bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourth moments of the acoustic wave forwardly scattered by a rough ocean surface
Authors: Yang C. C. , McDaniel S. T.
Published: October 2005

Various fourth moments of the acoustic wave field forwardly scattered by a rough ocean surface are evaluated. The fourth moment at the same position is related to the scintillation index. The fourth moments at two positions can be used for extracting the statistical information of the phase difference between two receiving points. The Kirchhoff approximation is utilized to formulate the scattered wave field. Also, the statistical fluctuation of surface height is assumed to follow a Gaussian correlation function. Two-dimensional wave propagation and scattering are considered in these derivations. The formulas for those fourth moments can be analytically reduced to a form of twofold integration. This twofold integration can be numerically completed by carefully dividing the integration range into three regions. In different regions, different approximations must be used for satisfactory accuracy. Numerical results are to be presented graphically. [Research supported by ONR and NOARL.]
The QRD® Diffractal™: A new 1- or 2-dimentional fractal sound diffusor
Authors: D'Antonio Peter
Published: October 2005

Number theoretic diffusors, as described by Manfred Schroeder, are characterized by a periodic grouping of a series of wells of equal width, but different depths, separated by thin dividers. Over the past 5 years, the quadratic residue depth sequence has been very useful in over 300 applications, including recording studios, concert halls, worship spaces, conference rooms, music education, and even home listening rooms. The frequency bandwidth is determined principally by the depth of the deepest well, which determines the low-frequency limit, and the well width, which determines the upper limit. Physical manufacturing contraints pose a limitation of approximate 1 in. on the well width and approximately 16 in. on the depth, after which the units become diaphragmatic and defeat the purpose of increasing the depth further. To extend the low-frequency range and bandwidth of the QRD, a fractal diffusor, the Diffractal, has been developed which is in effect a diffusor within a diffusor, each crossing over at different frequencies, much like a multiway loudspeaker. The mid-high-frequency diffusors are placed on the wells of a dedicated stiff and massive low-frequency diffusor. These bandlimited nestled diffusors allow virtually any bandwidth, limited only by the available depth and the surface detail. Two applications of the Diffractal will be described at Peter Gabriel's Real World Studios, Bath, England and INXS' Rhinoceros Recording Studios, Sydney, Australia. A two-dimensional diffractal capable of providing even further low-frequency control will also be described.
Ambient noise and elastic wave propagation in the deep seafloor
Authors: Stephen R. A. , Bibee D. , Farrell W. E. , Pattee W. , Spiess F. N. , Orcutt J.
Published: October 2005

In August/September 1989 a borehole seismic array was deployed at DSDP Site 534 in the Blake Bahama Basin. The purpose of the array was to study the physics of acoustic and elastic wave propagation and ambient noise near the seafloor. The array was inserted into the borehole using a wireline re-entry capability and was recovered by grappling. Each node was individually clamped into the hole. The borehole array consisted of four three-component seismometers (with a passband from 2–50 Hz) at depths of 10, 40, 70, and 100 m below the seafloor. A borehole hydrophone was also recorded at the top node. Over I Gbyte of data was acquired over a 2-week period from the array. A shooting program of air-guns and explosives was carried out. An array of ocean bottom seismometers and a vertical hydrophone array were also deployed. Preliminary observations are (1) the time spread as a result of late-arriving energy is much less at 10-m depth than at the seafloor; (2) the borehole hydrophone is susceptible to tube waves for transient signals and ambient noise; (3) ambient noise levels vary by at least 10 dB over time; (4) ambient noise levels decrease by 10 dB between 10- and 100-m depth; and (5) ambient noise levels on a vertical seismometer are 10 dB less than colocated horizontal seismometers.
Rate of transition as a cue for place perception in normal and hearing-impaired listeners
Authors: Zakia Renée A. E.
Published: October 2005

Recent research exploring the role of rate of transition in the identification of place of articulation of stop consonants revealed that rate of transition influences place perception when formant frequencies are ambiguous between [da] and [ga] [Zakia and Kingston, J. Acoust. Soc. Am. Suppl. 1 85, S 135 (1989)]. In the experiments reported here, variations in F1, F2, and F3 transitions between values appropriate for [dr] and values appropriate for [gɛ] were combined with variations in rate of transition in 5-ms steps between 20 and 60 ms. Stimuli were presented to two populations of young listeners, one with normal hearing and the other with mild hearing impairment of postlingual onset, in one-and two-interval forced choice identification of place of articulation tasks. It is predicted that normal-hearing listeners will identify stimuli with longer transition durations as [gɛ] and stimuli with shorter transition durations as [dɛ] at “intermediate” formant patterns (i.e., those which specify neither [dɛ] nor [gɛ]). Performance of hearing-impaired listeners on the same task is predicted to be poorer overall, as they suffer a decreased ability to identify place of articulation from transition information alone [Q. Summerfield et al., Speech Commun. 4, 213–229 (1985)]. Furthermore, if the poorer temporal resolution characteristic of hearing impairment leads to distortion of the distribution of spectral energy over time, it is predicted that rate of transition will not aid hearing-impaired subjects in identifying place of articulation or bias their judgment when formant frequencies are ambiguous between [dɛ] and [gɛ]. [Work supported by the International Center for Hearing and Speech Research.]
Some physiological aspects of pausing and speaking in dialog
Authors: Guaitella I. , Autesserre D. , Nishinuma Y.
Published: October 2005

Respiratory aspects of speech in four conversing subjects were studied. The data show that (1) the breath regulating mechanism is independent of speech (phonation and pausing); (2) total dialog duration can be segmented into approximately one-quarter of the time for breathing in, another quarter for phonation, and the rest for pausing, although the absolute durations show noticeable intra/intervariability; (3) breathing in takes less than 1 s, whereas expiration lasts four times as long; (4) “silent pausing” covers several physiological events: final expiration, breathing in, and prephonation pauses; (5) as a rule, interlocutors speak when their partner is pausing and listener/speaker speech overlapping is minimal.
Temporal variability of atmospheric acoustic absorption coefficients
Authors: Wilson D. Keith , Thomson Dennis W.
Published: October 2005

Atmospheric absorption coefficients depend strongly upon environmental temperature and humidity. Not only are temperature and humidity dependent upon location and altitude, but they also vary substantially on diurnal, synoptic (weather system), and seasonal time scales. The resulting temporal variability of acoustic absorption coefficients was evaluated using research quality micrometeorological data, recorded as half-hour averages, over the course of an entire year at the propagation research site located near Rock Springs in central Pennsylvania. Results demonstrate that the use of seasonal mean absorption coefficients can easily result in rms errors of 20% to 30%. When specific humidities are low, as most often will occur in the winter, the temporal variability of the absorption coefficients can be particularly dramatic. It is also shown that for studies of atmospherically propagated sound, substantial errors may result from the use of acoustic absorption coefficients that have been calculated from mean values of atmospheric temperature and humidity.
Residual pressure intensity index and performance evaluation of instruments to measure sound intensity
Authors: Krishnappa G. , Chiu V. J. , Matthews G. R.
Published: October 2005

Residual pressure intensity index measurements and performance evaluation of sound intensity probes and analyzers are discussed. The residual pressure intensity index was determined separately for the analyzers using identical electrical input signals, and for probe and analyzer combinations using identical sound-pressure inputs. Both FFT and digital frequency analyzers were examined in the investigations. The results show that the residual pressure intensity index depends on the input signal levels, and any phase compensation scheme should be considered in relation to these measurements. Performance of the probes was examined using a gating technique in a large enclosed space. The measured sound intensity levels using the sound intensity probe were compared with the levels derived from sound-pressure measurements from a single standard microphone. The results are in agreement with the predicted performance. Further discussions in the paper include the directivity of the probes and phase compensation schemes.
The concept of audibility-based aircraft noise contours
Authors: Fidell Sanford , Reddingius Nicolaas , Hodapp Steven
Published: October 2005

Conventional purposes for drawing aircraft noise contours differ from those of Public Law 100-91 in several important ways. These differences in purpose are related to differences between the nature of aircraft noise exposure in airport environs and in park and wilderness settings, and differences between noise exposure effects in residential and recreational environments. The differences are sufficiently great that alternatives to standard (that is, noise source-oriented) contours are required to support analyses of aircraft overflight impacts on outdoor recreation. Cartographically referenced, three-dimensional, observer-based audibility contours for both points and areas are one such alternative. A top-level discussion of means for producing such contours in a computer-based geoinformation system is provided.
Formant estimation in child and chimpanzee vocalizations
Authors: Bauer Harold R. , Robb Michael P.
Published: October 2005

The high fundamental frequency [F0] of human child and common chimpanzee vocalizations presents problems for formant estimation. Existing work on infant and chimpanzee vocalizations raises questions of formant accuracy, vocal tract configuration, harmonic-formant interactions, and voicing or noise source. The present study attempts a brief, systematic analysis of the relationship between F0 and formant frequency in the context of child and chimpanzee vocalizations. Selected examples of child and chimpanzee vocalizations are spectrally analyzed and presented for discussion. The findings will be discussed with respect to analysis of harmonic-formant interactions and published interpretations of child and chimpanzee vocalizations.
Evidence from glottal articulation for the analysis of intrusive stops in English
Authors: Lee Sook-Hyang
Published: October 2005

In American English, an intrusive stop occurs before the fricative in words such as tense and false, making them sound like tents and faults, where the stop is specified in the underlying phonological representation. Ohala (1975) treats the inserted stop as a universal phonetic artifact, whereas Zwicky (1972) treats it as the output of a language-specific phonological rule. However, Ohala's approach cannot explain why South African English speakers do not have intrusive stops, whereas Zwicky's cannot explain why the duration of the inserted stop closure is significantly shorter than that of the underlying stop (Fourakis and Port, 1986). Fourakis and Port therefore suggest that intrusive stops are not part of the phonological representation, but are products of language-specific phonetic rules. Clements (1987), on the other hand, uses autosegmental phonology to give them a different phonological representation from the underlying stops. He argues that in dialects where underlying voiceless stops in the syllable coda trigger rules of glottalization, the intrusive stops do, also. An examination of utterances by three speakers of a Midwestern dialect, where voiceless stops in syllable codas are glottalized, seems to support Clements's claim. Simultaneously gathered EGG data are being examined to provide a more objective confirmation of the impression that the inserted stops are glottalized.
Lip rounding in Amoy and Mandarin high vowels: Maximum dispersion, or adequate separation
Authors: Pan Ho-Hsien
Published: October 2005

There are two hypotheses about the relationship between phonological contrasts and phonetic feature scales. Some phoneticians propose that values are chosen so that contrasting phonemes are maximally separated [e.g., Liljencrants and Lindblom, Language 48, 840–862 (1972)], while others claim that they need only to be adequately separated [e.g., Maddieson, UCLA Working Papers in Phonetics 36, 49–69 (1977) ]. This paper tests the competing hypotheses by comparing lip position in Mandarin [i], [y], [u] and Amoy [i] and [u]. According to the maximum dispersion hypothesis, the degree of roundness of [i] and [u] in both languages should be the same. According to adequate separation, on the other hand, the lip position of Mandarin [i] will be more spread than [i] in Amoy, and Mandarin [u] will be more rounded, since there are three high vowels in Mandarain but only two in Amoy. Amoy and Mandarin data were collected from three bilingual speakers to ensure that differences in roundness were due to language differences, not personal characteristics. Preliminary results show that the lip position of [i] in both languages is the same, while the [u] in Mandarin is more rounded than Amoy [u]. Both hypotheses seem to be true here.
Lipreading with vibrotactile vocoders
Authors: Bernstein Lynne E. , Demorest Marilyn E. , O'Connell Michael P. , Coulter David C.
Published: October 2005

A training study was conducted to compare aided lipreading of normal-hearing and deaf adults, each assigned to one of three vibrotactile vocoders. Vocoders were (1) the Queen's University/Central Institute for the Deaf (QU/CID) vocoder, with one-third octave filter spacing and logarithmic output scaling; (2) the QU/CID vocoder with linear output scaling; and (3) the GU (Gallaudet University) vocoder designed for greater resolution than the others in the F2 region and linear output scaling. Subjects received stimuli in baseline (no vocoder) and treatment (vocoder) conditions. In addition, two subjects served as visual-only controls. Stimuli were provided by a live talker and two talkers prerecorded on laser videodisc (Bernstein and Eberhardt, 1986). Preliminary analysis of the results suggests that (1) the QU/CID linear vocoder was most effective, followed by the GU vocoder with linear output; and (2) regardless of experimental condition, normal-hearing subjects' lipreading improved over the approximately 65-h experiment. Results with deaf adults, along with results of the visual control subjects, suggest that careful control of visual learning is needed in experiments involving aided lipreading. Results will be compared with a previous study that involved similar procedures and several different transformations of fundamental frequency for a single vibrotactile channel. [Research supported by NIH.]
Finite-difference modeling of the response of piezoelectric transducers in complex surrounding media
Authors: Kostek Sergio , Randall Curtis J.
Published: October 2005

A finite-difference time domain (FDTM) modeling code was developed to simulate the response of axisymmetric piezoelectric transducers. The coupled elastodynamic electrostatic equations are solved using an explicit scheme. The piezoelectric element is supposed to have transverse isotropy regarding its elastic, piezoelectric, and dielectric behavior. Attenuation is also introduced to model backing materials. Applications range from modeling ultrasonic transducers using piezoelectric disks to acoustic pressure sources in fluid-filled boreholes as in oil well logging. Frequency domain characteristics are recovered from the computed current waveforms and compared to lab measured admittances revealing good agreement between the two.
Finite-element eigenmode analysis for the design of composite transducers under the effect of fluid loading
Authors: Chin Liang-Chih , Jeng Jiann-Hwa , Bao Xiaoqi , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

A finite-element eigenmode analysis is presented for analyzing the dynamic performance of a composite transducer interacting with a fluid medium. The composite transducer contains a periodic distribution of piezoelectric rods formed into a 1–3 composite. The mathematical model reduces the boundary value problem to a typical forced vibration problem. This permits the damping of the composite slab to be easily introduced into the formulation. By inputting the electrical admittance of the transducer, the transmission efficiency, reflection, and transmission coefficients versus frequency have been calculated for different piezoelectric (PZT) volume fractions and different aspect ratio (width/thickness). The results of this study may be utilized for composite design.
Gaussian transducer for ultrasonic detection
Authors: Wu Zhen , Bao Xiaoqi , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

For improved ultrasonic detection (nondestructive evaluation, NDE), an ultrasonic beam with weaker sidelobes and absence of amplitude nulls in the nearfield is desired. This goal can be accomplished by reconstructing the back electrode of a conventional transducer, such that the vibration amplitudes on the transducer surface exhibit a Gaussian distribution along the radial direction. The shape of the back electrode is computed based upon the Laplace equation of the electric field in the crystal with the corresponding boundary conditions of the Gaussian distribution. Experiments have been performed with a piezoelectric transducer (PZT) in water. Theoretical analysis supports experimental results.
Adaptation of a residential dosage-response relationship for aircraft noise annoyance to the remote outdoor recreational setting
Authors: Hartmann Lawrence A. , Fidell Sanford
Published: October 2005

Public Law 100-91 requires the U.S.D.A. Forest Service and the National Park Service to assess aircraft noise impacts on outdoor recreationists in national parks and Forest Service wildernesses. Differences in the nature of aircraft noise exposure in residential and remote recreational settings require that modifications be made to accepted dosage-response relationships before they may be applied to prediction of aircraft noise impacts in remote outdoor recreational settings. In particular, attention is needed to the difference in ambient noise levels, the choice of noise metric, the role of response bias, and the absence of structural transmission loss. This paper describes the nature and implications of some necessary modifications.
Secondary sound channel formation in the South Pacific Ocean between 40° and 50° South Latitude
Authors: Denham R. N. , Browning D. D. , Christian R. J.
Published: October 2005

A prominent feature of the thermal structure of the Southwest Pacific Ocean between latitudes 40° S and 50° S is an isothermal layer of subantarctic mode water. This layer occupies the water column between depths of 400 and 600 m and has a temperature of 7–8°C. In winter, this feature can give rise to a surface sound channel down to 600 m and in summer can result in a subsurface subantarctic duct with axis at 100–250 m above a SOFAR channel with axis at typically 1200 m. The acoustic characteristics of this profile are examined and typical results are given for various source and receiver configurations. [Work supported by DSE and NUSC.]
Objective assessment of noise quality using standard measurement instrumentation
Authors: Bareham John R.
Published: October 2005

Objective assessment of noise (“noise quality”) can be thought of as a three-step process including data recording, signal analysis, and psychoacoustic evaluation. Standard measurement instrumentation may be used for recording and analysis, resulting in data suitable for a variety of present and future psychoacoustic relations. The discrete Fourier transform in its usual implementation, the short-time Fourier transform, and the variable-window Fourier transform can all be used for analysis of noise signals, However, these techniques have some limitations, such as linear frequency resolution, assumption of a locally stationary signal, and consequences of analysis windows. Real-time digital filtering is frequently more appropriate for the analysis of nonstationary noise signals, because it can provide logarithmic frequency resolution, inherently real-time analysis, and well-defined analysis windows. These two classes of methods will be compared. Analysis parameters of an objective analysis system using real-time digital filtering techniques will be discussed. A calibration procedure for the entire measurement chain, including a head and torso simulator used as transducer, will be described.
On the excitation mechanism in reed wind instruments
Authors: Agulló J. , Barjau A.
Published: October 2005

The production of self-sustained oscillations in reed woodwinds in based mainly on two physical mechanisms: the coupling mechanism—which makes use of the reflections coming from bore discontinuities—and the Bernoulli mechanism—which consists of a Venturi effect acting on the reed. As far as woodwinds with striking inward reeds are concerned, the only widely studied instrument has been the clarinet—a roundly cylindrical bore driven by a single reed—in which the coupling mechanism plays an essential role while the Bernoulli mechanism can be neglected in a first approach. However, little attention has been paid in the literature to the wider set of double-reed conical woodwinds (oboe, bassoon, shawms, etc.), in which sound production is based on the cooperation between both coupling and Bernoulli mechanisms. In this paper, both mechanisms are assessed and a comparative analysis is made of cylindrical and conical bores' input impulse responses, whose shape and strength are related to the intensity of the coupling mechanism. Due to the low intensity of the impulse response reflections in conical bores, the coupling mechanism in this case behaves mainly as a trigger of the intense Bernoulli mechanism, which is the one that strongly acts on the reed. Experimental results are also presented showing the bore input pressure for several instruments when producing a note attack, and illustrating the collaboration between both mechanisms.
On sound production in brass instruments
Authors: Keefe Douglas H.
Published: October 2005

The brass player's lips under playing conditions are displaced both longitudinally along the axis of the air column entryway, and laterally, or perpendicular, to the axis. Existing theories have modeled the valving action of the player's lips as a simple oscillator, or lip reed, but fall into two classes, depending upon whether the lip reed displacement is assumed to be purely longitudinal or lateral. An alternative model of sound production is proposed, retaining the single degree-of-freedom oscillator description, but including both longitudinal and lateral displacements. The lip reed is assumed to execute a circular, outwardly rolling motion. In the limit of small oscillations, this simplifies to linear displacement along an axis inclined relative to the air column entryway axis. The angle of inclination is a model parameter, but should depend upon mouthpiece geometry and player's embouchure. The lip reed is driven longitudinally by the pressure difference between the player's mouth (upstream) and the mouthpiece (downstream). It is driven laterally by the pressure within the lip orifice, which is related to the downstream pressure by momentum flux conservation. The time domain model incorporates reflection functions looking downstream into the air column, and upstream into the player's respiratory tract. The upstream reflection function can similarly be incorporated into player-woodwind models.
Demonstrating vibrations of musical instruments by use of modal analysis
Authors: Hansen Uwe J. , Rossing Thomas D.
Published: October 2005

Modal analysis using impact excitation has been used to study the dynamical behavior of a wide variety of structures from B747 airplanes to handbells. Some modes of vibration of several musical instruments, including a guitar, a handbell, a Caribbean steel drum, a snare drum, and a piano soundboard, will be demonstrated on videotape.
Measurement and calculation of acoustic propagation constants in arrays of air-filled rectangular tubes
Authors: Roh Heui-Seol , Sabatier James M. , Raspet Richard , Arnott W. Patrick
Published: October 2005

The theory of sound propagation in rigid cylindrical tubes is established by the separate treatments of viscous and thermal effects [K. Attenborough, J. Acoust. Soc. Am. 73, 785–799 (1983)]. Such development is applied to investigate the theory of sound propagation in rigid rectangular tubes. Arrays of air-filled rigid parallel rectangular tubes are prepared to compare the theory with the measurements of propagation constants. [Roh et al., J. Acoust. Soc. Am. Suppl. 1 85, S82 (1989)]. The theoretical calculation of complex propagation constants is compared with experimental data as a function of frequency. The dynamic shape factor, which is related to deviation of propagation constants in cylindrical tube cross sections, is examined by comparison of propagation theories between rectangular and circular tubes. [Work supported by ONR and USA-CERL.]
Bistatic scattering from a stiffened elastic cylinder
Authors: Vogelsong Richard D. , LaShomb Susan M.
Published: October 2005

Submarine hulls are often modeled as stiffened elastic plates at frequencies above the plate coincidence frequency. At lower frequencies, hull curvature and stiffener characteristics become more important. At these frequencies, cylindrical shell and circular beam models may be more appropriate in predicting the acoustic scattered field from stiffened hulls. A theoretical approach is presented describing the bistatic acoustic field scattered from a stiffened elastic cylinder. A finite number of stiffeners are treated as nonuniform translational and rotational modal constraints upon the elastic motion of the fluid-loaded cylindrical shell. The stiffeners are modeled as curved beams that constrain the shell's three degrees-of-freedom at variable locations. This formulation allows the lighter hull rib stiffeners and more massive bulkheads to be considered as an elastic system. For M variably spaced stiffeners, the modal solution depends upon the calculation of seven sets of M(M − 1)/2 cylindrical, fluid-loaded, cross-admittance functions and the inversion of a 4M by 4M matrix.
On the extension of a variational principle for surface pressure to treat spurious interior cavity resonances
Authors: Kil Hyun-Gwon , Ginsberg Jerry H.
Published: October 2005

A variational principle for surface pressure, which is related to the surface normal derivative of the Kirchhoff-Helmholtz integral theorem, fails due to lack of uniqueness at the eigenfrequencies of the Neumann problem for the interior cavity [X.-F. Wu and A.D. Pierce, IMACS (1987)]. Boundary element formulations address this problem by introducing additional constraints, which in the context of a variational formulation leads to an isoperimetric problem. When the pressure is expanded in a series of assumed basis functions, satisfaction of constraint conditions introduces Lagrangian multipliers as unknowns, in addition to the amplitudes of the basis functions. Alternative constraint functionals, derived from the fact that the pressure in the interior cavity must vanish at all frequencies, are considered. An obvious constraint is that the integrated mean-square pressure on an interior surface must vanish, but this condition is shown to lead to a nonlinear system of equations. Suitable linear constraints are explored by using the (unconstrained) variational principle to generate erroneous predictions for the pressure on the surface of a sphere at several Neumann frequencies, and then using the Kirchhoff-Helmholtz integral theorem to obtain the corresponding interior field. [Work supported by the Office of Naval Research, Code 1132-SM.]
Complex wavenumber decomposition of cylindrical shell vibrations
Authors: Grosh Karl , Williams Earl G.
Published: October 2005

An extended Prony technique for analyzing the complex wavenumber content of the velocity field on the surface of a cylinder is described and tested. Radial velocity fields at the surface of a cylinder are decomposed into circumferential harmonics of order n via the FFT yielding vn (z,ω) × exp(±4 inθ). For each n and ω, the axial (z direction) wavenumber dependence consists of a sum of exponentials of the form exp(± ikzz)), where kz, is the wavenumber. There are three types of wavenumbers present on the vibrating cylinder: pure real, pure imaginary, and complex. The real wavenumber corresponds to a freely propagating wave, the imaginary wavenumber to an evanescent or neafield term (generated at discontinuities), and the complex wavenumber to a spatially decaying oscillatory wave. These complex wavenumbers cannot be determined from an axial FFT (as they are in the circumferential case). However, the extended Prony algorithm does extract the imaginary and the complex wavenumbers and determines the amplitudes of excitation of the associated waves. The effectiveness of this algorithm is demonstrated by decomposing the velocity of synthetic data. The effects of measurement noise and structural discontinuites are examined. Applications to experimental data are discussed.
Calculation of the acoustic field due to a circular, cylindrical shell with clamped hemispherical endcaps by the method of wave superposition
Authors: Fahnline John B.
Published: October 2005

The method of wave superposition is applied to the case of a circular, cylindrical shell with hemispherical endcaps. The velocity profile on the surface of the cylinder is taken to be the solution of the Donnell-Mushtari-Vlasov equations for a circular, cylindrical shell with clamped-clamped end conditions, while the velocity on the endcaps is taken to be zero. By determining a finite number of interior sources whose fields, when summed, closely approximate the acoustic field due to the shell, an equivalent representation of the field is generated. The velocities and pressures on the surface of the shell are then calculated, along with the power radiated by the shell. Convergence of the calculated power is shown to be a nearly linear function of the mean-square error in the reconstructed surface velocities. Also, the effect of small perturbations in the velocity input (for example, as a result of the inexactness of modal analysis techniques) is shown to have little effect on the calculated radiated power.
Acoustic scattering from an elastic plate reinforced with an infinite number of periodic ribs
Authors: Karali Angela K. , Hayek Sabih I.
Published: October 2005

The scattering of plane, time-harmonic waves, incident on a flat elastic plate of infinite length is studied. The plate is assumed to form the interface between an acoustic fluid and the vacuum and be reinforced with periodically spaced ribs. The reinforcements exert both forces and moments on the plate. The aim of this paper is to theoretically investigate the backscattered field of the incident sound wave for frequencies below and above the critical frequency of the plate.
A mathematical model for wave propagation in bilaminar composite plates
Authors: Yum Si-Hwan , Hayek Sabih I.
Published: October 2005

Refined models for plate deformation allow for new types of thickness and extensional displacements not currently feasible in the classical or Timoshenko-Mindlin plate theories. An infinite bilaminar composite plate is fabricated in such a way that the two plates, made of different isotropic, homogeneous materials, are perfectly bonded. A new mathematical model of the vibration of an infinite bilaminar composite plate has been obtained by using energy methods. The displacement field is based on symmetric and antisymmetric displacement functions in both the thickness stretch and the thickness shear of each layer. From this model, the Timoshenko-Mindlin thick plate theory and the Bernoulli-Euler classic plate theory for a single plate can be recovered as special limiting cases. For this model, a six-branched frequency-wavenumber spectrum of the composite layer is computed. This allows the introduction of suitable correction coefficients to correct the resulting frequency spectra so that they correspond to those of the exact elasticity theory.
Multichannel adaptive control of structural vibrations
Authors: Sommerfeldt Scott D.
Published: October 2005

Most of the adaptive vibration or noise controllers reported in the literature to date have been configured as single-input, single-output systems. A number of problems of interest in active vibration control require multiple actuators and sensors to achieve the desired control. For such problems, an adaptive controller that embodies multiple inputs and multiple outputs would be desirable. This paper will look at some of the considerations that should be kept in mind when developing a multichannel adaptive controller. The interaction of the control actuators not only with the structure, but also with each other, must be accounted for to maintain stability of the controller. Some of the additional complexities related to a multichannel algorithm will be presented by means of comparing a multichannel adaptive algorithm with an analogous single-channel algorithm. As well, some of the performance limitations associated with computational complexity and convergence will be discussed.
Shear mode piezoceramic sensors and actuators for active torsional vibration control
Authors: Sung Chia-Chi , Bao Xiaoqi , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

Shear mode transducers have been designed as sensors and controllers of shear stress/strain as exhibited on pure torsional flexible structures. The specific transducer material selection was chosen to exploit the “d 5” piezoelectric constant. The experimental setup included clamped-free phenolic and pyrex tubes with attached controllers. The output current of the sensors is shown to be proportional with the velocity of the modal vibration. A velocity feedback control technique was used for vibration control. The experimental measurement and theoretical modeling of free and controlled frequency responses are compared.
Overturning of nonlinear waves
Authors: Hammerton Paul W. , Crighton David G.
Published: October 2005

When considering nonlinear wave propagation through a medium, it is important to consider which linear attenuation mechanisms significantly affect wave profiles. Specifically, it must be asked whether a particular physical attenuation is sufficient to prevent the overturning of finite-amplitude waves. Thermoviscous dissipation, however small, will always prevent such overturning, but relaxation effects alone do not necessarily ensure single-valued solutions. In this paper, the attenuation effects of a relaxing medium are investigated. The model equation considered contains two parameters [D. G. Crighton, Ann. Rev. Fluid Mech. 11, 11–33 (1979)] related to a characteristic relaxation time and to the difference between equilibrium and frozen sound speeds. A method using intrinsic coordinates is described as a means of investigating the phenomenon of overturning. This is then applied to the case of a relaxing medium. In this way, the set of parameter values is divided into those for which single-valued solutions are obtained, and those for which overturning occurs. The latter case corresponds to the physical situation of normally insignificant thermoviscous dissipation becoming locally as important as the relaxation effects.
Transient evolution of steady-state shock profiles for sonic booms in a relaxing atmosphere
Authors: Kang Jongmin
Published: October 2005

When a shock wave propagates through a uniform medium over a long distance, there is an asymptotic tendency for the portion of the waveform that includes a sudden pressure rise (shock) to approach an invariant form F(x−Vl), where Vis the shock speed and where the function F, in addition to the indicated argument, depends only on the net pressure jump Psh and the local properties of the atmosphere (including relaxation times). The present paper is concerned with the broad question of how long it takes (or how far the shock must propagate) before this asymptotic limit is realized, given some other nonasymptotic profile at some initial time. Although this question has in principle been answered by Benton and Platzman [Q. Appl. Math. (1972)] for the one-dimensional Burgers' equation, new techniques are required when internal relaxation is to be taken into account. A perturbation theory is used here, with the shock profile taken as the steady-state profile plus a perturbation, which must asymptotically decay to zero. This perturbation, to lowest order, is found to satisfy a set of linear homogeneous partial differential equations with nonconstant coefficients. With the choice of l and ξ = x − Vl as the independent variables, the coefficients depend only on ξ. Consequently, the equations can be solved for any given initial value problem with the use of Laplace or Fourier transforms. The asymptotic decay of the inverse Fourier transforms to zero is developed by well-known techniques such as described in the text by Bleistein and Handelsman [Dover, New York (1986)]. [Work supported by NASA-LRC and by the William E. Leonhard endowment to Penn State Univ. The author acknowledges the advice of A. D. Pierce.]
Evoked potentials to shifts in the lateralization of a noise: Effect of stimulus frequency
Authors: McEvoy L. , Picton T. , Champagne S.
Published: October 2005

Changing the interaural time difference of a continuous noise arriving at the two ears causes a shift in the perceived lateralization of the noise. This shift in lateralization evokes from human subjects a late evoked potential with a positive-negative-positive waveform between 80 and 290 ms. To determine which frequencies of the broadband noise contribute to the response, two experiments were performed. In the first, the noise was low-pass filtered at 8000, 4000, 2000, 1000, and 500 Hz, and the late auditory-evoked potentials were recorded. In the second experiment, the noise was bandpass filtered between 250–500, 500–1000, 1000–1500, and 1500–2000 Hz. The results of both experiments show that the evoked potential is mainly mediated by the low frequencies (250–1500 Hz) in the noise. Since it is possible that the response may be elicited through the high-frequency region of the cochlea, the response in the presence of monaural high-pass masking noise was evaluated. These results indicate that the response is elicited through the region of the cochlea specific to the frequencies of the sound that carry the lateralizing information.
Some acoustical observations of internal waves and associated turbulence in the coastal ocean
Authors: Proni John R.
Published: October 2005

Outstanding features of the coastal ocean influencing the acoustical study of internal waves and turbulence include the large quantities of suspended particulates present therein and the regularity, both in characteristics and occurrence, of internal wave groups. The coastal ocean is often occupied by internal wave groups possessing a well-known and consistent structure, namely, a set of amplitude-ordered solitons followed by a sequence of quasilinear waves. Acoustical observations made using backscattered 20-kHz pulses, of two events conjectured to be internal wave group-generated mixing and resuspension events, will be presented. The first event occurs at the interface separating Hudson-Raritan water from continental shelf water; the second event occurs in the ocean bottom boundary layer. A third event generated by an oceanic discharge of material event wherein simultaneous generation of internal waves, turbulence, and a midwater column “turbidity” particulate surge will also be presented. Some implications for acoustical signal interpretation of temperature or salinity turbulent scattering events in the presence of a particulate distribution will be examined with specific emphasis on the implications for “calibration” of acoustical scattering instruments and the utility of acoustical devices for studying the decay of turbulent events.
A theory for the generation of multiscale structure in Langmuir circulations
Authors: Mourad P. D.
Published: October 2005

Extant theories and numerical simulations for Langmuir circulations [Leibovich, Ann. Rev. Fluid Dyn. (1983); Leibovich et al., J. Fluid Mech. (1989)] all show predicted circulation patterns characterized by a single horizontal, cross-wind scale. Recent research [Smith et al., J. Phys. Oceano. (1987); Weller and Price (1988); Pinkel and Smith (1989), unpublished acoustic data] show multiscale circulation patterns, including the organization of bubbles and phytoplankton, in the oceanic surface layer. An analytic theory for the evolution of two-dimensional disturbances in neutrally stratified, super-critical shear flows will be presented, done in collaboration with Chris Bretherton, UW-Applied Mathematics. This theory shows that initially favored, quickly growing disturbances evolve into catalysts for the transfer of mean flow energy into other scales of motion, producing multiscale circulation fields. This general result directly predicts the production of multiscale Langmuir circulations, which is supported here with theoretical calculations specialized to the oceanic surface layer.
The relationship between sound-power level and sound-pressure level in dwellings and offices
Authors: Blazier Warren E.
Published: October 2005

In 1985, Ted Schultz undertook a research project for the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to investigate the relationship between the sound-power level of a source and the sound-pressure level produced in “real” rooms typical of dwellings and offices. For many years, the use of the diffuse field theory of sound propagation had been suspect as not being applicable in normally furnished spaces to the prediction of sound-pressure level resulting from a known introduction of sound-power level. Ted's research confirmed that the use of this latter theory led to significant errors that both overestimated and underestimated true conditions depending upon the distance between the source and observer. Recognizing the complexity of developing a rigorous theoretical solution within the time frame of the project, he undertook an empirical approach and reviewed a large body of his own and others' reliable test data to develop an equation that predicted with considerable accuracy the measured results in rooms ranging from bathrooms and kitchens to plush furnished offices, conference rooms, and living spaces. In summarizing the conclusions of this study, Ted made several cogent observations, typical of the subtle Schultz style: “Since the room absorption, A, does not appear explicitly in the formula, the customary normalization with 10 log (A/A0) in transmission loss and impact noise tests is probably incorrect. In addition, since no uniform reverberant sound field occurs in normally furnished spaces, it is not clear what one ought to measure for the receiving-room sound pressure level in tests of transmission loss, noise reduction, and impact noise.” He was pursuing these concerns at the time of his death.
A microphone array for echo cancellation in audioconference rooms
Authors: Grenier Y. , Xu M.
Published: October 2005

This paper describes an adaptive acoustic antenna (or microphone array) designed for sound recording in audioconferencing rooms. This microphone array achieves three goals simultaneously: the sound from the useful sources (speakers) is recorded without distortion, several jammers emitting known signals can be cancelled (this is the case for the sound received from the other room and emitted by the loudspeakers), and finally, the ambient noise and the room reverberation are reduced. This last effect enforces the “presence effect” in the recordings. In the present approach, echo cancellation is seen as the problem of rejecting a jammer, and it is done by signal combination rather than by subtraction. To achieve these goals, the microphone array uses adaptive beamforming techniques. The beamformer is a compromise between data-independent or fixed beamformers and data-dependent or adaptive ones. This makes it robust with respect to localization errors: the beamformer uses an identified localization of the jammers but weighs this information by some knowledge of the signal-to-noise ratio. The localization of the main jammer (the echo coming from the loudspeaker) requres the identification of a long impulse response (the acoustic channel between the loudspeaker and each microphone). A model to identify this response in the time-frequency domain is developed. This model involves a “double convolution” and its adaptive identification has some analogies with subband adaptive methods. The estimated parameters of this model are used to compute the optimal weights for the beamformer every 8 ms. The paper will present simulations of these techniques based upon a first prototype that consists of an array of 15 microphones on a semicircle with diameter 1 m. The performances of this adaptive microphone array are characterized in terms of echo rejection, convergence rate, and level of dereverberation.
The story behind catacoustical measures
Authors: Pinkham Daniel
Published: October 2005

150 Chilton St., Cambridge, MA 02138-1227 Early in his architectural acoustics consulting career, Theodore Schultz reasoned that an acoustical test source comprised of real music was the ultimate method for true objective evaluation of listening spaces for music. A musical composition that incorporated chords designed by Ted to test the acoustics of a concert hall will be discussed by the composer. An audio recording of the work will be played. Other reminiscences of acoustical interactions between Schultz the scientist/musician that contributed to the work of Pinkham the musician/composer will be discussed.
Classroom demonstration—Generating an ROC curve from the energy detection of signals in random noise
Authors: Korman Murray S.
Published: October 2005

Students enrolled in “Underwater Acoustics and Sonar” at the Naval Academy benefit from a “hands-on” demonstration of binary detection theory. The relationships between the respective probabilities of detection, miss, false alarm, and null [P(D), P(MISS), P(FA), P(NULL)] are examined for different thresholds. Two loudspeakers, driven respectively by random noise and a pure tone, simulate the acoustical environment. The output of a microphone is sent through an analog multiplier and a low-pass filter, which act as the detector. An Apple IIe computer with a digital oscilloscope card displays the output and performs the probability density function on the processed signal. PDFs of (a) noise alone and (b) noise plus a signal are used to generate the receiver operating characteristic (ROC) curve. [Work supported by the Naval Academy Research Council.]