bluuebunny/crossref_metadata_2025 huggingface dataset:
Time domain simulation of flute-like musical instruments
Authors: Fabre B. , van Steenbergen A.
Published: October 2005

The time-domain description of musical flute-like instruments as proposed by Mc Intyre, Schumacher, and Woodhouse [J. Acoust. Soc. Am. 74, 1325–1345 (1983)] has not yet been fully exploited. A major problem is the very slow transient behavior of the model. For such models, based on the analysis of Fletcher [J. Acoust. Soc. Am. 60, 926–936 (1976)], the nonlinearity is only due to the jet drive saturation. The transient behavior is linear because this nonlinearity is “smooth” and does not affect low amplitude oscillations. Linear theory is most useful as it allows an analytical solution of the problem. Comparison between the analytical solution and the numerical results indicates that the discretization can significantly affect the oscillation behavior. This effect is demonstrated for a simple flute model.
Industrial audiometry: Do we ask too much of it
Authors: Roberts M. E.
Published: October 2005

As of 1978, industrial health and safety regulations in British Columbia have required annual hearing tests for workers exposed to eight hour-equivalent noise exposures of 85 dBA or greater. Industrial audiometric technicians are trained and certified by the WCB. In addition, the regulations require that facilities be inspected annually to ensure calibration procedures are used and background noise levels are monitored. All results are submitted to a central data bank. Audiometry and the extensive counseling that takes place at the time of the test have been useful in motivating workers to consider noise as a personal health hazard, particularly for those working in the lower range of hazardous levels. In addition, averaged audiograms for workers in specific occupations have been useful in predicting future claims costs and thus have also been an economic motivator for establishing and maintaining hearing conservation programs.
Determination of compressional wave speed profiles using modal inverse techniques in a range-dependent environment in Nantucket Sound
Authors: Frisk George V. , Lynch James F. , Rajan Subramaniam D.
Published: October 2005

An inverse method for determining geoacoustic properties in a horizontally stratified, shallow-water waveguide is extended to the case of a weakly range-dependent environment [Frisk et al., J. Acoust. Soc. Am. 86, 1928–1939 (1989)]. The technique consists of estimating the local modal eigenvalues from the beam-formed output of a horizontal array and using these data as input to modal inverse methods for obtaining the local bottom parameters. Specifically, the approach is applied to data at 140 and 220 Hz obtained in a shallow-water environment with a known abrupt change in bathymetry. First, a range-independent medium is assumed and both iteration of forward models and perturbative inversion methods are applied to the modal data to obtain estimates of the bottom sound velocity profile. Although the perturbative inversion results are clearly superior, neither approach reproduces the full dependence with range of the observed pressure fields or the complete modal peak structure. In particular, the data exhibit an apparent splitting of the modal peaks that is interpreted, within the context of adiabatic mode theory, as the superposition of the modal contributions from the two segments of the waveguide with differing depths. When the assumption of a range-independent medium is relaxed and the perturbative inverse technique is applied to the eigenvalue data from each portion of the waveguide, distinctly different bottom profiles are obtained for each part. These result in significantly improved agreement between theory and experiment, thereby demonstrating the effectiveness of the range-dependent inversion procedure.
Acoustic sensing of the upper crust
Authors: Diachok Orest I.
Published: October 2005

Acoustic interaction with the ocean bottom is dominated by the volcanic upper crust in virtually the entire Pacific and large portions of the Atlantic Ocean. Previously reported measurements by numerous investigators revealed very low sound speeds (∼2500 m/s) in recently formed crust, compared to ultrasonic measurements in dredged hand held samples (∼6000 m/s between 0–60 m.y.), hypothetically due to high large scale crack density. Recent measurements of the coherent component of the reflection coefficient in 40–60 m.y. old, nearly sediment-free (<40 m) crust, provide accurate measures of critical angles, and by inference, compressional and shear speeds. In the absence of fracture zones, the estimated compressional sound speeds in the older crust are generally only slightly greater than in young crust. Shear speeds at some sites in this age range exceed Vw, the speed of sound in water, whereas in young crust Vs < Vus. As a result, at sufficiently low frequencies and small grazing angles, where roughness effects are minimal, reflectivity is low (near zero when Vs ≲ Vw) in young crust and may be near unity in 40–60 m.y. old crust. Implications of these results for acoustic field prediction and future research in acoustic sensing of the crust will be discussed. [Work supported by ONR.]
Reconstructing the seafloor properties from acoustic reflection data
Authors: Papadakis John S. , Taraoudakis Michael I. , Papadakis Panagiotis J.
Published: October 2005

The determination of the structure of the seafloor using measurements of the acoustic reflected power is an important inverse hydroacoustic problem with many applications in ocean geophysics. A realistic description of the seafloor includes many sedimentary layers over a harder substrate. Assuming that a rough estimation of the thicknesses of the various layers is available (by suitable subbottom profiling) the important thing is to recover the properties of the various layers, that is, the density, the sound velocity, and the attenuation coefficient. A simple scheme for the reconstruction of the seabottom is presented based on the assumption that reliable reflection coefficient measurements from a broadband acoustic source are available. The scheme is based on a systematic variation of the geoacoustic parameters of a background bottom model, so as the calculated reflection coefficient converges to the measured data. It is shown that data from various frequencies are necessary in order to obtain satisfactory results. [Work supported by EEC/MAST program.]
Experimental aspects of sonoluminescence
Authors: Roy Ronald A. , Gaitan D. Felipe
Published: October 2005

It is well known that acoustically driven gas bubbles can generate light through a process known as sonoluminescence. Although readily observed, this phenomenon has, until recently, been poorly understood. in the past, the existence of competing models (i.e., hot spots, electrical microdischarge, etc.) inspired several “definitive” experiments, many of which led to ambiguous or erroneous conclusions. Since then, improvements in our ability to detect photons as well as monitor and manipulate bubble oscillations have resulted in a significant enhancement of our understanding of the sonoluminescence process. This talk will begin with a brief review of the early theories and experiments, to be followed by a detailed description of recent experiments involving acoustically levitated, light-emitting bubbles. At issue is the timing of light output vis á vis the bubble collapse, the role played by the equilibrium size of the bubble and the acoustic pressure amplitude, the estimated collapse temperatures, and the contribution of various cyclic cavitation processes to the dynamics of single and multiple-bubble cavitation fields. [Work supported by ONR.]
J. C. R. Licklider and the case of the missing fundamental
Authors: Plomp Reinier
Published: October 2005

In 1955, Licklider visited The Netherlands and demonstrated by means of masking noise that the presence of the fundamental is not essential for hearing the low pitch of a complex tone. The “case of the missing fundamental” was a very hot issue in this country after Hoogland, in his 1953 doctoral dissertation, suggested that Schouten's opposite conclusion from experiments with signals without the fundamental, carried out in 1938–40, should be explained by nonlinear distortion in his equipment reintroducing the fundamental. Of course, Schouten did not accept this ill-based criticism. He considered his results as evidence that the low pitch is based on the periodicity of the combined harmonics not resolved by the ear, his famous “residue” theory. With Licklider's demonstration, the classical controversy, going back to Seebeck and Ohm, seemed to be solved definitely in favor of Seebeck. “Periodicity pitch” theory, as elaborated by Licklider in his “duplex” (1951) and “triplex” (1955) theories, seemed to have succeeded “place pitch” theory, promoted by famous scientists such as Helmholtz and von Békésy, but for how long? The paper will review the significance of Licklider's contribution in the light of subsequent experimental evidence showing that frequency resolution does play an essential role in pitch perception.
Effects of signal-to-noise ratio on the frequency discrimination of complex tones with overlapping and nonoverlapping harmonics
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

Frequency difference limens for multiple-component complex tones (DLCs) were measured using an adaptive two-interval, two-alternative forced-choice task. The tones were presented either in quiet or in pink noise. The tones to be discriminated either had all harmonics in common or no common harmonics. DLCs for the tones with no common harmonics were generally, but not always, larger than those for complex tones with common harmonics. For the former, performance did not worsen “monotonically” with increasing noise level, but tended either to stay constant or improve at first, only worsening when the tones were almost completely masked by the noise. For the latter, performance tended to women “monotonically” with increasing noise level, although, again, large changes only occurred when the tones were almost completely masked by the noise. Even at the highest noise level used, DLCs for complex tones with no common harmonics were usually larger than DLCs for tones with common harmonics. The results suggest that the worse performance for tones with no common harmonics does not result from internal noise in the channels conveying information from the periphery to the mechanism determining residue pitch. Rather, spectral differences between tones with noncoincident harmonics appear to have a distracting effect that impairs pitch discrimination.
Feature detection using a connectionist network
Authors: Bradshaw Gary , Bell Alan
Published: October 2005

A feedforward connectionist network trained by backpropagation was used to detect 15 speech features. The network was trained over 240 sentences (40 men and 40 women), and tested over 200 sentences (10 men and 10 women), all part of the MIT Ice Cream database. Network input consisted of a smoothed spectral vector at 15-ms-intervals, plus two coefficients of amplitude and spectral change. The network achieves a signal detection discrimination level (a-prime) of 0.87 compared to a level of 0.76 for a ten-nearest-neighbor system. Almost identical training and test performances indicates excellent generalization to new speakers and text. Processing costs are mainly signal processing and network training; detection itself can be done in real time. Performance is much better for broad features like sonorance, which occur frequently, than for infrequent features like sibilance, partly because of their low frequency and partly because of other characteristics. [Work supported by USWest.]
A modified perturbation approach for calculating the vertical wave function required in normal mode theory
Authors: Zingarelli Robert , Werby M. F.
Published: October 2005

Perturbation approaches are useful when one wishes to solve a problem that does not differ significantly from a known solution. The conventional approach to derive perturbation methods is to begin with a solvable solution χi and then to expand the desired solution in terms of first- and higher-order contributions of the perturbing component—with a small coefficient ε—which differs from the exact solution only by the perturbing component. Then first-order perturbation theory is obtained by dropping higher powers of ε. In quantum physics this method is referred to as Fermi's second golden rule. This method can often fail as will be demonstrated and it can lead to erroneous results. This work reports on a new and refined perturbation method based on completeness considerations in which the exact expansion solution in matrix form is set up. Gauss-Seidel iteration is then employed and shows that the first iteration leads to an improved first-order perturbation theory, the second iteration leads to an improved second-order perturbation theory, etc. The method is illustrated with a few examples in which the old and new methods are compared with the exact solution for the case of vertical wave functions for variable speed profiles perturbed about an isovelocity case.
All-scale model measurements: The MIDAS system
Authors: Maynial Xavier , Dogg George , Polack Jean-Dominique , Marshall A. Harold
Published: October 2005

Acoustical measurements on models offer a time and cost efficient method for determining the acoustical properties of enclosures. In addition the use of models facilitates understanding as a result of the visible 3-D form of the models and the fact that the process can be interactive. Cooperation between Auckland and Le Mans Universities has resulted in the development of a computer-based measuring system for all-scale acoustical measurements. This system, intended for commercial availability, features a numerical compensation technique for air absorption, thus avoiding the need for air-drying or air-replacement and therefore allowing free access to models during testing. The present Macintosh-based system uses an FFT approach to compute the full range of accepted auditorium indices and other building acoustics measures (e.g., TL and sound power) using a range of possible sound sources both impulsive and continuous. It has been used successfully as a design aid in consultancy work on concert halls, for calibrating measurement chambers, and as a research and teaching tool. Results from specific applications and ideas for new uses will be presented.
Subjective and objective evaluations of classrooms and lecture halls
Authors: Chiang Wei-hwa , Siebein Gary W. , Cervone Richard P.
Published: October 2005

Speech intelligibility tests were given to groups of college students in ten classrooms and lecture halls of various sizes on the University of Florida campus. A series of acoustical measurements including reverberation time, early reverberation time, loudness, early to late temporal energy ratios, lateral energy fractions, interaural cross correlation, and speech transmission index were made at multiple locations in each of the rooms. Correlation analysis and statistical modeling identified significant relationships among intelligibility scores of the listeners with the physical measurements made in the room. Special attention was given to the architectural characteristics of the rooms in the analysis. The variations in intelligibility scores and the physical measurements among the different rooms and within each of the rooms are presented. [Work supported by NSF.]
Modern acoustic measurements on three types of concert platforms
Authors: O'Keefe John P. M. , Bracken Marc
Published: October 2005

Recent studies, particularly those by Gade and Naylor, have begun to quantify the acoustical requirements of performers on stage as expressed in measurable acoustic parameters. These parameters, originally based on laboratory findings, are now being measured in real concert halls. The purpose of this investigation is to add to this database by measuring the conditions on three different types of concert platforms: A proscenium theatre stage, a multipurpose room with a reflector above the stage, and finally, a traditional concert hall stage. Measurements in the multipurpose room will also quantify the effect of reflector height above the stage in terms of support (ST100) and modulation transfer functions. Measurements in the proscenium theatre will quantify conditions on stage, in the orchestra pit, and between the stage and the pit.
Underground sound: Applied seismic waves
Authors: White J. E.
Published: October 2005

The term underground sound is meant to encompass the instrumentation, observational methods, and interpretive techniques that have been developed for the utilization of seismic waves in the earth, quite analogous to the field of underwater sound. Wave propagation in the shallow crust of the earth is more complex than waves in water, simply because of the presence of shear waves in addition to compressional waves. Either type of wave is severely attenuated in traveling through earth materials, compared with similar distances of travel through the ocean. Finally, many rocks are anisotropic in average properties, resulting in further complexities. In exploration for petroleum, remarkably detailed images of geologic boundaries have been achieved by processing observed data so as to enhance reflected compressional waves and suppress shear waves and reverberations. Alternatively, shear-wave reflections can be observed by using a vibratory source which radiates strong shear waves and processing the data so as to suppress compressional “noise” waves. Used together, the two reflection methods yield lithologic information, such as distinguishing between gas saturation and water saturation in a porous rock. For soils and near-surface rocks, shear-wave speeds are directly useful for evaluation of building foundations and dam sites. Attenuation of seismic waves is both a fortunate characteristic and a strict handicap. If attenuation were quite small, multiple reflections among layers would result in uninterpretable reverberations. Since the actual attenuation increases with frequency, the resulting loss of high frequencies places a severe limit on the resolution obtainable with seismic waves. The presence of attenuation requires that the wave speed depend on frequency. When averaged over distances of a few meters, many geologic formations behave as “homogeneous” layers. However, the average properties may depend on direction and the layers must be recognized as anisotropic solids. Such anisotropy may be due to fractures caused by previous episodes of deformation, due to unequal stresses existing at present, or due to fine layering. Anisotropy clearly complicates seismic data processing. Because so many measurements are made in oil wells and test boreholes, suitable sources and detectors of seismic waves have been developed and the coupling of seismic waves to a fluid-filled borehole has been treated mathematically.
On violin plate and corpus tuning
Authors: Rodgers Oliver E.
Published: October 2005

The tuning of violin free plates in the manner advocated by Carleen Hutchins is now established practice. One can be sure of producing an instrument with good sound. However, the way to an instrument that has excellent sound is still elusive and seems to depend on details of construction that continue to elude investigators. This paper describes some of the existing clues that identify important details of violin design and construction that may lead to further progress toward achieving superior performance, including adjustment of the assembled corpus and complete instrument, guided by acoustical measures. Some suggestions are made of directions for further research on violins and the larger stringed instruments. Only measurement of the sound output of test instruments, tempered by what the human ear hears, will provide the information necessary to make additional progress.
The importance of overload distortion in hearing aids
Authors: Killion Mead C.
Published: October 2005

In a series of three separate experiments using a total of 5 talkers, 3 speech conditions, 20 normal and 20 hearing-impaired subjects, and 30 different hearing aid-receiver combinations, Harris and his colleagues concluded; “All three experiments show harmonic distortion, alone of all the several electroacoustic characteristics studied, to affect intelligibility in any really significant amount [J. Aud. Res. 1, 357–381 (1961)].” This paper will summarize (a) recent circuit developments that have made possible a reduction in both input-circuit and output-circuit overload distortion to inaudible levels (even for full-orchestra fortissimo inputs}, and (b) recent indications that the distortion-reduction capabilities of automatic signal processing (ASP) circuits may be more important than their level-dependent-frequency-response-shaping capabilities. Indeed, ASP circuits that do opposite things (decreased high-frequency or decreased low-frequency gain for high-level inputs) are both successful in the marketplace.
The nature of the generator of outer hair cell motility
Authors: Evans Burt N. , Hallworth Richard , Dallos Peter
Published: October 2005

Despite the lack of obvious substrates underlying the electrokinetic shape changes of mammalian outer hair cells (OHCs), much can be learned about the mechanism when cells are electrically and mechanically partitioned in a glass microchamber. The results of such studies employing photometric as well as video analysis support the notion that the cellular motor consists of a large number of small, independent elements restricted to the supranuclear region of the cell's cortex. The length changes measured in OHCs are highly nonlinear. They are subject to manipulation as well as vulnerable to overstimulation. Thus the mechanical response resembles the mechanism underlying sharp tuning in the intact cochlea. Interestingly, such nonlinearities can be shown to be inherent to each voltage-sensing element. The whole-cell movement is thus effectively the cumulative response of many such elements, each driven in parallel by the local transmembrane potential along the length of the cell.
Faith in natural systems
Authors: Libby E. Robert
Published: October 2005

The faith in natural systems principle holds that if an engineering effort is being directed at duplicating or simulating a natural system, that effort is most efficiently directed at incorporating critical functions and structures of that system. The faith in natural systems principle would say that if a person would want to design a more effective hearing instrument, that effort is most efficiently directed at incorporating the critical functions of the hearing mechanism, and the enhancement of the anatomical structures of that natural system. Binaurality is supportive of the faith in natural systems principle. The choice of an in-the-ear microphone location, ear canal resonances, and compensation for the recruitment phenomenon are also supportive of the faith in natural systems principle. The use of real ear measurements utilizing a probe tube microphone will demonstrate support of these principles.
Waves on fluid-loaded thin elastic plates: Analytical study based on full elastodynamic equations
Authors: Pierce Allan D. , Manley Martin G.
Published: October 2005

An elastic, infinite plate of finite thickness with fluid loading on one side and vacuum on the other is considered. Displacement of the plate surface is derived from the full elastodynamic equations, rather than from a plate model. Following Crighton's parametrization scheme, analytical expressions of the dispersion and polarization relations of the bending wave are derived. Systematic expansions of the dispersion and polarization relations are developed using a symbolic manipulation computer program. [Work of ADP is supported by ONR and by the William E. Leonhard endowment to Penn State Univ.; work of MGM is supported by the PSU Appl. Res. Lab. Exploratory and Foundational Res. Prog.]
Age differences in the processing of dynamic acoustic information
Authors: Fox Robert A. , Wall Lida G. , Gokcen Jeanne
Published: October 2005

The present study examines possible age-related differences in the use of dynamic acoustic information (in the form of formant transitions) to identify CVC words. Sixty-two high-frequency monosyllabic English words were recorded that began or ended in oral or nasal stops. From these words, two sets of tokens were created: an unmodified CVC token representing the whole word and a silent-center version in which approximately 70% of the medial vowel was replaced by silence. Two sets of listeners were required to identify these words in first the silent-center condition and then the whole-word condition. The listeners included 17 college sophomores or juniors and 22 older subjects aged 55–75. All listeners were screened for normal auditory sensitivity. Results demonstrated both age groups' identifications were somewhat better in the whole-word condition than in the silent-center condition. However, the mean correct consonant and vowel identifications of the older listener group was approximately 10% less than that for the younger listeners in the silent-center condition. No age difference was obtained in the whole-word condition. These data support the hypothesis that older listeners have greater difficulty than younger listeners in processing dynamic acoustic information in the perception of speech. [Supported by NIA Grant ♯1 R01 AG08353-01.]
Adjusting dysarthric speech timing using neural nets
Authors: Peters Shirley M. , Bunnell H. Timothy
Published: October 2005

Speech timing problems associated with dysarthria often involve the presence of periods of extraneous silence and nonspeech sounds as well as inappropriately timed or misplaced speech gestures. This study evaluated the performance of neural networks in detecting the presence of inappropriate or nonspeech sounds and extraneous silence. The “opt” neural network program [E. Barnard and R. Cole, OGC Tech. Rep. No. CSE 89-014] that uses a conjugate gradient algorithm to adjust node weights was trained to recognize breaths and silence in a reading of the rainbow passage by a single dysarthric (Cerebral Palsy) talker. Input to the network consisted of a sequence of frames of parameters derived from spectral analysis of the speech. The output was a binary (speech/nonspeech) decision for the segment of signal corresponding to the middle frame of the input sequence. Networks of various size and configuration were trained on half the available data and tested on the remaining data. The best network configurations correctly identified approximately 99% of the frames in the training set and about 97% of the frames in test datasets.
Restarting the adapted binaural system in a background of noise
Authors: Hafter Ervin R. , Saberi Kourosh
Published: October 2005

The rate-dependent reduced binaural sensitivity to interaural information coming after the stimulus onset has been called “binaural adaptation.” It has been shown that an appropriate restarting trigger presented during the ongoing stimulus can end the adaptation, allowing for lateralization based on information beyond the restart. Effective triggers include short bursts of noise and gaps in the stimulus. It has been reasoned that continuous spectral changes might constantly restart the system and thus preclude adaptation. To test this, click trains have been presented for lateralization in a continuous background noise and with click rates sufficiently high to produce adaptation in the quiet. Our hypothesis was wrong. While binaural thresholds increased with noise level as the noise spectrum levels rose from 0 to 20 dB, no change was observed between the forms of the functions obtained in quiet and in noise. Similarly, the inclusion of a gap in the center of the train triggered a restart both in the quiet and in the noise background. Thus a spread of energy into quiet bands as has been postulated in the past as an explanation for restarting is insufficient.
Human audition of ultrasound
Authors: Lenhardt Martin L. , Clarke Alexander M. , Skellelt Ruth A. , Soltanpour David A. , Ochs Alfred L.
Published: October 2005

Tones above 20 000 Hz are not inaudible to humans as the term “ultrasound” implies, but rather are audible only via bone conduction. Placing a high-frequency vibrator on the skin over the head, neck, or upper trunk results in a high-pitched auditory percept, yielding no sense of cutaneous stimulation. Audibility thresholds for tones of 25 and 62.5 kHz were determined in four normal-hearing subjects for various sites on the upper torso. The results of these ultrasonic “maps” indicate that the area of the mastoid bone is the most sensitive. Position and orientation of the vibrator on the mastoid influence sensitivity. Small changes of frequency and/or vibrator orientation affect the “ear” in which the sound is heard. This finding is in contrast to a previous report from this laboratory of 60- to 80-dB attenuation between mastoid bones in a dry skull [Dunlap et al., Otolaryngol. Head Neck Surg. 99, 389–391, (1988)]. By placing water in the cranial vault, skull attenuation of 17 dB (25 kHz) and 36 dB (62.5 kHz) was obtained, values better matching the perceptual findings. It is hypothesized that standing waves are created intracranially, which in part determine the ear of perception. It is possible that cochlea inner hair cell stereocilia and/or vestibular type I cells in the striolar region of the saccule are set into ultrasonic resonance [Strelioff et al., Hear. Res. 18, 169–175 (1985)], inducing a different form of stimulation than traditional air conduction hearing. [Work supported by Hearing Innovations, Inc., Tucson, AZ.]
Acoustic scattering in a three-dimensional oceanic waveguide using boundary integral equation methods
Authors: Dawson Trevor W.
Published: October 2005

This paper develops in more detail the theory for a fully three-dimensional version of a recently published [T. W. Dawson and J. A. Fawcett, J. Acoust. Soc. Am. 57, 1110–1125 (1990)] boundary integral equation method (BIEM) formulation, for the computation of the scattering of underwater sound from compact deformations of an oceanic waveguide's surfaces. The method allows for three-dimensional sources and boundary deformations in an otherwise uniform waveguide. The technique involves only integrations over the compact surface of the waveguide deformation. The implementation is illustrated for a seamountlike deformation in an oceanic waveguide.
Improvements to the resonance apparatus
Authors: Lee Gilbert F. , Miller Brian A. , Hanson David H.
Published: October 2005

The resonance apparatus has been used to determine the complex Young's modulus of polymeric materials. A bar of material is excited into resonance. One end of the test bar is adhesively bonded to a mechanical shaker via a mounting block, while the other end of the test bar is bonded to an accelerometer. A second accelerometer is bonded to the shaker mounting block. At resonance, the complex Young's modulus is determined at four to six discrete frequencies over 1.5 decades of frequency. There are two disadvantages to the above technique. The first disadvantage deals with accelerometer leads. Accelerometer leads are fragile and are easily broken off. Also the accelerometer lead on the free end of the test bar is an unknown added end mass. In addition, this lead may also be an unknown source of absorption. The second disadvantage is that the complex modulus is only determined at resonance. The goal of this presentation is to improve the resonance apparatus by replacing the accelerometers with a noncontacting magnetic pickup and to determine the complex modulus off resonance, which extends the usable frequency range to about 3 decades.
Noninvasive measurement of dynamic pressure inside pipes using piezoelectric strip
Authors: Carroll Gerard P.
Published: October 2005

This paper presents the use of piezoelectric material wrapped around the outside diameter of a pipe wall for measuring the dynamic pressure inside the pipe. Recently available piezoelectric materials such as polyvinylidine fluoride (PVDF) are flexible enough to wrap around a pipe wall and provide an excellent transducer for measuring the breathing response of the pipe wall to the internal dynamic pressure. The strain induced in the piezoelectric element associated with radial deformation of the pipe wall is measured. It is shown that the sensor, since it sums the response around the entire circumference, will discriminate against strains associated with bending of the pipe for all circumferential orders which occur below the ring frequency. The relationship between the measured piezoelectric element voltage and pressure, taking into account the pipe wall characteristics, is presented. Various configurations of the device are discussed and experimental results comparing the sensor output to that of a flush mounted hydrophone are presented.
Radiation control of sound due to evolving instability waves along a curved surface
Authors: Maestrello L. , El-Hady N.
Published: October 2005

Active control of the acoustic pressure in the far field resulting from the growth and decay of a wave packet convecting in a boundary layer over a concave-convex surface is investigated numerically using direct computations of the Navier-Stokes equations. The resulting sound radiation is computed using the linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. The acoustic far field exhibits directivity type of behavior that points upstream to the flow direction. A fixed control algorithm is used where the attenuation signal is synthesized by a filter which actively adapts itself to the amplitude-time response of the outgoing acoustic wave. This concept of active control may be applicable to wind tunnel contraction where noise radiated from the concave-convex surface is known to exist.
Diagnostic study of vibrational signals from a drill press
Authors: Marks P. C. , Angermund S. H. , Arya V. , Patel S. D. , Prasad M. G. , Chassapis C.
Published: October 2005

The objective of this study was to measure the vibration of a drill press in order to detect the onset of chatter and to evaluate the use of vibrational measurements in a control system design. Chatter is unwanted vibration caused by the interference of the flank face of the bit with the bottom of the drilled hole which can be brought upon either by excessive feedrate or excessive drilling speed. Chatter is a major source of tool wear, which serves to increase machine downtime, thereby reducing productivity. Data were acquired in order to determine the baseline amplitude at which chatter occurs. Measurements were taken at feedrates varying from 9.4 mm/min, to 94.7 mm/min and with varying drill bit diameters. Chatter was seen to occur at feedrates over 65.8 mm/min for a worn bit and at over 94.7 mm/min for a new bit with an aluminum workpiece in a frequency range between 1400 and 2000 Hz. In a wood workpiece, no chatter was observed throughout the entire range of feedrates. This study would be useful in the development of a feedback control system which would provide for drilling at the optimum feedrate for a given work piece based on chatter detection.
Wave propagation in solids: Computation versus experiment
Authors: Usman Ali , Everbach E. Carr
Published: October 2005

Via two complementary methods, compressive and shear wave propagation in solids possessing complex geometries have been investigated. First, the finite-element package ANSYS was adapted to determine the stress field as a function of time due to a known excitation in solids with specified material properties. Then solids were constructed with the same properties and the strain field was measured as a function of time using fast strain gauges and laser interferometry. The results of these computational and experimental determinations will be compared.
A coherent structure model to explain the quadrupole directivity of noise from impinging jet
Authors: Shen Jianping , Lee Seungbae , Meecham William C.
Published: October 2005

The quadrupole-like directivity patterns of jet noise, created by jet impingement on a large fiat plate were experimentally obtained by the authors previously [J. Acoust. Soc. Am. Suppl. 1 88, S8 (1990)]. Theoretical considerations have been examined to explain physically this directivity phenomena, and a model coherent structure called the “orientated vortex motion” is proposed. The model hypothesizes that a train of partially organized, large-scale vortices exists inside the boundary layer flow near the plate. By including their images in the rigid plate an oscillation is formed, resulting in a quadropole acoustical source, which explains the experiments quite well. This is analogous to the low Reynolds number free jet case that predicts a possible, similar directivity pattern for the noise from the free jet. A large eddy simulation (LES) computational technique for the simulation of turbulent flows seems to be a feasible approach to investigate the proposed organized motion. A simulated statistically stationary flow field will be discussed.
Optimization of the distance between transducer and scatterer in hydroacoustical modeling
Authors: Genis Vladimir , Oboznenko I. , Reid J. M. , Raghavan R. , Soetanto K. , Oung H. , Lu X. M.
Published: October 2005

This work was motivated by the need to understand the effect of phase and amplitude variations on the scatterer's surface as well as the reflecting boundaries of the hydroacoustical tank on the structure of the acoustical field in modeling. It is known that the null positions of the spectral characteristics of the backscattered signals from various objects in water can yield information about their shape, dimensions, orientation, and structure. Accuracy of such measurements is affected by the amplitude and phase variations on the scatterer surface and these variations depend on the minimum distance between the transmitter and scatterer positions. Calculations of these distances for acceptable dimensions of acoustical tanks were performed. Expressions were derived to correct the minimum allowable distance to prevent time coincidence of impulses from the scatterer and from the walls of the echoic acoustical tank.
Molecular relaxation is insufficient to explain the shock structure and rise times of sonic booms; turbulence is apparently important
Authors: Gionfriddo Thomas A. , Kang Jongmin , Sparrow Victor W. , Pierce Allan D.
Published: October 2005

The authors have been recently examining some sonic-boom waveforms that were recorded during overflights by the Air Force and that have become available to NASA and its contractors. The quality of the digitized data and the supporting meteorological data was such that one could test the applicability of molecular relaxation theories. In the late sixties it had been supposed that the finite rise times of sonic booms was attributable to atmospheric turbulence, but it was later pointed out that the first estimates of rise times in the absence of turbulence had neglected the vibrational relaxation of nitrogen molecules. Bass et al. [J. Acoust. Soc. Am. 74, 1514–1517 (1983)] have demonstrated that molecular relaxation definitely gives the correct order of magnitude of the observed rise times. However, the Air Force data in conjunction with the recent steady-state shock profile model theory of Kang and Pierce give the first opportunity to make a detailed quantitative assessment of the molecular relaxation hypothesis. The agreement of theory with experiment in some cases is remarkably excellent, but in the preponderance of cases the rise of the shock is slower and the rise time is longer, typically by factors of the order of 2 to 3. [Work supported by NASA-LRC and by the William E. Leonhard endowment to Penn State Univ.]
The influence of an ideal wind profile on sound propagation over a ridge
Authors: Jaye M. J. , Jacobson M. J. , Robertson J. S. , Siegmann W. L.
Published: October 2005

The effects on low-frequency acoustic propagation resulting from ideal atmospheric flow over a large ridge are investigated using the parabolic approximation. The ridge is taken to be triangularly shaped with a horizontal earth-air interface on both sides. A Schwarz-Christoffel transformation is employed to calculate the wind speeds that are then used to compute the effective sound-speed profiles. These profiles are used by an implicit finite-difference implementation of the parabolic approximation to estimate the intensity of the sound field. Several examples are examined to determine the effects of this wind-modeling method on sound pressure levels over rigid earth-air boundaries. [Work supported by NASA.]
Hybrid ray-mode resonance system format for the acoustic response of submerged structures
Authors: Felsen L. B.
Published: October 2005

Many submerged structures of interest are comprised of elastic shells with attached loadings and/or substructures. In the midfrequency range, traveling waves in shell segments between loads, and also in substructures, may become important, whereas complex loadings as such may be better characterized in terms of their modal resonances. This motivates the formulation of a self-consistent hybrid ray-(traveling mode)-resonance system that highlights the physical wave phenomena responsible for synthesizing the interactive fluid-structure acoustic response. Such an observable-based parametrization (OBP) generalizes the conventional approach based on modal resonances alone and reorganizes resonances compactly into propagators where these predominate. The OBP format for cw and transient excitation is illustrated on the example of an aperture-coupled ring-waveguide cavity in a rigid cylindrical baffle developed originally for electromagnetic radar scattering where the method was first applied [L.B. Felsen and G. Vecchi, IEEE Trans. Antennas Propag. (in press)]. Especially in the time domain, where successive early interactions are resolved by arrival times whereas later interactions are reconstituted as resonances, the ability of OBP to identify the physical observables is clearly evident. Similar behavior characterizes sound scattering from a submerged spherical elastic shell. [Work supported by ONR.]
Modal and wave approaches to the analysis of complex structures
Authors: Maidanik G. , Dickey J.
Published: October 2005

A complex structure may be analyzed by decomposing the structure into coupled elemental substructures, and, even further, into coupled elemental dynamic systems. To the latter decomposition a modal and a wave method of analysis may be applied. The two methods are complemental and supplemental. The analogies and the differences between the modal and the wave approaches will be discussed.
Experimental measurements of wave propagation on submerged shells
Authors: Williams Earl G.
Published: October 2005

Various signal processing techniques, combined with cylindrical near-field acoustical holography, are used to study wave propagation on thin, endcapped cylindrical shells excited with a point driver, and submerged in an external fluid. The upper frequency limit was doubled compared to previous experiments reported in previous meetings of the ASA. In this new frequency regime (2 < ka < 4] k-ω processing of the data reveal that an entirely new spectrum of supersonic helical waves is excited. Comparisons with infinite shell theory reveal that these waves are the well-known shear and extensional modes of propagation. These dominate the radiation to the far field whereas the subsonic helical waves due to bending are no longer important. The acoustic pressure in the extreme near field is used along with an assortment of k-space signal processing techniques to study the propagation on and radiation from these waves on the shell. It is shown how direction filtering in k space of helical wave components can be used to reconstruct the z-t domain representations of these filtered components, and the resulting wave propagation is recorded in a videotape display. With this display the group velocity and other physical parameters can be determined experimentally.
On wave-vector filter analysis of turbulent flow
Authors: Mellen R. H.
Published: October 2005

Convective turbulence models are based mainly on measurements of space/frequency correlation along the longitudinal and transverse axes and the wave-number/frequency spectrum is derived by Fourier transformation of an analytic model. It has been found that the low wave-number “convective ridge” resulting from the Corcos model is apparently an artifact of the rhombic Fourier window, since it does not occur with the smoother elliptic window [R. H. Mellen, J. Acoust. Soc. Am. 88, 2891–2893 (1990)]. Wave-vector filter arrays are also used for determining wave-number/frequency statistics in this region. Relative effects of the two window models on the analysis of experimental results are examined.
Calculation of shock spectrum from a discretely sampled velocity time history
Authors: Kasper Peter K. , Slupek Benjamin A. , Sawczyszyn Rosalyn F.
Published: October 2005

A shock spectrum corresponds to the maximum response of a mechanical resonator for a given time history excitation input. With modern computer-based instrumentation, the desired time history input is often provided as discretely sampled acceleration or velocity values. Determination of a shock spectrum requires a solution method for calculating resonator response to the transient input. Beck and Dowling [J. L. Beck and M. J. Dowling, Earthquake Eng. Struct. Dyn. 16, 245–253 (1988)] present an algorithm for computing resonator response given a discretely sampled input acceleration time history. The current paper extends the application to account for input excitation in terms of a transient base motion velocity. The algorithm is derived from a closed-form integration of the system response with linear extrapolation between discrete input values. Verification of the discrete velocity input algorithm is demonstrated by comparison with corresponding results using a continuous time history input excitation.
Factors determining speech-hearing handicap in noise
Authors: Plomp Reinier , Festen Joost M.
Published: October 2005

Frequently hearing impairment, particularly presbycusis and noise-induced losses, manifests itself primarily as a difficulty in speech understanding in the presence of other sounds. In many cases, the hearing-impaired listener needs a 5 to 10 dB larger speech-to-noise ratio (S/N) than normal-hearing listeners. Whereas the hearing aid is very effective in compensating for sound attenuation in the impaired ear, no easy remedy is available for improving the S/N significantly. As in critical listening situations every dB in S/N corresponds with 15%–20% difference in the intelligibility score for sentences, even a small loss in terms of S/N will represent a severe handicap in everyday listening situations. This will be illustrated with the results of experimental data collected by the authors and their co-workers in recent years. Various factors will be considered, including (1) speech-reception thresholds for different pathologies, (2) steady-state interfering noise versus competing speech, (3) the significance of binaural hearing, lipreading, redundancy of the speech, etc., and (4) the role of the environment (reverberation) and the effect of acoustical measures.
Interference reduction for the hearing impaired
Authors: Zurek Patrick M.
Published: October 2005

Despite continuing technical improvements to hearing aids, user dissatisfaction with the benefit provided remains high. The most frequent source of complaint concerns the interfering effect of environmental background noise on speech reception. This paper will review the factors thought to be responsible for this increased susceptibility to interference as well as approaches that are being taken to improve noisy speech reception through hearing aids. Two of the factors that often contribute to poor speech reception are decreased audibility of speech sounds and loss of binaurality. Techniques that have shown promise for reducing interference include adapting the frequency response of single-microphone hearing aids to minimize spread of masking, and fixed and adaptive beamforming using microphone arrays. A summary will be given of the benefits provided by these techniques and their dependencies on acoustic conditions. [Work supported by NIH.]