bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of iterative deconvolution for scattering function identification
Authors: Johnson Blane L. , Ricker Dennis W. , Sacha John R.
Published: October 2005

A deconvolution technique utilized in image restoration is applied to the problem of estimating the scattering function of a communication channel. Under wide sense stationary and uncorrelated scattering (WSSUS) conditions, the expected matched filter output is equal to the two-dimensional convolution of the scattering function with the ambiguity function of the interrogating waveform. This convolution process introduces a known blur, the ambiguity function of the transmitted signal, which can be partially removed using a constrained iterative deconvolution technique. A preprocessed matched filter output is used to lessen the amount of unwanted additive noise that is incorporated into the deconvolution process. In the no-constraint case, it is equivalent to the practice of performing a pseudoinversion using a truncated singular value decomposition (SVD). This particular preprocessed image effectively combines the truncated SVD and Van Cittert deconvolution schemes.
Ultrasonic spectroscopy of metallic spheres using electromagnetic-acoustic transduction
Authors: Johnson Ward L. , Norton Stephen J. , Bendec Felix , Pless Robert
Published: October 2005

An ultrasonic technique for studying vibrational resonant modes of metallic spheres is presented. The technique employs electromagnetic-acoustic transduction with a configuration consisting of a sample surrounded by a coil in a static magnetic field. Resonance spectra from 0.5 to 4.5 MHz with the coil axis parallel and perpendicular to the magnetic field are measured for a 3.145-mm-diam sphere of polycrystalline 2024 aluminum. Elastic constants calculated from the resonant peak frequencies are consistent with results obtained using an ultrasonic pulse-echo system. This new technique has advantages over pulse-echo and conventional resonance techniques for experiments where high absolute accuracy is necessary or where samples are heated far above room temperature.
Ultrasonic measurement of stress in weakly anisotropic thin sheets
Authors: Man Chi-Sing , Lu Wei-yang , Gu Qun , Tang Wenliang
Published: October 2005

A membrane theory is developed for measurement of stress in weakly anisotropic thin sheets. The thin sheets are modeled as prestressed planar membranes, and the application in stress evaluation of horizontally polarized quasishear waves (which correspond to the SH0 mode in a plate theory) is studied. In principle, the acoustoelastic theory presented here would be valid so long as the superimposed small-amplitude stress waves could be taken as hyperelastic, irrespective of the origin of the prestress and the thermomechanical history of the specimen in question. A series of experiments was performed to examine the validity of this theory for thin aluminum sheets that had undergone plastic deformations. By using a probe that consisted of three electromagnetic acoustic transducers (one transmitter and two receivers that were 30 mm apart), velocities of horizontally polarized quasishear waves were measured for various directions of propagation at various places of each sample sheet. There were indications that the present theory and measurement system delivered at each place a good estimate of the local principal surface-stress directions and difference in principal surface stresses. Some of the samples were annealed after the aforementioned experiments were completed. Ultrasonic measurements were repeated for the annealed samples; they showed that residual stresses were relieved by the annealing.
Free vibration of a sagged cable supporting a discrete mass
Authors: Cheng S.-P. , Perkins N. C.
Published: October 2005

A continuum model is presented that describes the nonlinear and three-dimensional response of an elastic cable that supports a single attached mass. Two asymptotic forms of this model are derived for the free, linear response of sagged suspensions having small equilibrium curvature (sag) and level supports. The first model, which is valid for relatively small attached masses, assumes that the cable stretches quasi-statically and results in uniform dynamic cable tension. The quasi-static stretching assumption is partially relaxed in the second model, which accounts for spatially varying dynamic tension in an approximate manner. In particular, the second model captures the discontinuous change in dynamic tension across the attached mass and the resulting tangential mass acceleration. The eigensolutions governing free response are compared for the two models. The comparison reveals that the first (simpler) model provides excellent approximations to the natural frequency spectrum for all cable modes having natural frequencies less than that of an (approximate) elastic mode.
Felt pad vibration properties and design criteria
Authors: Dunlop John I.
Published: October 2005

A new technique has been developed to measure the dynamic modulus and damping constants of felt pads in the frequency range 100–300 Hz under compression pressures up to 130 kPa. The technique makes use of a supported vibrator mass system and has been used to investigate the dynamic mechanical properties of felt pads of initial densities 130–230 kg/m3. The values of dynamic modulus observed were found to be in good agreement with those predicted from fiber mass compression theory and the dynamic modulus was found to decrease with increasing amplitude of vibration displacement and to be approximately linearly related to pressure loading. This latter relationship offers the opportunity of specifying design criteria for felt pads in such applications as resilient mounts. The damping loss was observed to be independent of frequency, but to increase with increasing amplitude of vibration. The damping was characterized by a constant loss angle, or tan δ, which ranged up to 0.1 depending on the pressure loading used, being generally lower at the higher pressures.
Sonic band structure in fluids with periodic density variations
Authors: Dowling Jonathan P.
Published: October 2005

In direct analogy to the electronic band structure found in semiconductors and the photonic bands for light in a medium with a periodic dielectric constant, a periodic density variation in a fluid can give rise to sonic frequency passbands and band gaps. Hence, a fluid medium can be constructed that prohibits sound propagation at certain frequencies while allowing practically free propagation at others. The effect of a sonic band medium on a monopole acoustic source is discussed in a simple one-dimensional model. In particular, the complete quenching of radiated power is seen for a harmonic radiator at a frequency that corresponds to a band gap—in analogy with a similar effect that is predicted for the atomic emission of electromagnetic waves in a photonic band structure. The ability to construct a medium that selectively prohibits sound propagation and emission in a certain range of frequencies, while allowing transmission and enhanced radiation rates at others, could have interesting practical applications.
Finite-amplitude wave propagation through a two-phase system of particles in a viscothermal fluid
Authors: Benharbit Abdelali , Margulies T. S. , Schwarz W. H.
Published: October 2005

The propagation of finite-amplitude, planar acoustic waves through a system of nonvolatile fluid particles dispersed in a fluid matrix has been examined theoretically by using the continuum volume-averaged balance equations and linear constitutive equations for a two-phase fluid system having a single variable temperature. These equations contain more information than those introduced by Marble [Ann. Rev. Fluid Mech. 2, 379–447 (1970)], and used by other workers to determine the attenuation and dispersion of sound propagating through a dilute dusty perfect gas. Specifically, terms that account for phoresis of the particles due to thermal and concentration gradients; Dufour heat transport; and the particles’ contribution to the viscous effects are included. We have manipulated the acoustic equations using the methods developed by previous investigators, and obtained coupled Burgers’ equations; one for each phase. In the limit of very small concentration of particles, these equations reduce to those obtained by G. A. Davidson [J. Sound Vibration 38, 475–495 (1975)]. Solutions to the equations were determined by expanding the velocity field in a regular perturbation series in terms of the acoustic Mach number. The attenuation and dispersion of the first- and second-order harmonic terms are presented. These results are not restricted to a perfect gas and should be applicable to semi-concentrated emulsions, suspensions, and aerosols.
Two-sensor power measurements in lossy ducts
Authors: Fusco Andrew M. , Ward William C. , Swift Gregory W.
Published: October 2005

Theory and measurements of the use of two adjacent pressure sensors to measure acoustic power flow of a simple harmonic sound wave in a duct are presented. This theory differs from the usual intensity-times-area formulation of this problem by including the phase shift between pressure gradient and velocity, which is caused by viscous drag on the gas at the duct wall. For high standing-wave ratios, the power obtained by this method differs significantly from the product of mid-duct intensity and duct area. These measurements confirm the method to an accuracy of 5%, even at high amplitudes where the acoustic flow is turbulent and the theory might not necessarily be valid.
A comparison of Shannon entropy versus signal energy for acoustic detection of artificially induced defects in Plexiglas
Authors: Hughes Michael S.
Published: October 2005

An experimental comparison of scanned images formed from Shannon entropy, total energy, and log energy measurements of acoustic wave propagation in a Plexiglas bar with drill-hole ‘‘defects’’ shows that Shannon entropy, in the instance investigated, is approximately two to three times as sensitive to the presence of small defects than are the two energy measures. This suggests that the Shannon entropy technique may be useful for flaw detection in materials that are too thick or lossy for the conventional use of acoustic energy for flaw detection.
Reference equivalent threshold levels for the Handtronix, Oto-Screenert
m
Authors: Alvord Lynn S. , Davenport Tim
Published: October 2005

Reference equivalent threshold sound-pressure levels (RETSPL) are determined for a new hearing screening device, the Handtronix, Oto-Screenertm Typical loudness balancing procedures result in calibration values for the device on a standard 6-cc artificial ear. Applying the RETSPL to various typical screening levels results in listed calibration levels for the device for various screening intensities.
Articulatory and social factors influence the acoustic structure of rhesus monkey vocalizations: A learned mode of production?
Authors: Hauser M. D.
Published: October 2005

This report presents results that show that the acoustic structure of the ‘‘coo’’ vocalization of rhesus macaques (Macaca mulatta) varies between members of different matrilines. In the case examined, members of one matriline produce coos that are acoustically distinctive from all other matrilines and the difference is primarily due to spectral dampening and the presence of energy bands between the primary harmonics of the call. Perceptually, these acoustic modifications lead to what human listeners hear as a ‘‘nasal’’ utterance, suggesting the possibility of supralaryngeal filtering. Moreover, because nasal-sounding coos were only produced by members of one matriline, learning may be the primary cause of such intrafamilial similarities.
Determining the extinction cross section of aggregating fish
Authors: Foote Kenneth G. , Ona Egil , Toresen Reidar
Published: October 2005

When fish are aggregated over a flat bottom, and fish and bottom echoes can be distinguished, it is possible to determine the fish extinction cross section by a simple application of the echo integration method. The theory for this is developed. Measurements at 38 kHz are presented for aggregations of the same 1983-year class of herring over flat-bottomed fjord areas in 1988, 1990, and 1991. The ratio of extinction and backscattering cross sections is found to lie in the approximate range from 1.2–2.3, depending on fish size and time of day.
Sound propagation in SiO2 aerogels
Authors: Gross J. , Fricke J. , Hrubesh L. W.
Published: October 2005

The longitudinal sound velocity vL of pure SiO2 aerogels with densities in the range of 5 to 500 kg m−3, either made from TEOS (tetraethoxysilane), TMOS (tetramethoxysilane), or waterglass was measured. The variation of vL with density ρ for evacuated aerogels is more complex than described earlier: The simple scaling law vL∝ρα, with α=1.3, only holds for ρ>100 kg m−3; below this density α≊0.8 is valid. Data are also collected for sintered SiO2 aerogels. For specimens with densities around 100 kg m−3 or below, sound velocity measurements under variation of air pressure have also been performed. The dependence of the sound velocity on air pressure can be correctly described by a simple theory involving quasi-isothermal compression of the gas within the pores. From these findings a reliable method to determine the macroscopic aerogel density is derived.
Resonance decomposition for the vibratory response of a viscoelastic rod
Authors: Jimeno-Fernandez Isabel , Überall H. , Madigosky W. M. , Fiorito R. B.
Published: October 2005

The vibratory response of a driven viscoelastic rod has been used in earlier investigations to measure the complex elastic modulus of the rod material. The transfer function T, i.e., the ratio of displacements (or accelerations) at the end of the rod divided by those at the driven end, is obtained as a function of frequency and rod length. In terms of these variables, it exhibits resonance peaks. In the present work, following the developments of Fiorito et al. [J. Acoust. Soc. Am. 79, 222 (1986)], the transfer function is represented as a meromorphic function of the frequency with complex poles, in order to isolate the individual resonances. Such a representation allows a clean determination of resonance frequencies and widths, and thus leads to a more sensitive measurement of the complex elastic modulus of the rod material. Comparison of exact theory and this resonance theory formulation of T is presented for various rod materials.
Object classification and acoustic imaging with active sonar
Authors: Kelly James G. , Carpenter Robert N. , Tague John A.
Published: October 2005

The theoretical underpinnings of underwater acoustic classification and imaging using high-frequency active sonar are studied. All essential components of practical classification systems are incorporated in a Bayesian theoretic framework. The optimum decision rules and array processing are presented and evaluated. A systematic performance evaluation methodology is derived. New results quantify the relationship between classifier performance and object geometry, acoustic imaging, and the accuracy of a priori knowledge infused into the processor.
Effect of ear-canal air pressure on evoked otoacoustic emissions
Authors: Naeve Susan L. , Margolis Robert H. , Levine Samuel C. , Fournier Eric M.
Published: October 2005

The effect of ear-canal air pressure on click-evoked otoacoustic emissions was measured for pressures ranging from 200 to −200 daPa and stimulus levels ranging from 60–90 dB PeSPL. Positive and negative ear-canal pressures (relative to ambient pressure) reduced the emission amplitude by 3–6 dB. A spectral analysis of the emissions revealed that the effect of ear-canal air pressure is that of a high-pass filter with a cutoff frequency of 2600 Hz and a slope of 4 dB/oct. The spectral changes are the expected effect of an increase in stiffness of the middle ear and were independent of pressure polarity and click level. Ear-canal air pressure substantially reduced the reproducibility of the emission waveform, in many cases rendering the emission indistinguishable from background noise. The implication of these findings for hearing screening applications is that a high false alarm rate may occur in normal-hearing patients with intratympanic air pressures that are significantly different from ambient pressure.
Reflection and transmission coefficients in fluid-saturated porous media
Authors: Santos Juan E. , Corbero Jaime M. , Ravazzoli Claudia L. , Hensley Jeffrey L.
Published: October 2005

Using Biot’s theory to describe the propagation of elastic waves in a fluid-saturated porous elastic solid (a Biot medium), the reflection and transmission coefficients were computed at a plane interface between a fluid and a Biot medium and at interfaces inside a Biot medium defined by either a change in saturant fluids or in the intrinsic rock permeability. The reflection and transmission coefficients were computed with and without the inclusion of a frequency correction factor that according to Biot has to be introduced in the equations above a certain critical frequency (‘‘frequency-dependent’’ versus ‘‘classic model’’). For a fluid–Biot medium interface and in the range 5 kHz–10 MHz for the example analyzed the two models show differences of the order of 11% for the reflection coefficients and between 11% and 31% for the type I, type II, and shear transmission coefficients. For the interfaces within a Biot medium, and for type II incident waves, in the same range of frequencies the cases examined showed differences in the reflection and transmission coefficients in the range 5%–80%. Because of the asymptotic properties of the frequency correction factor, the reflection and transmission coefficients coincide at very low and high frequencies. The analysis shows the importance of the inclusion of the frequency correction factor in analyzing wave propagation in Biot media for frequencies lying between the seismic and ultrasonic ranges.
Acoustic wave propagation in a fluid-filled borehole drilled in an unbounded viscoelastic medium
Authors: Yu Shoumian , Yu Tian
Published: October 2005

The problem of acoustic wave propagation in a fluid-filled borehole drilled in an unbounded viscoelastic medium excited by a point source on the axis is solved in the lowest order of approximation when the viscosity is much smaller than the elasticity. The fluid inside the borehole is assumed to be inviscid. Decay constants for various wave types are obtained. They are all proportional to ω2. The full wavetrain of the Green’s function (the fundamental solution) is derived and the space-time waveform plotted. The spectra of head waves are discussed in detail. The influence of the source spectrum on the full wavetrain is described only qualitatively. The spectrum of a full wavetrain observed by a long spaced logging tool in a production borehole is presented to show the general feature mentioned in the text.
Analysis of acoustic scattering in fluids and solids by the method of fundamental solutions
Authors: Kondapalli Prasanna S. , Shippy David J. , Fairweather Graeme
Published: October 2005

The method of fundamental solutions (MFS) is a boundary method for the numerical solution of certain elliptic boundary value problems. In the MFS, the approximate solution is a linear combination of fundamental solutions of the governing partial differential equation, with singularities placed outside the domain of the problem. In the present paper, the MFS is applied to acoustic scattering in fluids. The singularities are allowed to move during the solution process from arbitrary locations to more optimal locations. Numerical results demonstrate that the ‘‘fictitious eigenfrequency’’ difficulty encountered with the boundary element method (BEM) is not present in the MFS. In addition, MFS results obtained by the use of fixed singularities are presented for scattering of waves in elastic solids.
Midfrequency enhancement of the backscattering of tone bursts by thin spherical shells
Authors: Zhang L. G. , Sun N. H. , Marston P. L.
Published: October 2005

A broad enhancement of the form function f(ka) for steady-state backscattering by thin spherical shells in the midfrequency range has been noted by several investigators. Consequences of this enhancement on the backscattering of tone bursts are investigated with a Fourier synthesis of the temporal response from the exact f(ka). The emphasis is on incident bursts that are sufficiently short so that scattering consists primarily of distinct echoes associated with the specular reflection and different circumnavigations of a dominant surface guided wave. That wave lies on the subsonic branch of the lowest antisymmetric Lamb mode for a fluid-loaded shell designated as a0− by some authors. A ray method, previously verified for echo amplitudes from leaky (or supersonic) Lamb waves on thick shells [S. Kargl and P. Marston, J. Acoust. Soc. Am. 85, 1014–1028 (1989)], is generalized to subsonic waves. The ray method well approximates echo amplitudes from the Fourier synthesis provided the incident burst is sufficiently long that effects of dispersion are weak. Over a broad frequency range, the amplitude of the earliest a0− echo is enhanced relative to the specular echo. For the 2.5% thick stainless steel shell in water considered, the enhancement factor peaks near ka≊46 where the amplitude ratio ≊3.1. The ray theory suggests that the peak ratio depends only weakly on shell thickness and material parameters provided certain conditions hold. The a0− wave is also found to contribute a prominent wave packet to the far-field impulse response of the shell. The radiation damping and velocity of relevant surface waves were computed from the complete elastic equations and those results may be helpful for testing thin shell approximations near the coincidence frequency.
Comments on ‘‘Particle gathering and microstreaming near ultrasonically activated gas-filled micropores’’[J. Acoust. Soc. Am. 84, 1378–1387 (1988)]
Authors: Katz J. I.
Published: October 2005

It is suggested that surface forces on small particles may be important in particle gathering experiments. These forces may explain the observations of Miller [J. Acoust. Soc. Am. 84, 1378–1387 (1988)] that particles accumulate on the surface of a membrane containing ultrasonically activated gas-filled micropores, whether the particles are more or less dense than the fluid medium.
Analysis and performance of a large thermoacoustic engine
Authors: Swift G. W.
Published: October 2005

Measurements and analysis of a 13-cm-diam thermoacoustic engine are presented. At its most powerful operating point, using 13.8-bar helium, the engine delivered 630 W to an external acoustic load, converting heat to delivered acoustic power with an efficiency of 9%. At low acoustic amplitudes, where (linear) thermoacoustic theory is expected to apply, measurements of temperature difference and frequency agree with the predictions of theory to within 4%, over conditions spanning factors of 4 in mean pressure, 10 in pressure amplitude, 6 in frequency, and 3 in gas sound speeds. But measurements of the square of pressure amplitude versus heater power differ from the predictions of theory by 20%, twice the estimated uncertainty in the results. At higher pressure amplitudes (up to 16% of the mean pressure), even more significant deviation from existing thermoacoustic theory is observed. Several causes of this amplitude-dependent deviation are identified, including resonance-enhanced harmonic content in the acoustic wave, and a new, first-order temperature defect in thermoacoustic heat exchangers. These causes explain some, but not all, of the amplitude-dependent deviation of the high-amplitude measurements from existing (linear) theory.
Determination of sound speed in biological tissues based on frequency analysis of pulse response
Authors: Hachiya Hiroyuki , Ohtsuki Shigeo , Tanaka Motonao , Dunn Floyd
Published: October 2005

The sound speed in biological tissues provides important diagnostic and treatment planning information. Conventional methods of sound-speed determination generally require that transducers make physical contact with specimens in order to measure thickness and travel time in the time domain. The physical contact may cause deformation and affect blood flow and the measurement of travel time in the time domain may be sensitive to waveform distortion due to tissue inhomogeneity and surface roughness. A method for determination of the sound speed is proposed in which the sound travel time in the sample and the difference in total travel time from the transducer to the rigid reflector due to the presence of the sample are estimated in the frequency domain and which does not require physical contact of ultrasonic probes to living or freshly excised tissue specimens. Ultrasonic speed measurements in silicone rubber and acrylic resin specimens verified the method validity. The standard deviation of the measurements over a 10-×10-mm area is less than 4 m/s. Sound-speed distribution measurements of porcine muscle are in agreement with previously published results.
Acoustic bedload velocity estimates using a broadband pulse–pulse time correlation technique
Authors: Sutton Don W. , Jaffe Jules S.
Published: October 2005

A novel noninvasive instrument for measuring bedload velocity has been developed using a narrow beam, high-frequency underwater sonar system. Pulsed wideband signals centered at 2.2 MHz are used to insonify a bedload at a 30-deg grazing angle. Under these conditions the fine structure of the returned signals is dependent on the inter-particle spatial relation of the bedload particles within the acoustic beam. A cross correlation of two consecutive backscattered waveforms is used to obtain an estimate of the inter-pulse translation of the bed. This permits a maximum likelihood estimate of the velocity of the bedload. The results from a series of static experiments in which agar embedded sand was translated a precise distance showed an excellent correlation between measured and estimated translations using the signal processing method. In a set of dynamic experiments, the velocity of a jet-driven bedload was estimated with a standard deviation in the estimates of approximately 5%. These were found to be in good agreement with independent video camera estimates.
The time course and magnitude of perceptual acclimatization to frequency responses: Evidence from monaural fitting of hearing aids
Authors: Gatehouse Stuart
Published: October 2005

At high presentation levels, normally aided ears yield better performance for speech identification than normally unaided ears, while at low presentation levels the converse is true [S. Gatehouse, J. Acoust. Soc. Am. 86, 2103–2106 (1989)]. To explain this process further, the speech identification abilities of four subjects with bilateral symmetric sensorineural hearing impairment were investigated following provision of a single hearing aid. Results showed significant increases in the benefit from amplifying speech in the aided ear, but not in the control ear. In addition, a headphone simulation of the unaided condition for the fitted ear shows a decrease in speech identification. The benefits from providing a particular frequency spectrum do not emerge immediately, but over a time course of at least 6–12 weeks. The findings support the existence of perceptual acclimatization effects, and call into question short-term methods of hearing aid evaluation and selection by comparative speech identification tests.
Acoustic and perceptual effects of changes in vocal tract constrictions for vowels
Authors: Gay T. , Boé L-J. , Perrier P.
Published: October 2005

The purpose of this study was to use vocal tract simulation and synthesis as means to determine the acoustic and perceptual effects of changing both the cross-sectional area and location of vocal tract constrictions for six different vowels: Area functions at and near vocal tract constrictions are considered critical to the acoustic output and are also the central point of hypotheses concerning speech targets. Area functions for the six vowels, [i], [a], [u], [q], [1], and [c] were perturbed by changing the cross-sectional area of the constriction (Ac) and the location of the constriction (Xc). Perturbations for Ac were performed for different values of Xc, producing several series of acoustic continua for the different vowels. Acoustic simulations for the different area functions were made using a frequency domain model of the vocal tract. Each simulated vowel was then synthesized as a 1-s duration steady-state segment. The phoneme boundaries of the perturbed synthesized vowels were determined by formal perception tests. Results of the perturbation analyses showed that formants for each of the vowels were more sensitive to changes in constriction cross-sectional area than changes in constriction location. Vowel perception, however, was highly resistant to both types of changes. Results are discussed in terms of articulatory precision and constriction-related speech production strategies.
Speech changes following reimplantation from a single-channel to a multichannel cochlear implant
Authors: Economou Alexandra , Tartter Vivien C. , Chute Patricia M. , Hellman Sharon A.
Published: October 2005

The speech of a postlingually deafened preadolescent was recorded and analyzed while a single-electrode cochlear implant (3M/House) was in operation, on two occasions after it failed (1 day and 18 days) and on three occasions after stimulation of a multichannel cochlear implant (Nucleus 22) (1 day, 6 months, and 1 year). Listeners judged 3M/House tokens to be the most normal until the subject had one year’s experience with the Nucleus device. Spectrograms showed less aspiration, better formant definition and longer final frication and closure duration post-Nucleus stimulation (6 MO. NUCLEUS and 1 YEAR NUCLEUS) relative to the 3M/House and no auditory feedback conditions. Acoustic measurements after loss of auditory feedback (1 DAY FAIL and 18 DAYS FAIL) indicated a constriction of vowel space. Appropriately higher fundamental frequency for stressed than unstressed syllables, an expansion of vowel space and improvement in some aspects of production of voicing, manner and place of articulation were noted one year post-Nucleus stimulation. Loss of auditory feedback results are related to the literature on the effects of postlingual deafness on speech. Nucleus and 3M/House effects on speech are discussed in terms of speech production studies of single-electrode and multichannel patients.
Middle-ear phenomenology: The view from the three windows
Authors: Shera Christopher A. , Zweig George
Published: October 2005

To provide a common ground for the comparison between theory and experiment, this paper presents a framework for the phenomenological description of middle-ear mechanics. The framework defines those measurements sufficient to characterize the transduction properties of the middle ear and its components. Phenomenological equations are represented in the form of an equivalent electrical circuit that can be used to deduce testable relations among measurable quantities. Two applications are then discussed. First, the classical concept of the middle-ear transformer ratio is generalized to include any effects of eardrum flexion or nonrotational ossicular motion. Middle-ear models predict that the resulting transformer ratios vary considerably with frequency. Second, the conditions under which the topology of existing circuit analogs satisfactorily approximates middle-ear mechanics are given. Most middle-ear models cannot be used to correctly predict the absolute pressures in the cochlea.
An empirical bound on the compressibility of the cochlea
Authors: Shera Christopher A. , Zweig George
Published: October 2005

Effects of a possible inner-ear compressibility on middle-ear transfer functions are explored and a small upper bound on the magnitude of that compressibility established. Consequently, the traditional two-port representation of middle-ear mechanics remains valid to within a few percent. If the compressibility of the cochlea is small but finite, a simple phenomenological model of that compressibility correctly predicts hearing thresholds in the ‘‘middleless’’ ear at low frequencies. Experiments to establish the value of cochlear compressibility and to explore further its possible contributions to residual hearing in patients with missing or disarticulated middle-ear ossicles are suggested.
Temporal structure model of binaural masking level difference
Authors: Albeck Yehuda , Nebenzahl Isaiah , Lewis Aaron
Published: October 2005

It is shown that a simple cross-correlation model is not adequate to explain both binaural masking level difference (MLD) and spatial selective attention. The reason is that for a low-intensity signal in NoSπ condition the maximal activity in the binaural analyzer as a function of interaural delay in single spectral channel is independent of signal intensity. On the other hand, if detection ability is associated with the isolation of tonically firing units, MLD is simply explained as the increase in firing synchronization as a function of the signal’s interaural phase difference (IPD). Quantitatively results are presented based on numerical solutions of the model.
Musical fundamental frequency tracking using a pattern recognition method
Authors: Brown Judith C.
Published: October 2005

In a recent article [J. C. Brown, ‘‘Calculation of a Constant Q Spectral Transform,’’ J. Acoust. Soc. Am. 89, 425–434 (1991)], the calculation of a constant Q spectral transform that gives a constant pattern in the log frequency domain for sounds with harmonic frequency components has been described. This property has been utilized in calculating the cross-correlation function of spectra of sounds produced by musical instruments with the ideal pattern, which consists of one’s at the positions of harmonic frequency components. Therefore, the position of the best approximation to the ‘‘ideal’’ pattern for the spectra produced by these instruments has been determined, and in so doing the fundamental frequency for that sound has been obtained. Results are presented for scales produced by the piano, flute, and violin as well as for arpeggios played by a wide variety of instruments.
Optimal placement of piezoelectric actuators and polyvinylidene fluoride error sensors in active structural acoustic control approaches
Authors: Clark Robert L. , Fuller Chris R.
Published: October 2005

Optimization of the location of a rectangular piezoelectric actuator and both the size and location of a rectangular surface strain error sensor constructed from polyvinylidene fluoride (PVDF) for active structural acoustic control (ASAC) is studied in this work. An algorithm is proposed for choosing the optimal actuator/sensor configuration for controlling sound from a baffled simply supported plate excited harmonically, and the resulting acoustic response is predicted from analytical models. These results are compared to those measured in the lab on a test rig duplicating the appropriate boundary conditions and situated in an anechoic chamber. Results from a single optimally located control actuator are compared to those from control with a nonoptimally positioned actuator as well as multiple control actuators. In addition, either microphones are used to provide error information in the test cases or a single optimally located and dimensioned PVDF error sensor is implemented as the cost function. Results from this study indicate that optimization of control actuators and error sensors provides a method for realizing adaptive structures for active structural acoustic control (ASAC), rivaling in importance the performance increases gained when acoustic control is achieved with microphone error sensors and multiple control actuators.
A model reference approach for implementing active structural acoustic control
Authors: Clark Robert L. , Fuller Chris R.
Published: October 2005

A model reference active structural acoustic control (ASAC) approach is investigated as a method for replacing microphone error sensors located in the acoustic field with accelerometers located on the structure. The suggested controller is the multi-input/multi-output adaptive LMS algorithm. As opposed to driving the response of the sensor located on the structure to zero with the control inputs, the response is driven to some pre-determined ‘‘reference’’ value corresponding to an a priori training cost function, which is originally chosen to minimize either the far-field pressure at a number of acoustic field points, or the supersonic region of the wave-number transform. In effect, the uncontrolled structure is adaptively modified to behave like the reference structure. Results indicate that the identical optimal control solution can be obtained when implementing the structural sensors, and the required number of sensors must simply equal the number of control actuators. In addition, for the example studied here, significant reduction in far-field sound radiation can be achieved even when errors of ±5% are present in the reference model. A considerable level of attenuation in sound can also be achieved for a band of frequencies within ±5% of the reference frequency used to obtain the models for creating the disturbance. Thus it appears that the model reference approach is reasonably robust.
Auditory filter bandwidths as a function of level at low frequencies (125 Hz–1 kHz)
Authors: Rosen Stuart , Stock Daphne
Published: October 2005

Auditory filter bandwidths were measured using the symmetric notched-noise method in five normally hearing listeners at four masker levels (40–70 dB SPL/Hz in 10-dB steps) and four probe frequencies (125–1000 Hz in octave steps). Accurate stimulus spectrum shape and level were ensured by use of a headphone monitoring technique. Auditory filter bandwidths decreased with decreasing frequency from 1 kHz down to 125 Hz. On the whole, bandwidths increased with increasing level, but the effect of level on bandwidth was greater as frequency increased, with little or no effect of level at 125 Hz. Insofar as the results from the notched-noise method reflect basilar membrane vibration patterns, basilar membrane mechanics appear to become less nonlinear as one approaches the apex of the cochlea.
Use of sound-pressure level in auditory distance discrimination by 6-month-old infants and adults
Authors: Litovsky Ruth Y. , Clifton Rachel K.
Published: October 2005

Six-month-old infants have been found to respond differentially to sounding objects placed within reach and beyond reach when no visual cues were available. The goal of the present study was to investigate whether sound-pressure level (SPL) serves as an auditory cue in distance discrimination. Thirty-two 6-month-olds were presented with recordings of sounding objects first in the light at midline position, then in the dark at 45° to the right and left. On half of the dark trials the object was near (15 cm), and on half it was far (100 cm). For the control group the near sound was naturally 7 dB louder than the far. The experimental group had SPL counterbalanced across near and far locations to provide an inconsistent cue. Measures of infant reaching were scored from videotape. Two groups of adults were run under similar conditions; adults were tested on reaching as well as verbal reports of distance judgment. All infants reached more for the near object, regardless of the sound’s SPL, suggesting that infants did not rely on this as a major distance cue. In contrast, adults’ verbal judgments of distance were based heavily on SPL, a strategy that produced higher error rates in the group with SPL counterbalanced across distance. A followup study in which adults were instructed to move their heads before judging the sound’s distance did not support the hypothesis that infants’ head movements were responsible for their overcoming the misleading SPL information.
Time-frequency analysis by a real-time differential spectral method for an application on sonar signal
Authors: Bourguel Maurice A. , David Pascal M. , Dekeyser Ivan J.
Published: October 2005

The purpose of this paper is to present an algorithm (differential spectral analysis) for real-time analysis of nonstationary or slightly nonstationary signals. The differential spectral analysis (DSA) gives the time derivative of Fourier complex coefficients, calculated by using a rectangular sliding window whose duration T is decided. The time evolution of these complex terms allows one to get a time-frequency representation of the signal, i.e., the instantaneous amplitude, the phase, and the frequency. This method does not need an FFT calculation for each time window T. The small number of required operations makes this method useful for a real-time analysis. The method is applied in oceanography for the acoustic exploration of particles. The DSA is a very fast and simple method for signal analysis, which can be very easily set to work, before using more complicated methods such as Hilbert and wavelet transforms.
Reconstruction of the surface acoustic field on radiating structures
Authors: Sarkissian Angie
Published: October 2005

An algorithm is developed for the reconstruction of the surface acoustic field from measurements of pressure made in the far field for a structure with arbitrary geometry. The boundary elements method is applied. The presence of the evanescent-like field is treated by expanding surface normal velocity in a set of functions that form the eigenstates of radiated power, computed by diagonalizing the surface resistance operator. The result of the reconstruction is the observable part of the surface normal velocity that generates the far-field radiation and does not include the evanescent-like field that decays very rapidly away from the surface. The algorithm is tested by applying it to scattering from a rigid cylinder with hemispherical endcaps. It is also applied to the radiation problem of a small piston located on the same cylinder, where the resolution attained on the surface for this ill-posed problem is shown to increase with increasing frequency.
A design method for achieving weak radiator structures using active vibration control
Authors: Naghshineh Koorosh , Koopmann Gary H.
Published: October 2005

A general strategy is devised for achieving minimum radiation of sound from structures subjected to a harmonic excitation force. A quadratic expression is written for the total sound power radiated from a structure in terms of the primary excitation and actuator (control) forces. Using quadratic optimization of this expression, a single control force vector is found that minimizes the radiated sound power (weak radiator). A general formulation is presented for the single-frequency excitation case. This formulation is then extended to the case of a structure subjected to a broadband excitation force; i.e., the magnitude and the phase of the excitation force remain constant as the excitation frequency changes. The numerical implementation of these formulations is described for a baffled beam controlled by forces and moments generated by piezoelectric actuators. Results for a single-frequency weak radiator show that the radiation efficiency of the beam response with control is drastically lower than that of the beam response with no control. Also, when the response of the structure with control is compared to that of the structure without control, three important observations can be made. First, the controlled structure exhibits lower response amplitudes at frequencies near structural resonances. Second, the controlled structural response amplitude decreases near the boundaries. Third, the wave number content of the controlled structural response shifts from supersonic to subsonic regions. These observations are confirmed experimentally using a clamped–clamped beam excited at a single frequency with a shaker and four PZT actuators bonded to its surface.
Simple and shock waves in uniaxial nonlinear elastic solids
Authors: Singh M. C. , Tran D.
Published: October 2005

Uniaxial waves in nonlinear elastic solids are cosidered. The nature of waves whether simple or shock is characterized on the basis of nonlinear properties of the elastic material as well as the impact boundary conditions. For an analysis of shock front nonlinear shock evolution equations are obtained and solved for the evolution of shock in time. Numerical results for uniaxial waves in nonlinear elastic metallic and nonmetallic solids are obtained by two different methods. There is good agreement in the numerical results in both the simple and shock waves for all cases considered in this study.
Total power flow from a vibrating rigid body to a thin panel through multiple elastic mounts
Authors: Pan Jie , Pan Jiaqiang , Hansen Colin H.
Published: October 2005

When active control is used to reduce the vibration transmission through machine mounts into supporting structures, the vibratory power flow through the mounts is often used as the cost function to be minimized. This is because the mounts behave as vibration ‘‘sources’’ for the supporting structure and they have a finite number of degrees of freedom. To apply active control effectively to suspension systems, it is necessary to investigate the nature of the power flow from the vibrating machine to its supporting structure through the mounts. In this paper, a multi-mount suspension system is modeled analytically. The transmission of vibratory power flow from a vibrating rigid body into a thin supported panel through two elastic mounts is evaluated numerically. This power flow consists of the contributions from normal and shear stress forces, and moments. The magnitude of each power flow component is examined and the conditions under which the contribution of each component to the total power flow is significant, are addressed.
Spatial horizontal coherence of sound in shallow water
Authors: Zhu Ruichao , Guan Dinghua
Published: October 2005

A theory for the problems of spatial horizontal coherence of a sound field in shallow water was developed by using the concept of horizontal rays and vertical modes, and by adiabatic approximation. Both analytical and numerical results were presented for transverse coherence of sound in a shallow sea under summer and winter conditions, and the results were compared with those of measurements. Analysis showed that the higher-ordered modes are more sensitive to the disturbance of boundaries, but the sound-speed disturbance has similar influence on all modes; and that the absorption of the bottom has a significant influence on the range-dependent properties of coherence of sound in winter conditions.
Boundary integral equation method for source localization with a continuous wave sonar
Authors: Xu Yongzhi , Yan Yi
Published: October 2005

In this paper, matched-field processing is combined with the boundary integral equation method (BIEM) of scattering theory to study a sound source localization problem in a perturbed shallow ocean. It is assumed that there is a known inclusion embedded in a shallow water waveguide. Continuous waves (cw), produced by a sound source, are scattered by the inclusion and then received by a hydrophone array. Because the symmetry of the waveguide has been destroyed by the existence of the inclusion, a proper procedure is required to avoid the mismatching. A numerical scheme is presented that makes use of the separation of the source and the detection array, and greatly reduces the computation. A numerical simulation using this method is presented.