing scala tympani with artificial perilymph solutions containing those substances. In the past, this method has been used both with and without compensation for differences in the osmotic pressure of the test solutions. We studied the significance of perfusate osmotic pressure of solutions between 290 and 400 mOsmols/L (approximately 1–1.4 times normal) in guinea pigs by perfusing scala tympani with artificial perilymph solutions made hypertonic with sucrose. The cochlear microphonic-potential (CM), summating-potential (SP), and action-potential (AP) responses to 7-kHz tone bursts were recorded by differential electrodes in the first turn. The solutions with osmolality 316 mOsmols/L and higher significantly altered the cochlear potentials. The normally negative SP became positive. The AP was depressed to 50% of the preperfusion amplitude for up to 8 min after perfusion. The CM was sometimes augmented after a perfusion. [Supported by the Medical Research Council of Canada.]
Acoustic Imaging with a Focused Light Beam
Authors: Kessler L. W. , Korpel A.
Published: October 2005

A method is described whereby sound field distributions can be determined within optically transparent media with a focused beam of light. The optical methods that are well known employ a collimated beam of light and yield information that is averaged over the entire light-sound interaction region. With a focused light beam, however, the sound pressure at the focal region alone can be determined. The method makes use of either the periodic refraction of part of the light beam by the sound field or of acoustically induced birefringence, if it exists. The former has been described in a preliminary report by the authors [Intern. Symp. Acoust. Holography, 2nd March 1969]. The resolution obtainable is determined by the focal spot size and is approximately ΛF/D along the direction of the light beam, where Λ is the acoustic wavelength, F is the focal length of the lens, and D is the diameter of the light beam before focusing. The technique is useful for ultrasound microscopy and results of applications to acoustic imaging and holography will be presented.
Techniques for Identifying Sources of Noise
Authors: Fieldhouse K. N.
Published: October 2005

Reducing noise in a product requires identification of specific frequencies and then tracking these frequencies to the components producing them. Electronic filters are used to divide the over-all noise into a series of noise levels associated with specific frequency bands. Two types of electronic filters are generally used in noise analysis: the constant percent or octave bandwidth system and the constant bandwidth system. The constant percent system rapidly analyzes the areas of maximum noise, but lacks resolution to give a detailed knowledge of the frequency spectrum. The ultimate in spectrum definition is obtained with a narrow fixed-bandwidth filter system. This paper compares the two systems in analyzing noise spectrums; and discusses an automatically tuned fixed-bandwidth system, i.e., a tracking filter, in analyzing rotating machinery noise, random vibrations, and determination of mechanical and acoustical impedance.
Evolution of Explosion Pressure-Wave Characteristics in the Region Relatively Close to the Origin
Authors: Arons A. B.
Published: October 2005

The pressure pulse from an underwater explosion has an involved shape, consisting of the leading shock wave, followed by subsequent rarefaction and compression phases if the explosion occurs at sufficient depth to allow one or more subsequent oscillations of the gas globe. Propagation of the pulse is accompanied by progressive changes in shape (and therefore of “Fourier spectrum”) stemming from finite amplitude effects and selective dissipative attenuations. Alteration and redistribution of the energy content of the pressure wave is an essentially nonlinear phenomenon and is still in progress at ranges of the order of 104–105 charge radii. Successive reflections from surface and bottom further complicate the shape of the wave and introduce additional selective attenuations.
Spheroidal Wave Functions: Their Use and Evaluation
Authors: Baier R. V. , Van Buren A. L. , Hanish S. , King B. J.
Published: October 2005

The Helmholtz or scaler wave equation (▿2 + k2) ψ = 0 is separable in both oblate and prolate spheroidal coordinates. Solutions to this equation constitute an essential element in the numerical calculation of the diffraction, radiation, and scattering of acoustic and electromagnetic waves by spheroids. They also find considerable application in other areas such as signal processing and nuclear models. FORTRAN computer programs have been developed to evaluate both efficiently and accurately the radial and angular parts of the solution in both oblate and prolate spheroidal coordinates. Extensive tables of oblate and prolate radial functions containing entries for values of h up to 40.0 and for values of the prolate radial coordinate as low as 1.00000001 are being published. (h = kd/2, where d is the interfocal distance.) These tables as well as the capabilities of the capabilities of the various computer programs are discussed. Examples illustrating the use of this coordinate system in acoustic radiation calculations are presented.
Effect of Acoustic Streaming on Diffusional Mass Transfer
Authors: Fogler H. S. , Lund Kasper
Published: October 2005

Upon the passage of an acoustic wave through a duct, one can form time-independent vortices. This phenomenon, which is commonly called acoustic streaming, can enhance mass transport by superimposing a convective transport on a diffusive transport. The differential mass transport equation was coupled with the second-order time-independent acoustic streaming equations in a rectangular duct and solved by a finite difference technique. A frequency range of 5–800 kcps in liquids and gasses was investigated for different acoustic and physical parameters such as first-order velocity amplitude, diffusivity, viscosity, duct height, and length. Preliminary results show increases in the mass flux of up to at least 120% above the normal diffusive transport. Possible applications to membranes, catalysts, and drying will be discussed along with a complete physical and mathematical description of the phenomena.
Mechanically Simulated RDT
Authors: Ryan William W.
Published: October 2005

The construction and performance of a device for mechanically simulating rotating directional transmissions (RDT) of active sonar are described. Pressure envelopes and frequency functions of the mechanically generated signals are compared with analogous theoretical and experimental results for an electronic scanner. These comparisons show that mechanical generation yields a realistic simulation of operational RDT. [This work was performed under contract with Naval Ship Systems Command.]
Sound Generation by Turbulent Wall Jet Flow over a Trailing Edge
Authors: Hayden R. E. , Chanaud R. C.
Published: October 2005

A method for predicting the amount and directivity of sound generated by turbulent flow over a trailing edge was developed for the case where the acoustic wavelength is less than the characteristic dimensions of the surface. This case is important for sound radiated by flow over surfaces such as large fan blades. An analytical and experimental study is presented using for a flow model a turbulent wall jet. The wall jet had three different flow regions exhibiting behavior like a turbulent boundary layer, two-dimensional turbulent flow, and radial type or three-dimensional turbulent flow, respectively. Application of Curle's solution for sound radiated by a distribution of pressure over a rigid surface is extended to the case where a trailing edge exists. A similarity model is given relating the sound power to mean flow parameters. The diffraction of the dipole sound by the edge was analyzed and measured. The maximum acoustic intensity was found to be along the plate in contrast to the free-field dipole, which has minima in that plane.
Acoustic Properties of Transducer Window Materials
Authors: Ryan William W.
Published: October 2005

Acoustic properties of Lucite, silicone rubber (GE RTV-615), and two electrical potting resins (Scotchcast No. 2 and No. 221) have been measured. The properties measured are ρ0, c0, and the attenuation loss over the decade band of 50–500 kHz. Time delays in 1.0-in thick samples were measured by using short CW pulses. Measurements were made at a constant temperature. Scotchcast No. 2 and Lucite have very similar characteristics. Both have ρ0c0 values of about twice that of water. The average attenuation for these materials is about 2.5 dB. RTV-615 has a ρ0c0 approximately two-thirds that of water with an average attenuation of 1.0 dB. Scotchcast No. 221 has a ρ0c0 value approximately 1.25 that of water. [This work was supported by the U. S. Office of Naval Research.]
Limiting Sound-Pressure Levels in Aircraft Passenger Stereo Entertainment Systems
Authors: Cohen Abraham B. , Joscelyn Edwin R.
Published: October 2005

In choosing the electrical parameters for aircraft passenger entertainment systems, the peripherally important factors of size and weight of the electronic equipment will depend upon the required SPLs necessary to be developed at the ear to overcome the ambient noise level in the cabin. This required SPL will in turn be determined by the seat electrical transducer conversion efficiency and the transmission characteristics of the combined pneumatic tube and its ear tip terminating in the ear. Using a simulated cabin section of an aircraft outfitted with actual passenger seats and arm-rest-installed seat-control units housing both the transducer and the volume control, an analysis was made of the listening requirements of a mixed population of 30 people. In an ambient noise level of 86 dBA, the range for normal listening levels for music was 83–95 dB and for speech 88–104 dB; for the loudest acceptable levels the range was 93–115 dB for music and 89–119 dB for speech. For these required SPLs, correlation has been made with the required electrical input to the transducer developed for the new generation of passenger aircraft.
Surface Dipole Strength for Flow Past Airfoils
Authors: Siddon T. E.
Published: October 2005

A new correlation technique enables the determination of local acoustic source strength on the surface of flat plates and simple airfoil shapes. The method is based on Curle's equation for surface generated noise and involves cross correlation between local surface pressure and the farfield acoustic pressure. Flat plate airfoils of circular planform were positioned in a quiet open jet airflow. The distribution of dipole strength was obtained by moving the point of surface pressure measurement around on the surface. Distinctively different distributions were obtained for cases of vortex shedding (airfoil at zero angle of attack in core of jet), separated flow (airfoil at 16° angle of attack in core of jet), and incident turbulence (airfoil in turbulent mixing layer). The popular notion that noise comes dominantly from the edges of a plate was not strongly supported. In some cases, however, definite localized source regions were identified. The technique also enabled estimates of correlation area for the surface pressure pattern to be made. These were generally a small fraction of the plate area (1%–10%). [Facilities and support for this work were provided by the Trane Company Research Department, LaCrosse, Wisconsin.]
Application of Spinning Mode Theory to Submersible Vehicle Propellers
Authors: Russell G. A. , Webster W. J.
Published: October 2005

The pressure distribution on a propeller generates periodic pressure fluctuations in the surroundings, and consequently discrete frequency noise. If the propeller is enclosed in a rigid cylindrical duct, spinning mode theory [J. M. Tyler and T. G. Sofrin, “Axial Flow Compressor Noise Studies,” Trans. SAE (1961)], which has been used successfully to combat noise in jet engine compressors, can be applied. An arbitrary pressure distribution at the propeller is decomposed into radial and circumferential modes by Fourier analysis. Solution of the wave equation shows that modes spinning around the duct at speeds greater than the speed of sound propagate undiminished through the duct, while those spinning at lower speeds decay exponentially. The decay rate is related to the geometry and speed of the propeller. Numerical examples for a submersible vehicle propeller show that the SPL of primary modes produced by the ducted propeller alone can be reduced to negligible levels. Some interference modes arising from interactions between the propeller and stationary supports will propagate undiminished.
Temporal Decay of Central Masking
Authors: Kaplan E. , Zwislocki J. J.
Published: October 2005

The decay of central masking after the termination of a contralateral masker was determined by means of the psychophysical method of forced-choice tracking. The masker consisted of 250-msec bursts of critical-band noise centered at 1000 Hz and presented at 60 dB SL. The test stimuli consisted of 10-msec bursts of 1000-Hz tone. Both were turned on and off with a time constant of 10 msec. The results have revealed an unexpected time pattern. The threshold shift produced by the masker decreased from about 4.5 dB to less than 1 dB within 80 msec, but then it increased again to a relative maximum and did not reach zero even 500 msec after the termination of the masker. The pattern differs from that found in monaural masking but is similar to that recently discovered in a study of loudness of a burst pair as a function of the interburst interval. It implies complex physiological processes, which probably include the known poststimulatory reduction of spontaneous activity in eighth-nerve units.
Correlation Measurements of Airplane Fuselage Vibrations
Authors: Wilby John F. , Gloyna F. L.
Published: October 2005

The vibrations of the skin and stiffeners of an airplane fuselage have been measured in a region where the excitation is predominantly that due to the turbulent boundary layer, at Mach numbers 0.78, 0.6, and 0.45. The data have been analyzed to assess the relative importance of standing and running waves, and to determine the spatial coherence of the vibration field. In the longitudinal, or stream, direction, the broad-band correlation shows running wave characteristics, which depend on the aircraft velocity and cabin pressurization. The convection velocities are not necessarily the same as the broad-band convection velocities for the pressure field, but there is evidence of a coincidence-type condition at M=0.6. The correlation scale in the longitudinal direction is much larger than that in the circumferential direction, where there is no significant correlation between adjacent panels separated by a longitudinal stiffener. Cross power spectral density measurements have been used to determine spatial coherence and convection velocity at particular frequencies, for comparison with the broad-band data.
Changes in Laser Speckle as a Tool for Vibration Analysis
Authors: Fernelius Nils , Tome Conrad
Published: October 2005

An object that is vibrating in a resonant mode and has a moderately rough surface illuminated by dispersed laser light shows patterns analogous to Chladni (strewn sand) patterns. The laser speckle patterns differ from the rest of the surface by appearing as regions in which the laser speckle has more dark areas interspersed with brighter light areas. These patterns appear at antinodes and are thus complementary to most Chladni patterns. Some examples of this observation along with Chladni patterns at the same resonant frequency are given. A heuristic theoretical discussion is also presented. [This work was performed under the auspices of the U. S. Atomic Energy Commission.]
Operational Methods in the Solution of LaPlace's Equation, ∇2φ = 0, in Rectangular Coordinates
Authors: Schmitt J. A. , Selvaggi J. A.
Published: October 2005

The rules of LaPlace transforms are invoked in the solution of the above equation. In solving LaPlace's equation, the assumption that the variables separarate has always been made. Now separation of variables need not be assumed. By directly applying transforms techniques, we obtain the correct result. Hence this method is of significant value. The standard boundary conditions for LaPlace's equation were used. Also the method is extended to determine the Green's function. For this problem, the boundary conditions were zero and the impulse value was δ(x−a)δ(y−b)δ(z−c), where a, b, c were in the boundary.
Variational Formulation for the Fully Coupled Problem of a Vibrating Circular Plate in a Rigid Wall
Authors: Ellison W. T.
Published: October 2005

The problem to be undertaken is that of a thin elastic circular plate, clamped at the edge, set in an infinite rigid wall exposed to a dense acoustic medium on both sides, and excited by an obliquely incident plane wave. Using a variational procedure, Morse has obtained an approximate solution for this problem with a tensioned circular membrane in place of the plate [P. M. Morse, J. Acoust. Soc. Amer. 40, 354–366 (1966)]. The general procedure for the variational formulation to be presented for the case of the thin elastic plate is the same as that given by Morse. Approximate expressions are derived for the transmitted power and the angular distribution of the transmitted field. Tabulated results are given for a thin steel plate exposed to water on both sides. The various phenomena resulting from the finite nature of the plate and the denseness of the surrounding acoustic medium are discussed. [This research has been supported in part under contract, Acoustics Programs Branch of the Office of Naval Research.]
Air Pressure and Larygngeal Activity in Intonation
Authors: Lieberman Philip
Published: October 2005

The theory proposed in Lieberman (1967, Intonation, Perception and Language, MIT Press, Cambridge, Mass.) states that both subglottal air pressure and laryngeal muscular maneuvers control fundamental frequency. Two phonetic features, the breath group and prominence, account for some of the linguistic functions of intonation. In the archetypal unmarked − breath group, fo follows air pressure. The archetypal articulatory correlate of the marked + breath group is an increase in laryngeal tension. Recent electromyographic data show that laryngeal muscles are responsible for the terminal fo rises of + breath groups and nonterminal + prominences in − breath groups. In contrast, fo peaks of + prominent syllables in + breath groups are caused by air pressure peaks. Independent data of Fromkin and Ohala (1968, Kyoto Speech Symp.) are consistent with these electromyographic observations. The Fromkin and Ohala data also show that the mean rate of change of fo with respect to air pressure is 12.5 Hz/cm H2O. These data support the archetypal correlates of the breath group and the “motor theory” for the perception of intonation proposed in Lieberman (1967). They also support a phonetic theory in which implementation rules relate phonetic features to articulatory maneuvers.
Pitch and Sentence Intonation
Authors: Kumar A. , Ojamaa K.
Published: October 2005

Spectrograms of utterances consisting of various combinations of consonants and vowels were studied in order to determine what voice fundamental-frequency fluctuations are predictable from segmental structure. Questions and statements with different stress patterns were also recorded and studied. After corrections were made for predictable coarticulation effects, a characteristic fo contour was found to be associated with each sentence type. This relationship turned out to be a complex one; i.e., there is marked interaction between various stress patterns and sentence types. For example, the extent of terminal pitch rise in question sentences is affected by the relative positions of stress-bearing elements in the sentences. The observed effect can be explained by postulating differences in rates of lung volume change during the breath groups corresponding to different stress patterns. These findings seem to suggest that the perception of prominence and question intonation involves a special decoding device (be it innate or learned) that combines acoustic data with “knowledge” about articulation to derive the underlying linguistically relevant, phonemic intonation contour.
Coarticulation Effects on Pitch
Authors: Ojamaa K. , Erickson D. , Kumar A.
Published: October 2005

The effects of vowels and consonants on the fundamental frequency of syllables were explored by examining spectrograms of consonant-vowel (C-V) and V-C utterances spoken in isolation. Comparisons of the differences in average fundamental frequencies for these syllables revealed relatively little evidence of consonantal influence on the average fundamental frequencies of adjacent vowels. However, by comparing the degree and amount of rise in fundamental frequency (i.e., pitch contours) in syllable initial and final positions, certain interesting phenomena were observed. In general, syllables that begin with voiceless consonants have a pitch contour characterized by a higher initial Fo than their voiced counterparts and are followed by a sharper fall; syllables with voiceless consonants in final position have a characteristically sudden drop in the pitch contour. An explanation for these facts is offered in terms of changes in transglottal air-pressure drop as a result of variations in supraglottal vocal tract configuration as well as timing of laryngeal muscle gestures relative to consonant closure. It is felt that these predictable mechanical effects are among the variables that should be taken into account when analyzing the role of intonation in speech.
Relation between Syntactic and Perceptual Units in Speech Processing
Authors: Jarvella R. J. , Pisoni D. B.
Published: October 2005

A running memory-span technique was used to demonstrate effects on the processing of continuous speech that were related to its syntactic structure. Test pauses were introduced at and between sentence boundaries in auditorily presented narrative passages. Subjects were instructed to write down, maintaining correct word order, parts of the passages occurring just before the test pauses. Verbatim recall for sentences that were either interrupted or bounded by the pauses was nearly always perfect, while the great proportion of errors made occurred in sentences previously completed. The obtained results support a view of speech processing in which the unit of immediate comprehension corresponds to single sentence-sized linguistic segments; the psychological organization within this unit during comprehension is related isomorphically to its surface syntactic form. More generally, this research indicates the potential value of an approach to the analysis of speech and speech processess that considers more abstract linguistic levels than are overtly correlated with the acoustic signal itself.
Signal Splatter and the MLD
Authors: Wightman Frederic L.
Published: October 2005

Several experiments have shown that the S0M0-SπM0 MLD increases markedly with reduction in masker bandwidth. However, there are at least two inconsistencies in this result. First, apparently similar experiments conducted by different laboratories have produced quite different results. Second, the MLD-bandwidth relation appears to be nonmonotonic; when the masker is very narrow band (e.g., a pure tone), the MLD is rather small. The experiments to be described show that both of these problems arise from anomalies in the S0M0 data but not in the SπM0 data. It appears that in some conditions the S0M0 threshold is too low, resulting in a deceptively small MLD. One possible explanation is that observers detect signal energy outside the masker band, for when this energy is attenuated by severely filtering the signal, the S0M0 threshold rises dramatically and the MLD becomes large. Curiously though, the SπM0 threshold is unaffected by this manipulation. With a continuous pure-tone masker and hard-filtered signals, MLDs of over 30 dB are observed. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to the Center for Human Information Processing. Author is a NIH predoctoral fellow.]
Performance of Hearing Impaired Subjects with the Modified Rhyme Test (MRT)
Authors: Northern Jerry L. , Hattler Karl W. , Nilges Thomas C.
Published: October 2005

The modified rhyme test (MRT), as adapted by Stanford Research Institute for clinical audiometric speech discrimination evaluation, was administered to 80 sensorineural hearing impaired patients and 20 normal hearing subjects at five sensation levels (SLs) (10–50 dB) above the speech-reception threshold. Performance-intensity (PI) curves were established with MRT Form 1 (male speaker) at + 30 S/N, P83, and P75 listening conditions, as a function of severity of hearing loss, audiometric configuration, and live-voice clinical discrimination scores obtained with Harvard PB-50 word lists. Hearing-impaired PI functions averaged 12% higher with the +30 S/N listening condition when compared with the P83 and P75 listening conditions. The score advantage shown with the +30 S/N list increased linearly as a function of the SL, while PI functions with MRT lists P83 and P75 were flat with only slight improvement in percent-correct scores as intensity was increased. Hearing-impaired subjects demonstrated similar PI functions with MRT lists P83 and P75 in all categories. Recommendations are suggested for clinical utilization of the modified rhyme test.
Teach Yourself Absolute Pitch in 365 Hard Lessons
Authors: Brady Paul T.
Published: October 2005

With intensive training, the author, who had no previous ability in identification of randomly presented tones from the 12-tone musical scale, achieved a performance level of 65% exactly correct and 97% correct within ± 1 half step (semitone). The training task, an extension of Cuddy's method [J. Acoust. Soc. Amer. 43, 1069–1076 (1968)], consisted of spending many hours hearing and identifying randomly presented tones with feedback on the judgments. Successful acquisition of absolute tone identification contributes to the evidence that an adult can learn this task, but apparently only with great effort. It is suggested that naturally occurring absolute pitch is not an innate ability. Rather, this skill results from perceiving only one musical scale (for example, C major), and if music is played in a different scale the notes retain their C major perceptual values. This mechanism, which is probably acquired in early childhood, can account for much of the introspective and performance data from possessors and nonpossessors of absolute pitch.
Questions Concerning the “Singing Formant”
Authors: Sundberg J.
Published: October 2005

This paper describes investigations of the origin of the “singing formant,” a pronounced spectral envelope peak in the frequency region of 2.4–3.0 kHz normally regarded as an important characteristic of a sung vowel. In the spectra of nine vowels produced by four trained bass singers, a reduction of the frequency distance between the third, fourth, and fifth formants was observed for the sung vowels as compared with the corresponding spoken sounds. An x-ray analysis of these vowel articulations in speech and in singing revealed that these differences can be explained as the acoustical consequences of changes in larynx position, lip opening, and, for the back vowels, tongue shape. The source spectrum of the same spoken and sung vowels was studied by means of automatic spectrum matching. The source spectrum of the spoken vowels appeared to fall more steeply than that of the sung vowels. The differences between the spoken and the sung vowels as regards the frequency location of the third, fourth, and fifth formants, and the source spectrum seem to give rise to the “singing formant.” Thus the “singing formant” seems to arise as a result of the refined control of phonation and articulation that is often a characteristic of the trained voice.
Some Effects of Combined Ultrasonic Fields and Centrifugal Forces
Authors: Greguss P.
Published: October 2005

This project was designed to evaluate the possible effects of a combined ultrasonic field and centrifugal forces upon colloidal systems. A special laboratory centrifuge was designed to deliver about 20 acoustic watts at 850 kHz into a rotating volume of 100 cm3. The rpm could be varied from 0–6000 and the changes in the ultrasonic field monitored via stroboscopic illumination. Anomalies in the propagation of the ultrasonic waves were observed. Augmentation or diminution in the rate of sedimentation of suspensions could be obtained. The increase in diffusion induced by the ultrasonic field combined with the separation effect of the centrifugal field can be used to improve biological and chemical preparation techniques.
Refracted, Bottom-Reflected Ray Propagation in a Shallow-Water Channel with Slowly Time-Varying Stratification
Authors: Clark John G. , Weinberg Norman L.
Published: October 2005

The shallow-water regions of the ocean are subject to low-frequency fluctuations in stratification spacially coherent over long distances. Internal tides, which are now considered a permanent feature of many coastal areas, are an example. The present study is a preliminary investigation of the influence of these fluctuations on RBR (Refracted, Bottom-Reflected) ray propagation in a shallow water channel. The principal assumptions are that the spatial scale of the stratification fluctuations in the channel is long compared to the distance between source and receiver, and that the fluctuation time scale is long compared to the ray travel time. In addition to general relationships, a particular case with realistic channel parameters in terms of continental shelf conditions is discussed in detail. In the detailed study, it is shown that both the amplitude and phase angle of a CW signal associated with any given ray are modulated at the fluctuation frequency of the channel stratification. The amplitude modulation, however, is negligibly small so that the resultant multipath signal at the receiver is a sum of several signals nearby, constant in amplitude but phase-angle modulated.
Cockpit Noise Measured Within Aircraft Used to Train Pilots in the Air Force
Authors: Gasaway Donald C.
Published: October 2005

The United States Air Force employs a variety of aircraft to train pilots. The noise encountered by pilot trainees is described and illustrated. The character of the noise encountered within the cockpits of fixed- and rotary-wing aircraft used for flying training has changed considerably during the past 25 years. The author describes and illustrates noise spectra found within fixed-wing aircraft powered by reciprocating and turbojet engines and rotary-wing aircraft powered by reciprocating and turboshaft power plants. The effects of various acrobatic and flight training maneuvers on cockpit noise are included and factors of aeromedical significance associated with the operation of different training aircraft are identified and described.
Prediction of Sound Attenuation by Barriers
Authors: Kurze U. J.
Published: October 2005

A simple analytical approximation for the sound attenuation by barriers is derived on the basis of prior theoretical and experimental results. The approximation takes into account oblique sound incidence at the barrier and also applies for the transition region between the “bright” zone and the shadow zone behind the barrier. Results for a point source are compared with those for a line source parallel to the edge of the barrier. Engineering estimates are given for the aspect angle of an incoherent line source, for which the barrier attenuation can be calculated by considering only a single diffracted ray. Predictions of the sound attenuation by a barrier parallel to a number of incoherent line sources agree well with experimental results reported for an acoustical model of a multilane highway. The length of a barrier along a highway required for efficient sound attenuation is calculated in terms of the angle at the observer that encompasses the barrier. [These studies were carried out in part under Contr. No. DOT-OS-A9-018, under subcontract with Serendipity, Inc., Arlington, Virginia.]
The Case of the “Missing MLD”
Authors: Wightman Frederic , Green David M.
Published: October 2005

The decrease in the size of the MLD with signal frequency is presumably caused by the inability of the auditory fibers to follow details of the waveform at high frequencies. The ear appreciates slow frequency envelope variations even at high carrier frequency, however, as the residue attests. Using amplitude modulation, we attempted to obtain an MLD by manipulating the phase of a 250-Hz envelope on a 2000-Hz carrier. Essentially no MLD was observed. Attempting to create a more salient low-frequency pitch sensation we used a high-pass filtered pulse train. Delaying the pulse train, 250 ips, by half a period in the opposite ear had essentially no effect on the detectability of the binaural stimulus in wide-band masking noise. Our procedure is different from that used by Small who showed that simply inverting the waveforms at the two ears produced no MLD. These results replicate some of a more extensive series of measurements carried out by Dr. G. Bruce Henning. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to the Center for Human Information Processing.
Tone-on-Tone Masking for the M0-S0, M0-Sπ, and M0-Sm Conditions
Authors: Yost William A.
Published: October 2005

Using a two-alternative temporal forced-choice technique (2ATFC), the detectability of a 250-, 500-, or 3000-Hz 120-msec tonal signal masked by a gated 70 dB SPL tone of the same frequency and duration was measured as a function of the signal level, the phase angle at which the signal was added to the masker (0°, 45°, 90°), and the interaural stimulus condition (M0-S0, M0-Sπ, M0-Sm). The data for all interaural conditions and frequencies were plotted as the signal-to-masker ratio (20 logS/M required for 75% correct detection in the 2ATFC task) versus the signal-plus-masker phase angle. At all three frequencies, the detectability of the signal for the M0-S0 condition followed a simple energy- or power-detection model. At 250 and 500 Hz, the functions for the M0-Sπ and M0-Sm conditions were “U” shaped with the M0-Sm condition requiring 6 dB more signal for detection than the M0-Sπ condition. At 3000 Hz, the signal-to-masker ratio for both the M0-Sπ and M0-Sm conditions increased as the signal-plus-masker phase angle increased with the M0-Sm condition requiring approximately 3 dB more signal than the M0-Sπ condition. The MLDs for the M0-Sπ condition were always positive, whereas for the M0-Sm condition negative MLDs were found for a signal-plus-masker phase angle of 0°. The results are discussed in terms of three models regarding detection for binaural masking. [The research was supported by a Public Health Service Predoctoral Fellowship.]
Direct Measurement of the Vocal Tract
Authors: Ladefoge Peter , Anthony James , Riley Cordell
Published: October 2005

Previous measurements of the vocal tract have been based on lateral x rays, laminagrams, dental casts of the oral cavity, and readings from specially constructed calipers. The present study extends the basis for these measurements by the use of a cast of the pharynx. The subject was inverted and dental impression material was inserted up to (sic) the level of the arytenoid cartilages. Tables have been constructed which relate the cross dimensions of the vocal tract as seen on lateral x rays and the cross-sectional areas as required in calculations of the corresponding sound waves.
Use of Splines and Numerical Integration in Geometrical Acoustics
Authors: Solomon L. P. , Moler C. B.
Published: October 2005

Two contributions are made to ray-theory techniques for propagation through continuously stratified media. The first makes use of spline polynomials to approximate speed of sound profiles smoothly. The second eliminates the singularity occurring in the usual range integral. A versatile automatic numerical procedure for solving a wide variety of acoustic propagation problems results.
Air-Conditioning Cooling-Tower Noise Calculation
Authors: Schwartz A.
Published: October 2005

For the plant designers' practical purposes, it was found by laboratory and in situ research on air-conditioning cooling towers of 3–300 T.R. nominal capacity, that it is possible and very easy to calculate the noise level, Lw (dB re10−12W), that we can expect from the cooling tower, as a function of the nominal water rate, G (GPM), as Lw=72+10 logG in the case of axial-fan cooling tower; Lw=66+10 logG in the case of centrifugal fan cooling tower; and Lw=74+5.5 logG in the case of water noise only.
Development of a Spinning-Mode Synthesizer to Study Complex Propagating Duct Modes
Authors: Seiner John M.
Published: October 2005

The use of commercial fan engines or model fan test rigs in studies attempting to relate the pertinent parameters of spinning modes to the acoustical characteristics of various duct treatments has been frustrated by the presence of a high level of broad-band noise and all the harmonics of the discrete tone spectrum. These facts reduce the possibility for meaningful parameter variation. Therefore, a flexible source of spinning modes has been developed which is capable of generating independent spinning waves of controlled complexity and spin speed without the introduction of broad-band elements. These features were accomplished through the use of broad-band elements. These features were accomplished through the use of eight commercial loudspeakers located in an equally spaced circular array and properly phased so that the system could generate a spinning wave. The constructed apparatus was tested in an anechoic environment and found capable of generating a plane, one- and two-lobed spinning wave of high quality at 120 dB, and a farfield distance of 7 ft. The phase velocities of those waves investigated varied from 8000 to 18 000 rad/sec, which represented propagating modal patterns.
Absorption of Sound in Air
Authors: Evans L. B. , Sutherland L. C.
Published: October 2005

Experimental measurements of the absorption of sound in still air exhibit a distinct deviation from the theoretical predictions based on known classical and molecular absorption losses. Absorption coefficients have been measured in humid air over the humidity range of 0% to 100% relative humidity. These measurements show the same type of low-frequency-absorption anomaly as has been found previously, but to a lesser extent. It is thought that the anomaly is due to the vibrational relaxation of nitrogen catalized by either water vapor, carbon dioxide, or a combination of both. Experimental sound-absorption measurements have also been made in humid nitrogen at room temperature. The data from these measurements, while quite scattered, do show a definite shift of the absorption peak with water-vapor content. These measurements also show fair agreement with values deduced from air-absorption measurements. [This work was supported by the U. S. Army Research Office—Durham, under contract.]