bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms for the generation of railroad wheel squeal
Authors: Dixon Nicholas R. , Remington Paul J.
Published: January 2006

Railroad wheel squeal is associated with rail vehicles rounding curves of small radii, and it is regarded as one of the most intense and annoying noise mechanisms on rapid transit systems. This paper reviews a theory for the generation of wheel squeal and provides experimental data from laboratory and field measurements that are compared with the theoretical analysis. Squeal occurs when the railroad wheel slides laterally across the rail head, and the theoretical analysis shows that the friction forces generated by this sliding can cause squeal if the coefficient of friction decreases with increasing relative velocity between the wheel and rail. Laboratory measurements of the coefficient of friction (μ) versus the lateral creep of a railroad wheel are discussed that verify the decrease in μ with increasing wheel rail relative velocity. A series of field measurements on several rapid transit lines is described that determined the influence of the ratio of curve radius to truck wheelbase on the occurrence of squeal and provided good agreement with the theoretical prediction for the onset of wheel squeal. Methods of controlling squeal have involved special damped or resilient wheels. A recent survey of the loss factor data of specialized wheels, known to suppress squeal, indicates that less wheel damping is required than that predicted by the present theory. Reasons for this discrepancy are discussed.
In-service evaluation of damped subway wheels
Authors: Manning Jerome E.
Published: January 2006

A 1-yr in-service evaluation of damped subway wheels is being done on the New York City Transit Authority system as part of the Urban Mass Transportation Administration's Urban Rail Noise Abatement Program. Four types of damped wheels are being evaluated to determine their effectiveness in reducing wheel squeal. Acoustic data are being collected throughout the 1-yr program to monitor the acoustical performance of the wheels. Data are also being collected to determine the cost of the wheels, including any additional maintenance and inspection. This presentation focuses on results obtained through the first 6 months of the 1-yr evaluation. [Work supported by the United States Department of Transportation.]
Comparison of physical acoustics and geometric theory of diffraction predictions for backscattering by impedance-covered wedgelike scatterers
Authors: Sachs D. A.
Published: January 2006

Radar scattering studies have shown that scattering predictions based on physical acoustics are generally invalid away from specularly reflecting directions. In this paper, comparisons are made between the predictions of physical acoustics and the geometrical theory of diffraction for acoustic backscattering by impedance-covered wedgelike scatterers. Substantial differences are seen in the results at angles of incidence well off the specularly backscattering direction where diffraction by the wedge edge dominates the return. [Work sponsored by Naval Underwater Systems Center, New London, CT.]
Acoustic resonance scattering by a cylindrical shell
Authors: Brill D. , Gaunaurd G. C.
Published: January 2006

We present a study of the resonance scattering process that takes place when plane acoustic waves are incident on elastic cylindrical shells in water. The analysis proceeds along the lines described by us earlier [D. Brill and G. Gaunaurd, J. Acoust. Soc. Am. 73, 1448–1455 (1983)] for solid elastic cylinders, and extends it to (hollow) shells. For aluminum gas-filled cylindrical shells of various thicknesses, we construct the families of zeros in the complex k1a (≡ x) plane that give rise to the Rayleigh and the whispering gallery waves circumnavigating the shell. We have isolated the proper modal shell resonances from their modal backgrounds and we have generated monostatic plots of background-supressed form functions (i.e., cross sections) that agree well with recent experimental observations made by a team in France. We have noticed that as the shells become thinner, fewer families at poles seem to offer contributions, until for very thin shells, only one type of circumnavigating surface wave seems to be possible. Finally, by means of the RST-pole diagrams, we have also studied the more attenuated (and less significant) contributions of the Franz or creeping waves to the overall resonance scattering process. Work continues.
Angular spectrum characterization of acoustical transducers
Authors: Johnson Richard K.
Published: January 2006

The transmitting and receiving responses of an acoustical transducer in a fluid are characterized using the angular spectrum of plane waves representation. Nearfield and farfield calibration procedures for determining the parameters of the representation are described. Some of these procedures have been implemented, and results are shown. A simplified description is developed for the case of a circularly symmetric transducer which permits a significant reduction in computation. Forward and backward propagation of the radiated acoustical field can be performed using Fourier transform methods. This characterization is very effective for analysis of scattering problems, particularly when they are expressed in the T-matrix formalism. An example is shown for normal incidence backscattering from a layered viscoelastic half-space.
Selective observation of elastic body resonances by using long pulses to excite a ringing response in the body
Authors: Numrich S. K. , Howell W. E. , Uberall H.
Published: January 2006

An elastic body submerged in water will ring when insonified by sound whose frequency is the same as one of the resonances of that body. Correspondence has been established between these normal mode resonances of the body and the individual circumferential waves predicted by creeping wave theory. Insonifying the target with a relatively long sinusoidal pulse results in a series of superimposed responses consisting of the specular reflection and a series of creeping waves arriving after successive circumnavigations of the body. Echoes, both analytically and experimentally obtained, from spherical targets will be used to identify the properties of the resonance ringing and associate the superimposed echoes with the resonance poles that can be predicted theoretically.
Effects due to elastic response of some simple bodies on coherently processed broadband echoes
Authors: Gaumond C. F. , Numrich S. K. , Dragonette L. R.
Published: January 2006

As an approximation underwater targets are sometimes modeled as point scatterers. However, broadband echoes from elastic bodies of finite extent can be modulated by circumferential or internal elastic waves. This modulation causes the echoes to be temporally broadened and more widely distributed on a cross-ambiguity plot. The extent of these elastic effects on pulse width, coherence, and ambiguity will be shown for several cases of solid and hollow bodies.
Octave equivalence in the processing of tonal sequences
Authors: Deutsch Diana
Published: January 2006

An issue of considerable debate concerns octave equivalence of tones that are presented in a sequential setting. In a previous study, Deutsch [Perception Psychophys. 6, 411–412 (1972)] showed that a well-known melody became unrecognizable when its component tones were displaced randomly to different octaves. It was concluded that, in accordance with the two-channel model for the abstraction of pitch relationships proposed by Deutsch [Psychol. Rev. 76, 300–307 (1969)], octave equivalence effects do not operate directly in a sequential setting. It has, however, been argued that distortion of melodic contour was responsible for the recognition performance obtained. To settle this issue, a new paradigm was employed. Musically trained listeners were presented with novel sequences of tones, which they recorded in musical notation. When the tones within a sequence were in the same octave, a high performance level was obtained. However, when the tones within a sequence were distributed across octaves, performance deteriorated sharply. This result confirms the hypothesis that octave equivalence effects do not operate directly in a sequential setting. [Work supported by NIMH.]
Patterns of phoneme identification errors in cochlear and eighth nerve disorders
Authors: Hannley Maureen
Published: January 2006

The purpose of this study was to determine whether patterns of phoneme identification errors differ as a function of signal presentation level among listeners with cochlear and retrocochlear auditory disorder. An analysis of the speech intelligibility performance of 15 patients with confirmed eighth nerve disorder was conducted, using confusion matrices derived from responses to a monosyllabic word list. The same analysis was conducted on the responses of a group of 15 patients with cochlear disorders, matched to the retrocochlear group for age and audiometric configuration. The results indicated that: (1) vowel errors were more prevalent and varied directly with increasing stimulus presentation level in the retrocochlear group; and (2) consonant errors did not differ in type or relative frequency between the two groups, nor was there a level-dependent effect. These results are supported by closed-set vowel identification tests and thus do not appear to be an artifact of open set testing. Vowel errors may account for a major part of the speech “rollover” phenomenon typical of retrocochlear dysfunction.
Hearing aid using an emphasized speech for hearing-impaired subjects
Authors: Harasaki Hidenobu , Ozawa Shinji , Ono Hiroshi , Deguchi Toshisada
Published: January 2006

A new hearing aid which emphasizes the phonetic features of monosyllables is suggested in this paper. In vowel parts of speech, we applied a digital filtering technique to a formant emphasis. The 101 order transversal filter emphasizes formant frequencies (+ 10 − + 30 dB). This filter enabled us to reduce misrecognitions of /i/ and /e/, /u/ and /o/ for hearing-impaired children. To emphasize consonant parts, three emphasis methods are experimented and discussed. One is an emphasis of amplitudes in consonant part, the next is a duration expansion of nasal consonant, and the last is an insertion of silence between stop consonants and the following vowels. The combinations of these methods were also experimented. The results of these experiments showed a distinct improvement in the recognition ratio of monosyllables.
Electrical stimulation of the auditory nerve in man: Dynamic range as a function of stimulus duration
Authors: White Mark
Published: January 2006

Psychophysical tests with implanted subjects indicate that responses to short duration electrical stimuli (similar in duration to transitional segments in speech) exhibit very narrow dynamic ranges, on the order of 6–10 dB; whereas responses to longer duration stimuli can exhibit considerably larger dynamic ranges, on the order of 17–40 dB. A specialized form of compression that compensates for this variation of the subject's dynamic range may be useful. A very significant amount of compression is essential because of the narrow dynamic range elicited by electrical stimuli in these subjects. We have investigated a set of “split-spectrum,” multi-channel speech processor configurations. These speech processors have been designed to compress the wide dynamic range of the acoustic environment into the very narrow dynamic range of the implant recipient. A set of compression systems have been compared to determine which strategies offer the most effective control of stimulus amplitude. [Work supported by NIH and Hearing Research, Inc.]
Acoustic fatigue failure of aircraft component
Authors: Girgis Sabry F.
Published: January 2006

Rudder skin cracks were noticed on the lower part of most aircrafts of one series. The series of aircraft were grounded for rudder repair. Investigations were made later and a permanent solution to overcome this failure was devised. The stresses that cause failure depend on the dynamic characteristics of the panel and on the external excitation. The dynamic characteristics were determined by ground resonance tests, in the form of resonant frequencies and mode shapes. The external excitation was due to intense sound pressure generated by the jets of engines. The excitation of both turbulent boundary layer and vortex effects are at low level. Equivalent specimens of the rudder panel were constructed but with the different design approaches. Specimens were installed on elastic mountings and hinged to rigid frames in a similar manner to the lower part of aircraft rudder of the jet trainer. The specimens were subjected to the same excitation of the jets of the engines. The duration of testings were accumulated to the same period in which the first crack was detected on the aircraft (100 h). Tests showed that improvement could be achieved by introducing intermediate support in the form of a spacer between the skins of the panel, or by increasing the number of stiffeners or ribs, or by just enlarging the rib flanges and adding one more rivet row. Initial tension of the skin also had a better effect, for example, applying air pressure between the skins produced such tension. Alternatively the reduction in skin stiffnesses caused by jet temperature had an adverse effect. Extensive theoretical calculations for panel instabilities under various support conditions were made. There was a close relationship between the static buckling mode and the mode causing acoustic fatigue failure.
Alternative concept for aircraft interior noise control
Authors: Holmer Curtis I.
Published: January 2006

Current technology for aircraft interior noise control depends on the use of weighted barriers and absorbing layers to control noise radiation into the cabin environment. This ignores the presence of structureborne flanking paths to interior structural/decorative surfaces which contribute significantly to the total cabin noise level. An alternative approach is to employ structural damping with (or without) vibration isolation to reduce noise radiated. This concept has significant potential for reducing treatment weight, because it can make use of the weight of decorative surfaces for acoustic functions. In this paper we review the results of a flight test demonstration program for this damped trim panel concept. The treated aircraft (a 12–14 passenger business jet) exhibited equal or lower noise levels to that achieved with weighted-layer treatments with more than a 40% reduction in the weight of acoustical materials used.
Water-flow-induced tones associated with resonant fluctuations of a free flooding cavity
Authors: Elder S. A.
Published: January 2006

A towed-model apparatus designed to study nonresonant water-flow-induced cavity tones was found to exhibit strong fixed-frequency oscillation at certain speeds. Stationary ensonification of the model by means of a J9 projector disclosed six apparent resonances in the range 0–200 Hz, five of which could be excited by flow over the cavity. Accelerometer measurements of the cavity wall vibration are consistent with the hypothesis that the acoustic oscillation is due to fluctuations in the chamber cross section. The strongest mode was found to occur at a Strouhal number predictable by a formula previously derived for air pipetones. [Work supported by Naval Sea Systems Command General Hydromechanics Research Program, administered by the David W. Taylor Naval Ship R & D Center, Bethesda, MD.]
Correlation of flight effects on centerline velocity decay for cold-flow acoustically excited jets
Authors: von Glahn Uwe H.
Published: January 2006

Acoustic excitation can influence the large-scale shear layer structure of jet flow, thereby causing the jet centerline velocity to decay more rapidly. This phenomena has numerous practical applications, such as the reduction of jet/flap impingement velocity in order to reduce flap structural loads for under-the-wing STOL aircraft concepts. In the present paper, cold-flow centerline velocity decay data obtained with acoustic excitation of the jet exhaust flow are correlated with and without flight effects. Initially, static data are correlated in terms of a new acoustic parameter involving the threshold sound level needed to initiate acoustic excitation of the jet plume. It is shown that for a given flight speed, the same acoustic excitation parameter is valid as that developed for the static condition. Finally, an aerodynamic flight effects parameter is included to correlate the static and flight centerline velocity decay data with and without acoustic excitation.
Architectural acoustics for the organ
Authors: Newman Robert B.
Published: January 2006

Organs are used in many settings: churches, concert halls, recital halls, and even practice rooms. An organ may be used as a solo instrument, as accompaniment to a chorus, or as part of an orchestral ensemble. There is a wide range of appropriate acoustics for the auditorium as well as placement of the instrument and performer with relation to the audience and to the other performers. These matters will be discussed.
Room acoustics for organs
Authors: Kinzey Bertram Y.
Published: January 2006

Traditional criteria of very reverberant environments for organ music are cited. These are compared to such considerations as small instruments in small spaces vs larger ones in large volumes. The need for clarity in the audition of the polyphonic literature for the organ is discussed and compared to the requirement of speech intelligibility in churches where good acoustics for both music and speech are a goal. All the factors presented relative to acoustical environments for organs indicate the need for a broader range of criteria than organists and organ builders and others typically accept.
Stability analysis of the human vocal cords
Authors: Thompson Charles , Grant J. Wallace , Starowicz Sharon A.
Published: January 2006

A mathematical model will be presented to describe the behavior of the vocal cords during the production of speech. The model for the folds consists of two-hinged gates which serve to modulate the flow through the glottis. The degree of flow modulation is related to the angular displacement of the gates. Equations governing the mechanical motion of the gates are derived by satisfying conservation of mass and momentum across the glottis. The introduction of acoustic impedance of the vocal tract serve to couple mechanical, acoustic, and fluid dynamic elements of the model. A linear stability analysis will be presented detailing the range of mechanical constants for which the motion of the gate will become stable. It is shown that stability of the gate motion is not dependent on the trans-glottal pressure distribution but on the acoustic-mechanical interaction.
Durational characteristics of vocal and subvocal speech
Authors: Smith Bruce L. , Hillenbrand James
Published: January 2006

In an attempt to investigate issues related to speech timing, adult subjects were asked to perform two tasks. They produced a number of disyllabic words and phrases orally, and they also “thought” the same words and phrases without vocalizing them. Some of the stimuli were easy to pronounce (e.g., “baseball”), while others were more difficult (e.g., “wrist watch”). Subjects repeated each stimulus 20 times in succession as rapidly and as accurately as possible. Durations of vocal and subvocal productions were measured by having subjects tap the space bar of a computer terminal each time they said or thought the word. Measurements of inter-tap intervals suggest that stimuli which were more difficult to pronounce vocally (indicated by longer inter-tap intervals) were also more difficult to produce subvocally (r = 0.86). However, subvocal durations averaged about 15% shorter than oral productions. These findings appear to support models of speech production which propose that speech segments have temporal characteristics associated with them at the abstract organizational level, but the results also seem to show output-level effects as well.
Signal design considerations for long-range shipboard active sonar
Authors: Bell Thaddeus G.
Published: January 2006

If a long-range shipboard active sonar is to successfully cover target ranges out to the first convergence zone at 35 miles, an optimum frequency about 3 kHz is implied along with a usable band approximating 1.5 kHz. This modest band has many competing demands on its utilization besides signal design, some of which are subband allocations for: multiple-ship mutual interference, increased data rate, and adjacent sector coverage without reverberation buildup. The basic band segment available for signal design must be used to cope with either high or low Doppler echoes in a combination of noise and reverberation interference. Echoes differ significantly from the transmitted signal from spreading effects both in time and frequency. Time spreading can be produced by multiple paths and target structure. Frequency spreading can be produced by target and own ship motion. Reverberation spectra can be significantly influenced by wave motion, own ship motion, relative bearing of transmission and biological scattering resonances. Selected signal design options are considered for coping with the foregoing signal and interference characteristics. Methods of estimating consequent detection performance are presented.
Source depth classification by modal decomposition and correlation
Authors: White DeWayne , Chin-Bing Stanley
Published: January 2006

Various methods have been and are being used to classify and localize submarine targets using real-time information from acoustic sensors. We have investigated another technique which utilizes the environment and its variability to exclude (theoretically) all possible target depths except the correct one. The method involves synthesizing the normal modes using the best available sound speed profile and geoacoustic model as inputs to a complex normal mode model. Both single frequency and broadband fields can be modeled. These synthesized modes are sampled in depth (or range) to form a suite of replicas. The synthesized replicas are then correlated with the modally deconvolved incoming data having the same spatial sampling as the replicas. The ambiguity surface shows relatively high correlation for replicas having the target's true depth. At present, synthesized data containing noise has been used for comparisons. However, the method shows promise of being a useful tool for depth localization. Examples will be presented for both vertical and horizontal arrays.
Response of a towed array to acoustic fields in shallow water
Authors: Buckingham M. J.
Published: January 2006

An analysis of the response of a towed array to the modal field in isovelocity shallow water is presented. In general, the response consists of a coherent sum over all the modes. However, when the source is endfire-on to the array, or in that vicinity, the towing motion introduces a certain amount of range averaging into the response to the farfield radiation. A criterion is given, in terms of the interference length between the two lowest order modes in the field, for the degree of range averaging required to reduce the output of the array to an incoherent sum over the modes. This sum is associated with a set of virtual sources distributed in azimuth, each of which is associated with a particular normal mode. This means that some signal energy is rejected by the array, which results in a reduction in the signal gain. At the same time beam broadening, or in extreme cases beam splitting, arising from the angular spread of the virtual sources, occurs and this may give rise to a significant bearing error.
A look at detection performance for maximum entropy beamforming
Authors: Collier Arthur J.
Published: January 2006

A statistical investigation of the detection performance of maximum entropy beamforming for low level signals is described. The investigation was performed for a horizontal line array with a half-wavelength frequency of 500 Hz. Both sparse and filled array configurations were investigated. Realistic models of a deep-water ambient noise field and array self-noise were used to define the expected cross-spectral matrix for the array in a noise field. Signals of 60, 200, and 400 Hz coming from near broadside and near end-fire were considered. The detection statistics were obtained by generating sample mean cross-spectral matrices with a Wishart distribution, using the Bartlett decomposition as implemented by Smith and Hocking [Applied Statistics, 1972]. The results are summarized in ROC curves.
Initial sea test results of a multi-hydrophone digital buoy system with in-situ FFT processing capabilities
Authors: King Peter C. , Herstein Peter D.
Published: January 2006

Two major problems have been historically associated with self-contained analog acoustic data acquisition buoy systems. First, analog tape recorder characteristics bound the obtainable dynamic range of the received data. Second, post-processing of the data tapes to obtain the required acoustic information can be both time consuming and expensive. To address these problems, a new buoy has been developed at NUSC. Acoustic data from each of eight hydrophones is digitized and then fast Fourier transformed by the buoy's micro-processor. Complex and ensemble averaged spectral results are then written onto a digital cassette tape. An instantaneous dynamic range of more than 72 dB is available over the frequency band 2–350 Hz. The spectral results are computed in 2 Hz increments and Harming weighting is used. The first at-sea test of the system occurred in August 1983 at a deep water location near Bermuda. In this paper we will present results from that test. Received signals from stationary and moving cw sources will be emphasized. [This work was sponsored by the Surveillance Environmental-Acoustic Support Project (SEAS), Naval Ocean Research and Development Activity, Code 520 (C. E. Stuart, Program Manager).]
Another round with nonlinear acoustics
Authors: Beyer Robert T.
Published: January 2006

Early work in nonlinear acoustics largely followed the behavior of one or two idealized beams of high intensity sound. More recent work has centered on attempts to make the beams more realistic in nature, and to follow up on possible ways in which nonlinear acoustics can be applied to other problems of acoustics. In the former case, such analyses as that of Zabolotskaya-Khokhlov on a tapered beam, or the use of truncated equations, especially in the study of nonlinear interaction of sound with air bubbles in water come to mind. There has also been considerable attention to the physical meaning of the nonlinear parameter. On the experimental side, much work has been done on the sound-bubble interaction. In addition, the existence of higher harmonics in a search beam of finite amplitude means that some of the limitations presented by the frequency of the fundamental beam can be favorably modified. Examples will be discussed.
Ocean ambient noise at very low frequencies
Authors: Cotaras Frederick D. , Merklinger Harold M. , Fraser Ian A.
Published: January 2006

Ambient noise in the frequency range 1 to 20 Hz was measured at a number of sites in the North Atlantic. Freely drifting, surface-suspended hydrophones were used. A digital radio telemetry link was used to transmit the acoustic data to an attending ship. It is shown that the character of the noise in the 1–4-Hz range is different from that in the 6–20-Hz range. The distribution of 5-min averages of noise power in narrow frequency bands shows significant differences in standard deviation, skew, and kurtosis observed above and below 5 Hz. The high coherence of noise measured by two independent measurement systems 150–300 m apart horizontally gives strong evidence that the noise measured in the 1–5-Hz range was not flow, turbulence, or electrical noise related. There is an indication in the data that two noise mechanisms may be responsible for the noise in the 1–5-Hz range; at least one of these is wind speed related.
Industrial machines employing resonance wave systems that are inductively excited by reactive mass vibrators
Authors: Bodine A. G.
Published: January 2006

For the field of macrosonics employing resonance technology with a mechanical oscillator, the system is driven at a low impedance region in order to have ample current flow (elastic stroke) at the oscillator. The oscillator is analogous to a constant voltage generation, so it has to function with an unconstrained or variable amplitude rather than with a fixed stroke limitation like a crank mechanism, for instance. The true mechanical oscillator is thus an inductive coupling of a dynamic mass. The best form is an orbiting mass describing its path in free space except for the constraint which confines the mass to its orbit. It is the inductively phased reactance of this constraint which provides the constant voltage ac drive for the resonance system frequency. This kind of oscillator thus adapts its cyclic stroke to the freedom of the resonance system. A very useful technique is to determine and maintain the frequency of the oscillator at that which would be the resonance frequency of the system if the work load at the output region of the system were infinite. Maximum Q thus occurs with a “locked” load. Then, for all finite loads, the output amplitude stays constant because a drop in load means reduction in mechanical amplification as the fixed frequency system strays from the peak resonance wave pattern environment.
Exploring phonotactic lexical constraints in word recognition
Authors: Huttenlocher Daniel P. , Zue Victor W.
Published: January 2006

In a previous meeting of the Society, Zue and Shipman demonstrated that the constraints imposed by the allowable sound sequences of a language are extremely powerful. Even at a broad phonetic level of representation, sequential constraints severely limit the number of possible word candidates [J. Acoust. Soc. Am. Suppl. 1 71, S7 (1982)]. This provides an attractive model for lexical access based on partial phonetic information. However, Zue and Shipman's results did not take into account the fact that the acoustic realizations of phonetic segments are highly variable, and this variability introduces a good deal of recognition ambiguity in the initial classification of the signal. We have conducted a set of studies investigating the robustness of sequential phonetic constraints with respect to variability and error in broad phonetic classification. In these studies segment misclassifications or deletions are permitted. In one study it was found that the phonetically variable parts of words (around reduced syllables) provide much less lexical constraint than the phonetically invariant parts. Thus, by utilizing the information from robust parts of a word, a large lexicon can still be partitioned into small equivalence classes. Detailed results of the studies will be presented. [Work supported by the Office of Naval Research under contract N00014-82-K-0727 and by the System Development Foundation.]
Unsupervised speaker adaptation in feature-based isolated letter recognition
Authors: Lasry Moshé J. , Stern Richard M.
Published: January 2006

This paper describes two new methods by which a feature-based isolated letter recognition system, FEATURE [Cole et al., Proc. ICASSP-1983, pp. 731–733], can learn the acoustical characteristics of individual speakers without feedback from the user. The original tuning algorithm of FEATURE made use of labeled observations from a given speaker, and of the a priori covariances of the feature mean values within the across decision classes, to optimally adjust the expected feature values of all the decision classes. In the first new procedure the system assumes a correct decision every time it classifies a sound with a high confidence level. The class-conditional mean vectors and covariance matrices are then computed in the same way as in the tuning-with-feedback procedure. In the second new procedure the system records the average observed feature values over all possible classes on a feature-by-feature basis. The a priori covariances between the mean values of a feature for each decision class with its mean values over all possible classes are then used to update the class-conditional means and covariances. Experiments were conducted on confusable sets of letters using both speaker adaptation procedures. A significant improvement in letter recognition performance using both analyses was observed after a small number of iterations. [Supported by NSF and DARPA.]
Stop identification using hidden Markov models
Authors: Kopec Gary E.
Published: January 2006

A series of experiments has been undertaken to assess the power of discrete spectral slices for automatically discriminating between the voiceless plosives /p,t,k/ in CV syllables. These experiments involve a 936-token data base consisting of 52 instances of each of the 18 syllables /p,t,k/ × /i,e,ae,a,ow,u/ spoken by 13 male and 13 female talkers. In one experiment, identification was attempted using a single 12-pole LPC onset spectrum. The onset spectra from each talker were compared, using a log-likelihood distance measure, with the 900 onset spectra of the remaining 25 talkers. An overall classification accuracy of 92% was achieved using a k-nearest-neighbor decision strategy. A second experiment involves classifiers which use a series of LPC spectra computed during the first 50 ms of the stop release. Each CV syllable is modeled as a hidden Markov process which generates a spectrum every 5 ms. Classification is performed using either a Viterbi or forward-backward decoding strategy.
A study of correlation methods for phoneme identification
Authors: Engebretson A. Maynard , Tadlock John P.
Published: January 2006

With current availability of high-speed digital signal processors and inexpensive memory, correlation methods of real-time speech recognition may be practical. In the methods presented here, speech is segmented into overlapping 25.6-ms windows. A spectrum is calculated for each window and correlated with speaker-independent reference patterns. Each windowed speech fragment is identified with the reference pattern yielding the highest correlation. Average spectral patterns are created automatically from “stable” segments of speech. A high correlation between spectra of adjacent windows is used as a measure of stability. The average patterns are categorized across speakers and averaged within categories to create the reference patterns. We have studied standard and Mellin (scale invarient) correlations in combination with linear magnitude and cepstral-smoothed log magnitude spectra. Mellin correlation normalizes spectra that are scaled with respect to frequency. Cepstral-smoothing reduces the number of coefficients required to represent the spectrum. Also cepstral coefficients can be normalized with regard to transmission characteristics. Results will be presented for vowels recorded from six male and six female speakers. [Work supported in part by NIH Grant NS-03856].
Digital processing of instrumental sounds
Authors: Reynolds Roger
Published: January 2006

In work at IRCAM (Paris), digital processing techniques were developed to alter pre-recorded instrumental materials in perceptually novel ways. The goal of this processing was to create sound materials that were fundamentally unfamiliar but could co-exist with natural instruments in muscially satisfying ways. (1) Because sounds are represented numerically for digital purposes, the potential for sound editing is changed qualitatively. Musical phrases were extended and transformed by replicating segments of them in ordered patterns whose structural properties dominated those of the original without eclipsing its identity. (2) Phase vocoding techniques were used to analyze instrumental sounds. Resulting data were appropriately reduced to form the basis of resynthesis through the MUSIC X program. In this way, independent access to arbitrary groups of partial components was attained. Odd and even partials were presented over spatially distinct speaker channels and subjected to dynamically changing vibrato functions with differing rates and depths. Additional distinct auditory images arose in the stereo field while the sonic image of the original instrument remained. Examples of instrumental recordings and their digital transformations are presented in isolation and in musical contexts.
The addition of piezoelectric properties to structural finite element programs by matrix manipulations with applications to underwater acoustics
Authors: McDearmon Graham , Pauer Lyle , Scherch Richard
Published: January 2006

The capability to analyze materials having linear piezoelectric properties was developed for structural finite element programs. Of the many methods with which this could be achieved, the method chosen was to add the piezoelectric properties by matrix manipulation of elastic and heat transfer element matrices. This method is independent of the elemental shape functions. It therefore has the advantages of converting many varieties of structural finite elements into piezoelectric finite elements with one general coding and as the state of the art improves for the structural elements so will the piezoelectric ones without additional or new programming. Otherwise, each variety of piezoelectric element and improvements would have to be programmed separately. This capability was added to MSC/NASTRAN by Goodyear Aerospace Corporation. The theory behind this method and comparison of finite element models of several piezoelectric ceramic underwater acoustic projectors to experimental data are presented.
An improvement of the finite radiating element formulation—Application to the modeling of a radiating free-flooded transducer
Authors: Bossut Régis , Decarpigny Jean-Noël
Published: January 2006

At low frequencies, the limit of a free-flooded cylinder farfield is very far from the acoustic center. Thus, modeling this submerged structure by the finite element method requires a large number of fluid elements, when the radiation boundary condition is represented by an outgoing spherical (monopolar) wave. A radiating element has been created, that uses a radiating impedance of both monopolar and dipolar waves. With this new element, the radiating surface can be much closer to the transducer, and then the number of fluid elements decreases significantly. Unfortunately, one cannot obtain directly the farfield directivity pattern, because the radiating surface is inside the nearfield zone. However, it is possible to find it by a simple algorithm. This algorithm can also be used in an acoustical tank whenever its size is too small to measure the far acoustic field of a large transducer.
Efficiency enhancement of thermo-acoustic sources through high-velocity motion
Authors: Chotiros N. P.
Published: January 2006

A theoretical study of thermo-acoustic sources in the context of sonar applications was undertaken. The main objectives were to improve energy efficiency and to provide a means for beamsteering, using a moving thermo-acoustic source. The results show that improvements in energy efficiency of several orders of magnitude are possible at very large Mach numbers. (This is quite distinct from peak intensity efficiency which occurs at Mach 1.) The results also show the possibility of beamsteering by moving the thermo-acoustic source in a number of ways. The results suggest that the thermo-acoustic source may, in certain sonar applications, be a viable acoustic projector. [Work supported by Office of Naval Research.]
Active noise cancellation in ducts
Authors: Tichy Jiri , Warnaka Glenn E. , Poole Lynn A.
Published: January 2006

This paper summarizes the state of active noise cancellation in ducts. The application of active feedback to reduce the sound energy propagation through the duct is primarily important at low frequencies because passive silencers are very large, and the attenuations achieved are relatively small. In its classical configuration, the noise field detected by a signal microphone is phase inverted and time delayed by an adaptive filter. This signal is then reradiated into the duct from a sound source at the duct wall or located remotely and connected by means of a waveguide. The adaptive filter is controlled by a microphone located in the duct to sense the noise reduction and adjust the entire system for optimum operation. This paper analyzes the effects of the signal microphone position, type, and location of the cancellation sound sources, and sensing microphone location. Optimum operation requires consideration of higher order modes and the nearfield of the cancellation source, including evanescent waves. Results obtained with practical constructions illustrate the great potential of active systems to attenuate noise with discrete spectra, random noise, as well as transients are presented.
Active systems for global attenuation of noise
Authors: Jessel M. J. M. , Angevine O. L.
Published: January 2006

Theoretical approaches to active noise absorption [G. A. Mangiante, J. Acoust. Soc. Am. 61, 1516–1523 (1977)] provide criteria that may prove useful for the design of any system for active noise attenuation, especially one which must produce attenuation in all directions around a complex sound source. (1) Topological fitness: a proper net of “anti-sources” ought to surround completely either the primary noise source(s), or the space to be silenced. (2) Directivity: each anti-source ought to radiate only towards the space to be silenced. (3) Concentration: practical system design requires substituting the theoretical continuous distributions of anti-sources by discrete ones. This approach has been successfully applied to reducing the audible hum of an actual electric substation transformer. The active abatement method is easier for discrete frequencies, such as the spectrum of transformer hum, and is most effective at the relatively low frequencies—120, 240, 360, and 480 Hz—most prominent in the transformer hum spectrum. A relation has been found experimentally for the attenuation achievable versus the number of sources for each of these hum frequencies. The active attenuator interferes less with the normal ventilation and cooling of a transformer than do passive methods. Active abatement also allows attenuation differing in different directions.
Coherent active methods for applications in room acoustics
Authors: Guicking Dieter
Published: January 2006

An adjustment of reverberation time in rooms is often desired even for low frequencies where passive absorbers fail. Among the active (electroacoustic) systems, incoherent ones such as “assisted resonance” permit prolongation of reverberation time only, whereas coherent active methods—as proposed by H. F. Olson since 1953—allow sound absorption as well. A coherent-active wall lining consists of loudspeakers with microphones in front and adjustable control electronics. The microphones pick up the incident sound and drive the speakers such that the reflection coefficient takes prescribed values. An experimental device for the one-dimensional case has been developed and allows reflection coefficients between almost zero and about 1.5 to be realized below 1000 Hz, employing moving coil or specially developed extremely flat electret loudspeakers. The extension to three dimensions is being investigated; problems arise mostly from diffraction effects. The actual state of the experimental work including a comparison with model computations will be outlined. Furthermore, some ideas about active diffusers are presented. In contrast to passive “Schroeder diffusers” with inherent frequency dependence, active diffusers are basically broadband systems.
Nearfield of a piston source in an absorbing medium
Authors: Nyborg Wesley L. , Steele R. Bruce
Published: January 2006

Medical exposures to ultrasound from unfocused source transducers usually occur at distances from the source which are not great enough to justify a farfield approximation. In order to analyze biophysical interactions which occur in the exposed medium, it is necessary to consider details of the nearfield, taking absorption into account. A formulation, in terms of a line integral, given by Schoch [A. Schoch, Akust. Z. 6, 318–326 (1941)] for a piston source proves to be useful for this purpose. A paraxial approximation which he derived leads to an analytical expression which applies even to a central region of the important, but complex, field which exists just in front of the source. In this paper computed plots will be shown, comparing results obtained by use of solutions and approximations given by Rayleigh, Schoch, and others. These comparisons give information on the conditions under which various approximations are valid, and on the influence of absorption on the field distributions. [Work supported by the National Institutes of Health, Research Grant GM-08209.]
Shape oscillations of microparticles on an optical microscope stage
Authors: Zhe-ming Zhu , Apfel Robert E.
Published: January 2006

Forces arising from modulated acoustic radiation pressure have been used in the past to produce shape oscillations of drops in order to study surface properties [e.g., P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27 (1980) and C. -J. Hsu and R. E. Apfel, J. Acoust. Soc. Am. 70, S90 (1981)] and to study the oscillating drop's internal flow patterns [E. Trinh, A. Zwern, and T. G. Wang, J. Fluid Mech. 115, 453 (1982)]. We have extended this work to study surface properties of much smaller particles (8 to 200 μm, approximate diameter) by fabricating a stage for an optical microscope that incorporates a 10-MHz, piezoelectric, quartz disk electroded in such a way as to allow the transmission of light through a central region. The quartz disk forms part of a thin chamber into which the microparticles in a host liquid can be injected. Establishing an a acoustic standing wave in the chamber has enabled us to study shape oscillations for drops resting on a surface of the chamber and for drops acoustically levitated away from solid container surfaces. At high acoustic amplitudes drop fission has been produced. We shall present data and a photographic record for hydrocarbon drops in water. We hope also to present results for biological cells, since the investigation of the properties of their membranes was the original motivation for this work. [Work supported by the National Institutes of Health, Grant 1R01-GM30419, and the U. S. Office of Naval Research.]
The effects of the flaring bell on the normal frequencies of a trombone
Authors: Dudley J. Duane , Strong William J.
Published: January 2006

As sinusoidal waves encounter the bell of a brass wind instrument, they are effectively reflected by the flaring part of the bore. A given frequency is effectively reflected from that part of the bell where a significant change in bore radius occurs within a wavelength. Hence the longer wavelengths reflect from points closer to the inlet end of the bell than do the shorter wavelengths. A computer calculation of the equivalent lengths corresponding to the normal frequencies shows this effect, and shows how the frequency shifts depend on the shape of the bore. Through this effect, the bell makes an important contribution towards making the normal frequencies harmonic.