bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater bubble sizing using a pulsed double frequency technique
Authors: Li Y. , Koller D. , George G. , Shankar P. M. , Newhouse V. L.
Published: October 2005

A pulsed double frequency technique has been developed for detecting and sizing underwater air bubbles. The technique permits little or no contribution from nonresonant bubbles at each frequency of interest and thus provides an accurate estimate of the bubble sizes present. Evaluation of the system was made through tests in a small pool at ranges as far as 2 m. The results obtained with the system were compared to data obtained through passive listening.
Time-domain simulation of the flute
Authors: Coltman John W.
Published: October 2005

A time-domain simulation of the flute dealt entirely with volume velocities or currents. The pipe was driven by jet current inserted at the end correction, while the jet shape characteristic was approximated by a truncated saturating cubic function of the delayed mouth current. An empirically derived reflection function yielded a pipe frequency response closely approximating that of a real flute. Jet offset was provided. At zero offset, near-triangular waveforms of three lower modes resulted. Their frequencies as a function of blowing velocity matched those calculated in the frequency domain. An edgetone curve produced by the model was properly tangent to the lower ends of the mode curves. With high jet offset and high blowing velocity large second harmonic content resulted. The maximum second harmonic achievable diminished sharply when mode shrinking was used rather than the mode stretching afforded by the original reflection function.
Mechanisms of ocean acoustic attenuation: Scattering by internal solitons, by sea surface waves, and by fish
Authors: Weston David E.
Published: October 2005

A recent paper by Zhou et al. [J. Acoust. Soc. Am. 90, 2042–2054 (1991)] presents evidence for an extra attenuation in shallow water, occurring over a limited frequency range, and hypothesizes that it is due to internal solitons. Three linked comments are made here. First it is noted that the real sea is three dimensional, which increases the likelihood of soliton scattering being smeared in frequency, and leads to a connection with the contribution from surface-wave scattering. Second a review is given of some early observations on shallow-water scattering by solitons, which resulted in fluctuation rather than attenuation. Third there is the alternative hypothesis of absorption and scattering by fish, drawing on early and extensive observations of attenuation effects that were often limited in frequency. There is no absolute proof here for or against either hypothesis, and although internal wave scatter is accepted as a loss mechanism in general, the case seems stronger for fish in the present application.
Ocean acoustic signal processing: A model-based approach
Authors: Candy J. V. , Sullivan E. J.
Published: October 2005

A model-based approach is proposed to solve the ocean acoustic signal processing problem that is based on a state-space representation of the normal-mode propagation model. It is shown that this representation can be utilized to spatially propagate both modal (depth) and range functions given the basic parameters (wave numbers, etc.) developed from the solution of the associated boundary value problem. This model is then generalized to the stochastic case where an approximate Gauss–Markov model evolves. The Gauss–Markov representation, in principle, allows the inclusion of stochastic phenomena such as noise and modeling errors in a consistent manner. Based on this framework, investigations are made of model-based solutions to the signal enhancement, detection and related parameter estimation problems. In particular, a modal/pressure field processor is designed that allows in situ recursive estimation of the sound velocity profile. Finally, it is shown that the associated residual or so-called innovation sequence that ensues from the recursive nature of this formulation can be employed to monitor the model’s fit to the data and also form the basis of a sequential detector.
Coherent source location using a pattern diversity technique
Authors: Sun Y. , Roy S. , Kassam S. A. , Haber F.
Published: October 2005

A high-resolution pattern diversity method is presented for resolving multiple coherent plane waves impinging on a linear array. In this method, use is made of several different choices for the common directional response or array pattern to form an averaged covariance matrix. A full rank (equal to the number of plane wave arrivals) signal-only covariance matrix can be achieved in the presence of multiple coherent sources, irrespective of the coherence structure. The underlying method does not require a uniform array, and can also be implemented using subarrays to effect the pattern diversity. The theoretical development of the method along with simulation results are provided.
The thermoelastic surface strip source for laser-generated ultrasound
Authors: Aharoni A. , Jassby K. M. , Tur M.
Published: October 2005

The vertical ultrasonic surface displacement generated by a laser-induced, thermoelelastic, rectangular surface strip source is formulated. The main features of this source, ultrasonic rise times comparable to those of the generating light pulse derivatives, and a large amplitude, double-pulsed waveform, are advantageous for ultrasonic spectral- and time-domain measurements for nondestructive material evaluation. The analysis shows that, for laterally symmetric sources in the thermoelastic regime, only one tangential thermoelastic stress component contributes to the vertical displacement. Therefore, the strip source is equivalent to two, tangential line forces acting outward at the strip’s front and back edges. The leading-edge rise time of the signal is virtually independent of the lateral extent of the source, which mostly affects the trailing portions of the ultrasonic pulses. Consequently, a particularly simple expression, which compares favorably with experimental results, is obtained for short strips (subtending small angles at the observation point). In conjunction with this formulation, the thermoelastic strip source is an important tool for quantitative, laser-based, ultrasonic nondestructive material evaluation.
Resonance and interference scattering near the coincidence frequency of a thin spherical shell: An approximate ray synthesis
Authors: Marston P. L. , Sun N. H.
Published: October 2005

An enhancement of the steady-state backscattering by an evacuated thin spherical shell is synthesized using surface-guided rays. This midfrequency enhancement has been predicted to occur near the critical coincidence frequency of thin shells in water. On the high-frequency side of the enhancement, the nearly periodic scattering variations primarily arise in the ray picture from the interference of a contribution of a subsonic guided wave with the specular reflection. Distinct resonances become important at lower frequencies. The pole locus of the complex partial-wave index is shown for the subsonic guided wave in the region where the coupling of the wave with the incident and scattered acoustic fields increases. The sphere studied is 2.5% thick stainless steel.
Viscous damping in one-dimensional wave transmission
Authors: Duan B. , Zamir M.
Published: October 2005

The use of one-dimensional transmission line theory as a model for wave propagation in vascular systems is considered, particularly in relation to the damping effect of viscosity of the fluid. It is shown that the accuracy and range of validity of the theory can be increased considerably by two modifying assumptions concerning the form of the velocity profile across a vessel. If the profile is assumed to be the same as that of pulsatile flow in a rigid tube, a uniformly valid solution is obtained which embodies earlier approximations for small and large values of viscosity. If the profile is assumed to be the same as that of pulsatile flow in an elastic tube, a further improvement in the accuracy of the solution is obtained which brings the results closer to those obtained from more elaborate two-dimensional solutions. The simplicity of the one-dimensional solution is important not only as a matter of convenience but because it provides an indispensable tool for the study of wave propagation and wave reflections in arterial trees and other complex tubular structures, where two-dimensional analysis would be impractical. The two-dimensional theory is best suited to analysis in a single tube.
Measurement and prediction of the frequency spectrum of piezoelectric disks by modal analysis
Authors: Guo Ningqun , Cawley Peter
Published: October 2005

The dependence of the vibration characteristics of a piezoelectric disk on its geometry, particularly the diameter to thickness ratio (D/T ratio), is studied by a finite element model and modal analysis. The frequency spectrum that correlates the vibration characteristics (product of resonance frequency and the thickness of the disk, fT) with the geometrical properties of the piezoelectric disk (D/T ratio) is predicted by the finite element model in the D/T ratio range from 0.1 to 20. The modal constant at each resonance is calculated using modal analysis techniques to obtain the strength of each resonance in the frequency spectrum when the disk is excited by a voltage applied to electrodes on its top and bottom surfaces. It is shown that the thickness extensional modes have much larger modal constants than the other modes in the spectrum especially in disks with D/T ratios larger than 5, and as the D/T ratio of the disks increases the number of the thickness extensional modes increases, while the response is gradually dominated by fewer and fewer modes, and finally by a single mode. The predictions have also been checked by experiment and in general good agreement has been obtained between the experiments and the predictions. The results indicate that the modal constant approach is a convenient and reliable means of assessing the strength of excitation of a given mode both numerically and experimentally.
The coding of vowel identity by patients who use the Ineraid cochlear implant
Authors: Dorman Michael F. , Smith Luther , Smith Michael , Parkin James
Published: October 2005

The aim of this experiment was to determine whether patients who use the Ineraid cochlear implant code formant frequency by means of the information in the time waveforms presented to the electrodes, or by the information in the distribution of energy among the electrodes. Six patients were presented three vowels for identification. The vowels presented in two configurations. In one, the temporal cues and distribution of energy cues were both appropriate for a given vowel. In the other, the temporal information specified one vowel while the distribution of energy specified another vowel. The results of the identification task indicated that patients relied on information contained in the distribution of energy for vowel identification. These results can be interpreted as indicating that the Ineraid overcomes the limited spatial resolution afforded by four monopolar electrodes by using the balance of energy among electrodes to produce a continuous, rather than discrete, coding of cochlear place of stimulation.
Elasticity and active force generation of cochlear outer hair cells
Authors: Iwasa Kuni H. , Chadwick R. S.
Published: October 2005

The cochlear outer hair cell is described by a cylindrical membrane model, characterized by area and shear moduli for a passive elastic element and an active tension element dependent on the membrane potential. In passive experiments, these moduli are determined from the pressure-strain relations. The area modulus obtained is 0.07 N m−1, similar to a lipid bilayer and the shear modulus is 0.007 N m−1. These moduli combined with previous active experiments show that the active tension is nearly isotropic and is about 1.6×10−2 N m−1 V−1, resulting in a 0.5 nN/mV force per cell. This implies that the receptor potential for acoustical stimulation produces an active force comparable to the acoustic force applied to the basilar membrane per outer hair cell. This finding supports the hypothesis that the outer hair cell acts as feedback motor in the fine tuning mechanism of the mammalian ear.
Electromagnetic midsagittal articulometer systems for transducing speech articulatory movements
Authors: Perkell Joseph S. , Cohen Marc H. , Svirsky Mario A. , Matthies Melanie L. , Garabieta Iñaki , Jackson Michel T. T.
Published: October 2005

This paper describes two electromagnetic midsagittal articulometer (EMMA) systems that were developed for transducing articulatory movements during speech production. Alternating magnetic fields are generated by transmitter coils that are mounted in an assembly that fits on the head of a speaker. The fields induce alternating voltages in a number of small transducer coils that are attached to atriculators in the midline plane, inside and outside the vocal tract. The transducers are connected by fine lead wires to receiver electronics whose output voltages are processed to yield measures of transducer locations as a function of time. Measurement error can arise with this method, because as the articulators move and change shape, the transducers can undergo a varying amount of rotational misalignment with respect to the transmitter axes; both systems are designed to correct for transducer misalignment. For this purpose, one system uses two transmitters and biaxial transducers; the other uses three transmitters and single-axis transducers. The systems have been compared with one another in terms of their performance, human subjects compatibility, and ease of use. Both systems can produce useful midsagittal-plane data on articulator movement, and each one has a specific set of advantages and limitations. (Two commercially available systems are also described briefly for comparison purposes.) If appropriate experimental controls are used, the three-transmitter system is preferable for practical reasons.
Matched-field processing for a moving source
Authors: Zala Cedric A. , Ozard John M.
Published: October 2005

Methods are presented for applying matched-field processing (MFP) to the estimation of the position and velocity of a moving source. These MFP methods for nonstationary sources match the full set of data obtained for an observation time during which the motion of the source is linear. Two classes of processor are presented. The first matches the observed vectors of hydrophone field values for each frequency bin and time segment with corresponding replica vectors. The second processes the observed data to form a time-averaged covariance matrix for each frequency bin and then matches these matrices using the largest eigenvectors of corresponding replica matrices. Versions of the Bartlett, maximum likelihood, and MUSIC beamformers are proposed for the new MFP procedures, and their performance is illustrated in tests with synthetic data. It is concluded that for the Bartlett processor, the vector matching method gives the greatest gain, and that for the maximum likelihood and MUSIC procedures, the use of the largest eigenvector of the replica matrix substantially improves source estimation relative to the use of hydrophone field vectors. The benefits of the largest eigenvector technique for matching are especially pronounced for horizontal arrays.
Ultrasonic scattering by a flat-bottom hole in immersion testing: An analytical model
Authors: Sedov Alexander , Schmerr Lester W. , Song Sung Jin
Published: October 2005

In ultrasonic nondestructive evaluation tests, a flat-bottom hole is often used as a reference scatterer for calibration, sensitivity, and sizing studies. Here, an analytical model is derived for the response of a flat-bottom hole in an immersion testing setup where the model is not restricted to the small hole, far-field conditions required by previous theories. Tests of the model demonstrate that it is able to predict single frequency DGS curves for the hole that agree well with experiments, even in the very near field of the transducer. Thus, the model may serve as a new and useful theoretically based calibration ‘‘standard’’ for a variety of ultrasonic applications.
Low-frequency acoustic scattering by slender bodies of arbitrary cross sections
Authors: Wong Seung Kai , Bush William B.
Published: October 2005

The scattering of acoustic waves from soft and hard slender bodies with arbitrary cross sections is considered in the limit ka≪1 and kl∼1, where k is the wave number, a is the lateral dimension of the object, and l is its length. Using the method of matched asymptotic expansions, formulas valid to the leading order in the slenderness ratio a/l are derived for the scattering amplitudes. They are expressed in terms of the cross-sectional area of the object and the induced-mass tensor for the two-dimensional inviscid flow generated by a moving infinite cylinder with the same cross section. The results satisfy the reciprocity relation.
Computational structural acoustics applied to scattering of sound by spherical shells
Authors: Hickling Robert , Ball James F. , Burrows R. Kirk , Petrovic Mirjana
Published: October 2005

Computational structural acoustics is the use of exact large-scale computations and computer graphics to study the behavior of elastic waves in structures. This approach is applied here to the scattering of sound by spherical shells in water. It is shown that rotational waves, found earlier in solid spheres and cylinders [Hickling et al., J. Acoust. Soc. Am. 89, 971–979 (1991)], continue to occur even for shells that are quite thin. In particular, when a thin shell in water is excited by incident continuous sound waves, small rotational waves occur, whose center of rotation and surrounding rotational displacement are inside the boundaries of the shell structure. For a thin shell, it appears to be impossible to excite a natural mode of the shell. This is probably due to the dense confluence of the frequencies of the fundamentals of the natural or free modes of vibration that occurs as the shell becomes thin. Radiation damping will cause these fundamentals to overlap, making it difficult to excite any particular natural mode. This is in contrast to the results obtained previously with the solid sphere, where it appeared to be possible to excite natural modes with continuous sound in water. The results for a thin shell are shown to be consistent with thin-shell theory for low and intermediate values of ka.
Synthesis of the driving functions of an array for propagating localized wave energy
Authors: Hernandez J. E. , Ziolkowski R. W. , Parker S. R.
Published: October 2005

This paper presents a framework for designing the driving functions of an array of radiating elements given a scalar representation of the desired propagating field at a finite number of remote spatial locations. Based on a point source propagation model in a homogeneous media, the relationship between the driving functions and the resulting field leads to a system of linear equations in the frequency domain. A least-squares solution to the inverse problem is obtained by solving the system of linear equations for the unknown array driving functions. The proposed framework is suitable for designing array driving functions that could be used to generate ‘‘source-free’’ (homogeneous) solutions to the wave equation. This paper focuses on the use of the proposed technique for calculating array driving functions for generating localized wave energy. Two cases are discussed; one based on a source-free solution to the wave equation, and the other based on a numerical traveling impulse function. The results are compared to the beam generated by driving the array uniformly with a continuous-wave (cw) signal.
Multirate digital signal processing algorithm to calculate complex acoustic pressure fields
Authors: Orofino Donald P. , Pedersen Peder C.
Published: October 2005

An efficient algorithm to compute complex (magnitude and phase) acoustic pressure field data that uses a multirate digital processing architecture is presented. The algorithm is based on the discretization of the velocity potential function, sampled at a rate that varies as a function of field point location and transducer geometry. The algorithm can be used to determine accurate magnitude and phase information at any field point location, and for any transducer geometry with a closed-form velocity potential function, including planar pistons, spherically focused pistons, and planar annular array transducers (e.g., the nondiffracting or J0-Bessel transducer). Numerical simulations based on this algorithm are presented together with exact field calculations wherever possible in order to make absolute error comparisons. Additionally, results based on a standard Gaussian quadrature integration scheme are presented in order to compare computational speed and accuracy in the near field. Results indicate improvements in numerical efficiency of 15 to 30 times over standard numerical integration techniques.
Reply to ‘‘Comments on ‘Unidirectional, second-order gradient microphone’ ’’ [J. Acoust. Soc. Am. 9
2, 583 x584 (1992)]
Authors: Sessler Gerhard M. , West James E.
Published: October 2005

A statement by Korenbaum [J. Acoust. Soc. Am. 91, XXX–XXX (1992)] referring to ‘‘ a more sophisticated choice’’ of a design parameter of directional gradient microphones is questioned.
Observations on a principal components analysis of head-related transfer functions
Authors: Middlebrooks John C. , Green David M.
Published: October 2005

A recent principal components analysis (Kistler and Wightman, 1992) has shown that the transfer functions of the human external ear, for a wide range of source locations, can be expressed as weighted sums of a small number of basis vectors. Directional transfer functions obtained in this laboratory, using substantially different measurement techniques, yielded principal component basis vectors that are remarkably similar to those reported by Kistler and Wightman. When this subject population was divided in half according to the overall physical sizes of subjects, basis vectors computed for the subpopulation of smaller subjects were shifted systematically to higher frequencies relative to those computed for the subpopulation of larger subjects.
A statistical model based fundamental frequency synthesizer for Mandarin speech
Authors: Chen Sin-Horng , Chang Saga , Lee Su-Min
Published: October 2005

A novel method based on a statistical model for the fundamental-frequency (F0) synthesis in Mandarin text-to-speech is proposed. Specifically, a statistical model is employed to determine the relationship between F0 contour patterns of syllables and linguistic features representing the context. Parameters of the model were empirically estimated from a large training set of sentential utterances. Phonologic rules are then automatically deduced through the training process and implicitly memorized in the model. In the synthesis process, contextual features are extracted from a given input text, and the best estimates of F0 contour patterns of syllable are then found by a Viterbi algorithm using the well-trained model. This method can be regarded as employing a stochastic grammar to reduce the number of candidates of F0 contour pattern at each decision point of synthesis. Although linguistic features on various levels of input text can be incorporated into the model, only some relevant contextual features extracted from neighboring syllables were used in this study. Performance of this method was examined by simulation using a database composed of nine repetitions of 112 declarative sentential utterances of the same text, all spoken by a single speaker. By closely examining the well-trained model, some evidence was found to show that the declination effect as well as several sandhi rules are implicitly contained in the model. Experimental results show that 77.56% of synthesized F0 contours coincide with the VQ-quantized counterpart of the original natural speech. Naturalness of the synthesized speech was confirmed by an informal listening test.
Formant movements of Dutch vowels in a text, read at normal and fast rate
Authors: Van Son R. J. J. H. , Pols Louis C. W.
Published: October 2005

Speaking rate in general, and vowel duration more specifically, is thought to affect the dynamic structure of vowel formant tracks. To test this, a single, professional speaker read a long text at two different speaking rates, fast and normal. The present project investigated the extent to which the first and second formant tracks of eight Dutch vowels varied under the two different speaking rate conditions. A total of 549 pairs of vowel realizations from various contexts were selected for analysis. The formant track shape was assessed on a point-by-point basis, using 16 samples at the same relative positions in the vowels. Differences in speech rate only resulted in a uniform change in F1 frequency. Within each speaking rate, there was only evidence of a weak leveling off of the F1 tracks of the open vowels /a a/ with shorter durations. When considering sentence stress or vowel realizations from a more uniform, alveolar-vowel-alveolar context, these same conclusions were reached. These results indicate a much more active adaptation to speaking rate than implied by the target undershoot model.
Concert hall acoustics—1992
Authors: Beranek Leo L.
Published: October 2005

The modern age of concert hall acoustics began with the development of the reverberation equation by Wallace C. Sabine in 1895. Between then and 1950, little was added to the literature that assured the successful design of concert halls. This paper documents world-wide research in this field and the succession of conert halls that have been pivotal in arriving at today’s results. Four basic concert hall designs offer the architect high probability of good acoustics, provided the necessary acoustical details are incorporated. The four types are the classical rectangular hall, the wide fan-shaped hall with overhead suspended panels, the segmented, asymmetrical, vineyard design, and the arena type with large sloping sidewall panels. In each of the designs, seven acoustical features must be provided: (1) acceptable reverberation time; (2) adequate loudness; (3) a short initial-time-delay gap between the direct sound and the first reflection reaching a listener; (4) a number of early lateral reflections that immediately follow the first reflection—these contribute to the feeling of ‘‘spaciousness’’; (5) a diffuse sound field created by an adequate number of reflections from all angles plus irregularities and ornamentation to eliminate acoustical ‘‘glare’’; (6) the ratio of energy in the first 80 ms to that in the next 2 s; and (7) warmth of the sound by properly shaping the reverberation-time curve at low frequencies. Successful examples of the four designs conclude the review.
A statistical study of cochlear nerve discharge patterns in response to complex speech stimuli
Authors: Miller Michael I. , Mark Kevin E.
Published: October 2005

Cochlear nerve discharge patterns in response to the synthesized consonant–vowel stimulus /da/ were collected from a population of 223 auditory-nerve fibers from a single cat. For each nerve fiber, discharges were measured from multiple, independent stimulus presentations, with the means and variances of the post-stimulus time histograms and Fourier transforms of response generated from the ensemble of stimulus presentations. The statistics were not consistent with those predicted via an inhomogeneous Poisson counting process model. Specifically, the synchronized components as measured by the Fourier transforms of post-stimulus time histogram responses have variances that are as much as a factor of 3 times lower than that predicted by the Poisson model. To account for the non-Poisson nature of the statistics, the Markov process model of Siebert/Gaumond was adopted. Using the maximum-likelihood and minimum description length algorithms, introduced by Miller [J. Acoust. Soc. Am. 77, 1452–1464 (1985)] and Mark and Miller [J. Acoust. Soc. Am. 91, 989–1002 (1992)], estimates of the stimulus and recovery functions were computed for each nerve fiber. Then, Markov point processes were simulated with the stimulus and recovery functions generated from these nerve fibers. The statistics of the simulated Markov processes are shown to have almost identical first- and second-order statistics as those measured for the population of auditory-nerve fibers, and demonstrates the effectiveness of the Markov point process model in accounting for the correlation effects associated with the discharge history-dependent refractory properties of auditory nerve response.
A low sea-state study of the quieting effect of monomolecular films on the underlying ambient-noise field
Authors: Rohr Jim , Detsch Richard
Published: October 2005

A series of tests, conducted at low sea states, show that the reduction of surface-related ambient noise beneath monomolecular (slick-forming) films begins between 1 and 2 kHz and extends to at least 70 kHz. Although the amount of noise reduction varies between experiments, attenuations of up to 8 dB are common. Most of the experiments are conducted in the absence of whitecapping, where for wind speeds greater than 2 m/s, the ambient noise spectra beneath the films generally resemble those of nonfilmed, lower sea-state conditions. Laboratory experiments conducted with these same films spread upon a reservoir of seawater show that the regular bubble entrainment associated with vertically falling drops can be dramatically suppressed, and the air entrainment accompanying plunging liquid jets is characterized by a conspicuous increase in the number of smaller bubbles. Preliminary studies providing simultaneous in situ acoustic and video monitoring of the ocean surface from a meter beneath it suggest that, in the absence of whitecapping, the ambient-noise reduction beneath the slick results from a dramatic decrease of microbreaking events within it. The acoustic signatures of these microbreaking events are distinguished by individual oscillating bubbles.
Transient radiation of ultrasonic waves in solids by nonuniformly excited and focusing annular arrays
Authors: Kažys R. , Baboux J. C.
Published: October 2005

Analysis of the transient ultrasonic fields radiated in solids by nonuniformly excited and focusing annula has been performed. The influence of the number of annula in the array on the structure of the particle velocity fields radiated has been investigated. The different driving stress profiles on the radiating surface create substantially differing spatial-temporal distributions of axial and radial components of the particle velocity.
Broadband detection of laser-excited surface acoustic waves by a novel transducer employing ferroelectric polymers
Authors: Coufal Hans , Grygier Robert , Hess Peter , Neubrand Achim
Published: October 2005

Broadband detection (150-MHz range) of surface acoustic wave transients excited by absorption of ps laser pulses in the sample under study is demonstrated. A novel transducer employing a ferroelectric polymer foil as piezoelectric sensor is described. In a silicon single crystal the width of the observed acoustic pulses was limited to 4 ns by the spatial resolution of pulse generation and detection. In the polycrystalline materials under study the minimum observable pulse width was determined by materials properties. Accurate values for the phase velocity of surface acoustic wave propagation are given for silicon, aluminum, steel, copper, and brass.
Reply to ‘‘Comments on ‘A general formulation for the sound radiation from rectangular, baffled plates with arbitrary boundary conditions’ ’’ [J. Acoust. Soc. Am. 9
2, 2990 (1992)]
Authors: Berry A. , Guyader J.-L. , Nicolas J.
Published: October 2005

This Letter provides answers to the questions raised by Laura and Ercoli in their comment [P. A. A. Laura and L. Ercoli, J. Acoust. Soc. Am. 92, XXX (1992)].
On the reflection of plane waves in transversely isotropic media
Authors: Ditri John J. , Rose Joseph L.
Published: October 2005

Formulas for the reflection factors of plane quasilongitudinal and quasitransverse waves from free surfaces in transversely isotropic media are used to generate necessary conditions for no mode conversion at such surfaces. The conditions enable the determination of incident angles where no mode conversion occurs without having to solve the reflection problem in detail. These results are of practical importance in the nondestructive evaluation of transversely isotropic (or higher symmetry) materials since inspecting at an angle where no mode conversion occurs will greatly simplify the analysis of the returning echoes by reducing the number of waves (homogeneous or inhomogeneous) that are generated at the surface.
Numerical modeling of acoustic radiation and scattering from thin bodies using a Cauchy principal integral equation
Authors: Wu T. W. , Wan G. C.
Published: October 2005

In this paper, the Helmholtz integral equation and its normal derivative are used for the numerical solution of acoustic radiation and scattering from thin bodies. A regularized form of the normal derivative integral equation, originally derived by Maue, is adopted to calculate the pressure jump across the thin body. This regularized normal derivative integral equation converges in the Cauchy principal value sense rather than only in the finite-part sense. The Cauchy principal value integral can be further transformed into an integral that converges in the normal sense. The C0 continuous isoparametric elements are used in the formulation so that the numerical model is compatible with other analysis tools such as the finite element method. Collocation points are placed inside each element to insure a unique normal direction and the C1 continuity condition. The pressure jump is forced to be zero at the knife edge where the 1/(r)1/2 singularity of the tangential velocities is modeled by the quarter-point technique. Numerical examples on scattering from a circular disk and an open cylindrical shell are given to verify the formulation.
Behavioral measures of frequency selectivity in the chinchilla
Authors: Niemiec Andrew J. , Yost William A. , Shofner William P.
Published: October 2005

A simultaneous masking procedure was used to derive four measures of frequency selectivity in the chinchilla. The first experiment measured critical masking ratios (CRs) at various signal frequencies. Estimates of the chinchillas’ critical bandwidths derived from the CRs were much broader than comparable human estimates, indicating that the chinchilla may have inferior frequency selectivity. The second experiment measured critical bandwidths at 1, 2, and 4 kHz in a band-narrowing experiment. This technique yielded narrower estimates of critical bandwidth; however, chinchillas continued to exhibit poor frequency selectivity compared to man. The third experiment measured auditory-filter shape at 0.5, 1, and 2 kHz via rippled noise masking. Results of the rippled noise masking experiment indicate that auditory filters of humans and chinchillas are similar in terms of shape and bandwidth with chinchillas showing only slightly poorer frequency selectivity. The final experiment measured auditory filter shape at 0.5, 1, 2, and 4 kHz using notched noise masking. This experiment yielded auditory filter shapes and bandwidths similar to those derived from man. The discrepancy between the indirect estimates of frequency selectivity derived from CR and band-narrowing techniques and the direct estimates derived from rippled noise and notched noise masking are explained by taking into account the processing efficiency of the subjects.
Influence of spectral locus and  F0 changes on the pitch and timbre of complex tones
Authors: Singh Punita G. , Hirsh Ira J.
Published: October 2005

Harmonic complex tones comprising components in different spectral regions may differ considerably in timbre. While the pitch of ‘‘residue’’ tones of this type has been studied extensively, their timbral properties have received little attention. Discrimination of F0 for such tones is typically poorer than for complex tones with ‘‘corresponding’’ harmonics [A. Faulkner, J. Acoust. Soc. Am. 78, 1993–2004 (1985)]. The F0 DLs may be higher because timbre differences impair pitch discrimination. The present experiment explores effects of changes in spectral locus and F0 of harmonic complex tones on both pitch and timbre. Six normally hearing listeners indicated if the second tone of a two-tone sequence was: (1) same, (2) higher in pitch, (3) lower in pitch, (4) same in pitch but different in ‘‘something else,’’ (5) higher in pitch and different in ‘‘something else,’’ or (6) lower in pitch and different in ‘‘something else’’ than the first. (‘‘Something else’’ is assumed to represent timbre.) The tones varied in spectral loci of four equal-amplitude harmonics m, m+1, m+2, and m+3 (m=1,2,3,4,5,6) and ranged in F0 from 200 to 200±2n Hz (n=0,1,2,4,8,16,32). Results show that changes in F0 primarily affect pitch, and changes in spectral locus primarily affect timbre.

However, a change in spectral locus can also influence pitch. The direction of locus change was reported as the direction of pitch change, despite no change in F0 or changes in F0 in the opposite direction for ΔF0≤0−2%. This implies that listeners may be attending to the ‘‘spectral pitch’’ of components, or to changes in a timbral attribute like ‘‘sharpness,’’ which are construed as changes in overall pitch in the absence of strong F0 cues. For ΔF0≥2%, the direction of reported pitch change accorded with the direction of F0 change, but the locus change continued to be reported as a timbre change. Rather than spectral-pitch matching of corresponding components, a context-dependent spectral evaluation process is thus implied in discernment of changes in pitch and timbre. Relative magnitudes of change in derived features of the spectrum such as harmonic number and F0, and absolute features such as spectral frequencies are compared. What is called ‘‘spectral pitch,’’ contributes to the overall pitch, but also appears to be an important dimension of the multidimensional percept, timbre.
Physiological studies of central masking in man. I: The effects of noise on the 40-Hz steady-state response
Authors: Galambos Robert , Makeig Scott
Published: October 2005

In a typical masking situation, two Békésy waves overlap on the basilar membrane, and each of them initiates a stream of nerve impulses that enters the brain via the auditory nerve. Much is known about the overlapping of the cochlear waves, but much less about where, how, and even if at all, the impulse streams interact once they get inside the brain. In these experiments the incoming impulses are measured electrophysiologically using the auditory brainstem response (ABR), and, simultaneously, using the 40-Hz auditory steady-state response (SSR) to monitor events at a probable site of their interaction, the auditory cortex. The principal finding is that, when progressively increasing levels of continuous noise are presented to the contralateral ear, the SSR to the signal drops to about half its control amplitude. Second, low levels of ipsilateral noise reliably enhance SSR amplitude. Third, moderate levels of ipsilateral noise reduce SSR latency. In none of these cases does the ABR show similar effects. These findings are interpreted to mean that, in each case, impulses excited by the signal interact with impulses excited by the noise, and regardless of ear of origin the interactions take place beyond the brainstem level where ABR wave V is generated, either before the impulses reach the cortex, or in the cortex itself.
Physiological studies of central masking in man. II: Tonepip SSRs and the masking level difference
Authors: Galambos Robert , Makeig Scott
Published: October 2005

The auditory steady-state response (SSR), an evoked response generated in the auditory cortex, was initiated by monaural trains of 500-Hz tonepips repeated at rates near 40 Hz while wideband noise was being delivered to the same or opposite ear. Contralateral noise reduced SSR amplitudes in an intensity-dependent manner, whereas ipsilateral noise enhanced the SSR amplitudes at low levels and depressed them at high levels. Systematic phase changes accompanied the amplitude changes. These results, obtained with tonepips, closely resemble those previously reported for clicks. A third experiment, a masking level difference (MLD) experiment, examined changes in the SSR measures during four successive tonepip-plus-noise conditions: (1) monaural tonepips alone; (2) adding ipsilateral noise; (3) then adding contralateral noise; (4) finally, adding contralateral tonepips. The SSR amplitude changes measured in the experiment did not always correspond with the changes in perception reported by the subject.
Frequency window method for forced vibration of structures with connected substructures
Authors: Min Kyung-Won , Igusa Takeru , Achenbach Jan D.
Published: October 2005

A novel method is presented to analyze the harmonic forced vibration of a main structure with multiple connected substructures. The response of the combined system is represented in terms of the uncoupled modes of the system components. Then, the response equations are given in terms of rational polynomial expansions for the main structure mobility, substructure impedances, and the forcing function. Next, the uncoupled modes with natural frequencies closest to the excitation frequency are isolated by a frequency window. The essential idea of the frequency window method is to retain full mathematical detail for these modes and to retain only the essential effects from all remaining modes. This results in both a reduction of complexity and computation effort. The method differs fundamentally from mode truncation and Taylor’s series methods. Furthermore, the method gives parameters which provide insight into the coupling effects between the main structure and the substructures.
Slightly inhomogeneous surface wave in an isotropic half-space in the presence of weak anisotropy by its surface
Authors: Rossikhin Yuriy A.
Published: October 2005

The solution of the problem concerning the transformation of a volume SH wave propagating along an isotropic elastic half-space with a free surface into a new wave by laying on the half-space boundary a weakly anisotropic layer with cubic symmetry is presented. Two types of the weakly anisotropic layers are considered: the layer in which the shear wave velocity is the same as the half-space (‘‘neutral’’ layer) and the layer in which the velocity of the shear wave is smaller than the velocity of the shear wave in the half-space (‘‘decelerating’’ layer). The elastic moduli of a layer’s material are slightly distinguished from corresponding elastic moduli of the isotropic half-space. It is shown that the new wave is the slightly inhomogeneous quasitransverse surface wave of SH type, because among three displacement components on this wave, the transverse one, which is parallel to the interface of two mediums, predominates. Wave velocities are slightly distinguished from the velocity of the volume SH wave, but their depths of penetration into the half-space are considerably more than a depth of the Rayleigh wave localization. As an example, a two-layered medium is considered, where materials for the layer and half-space used are anisotropic and isotropic tungsten, respectively.
Narrow-band sound localization related to external ear acoustics
Authors: Middlebrooks John C.
Published: October 2005

Human subjects localized brief 1/6-oct bandpassed noise bursts that were centered at 6, 8, 10, and 12 kHz. All testing was done under binaural conditions. The horizontal component of subjects’ responses was accurate, comparable to that for broadband localization, but the vertical and front/back components exhibited systematic errors. Specifically, responses tended to cluster within restricted ranges that were specific for each center frequency. The directional transfer functions of the subjects’ external ears were measured for 360 horizontal and vertical locations. The spectra of the sounds that were present in the subjects’ ear canals, the ‘‘proximal stimulus’’ spectra, were computed by combining the spectra of the narrow-band sound sources with the directional transfer functions for particular stimulus locations. Subjects consistently localized sounds to regions within which the associated directional transfer function correlated most closely with the proximal stimulus spectrum. A quantitative model was constructed that successfully predicted subjects’ responses based on interaural level difference and spectral cues. A test of the model, using techniques adapted from signal detection theory, indicated that subjects tend to use interaural level difference and spectral shape cues independently, limited only by a slight spatial correlation of the two cues. A testing procedure is described that provides a quantitative comparison of various predictive models of sound localization.
Discriminability of bursts of reproducible noise
Authors: Fallon Coble Susan , Robinson Donald E.
Published: October 2005

The ability of human listeners to discriminate pairs of bursts of reproducible noise was examined. A same–different psychophysical method was used. Bursts in a pair were identical on same trials. On different trials, bursts were identical except for τ ms of independent noise located at either the beginning, middle, or end of the pairs of bursts. As the temporal position of the τ ms of independent noise was moved from the beginning to the end of the bursts of noise, discriminability increased. For each temporal position of the independent noise, discriminability was a function of the ratio of the duration of the independent noise (τ) to the total burst duration.
Frequency-domain travel time (FDTT) measurement of ultrasonic waves by use of linear and nonlinear sources
Authors: Johnson Paul A. , Hopson Thomas M. , Shankland Thomas J.
Published: October 2005

This paper describes a frequency-domain travel time (FDTT) method for measurement of direct and reflected travel times of sound waves based on the change in phase with frequency between a reference signal and a transmitted wave. An ordinary (linear) source can be used for measuring delays over shorter path lengths, and a parametric array (nonlinear) source can be used for measuring delays over longer path lengths. In the ordinary source measurement a reference signal is electronically multiplied with a signal that is time delayed by propagation through a sample. As frequency is incremented stepwise, the relative phase difference generates a corresponding stepwise dc output from the multiplier. For any travel path within the sample, there is a characteristic period of the dc signal whose reciprocal is proportional to the group time delay along the path. If more than one arrival exists, characteristic periods are superposed. An inverse Fourier transform of the frequency signal gives the discrete arrival times for each path. In the parametric measurement, a second electronic multiplier is used to create an electronic difference frequency signal for phase comparison with a wave at the difference frequency created by nonlinear elastic interaction in the material. The FDTT method should be applicable to ultrasonic investigation of material properties, nondestructive evaluation, seismology, sonar, and architectural acoustics.