bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstrated real-time continuous speech recognition performance
Authors: Bahler Larry , Moshier Steve , Brown Peter , Baker James
Published: October 2005

The Dialog Continuous Speech Recognition System has demonstrated real-time continuous speech recognition on a set of test material obtained from an independent source demanding very high performance in a procurement advertised to makers of automatic speech recognition systems. The five test speakers (three male, two female) were selected to have widely varying American dialects. The test sets themselves were recorded in two sessions, with the second session recorded at least two weeks after the training and first sessions, there was no opportunity for the Dialog system to be either refrained or even retuned for the second test session. These recordings consisted of individuals speaking in their regular noisy work environment, with noise levels of up to 85 dB octave band sound pressure. The test material consisted of the ten digits plus ten control words. Over the entire test set only five digit strings and five control words were rejected, and from the set of l0 000 digits, only 50 digit substitutions were made, yielding 99.5% digit recognition performance. From the set of 200 control words, no substitutions were observed. yielding 100% control word recognition.
Qualifications required by noise-control engineers in industry
Authors: Hickling Robert
Published: October 2005

Currently one of the major needs is for persons qualified in the use of Fourer analysis equipment. In recent years, many forms of this type of equipment have appeared on the market, particularly real-time systems that utilize two or more channels of input data. This equipment is now being widely used. The auto industry, for example, is applying it in all areas of vibration analysis and noise control. However, colleges and universities have not been adequately training people in this field. Mechanical engineers in particular are often lacking in basic understanding of multichannel analysis, i.e., transfer functions, cross-spectra, correlation functions, and the like. In addition to providing instruction in the theory of this form of data analysis, it is necessary to demonstrate its use with appropriate equipment. The cost of such equipment is presently a difficulty, but it need not be prohibitive. Recognition of this equipment need is required by instrument manufacturers, funding agencies, and university administrators.
Physical approach to the acoustic force on an object in a standing wave
Authors: Apfel Robert E. , Chu Boa-Teh
Published: October 2005

Theories for the acoustic radiation force on an object in a standing wave are complex—involving Bessel functions, complex integrations, and a bunch of cancelling terms. What is lost in the mathematics is a simple physical picture of the forces involved. For the case of the acoustic wavelength much larger than the object, this physical picture can be retrieved as the sum of results for simple elementary phenomena of fluid mechanics. And the result is the same as the comprehensive theory in the long wavelength limit. This physical approach will be presented. [Work supported by the Office of Naval Research, Physics Program.]
Precision acoustic measurements with a spherical resonator
Authors: Mehl James B. , Moldover Michael R.
Published: October 2005

Measurements of the frequencies and widths of the radial modes of a spherical resonator have been used to determine the speed of sound in low-density gases. The analysis of the experiment includes corrections for the effective surface impedance associated with the thermal boundary layer and the resonator elasticity, bulk dissipation, and the tubes which couple the transducers to the resonator. Measurements of the speed of sound as well as surface and bulk dissipative effects in argon and ethylene at 0 ⩾ T ⩾ 100°C and 0.1 ⩾ p ⩾ 1 MPa will be presented. At this stage of development, measurements of the speed of sound determined with the first several radial modes are typically consistent at the 10 ppm level. Further improvements are anticipated.
Sparse planar array for estimating bearing to near-ground sources: Theory
Authors: Babian Fred E. , Miller G. Kirby
Published: October 2005

A short-based planar array using omnidirectional microphones was chosen for bearing estimation as the result of the Cramer-Rap bound analysis done. The acoustic wavefront traversing the horizontal array is assumed to be a plane wave. Information about the space-time correlation function of the noise signal and knowledge about the signal spectrum are used in the bearing estimator to improve performance. The array is steered to different angles by introducing time delays into each microphone. The delays introduced cause the signal arriving from one specific angle to be phase matched for each microphone. The microphone signals are added, squared and integrated over a period of time. This steering is done for a number of angles and the maximum value of this process is the bearing angle of the most intense source.
Pitch of the residue for nonsimultaneous harmonics
Authors: Hall Joseph W. , Peters Robert
Published: October 2005

When three nonsimultaneous harmonics of a fundamental were presented to six trained observers at 50 dB SL, pitch perception was based on spectral frequency in quiet, but based on fundamental frequency when white noise was present (signal 6 dB above threshold in noise). Harmonics were of 40 ms duration, with 10 ms ISI. Harmonics of 200 Hz (600-800-1000 Hz) were paired with harmonics of 100 Hz (720-900-1080 Hz) for observers' 2AFC judgments of lowest pitch. Thus the stimulus with the higher fundamental (200 Hz) had relatively lower frequencies, while the stimulus with the lower fundamental had relatively higher frequencies. With close to 100% observer reliability pitch judgments in quiet were based on spectral properties and those in noise on residue. When subjects subsequently adjusted a tone to match the lowest pitch heard in such nonsimultaneous three-component stimuli, spectral pitch matches occurred in quiet while residue pitch matches occurred in noise. When a pitch-shift stimulus (650-850-1050 Hz) was matched in this paradigm, a frequency of 650 Hz was matched in quiet and 211 Hz was matched in noise.
Stimuli producing different apparent frequencies for periodicity analysis and for place analysis
Authors: Warren Richard M. , Wrightson John M. , Storck Herbert E.
Published: October 2005

Segments derived from Gaussian noise served as exemplars of complex waveforms, and were repeated with alternate antiphasic (180° phase-shifted) statements: [A+, A−, A+, . . .]. For repetition frequencies of (A+, A−) from 2–2000 Hz, listeners matched apparent frequencies using adjustable unipolar pulse trains: from 200–2000 Hz, apparent frequency = fundamental frequency = (1/τ Hz, where τ = duration (s) of [(A+) + (A−)]; from 2–30 Hz, apparent frequency = (2/τ Hz; from 30–200 Hz, apparent frequency was between (1/τ) and (2/τ) Hz. For 30–200 Hz, low-pass filtering at (10/τ) Hz favored matches of (2/τ) Hz and high-pass filtering at (10/τ) Hz favored matches of (2/τ) Hz. Results resemble earlier observations with bipolar (alternating polarity) pulse trains matched with unipolar pulse trains, then attributed to special characteristics of pulses. Our observations, together with other evidence, suggest rather that periodic waveforms consisting of antiphasic alternation produce different apparent frequencies for neural periodicity analysis and for neural place analysis, since: (1) periodicity analysis is insensitive to phase inversion [(A+) ≡ (A−)]; (2) place (spectral) analysis is sensitive to phase inversion [(A+) ≢ (A−)]. [Work supported by NSF.]
Contributions of attack and decay to loudness; more on the Rawdon-Smith illusion
Authors: Darwin C. J.
Published: October 2005

Jesteadt, Green, and Weir [Percept. Psychophys. 23, 244–250 (1978)] found that the second of two equally intense tones was heard as louder when the tones were separated by intensity transitions which decayed slowly and rose abruptly: an auditory analog of the Cornsweet illusion in vision. The experiments to be reported attempt to distinguish two types of explanation of this effect: (i) that slow changes in intensity are less perceptually salient than fast, (ii) that the attack, or onset of a note is more salient in determining loudness than is offset. Preliminary experiments indicate that the attack is more important than the relative amount of rapid or slow intensity changes. [Work supported by Science Research Council, U.K.]
Visual influence of outdoor vegetation on loudness
Authors: Mulligan B. E. , Goodman L. S. , Goodman H. Z. , Anderson L. M.
Published: October 2005

Loudness of sounds heard outdoors may be influenced by visual features of the listener's environment. Aylor and Marks [J. Acoust. Soc. Am. 59, 397–400 (1976)] found that estimated loudness magnitudes of noise diminished at visibility of sound sources in an outdoor environment improved. The present study sought to determine whether the visibility of vegetation and man-made structures would exert any influence on estimated loudness magnitudes of tones presented to listeners through headphones under outdoor conditions. Data were collected within five sites that differed systematically in visible vegetation (trees, shrubs, etc.) ranging from a site with no visible man-made structures (woods) to a site with no visible vegetation (city street). Equal numbers of male and female listeners generated loudness functions for each site. Trend analysis indicated that the obtained functions differed significantly across sites both in overall means (p < 0.01) and slopes (p < 0.01). None of the functions departed significantly from linearity in log-log coordinates, i.e., power functions. Loudness magnitudes were largest in the completely wooded site and diminished as the proportion of visible vegetation in sites decreased. [Work supported by USDA USFS.]
Binaural intensity discrimination data compared with left-right-averaged and with superior-ear data
Authors: Watkins W. H.
Published: October 2005

Binaural intensity difference thresholds were compared with monaural thresholds based upon left- and right-ear means, and with the thresholds of the ear showing superior intensity difference sensitivity for the test frequency. Consistent with other recent finding [W. Jesteadt and C. C. Wier, J. Acoust. Soc. Am. 61, 1599–1603 (1977)] the ΔI/I ratios for binaural listening were lower than the averaged monaural ratios for frequencies 250, 1000, and 3000 Hz. The superior-ear data, however, matched the binaural data well, and appeared to separate from left-right-averaged ΔI/I ratios. The suggestion is offered that the contribution of the less sensitive ear, in amplitude discrimination, may be negligible, at least for some varieties of stimuli.
An excitation-level model for intensity discrimination
Authors: Florentine Mary , Buus Søren
Published: October 2005

A new psychoacoustical model of intensity discrimination is proposed and its predictions are compared to data from the literature. The model is based on excitation patterns derived from masking patterns [Zwicker, Acustica 8, 237–258 (1958)] and is similar to Maiwald's model [Acustica 18, 81–92 (1967)]. We assume that (l) the excitation in each of 24 critical bands forms the input to 24 independent excitation-level discriminations—one for each critical band, (2) the individual excitation-level discriminations adhere to Weber's Law, and (3) the outputs of the excitation-level discriminators combine through an optimum decision rule. On the basis of this model, predictions are made for intensity discrimination of tones as a function of level and frequency and for several conditions of partial masking (including low pass, band pass, high pass, band stop, and wideband). In general, the model's predictions are in good agreement with the data in the literature, except at high frequencies. [Work supported by NIH.]
The measurement of the bulk modulus of polymers and its loss factor in the 1 to 10 kHz frequency range
Authors: Wilson Geoffrey L.
Published: October 2005

The bulk modulus and its loss factor are difficult to measure directly and are usually obtained indirectly from measurements of the Young's modulus and the shear modulus. This paper will discuss methods that have been used for the direct measurement in the frequency range of 1 to 10 kHz.
The determination of the loss tangent of PVAc derived from measurements with a creep torsiometer
Authors: Knauss W. G.
Published: October 2005

Damping characteristics or energy dissipative characteristics of materials can be determined in a variety of ways. If a proven or acceptable constitutive description for a material at hand exists, virtually any physical measurement can be converted into a description of energy loss, provided the measurements are sufficiently accurate and are made over a suitable range of parametric interest. In many applications, particularly acoustics, deformations are so small that linearly viscoelastic behavior represents an appropriate constitutive description. Starting from a description of the apparatus shear creep measurements are converted exactly and approximately to loss tangent (storage and loss modulus) data. A comparison of the approximate and exact representation is made. The description of the test procedure and computations allows the comparison to other methods with respect to ease and accuracy of property determination.
Automated dynamic Young's modulus and loss factor measuremeats
Authors: Madigosky Walter M. , Lee Gilbert F.
Published: October 2005

A progressive wave apparatus featuring an automated data processor is described. The apparatus accurately determines the propagation constants of an extensional acoustic wave by exciting one end of a strip of material while the other end is suspended under constant tension. The apparatus is capable of making measurements in the frequency range of 100 Hz to 40 kHz, depending on the extensional wave velocity and attenuation in the material. As illustrations of the technique, measurements were made on several rubber compounds of different polymer type and compounding ingredients. Extensional sound speed, attenuation, modulus, and loss factor were determined over a frequency range of 1–10 kHz and a temperature range of 4°–47°C. Applying the time-temperature superposition principle to the data, master curves were constructed and WLF shift constants were determined. The apparatus was found to be a fast and reliable method to determine the dynamic viscoelastic constants.
The effect of wall thickness on the wave speed of breathing waves
Authors: Jameson Paul W.
Published: October 2005

A very accurate and convenient way to measure the complex Young's modulus of a viscoelastic material in the form of thin-walled tube is to measure the speed and decay rate of the breathing waves which propagate when the tube is filled with a fluid. Use of the formula for the speed of breathing waves in thin-walled cylinders leads to substantial error when applied to tubes having thick hosewalls however. Considerably more accurate results are obtained by using simple relations derived from the Airy stress function for the stress and strain of a thick-walled cylinder in a state of zero axial stress. The expressions are used to interpret measurements performed by R. Hauptman on thick-walled cylinders. Values of Young's modulus obtained this way are shown to agree with values obtained from measurements of small cylinders in a Rheovibron device. The validity of neglecting axial stress and the hosewall mass is theoretically assessed.
Fluid-coating interface wave methods for the determination of coating properties
Authors: Kerwin Edward M. , Berkman E. F.
Published: October 2005

An experimental method of determining the properties of a compliant layer by layer/fluid interface wave methods is investigated. The phase and/or group speed and spatial attenuation of such waves can be used to infer the layer stiffness per unit area (and, hence, material modulus) and the loss factor. An analysis of the propagation of interface and acoustic waves in a water-filled trough with one lossy-compliant surface is presented. The analysis is a general One including the case of finite water depth. It is concluded from the analysis and from the experimental results that the experimental setup investigated can give readily interpretable results over only a limited frequency range and is appropriate only for materials with relatively low loss factors.
A model of formant frequency patterns in Russian VCV utterances
Authors: Purcell Edward T.
Published: October 2005

A recent article in JASA described Russian formant frequency patterns in VCV utterances. Based on a stepwise multiple regression analysis of the data, that article showed the influence of articulatory predictors on each of four measurement points within the VCV test words. The analysis was limited to a separate consideration of each measurement point and the relative influence of the various articulatory parameters on the formant frequency at that point. The present paper presents a more comprehensive, more theoretically oriented analysis of the data. Using LISREL, a statistical package for the analysis of linear structural relations, it was possible to study the interactions of the measured variables and the effects of the articulatory parameters on these measured variables in one pass. The results of this analysis should be more interesting from a theoretical point of view.
Phonological constraints in speech perception
Authors: Massaro Dominic W. , Cohen Michael M.
Published: October 2005

Speech perception can be viewed in terms of the listener's integration of two sources of information: the acoustic features transduced by the auditory receptor system and constraints in the spoken language. In order to assess how these sources are evaluated and integrated, a speech continuum between the liquid-vowel syllables /ri/and /li/ was generated by varying the onset frequency of the third formant. Each sound along the continuum was placed in a consonant-cluster vowel syllable after an initial consonant /p/, /t/, /s/, and /v/. In English, both /r/ and /l/ are phonologically legal following /p/ but are not legal following /v/. Only /l/ is legal following /s/ and only /r/ is legal following /t/. Listeners identified the sounds as one of the eight alternatives /pri/, /pli/, /tri/, /tli/, /sri/, /sli/, /vri/, and /vli/ or simply identified the liquid portion of the test sound. These identifications to sounds generated by the factorial combination of acoustic featural information for the /r/-/l/ distinction and the legality of the phonological context allow quantitative tests of various models of how these two sources of information are evaluated and integrated together in speech perception. [Work supported by NIMH.]
Acoustic cues for place of articulation in the one-word stage of language acquisition
Authors: Chapin C. , Tseng C. Y. , Lieberman P.
Published: October 2005

The theory developed by the Haskins group claims that place of articulation is cued by context dependent, formant frequency transitions. An alternate theory [S. E. Blumstein and K. N. Stevens, J. Acoust. Soc. Am. 66, 1001–17 (1979)] proposes that children initially use innate, invarient cues to identify place of articulation and learn to use formant frequency transitions. We analyzed 30 word-initial voiced stops of two children in the one-word stage of speech acquisition. Onset spectra computed using LPC analysis with a 25.6 ms window were compared with the Blumstein and Stevens templates. In addition, computer editing techniques were used to produce three series of stimuli for psychoacoustic tests. Listeners were asked to identify place of articulation when they heard only the first 15, 40, or 135 ms of each utterance. Approximately 80% of the stops had invarient cues. Context dependent cues clearly are not the sole cues as the Haskins theory implies. However, place distinctions for some stops which could not be determined using the templates, were identified in the longer computer-edited versions, where formant transitions were present. [Work supported by NIH.]
Native language effects on the perception of liquids
Authors: MacKain K. S. , Best C. T. , Strange W.
Published: October 2005

In a study of the effect of language experience on speech perception, Miyawaki et al. (Percept. Psychophys. 1975) found classic categorical perception of the liquids [r] and [l] in native speakers of American English, but not in native Japanese, whose language lacks a liquid contrast. They tested oddity discrimination, using a synthetic [r]-[l] continuum containing systematic variations in the F3 transition. Since the oddity task is believed to be very difficult, the current research investigated effects of the task requirements on discrimination via comparison of A × B and oddity discrimination tests with American and Japanese adults. Because spoken liquids show F1 and F2 differences in addition to the F3 difference, a new ten-item synthetic continuum was used, which involved concurrent changes between [r] and [l] in all three formants. The American results replicated the earlier findings. Peaks and troughs in their performance on A × B and oddity tasks reflected categorical discrimination, and corresponded with predictions from the sharp category boundary they produced in an absolute identification test. The Japanese data also replicated Miyawaki et al., and contrasted with the Americans' results. Their identification functions were near chance throughout the continuum, and their discrimination performance for both tasks was non-categorical, as predicted from identification results. Implications for effects of native language on phoneme perception will be discussed, along with methodological comparisons of the A × B and oddity tasks. [Supported by NICHD and NINCDS.]
Annoyances due to multiple airplane noise exposure
Authors: Powell Clemans A.
Published: October 2005

A laboratory study was conducted in which 250 subjects judged the annoyance of one-half hour periods of airplane noise simulative of typical indoor home exposures. The variables of the aircraft noise exposure were the peak noise level of flyovers (56, 62, 68, 74, and 80 dBA) and number of flyovers (1, 3, 5, 9, and 17 per period). Each subject judged five of the possible 25 factoral combinations of level and number. Other variables investigated included the experience of the test subjects in making annoyance judgments and their home airplane noise exposure. The annoyance judgments increased with both level and number of flyovers such that the increased annoyance produced by doubling the number of flyovers was found to be the equivalent of a 4- to 6-rib increase in noise level. The subjects' differential sensitivity to both noise level and number of flyovers increased with laboratory experience. Although the laboratory annoyance judgments were found to be inversely related to the subjects' home aircraft noise exposure, their differential sensitivity to level and number was unaffected by their home exposure.
Backward masking and interference within the same psychophysical continuum
Authors: Ahroon William A.
Published: October 2005

A number of attempts have been made to compare temporal masking, a threshold phenomenon, and the interference in the recognition or discrimination of a clearly detectable signal by another, temporally discrete, signal. Typically, traditional backward and/or forward masking functions are compared with functions relating frequency discriminations of pure tones which are preceeded or followed by another, interference, stimulus [cf., Sparks, J. Acoust. Soc. Am. 60, 1347 (1976)]. One notable feature of these studies involves the comparison of metathetic frequency discrimination tasks with prothetic intensity detection tasks. The present research was designed to compare backward masking and backward interference more directly, using detection and discrimination tasks within the same stimulus continuum. Backward masking functions were obtained using a 50-ms broadband noise signal followed in time by another 50-ms noise masker. Backward interference functions were obtained also using 50-ms noise signals and 50-ms noise maskers, in which the observer's task was to indicate which of two intervals contained the louder signal. The results are discussed in terms of threshold and suprathreshold intensity discriminations in the presence of temporal maskers.
Load-induced resonant frequency changes in hearing aid receivers
Authors: Gilman Samuel , Dirks Donald D.
Published: October 2005

Results from an investigation of acoustic interactions between hearing aid receivers and ear simulators indicated that the receiver resonant frequencies changed as a function of load impedance. At resonance, the receiver's impedance changes quickly and can approach the conditions for maximum power transfer, i.e., the load and source impedances are conjugate. If the conjugate condition occurs at frequencies near to but not equal to the receiver diaphragm resonance, the system will show the resonance at the frequency where the reactive components are equal and opposite. Using different reactive loads, the change in system frequency can be used to determine the inertance and compliance of the receiver diaphragm. An analysis has been made of a typical receiver using four known loads. These same loads used in the interaction investigation provided data which were then available for computing actual receiver constants. The overall results corresponded closely with the theoretical analysis. From the procedure used it appears that a method can be derived for determining the acouslic characteristics of a receiver under actual loaded operating conditions. Its application to the fitting of hearing aids is being investigated.
The duration of normally articulated and functionally misarticulated [s] in preschool children
Authors: Weismer Gary , Elbert Mary
Published: October 2005

The duration of [s] was measured in two groups of children aged 4–6 years; one of these groups contained children with “normal” [s] articulation whereas the other group contained children with functional misarticulation (i.e., misarticulation which has no known organic etiology) of the [s] sound. The speech sample consisted of [s] sounds embedded within 36 nonsense sequences the form of which was variously mono or bisyllabic. Within these sequences [s] was varied with respect to position and phonetic context. Each one of the sequences was produced in the carrier phrase I like to say _____ and was replicated six times by each subject. Measurements of [s] duration were derived from oscilloscopic displays, and the resulting data were examined for trends of central tendency and dispersion. One interesting result was that average intrasubject variabilities were greater for the misarticulating, as compared to normally articulating children. This finding is considered relative to potential motor control deficits which may be associated with functional misarticulation. [Work supported by NINCDS Award No. PHS R01 15551-01.]
Acoustic parameters of plain and pharyngal fricatives in Lybian Arabic
Authors: Krieg Laurence J. , Benson Peter J. , Catford J. C.
Published: October 2005

Arabic fricatives, particularly those differentiated by pharyngalization, still present unanswered questions to phonetic investigators: the acoustic cues differentiating the contrasts have only been partially specified [e.g., al-Ani, Arabic Phonology, The Hague (1970)]; it has not been satisfactorily demonstrated whether fricative noise itself or only the surrounding vowels differentiate between corresponding pairs of pharyngalized (emphatic) and nonpharyngalized fricatives [e.g., Jakobson “‘Mufaxxama’…”, in Selected Writings, Vol. 1, pp. 510–522 (1962); Bonnot, “Recherche expérimentale sur la nature des consonnes emphatiques de l'arabe classique,” Traveaux de l'Institute Phonétique de Strasbourg 9, 47–88 (1977)]. A dialect of Lybian Arabic which, according to native linguists, contrasts an unusually large number of plain versus pharyngalized fricatives [s ᵴ ∫ ⨏ χ χ/ h; ℏ ð ð/] is recorded; measurement is made of time-domain variables such as VOT, rise time, and relative amplitude of the fricative. Spectral information is averaged together to provide representative spectra of each of the contrastive fricatives. These spectra are then transformed using various weighting functions; the original, the transformed spectra, and time-domain measurements are then compared and grouped by multivariate analysis techniques to provide evidence for the general phonological groupings of fricatives in this dialect and the role of the pharyngalized/plain contrast.
On elastic wave scattering from planar cracks
Authors: Visscher William M.
Published: October 2005

Cracks, which constitute an important class of defects in materials, are mathematically idealized by planar voids of zero thickness whose surfaces are traction-free. A longitudinal or transverse plane wave propagating in a homogeneous isotropic elastic medium will be scattered by such a flaw. The following properties of the scattering cross section will be established. (i) In the Rayleigh limit the longitudinal and transverse scattered amplitudes can be described by 6 parameters which represent (1) the area of the crack, (2) its aspect ratio, (3) the deviation of its shape from symmetry under inversion through its center. (4, 5) two angles specifying the orientation of the crack plane, and (6) the orientation of the crack in its plane. Formulae for the scattered amplitudes in terms of these parameters will be displayed. (ii) For any wavelength whatever and the incident direction normal to the plane of the crack the scattered intensity in either the longitudinal or the transverse mode is symmetric under reflection through the plane of the crack, and the transverse intensity vanishes in the plane of the crack. [Work supported by DOE.]
Two-moras-cluster as a rhythm unit in spoken Japanese sentence or verse
Authors: Teranishi R.
Published: October 2005

In spoken Japanese sentence, mora is regarded as a temporal unit because of its isochronous tendency. However, in slowly spoken Japanese sentence or verse, two moras tend to be read as one cluster and the isochrony of more looks gone. So the cluster comes up as a rhythm unit. This tendency is quite clear in recitation of verse. Some people have taken notice to such a phenomenon, but nobody confirmed it by physical measurement. Here, durations of moras are measured systematically according to speaking speed, in order to study how the cluster consists of two moras. As a result, it is found out that a waiting interval comes up between the second mora in the cluster and the first mora of the next cluster, whenever the speed comes fairly slow. During the waiting interval, voicing action usually still continues. So, the apparent duration of the second more looks longer than the first one. This is the reason why the waiting intervals have never been revealed unless they are studied and measured systematically.
Ears adapted to detect motion, or how echolocating bats exploit the capacities of the mammalian auditory system
Authors: Neuweiler Gerhard
Published: October 2005

Bats avail themselves of the rich food resources of the night by specializing in audition. They emit short echolocation sounds and listen to the echoes returning from potential prey and the environment. The bat's auditory system analyzes spectral and temporal parameters of echoes for detecting, precisely locating, and identifying a target. Different bat species have solved the problem of acoustic target detection and pattern recognition even in heavily clustered situations by focusing on certain acoustical features of the targets. The specialized motion defection by Horseshoe bats, for instance, analyzes small echofrequency shifts modulated onto a long constant frequency echolocation signal. These frequency modulations are Doppler shifts of echoes returning from wing beating insects. For detecting modulations as small as 10 Hz or 0.01%, Horseshoe bats have in the cochlea an extremely narrow filter (Q = ca. 500) matched to the carrier frequency (i.e., echolocation sound) of 83 kHz. The filter is based on mechanical principles and realized by structural differentiations of the basilar membrane. We have called this specialized patch of the basilar membrane an “acoustical fovea.” In analogy to the visual fovea the “foveal frequencies” are largely over-represented in the tonopical arrangement of the ascending auditory pathway. The bats have developed a feedback system which lowers the emitted echolocation frequency in such a way that the Doppler shifted echofrequency is kept precisely at a fixed reference frequency close to 83 kHz. This feedback system and additional neuronal data disclose an intricate coupling of the auditory and vocalizing system. The evolution of echolocation in bats has driven the analyzing capacities of audition close to theoretical limits. Investigations in such specialized systems give fascinating insights into possible general principles of auditory information processing.
Theory of elastic-wave propagation in composite materials
Authors: Berryman J. G.
Published: October 2005

A self-consistent method of estimating effective macroscopic elastic constants for inhomogeneous materials with ellipsoidal inclusions has been formulated based on elastic-wave scattering theory [J. G. Berryman, Appl. Phys. Lett. 35, 856 (1979)]. The self-consistent effective medium is determined by requiring the scattered, long-wavelength displacement field to vanish on the average. The resulting formulas are simpler to apply than previous self-consistent scattering theories due to the reduction from tensor to vector equations. The results are compared to the rigorous Hashin-Shtrikman bounds, Miller bounds, and Kuster-Toksö estimates for the elastic module. For spherical inclusions, our formulas agree with statically derived self-consistent moduli of Hill and Budiansky. For general ellipsoidal inclusions, our results always satisfy both the Hashin-Shtrikman bounds and the more stringent Miller bounds. Furthermore, our theory reduces correctly to all known exact results in the appropriate limits. The theory is used to calculate velocity and attenuation of elastic waves in fluid-saturated media.
Multiple scattering theory for discrete, elastic, random media
Authors: Devaney A. J. , Levine H. , Plona T.
Published: October 2005

A theory is presented for determining the ensemble-averaged Green's function of a random distribution of identical, randomly oriented elastic scatterers embedded in an infinite, homogeneous, and isotropic matrix. The average Green's function for such a medium is characterized by three parameters which are analogous to the Lame constants and density of an ideal, homogeneous, and isotropic medium. The theory can thus be thought of as having as its goal the determination of “effective” elastic parameters and density which characterize the composite medium. The theory is based on the self-consistent formulation of Lax's multiple scattering theory [M. Lax, Phys. Rev. 85, 621 (1952)] due to Gyorffy [B. L. Gyorffy, Phys. Rev. B1, 3290 (1970)] and Korringa and Mills [J. Korringa and R. L. Mills, Phys. Rev. B5, 1654 (1972)]. Application of the quasicrystalline approximation (QCA) results in three coupled equations which must be solved jointly for the ensemble-averaged Green's function. These equations are solved approximately for the case of an ensemble of identical, homogeneous, and isotropic spherical scatterers and found to yield accurate estimates of the velocity and attenuation of the coherent compressional wave in random composites of loose glass beads in a fluid matrix.
Observations on the generation mechanism of stimulated acoustic emissions
Authors: Kemp D. T.
Published: October 2005

Acoustic emissions originating in nonlinear cochlear mechanical processes have been re-examined using improved cochlear signal recovery and analysis techniques. The complex value of the effective cochlear reflection coefficient and also reflector frequency selectivity has been determined for several ears as a function of frequency using various stimulus and masking conditions. These data will be presented and used with additional data in a critical examination of the hypnothesis that the second filter mechanism has, as a necessary product or by-product of its operation, a mechanical output component which is unevenly coupled back to gross basilar membrane motion by permanent mechanical imperfections.
Some aspects of the control and measurement of the dynamic properties of fiber reinforced plastics
Authors: White R. G.
Published: October 2005

The damping of carbon fiber reinforced plastics (CFRP) is generally low at fiber volume fractions used for practical structures, such as aircraft components. If resonant behavior is induced in service, there is obvious merit in increasing material damping. Experimental and theoretical studies have been carried out to examine methods for increasing the damping of CFRP by use of short aligned fibers and combinations of fiber types; some configurations yielding moderate damping increases have been found. Stiffness to weight ratio is also a significant parameter for high performance structures, therefore both the loss factor and dynamic modulus of elasticity of specimens must be measured if experimental studies are carried out. Techniques for measuring these dynamic characteristics of material specimens have been developed. Attention has been given to the development of simple, rapid methods for measuring the properties, such as structural loss factor, of beams through a frequency range for comparative purposes. A technique for the more fundamental determination of material loss factor is also described. Results from tests on various types of CFRP are given. [Work supported by the Ministry of Defence.]
Costly low pressure bearing support cracking problem resolved through additive damping
Authors: Drake M. L. , Goodman R. C.
Published: October 2005

The component is the low pressure bearing support (LPBS) of the TF-41 jet engine. The LPBS was experiencing high cycle fatigue failures in the four vanes used to supply and scavage oil for the front bearing. High cycle fatigue failure in this vane case assembly is a general problem in currently operating turbine engines. A program was conducted to design and engine test a constrained layer damping wrap to control the problem. This project was conducted as a cost savings alternative to the current high maintenance effort to repair the high cycle fatigue cracks, and the redesign of the component and implementation of the new component in the fleet. The requirement for the damping treatment was to significantly reduce the dynamic response (and thus reduce the dynamic stresses) of the oil carrying vanes in their operating temperature range; and, the thickness of the application was to be not greater than 0.016 in., so as not to affect engine performance. The laboratory test showed a factor of ten decrease in dynamic response due to the application of the damper wrap, while the engine test cell run showed a dynamic stress reduction of eighty to ninety percent. This paper will describe the utilization of modal analysis data for damping treatment planning, the process for damping treatment design optimization, and proof testing on an operational engine. [This work was supported by the United States Air Force Materials Laboratory.]
Noise suppression due to annulus shaping of a conventional coaxial nozzle
Authors: von Glahn U. , Goodykoontz J.
Published: October 2005

Previous studies have shown that increasing the annulus width of a conventional coaxial nozzle with constant bypass velocity will lower the noise level. In the present model-scale study, the annulus was shaped by an eccentric mounting of the annular nozzle with respect to the conical core nozzle. Acoustic measurements were made in the flyover plane below the widest portion of the annulus and at 90° and 180° from this point. The model-scale spectra are scaled up to engine size (1.07-m diameter) and the perceived noise levels for the eccentric and concentric coaxial nozzles are compared over a range of operating conditions. The implications of the acoustic benefits derived from the eccentric nozzle to practical applications are discussed.
Noise suppression due to annulus shaping of an inverted-velocity-profile coaxial nozzle
Authors: Goodykoontz J. , von Glahn U.
Published: October 2005

Previous studies have shown that an inverted-velocity-profile coaxial nozzle for use with supersonic cruise aircraft produces less jet noise than an equivalent conical nozzle. Furthermore, decreasing the annulus height (increasing radius ratio with constant flow) results in noise reduction benefits. In the present model-scale study, the annulus was shaped by an eccentric mounting of the annular nozzle with respect to the conical core nozzle. Acoustic measurements were made in the flyover plane below the narrowest portion of the annulus and at 90° and 180° from this point. The model-scale spectra are scaled up to engine size (1.07-m diameter) and the perceived noise levels for the eccentric and concentric inverted-velocity-profile coaxial nozzles are compared ovcr a range of operating conditions. The implications of the acoustic benefits derived from the eccentric nozzle to practical applications are discussed.
Farfield radiation of aft turbofan noise
Authors: Rice Edward J. , Saule Arthur V.
Published: October 2005

The farfield radiation of turbofan noise from the inlet of an engine has recently received considerable study. Relatively simple approximate expressions have been developed for single mode radiation as a function of cutoff ratio and for multimodal radiation. Convective effects upon radiation which are essential for interpreting static engine tests have been developed. This information has been essential for the design of inlet suppressors. This paper represents an initial effort to provide the same type of radiation expressions for the noise radiation from the aft duct. The results of approximate aft radiation equations are compared to more exact Wiener-Hopf radiation results. Refraction as well as convective effects in the multiple flow streams must be considered. The possibility that the acoustic power distribution is altered during transmission is also discussed. This has an impact on the design and testing of aft duct suppressors.
Noise reduction for floating compartment and damped deck treatments in ship living spaces
Authors: Burroughs C. B. , Fischer R. W. , Shiflet F. L.
Published: October 2005

Airborne and structureborne noise measurements were made in two identical full-scale ship living compartments in the laboratory at Hopeman Brothers (1) with and without a floating compartment treatment and (2) with and without damping noise reduction treatments applied to the deck. An impact hammer was used to drive the deck from underneath. The structureborne noise transmission losses across the floating deck and the reductions in airborne noise levels inside the space due to the floating compartment are presented. For the damped deck treatment, measured data on airborne and structureborne noise reductions are given, along with measured damping loss factors for the deck, with and without the damping treatment in place. Results from noise measurements conducted on identical ships with and without floating decks and on a ship before and after a deck damping treatment was installed are presented and compared to results measured in the laboratory.
The influence of preceding syllable structure on intervocalic voicing boundary
Authors: Fitch Hollis L.
Published: October 2005

The perception of an intervocalic b can be changed to p by lengthening the silenced closure interval. The slower the speaking rate, the longer the closure interval needed, roughly in proportion to the duration of the preceding syllable [Port, J. Acoust. Sec. Am. Suppl. 1 63, S20 (1978)]. To see whether the structure of that preceding syllabic also affects the voicing boundary, slowly spoken /dab/ syllables were shortened to match the durations of medium rate and fast rate /dab/ syllables by deleting pitch pulses from the steady-state region of the vowel. A variable silent interval and a constant /bi/ were appended to each of the /dab/ syllables, making /dabi/ to /dapi/ continua. The voicing boundary was at a nearly identical ratio of closure duration to preceding syllable duration for unmodified syllables at all speaking rates, but it was at a lower ratio (proportionally less silence was needed) for the originally slow syllables in which the vowel had been shortened. In fact, it was found using synthetic speech that longer syllables with proportionally short steady-state sections needed less silence than shorter syllables with proportionally long steady-state sections. Thus, the perceptual voicing boundary is sensitive to the dynamic structure of the preceding syllable and not simply its duration. [Research supported by NICHD.]
Fundamental frequency as a cue to postvocalic consonant voicing in production: Developmental data
Authors: Krause Sue Ellen
Published: October 2005

Several studies by Lehiste have indicated that fundamental frequency (F0) contour affects perception of vowel length and of postvocalic consonant voicing; however, recent evidence from speech production showed no such relationship between F0 contour and voicing of postvocalic consonants [T. M. Gruenenfelder, J. Acoust. Soc. Am. Suppl. 1 65, S8(A) (1979)]. The present study was designed to investigate F0 contours in relation to postvocalic consonant voicing in speech production from a developmental perspective. The experimental stimuli consisted of three minimal word pairs, which differed in the voicing feature of the postvocalic stop consonant. Subjects. as young as three years of age and with normal language and articulation skills and normal heating sensitivity, named the stimuli in single word productions. The F0 at the start of the vowel (F0s), F0 at the end of the vowel (F0e), and the change in F0 (ΔF0 = F0s − F0e) were calculated for each trial of all six stimuli for each speaker. Findings will be discussed with regard to the voicing feature of the postvocalic consonant, the minimal word pairs studied, and subject age. [Work supported by NIH.]
Vocal fry: A cue for voicing in postvocalic stops
Authors: Walsh Thomas , Parker Frank
Published: October 2005

The hypothesis that vowel-termination characteristics signal the voicing distinction of post-vocalic stops in English [F. Parker, J. Phonet. 2, 211–221 (1974)] was investigated by recording CVC(C) monosyllables produced by six speakers and analyzing the utterances spectrographically. Although the vowel terminations before voiced stops were asystematic, the voiceless stops typically displayed a coarticulated glottal stop (evidenced by vocal fry). More importantly, the glottal stop appeared only with labial and alveolar voiceless stops, thus accounting for two phenomena noticed (but not explained) in the literature. (1) Vowel durations preceding voiced/voiceless nonvelar stops overlap, whereas those preceding velars do not [L. Raphael, J. Acoust. Soc. Am. 51, 1296–1303 (1972)]. (Vocal fry is not available as a voicing cue in velars, thus making vowel-length crucial.) (2) Final voiced/voiceless velar stops are confused more often than voiced/voiceless labials and alveolars [M. Wang and R. Bilger, J. Acoust. Soc. Am. 54, 1248–1266 (1973)]. (The latter had vocal fry as a secondary cue, thus enhancing their perceptibility.) In short, a glottal stop coarticulated with a following nonvelar voiceless stop produces vocal fry, which not only serves as a secondary cue for voicelessness, but also helps explain the differences in vowel length and perceptibility exhibited by velar and nonvelar postvocalic stops.