bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental observations on liquid/solid interface waves
Authors: Chamuel Jacques R.
Published: October 2005

Elastic waves propagating at the interface between a liquid and a solid present interesting complex phenomena as the relative elastic properties of the liquid and the solid are varied. It is difficult to obtain a good physical interpretation of the mathematical solutions of the Stoneley wave equation. Experimental results are presented using limestone/water, aluminum/water, Plexiglas/water, and ice/water. A barrier was placed between source and receiver to isolate the Scholte wave from the water and pseudo-Rayleigh waves. The experiments were repeated with a deep narrow cut made in the solid to stop the seismic waves. The measured Scholte (Stoneley) wave velocities agreed with Strick and Ginzbarg's calculations (1956). For the limestone/water case, the barrier stopped the Scholte wave and did not affect the pseudo-Rayleigh wave. The barrier did not stop the Scholte wave for the Plexiglas and ice cases. The deep narrow cut in the solid stopped the pseudo-Rayleigh wave for the limestone/water case, and did not affect the Scholte wave. The Plexiglas and ice Scholte waves were interrupted by the deep cut. The reported experimental findings provide insight into the physical understanding of interface wave propagation.
Approximate expressions for on-axis pressure of piston source radiation transmitted through a liquid-solid interface
Authors: Thompson R. B. , Gray T. A.
Published: October 2005

The fields of a piston source in a baffle, radiating into a half-space, are well known. Approximate analytical expressions are presented which extend these to the cases of transmission through planar or cylindrically curved interfaces at normal or oblique incidence. Included are results for both the cases of longitudinal wave and transverse wave generation. In order to obtain analytically tractable results for these complex interactions, it is necessary to make a number of simplifying assumptions, such as the neglect of the variation of interface transmission coefficients over the range of angles of incidence contained within the beam. Hence, application of the results are restricted to illumination away from critical angles. Comparison to experimental measurements of scattering from on-axis reflectors are presented. The results are interpreted in terms of the change in beam cross section from circular to elliptical due to the refraction induced change in propagation direction, coupled with the focusing effects of the cylindrical surface. [Work sponsored by Center for Advanced NDE, operated by Ames Laboratory, USDOE, for AFWAL and DARPA under Contract No. W-7405-ENG-82 with Iowa State University.]
Tonpilz head mass studies
Authors: Douglas George R. , Wilson Charles R.
Published: October 2005

Alumina and composites of graphite/epoxy were used as head mass materials in two separate applications. In the first application alumina and composites of graphite/epoxy head masses were used to produce a low mechanical Q, high electroacoustic efficiency transducer. The initial results show that graphite/epoxy composites especially have great promise as head mass material because of its light weight and high tensile strength. In the second application an alumina head mass was used in a dual mode transducer. This configuration consists of an array of smaller tonpilz elements mounted in the head mass of larger tonpilz elements. This unique method required a very stiff secondary head mass to transfer acoustic energy (without storing strain energy) to the primary radiating surface of the smaller elements. Work in first application was sponsored by Westinghouse in-house R&D Program of FY 81 & 82. [The work in second application was supported by the dual mode transducer program Navy contract No. N00140-80-R-6916.]
Pressure release study of materials and configurations applicable to large sonar transducer
Authors: Wilson Charles R.
Published: October 2005

Polyimide and polyester elastomer reinforced with 20% random glass were developed and tested as a pressure release material for sonar transducer applications. Tonpilz-type transducers using these materials as a pressure release were subjected to various high pressure conditions and intensive qualification tests including acoustic, extraneous noise, and shock. The results show that both polyimide and polyester elastomer reinforced with 20% random glass are excellent, cost efficient, pressure release configurations that can replace existing belleville springs and sonite pressure release systems now in use. [Work supported by Sonar Transducer Reliability Improvement Program FY 80 under Navy contract No. N00173-79-C-0390.]
Effect of the inharmonicity of stiff strings on piano tuning
Authors: Suzuki Hideo
Published: October 2005

The presently used tuning theory [A. A. Reblitz, Piano Servicing, Tuning, and Rebuilding, 5th Printing (Vestal Press, Vestal, NY, 1981)] uses the beat rates calculated from the ideal harmonics of notes in the temperament octave. Following this theory, the note F3 is tuned sharp to C4 (middle C) with a 0.59-Hz beat rate. Then, the note F4 is tuned to the note F3, beatless. Theoretically, assuming the ideal harmonic relationship of partials, the best rate between notes C4 and F4 (test interval) is 1.18 Hz with F4 sharp. This is not true, however, for real piano strings with some amount of inharmonicity. If the inharmonicity index B, which describes the degree of inharmonicity of a string [H. Fletcher, J. Acoust. Soc. Am. 36, 203–209 (1964)], is assumed to be 0.0004 for notes F3, C4, and F4, the beat rate between notes C4 and F4 becomes 0.696 Hz with F4 flat. This is a self-contradiction inherent in the present tuning theory. A method will be presented to calculate the beat rates when the inharmonicity indexes are known for all thirteen notes of the F3–F4 octave.
Sound pressure distributions and resonances in the human ear canal in the presence of a measuring microphone
Authors: Kuhn George F. , Greller Larry D.
Published: October 2005

The effect of measuring microphones on the acoustic pressure distribution in ear canals has been studied analytically and experimentally up to 20 kHz using scaled model ear canals and real ear canals molded from cadavers. These pressure distributions are a function of frequency, microphone size, microphone location, and ear canal geometry. The presence of the microphone causes not only a localized disturbance of the sound field, producing an erroneous pressure measurement, but also disturbs the pressure distribution across the eardrum, beginning in the mid-frequency range. Furthermore, the measuring microphone as well as the nonuniform canal geometry in the vicinity of the eardrum cause the longitudinal resonances of the ear canal to become anharmonic. This anharmonicity is analytically predictable for canals of sufficient crossectional uniformity and with sufficiently well behaved, but not necessarily uniform, crossectional canal-geometry near the eardrum. [Work supported by NIH.]
Optical measurement of ear canal length
Authors: Zemplenyi Jan , Gilman Samuel , Dirks Donald
Published: October 2005

This paper reports an optical, noninvasive technique for measurement of both open and occluded ear canal length. The method is based on the use of an operating microscope set at a standard magnification. Initially the microscope is adjusted so that the umbo is sharply in focus when the body of the microscope is close to fully “down” position on its track. The microscopic support is then locked in all directions of motion and the microscope body position is measured. The microscope is then refocused on a reference point along the ear canal. The distance that the microscope body traveled along the track is then measured. This measurement is equal to the distance between the umbo and the previously chosen reference point. The length of an occluded ear canal can be measured by choosing the lateral plane of the earmold as the new reference and then subtracting the earmold length. The distance from umbo to the junction of the concha cavum and the ear canal can also be measured directly. The depth of focus of the microscope optics is selected to provide a maximum error no greater than ± 1 mm. Measurements obtained by this technique were compared to those made by invasive methods reported in the literature.
Localized distribution of olivocochlear fibers
Authors: Stopp Phyllis E.
Published: October 2005

One of the problems the auditory system has to deal with is that of preserving the identity of a signal against a distracting background, a role in which the centrifugal pathway has been implicated. There are two ways in which this might act: (a) by adjusting the general threshold level of the hair cells to be below saturation level, (b) by inhibition at the boundary edges of the active-fiber array. The hypotheses were tested anatomically by studying the organization of the olivocochlear bundle using retrograde axonal transport. True Blue, (TB) a fluorescent dye was introduced into discrete regions of the guinea pig cochlea. When TB contacted the whole cochlea labeling appeared throughout the whole ipsilateral lateral superior olive (LSO), together with some lesser labeling in the contralateral periolivary nuclei and trapezoid body. When TB was applied only to the apical turn labeling was confined to the dorsolateral region of the LSO, while basal turn treatment resulted in labeling restricted to the medial region. This cochleotopic organization corresponds to the tonotopic arrangement of the afferent cells (cat) and suggests that the OCB acts by a localized rather than a diffuse mechanism.
The piezoelectric properties of some polar glass-ceramics
Authors: Ting R. Y. , Bhalla A. S.
Published: October 2005

A completely new family of nonferroelectric polycrystal materials was recently developed. The samples were prepared by recrystallizing the glass of suitable composition in a very strong temperature gradient. The thermal gradient produced a driving force which gave strong preference to crystal nuclei of a given polarity, resulting in a highly oriented polar phase. The hydrostatic piezoelectric coefficient dh and hydrostatic voltage coefficient gh of this new class of transduction material were measured as functions of temperature, pressure, and frequency. The dh, and gh, values were found to be comparable to those of the state-of-the-art piezoelectric PVDF polymers, but independent of hydrostatic pressure up to 35 MPa. This effect may be attributed to the high stiffness of the glass and the firm polar character of the polarization. The advantages of glass-ceramics for hydrophone applications will be discussed.
Some possible novel configurations for optico-acoustic transducer arrays created by controlled motion of laser beams across water surfaces
Authors: Hsieh Hsiao-an , Pierce Allan D.
Published: October 2005

Laser beams impinging on water surfaces will generate underwater sound if the beam intensity is modulated or if the beam is moving, although the optical-to-acoustical energy conversion efficiency is typically extremely low. Previous analyses have been confined to modulated beams impinging at a fixed point or moving rectilinearly at constant speed, but the present paper adopts a futuristic view that intricate moving and rotating mirror systems can be designed that will allow the entry point to move in any desired pattern (including skips and zig-zags) and with any velocity versus time profile; the only constraints are that the beam entry angle be fixed and that the exponential decay rate of beam intensity with depth be fixed. This latitude in beam configuration allows a systematic exploitation of the pumping principle, that local energy conversion efficiency is proportional to product of acoustic pressure and beam intensity, by placing the beam wherever and whenever the acoustic pressure is currently the highest. Directed acoustic waves pointed obliquely downwards can be created by moving an obliquely incident beam through a sequence of short parallel path segments, the first sequence pattern simulating a sinusoidal heat deposition wave of fixed wavelength and beam width, the next sequence causing this pattern to move at the sound speed in the desired propagation direction. [Work supported by ONR.]
Dynamical equations for sound generation in wind instruments
Authors: Davis R. E. , Tubis A.
Published: October 2005

An exact set of coupled ordinary, nonlinear differential equations is derived for the mouthpiece pressure in reed wind instruments for cases in which the mouthpiece impedance function is expressible as a series of pole terms in the complex frequency plane. The equations are applicable even in the “beating reed” regime. The integration of the equations to obtain transient and steady state behaviors of the instrument apepars to be a practical alternative to integral equation approaches.
Exploring the concepts of music and sound: Instructional methods and techniques
Authors: Lederman Norman
Published: October 2005

Over the past five years, the author of this paper has developed a sound demonstration lab and taught interdisciplinary courses in sound and music at the Model Secondary School for the Deaf (M.S.S.D.), a pre-college program of Gallaudet College. The courses have been unique in their approach to demonstrating auditory events (which the hearing impaired individual may not be able to detect) through multisensory (visual and tactile) means. By way of classroom demonstrations, hands-on experiments, a student workbook, and teacher's guide; the students gain an increased self-awareness and understanding of the physical/scientific concepts of sound, the hearing process, the speech mechanism, musical instruments, and associated technology (e.g., hearing aids, equipment used in testing hearing, etc.). In addition to its involvement with hearing impaired individuals, the M.S.S.D. sound lab has been visited by various professional organizations and other school programs. Upon experiencing the sound lab, these visitors (many from hearing schools) have cited the usefulness of the multisensory approach to teaching material of this nature. For the Acoustical Society meeting, the author intends to present an overview of the techniques used in the sound lab, show student response (videotape), and invite audience participation. There will be live demonstrations as well as slides and video.
The practical side of determining feasibility of engineering noise controls
Authors: Chadd Charles M.
Published: October 2005

As set out in Continental Can Company, Castle & Cooke and other noise cases decided by the Occupational Safety and Health Review Commission before its Sun Ship decision, determination of the economic feasibility of engineering controls is a practical matter which balances all costs and benefits of engineering and compares them to the costs of hearing conservation. Under OSHA's new instruction CPL 2-2.35, the agency has adopted this approach. Factors that must be considered in determining the costs of engineering controls include not only the costs of design, development, construction, and implementation, but also the continuing costs of living with the controls such as lost production or efficiency, decreasing product quality, increasing amount of rejects, maintenance of the equipment with which the controls are associated, and maintenance of the engineering controls. Because many purported engineering controls merely involve encasing or blocking the sound by some type of enclosure or barrier, or enclosing the employee, important factors in determining the feasibility are the effects of a control on employee's ability to perform his job and the acceptance level of the control as compared to ear protection.
Acoustic intensity measurements at the surface
Authors: Hodgson Thomas H.
Published: October 2005

A surface acoustic intensity meter is described for measuring acoustic intensity at a vibrating surface using a fiber optic lever as a displacement transducer and a condenser microphone to measure surface pressure. Digital signal processing using a two-channel FFT analyzer allows the calculation of surface intensity as a function of frequency. The technique has been tested in an anechoic chamber on a point monopole and a steel plate clamped at the edges. Calculated sound power levels are compared with results obtained by traditional techniques.
Feasible engineering noise controls in General Motors Corporation
Authors: Pyne James H.
Published: October 2005

The implementation of engineering noise controls on existing, rebuilt, and new equipment must take into account both technological and economic feasibility. Retro-fitting engineering controls to existing noisy equipment on the production floor, while desirable and in some instance necessary, can have serious negative economic consequences. Costs resulting from decreased productivity, increased maintenance, frequency of replacement, and possible increased floorspace requirements are all factors which must be considered. General Motors Corporation, (GM, while pursuing the investigation and implementation of feasible engineering noise controls on existing equipment, places special emphases on the purchase of new equipment. The “General Motors Corporation Sound Level Specification for Machinery and Equipment,” Revision February 1979, specifies a maximum time-weighted average sound level of 80 dB (A). Measurements are taken at the operator's ear location and on the measurement envelope as specified in “NMTBA Noise Measurement Techniques” Second Edition dated January 1976. GM, working in conjunction with its suppliers, has experienced considerable success in achieving feasible engineering controls through the application of the GM Purchase Specification.
Discrimination of binary tone sequences
Authors: Sorkin Robert D.
Published: October 2005

Subjects were presented with two sequences of tones, e.g., HLLHHHLL, HLHLHHLL. The tones were either 669 Hz or 1621 Hz. Subjects were instructed to respond “same” if the same serial pattern of high and low tones were repeated in the second sequence. They were to ignore any variation in the time between the tones. Performance was assessed in a variety of task conditions. The variables studied included: the number of tones, the mean time separation between tones, the magnitude of variability (jitter) in the time between tones, the correlation between the jitter pattern in the two sequences, the pattern variability in the sequences, and the serial position of pattern differences between the sequences. The results are interpreted using an extension of the auditory memory model developed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372–383 (1969)]. This model postulates two independent memory modes, a trace (time-dependent) mode, and a context coding (set-size-dependent) mode. The data provide general support for the extension of the dual mode model to this task. [Work supported by NSF.]
Pitch discrimination as a function of tone duration
Authors: Hartmann W. M. , Packard T. N.
Published: October 2005

Numerous experiments have studied pitch discrimination for sine tones as a function of the duration T of the two tones to be discriminated. All the data agree that as T decreases the uncertainty in pitch discrimination becomes larger, and the functional dependence of the uncertainty on T has been used to test various models of pitch perception. However, all simple models, whether temporal or spectral, predict that if the two tones have different durations, T1 and T2, then the uncertainty should lie between the uncertainty obtained when both tones have duration T1 and the uncertainty obtained when both tones have duration T2. To find out whether this is so we measured the variability in a pitch matching task where the tones to be matched had different durations. The matching task provides data on pitch uncertainty in the presence of large duration-dependent pitch shifts whereas a standard discrimination experiment does not. We studied seven different frequencies between 200 and 7000 Hz and all combinations of 12, 25, and 50 ms for T1, and T2. Ninety percent of the data with T1 ≠ T2 show a variability which is larger than would be expected based upon the variability in the data with T1 = T2. We believe that it is possible to understand these results in terms of an improved statistical decision theoretic model of pitch perception. [Work supported by the National Institutes of Health Grant 17917.]
Frequency discrimination for conditions of roving standard and random interstimulus interval
Authors: Kidd Gerald , Neff Donna L.
Published: October 2005

A two-interval forced-choice adaptive tracking procedure was used to estimate the frequency difference limen (DL). In one condition, the frequency of the standard tone was constant for every trial with the frequency of the comparison tone varied according to the adaptive procedure. The interval between standard and comparison stimuli (ISI) was fixed. In contrast to this “fixed-standard fixed-ISI” condition, other conditions were tested in which the standard frequency and/or the ISI were chosen on each trial according to pseudo-random algorithms. The results indicate that the frequency DL may increase by as much as a factor of 2 for some roving-standard and random ISI conditions. In addition, a trial-by-trial record of each run was used to assess discrimination performance as a function of frequency and ISI. The decay of the sensory trace with increasing ISI, and uncertainty about signal frequency and timing appear to account for the changes in discrimination. [Supported by NIH.]
Two kinds of pitch: Matching and discrimination with complex signals
Authors: Creelman C. Douglas , Komar Anthony
Published: October 2005

With specially constructed harmonic stimuli, observers matched pitch neither to the period of the stimuli nor to the fundamental of components in the spectral “critical region.” The lowest and highest components of the stimuli were multiples of three times the (missing) fundamental frequency, while the central components were multiples of twice the (missing) fundamental frequency. Matches were almost equally divided between the two secondary fundamentals, with very little variability. There were no matches to the fundamental. In a second experiment, observers discriminated between the frequencies of complex stimuli, including those used in the first study as well as more traditional “missing fundamental” stimuli. The data suggest that pitch-discrimination is based on the actual frequency components present in the stimuli, rather than on the apparent or perceived pitch. These findings imply at least two “pitch” mechanisms, one responsible for perceived pitch, and the other required for relative judgment and fine discrimination. [Work supported by NSERC.]
A dynamic analysis of reiterant speech production
Authors: Kelso J. A. S. , Bateson E. V. , Saltzman E. L. , Kay B.
Published: October 2005

Speaking, like other biological activities, emerges from a neuromuscular basis of high dimensionality as a coherent pattern of articulator motions. What form, if any, does such coherence take and how might it be rationalized? Conventional analyses of articulatory motion are not always informative. Here we use the tools of qualitative dynamics, particularly phase portrait techniques [cf. J. A. S. Kelso and E. V. Bateson, J. Acoust. Soc. Am. Suppl. 1 73, S67 (1983)] to analyze articulatory gestures from an experiment in which speaking rate and stress are naturally varied. We show that the strong relationship between a gesture's amplitude and peak velocity may be accounted for when movements are analyzed in an action (energy × duration) versus amplitude performance space. The action for a given gesture (associated with consonant-vowel and vowel-consonant transitions) and for a given speaker scales to (amplitude)2. This finding suggests (1) that stiffness is a key dynamic parameter of the articulatory system, and (2) that an elastic similarity principle may underlie the articulatory behavior of different speakers. [Work supported by NIH, BRSG, and ONR.]
Modeling the source for fricative consonants
Authors: Shadle Christine H.
Published: October 2005

Turbulence noise in the vocal tract, which plays a role in the production of fricative and stop consonants, is usually modeled by placing one or more sound-pressure sources with smooth spectra in series with a one-dimensional model of the vocal tract [G. Fant, Acoustic Theory of Speech Production (Mouton, 1960)]. In this paper it is shown that this model is consistent with the sound generated when a jet of air impinges on an obstacle. Theoretically, the sources at the obstacle are dipoles, and thus are equivalent to a pressure source. Experimentally, the power spectrum of the sound generated by a mechanical model corresponds closely to the transfer function simulated for a tube with identical area function and a pressure source at the location of the obstacle. When no obstacle is present downstream of the constriction in the model, no such correspondence is observed, indicating that for this case a distributed source is a better model of the sound generation mechanism. Analysis of spoken sustained fricatives shows a similar division between stridents (with obstacle) and non-stridents (without an obstacle). [Work supported by NIH.]
Catastrophe theory, caustics, and travel time diagrams
Authors: Brown Michael G. , Tappert Frederick D.
Published: October 2005

A commonly used technique in the analysis of broadband underwater acoustic wave data is to display the times of arrival of geometric rays as a function of position (typically range or depth). When caustics are present these travel time diagrams are multivalued functions of the position coordinate. Catastrophe theory may be used to classify these caustics. When the ocean properties vary as a function of depth or depth and range only and the waves are excited by a compact source then all of the caustics formed belong to the cuspoid family. The following result, which pertains to this situation, is proved: the locus of travel times of the geometric rays which form a cuspoid caustic of codimension n form a surface in the n + 1 dimensional space (t,x1,x2,…,xn) which is identical (after a stretching of coordinates) to the locus of singular points (the caustic surface) of the cuspoid caustic of codimension n + 1 in the (n + 1)-dimensional space (x1,x2,…,xn + 1). A consequence of this result is that any structurally stable travel time diagram corresponding to a one-dimensional ocean model must be a two-dimensional slice of one of the cuspoid caustics. Some of the implications of this result are discussed including how constraints imposed on travel time diagrams by catastrophe theory might be exploited in the inverse travel time problem.
Inversion of shallow water reciprocal transmission data to determine current profiles
Authors: DeFerrari H. A. , Williams N. J. , Ko D. S.
Published: October 2005

Acoustic reciprocal transmission geometries have been used to remotely measure fluctuations of ocean current and temperature. Usually, the travel time of a pulse is used as a measure of the integrated sound speed or current along a ray path. Reciprocal transmission experiments in the Florida Straits are characterized by refracted, bottom reflected rays making multiple bottom reflections resulting in a continuum of multipath arrivals. Owing to interference, distinct arrivals cannot be identified and used for travel time measurements. As an alternate method, we are comparing the phase differences for the upstream and downstream pulse arrival patterns. Modeling the sound channel with a linear sound speed profile, sloping bottom, we find that arrival time is linearly related to the average height of the rays above the bottom. Thus phase differences for upstream and downstream transmissions are proportional to depth average currents making possible a simplified inversion to obtain current profiles. At the time of this writing, we are attempting to demonstrate the method with existing data from recently completed experiments in the Florida Straits. Results of the data analysis will be presented along with the details of the models.
A comparison of parabolic equation predictions with reciprocal transmission measurements in the Florida Straits
Authors: Nghiem-Phu L. , DeFerrari H. A.
Published: October 2005

A parabolic equation model has been developed to study transmission in the Florida Straits and to interpret the results of reciprocal transmission experiments. The model source is both broadband and narrow beam. The bandwidth makes possible prediction of pulse arrival patterns and travel times. The narrow beam shows the path of sound energy between source and receiver. Both arrival times and sound paths are necessary to invert acoustic measurements to give oceanographic measurements of currents and water temperatures. Color graphic displays are used to demonstrate ray-type paths through the medium, using environmental data as inputs; model results are compared with results of pulse reciprocal transmission experiments for several geometries and range-dependent soundspeed profiles and bottoms.
A high-speed, compact, and interactive Parabolic Equation SOlution GENerator (PESOGEN) system
Authors: Nghiem-Phu Lan , Daubin Scott C. , Tappert Fred
Published: October 2005

A special purpose microcomputer to solve the parabolic approximation to the acoustic wave equation using the split step Fourier algorithm has been developed. The Parabolic Equation SOlution GENerator (PESOGEN) is a dedicated, fast, compact, and interactive computer system consisting of a host processor, a high-speed array processor, a graphic processor, and a color display monitor. PESOGEN is able to compute the acoustic field in a fully range dependent environment for both deep and shallow water scenarios with computational speed an order of magnitude faster than current mainframes such as the UNIVAC 1108. Transmission loss values are color contoured and are available as the solution is being generated, providing almost real time interaction with the acoustic modeler. Additional graphic capability includes transmission loss displayed as a function of range at any depth, bathymetry, and sound speed profiles superimposed on TL color contoured field. Typical throughput time for a deep ocean environment to cover 14 CZs ranges from 16 to 100 s. Sample outputs from the PESOGEN that clearly demonstrate acoustic energy distribution in the acoustic field are presented.
The numerical modeling of underwater acoustic wave propagation using finite element or finite difference methods
Authors: Goldstein Charles I. , Bayliss Alvin , Turkel Eli
Published: October 2005

The Helmholtz equation with wavenumber K in vector and scalar form describes a wide range of acoustic phenomena. As one example, the propagation of sound waves underwater in the presence of strong lateral variations in topography and sound speed must often be described by the Helmholtz equation since approximate propagation models can be inadequate. If the equation is discretized by a numerical scheme with mesh size h, the accuracy of this discretization is generally measured by the number of points/wavelength, 2π(Kh)−1. We show that Kh is not a good indicator of the accuracy of the discretization. If a scheme of order m is used, then we show that mean square errors depend on KL (Kh)m, where L is a measure of the size of the computational region. Thus for a standard second-order scheme, h ∼ (KL)−3/2 is required in order to maintain a fixed accuracy as K or L increases. This is a much more stringent requirement than the behavior h ∼ (KL)−1, which follows from using a fixed number of points/wavelength. Several practical consequences of this result will be enumerated. The result will be justified mathematically and illustrated by numerical examples for a model of underwater acoustic wave propagation. The numerical results will be obtained using an efficient iterative technique we have recently developed for solving the discrete equations.
Extraction of acoustic signatures from animal signals using a set of pattern discrimination techniques
Authors: Wheeler Leslie A. , Lefebvre Jacques , Wimitzky Michel
Published: October 2005

Acoustic recognition of individuals has been demonstrated experimentally in most, if not all, birds and mammals studied from this point of view. The investigator trying to identify the “acoustic signatures” on which recognition is based invariably finds what he seeks, sooner or later, depending on the degree of intra-individual variation in vocalizations compared to inter-individual variation. However, acoustic signatures brought out using analytical methods are not necessarily those used by the animals themselves. Such is the case for peach-faced lovebirds (Agapornis roseicollis). In an attempt to overcome this problem, we designed a set of pattern discrimination techniques which are based on previous psychoacoustic and neurophysiological data and whose validity could be tested experimentally. Our techniques exploit temporal evolution of energy spectrum density and comprise Fourier analysis, various standardization procedures, and three multivariate statistical analyses. Use of these techniques in further psychoacoustic and neurophysiological investigations, particularly those concerning the functioning of “complex” neurons, is discussed.
On validity of in situ sound intensity estimation
Authors: Mathur Gopal P.
Published: October 2005

In many noise control engineering applications, estimation of sound intensity in the nearfield of sound source under in situ measurement conditions is of considerable importance. This paper presents an analytical examination of statistical errors involved in estimation of sound intensity variables under in situ conditions. In view of the recent development of a stochastic theory for sound intensity method [G. P. Mathur, J. Acoust. Soc. Am. 74, 1752–1756 (1983)], results are first obtained for the new stochastic estimation procedures and a comparison is then made between finite difference based estimation procedures and stochastic estimation procedures of evaluating sound intensity variables. It is shown that unbiased in situ sound intensity estimates can be obtained using stochastic estimation procedures if the spatial correlations obtained from the two-microphone intensity probe conform to those typical of plane wave, periodic, or nonperiodic type stochastic processes. On the basis of results presented in this paper, a new stochastic criterion is thus evolved to check whether there will be significant errors in measuring sound intensity in a practical sound field.
A model for the cross spectra between pressure and temperature downstream of a combustor
Authors: Miles J. H. , Krejsa E. A.
Published: October 2005

Recently, measurements of pressure-temperature cross spectra were made in a duct downstream of a combustor to provide additional information beyond that available from pressure spectra and cross spectra measurements so that an appropriate source region model could be selected and to provide information on the physical mechanisms active at the combustion noise source. The model developed to interpret the measurements is presented and compared with the data. The results show good agreement with the data.
High resolution bottom backscatter measurements
Authors: Roderick W. I. , Dullea R. K. , Syck J. M.
Published: October 2005

Acoustic bottom backscattering measurements and the corresponding geoacoustic properties of the ocean bottom are presented for an experiment conducted in the shallow waters of the North Atlantic. The bottom scattering strength data, which were obtained with a high resolution (narrow beamwidth) parametric sonar, were measured as a function of frequency (5–20 kHz), grazing angle (4°–10°), azimuthal angle (± 55°), and pulse length (0.4–10 ms). The supporting environmental measurements included box cores for determining the acoustic properties of the sediment and stereo photography for calculating the two-dimensional roughness spectrum of the sea floor. [Work supported by NAVSEA 63R.]
High-frequency acoustic backscatter sea surface
Authors: Roderick W. I. , Dullea R. K. , Chester J. B.
Published: October 2005

A high resolution acoustic surface scattering experiment was conducted in the shallow waters of the North Atlantic. A narrow beam parametric array, which was rotatable in both azimuth and elevation, was utilized as a broadband high-frequency acoustic projector. Acoustic surface scattering data were obtained at normal incidence and low grazing angles (less than 10°) as a function of acoustic transmit frequency and sea state conditions. Meteorologic and oceanographic data were obtained in concert with the acoustic measurements and included wind speed and direction, ocean surface wave spectra and currents, and ocean sound speed. Surface back-scattering strength, Doppler spectra (shift and spread), and envelope statistics were some of the measured parameters. It will be shown that the Doppler spectra are approximately Gaussian and the spectral shift could be predicted from Bragg diffraction theory modified by the induced Doppler due to surface currents. At normal incidence, the surface loss varied 20 dB as the frequency changed from 5 to 80 kHz, under nearly constant sea surface conditions. [Work supported by NAVSEA 63R.]
Electrical tinnitus control
Authors: Shulman Abraham , Tonndorf Juergen
Published: October 2005

Tinnitus can be suppressed electrically in various ways: Grapengiesser (1801), Wreden (1887), Aran (1981), and Chouard (1981). The present portable instrument uses a new technique: audio frequencies that vary continuously but slowly between 0.2 and 20 kHz modulate a 60-kHz carrier. The combined signal (1.77 V rms, 5–6 mA) is applied to stainless-steel electrodes placed on both mastoids. Exposure starts with 1 h/day, increasing up to 5 h/day. It may be reduced again, once supression is achieved. This mode of control is currently tested on a number of patients, who complain of severe tinnitus. If results continue to be favorable (50%–60% success), this method appears to be superior to acoustic masking because (1) patients have no sensations during exposure, the signals being much below auditory or tactile thresholds, (2) simultaneous auditory inputs are neither masked nor attenuated, (3) the ear canals remain free, without irritation, and (4) “residual inhibition” (continued suppression after cessation of stimulation) lasts for several hours or even days, instead of minutes or a few hours, although suppression is not immediate, taking 2–5 h to take effect.
High-frequency audiometry
Authors: Tonndorf Juergen , Kurman Barbara
Published: October 2005

High-frequency hearing was routinely, although not very precisely, tested with the monochord, but this was no longer done after the advent of electronic audiometers. For many disorders, high-frequency losses were recently shown to precede losses in the speech frequencies. At f> 6–8 kHz, precalibrated earphones become increasingly unreliable. Replacing the air conduction input by bone conduction, generated by electrical inputs (fixed carrier signal of 60 kHz, modulated by audio signals) overcomes these difficulties. Electrodes, placed on the mastoid and on the forearm, are Mylar-coated to provide capacitive coupling, the subject becoming part of a tuned circuit. The nontest ear was being masked. Input voltage was kept constant at 1.77 V rms, since signal magnitude is mainly determined by current. For normal-hearing subjects, thresholds varied with frequency between 1 and 25 mA. The current required rose with about 130 dB/oct near the upper frequency limit, which for young adults was found at about 18 kHz, with testing limited at 30 mA for safety reasons. However, some subjects with upper limits as low as 11 kHz still showed “normal” air-conduction thresholds at 8 kHz.
Consequences of audiovisual asynchrony for speech perception: Implications for signal processing in aids to lipreading
Authors: McGrath Matthew , Summerfield Quentin
Published: October 2005

Audiovisual identification of sentences was measured as a function of audio delay in untrained listeners with normal hearing; the sound track was replaced by rectangular pulses originally synchronized to the closing of the talker's vocal folds and then subjected to delay. Although group-mean performance declined monotonically with delay, systematic decrements occurred only when delay exceeded 80 ms. A similar tolerance of delay was found in judgments of audiovisual onset time when observers determined whether a 120-Hz triangular wave started before or after the opening of a pair of liplike Lissajou figures. Group-mean 70% DLs were − 78 ms (sound leading) and + 137 ms (sound lagging). This result suggests, first, that most observers possess insufficient sensitivity to intermodal timing cues in audiovisual speech for them to be used analogously to VOT in auditory speech perception, and, second, that the effects found in the first experiment derive from syllabic rather than phonemic interference. However, the best lipreaders, who also gained most from the audio signal in that experiment, were affected by delays shorter than 80 ms. Accordingly, we suggest that signal processing in aids to lipreading should be allowed no more than 40 ms to do its work. Supported by a studentship from the TWJ Foundation.
Sound absorption by inhomogeneous porous layers
Authors: Burke Shawn
Published: October 2005

A three-dimensional governing equation is derived from first principles that describes the effect of an inhomogeneity of acoustical parameters in rigid, porous sound absorbers. The equation contains a scattering term expressed in terms of the gradient of the material's complex fluid density. An expansion of the equation for weak inhomogeneities yields a source component containing the perturbations, giving rise to a secondary scattered acoustic field in the material. The analysis is then specialized to the exact solution of the oblique incidence problem for plane waves striking a layer of such a material with arbitrary (but continuous) inhomogeneity in the direction normal to the layer's surface. This analysis is applicable to the description of wicking (or fouling) of porous absorptive treatments in industrial or aircraft applications. The transformed governing relation is solved numerically assuming the acoustical parameters vary linearly with space in a 2.54-cm layer of fiberglass. These results imply that the inhomogeneity degrades the layer's absorptive characteristics, as expected.
Theoretical study of the acoustical resistance of small orifices
Authors: Donato R. J.
Published: October 2005

The power dissipation produced by small holes to an incident sound field is important, for instance, in the design of hearing defenders and mufflers. No satisfactory theory for the acoustical resistance of a small hole in a thin plate appears to have been developed. A possible approach to the problem, using a variational technique, is presented for the linear region of small amplitudes.
Low-frequency sound absorption in air
Authors: Zuckerwar Allan J. , Meredith Roger W.
Published: October 2005

An extensive set of sound absorption measurements was taken in air over a range of frequency from 20–2500 Hz, of temperature from 20°–50 °C, and of relative humidity from 0.3%–100%. Over the lower portion of this frequency range, where relaxation in N2 is prominent (except in very dry air), prior measurements are scanty. This study yielded the following conclusions: (1) The humidity dependence of the relaxation frequency of N2 differs in air from that in binary N2-H2O gas mixtures (246-Hz/atm. mole % in air vs 184-Hz/atm. mole % in binary mixtures at 20 °C). (2) The temperature dependence of the relaxation frequency of N2 is the same in air as in binary mixtures. (3) At low humidities (∼0.01% mole ratio), where relaxation in O2 dominates sound absorption in air, the measured relaxation frequencies of O2 agree with those reported by Harris and Tempest [J. Acoust. Soc. Am. 36, 2390–2394 (1964)] and lie substantially lower than specified by ANSI Standard S1.26-1978.
Gain and efficiency of a short traveling wave heat engine
Authors: Ceperley Peter H.
Published: October 2005

Gain and efficiency equations are derived and evaluated for a traveling wave heat engine having a regenerator of short length compared with an acoustic wavelength. A traveling wave heat engine is a modified Stirling engine in which acoustic waves replace the usual pistons and energy is transferred between thermal and acoustic forms, depending on the wave direction [P. H. Ceperley, J. Acoust. Soc. Am. 66, 1508–1513 (1979)]. This paper is similar to another paper on gain and efficiency [P. H. Ceperley, J. Acoust. Soc. Am. 72, 1688–1694 (1982)] except that the present paper assumes that the wave impedance is not determined by the regenerator's properties, but instead by the acoustic circuit exterior to the regenerator. For acoustic impedance of freely propagating traveling waves in air, the efficiency is limited to 11% of Carnot efficiency due to visious heating in the regenerator. This can be greatly increased by going to higher impedances; e.g., 79% is possible at ten times greater impedance.
Sound propagation phenomena relevant to prediction schemes
Authors: Embleton Tony F. W.
Published: October 2005

Interference between direct and reflected waves can produce a shadow region near the ground because most ground surfaces have a detectably finite acoustic impedance. In a steady isotropic atmosphere this region is penetrated at low frequencies by a ground wave, especially at short ranges, or by a trapped surface wave, significant at longer ranges. The thickness and flow properties of surface layers, (e.g., snow) also affect the propagation of low frequencies near the surface. For ground having impedance discontinuities (e.g., asphalt/grass) diffracted waves originated at the interface. Diffraction theory allows prediction of sound pressures in the shadow region behind thin barriers and has been applied to thick barriers, multiple barriers, and ground surfaces of various shapes. In a downward-refracting atmosphere, such as propagation downwind or in a temperature inversion, the shadow region is diminished: conversely, in upward refraction, a refractive shadow reinforces the ground impedance shadow region. Wind and temperature fluctuations (turbulence) cause sound energy to be redirected by scattering or variable refraction: this occurs most noticeably at high frequencies and where coherent theory would otherwise predict reduced sound pressure levels. For most of these phenomena quantitative agreement has been achieved between measurements and predictions of the relevant theory: however, the situation in real life is complicated by the fact that several effects usually coexist.
Quantitative sound exposure level spectra of some sonic booms
Authors: Young Robert W.
Published: October 2005

The spectrum of a continuing sound pressure waveform often supplied by a digital spectrum analyzer can be interpreted as a spectrum of time-mean-square sound pressure during a sample time window T, within a succession of “bins” whose frequency width is b = 1/T. But a time-mean-square sound pressure during a time window that is not filled by a transient, is not an appropriate measure of the transient. The quantity needed is the time integral of squared, somehow frequency-weighted, sound pressure; this time integral is called sound exposure. Sound exposure per unit bandwidth (sound exposure spectral density) can be calculated by multiplying by T the time-mean-square sound pressure during T in bin b, and dividing by b. The practical form of this is sound exposure\ spectrum level (1-Hz SEL). Sound exposure per unit bandwidth can be integrated over the wide passband of the transient; the practical form of the integral is flat sound exposure level (TSEL). Frequency weightings such as A can be applied before integration; the practical form of the integral is A-weighted sound exposure level (ASEL). Quantitative spectra of more than a dozen sonic booms are here reported, which have been measured by procedures just described. For example, the 150-ms wave of an F-15 aircraft maneuvering at Mach 1.1, at a slant range of 35 km caused TSEL = 116.1 dB; ASEL = 82.9 dB. Reference sound exposure is E0 = (20 μPa)2⋅1 s. The 96-ms N wave of an F-15 aircraft maneuvering at Mach 1.2, at a slant range of 9 km caused TSEL = 120.5 dB; ASEL = 93.6 dB.