bluuebunny/crossref_metadata_2025 huggingface dataset:
The inlet vortex as a source of tonal rotor noise
Authors: Leggatt L. J. , Siddon T. E.
Published: October 2005

This work was motivated by evidence of naturally occurring inlet vortices as an important source of tonal noise from axial flow fans. Inlet vortices are a recognized consequence of confined inlet conditions, as especially when rotors operate near adjacent bounding surfaces. Experimental observation suggests that the inlet vortex field is characterized by very long streamwise scales with a relatively stationary field of circulations in the rotor plane. A combined theoretical and experimental study of a single inlet vortex penetrating the rotor plane reveals the separate roles of vortex properties of circulation strength, core radius, and core velocity deficit in influencing harmonic noise levels. Experimentally, half-delta wings were mounted at various incidence angles in the inlet bell-mouth to produce vortices of known properties. Theoretically, vortices of equivalent properties were impressed on the rotor blades, using linearized unsteady aerodynamics to calculate the fluctuating blade loads. Dipole radiation from individual blades was summed with appropriate phase relationships to estimate the total noise field and its harmonic content. Measured and predicted acoustic levels agreed reasonably well. Some discrepancies are noted and discussed. [Work supported by Canadian DRB & NRC.]
Acoustic reflex threshold and loudness discomfort level relationships in deaf children
Authors: Holmes D. W. , Woodford C. M.
Published: October 2005

Threshold of audibility, loudness discomfort level (LDL), and acoustic reflex threshold (ART) were obtained by the tracking method on 51 cars of 34 children enrolled in a residential school for the deaf. Stimuli consisted of broad-band noise and pure-tone frequencies of 0.5, 1, 2, and 4 kHz. Stimulus duration was 500 msec, with approximately 30-msec rise time and approximately 50-msec fall time and 500-msec interstimulus interval. Relationships between loudness discomfort level (LDL) and acoustic reflex threshold (ART) fell into four distinct categories. That is, those subjects without loudness discomfort level and acoustic reflex threshold, those with LDL present and ART absent, those with ART present and LDL absent, and those with LDL and ART present. The results of this study will be discussed in terms of its relationship to the fitting of hearing aids on deaf children.
Estimating the ability of animals to recognize auditory signals
Authors: Corliss E. L. R.
Published: October 2005

From such nonverbal tasks as recognizing the intensity modulation in pure tones (DLI) and detecting a pure tone in masking noise, the author has computed “circuit parameters” for the human ear and calculated from these a “channel capacity” for the ear just as though it were a communication circuit. The difference limen for intensity (DLI) gives a measure of an effective S/N ratio, and from such discrimination tasks as detecting a sinusoidal signal in masking and discriminating changes in frequency, an effective integration time can be computed. Similar tests of DLI, frequency resolution, and masked threshold have been reported in the literature for animals. This paper will demonstrate how the degree of complexity of auditory signals to which a normal animal might respond is computed from experiments on hearing. As one might expect, the channel capacity seems to be generally less than for human subjects. In the study of noise damage to hearing for animal subjects, it might be possible to use the channel capacity as a more precise measure of the degree of impairment.
Variable responses of cerebral palsied speech production under masking
Authors: Farmer A. , Green W. B.
Published: October 2005

Three adult cerebral palsied speakers spontaneously “read” sentences presented in rebus form under two control and one white-noise-masking condition. Durational measures from wide-band spectrograms indicated individual variation in word, interword, extraneous vocal behavior, and total utterance measures among conditions. These variable durational differences were compared with articulatory patterns. The predominantly spastic speaker demonstrated decreases in durational measures and extraneous vocal behaviors with a slight increase in articulatory errors under the masking condition. One predominantly athetotic speaker demonstrated decreases in total utterance time and a slight decrease in articulatory errors while the other athetotic speaker demonstrated increased durational measures with a decrease in articulatory errors. These results are graphically illustrated. Individual variability is discussed in relation to the nature of the dysarthrias.
Effect of aging on speech reception in noise
Authors: Mayer C. L. , Levitt H. , Bergman M.
Published: October 2005

An attempt was made to isolate the effect of aging for listeners of speech in noise. Chaba sentences of everyday American speech and monosyllabic word lists with a closed-set response (Mitchell Test of Phonemic Differentiation) were recorded by male and female speakers. The speech materials were systematically combined with subway and traffic noise samples. The tapes were presented in a balanced design to 160 listeners who represented a nonclinic population with essentially normal hearing. The subjects were divided into decade groups: 20–29 through 60–69, and the data were analyzed for each age group. Results show a decline in speech intelligibility scores for every condition presented. This effect was greatest where the speech-to-noise ratios were poorest.
Generation of sound by vortex shedding-the relevance of the Kutta condition
Authors: Howe M. S.
Published: October 2005

The generation of sound by the fluctuating lift forces on a strut or airfoil is reexamined by treating the wake vorticity as the aerodynamic source and using the appropriate Green's function. It is shown that at low Mach numbers the intensity of the radiated sound is effectively independent of whether or not a Kutta condition is imposed at the trailing edge. It is argued that recently published theoretical results which predict a large increase in the radiated sound power when the Kutta condition is imposed, and also those which predict a channelling of an intense sound wave along the wake, are in error.
Interpretation of radiation field in terms of sub-beams
Authors: McCoy John J.
Published: October 2005

Two frequently employed measures of a statistical radiation field, i.e., the mutual coherence function and the intensity directional spectral density, are considered as they apply to deterministic beamed signals. Mathematical formulations, in the form of differential equations, that govern the propagation of these measures, had previously been presented. Here, we show that solutions of these formulations suggest an interpretation of a radiation field in terms of sub-beams. These sub-beams are the natural extensions of the ray tubes of the geometric theory. We apply the formulations to propagation through a grating. Several classical results, as well as some extensions of these classical results, are obtained.
Bubble-enhanced nonlinear sound generation
Authors: Clynch J. B. , Dittman C. W.
Published: October 2005

In a previous presentation [J. Acoust. Soc. Am. 55, S51(A) (1974)] it was shown that when two pure tones pass through cavitation microbubbles the nonlinear generation of difference frequency sound is greatly enhanced. In data presented here the primary frequency sound field directly drives a ring transducer and creates microbubbles via acoustic cavitation. Data on the variation of difference frequency SPL with difference frequency, primary frequency power, primary frequency, and ambient pressure are presented. Data for primaries consisting of two pure tones and a band of random noise are shown. In general the data agree with simple theoretical predictions only at the highest power levels where the bubble field is well established. Agreement with theory is best for the dependence of difference frequency SPL on difference frequency fs in the pure tone case and spectral shape in the band limited noise case. [Work supported by Naval Coastal Systems Laboratory.]
Spatial interfrequency correlation effects in a surface-scatter channel
Authors: McDonald J. F. , Tuteur F. B. , Zornig J. G.
Published: October 2005

The effect of spatial separation on the cross correlation between the system response functions for a two-receiver surface-scatter channel is investigated. The system response at the two receivers is determined for all possible pairs of frequencies. The analysis assumes relatively close separation of receivers and uses the Fresnel corrected model for surface scatter in the specular direction. The surface is assumed to be Gaussian, with typical size of boundary deformations small compared to typical Fresnel zones. The analysis shows that the correlation is approximately maximum for zero frequency separation and drops off at a rate determined by the reverberation time. For small reverberation times and small grazing angles correlation may extend over fairly large values of frequency difference. The effect of spatial separation is generally a reduction in correlation and a more rapid decrease of correlation with frequency, but this can be compensated to some extent by time shift between the two system responses. Experimental evidence is included to support the theoretical predictions presented. [Supported by ONR, Code 480.]
Edge diffraction effects on acoustically baffled, phased arrays
Authors: Brigham G. A.
Published: October 2005

The two-dimensional scattering of plane waves by a thin, semi-infinite plate with either Neumann boundary conditions over both surfaces or mixed Neumann/Dirichlet conditions on opposing sides may be readily calculated. Since wave components in any plane parallel to the barrier edge undergo specular reflection, the two-dimensional formulation may be easily extended to three dimensions. The distribution of the total pressure amplitude and phase on both sides of the barrier as a function of aspect angles is shown in this paper for both types of boundary conditions. The effects of edge diffraction on acoustic array performance is demonstrated first in the calculated receiving patterns of a summed five wavelength array steered towards the baffle edge and then away from it, and second in the calculated beam patterns of a two element, two and one-half wavelength array used for phase detection. The estimated bearing error versus bearing for the null array is shown for different tilt angles and different distances of hydrophones from the baffle edge.
Statistical scattering model for time-spread sonar targets
Authors: Nelson David E. , Titlebaum E. L.
Published: October 2005

A simple statistical model of a distributed radar/sonar target has been proposed. The model consists of point scatterers of random amplitude and spacing distributed within the physical dimensions of the target. The characteristics of the model echoes are shown to match those from a real target, both statistically and dynamically. Approximately 50 scatterers were required to simulate the real target. The number was found experimentally with the use of a new measure of echoes from distributed targets: target-time spreading loss (TSL). TSL is a quantitative measure of the time dispersion imparted to the echo-ranging signal by the finite extent of the target. TSL can also be used to predict the loss of correlation experienced by matched filter receivers when detecting distributed targets. The proposed use of the model is in range prediction and detector design. It is shown that detectors properly matched to the distributed target can have an advantage of several decibels over mismatched detectors and, in reverberation-limited echo-ranging conditions, can yield range advantages of up to 3:1.
Backward lateral displacement of an ultrasonic beam reflected from a liquid-solid interface
Authors: Torbett Michael A. , Breezeale M. A.
Published: October 2005

Tamir and Bettoni [J. Opt. Soc. Am. 61, 1397 (1971)] have predicted that light reflected from a dielectric interface can undergo a backward beam shift under special conditions. When applied to the reflection of an ultrasonic wave from a liquid-solid interface, this means that a negative “Schoch displacement” exists. Such a reverse lateral displacement can be obtained by reflection from an interface formed into a periodic structure. Using a new schlieren system with a unique goniometer, we have been able to photograph the backward displacement of an ultrasonic wave at a water-brass grating interface and thus demonstrate the basic validity of this aspect of the Tamir and Bertoni theory. [Research supported by the Office of Naval Research.]
Energy redistribution of an ultrasonic beam reflected from a solid plate in a liquid
Authors: Pitts Leslie E.
Published: October 2005

Nonspecular reflection effects are known to occur when a Gaussian ultrasonic beam is incident at the Rayleigh angle at a liquid-solid boundary [Bertoni and Tamir, Appl. Phys. 2, 157 (1973)]. Nonspecular reflections are also present when an ultrasonic beam is incident on a solid plate of finite thickness, immersed in a liquid, provided the incidence angle corresponds to a Lamb angle. A theoretical analysis is given which shows that the reflected sound energy profiles depend on the plate thickness and the sound frequency. The results of the analysis are compared to existing experimental data.
Short-wavelength diffracted surface pressures on a prolate spheroid
Authors: Blake William K. , Wilson George A.
Published: October 2005

This paper will describe measurements of sound pressures on the surface of a prolate spheroid whose length to diameter ratio is 6.9. The sound source was positioned a distance from the illuminated pole equal to the length of the body; irradiation was axisymmetric. Data at surface locations along the axis of the body was collected for acoustic wavelengths λ ranging from 1/150 to 1/38 of the interfocal distance d. A condenser microphone equipped with a long probe tube was used to avoid extraneous scattering from the sensor. Sound pressure levels, expressed relative to those measured on the illuminated pole, showed the existence of expected creeping-wave interference patterns near the antipode and an illuminated spot on the pole. The measured levels on that pole are shown to decrease roughly as the reciprocal of frequency; they are 13 dB less than those at the illuminated pole for d/λ = 38. In the shadow zone the measurements are shown to be well approximated by Keller's deo-metric theory of diffraction. Deviations from the theory on the order of 3 dB are observed at high frequencies and at coordinates off the antipode.
Quantitative acoustic schlieren determinations by means of phase resolved images
Authors: Bucaro J. A. , Flax L. , Dardy H. D.
Published: October 2005

Image intensity functions have been calculated for acousto-optic phase-resolved schlieren in the phase grating (Raman-Nath) diffraction limit. The calculation applies to the case where a circular stop is used. Any number of diffraction orders may be stopped. The results are programmed into a laboratory GT-44/PDP-11 real-time graphic system and compared to experimental observations. The latter include TV monitoring of both the diffraction orders and the image distribution and photomultiplier-pinhole recording of the image intensity distribution. It appears that phase resolution will permit quantitative pressure level determinations. The results aid significantly in interpreting phase-resolved schlieren observations from radiation and scattering mechanisms.
Spectral broadening of waves propagating in a random medium
Authors: Wenzel Alan R.
Published: October 2005

A theoretical investigation of the wave field radiated by a point source in a homogeneous, isotropic random medium is described. The smoothing method is used to study the frequency spectrum of the wave; particularly the evolution of this quantity with propagation distance. An approximate expression for the spectrum is obtained for the case in which the characteristic frequency of the wave is much greater than that of the medium. Numerical results obtained using this expression show that the spectrum broadens with propagation distance in a manner similar to that observed in experimental studies.
The elementary acoustical signal explained as a quantum phenomenon of macroscopic physics resulting from the minimization of a potential function
Authors: Barrett T. W.
Published: October 2005

The boundary conditions for the minimum elementary signal defined: f0 t0 = ΔfΔt= 1/2 (where f0 is signal midfrequency, t0 is signal midperiod. Δf is signal bandwidth, and Δt is signal duration) also describe the topologically defined condition known as either (i) a critical point, (ii) a singularity in mapping one manifold into another, (iii) a local potential fluctuation, or (iv) a flow on a cusp catastrophe. An elementary signal, or any quantum, is a limit cycle or oscillation hysteresis defined within an area of instability of a precisely defined mapping plane. The collection of unstable maps of the potential function, from which the elementary signal is derived, defines those instances in which quantum theory is applicable. Thus, a wave event cannot become infinitely small and still be meaningful, i.e., informationally relevant. This result provides an explanation for parametric excitation, as well as a tool for the study of cochlear fluid mechanics.
Differential ototoxic reaction to dihydrostreptomycin in two species of Old World monkey
Authors: Stebbins W. C. , Hawkins J. E. , Johnsson L.-G. , Moody D. B.
Published: October 2005

Unlike the macaques and most commonly used species of laboratory animals, the African military monkey (Erythrocebus patas) is sensitive to the ototoxic action of dihydrostreptomycin (DHSM) administered daily in doses ranging from 100 to as low as 20 mg/kg. Progressive hearing loss (from high to low frequencies) develops during treatment and continues for some time thereafter. It is irreversible and is correlated with extensive cochlear histopathology, typical of ototoxic injury, including loss of inner and outer hair cells and supporting cells, and degeneration of auditory nerve fibers. The Asian pigtail monkey (Macaca nemestrina), although sensitive to other aminoglycosidic antibiotics (e.g., neomycin and kanamycin), is unaffected by DHSM 100 mg/kg given daily for as long as eight months. This striking difference in sensitivity to DHSM may be related to differences in physiologic function which reflect adaptation to the dissimilar environments in which the patas and the nemestrina live. [Supported by NIH Program Project Grant 05785 and by Research Grants NS 05065 and NS 05077.]
Ribonucleic acid changes in spiral ganglion neurons of noise exposed rats
Authors: Bennett T. E. , Anthony A.
Published: October 2005

Quantitative cytochemical studies of RNA alterations in individual spiral ganglion neurons (apical, middle, and basal turns) of 20 adult Wistar rats were made at 1-, 4-, 8-, and 24-h intervals after a 60-min exposure to intense noise (120 dB unweighted, re 20 μN/m2, 800–20 000 Hz). RNA was quantified using the two wavelength method of microspectrophotometry on DNase-pretreated azure-B stained midmodiolar sections. Other aspects included measures of spiral ganglion neuronal perikaryon volume changes and cytomorphological examination of cochlear hair cells. The data revealed a progressive reduction in RNA content of spiral ganglion neurons at 4-, 8-, and 24-h intervals; (2) a decrease in perikaryon volume evidenced at all four intervals; (3) an identical pattern and extent of RNA and volume changes evidenced in spiral ganglion neurons of apical, middle, and basal cochlear turns. No hair-cell disruption or related cytological evidence of pathology was evidenced. The data indicate that intense noise causes a marked inhibition of spiral ganglion functioning in the absence of hair-cell disruption.
Kangaroo rat Hensen's and Claudius' cells
Authors: Webster Molly
Published: October 2005

The kangaroo rat organ of Corti is characterized by the unique morphology and relationships of its border cells. The Claudius' cells abut the Deiters' cells and one or more Claudius' cells “support” the Hensens cells. Claudius' cells' cytoplasm is mostly clear with few organelles. Hensen's cells contain much endoplasmic reticulum, free ribosomes, scattered mitochondria (often bizarrely shaped), and other organelles. The Hensen's cells are flask shaped; their long axes are inclined toward the outer hair cells medially and toward the outer wall laterally. Narrow cell processes extend upward and form an elevated “reticular lamina” with a few microvilli on its endolymphatic surface. This “reticular lamina” bridges extracellular spaces between the Hensen's cells processes; it extends from the reticular lamina of the hair cells to the apical border of Claudius' cells. Fibrils in these processes and their “reticular lamina” apparently give support similar to that provided by the larger tonofilaments of pillar and Deiters' cells. [Supported in part by a grant from The Deafness Research Foundation.]
Brainstem auditory nuclei after sound deprivation
Authors: Webster Douglas B. , Webster Molly
Published: October 2005

Neuron size and neuron packing were measured in three groups of 45-d CBA/J mice. A deprived group was used with a “devocalized” mother in a sound chamber with ambient noise below their auditory thresholds. An operated group had their external auditory meati and tympanic membranes removed at three days of age. A normal group served as controls. Neurons of the globular cell area of the cochlear nuclei and medial nuclei of the trapezoid body were significantly smaller (p<0.01) in the deprived and operated groups than in the control group. No neuron size differences were found in the other hindbrain and midbrain auditory cell groups. No differences were found in cell packing except in the central region of the dorsal cochlear nucleus where there were fewer neurons per unit area in deprived and operated mice than in normal mice (p<0.02). The data suggest that congenital conductive hearing losses may adversely affect development of parts of the central auditory system.
Sonic booms in relaxing gases
Authors: Sinai Y. L
Published: October 2005

The method of matched asymptotic expansions is applied to the problem of supersonic, nonequilibrium, axisymmetric flow about a slender, pointed body of revolution with thickness/length ratio ε. The form of the nonlinear equations which govern the first-order perturbations in the far-field depend on the relative orders of magnitude of ε, δ, and τ (δ is a measure of the nonequilibrium effects and τ is a characteristic time of the nonequilibrium process). A comparison is made between the axisymmetric and plane-wave solutions under typical sonic boom conditions, and it is suggested that the one-dimensional theory is limited in its applications.
Application of digital cross-spectral analysis to outdoor sound propagation
Authors: Slutsky Simon S. , Lee Van M.
Published: October 2005

Digital spectral and associated correlation analysis techniques have been used extensively for time series arising from various physical phenomena. In the field of acoustics, these techniques have found a wide range of application in underwater sound, measurement of acoustical properties of materials, system response functions, noise source location and diagnostics, etc. In this paper, the digital cross-spectral technique is used to study the propagation losses of sound from 22 to 11 314 Hz from a sorce in a given outdoor environment under given meteorological conditions. This technique is particularly applicable when the sound is severely masked by the ambient background noise. The problems encountered in data collection, data processing and digitization, and conversion of power spectral densities to octave-band decibel values are discussed. Results are shown as auto-spectral, cross-spectral, coherence-function, and phase-angle plots. Comparisons of the “environment response function” evaluated using this experimental procedure and predicted attenuations from a simple semianalytical model in octave-bands are made to point out the conservatism of that model. This experimental procedure can be applied as a site-calibration procedure under representative weather conditions for community noise impact evaluation taking into account the complex effects of terrain and atmosphere.
Modelling of environmental acoustics
Authors: Jones H. W. , Stredulinksy D. , Vermeulen P. J.
Published: October 2005

A facility has been built for studies of the propagation of sound in a model at roughly 1/50 to 1/100 of full scale. This facility which consists of a high-frequency anechoic chamber and reverberation room is described. Sound sources which are modulated Hartmann whistles are described and their performance discussed. A method of measuring the acoustic impedance of materials at high frequencies and grazing angles is described and some typical results presented. The use of gases other than air is discussed and the results of some experimental work is described.
Acoustic spectral analysis of three tornadoes
Authors: Arnold Roy T. , Bass Henry E. , Bolen Lee N.
Published: October 2005

Three sound recordings of tornadoes have been analyzed over the frequency interval between 100 and 2000 Hz. The low-frequency analysis was limited by the spectral response of the microphones, and the upper limit was imposed both by the microphone response and the low signal level. Although the recordings are of low quality and the audio information required major spectral corrections, the data do indicate that the recorded audio emissions from the tornadoes decrease in intensity as a function of increasing frequency. An attempt has been made to correlate the spectra with real (and conjecture) physical properties of the tornadoes. It is clear to us from our objective analysis (and the more difficult subjective evaluation of the recordings) that audible identification of tornadoes is possible, and a study of tornadic sounds might provide a new tool for gaining insight into electrical and mechanical disturbances within a tornado's funnel system. Study of the change in intensity of the sounds emitted by the approaching Guin storm at both high and low frequencies suggests that noises generated by the high speed winds of the tornado cyclone as it scours the ground can be discerned from noises associated with the winds and/or electrical discharges aloft.
Some comparisons of the flyover noise characteristics of DC-9 aircraft having refanned and hardwalled JT8D engines, with special reference to measurement and analysis
Authors: Hosier Robert N.
Published: October 2005

FAR-36-type noise measurements and analyses of selected refan and hardwall DC-9 aircraft flyovers were made in parallel with the Douglas Aircraft Company (DACO) at the DACO Yuma, AZ test site in order to evaluate the refan modifications as well as data acquisition and analysis procedures. A limited comparison of results from NASA and DACO measurements and analyses for landing approach conditions indicated agreement within ±1 EPN dB. The worst repeatability results in the NASA analyses (±3 EPN dB), were obtained for the refan takeoff-with-cutback condition. It is believed that the difficulty is associated with the duration factor computation rather than being due to measurement systems performance or atmospheric effects. NASA analyses of the refan and hardwall data indicated that the refanned aircraft provided a centerline noise reduction of about 9.1 EPN dB for takeoff with cutback and about 10.0 EPN dB for 50° flap landing approach. This paper provides a general description of the measurement and analysis systems and procedures used by NASA in these tests.
Investigation of noise sources for a STOL-UTW configuration
Authors: Olsen W. A.
Published: October 2005

Noise data were obtained with a model of an externally blown flap STOL configuration with the nozzle under the wind (UTW). The wing had three flap segments with the last flap at 20° or 60° from the nozzle centerline. A slotless wing conforming to the 60° three-flap wing was also tested. The objectives of the program were to investigate the noise sources associated with the UTW configuration and to compare the results with available three-dimensional noise field analyses. Narrowband and one-third-octave band spectral data in three dimensions were taken for these configurations over a large range of jet velocities. Free-field data were obtained to avoid problems evident in previous data. Acoustical shields were used to partially isolate selected noise source regions. The results are compared with analytical models.
Independence of noise levels for propeller-driven small aircraft on test altitude
Authors: Galloway W. J. , Mills J. F. , True H. C.
Published: October 2005

Noise certification under FAR 36, Appendix F, requires the measurement of maximum A-weighted sound level during flyovers at maximum continuous power, 1000 ft above ground, at a sealevel airport. In order to investigate the effect of altitude and horsepower on sound-level measurements, tests on a Cessna 172 and Beech 33 were made at three airports having elevations of 42, 2350, and 6750 ft. Engine power was varied from approximately 50% of raged maximum continuous to the maximum available at the test altitude. The results for these two representative general aviation aircraft show that above approximately 65% power A-weighted sound level is essentially constant and independent of altitude, depending primarily on propeller tip helical Mach number. Noise certification of propeller-driven small aircraft can thus be reliably performed at a wide range of test sites irrespective of site elevation. [Work supported by FAA.]
Two-point correlations of sound pressure in the far-field of a jet: experiment
Authors: Maestrello Lucio
Published: October 2005

Correlation of sound pressure between two microphones yield substantially more information than single microphone data; hence, they provide a useful diagnostics tool for jet noise. In the present experiment, the two microphones were located at (R, θ, φ) and (R, θ, φ′), respectively, in spherical polar coordinates. The jet was directed along the polar axis (θ = 0) with the nozzle at the origin. Two sets of space-time correlation were carried out (1) φ′ = 0; 0 ⩽ θ ⩽ 180°; θ′ = 0, 30°, 45°, 60°, 90°, 120°, 135°; (2) φ′ = 0; 0 ⩽ θ ⩽ 180°; θ′ = 0, 30°, 45°, 60°, 90°, 120°, 135°. Jet diameters were 1, 2, and 3 in. with a range of nozzle velocities from 500 to 1000 ft/sec, and R/D was 166 for the 1-in. jet. Nineteen carefully phase-matched microphones were employed. Polar plots of these correlations show a definite cusp at the origin (φ = φ′), unlike polar plots of p̄2. among other interesting features.
Two-point correlations of sound pressure in the far-field of a jet: theory
Authors: Ribner Herbert S.
Published: October 2005

A large body of careful experimental measurement of two-point jet noise correlation have been carried out and are reported in a companion paper by Lucio Maestrello. The result were not altogether as expected and motivated the present effort to bring theory to bear. The model of jet noise generation is that of Ribner (1963, 1964, 1969), which is development of the Lighthill for malism. It postulates isotropic turbulence superimposed on a specified mean shear flow, with assumed space-time velocity correlations. The particular vehicle is the Proudman format, which is extended from the 1969 work (mean square pressure) to display the two-point space-time correlations of pressure. Here, again, the self-noise (from turbulence alone) is accompanied by shear noise (from turbulence-mean flow interaction), with distinct and different contributions. The shape of polar plots of correlation derives from two main factors: (1) the derivatives of the constituent quadrupoles and (2) the noncompactness of the source region which allows differences in travel time to the two microphones. Comparisons are made with the results of Maestrello's measurements.
Speaker verification using passwords
Authors: Helms R. E. , Doddington G. R.
Published: October 2005

The use of passwords embedded in free text for speaker verification increases system integrity through privileged knowledge (of the passwords). Two problems arise, however: the stability of the password speech data suffers from changing context, and the password must be detected reliably with few false alarms. Sensitivity to context is minimized by choosing passwords to be content words that begin and end with “hard” consonants. Password detection is based upon finding key reference points within each password through speaker-specific data comparison. An evaluation was performed using ten 3-min sessions of read text from each of eight subjects. A total of 160 tokens of each of five passwords was processed. The results, using filter bank spectra, are

word false alarms/hour SV error, %

(at 10% miss) (TS = IMP)

congress 1.5 6.7

candidate 2.5 9.1

pentagon 0.5 8.8

constitution 0 3.5

secretary of state 0 4.4

[Research was sponsored by the Air Force Systems Command, Rome Air Development Center.]
Continuous speech recognition via centisecond acoustic states
Authors: Bakis R.
Published: October 2005

Continuous speech was treated as if produced by a finite-state machine making a transition every centisecond. The observable output from state transitions was considered to be a power spectrum—a probabilistic function of the target state of each transition. Using this model, observed sequences of power spectra from real speech were decoded as sequences of acoustic states by means of the Viterbi trellis algorithm. The finite-state machine used as a representation of the speech source was composed of machines representing words, combined according to a “language model.” When trained to the voice of a particular speaker, the decoder recognized seven-digit telephone numbers correctly 96% of the time, with a better than 99% per-digit accuracy. Results for other tests of the system, including syllable and phoneme recognition, will also be given.
Parameter-independent techniques in speech analysis
Authors: Goldberg Henry C. , Reddy D. Raj
Published: October 2005

Most present programs for feature extraction, segmentation, and phonetic labeling of speech are highly dependent upon the specific input-parametric representation used. We have been developing approaches which are relatively independent of the choice of parameters. Vectors of parameter values are dealt with uniformly by statistical pattern-recognition methods. Such an approach permits systematic evaluations of different representations (be they formants, spectra, LPC's, or analog filter measurements). Cost can be balanced against performance. Given the large number of design choices in this area, careful attention must be paid to methods which are invariant under change of parametric representation. For segmentation, regions of acoustic change are detected by functions of parameter vector similarity and by amplitude cues. The basic model of signal detection theory can be applied to quantify the missed/extra-segment error trade-off. Error rates of 3.7% missed for 19% extra have been achieved. To account for allophonic variability when acquiring labeling knowledge (training), a clustering algorithm was developed to empirically discover the acoustic variations inherent in each phonetic class. Labeling then proceeds by nearest-neighbor match. Accuracy for 29 phonetic classes was 35% correct in the first choice and 60% correct in the first three choices. For details, see H. G. Goldberg, Ph.D. Thesis (Carnegie-Mellon University, 1975).
Nonlinear autocorrelation function (FNLAF)—Real-time pitch extractor
Authors: Garland C.
Published: October 2005

This paper describes a digital imprementation of a pitch-extraction algorithm which is based on bit-pattern comparison. The NLAF is a variation on autocorrelation analysis where, instead of correlating the input speech waveform, the autocorrelation is computed either on the sign of the signal or on the sign of the first derivative of the signal. After a review of the method, the pitch extractor implementation is described. Then, experimental results are presented when analysis is first performed on glottal waveform, and then on speech waveform. The comparison of the results leads to the necessity of preprocessing the speech waveform in order to eliminate the adverse effects of the frequency components generated by resonances within the vocal tract. This preprocessing is performed by use of a very simple digital fileteter which considerably decreases the probability of an erroneous determination of the pitch period.
Low-bit-rate voice transmission based on transversal block coding
Authors: Esteban Daniel , Menez Jean
Published: October 2005

A low-bit-rate voice coding scheme, in the range of 10 to 20 KPS, based on predictive transversal block coding is described. This voice coding scheme assumes the use of short- and long-term linear prediction and an optimum PCM/DPCM block companding quantizer which ensures the same dynamic as a standard PCM companded law. It accommodates various data rates by simply modifying the number of bits allocated to the quantizer. Examples based on 8-kHz sampling rate and data rates of 8 to 16 KBPS are investigated. It is shown that a two-bit coding scheme at 20 KBPS provides a quality and intelligibility which is quite the same as the standard A-law 84-KBPS coding scheme and that with one-bit coding at 12 KBPS the quality degradation is practically not noticeable in telephony applications. Tape recordings of the investigated cases will be played at the conference.
Optimum one-bit block quantizing
Authors: Esteban D. , Menez J. , Temine J. P.
Published: October 2005

An iterative method is described which allows determination of the optimum parameters of a first-order one-bit quantizer in the least-mean-square error sense. Those parameters are computed from a finite sequence of a block of samples. The reference first-order equation being nonlinear, an iterative substitution method is used to obtain the optimum parameters. The basic formula and the procedure are independent of the chosen type of coding scheme and can be applied indifferently to either one-bit PCM or delta modulation or adaptive delta modulation or any method supplying a binary quantizer sequence (for instance, Viterbi algorithm). This method has been applied with success in the area of voice encoding at low bit rate. Experimental simulations will be played during the presentation.
Continuous measurement of an individual's 24-h noise exposure for 31 consecutive days
Authors: Johnson Daniel L. , Farina Edward
Published: October 2005

A dosimeter based on the equal energy rule with a range from 55 to 110 dB was used to continuously monitor the noise exposure of one subject. The subject, who is the second author of this report, works in a relatively quiet laboratory area. The daily A-weighted average sound level for each 24-h period [Leq(24)] beginning at approximately 7:30 a.m. was measured. During the day the noise exposure from specific activities was also measured. The 31-d average sound level was 76 dB while the daily Leq (24) values varied from a low of 59 to a high of 83 dB. The type of activity that contributed most of the subject's total noise dose was night-time parties at private homes or nightclubs. Five such parties account for 42% of his total dose. One exposure at an automobile hobby shop and three outings at a bowling alley contributed another 27% of the total noise dose. If these outside recreational activities had been avoided, the 31-d average sound level would have been reduced to 71 dB. The problems involved in measuring a 24-h noise exposure as well as future plans for more elaborate studies will be discussed.
Relative effectiveness of several simulated jet engine spectral treatments in reducing annoyance response of test subjects engaged in a TV-viewing task
Authors: Gunn W. J. , Shigehisa T. , Shepherd W. T.
Published: October 2005

Twenty-four test subjects watched television shows in a simulated living room. There were 27 different stimuli (nine spectra at three overall levels) presented at an average rate of approximately one flight every 2 min. One spectrum was an untreated VC-10 landing. The eight others were the same as the first but with one of two amounts of energy removed from a one-octave-wide band centered at 315, 800, 1600, or 4000 Hz. Subjects judged the annoyance value of individual overflights using either a category rating method or magnitude estimation method in each of two one-hour test sessions. The spectral treatments most effective in reducing annoyance were at 1600 and 800 Hz, in that order. The amount of annoyance reduction resulting from all treatments was affected by the overall sound level of the stimuli, with the greatest reduction at the intermediate overall sound level. The results are interpreted as supporting the hypothesis that speech interference (at least in part) mediates annoyance with aircraft noise in a TV-viewing situation.
Analytical method for calculating driving-point pressures and velocities on an infinite fluid-loaded elastic plate
Authors: Benthien G. W. , Gonzalez M. A.
Published: October 2005

In this paper we present numerical results for driving-point pressures and velocities on an infinite, fluid-loaded, thin elastic plate as a result of the plate being driven by a line or point force, and/or a line moment. These results were obtained by simple analytical integration rather than by numerical quadratures. Comparison with other published results will also be presented.
Vibration isolation provided by attaching a rib on a panel
Authors: Maidanik G. , Tucker A. J. , Vogel W. H.
Published: October 2005

The response of a fluid-loaded single-ribbed panel was derived and discussed by the authors in the last meeting [J. Acoust. Soc. Am. 58, S42 (A) (1975)]. In that paper the panel was simulated by a membrane. The tension in the membrane was made frequency dependent so that it would simulate the dispersive properties era plate. In this paper emphasis is placed on the type of vibration isolation that a rib can provide between a localized driving field and a vibration sensitive observer located on the panel across the rib. The finding can be related to the vibration isolation that a rib provides against free waves on the panel. It is shown that the isolation that can be provided by the rib can be severely limited, in the lower frequency range, by moderate fluid loading. The frequency range is roughly confined to that below the critical frequency of the panel It is argued that the inclusion of fluid loading in structural vibration problems may be imperative, not only in situations in which estimates of acoustic radiation are sought; the nature of structure-borne sound may be significantly influenced by fluid loading.
Environmental vibration criterion for scientific laboratories
Authors: Walker David Q.
Published: October 2005

The degradation of scientific instrument performance due to excessive environmental vibration is a common problem, and one that requires recognition during the early stages of any new scientific facility. Nearby transportation systems, building mechanical equipment, and pedestrian activity at above-grade locations are usually the vibration sources of primary concern. However, in addition to the recognition of sources and the estimation of their magnitude, the potential for problems in a proposed facility cannot be quantified in the absence of a meaningful vibration criterion. Many criteria which exist for specific instruments are often vague, based on poorly defined measurements, and as a result are easily misinterpreted. In this paper, the development of a vibration criterion for general laboratory work spaces is described. The criterion is formulated primarily from the measurement of vibration environments in existing laboratories and is particularly relevant to the requirements of instruments such as electron microscopes, microtomes, analytical balances, and optical microscopes.
Extension of scaling laws for model experiments
Authors: Junger M. C.
Published: October 2005

Of the four dimensionless ratios required to characterize acoustic data [I.C. Romer, Jr., J. Acoust. Soc. Am. 59>, 1227–1229 (1976)] two depend exclusively on the physical properties of the acoustic fluid. A third ratio is kept invariant in the usual scaled models, whereby dimensions L and frequencies f are modeled respectively, as L/s and sf. A fourth ratio is the “sonic Reynolds Number”, ρL2f/μ, which controls boundary layer phenomena. It remains invariant if linear dimensions are scaled as L/s1/2. Reflection and absorption by Rayleigh solids, and other boundary phenomena can be modeled by scaling boundary statistics, e.g., boundary roughness, and interstitial spaces in porous layers (fibrous blankets and sandy ocean bottoms) as L/s1/2, while scaling macroscopic dimensions, e.g., layer thickness, as L/s. [Work supported by USN Office of Naval Research.]
Reflection instabilities of large-amplitude acoustic waves
Authors: Clark J. A.
Published: October 2005

Effects of the phase reversal which occurs when large-amplitude acoustic waves are reflected by a pressure-release boundary have been investigated experimentally. Large-amplitude, waterborne acoustic waves were generated by an induction type of electroacoustic transducer. Instantaneous pressure distributions associated with the propagating acoustic waves were determined by a whole field optical measurement method described elsewhere [Whole Field Measurements of Acousto-Optic Refraction, J. A. Clark, J. Sound Vib. 46, 306–310 (1976)]. Nonlinear deformations of the acoustic waves were analyzed both before and after reflection at the pressure-release boundary in order to verify theoretical predictions that large-amplitude sawtooth waves will deform back into sinusoidal waves under these conditions. [Research supported by ONR.]
Propagation of acoustic waves in steady extensional flows on non-Newtonian fluids
Authors: Schwarz W. H. , Powell R. L.
Published: October 2005

An analysis for the calculation of the attenuation and sound speed of a plane acoustic wave propagating through a non-Newtonian fluid that is undergoing a simple steady extensional motion is presented. The constitutive representation for the stress tensor in terms of the deformation gradient is developed for the model of a simple fluid, An explicit form is obtained for the superposed acoustic motion on the basic flow by using a functional Taylor's series having linear forms that are represented by integrals whose kernels are relaxation functions that depend on the extensional rates. An alternative representation is given as rate-dependent complex viscosities that depend on the relative orientation of the acoustic vector to the axes of extension. Several examples are described that are experimentally realizable and that can provide information on the rheological nature of the non-Newtonian fluid. [Work supported by NSF.]
Does the hearing among people with hearing loss have a normal distribution?
Authors: Thiessen G. J.
Published: October 2005

We make the assumptions that a person's hearing cannot be improved by aging, noise exposure, or any other otologically pathogenic agent, and that persons differ in their susceptibility to this agent. This has the logical consequence that an initially. normal distribution of hearing in a given population cannot remain so after the action of the pathogenic agent. The distribution must become skewed. Data in the literature confirm this change in distribution. This result has the further consequence that skewness in the distribution provides no evidence as to which group is the most susceptible.