bluuebunny/crossref_metadata_2025 huggingface dataset:
Weighted optimization analysis of auditory-nerve fiber responses to complex sounds
Authors: Lim D. , Capranica R. R.
Published: October 2005

An experimental technique has been developed to identify the hierarchical importance of characteristic features in the complex sounds to which an auditory neuron is most selective. Single-unit spike rates are measured in response to variation of component intensities and frequencies, using a subset of single and paired tone stimuli. The response profiles are used to rank the importance of nonlinear interactions between component frequencies as well as component intensity levels, and a multidimensional matrix is derived that enables prediction of the neuron's response to sounds in a more general, complex set. The derivation is based on weighted inner product space optimization (WIPSO) and singular valne decomposition (SVD) analysis. To test this general method, the activity of single auditory fibers in the eighth nerve of the green treefrog (Hyla cinerea) was recorded in response to computer-synthesized stimuli. Results indicate that this is a very promising, powerful approach for characterizing the selectivity of individual auditory neurons to synthetic and natural sounds of interest. [Work supported by NINeDS.]
Cardiovascular responses of CCU patients to simulated noise and conversation
Authors: Baker Carol F. , Garvin Bonnie , Kennedy Carol , Polivka Barbara
Published: October 2005

The coronary care unit (CCU) is an environment that serves as a constant source of sensory stimulation in the form of noise and human interaction. Researchers have noted cardiovascular (CV) changes with human communication. It is not clear whether the CV changes are in response to the sound level or the meaning of the content. To test for the difference in meaning of conversation, cafeteria babble was taped to use as a controlled intervention. The purpose of the study was to determine differences in CV responses between a quiet condition, conversation, and meaningless noise at the same loudness as human communication. The sample was 20 cardiac patients. Sound-pressure level (dBA), actual sound, and heart rate (patient monitor) were recorded on a TEAC physiological tape recorder in patients' rooms. Blood pressure was measured with a Dinamap. Taped meaningless sound, alternating with quiet, was played at 3-min intervals for 18 min. Conversation was recorded as it occurred naturally during five different recordings. Data analysis is in progress with repeated measures ANOVA to compare heart rate and blood pressure response between the three noise conditions. This research provides a foundation for future studies that will distinguish patients' CV responses to specific types of noise and meaningful human communication. [Work supported by AREA, NIH.]
Auditive and cognitive factors in speech perception by elderly listeners
Authors: van Rooij John C. G. M. , Plomp Reinier
Published: October 2005

A key issue in research on speech perception in the elderly is whether the difficulties in understanding speech are caused by auditive and/or cognitive factors. A test battery was developed comprising auditive (sensitivity, frequency selectivity, and temporal resolution), cognitive (memory performance, processing speed, and intellectual abilities), and speech perception tests (at the phoneme, spondee, and sentence level). This test battery was administered to 72 elderly subjects (aged 60 to 93 years). The results show that the deterioration of speech perception in the elderly consists of two statistically independent components: (a) a larger component, mainly representing the progressive high-frequency hearing loss with age and (b) a smaller component, mainly representing a general performance decrement due to reduced mental efficiency (indicated by reduction of processing speed and a diminished memory capacity). Although both components are correlated with age, it was found that the balance between auditive and cognitive contributions to speech perception performance did not change with age. [Work supported by Netherlands Organization of Scientific Research (NWO).]
The scientific career of Theodore J. Schultz
Authors: Beranek Leo L.
Published: October 2005

Theodore J. (Ted) Schultz combined two careers and a cheerful, friendly personality during his span of years as a scientist and consultant in the field of acoustics. His first career, music, began at the Eastman School of Music where he became an accomplished bassoonist. Electrical engineering followed at the University of Missouri, Acoustics began when he enrolled in Harvard's Graduate School of Arts and Sciences where he received his M.Sc. and Ph.D. under Professor F. V. Hunt. His major life work was devoted to acoustical research and consultation at Bolt Beranek and Newman in Cambridge, MA. Both during his academic years and later, he remained a professional bassoonist, playing in municipal symphonies in Providence, RI, Portland, ME, and Worcester, MA. This paper reviews his overall career as a scientist, particularly as the author knew him for 22 years at BBN, where he rose to the position of Principal Scientist.
DSP beamforming and talker tracking with a linear microphone array
Authors: Silverman Harvey F.
Published: October 2005

One of the problems for all speech input is the necessity for the talker to be encumbered by a head-mounted, hand-held, or fixed position microphone. An intelligent, electronically aimed undirectional microphone would overcome this problem. Array techniques hold the best promise to bring such a system to practicality, although the acoustic problems are manifold. High-speed digital signal processing (DSP) chips have made it possible to attack the essential problems of forming the beam, aiming the microphone, and tracking a unique talker. A useful beamforming algorithm and a two-step talker-tracking algorithm are introduced. In the latter, step 1 is a rather conventional filtered cross-correlation method; the delay between some pair of microphones is determined to high accuracy using interpolation on the sampled data. Then, using the fact that the delays for a point source should fit a hyperbola, a best hyperbolic fit is obtained using nonlinear optimization. Results indicate that this method works reliably for signal-to-noise ratios of less than 10 dB. [This work principally supported by NSF Grant No. MIP-8809742 and DARPA/NSF Grant No. IRI-8901882.]
Concert hall design: The legacy of Ted Schultz
Authors: Wetherill Ewart A.
Published: October 2005

Ted Schultz brought to the study of music room acoustics the perception of a professional musician, familiarity with the musical literature, theoretical understanding of the physics of sound, and a remarkable ability to evaluate architectural designs and to present difficult acoustical concepts by analogy to more easily visualized situations. This paper presents the author's observations from almost 20 years of close association, including a 4-year period of simultaneous involvement in the design of five major concert halls.
Contributions of Theodore Schultz to understanding community response to environmental noise exposure
Authors: Fidell Sanford
Published: October 2005

This presentation reviews contributions made over 2 decades by Ted Schultz to the technical literature on community effects of environmental noise exposure. Two of his best-known contributions to assessment of environmental impacts of noise exposure are: (1) a much-cited reference book and (2) a well-known (and initially highly controversial) empirical dosage-response relationship for the prevalence of annoyance. Ted made a number of important, but less well known, contributions as well, however. At the time of his death, he was collaborating on development of another, theoretically based dosage-response relationship for the U. S. Air Force NSBIT program, as well as on a handbook chapter on annoyance.
Speech acoustics multimedia courseware for the Macintosh
Authors: Allen George D.
Published: October 2005

This paper will present a number of instructional applications in the area of speech communication and phonetics that use the Apple Macintosh microcomputer. These applications range from the fast display and analysis of speech spectra using Farallon Computing's MacRecorder, and an interactive tutorial on the decibel, to several large HyperCard stacks, such as the UCLA phonetics collection and my own evolving “translation” of Pullum and Ladusaw's Phonetic Symbol Guide. Emphasis will be placed on the potential of this medium for the relatively efficient creation of truly interesting, and therefore truly educational, computer software.
Thermoacoustic heat pumps
Authors: Atchley Anthony A. , Hofler Thomas J.
Published: October 2005

Although thermoacoustic heat transport is an active area of research, there are relatively few devices that can be used to demonstrate the effect outside the laboratory. One such device, the “Hofler tube,” was demonstrated at the Syracuse Meeting [Hofler et al., “Simple demonstration of a thermoacoustic sound source,” J. Acoust. Soc. Am. Suppl. 1 85, S112 (1989)]. Two other demonstrations will be presented in this paper. The first is a live demonstration of a miniature thermoacoustic refrigerator—the “minifridge.” In the second demonstration, presented on videotape, strips of liquid crystal, temperature-sensitive sheets are exposed to a large-amplitude acoustic standing wave setup in a Plexiglas resonator. When the sound field is turned on, a visible color gradient is set up in the strip, indicating the presence of a temperature gradient. [Work supported by ONR and NPS Research Program.]
Modes of a bar
Authors: Garrett S. L. , Rudnick I.
Published: October 2005

An aluminum rod (≈ 30 cm) of circular cross section (≈ 1.2-cm diameter) can be excited electrodynamically in its longitudinal, torsional, and flexural resonant modes using a pair of coils glued to the ends and placed in a magnetic field. Several harmonics of all three “free-free” modes can be easily observed using a signal generator and oscilloscope. The nondispersive modes (longitudinal and torsional) are harmonic to better than ± 0.5%, and the anharmonicity of the flexural modes is apparent. The Young's modulus of the bar determined by the flexural modes and the longitudinal modes also agree to better than + 0.05%, so this laboratory exercise demonstrates excellent quantitative agreement with theory. The exercise can be extended to provide an introduction to Rayleigh's method [J. W. Strutt (Lord Rayleigh), The Theory of Sound (Dover, New York, 1945), 2nd ed., Vol. I, Secs. 155 and 185] for calculation of resonance frequency shift due to the imperfect boundary conditions created by the mass of the coils and their adhesive. The agreement between theory and experiment increases to ± 0.1% when the mass loading is included. [Work supported by N.P.S. Direct Funded Research Program.]
Demonstrating modes of vibration in bars and plates with simple apparatus
Authors: Russell Daniel A. , Korte Rodney R.
Published: October 2005

A small cylindrical magnet is attached to a bar or plate supported by rubber bands. A coil of about 300–400 turns, driven by an audio generator, supplies an alternating magnetic field. In order to determine the modal shapes, a small tie clip microphone is used to scan the sound field near the bar. In a noisy room, it is desirable to add an octave-band filter set (stereo equalizer). Modes of vibration in a rectangular bar, a circular plate, and a square plate will be described and demonstrated.
Demonstrating “privileged frequencies” of a pipe
Authors: Rossing Thomas D.
Published: October 2005

The resonance frequencies of an open pipe are harmonics of the fundamental frequency: fn = nf1. Each of these resonances can be excited by sound pulses occurring at the mth submultiple of the resonance frequency fn/m = n/mf1. These lead to a large number of “privileged frequencies” at which a woodwind reed or the brass player's lips can “lock in” to a wind instrument bore [A. H. Benade, Horns, Strings & Harmony (Doubleday, Garden City, NY, 1960), pp. 166–170]. Resonances and privileged frequencies of a 60-cm pipe will be demonstrated with simple apparatus.
Ray synthesis of the form function for backscattering from hollow elastic spherical shells including leaky Lamb waves and longitudinal axial resonances
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

A ray synthesis [P. L. Marston, J. Acoust. Soc. Am. 88, 25–37 (1988)] is employed for describing the form function f (θ = π,ka) for backscattering from a hollow, elastic spherical shell. The synthesis of f contains a component associated with a specular reflection fsp and contributions from leaky Lamb waves. The contribution fl, of the l th leaky Lamb wave is expressed in a Fabry-Perot form. The present synthesis differs from previous results by including the effects of longitudinal axial resonances on fsp. A novel ray synthesis of fsp, which sums amplitudes associated with multiply reflected rays within the shell, indicates a significant resonance effect near the condition kt/h = nπ (n = 1,2,…,), where kL is the longitudinal wavenumber of the shell's material and h is the thickness of the shell. The ray synthesis shows that the curvature of the shell is essential to the modeling of longitudinal resonances. The ray synthesis of f is compared with the exact partial-wave series representation for a 440c stainless steel shell where the inner-to-outer radii ratio is b/a = 0.838. The synthesis works well down to ka = 7. The first longitudinal resonance occurs at ka ≈ 77 and inclusion of its effect on fsp improves the ray synthesis of f in this region of ka. [Worked supported by ONR.]
Insertion loss studies of a mechanical vibration isolation system
Authors: Nam M. , Prasad M. G.
Published: October 2005

Machinery noise control along the path can be classified into three approaches, namely, by enclosure, absorption, and vibration isolation. The transmissibility of a vibration isolation mounting is given by the ratio of transmitted force to foundation and the excitation force, whereas the insertion loss is obtained by the ratio of forces at the foundation without and with isolation mounting. The performance of a vibration isolation system is usually described using transmissibility which depends on the isolation system parameters with the machine considered as a rigid mass. However, the insertion loss of a vibration isolation system depends on the system parameters and source impedance, which accounts for the nonrigid characteristics of the machine. The nonrigidity of the machine can also be characterized through a base plate supporting the machine. This study deals with analysis of a system consisting of machine, isolation mounting, and rigid foundation in terms of insertion loss and transmissibility using a single degree of freedom model. Such studies would be useful in isolation mounting design for reducing machinery vibration and noise.
A psychoacoustic model of the ba/wa boundary shift
Authors: Oller D. Kimbrough , Eilers Rebecca E. , Ozdamar Ozcan
Published: October 2005

Previous studies have shown that the ba/wa boundary (cued by formant transition duration) shifts in the context of different vowel durations. The shift has the appearance of a “rate normalization,” but modeling of potential auditory factors involved in perception of transition durations suggests that the effect may be qualitatively different from other cases of rate normalization. The present model suggests that the shift of boundary may result from a difficulty of the perceiver to recognize exactly when a change in frequency trajectory (a pivot point) of a formant occurs. The model predicts an auditory overestimation of formant transition durations in cases where the following vowel is short, and a progressive correction of that overestimation as the vowel increases in duration. The model accounts for the magnitude of the ba/wa shift in speech and analogous nonspeech stimuli, and also provides a natural account of the asymptotic characteristic of the ba/wa shift (i.e., the fact that the shift essentially disappears after vowels reach 200 ms or more). Finally, the model offers a natural account of the previously unexplained fact that the ba/wa boundary sometimes shifts at times that the rate normalization hypothesis would not appear to predict (as in the case of lengthening syllables by adding arresting transitions such as occur in bad/wad).
Efficient vector quantization of LPC parameters at 24 bits/frame
Authors: Paliwal K. K. , Atal B. S.
Published: October 2005

Linear prediction coding (LPC) parameters are widely used in various speech processing applications for representing the spectral envelope information of speech. For low-bit-rate speech coding application, it is important to quantize these parameters accurately using as few bits as possible without sacrificing the speech quality. Though the vector quantizers are more efficient than the scalar quantizers, their use for fine quantization of LPC information (using 24–26 bits/frames) is impeded due to their prohibitively high complexity. In this paper, a split vector quantization approach is used to overcome the complexity problem. Here, the LPC vector is divided into two parts and each part is vector-quantized separately. The splitting of LPC vector is studied in the following three domains: (1) line spectral-pair frequency (LSF), (2) arc-sine reflection coefficient, and (3) log area ratio. Splitting in LSF domain is found to be the best. Using the localized spectral properties of the LSF parameters, a weighted LSF distance measure is proposed. Using this distance measure, it is shown that the split vector quantizer can quantize LPC information in 24 bits/frame with 1-dB average spectral distortion. In terms of average spectral distortion and number of outliers, its performance is better than the 32 bits/frame scalar quantizer.
An adaptive modal-based active control system
Authors: Morgan Dennis R.
Published: October 2005

Active control for silencing sound and vibration has recently become the subject of much investigation, and is now being enhanced by the advent of adaptive filtering techniques. On another front, modal decomposition for active control problems has been shown to offer a number of practical advantages, as independent modal control can minimize the number of actuators, sensors, and corresponding dimensionality of the controller, as well as minimize the control energy; provide robustness to system parameter uncertainty; and, minimize the adaptive convergence time by uncoupling the modal responses. In this paper, details are sketched for a narrow-band adaptive modal-based active control system that incorporates all of these features. The major topics addressed deal with modal filters, actuator prefilters, spatial sampling effects, and design methodology. Although this work pertains only to the narrow-band disturbance problem, these techniques can be readily generalized to the wideband case by using temporal filters to separate out different spectral bands for narrow-band modal-based processing. The analytical results are illustrated by numerical example for a vibrating cantilever beam, using a graphics display that was developed for real-time interactive design.
Computer-assisted interactions between two musicians
Authors: Wessel David , Waxman David
Published: October 2005

A novel improvisation-oriented live performance situation is proposed. Its implementation is described, and results from actual performances are presented. This performance context involves a musician performing on an instrument outfitted with sensors which feed a computer system that monitors certain aspects of the instrument's behavior such as its pitch, loudness, and timbre. Another performer interacts with the system to selectively record, transform, and play electroacoustics materials derived from the instrumentalist's performance. This situation might be characterized as one involving an improvising soloist with an accompanist who constructs the accompaniment from phrases attentively trapped from the soloist's ongoing performance. The system requires a running or short-term memory mechanism with procedures that aid in the parsing of selected phrases, a supple user interface for the accompanist that facilitates the selection and transformation of the musical materials as well as their expressive performance, and a rich set of procedures for producing variations. A number of successively refined implementations of this idea have been made, the most recent of which uses the MAX programming environment developed by Miller Puckette at IRCAM. The system provides for musical intimacy between the performers. It also provides the accompanist with an interesting set of tasks and the soloist with a stimulating accompaniment based on variations of his own materials.
Multiple scattering from many bounded obstacles: An improved matrix formulation
Authors: Lim Raymond , Hackman Roger H.
Published: October 2005

The acoustic scattering from many interacting, bounded, three-dimensional obstacles has been treated by several authors [see for example, V. Twersky, J. Math. Phys. 8, 589 (1967) or B. Peterson and S. Ström, J. Acoust. Soc. Am. 56, 771 (1974)]. In particular, Peterson and Ström exended the single-scatterer transition (T) matrix formalism to several obstacles (including all orders of multiple scattering) by using the translation properties of the spherical basis functions to translate the multiple scattered fields of each scatterer. However, for numerically exact results, the present state of development is cumbersome to apply to more than two scatterers, and convergence of the rescattering matrices is sensitive to scatterer separation. in this paper, an improved matrix formalism, which also incorporates the single-scatterer T matrix and sums the multiple-scattering series exactly, is given by using the transformation between the cylindrical and spherical basis sets to perform the translations among the origins of the various scatterers in the cylindrical basis set. A formalism that is both simpler and less numerically sensitive to the separation of the various obstacles results. Exact numerical calculations of the scattering from a linear array of as many as ten spherical scatterers are presented.
Scattering of elastic waves by solid chiral half-spaces and spheres
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The displacement field u in an isotropic, noncentrosymmetric (chiral) elastic solid has to be supplemented by the independent microrotation field φ. Six different wavenumbers are possible in a chiral elastic solid: Of these, two represent longitudinal fields and the remaining four are circularly polarized. This paper is concerned with the reflection and refraction of elastic plane waves by planar achiral-chiral interfaces, and the scattering of elastic waves by a chiral sphere.
The numerical calculation of scattering by rough surfaces
Authors: Wombell Richard J. , DeSanto John A.
Published: October 2005

The calculation of scattering by random rough surfaces has recently received much interest. Exact integral equations, usually based upon a coordinate-coordinate Helmholtz integral formulation, are solved numerically and the ensemble scattered field calculated by Monte Carlo methods. Currently, such techniques are limited to surfaces rough in one dimension only. Here, an alternative approach to these calculations is described. This is based upon a mixed spectral-coordinate integral equation and the use of appropriate expansions of the surface fields. The extension of this approach to two-dimensional rough surfaces will also be discussed.
Acoustical resonances of an elastic cylinder: Parametrical study
Authors: Batard H. , Ouentin G. , Conoir J. M. , Rousselot J. L.
Published: October 2005

The authors achieve a parametrical study of the acoustical resonances frequencies of an elastic cylinder versus the elastic parameters of the scatterer (longitudinal sound velocity cl, shear sound velocity ct, density ρ). They use numerical computations because of the complexity of the equations obtained in the resonance scattering theory, even for this simple geometry. The result obtained is quite surprising. Most of the resonance of a given mode n belong to specific planes in the 3-D space (x1, cl, ct), where x1 is the dimensionless frequency (x1 = k1a). These planes obey very simple equations and belong to two families. The implications of these results are discussed.
Visualization of acoustic scattering from submerged sphere
Authors: Gaumond Charles F. , Dragonette Louis R. , Schuette Lawrence C.
Published: October 2005

The scattering of harmonic, plane waves from an aluminum sphere and a rigid sphere were visualized using normal mode series solutions displayed on an IRIS-4D color graphic super workstation. The temporal behavior of the scattered pressure fields were studied in the frequency region for 1 < ka < 7 in the region surrounding the scatterer. The effects of elasticity, namely the existence of Rayleigh-type waves, were seen after the field scattered from a rigid sphere was subtracted from the field scattered from the aluminum sphere. The nearfield formation of a null at ka = ∼5.5 near the bistatic angle of 155° was seen in a video presentation of the temporal behavior.
In-plane acoustic scattering measurements at NRL
Authors: Houston Brian H. , Gaumond Charles F. , Schuette Lawrence C. , Dragonette Louis R. , Saniga Michael L.
Published: October 2005

The Naval Research Laboratory's pool facilities provide a unique capability for the investigation of underwater acoustic scattering and radiation phenomena. Scattering measurements are often preceded by calibration or test series, and the results presented here were obtained in a calibration performed with a solid aluminum sphere as a reference target. The source, receiver, and target center are coplanar in the measurements, and the data were acquired as the receiver was rotated a full 180° about the sphere; the data set thus includes scattering in the forward direction. The ka range of the results presented extends between 0.9 and 7.0 ka; here, ka is 2Πa/λ, where a is the sphere radius and λ is the sound wavelength in water. Specular reflection, the creeping wave, and the leaky-Rayleigh surface wave are the mechanisms that produce the scattered field in this ka region. The data and theoretical predictions are displayed in a variety of ways to expose their functional dependence on angle and ka.
A method for reducing radiation from plates by actively controlling the restoring forces applied to the plate
Authors: Naghshineh Koorosh , Koopmann Gary H. , Lamancusa John S.
Published: October 2005

A novel method of active control is proposed that focuses on controlling the acoustic radiation of a plate by directly altering forces applied to the plate. By integrating active elements into the surface of the plate, its vibration characteristics can be made time dependent and thus, given a fluctuating load, the natural frequencies and their corresponding mode shapes can be actively adjusted to produce a minimum radiation condition. In this study, a model of an epoxy plate with shape memory alloy actuators is used in conjunction with an acoustic radiation model to predict the effectiveness of this concept. To demonstrate this behavior on a physical model, a cantilever beam is constructed of epoxy and shape memory alloy actuators. The actuators are attached to the surface of the beam in such a manner to put the beam under a state of localized axial compression that results in a shift of beam natural frequencies. Comparisons of the experimental results versus finite element analysis and an analytical model are presented.
Optimization of location and amount of viscous damping to minimize random vibration
Authors: Neubert Vernon H.
Published: October 2005

The random vibrations of a truss were minimized analytically by placing viscous dashpots where they would be most effective. It was assumed that there was a limited amount of damping available and the question was, where can the damping be used most effectively? Dashpots were placed parallel to the truss members, which deform only axially. The problem was developed as a nonlinear optimization problem. The response of the structure is represented in terms of its complex normal modes. The sensitivities of the individual modal natural frequencies, loss factors, and complex eigenvectors were obtained for nonproportional damping. The excitation was white noise applied as concentrated forces at nodal points. The mean-square displacement was minimized using a modification of the method of steepest descent. An example is given for a 10-bar truss. The problem was also formulated for the optimization program CONMIN and the results are summarized for several constraint situations. The work is related to a previous paper dealing with the minimization of settling time of free vibrations by maximizing the energy dissipation rate [V. H. Neubert, Proc. DAMPING89, Int. Symp., W. Palm Beach. FL, February 1989].
Control of flow-induced vibrations in Nitinol-reinforced composite beams
Authors: Baz A. , Poh S. , Gilheany J.
Published: October 2005

Flow-induced vibrations of flexible fiberglas composite beams are attenuated by activating optimal sets of NIckel and TItanium alloy wire, called NITInol, which are embedded inside these beams. The dynamic and thermal characteristic of the Nitinol-reinforced composite beams are determined by monitoring the vibration's modes, as well as the temperature of the wires and beam during various activation and de-activation strategies of the Nitinol wires. The resulting shift of the vibration modes, which accompanies the activation of the Nitinol wires, is utilized to influence the fluid-structure interaction in such a way that results in attenuating the flow-induced vibrations. Experiments are conducted on 30-cm-long and 0.156-cm-thick prototypes of these beams that are mounted in a clamped-clamped fashion inside a wind tunnel. The effect of varying the flow speed on the induced vibrations is determined with and without the activation of the Nitinol wires. The results obtained indicate that there is an optimal number of Nitinol wires that should be activated to attain the maximum frequency shift. This number ensures a balance between the amount of strain energy added to the composite beam and the softening effect imparted to the resin used due to the heating of the Nitinol wires. With such optimal configuration, it was possible to shift the first mode of vibration from 42 to 61 Hz in about 3 min during the activation phase. About 6 min was required to bring the beam back to its original frequency during the de-activation phase. At steady-state conditions, vibration attenuations in excess of 60% were attained near and at the resonance. [Work supported under a grant from ARC.]
Wall pressure fluctuations in the transition region
Authors: Galib Thomas A.
Published: October 2005

Wall pressure fluctuations on an axisymmetric body of revolution were measured with piezoelectric pressure transducers. Spectral analysis of the data showed discrete frequency bands of the pressure fluctuations corresponding to predicted Tollmien-Schlichting disturbance frequencies, in the transitional boundary layer. Nondimensional power spectra showed that the peaks of the disturbance frequencies (for three free-stream velocities) collapsed to a single Strouhal number. Further manipulation of this result yielded an expression for the Tollmien-Schlichting frequencies in terms of a constant and the displacement thickness Reynolds number. These results were for a near-zero pressure gradient. They were later reproduced in an adverse pressure gradient for a variety of Reynold's numbers.
Application of surface acoustic waves for marine fouling prevention
Authors: Roh Yongrae , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

For ships, the attachment of marine fouling species on the hull causes a lot of problems. Conventional methods for antifouling include toxic painting and hull vibration. But these used to be expensive and ineffective. A new antifouling technique is developed by employing surface acoustic waves. Of various types of surface waves, SH plate mode waves are chosen, which turn into Love waves when the thickness of a hull is much larger than the wavelength of the waves, because they are most effective in shaking off the attachments. All the energy of the waves are confined to the surface of the hull and leaks very little into water. PVDF thin film and interdigital transducers are used to launch the waves and occupy only a small fraction of the hull surface. The energy transfer of the waves across vertical discontinuities in their propagation path is found to be satisfactory for the application. Compared with conventional methods, this new technique is more practical, powerful, and cost effective.
Algorithm-based method for suppressing the transmission of sound in a fluid-filled waveguide
Authors: Homer R. , Dubbelday Pieter S. , Park Ben A.
Published: October 2005

A 4-in.-diam open-ended water-filled tube is excited at its base by an electrodynamically driven piston which is 2 in. in diameter and suspended by two sheets of rubber. Directly above the piston, a thin disk of piezorubber encapsulated in rho-c rubber occupies a full cross section of the tube. The piston is driven with constant force over the range of frequency from 1–2 kHz. The piezorubber is driven by a source that is synchronized to the piston's excitation frequency with a phase-locked loop. A hydrophone located above the piezorubber disk is connected to a lock-in amplifier and is used to detect the transmitted signal. Based on the inphase and quadrature components of the transmitted signal, an amplitude and phase for the piezorubber's source is algorithmically determined such that the transmitted signal will be minimized. The process is iterated until the transmitted signal is reduced to the noise level of the hydrophone. The algorithm chosen is well suited for a noisy environment and was successfully applied in our experiments.
Fiber-optic interferometric differential strain sensor: “The smart strutt.”
Authors: Brown D. A. , Garrett S. L.
Published: October 2005

Two optical fibers, comprising the legs of a Michelson interferometer, are cast into a long rod (1.33-cm diameter, 35. 1-cm length) of epoxy at off-axis coplanar distances of 5.3 _+ 0. I min. The free-free bar is electodynamically excited in its gravest flexural, torsional, and longitudinal modes. The absolute displacement of the bar end for each mode was measured using the MTI fotonic vibration sensor and compared with the change in optical path length induced in the interferometer. At the fundamental flexural resonance of the bar (158.5 Hz), the correlation between measured transverse peak displacement (15.4 μm) and the measured number of strain-induced optical fringes (14.5 at a wavelength of 817 nm) was within 7% of theoretical predictions. No fringes were observed for the torsional and longitudinal modes, as expected, since those modes produce equal strain in each leg of the interferometer. Experimental values and techniques used to obtain data for the complex Young's and shear modulus for the elastomeric casting material (Stycast 1266) will also be presented.
Fundamental frequency and pitch: A perceptual study of Mandarin tonal coarticulation
Authors: Shen Xiaonan Susan , Lin Maocan
Published: October 2005

Rose [Pacific Ling. 55–82 (1989)] claimed that there is a nonequivalence between F0 and pitch, because native listeners were unable to perceive the tonal transient caused by tonal coarticulation. To test his claim, the stimulus consisted of 48 middle tones in Mandarin tritonemes: Six syllables [ma, na, la, ai, ao, aŋ] of the high-level tone preceded by the high-level tone (L tones) and the falling tone (R tones) and followed solely by the high-level tone over the syllable [pa] were spoken by two native Mandarin speakers, cross sliced by computer, and copied twice into a test tape in random order. The 24 R tones had F0 increments beyond the perceptual threshold while the 24 L tones did not. Sixteen Chinese and ten American listeners judged, through binary forced choice, whether the test tones were rising or level. The responses of the Chinese (z = 2.82, p < 0.01) and American listeners (z = 1.91,p < 0.05) were at 83.85% and 71.25% correct levels, respectively. However, Americans were less sensitive than Chinese listeners [t(24) = 10.25, p < 0.001]. The results refute Rose's claim. [Work supported by TAMU.]
Context effects as a function of perceptual set
Authors: Ralston James V. , Johnson Keith
Published: October 2005

There has been continuing debate regarding claims that human listeners process tonal stimuli differently as a function of perceptual set. To address this issue, the identification of sinusoidal stimuli in subjects reporting either speech or nonspeech percepts was examined. One set of stimuli were constructed from sinusoids modeled after the formants present in a [wi-ju] continuum. Subjects reliably classified stimuli with two response categories, regardless of their perceptual set. Probit analysis revealed steeper slope for speech labeling functions. Item-by-item analysis revealed larger effects of stimulus context for nonspeech listeners. Finally, increases in response latencies were larger for speech listeners for stimuli near the labeling category boundary. The major trends observed with the first set of stimuli were also obtained with smaller magnitudes with a second, simpler set of stimuli ([æ-uh]). Taken together, these results suggest that speech listeners process sinusoidal stimuli in a qualitatively different manner than nonspeech listeners. Speech listeners appear to weight stable internal criteria more heavily than nonspeech listeners, who weight stimulus context more heavily.
The effect of mode truncation in an analysis of acoustic radiation from spheroidal shells
Authors: Chen Pei-Tai , Ginsberg Jerry H.
Published: October 2005

A previous presentation [P. T. Chen and J. H. Ginsberg, J. Acoust. Soc. Am. Suppl. 1 85, S139 (1989)] outlined a general procedure by which variational principles may be employed to analyze the surface pressure and structural response of a shell in the shape of a surface of revolution. The displacement in this treatment may be described directly as a set of admissible, linearly independent, but otherwise arbitrary, basis functions, in conjunction with a comparable description of the surface pressure. An alternative is to perform an intermediate analysis to determine the in-vacuo displacement modes, and then to truncate the modal series based on a comparison of the eigenfrequencies and the frequency of excitation. This paper assesses the ability of these alternative strategies to treat the response of a prolate spheroidal shell. A matter of specific concern is the situation where proximity of two natural frequencies produces high-frequency in-vacuo modes whose localized displacement patterns suggest that they might be efficient radiators for low-frequency excitation in the fluid-loaded case. [Work supported by the Office of Naval Research, Code 1132-SM.]
Vibration and radiation from capped cylindrical shells in water
Authors: Williams Earl G.
Published: October 2005

Extensive experimental results will be presented of the vibration and radiation from shaker-driven, cylindrical shells with enclosed ends. Through the past 3 years, a great deal of knowledge about these shells has been gained through the use of nearfield acoustical holography to probe the vibration and radiation fields. These fields are represented globally over the shell, with the help of color displays, and from these pictures the mechanisms involved in vibration and radiation become apparent. Furthermore, with the help of thin shell theory these results are interpreted so that some generalizations can be made about the physics. The importance of a thorough understanding of the theory of vibration and radiation from an infinite cylindrical shell is demonstrated in comparisons of the dispersion relations to the measured data. Also the spatial filtering effect of the fluid on the modes of vibration is shown. This filtering effect is shown to retain the modal nature of the surface vibration leading to a powerful new approach for modal analysis. Also, the effects of the spherical-like endcaps on the vibration and radiation will be discussed.
Tuning logarithmic spectrum analyzers for music analysis
Authors: McGee W. F.
Published: October 2005

Logarithmic filter banks for the real-time analysis of musical signals permit the examination of the partials of notes in real time for transcription or analysis using low-cost digital signal processors. However, many recordings (even CDs) are mistuned, sometimes approaching a quarter-tone. Therefore, a tuning technique has been developed to allow the alteration of the filter center frequency, or all the filter center frequencies. The basis of the technique is to use a filter bank that results in complex outputs (magnitude and phase). The algorithm detects the imaginary part of the product of the filter output and the conjugate of the product of the filter output at the previous sample time and the expected phase shift. This quantity is positive for a sine wave below the filter center frequency and negative above, thus permitting a correction to the center frequency, and it is readily computed. Applications will be presented using a Motorola 56000 DSP and covering 7 octaves at the highest 85 piano frequencies.
Results of experiments to detect moving vehicles with a one-bit correlator
Authors: Gonter Robert H.
Published: October 2005

Moving vehicles such as automobiles, trucks, and aircraft can be tracked with a one-bit correlator using a technique similar to pattern velocity computers [G. R. Ochs and O. F. Miller, Rev. Sci. Instrum. 43, 879–882 (1972)]. Using two microphones spaced 30 cm apart, vehicles passing at a distance of 30 m or farther give significant correlation when the signals are in phase. Beamforming is easily done with shift registers so that the direction of movement can be determined as vehicles cross the beams. Although the correlations are confounded when more than one vehicle is passing, approximate vehicle counts were made using an AIM 65 microcomputer. It is possible that aircraft could be tracked by their sound using a three-microphone array and an oscilloscope with X-Yinput capability.
Numerical errors of superposition solutions to the acoustic radiation of a vibrating structure
Authors: Song Limin , Koopmann Gary H.
Published: October 2005

The superposition method is a newly developed method for computing the acoustic field radiated or scattered from a structure. By this method, a solution to the acoustic field is obtained by superposing the waves from a number of equivalent point sources interior to the surface of the structure. The strengths of the sources are determined such that they give the same velocity at each mode on the surface of the structure as prescribed. This paper presents an analysis of the numerical error of the superposition solution. It has been shown that the maximum error of the superposition solution can be estimated by the surface velocity reconstruction error. The surface velocity reconstruction error, which can be computed directly, depends on the surface velocity distribution and velocity interpolation functions associated with the surface nodes. A spherical radiator with different surface velocity distributions is chosen to demonstrate how acoustic wavenumbers, the number of the surface nodes, and locations of the sources affect the surface velocity reconstruction error and, consequently, the accuracy of the superposition solution.
Rayleigh scattering revisited
Authors: Junger Miguel C.
Published: October 2005

Two basic aspects of the scattering action of elastic spheres small in terms of acoustic wavelengths are developed in Lord Rayleigh's Theory of Sound, 2nd ed., Vol. II: (1) The scattered field of a compressible, movable sphere expressed as the sum of a monopole and a dipole component (pp. 282–284), a solution that rightfully gave rise to the term “Rayleigh scattering” in the author's honor; (2) the contribution to the scattered field by a sphere's resonance of any order (pp. 284A–284D), a solution Rayleigh credits to Lamb, which was subsequently extended to other frequency ranges and to arbitrary scatterer configurations by P. W. Smith, Jr. [J. Acoust. Soc. Am. 34, 640–647 (1962)]. The underlying assumptions and the relation between these two formulations are examined. Finally, the physics of a few familiar scattering situations is explored in light of these results.
Spatial, spectral, temporal, and statistical characterization of scattering from elastic shells in a fluid
Authors: Schenck Harry A.
Published: October 2005

The scattering strength of a rigid object in a fluid is a mild function of its shape and acoustic size (kd, where d is some characteristic dimension). On the other hand, the scattering strength of a closed air-filled elastic shell of the same shape often exhibits much more rapid variations over a very large dynamic range. No single value or sparse set of measurements or calculations can adequately describe the scattering strength of such an object. The construction of a complete scattering signature for a highly elastic scatterer therefore imposes a requirement for high resolution and large data sets, whether they are obtained experimentally or by computation. The purpose of this presentation is to illustrate several practical means to construct and display spatial, spectral, temporal, and statistical descriptions of elastic scatterers. [Work supported by the Naval Res. Lab.]
Large-scale numerical treatment of structural acoustics problems
Authors: Everstine Gordon C.
Published: October 2005

Alternative large-scale computational approaches are described and reviewed for predicting the dynamic response of submerged elastic structures subjected to time-harmonic mechanical or incident pressure loadings. Such problems can be solved by combining a finite element model of the structure with a fluid-loading model computed using finite element, boundary element, infinite element, or doubly asymptotic techniques. For each of these approaches, a variety of other choices must be made concerning the details of the formulation. Also discussed are the trade-offs between accuracy and efficiency in the calculations.
Differences in the echoes from an air-filled shell and one that is water flooded
Authors: Strifors H. C. , Gaunaurd G. C.
Published: October 2005

It is desirable to be able to distinguish between a submerged metal solid object and one essentially composed of air-filled membranes, such as fish. This target-ID problem has been addressed before. Another target-ID problem still to be addressed is that of distinguishing between a (water-tight) metal shell containing air inside and the same shell with defective seals that flood it with water. As examples, one could mention empty oil drums or old refrigerators that may be lying on the sea floor before and after becoming flooded. Apparently, debris of this type is quite abundant in shallow coastal U.S. waters. The characterization is to be done remotely, by analysis of the acoustic echoes returned by these scatterers. A predictive model has been constructed that simulates the resonance echoes returned by a spherical steel shell (of various thicknesses), first air-filled and then flooded with water. As a first approximation, the shell is assumed to be many characteristic dimensions away from the sea floor. Then the spectrum of resonances is extracted in both cases, and the extraordinary difference in their features is exhibited. These could then be used to distinguish easily between both active signatures, remotely and in situ.