bluuebunny/crossref_metadata_2025 huggingface dataset:
Fan noise and unsteady rotor forces
Authors: Chiu Wen-Shyang , Lauchle Gerald C. , Thompson D. E.
Published: October 2005

The noise radiated by a subsonic, axial-flow fan at its rotational frequency and harmonics is related to the nonsteady force field created at the rotor blade/fluid interface. This force field is highly dependent on the time-invariant flow distortions that enter the fan. In this basic study, a typical cooling fan used in the electronic and computer industry was instrumented with an unsteady axial force sensor. Its output is proportional to the total unsteady axial force created by the rotor. The inflow field of the fan was systematically distorted by placing a small cylinder at various positions in the inlet plane. The nonuniform, three-dimensional flow field entering the rotor was measured by traversing a miniature five-hole pressure probe. The total pressure outputs from this probe can be related to the axial, tangential, and radial velocity vectors. Fourier decomposition of the inflow velocity data is coupled with analysis to give information on the unsteady rotor force harmonic content. The on-axis sound pressure levels were measured and compared to coherent output power spectra involving the unsteady force sensor and the microphone. Very good coherence at the discrete tones is observed. [Work supported by IBM Corp.]
Model and full-scale testing of a modified cutoff bar for a centrifugal fan
Authors: Brittain Frank H. , Nordstrand David A.
Published: October 2005

Controlling centrifugal fan noise by modifying the design of the fan is very appealing because the cost could be considerably lower than for an in-duct silencer. Pressure drop, fouling, and other problems frequently associated with silencers can also be avoided. Previous attempts at modifying an existing centrifugal fan to control noise have often met with limited success. To reduce the cost of controlling blade passage tones in the community, modification of the induced draft (ID) fans at a power plant was evaluated. Model testing was conducted for ten different designs of the cutoff bar for the centrifugal fan. The noise reductions and fan efficiencies varied widely for six of the ten cutoff bars tested. The best design gave better noise reductions than expected and higher efficiencies at usual settings of the variable inlet vanes. The best cutoff bar design was installed (full scale) on one of the ID fans and fields tested. The noise reductions on the full-scale fan tests were better than obtained for the scale model tests. Results of both the model and full-scale tests are presented, compared, and discussed.
Frequency domain analysis of dipole source strength and correlation area
Authors: Yeager David M.
Published: October 2005

The generation and radiation of noise from a rigid surface immersed in a turbulent flow field may be characterized by the strength of the dipolelike sources associated with the normal surface pressures acting on the fluid at the surface, and by the regions over which these sources are partially correlated. New frequency-domain expressions have been developed for the dipole source strength per unit area, based on mean-square pressure and acoustic intensity, and for the correlation area. The equations are similar to time-domain expressions developed earlier [T. E. Siddon, J. Acoust. Soc. Am. 53, 619–633 (1973)]. The equations show that the correlation area can be thought of as a complex radiation efficiency that is normalized by its maximum value, the total area of the surface immersed in turbulence. Both the correlation area and dipole source strength per unit area reflect the noise generation characteristics of the local turbulence regions and mutual interactions between regions. Results of experiments will be presented in which a single blade, removed from a rotating centrifugal air moving device, was immersed in a turbulent flow field.
Scale model of an active noise reduction system
Authors: Angevine O. L.
Published: October 2005

Scale modeling has been used often for predicting acoustical properties of architectural structures such as music halls. In this experiment, it is an active noise attenuating system that is modeled. By using a scale factor of 8 or 16, tests can be conducted on a table top simulating those of a fullscale system at a distance of 24 m. Since active attenuation is most successful at frequencies below about 500 Hz, the scale frequencies remain in the audible spectrum, and measurement does not require special equipment. [Work supported by EPRI and NMPC.]
Ambient noise in Baffin Bay
Authors: Farrell Joseph B. , Heard Garry J.
Published: October 2005

This paper presents the results of ambient noise measurements taken in Baffin Bay in August-September of 1986. Noise measurements were taken in conditions ranging from open water to iceberg-infested water near the edge of pack ice. Differences in the character of ambient noise at the experimental sites will be noted and discussed. The frequency range investigated in this work was 10–1000 Hz. Comparisons will be made with noise measurements taken by Defence Research Establishment Atlantic (DREA) in Baffin Bay in the 1970s.
Super-resonant scatter under ice sheets and in full spaces
Authors: Tolstoy Ivan , Tolstoy Alexandra
Published: October 2005

Systems of monopole scatterers interacting through multiple scatter may develop normal modes, i.e., true resonant behavior at certain frequencies (the equivalent source coefficients of each scatterer have real poles). This occurs when the single scatter cross sections are large enough to give significant interaction. This happens for highly tuned scatterers, e.g., gas-filled balloons, bubbles, and thin shells in water, insonified at frequencies near their characteristic “bubble” frequencies. This kind of super-resonance (SR) occurs when the system is at or near the interface with an elastic medium, e.g., a thin elastic plate [I. Tolstoy, J. Acoust. Soc. Am. 80, 282–294 (1986)]. Energy transport between scatterers is then mediated by boundary modes excited by the scatterers acting as point sources (e.g., the flexure waves of a thin plate). The case of two and three bubble systems at an ice-water or lucite-water interface is explored, with particular reference to the parameters ka, kl (k is the acoustic wavenumber, a the scatterer radius, l the spacing between scatterers) and the plate elastic constants. For a pair (doublet) the pressure amplification re: the free-field value is ≅ 2 × 103 for kl values as small as 0.5, with a directionality factor of 30: This is a passive, highly tuned, high magnification, strongly directional compact array (≅λ/12 size). A 30-Hz system would consist of two ballons of 10-cm radius near an ice boundary, with a discrete set of permissible l values ranging from about 5–20 m. Optimum spacings and magnifications depend upon the ice thickness (≅5 m). In an acoustic full space, energy exchange between scatterers is mediated less effectively by volume waves, and the scatter coefficient poles vanish: Bona-fide SR does not take place. Nevertheless, strong peaks may occur, giving magnifications ≅103. This quasiresonant behavior is discussed for simple two-, three-, four-, and six-element plane and polyhedral configurations. However, true SR behavior is reintroduced in full spaces by partially blocking selected pathways between scatterers. [Work supported by ONR.]
A study of reflection and refraction of waves at the interface of water and sea ice
Authors: Yew C. H. , Weng X.
Published: October 2005

The sea ice is modeled as a transversely isotropic brine-saturated porous medium, in accordance with the model proposed by Schwarz and Weeks (1977). The reflection and refraction of waves at the water-ice interface are studied. The numerical results obtained in this study indicate that the porosity of the ice has a noticeable effect on the wave reflectivity. Its effect, however, becomes small when the grazing angle of the incident wave becomes small. The existence of a thin and porous ice skeleton layer on the ice medium further reduces the reflectivity. The reduction of reflectivity becomes more distinct as the frequency of the incident wave is high. Numerical results point out that, in addition to the porosity, the ice layer thickness is the most dominant property influencing the under ice wave reflectivity. The calculated results show a qualitative agreement with the in situ experimental results by Yang and Votaw (1981).
Under-ice scattering mechanisms
Authors: Mellen R. H. , Scheifele P. S.
Published: October 2005

Underwater acoustic propagation in the Artic Ocean is characterized by a refractive surface channel with a rough boundary. Scattering estimates based on free-surface theory have proven low by more than a factor of 2 in forward-scatter loss and low by 20 dB or more in backscatter strength. Failure to account for either attenuation or backscattering indicates that impedance effects must be involved. The ice layer is modeled as a uniform elastic solid. Perturbation analysis shows scattering from slopes as well as displacements. Displacements produce pistonlike reradiation in addition to the usual vertical-dipole type associated with free surfaces. However, the “rocking” horizontal dipole produced by slopes is evidently the dominant mechanism at the lower frequencies and estimates of both attenuation and backscatter strength show reasonable agreement with experimental data when included. [Work supported by NUSC/NL.]
An array to produce convected normal velocity and pressure fields for wavenumber calibration and boundary layer modification
Authors: Schau H. C. , Luker L. Dwight , Petrie S.
Published: October 2005

A transmitting array is described that is capable of producing specified normal velocity distributions at the surface of the array. Such an array is useful in the production of convected normal velocities and pressure fields that may emulate turbulent boundary layer pressure fields. The pressure fields are convective in nature, moving parallel to the plane of the array with a phase velocity that is slow, i.e., less than the speed of sound in the medium. A slow phase velocity corresponds to a spatial wavenumber k that is greater than the corresponding acoustic wavenumber in the medium. Applications include boundary layer modification, testing of sensors in controlled TBL flows, and wavenumber calibration of sensors. Results are presented for several prototype arrays involving different construction methodologies. Shading schemes for the production of uniform convected pressure fields are discussed relative to the physical limitations of the device and electronics. Measured pressure fields and phase velocity are contrasted with those predicted theoretically. Plans for producing larger and more complex arrays are discussed relative to current prototype results. [Work partially supported by ONT.]
Spherical nearfield calibration array for three-dimensional scanning
Authors: Van Buren A. L.
Published: October 2005

Nearfield calibration arrays (NFCAs) are used to determine the farfield acoustic radiation from a transducer by measurements made in the nearfield. The original Trott NFCAs were planar arrays. More recently, cylindrical NFCAs have been developed. This paper describes a spherical NFCA for determining the full three-dimensional radiation pattern of an enclosed transducer. In theory, the NFCA consists of a large number of discrete hydrophone elements arranged over a spherical surface in N equi-spaced constant latitude bands. In practice, the array can be synthesized by use of a single semicircular are containing relatively few elements and by either rotation of the transducer or revolution of the are about the polar axis. Individual hydrophone sensitivities (both amplitude and phase) are selected so that the NFCA serves as a plane-wave filter for acoustic radiation from inside the sphere. The relative sensitivities, called shading coefficients, are computed using the NFCA reciprocity principle and a least-squares procedure. Only a few sets of N/2 shading coefficients are required for full three-dimensional operation of the NFCA over a frequency range of three octaves or more. Design criteria are discussed and sample numerical results are presented.
Design of a transducer element for an acoustic mutual impedance measurement experiment
Authors: Johnson Michael P.
Published: October 2005

A companion paper in this session has described an experiment to measure the acoustic mutual impedances in a resonant, close-packed sonar array [S.C . Thompson, J. Acoust. Soc. Am. Suppl. 1 82, S2 (1987)]. This experiment requires the use of special measurement transducers in place of the elements in the array under study. There were several special requirements for these transducers: (1) high mechanical input impedance at the element radiating face; (2) accurate knowledge of the transducer electromechanical impedance matrix; and (3) radiating face dimensions that are identical to those of the elements of the array under study. The first requirement reduces the effects of interelement coupling and, consequently, reduces the sensitivity in the calculations to errors in the measurement. The second acknowledges that the electromechanical impedance matrices of the transducer elements are needed in the calculation. The third requirement provides a measurement array with the same mutual impedance coefficients as the array under study. A prototype transducer element that seems to meet these requirements is a doubly resonant piston element. The element is designed so that the operating band of the array under study falls between the two resonant frequencies of the measurement transducer. The design and performance of this element will be described.
Sound absorption in Arctic regions
Authors: Mellen R. H. , Scheifele P. S. , Browning D. G.
Published: October 2005

Sound absorption in seawater involves relaxations of magnesium sulfate, boric acid, and magnesium carbonate. Absorption varies with both region and depth, due mainly to the pH dependence of the boric acid relaxation. The nominal seawater pH range is 7.7–8.3 and magnitudes can vary over nearly a factor of 4 at low frequencies. A global model for World Ocean prediction has been developed, employing contour charts of the pH factor at several depths. Profiles for integration of loss along ray paths are generated by algorithm. The pH range in the Arctic is nominally 8.0–8.3 and similar contour charts are provided for the pH factor in these regions. Although long-range propagation is generally limited by under-ice scattering, absorption can be the dominant loss mechanism under ice-free conditions and for ranges less than 50 km at sonar frequencies with an ice cover. Predicted absorption spectra are presented and compared with the limited data available. [Work supported by NUSC/NL.]
A bistatic, high-frequency, under-ice, acoustic scattering model
Authors: Bishop Garner C.
Published: October 2005

A model has been developed to evaluate the scatter produced by a high-frequency acoustic pulse originating from an arbitrarily located source, incident on the under-ice surface characteristic of pack ice regions of the interior Arctic and detected by an arbitrarily located receiver. Measured, two-dimensional, under-ice, acoustic profile data and several empirical results that relate various geometric parameters of the large scale under-ice relief features, e.g., ice keels are used to construct a three-dimensional, bimodal, under-ice surface model consisting of first-year ice keels and sloping flat ice regions. A first-year keel is modeled as an ensemble of randomly oriented ice blocks on a planar surface inclined at some slope angle with respect to a horizontal plane at sea level. Ice blocks are modeled as layered, viscoelastic, rectangular solids. A region of flat ice is modeled as a smooth planar surface whose slope angle is less than some arbitrary minimum keel slope angle. The Helmholtz-Kirchhoff integral and the Kirchhoff approximation are used to evaluate the scattered field. Time is partitioned into bins and then, beginning at the bin corresponding to the time the scattered field of each scattering facet arrives at the receiver, the scattered field is added coherently in all bins spanning the temporal duration of the incident pulse. The resulting scattered field time series is used to calculate the corresponding reverberation time series. Modeled reverberation levels are compared with measured levels for several Arctic sites and modest agreement is obtained.
An experimental study of the coherent under-ice reflectivity of sound in the Greenland Sea Marginal Ice Zone (MIZ)
Authors: Gruber Patricia L. , Dicus Ronald L.
Published: October 2005

The coherent component of acoustic under-ice reflectivity was investigated as a function of frequency and grazing angle in the MIZ. Measured reflectivity was compared with scattering theory predictions to test the hypothesis of ridge scattering dominance in the MIZ. Explosive source acoustic signals were received on a vertical array, during the Marginal Ice Zone Experiment (MIZEX 84), and deconvolved to separate the direct and ice-reflected arrivals. Ice-reflected signals received on individual hydrophones at different ranges and depths, and on different days, were aligned in time and coherently ensemble averaged within a moving 10-deg grazing angle window. The resulting reflectivity was found to decrease with increasing frequency from 64–256 Hz and with increasing grazing angle from 12–35 deg. Comparison was made with predictions from smooth elastic plate theory, perturbation theory for a rough pressure release surface, perturbation theory for a rough elastic surface, Twersky theory for hemispherical bosses on a plane, and Twersky theory for infinite, semielliptical cylinders on a plane. The Twersky theory for semielliptical cylinders gave a significantly better fit to the data than the other theories. This suggests that, although the under-ice topography may be a good deal more complicated, scattering may, nevertheless, be dominated by remnants of elongated pressure ridge keels. Remote sensing data, taken during the experiment, showed that the ice cover was primarily composed of small floes (< 200 m in diameter). Laser ice-surface height measurements were analyzed to obtain the pressure-ridge sail-height distribution. The Twersky theory modeling gave predictions within 1 dB of the measured mean reflectivity when a ridge keel-to-sail ratio of 6.5 was assumed.
Elements of Arctic surface scatter: Part III, the head wave
Authors: Medwin Herman , Reitzel Ken J. , Browne Michael J.
Published: October 2005

Laboratory scale model studies have the virtue of revealing the detailed behavior of the elements of scatter from a complex ice field. Previous model studies have demonstrated the quasidipole radiation pattern of low-frequency scatter from an open lead. It has also been shown that leads and ridges backscatter principally from a one wavelength extent near the least-time intercept of the radiation from a point source. At this time, evidence is presented that mode conversion generates a compressional wave that propagates parallel to the surface of the ice. This mode is driven, and will radiate into the water, at the critical angle. The reradiated sound, an example of a head wave, causes a significant precursor to appear before the specular reflection from the ice canopy. In agreement with theory, the measured head wave amplitude is proportional to k−1 x−1/2 × L−3/2 where k is the wavenumber in the water, x is the horizontal range, and L is the path length in the ice. [Work supported by the Office of Naval Research.]
Laboratory scale investigation of the amplitude and phase of signals reflected from sea ice ridges
Authors: McLanahan T. , Diachok O. I. , Wales S. C.
Published: October 2005

Acoustic reflectivity from plastic models of sea ice ridges on a thin plate were investigated for 0.67 < ka < 6 (where k is the wavenumber and a is the mean ridge depth). Models were constructed of lucite, which has acoustic velocities consistent with analytically estimated velocities of sea ice ridges, and of “fast cast,” a material with much lower velocities. For ka > 1 measurements from randomly oriented and parallel lucite and fast cast ridges on a thin plate and on an infinite half-space were nearly identical, and in good agreement with Twersky theory prediction. At the lowest frequency, ka = 0.67, and at grazing angles less than 20°, measured reflection losses were significantly greater than predictions: twice as large for randomly oriented lucite ridges on a thin plate. The phase change upon reflection was strongly dependent on the material properties of the ridges and their orientation. Results for randomly oriented lucite ridges were found to be reasonably consistent with previously reported inferences of reflection loss and phase based on matched field processing of data recorded on a large aperture vertical array in the Arctic [Livingston and Diachok, J. Acoust. Soc. Am. Suppl. 1 81, S85 (1987)].
Low-frequency transmission loss modeling in the Arctic using measured mode attenuation coefficients
Authors: Yang T. C.
Published: October 2005

Low-frequency transmission loss in the Arctic can be effectively described by the reflection/scattering loss at the ice-water interface due to the upward refractive sound-speed profile; the sound field that interacts with the bottom is quickly attenuated as to be unimportant at long ranges. Various models for the reflection/scattering loss have been proposed in the literature and can be shown to agree with single hydrophone data by adjusting the ice roughness or other parameters in the model. However, a critical test of the model predictions has to be conducted using vertical array data, since the depth dependence of the sound field provides a more meaningful measurement of the angular dependence of the reflection/scattering loss. In this paper, the angular and frequency dependence of the reflection/scattering coefficients was investigated, based on the mode attenuation coefficients previously deduced from vertical array data. It was found that the measured reflection/scattering loss was larger than most model predictions using realistic ice roughness parameters. A transmission loss model, based on a simple parametric fit to the reflection/scattering data, was shown to agree well with previously published data.
Sea ice reflection coefficient estimates at low frequency
Authors: Giellis George R. , Yang T. C.
Published: October 2005

Results of a sea ice reflectivity experiment conducted at the FRAM IV ice camp will be presented. A vertical array with 27 receivers at depths ranging from 30–960 m was employed. Implosive sources at various depths (30–120 m) were set off at a range of 1145 m from the receivers. Analysis of direct and reflected pulses at the receivers resulted in reflection coefficient estimates at frequencies in the 50 Hz to 1 kHz range for reflection angles between 6° and 60°. The results will be compared with previous data [T. C. Yang and C. W. Votaw, J. Acoust. Soc. Am. 70, 841–851 (1981)] and model calculations.
Two numerical models—one simplistic, the other sophisticated—applied to under-ice acoustic propagation and scattering
Authors: Chin-Bing Stanley A. , Murphy Joseph E.
Published: October 2005

Many factors make modeling under-ice acoustic propagation and scattering difficult: Interfaces are rough with random protusions; ice is acoustically penetrable; little data exist; few validated models exist; frequencies of interest range from the hertz to the kilohertz region. Thus no one model appears sufficient for all conditions. With this in mind, two under-ice acoustic models at opposite extremes are examined. One model is simplistic, using Kirchhoff approximation, ice reflection coefficients [S. A. Chin-Bing, J. Acoust. Soc. Am. Suppl. 1 78, S57 (1985)] and rms roughness. Model results compare favorably with high-frequency measurements from a flat cylindrical ice block. Implications are that simplistic models may be useful in generating synthetic under-ice acoustic data to augment sparse experimental data bases. The other model is sophisticated in that it is a full-wave range-dependent acoustic propagation model based on the finite element method [J. E. Murphy and S. A. Chin-Bing, J. Acoust. Soc. Am. Suppl. 1 81, S9 (1987)] and applied to an under-ice surface simulated by fractals superimposed on an ice keel representation. Numerical results are presented for this low-frequency model. [Work supported by ONR/NORDA.]
Low-frequency propagation across the East Greenland and Frontal Zone: Depth dependence of transmission loss
Authors: Mellberg Leonard E. , Connors D. N. , Browning D. G. , Botseas G. , Johannessen O. M.
Published: October 2005

In a previous paper [L. E. Mellberg et al., J. Acoust. Soc. Am. Suppl. 1 78, S71 (1985)] the directional dependence of acoustic modes across the East Greenland Frontal Zone was examined. However, for a given source and receiver depth, transmission loss can be due to a combination of these directionally dependent acoustic modes. By changing the depths of the source and receiver, the directional dependence of the transmission loss may be changed, in some cases to the extent of causing a reversal in the dependency. Results are given for a series of source and receiver depths located at various ranges relative to the frontal zone. [Work supported by NUSC and ONR.]
Relative scattering from dry cracks, ice ridges, and leads
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

Little is known about the characteristics of dry cracks in Arctic sea ice and their effect on low-frequency underwater acoustic waves interacting with the ice. Ultrasonic modeling results are presented showing the relative scattering from dry cracks, leads, and ridges in floating plates bounding a long shallow-water waveguide. Backscattering from solid ridges and ridges with internal cracks reveal the potential importance of dry cracks on low-frequency transmission loss prediction. In models with a large number of rectangular ridges, great transmission losses were observed at frequencies nearly coinciding with twice the ridge width. The article focuses on multiple scattering from infinitely long shallow parallel cracks, where the crack depth is much smaller than the wavelength. For a given number of cracks or ridges, the attenuation of low frequencies propagating in the waveguide is greatly affected by their spatial distribution along the waveguide boundary. [Work supported by DREP and ONR.]
New theatres for old
Authors: Strawbridge Norris
Published: October 2005

The Miami Beach Theatre for the Performing Arts, recently renamed The Jackie Gleason Theatre, began its life as a multipurpose theatre/sports facility. In the mid-1960's a combination of community needs and a decision by Jackie Gleason to broadcast his television programs from Miami Beach resulted in a renovation of the hall as a performing arts/television studio venue. Although the theatre lacked certain amenities, it fostered the growth of one of the largest concert/opera/dance series in America and has become the home for a 26-week Broadway show season. Recognizing the inherent problems in the facility, the City recently commissioned a second renovation to bring the space up to contemporary acoustic and theatre standards. The paper discusses the methods used to develop an architectural program for the renovation and the solutions developed by the design team to attain desired goals.
Renovation of the Orpheum Theatre, Vancouver, Canada
Authors: Wetherill Ewart A.
Published: October 2005

Despite the ever-increasing cost of performance facilities, the design and construction of a completely new auditorium is preferred with remarkable consistency to the alternative of renovating or remodeling an existing unused, or under-used, auditorium. However, the reuse of an existing hall may yield—in addition to substantial cost savings—such advantages as prime location, existing social recognition, and historical significance. This paper reviews the remodeling of the Orpheum, originally a vaudeville theatre, from cinema to concert hall as an alternative to its conversion to several small cinemas. In most respects, the renovation has preserved the original architectural character while attaining a critically acclaimed performance facility.
Acoustics of the new Filene Center, Wolf Trap Farm Park for the Performing Arts
Authors: Horrall Thomas R. , Pirn Rein
Published: October 2005

To replace the original Filene Center that was destroyed by fire, a new structure was designed and built in a scant 2 years (1982–84). Like its predecessor, the 3800-seat covered house, with an additional 3000 seats on the lawn beyond, serves as a summer home for the National Symphony Orchestra and caters to many other forms of artistic production. Under a mandate to rebuild the structure as it had been, the acoustical options were limited. Known problems such as discrete echoes off the high ceiling were eliminated. Stage acoustics were greatly improved by incorporating a totally new shell. Most significantly, the center was equipped with state-of-the-art sound systems, including a sophisticated enhancement system that covers the under-balcony areas. The principal acoustical characteristics of the center are discussed and the sound systems, their purpose, and their operational parameters described.
Simulated wave-vector filtering of impact-generated flexural wave disturbances on a finite thin-walled cylinder
Authors: Pierce Allan D. , Ginsberg Jerry H. , Schwaiger Gary P.
Published: October 2005

The authors have recently undertaken a theoretical simulation of experiments similar to those performed recently at NRL by Earl G. Williams and his colleagues, in which a submerged cylinder is transiently excited and normal displacements are inferred using the generalized nearfield acoustical holography (GENAH) technique. In the present paper, the cylinder is modeled as a thin-walled shell with rigid immovable end caps and with the end conditions taken as being that of simply supported. A short duration point force f(t) is applied normally to the surface and one seeks to describe the resulting normal displacement field using a high-frequency (and short wavelength) asymptotic theory of propagating and evanescent flexural wave pulses on a curved plate. Fluid loading is taken into account approximately with modifications derived using the assumption that the flexural wavelengths are short compared to the length and radius of the cylinder. One asks for the time and surface position dependence of the normal surface displacement within a local region of the cylindrical surface before and after a simulated wave vector filtering has been applied. The filtering process is such that one seeks to isolate only that contribution from a narrow frequency band and from a localized region of wavenumber space. The exercise is intended to demonstrate that one can isolate and follow traveling wavelets propagating away from the source, spiraling around the cylinder, and undergoing successive reflections at the end caps. [Work supported by ONR.]
Numerical implementation of variational techniques for sound radiation from axially and radially vibrating finite cylinders
Authors: Wu Xiao-Feng
Published: October 2005

Previous work by the author with Pierce and Ginsberg [J. Acoust. Soc. Am. Suppl. 1 79, S35 (1986)] using a variational formulalion has been extended to axisymmetric bodies in a general state of axisymmetric vibration. A Rayleigh-Ritz technique is used to calculate the acoustic pressure distribution on the surface of axisymmetrically vibrating finite cylinders. The computed surface acoustic pressure and the given normal surface velocity are then taken as inputs into an integral relation for determination of the farfield radiation patterns. Different trial functions are employed in the expansion for the unknown surface pressure and results are compared with each other. It is demonstrated that the computational solutions converge much faster toward the correct answers if one incorporates his physical insight and prior knowledge into the construction of admissible trial functions for the unknown surface pressure. Examples studied include finite cylinders vibrating, respectively, in the radial direction and axial direction as a rigid body. Numerical results agree well with those previously published by Copley and by Fenlon and with those computed using Rogers' SHIP program. [Work supported by ONR.]
Impulse response of a continuously ribbed panel
Authors: Maidanik G. , Dickey J.
Published: October 2005

The impulse response function of a uniform panel immersed in a uniform environment is assumed known. The modification in this impulse response function due to the attachment of identical and regularly spaced ribs is derived. The manner of negotiating this modified impulse response function from the discreteness to the continuum of ribs is discussed. The negotiation reveals the criteria that need to be satisfied for uniformly lumping the ribs in the panel. When the criteria are substantially satisfied, the ribbed panel becomes essentially a uniform panel. The ribs are then accounted for by lumped modification of the uniform impedance of the unribbed panel.
Vibration of a plate with distributed structural stiffness
Authors: Pierucci Mauro
Published: October 2005

In most analyses of plates, only two types of plate vibrations have received wide attention: homogeneous plates and plates with discrete discontinuities. In this work, the structural inhomogeneity has been selected to be continuous and distributed. The plate is assumed to be infinite. The stiffness has been assumed to vary in a sinusoidal manner. The resulting differential equation has been solved by the use of Fourier transforms and the solution in the wavenumber space is presented. The plate admittance is a function of the structural wavenumber and the wavenumber of the distributed inhomogeneity. The results for the in vacuo and the fluid-loaded plates are presented. In the very short and the very long inhomogeneity wavelength limits, the effect of the structural inhomogeneity is very weak at all structural wavenumbers. The main contribution to the structural admittance is present when the value of the structural inhomogeneity wavenumber is close to the coincidence structural wavenumber. For the in vacuo cases, it is shown that the effect of the inhomogeneity is limited to values of the structural wavenumber equal to the coincidence wavenumber plus or minus an integral multiple of the inhomogeneity wavenumber.
Resonant response of elastically supported, fluid-loaded plates
Authors: Hammouda Jamel , Burroughs Courtney B.
Published: October 2005

An analytic model of the response of finite plates simply supported on two opposing edges and elastically supported on the other edges is derived. Transverse shear and rotary inertia in the plate and adjustable stiffness constants in the elastic supports are included in the model. The elastic support stiffness constants are adjusted to simulate simply supported, clamped, and free boundary conditions, and the results are compared to published results. The variation of resonant frequencies with the stiffnesses of the elastic supports is shown. The effect of fluid loading on the resonant responses of the elastically supported plate is presented.
Dynamic response of submerged layered composites
Authors: Braga Arthur , Herrmann George
Published: October 2005

The dynamic interaction between elastic and homogeneous two-phase periodically layered bodies and a surrounding acoustic fluid has been studied. The plane-strain elastodynamic behavior of the composite has been modeled on the basis of Floquet's theory for periodic structures. This approach consists of solving the equations of motion for a cell that repeats periodically, and then applying Floquet's theorem to extend the solution to the entire body. The dispersion spectrum exhibits the classical Brillouin structure of stopping and passing bands. Even though Floquet's theory applies essentially to infinite regions, it is nevertheless possible to adapt the scheme for finite boundaries and to formulate interface conditions with an acoustic fluid. Qualitative and quantitative results are presented for harmonic motions of two geometries, namely, a layered half-space with an overlying acoustic fluid and a submerged infinite laminated plate. Special attention is paid to the energy partition between the layered solid and the fluid for the complete range of frequencies. [Work supported by ONR.]
New approaches in vibroacoustic measurement system design
Authors: Clark Joseph A. , Honke Paul M.
Published: October 2005

Recent advances in measurement instrumentation and in computer hardware such as more fully programmable signal conditioners, faster data convertors, processors and other handlers, higher resolution displays, and larger memories invite the development of new vibroacoustic measurement approaches. In this talk, the design and implementation of a new system for measuring radiated and self-noise paths associated with complex, large-scale, immersed structures will be described. New approaches will be presented in the context of software developed or utilized to achieve improved performance of control, processing, display, and analysis functions. Advantages of the new approaches for studies of more subtle and complex vibroacoustic effects will be discussed.
Performance benchmarks for isolated word recognition
Authors: Rabiner Lawrence R. , Wilpon Jay G.
Published: October 2005

The performance of isolated word speech recognition systems has steadily improved over time as more is learned about how to represent the significant events in speech and how to capture these events via training algorithms. In particular, algorithms based on both template matching and hidden Markov models (HMMs) have been developed that yield high accuracy on several standard vocabularies including the ten digits (zero to nine) and the set of letters of the English alphabet. Results are presented here that show the effect of analysis parameters (e.g., frame size, frame rate) on recognition performance for a speaker trained system and the performance of both template and HMM-based recognizers (both speaker trained and speaker independent) on the digits and the alphabet vocabularies.
Classification of fluent speech in coarse acoustic classes
Authors: Stern Paul-Eric
Published: October 2005

Broad phonetic classes have been demonstrated to be useful for constraining search during lexical access but necessitate that the recognition of broad phonetic features be achieved in an error-free mode. This goal is not realistic due to the abstract definition of phonetic classes. However, a similar task may be performed through the recognition of acoustic classes that are subsequently mapped to phonetic categories. A coarse acoustic recognizer has been implemented in the context of a multispeaker fluent speech recognition system. It furnishes robust acoustic representations corresponding to different degrees of granularity of speech that will constrain further processing on the signal. This classifier has been implemented using a Bayesian technique allowing the application of different kinds of class recognition decisions. The parameters used to represent the speech signal are dependent on the acoustic classes and range from whole spectrum characteristics to specific discriminating features. The choice of acoustic classes is discussed, one main criterion being the maintenance of a correspondence between acoustic and phonetic labels. Because of the variability of the signal, but also of the propensity to error of any recognizer, multiple and contextual mapping is advocated. Results are reported and commented upon. [Work supported in part by INRIA and DARPA.]
Using features to empirically generate pronunciation networks
Authors: Rudnicky Alexander I.
Published: October 2005

The construction of high-quality lexical models for speech recognition systems is a labor-intensive process, requiring not only a great deal of time but also appreciable expertise on the part of the human model builder. Techniques that automate all or parts of this process are therefore highly desirable. Two approaches have been used: the generation of pronunciation networks from baseforms by application of phonological rules and the abstraction of such networks from transcription data. This paper describes a semiautomatic procedure for deriving lexical models from manual phonetic transcriptions. The algorithm uses a feature-based distance metric to align different pronunciations and produces phonetic networks that specify alternate pronunciations for words. The paper describes the results of constructing lexical networks for a 1000-word vocabulary, using a corpus of 10 000 work tokens. It should be noted that the technique described here is not restricted to manual transcriptions, but can be extended to automatic transcription such as the one produced by a front-end component of a speech recognition system.
A word classification method for the recognition of Japanese from a large vocabulary
Authors: Yoshida Kazunaga
Published: October 2005

This work is motivated by results of recent studies which show that lexical access using robust broad phoneme classes can potentially result in small sets of candidate workds from a large lexicon, and thus is effective for large vocabulary word recognition. In this paper, a set of broad phoneme classes suitable for Japanese and a new multilevel lexical access model are proposed. First, broad phoneme classes that have robust features for Japanese are investigated, and their constraining power is examined using a dictionary containing over 20 000 words. Next, a multilevel lexical access model is proposed based on our study about the broad phoneme class. The model consists of four stages: syllable nucleus detection, consonant classification, syllable nucleus classification, and detailed phoneme classification. The lexical search space can be significantly reduced using the access model. Finally, a word classification method based on the access model is also proposed. Results of recognition experiments were encouraging. [This study was conducted while the author was visiting at the Research Laboratory of Electronics, MIT, Cambridge, MA 02139.]
Application of hidden Markov models to automatic speech endpoint detection
Authors: Wilpon J. G. , Rabiner L. R.
Published: October 2005

Accurate detection of the boundaries of a speech utterance during a recording interval has been shown to be crucial for reliable and robust automatic speech recognition. The endpoint detection problem is fairly straightforward for high-level speech signals spoken in low-level stationary noise environments. However, these ideal conditions do not always exist. One example, where reliable word detection is difficult, is speech spoken in a mobile environment. Currently, most endpoint detection algorithms use only signal energy and duration information to perform the endpoint detection task. In this paper, an endpoint detection algorithm is presented that is based on hidden Markov model (HMM) technology. Based on a speaker-dependent speech database from four talkers, and recorded in a mobile environment under five different driving conditions (including while traveling at 60 mph with the fan on), several endpoint detection schemes were tested. The results showed that the HMM-based approach to endpoint detection performed significantly better then the energy-based system. The overall accuracy of the system using the HMM endpoint detector, when tested on the 11 word digits vocabulary (zero through nine and oh) with speech recorded in various mobile environments, was 99.4%. A top recognition performance of 99.7%, on the same conditions, was achieved by using an HMM recognizer with explicit endpointing.
Some techniques for creating robust stochastic models for speech recognition
Authors: Lee Chin-Hui
Published: October 2005

Recently, hidden Markov models (HMM) have been applied successfully to both isolated and connected word recognition. However, when the same formulation is adopted for recognition of more confusable vocabularies such as English alphabets, the recognition performance is often less satisfactory. The main reason is that a more accurate model is required. Such a model should be more robust against small training sample sizes and should also be properly initialized so that the finer features used to discriminate confusable word pairs can be extracted. In this paper, three specific robustness issues will be investigated: choice of observation densities, model initialization, and incorporation of duration information. In a step-by-step attempt to address those issues, it was found that the same HMM formulation can still be adopted if acoustic/phonetic knowledge about the vocabulary is taken into account in the model parameter estimation and recognition phases. Testing on a 39-word English alpha-digit vocabulary, in a speaker trained mode, indicates that the recognition performance can be significantly improved and the results are comparable to the template-based DTW recognizer if model parameters are properly initialized and durational information is adquately incorporated.
Probabilistic estimation of lexical stress
Authors: Freij Ghassan J.
Published: October 2005

A probabilistic technique is described for the automatic estimation of lexical stress pattern of isolated words using hidden Markov models (HMMs) with continuous asymmetric probability density functions. Stress information is potentially useful for large-vocabulary speech recognition in that it facilitates the extraction of more robust phonetic data within stressed syllables and leads to more efficient lexical access. Adopting a binary stressed-unstressed strategy, a constrained HMM network was trained using observation vectors consisting of ten acoustic measurements of intensity, pitch, and spectral balance. These measurements were extracted from a corpus of disyllabic stress-minimal word pairs, each word embedded in a phrase and repeated eight times. Further, the underlying temporal structure of the data is represented implicitly by the probability of remaining in a state in relation to the probability of exiting from it. Using this technique, correctness of classification was measured to be 89% for stressed syllables and 81% for unstressed syllables.
Should ASR front-end be insensitive to fundamental frequency? (perceptual shift of formant position due to fine harmonic structure of voiced speech
Authors: Hermansky Hynek
Published: October 2005

Due to the fine harmonic structure of the source spectrum of voiced speech, most automatic speech analysis techniques estimate formant positions that systematically deviate from the resonant frequencies of the vocal tract. This property is in conflict with linear source-filter models of speech production and an effort is made to minimize the effect of the fundamental frequency F0 on the analysis result [e.g., Hermansky et al., Proceedings ICASSP-83 (IEEE, New York, 1983), pp. 778–780]. Our experiments show that the human auditory perception has properties similar to the above described properties of automatic analyses. The method of confusion scaling is applied in paired comparison of synthetic vowel-like stimuli with varying F0 and the second formant frequency F2. The results show that the perceptual estimate of formant position goes through a cycle of positive and negative deviations as the relative F2/F0 frequency goes from one integral number to the next. The position is estimated the most accurately when the formant peak falls either into a harmonic peak or if it lies right between two harmonic peaks. The maximal deviation of the estimate due to harmonics of the F0 from the 120-Hz neighborhood in the 2-kHz second formant region is about ± 0.5%. Our findings imply that when modeling the speech perception, as in the automatic speech recognition, a certain degree of sensitivity of the analysis technique to F0 might be beneficial.