bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of sea beam acoustic backscatter from ridge–crest terrains.
Authors: Matsumoto Haru , Dziak R. , Fox C. , Lau T. K.
Published: October 2005

An approach based on a Kirchhoff approximation model [D. Jackson etal., J. Acoust. Soc. Am. 79, 1410–1422 (1986)] conveniently relates to a power law the ocean bottom roughness spectrum based on two parameters α and β, i.e., W(k)=βk−γ, where γ=2(α+1). Initial studies [R. Dziak etal., Eos 70, 71 (1989, 1990)] revealed that α and β, solved by multiregression analysis using sea beam data from the Juan de Fuca Ridge, compared favorably with the spectral models derived from similar tectonic provinces by Fox etal. [Rev. Geophys. 23 (1985)]. In comparison to a similar method applied to a heavily sedimented area by de Moustier etal. [J. Acoust. Soc. Am. 89, 1962–1963 (1991)], a lack of volume reverberation in hard-rock areas aids in deriving solutions for the model since less bottom parameters are involved. On the other hand, the fluctuation of the echo levels between the pings from the rough and hard bottom made it difficult to fit to a realistic bottom roughness model. The statistics of the peak echo amplitudes from the sea beam system and a method adopted to reduce their standard deviation are described.
Accuracy of scattering approximations for acoustical remote sensing.
Authors: Thorsos Eric I.
Published: October 2005

Acoustical remote sensing of interface roughness usually involves an interpretation of the scattered signal assuming the forward problem is understood. The accuracy of the standard scattering approximations for power law roughness spectral densities typical of the seafloor will be reviewed. The approximations include the Kirchhoff approximation and the lowest-order perturbation approximation. The effects of roughness at wave numbers higher than the Bragg wave number will also be considered. Exact integral equation results for 1-D surfaces are used for ground truth. [Work supported by ONR.]
Real-time seabed discrimination and logging.
Authors: Chivers R. C. , Burns D. R.
Published: October 2005

The concept of using the information contained in the first and second echoes of conventional echo-sounder systems for seabed discrimination has been developed both analytically and instrumentally. Isolation and quantification of the portion of the first echo originating in oblique back reflection of the incident sound pulse gives a measure (E1) of the roughness and hardness of the seabed. Quantification of the second echo gives primarily a measure (E2) of the hardness of the seabed. In combination, these two parameters have been shown to provide a sensitive and reliable identification of the nature of the seabed. This identification can even be achieved in bad weather conditions. Computational studies have been supported by extensive sea trials over a wide range of grounds. There is clear evidence that the signal processing described can identify not only the type of ground (e.g., mud, sand, gravel, rock) but also its surface texture−at least in broad terms.
Modeling acoustic backscatter from the seafloor by long-range side-scan sonar.
Authors: Lyons Anthony P. , Anderson Aubrey L.
Published: October 2005

An existing model of seafloor backscattering [Jackson etal., J. Acoust. Soc. Am. 79, 1410–1422 (1986)] was extended to include volume scattering from a random homogeneous continuum and scattering from subbottom interfaces. Results of computer simulations with the extended model were compared with values of scattering strength obtained from processed gloria data from the Monterey Fan off the coast of California. Regions of well delineated high and low backscatter are seen in the gloria imagery. The geoacoustic input parameters for the simulation runs were either taken directly from or estimated from core data obtained by ground truth sampling in the image area. From the model simulation results, it was found that the low backscatter region is dominated by interface scattering from a single subbottom interface over a thick homogeneous sand layer. The high return regions are dominated by scattering from the random inhomogeneous continuum. These two additions to the scattering model allow use of the ground truth measurements to constrain the input parameter values. No free parameters are required to fit the scattering strength data. [Work supported by Naval Research Laboratory, Code 5100.]
Neural networks for pattern recognition with applications to acoustics and speech.
Authors: Grossberg Stephen
Published: October 2005

This tutorial will introduce neural network models that clarify how an animal or autonomous machine can function adaptively in an uncontrolled environment wherein unexpected and noisy events can occur. The tutorial will emphasize biological and technological models of spatiotemporal pattern recognition that are useful for real-time processing of acoustic and speech signals. Neural networks will be first described that are capable of autonomously learning to classify individual input patterns that are presented in an arbitrary order and at variable rates. These networks illustrate how the processes of paying attention, learning expectations, and hypothesis testing are joined together for purposes of pattern recognition and prediction. In these networks, rare but important events can be learned and recognized even if they are similar to frequent events with different consequences. Neural networks will next be described that are capable of recognizing temporally ordered sequences of events. With this background, a neural architecture for perception and production of speech and related acoustic signals will be introduced and discussed.
Acoustical design of the National Center for the Performing Arts of Perú.
Authors: Jiménez-Dianderas Carlos R. , Panduro-Manrique Manuel
Published: October 2005

This project is based in the design of a cultural complex for the National Center for the Performing Arts, which includes a 1200-seat opera house, a 750-seat concert hall, a small auditorium for master classes, and an amphitheatre for 1500 locations. The interest in this project came from the lack of cultural facilities in Perú. Furthermore, it established a methodological alternative for the architectural acoustic design, so the Center is consequently of the integrity of a two-design process in only one: architectural and acoustical design. The site for the project was determined from the evaluation of several possibilities through analysis of successive approximations. The analysis includes the urban acoustical study of the metropolitan area of Lima. The final decision about the site was made using acoustical measurements of urban noise. The acoustical design of the auditoria includes ray-diagram analysis, reverberation time, early decay time calculation, and final sound level in some positions.
Image method for simulating reverberant room response with directional receiver and source.
Authors: Czyzewski Zbigniew , Nabelek Anna K.
Published: October 2005

Image methods are commonly used for computing and analyzing acoustic responses of enclosures. The image method employed by Allen and Berkley [J. Acoust. Soc. Am. 65, 943–950 (1979)] digitally simulated acoustic echoes in a reverberant room by constructing a discrete-time impulse response in which each echo contributed a single impulse. The authors assumed a rectangular enclosure with an omnidirectional receiver and an isotropic acoustic source. Their calculation procedure was modified to allow its use with directional receiver and source. Introduction of a nonomnidirectional receiver to the method was accomplished by changing the contribution of each image according to a directional characteristic of a receiver. Introduction of an anisotropic sound source to this method was achieved by assignment of a spatially oriented source characteristic to each source image. The latter approach, however, may no longer be valid because the image method assumes full source symmetry. The usefulness of the proposed modification for small reverberant enclosures was proven by comparing the results of the modified image method with data obtained by a ray tracing technique. [Research supported by the National Institute on Deafness and Other Communication Disorders.]
Field testing of operable walls.
Authors: Lilly Jerry G.
Published: October 2005

In addition to submitting laboratory test results prior to approving an operable wall assembly for a given project, it is common practice to require field testing of the noise reduction provided by operable partitions using ASTM E-336 to ensure that each partition is properly installed and adjusted. This paper discusses the various testing methods commonly used with particular attention to measurement problems typically encountered in the field. The dependence of NIC on the measurement microphone locations in the source and the receiving room is examined. The paper also proposes a simple normalizing procedure that should help reduce variations in the measured NIC values for different room arrangements and geometries.
A study on designing the amplitude gain of the feedback loop of an electroacoustic system.
Authors: Minowa Toshimitsu , Riko Yasuhiro
Published: October 2005

The acoustic feedback from a loudspeaker to a microphone forms a closed loop and is the cause of instability (howling). When the electrical amplifier gain is fixed on maximum within a designed range, it is the excess amplitude of the open-loop gain over the unity (0 dB) that should be minimized by a howling suppression technique. It can be designed using a diffuse sound field model [Diestel, J. Acoust. Soc. Am. 35, 2019–2022 (1963)]. According to this method, the designed value was 18–24 dB in the case of a single loudspeaker and single microphone system located in a room with dimensions of 10×20×6 m and sound absorption coefficient of 0.05–0.5 and the gain of the electrical amplifier being fixed so that the farthest located attendant from the loudspeaker could perceive 62.9 dB (SPL). In order to evaluate the result, measurements were carried out in a conference room.
Estimation of the acoustic field directionality by use of planar and volumetric arrays via the Fourier series method and the Fourier integral method
Authors: Nuttall Albert H. , Wilson James H.
Published: October 2005

The possibility of estimating the directionality of a stationary homogeneous noise field, directly from the element outputs of a line array, is investigated and found to be feasible for large arrays without encountering ill conditioning. This technique, called inverse beamforming for historical reasons, is applicable to line and planar as well as volumetric arrays, and requires no more than two-dimensional fast Fourier transforms (FFTs) for its realization. Derivations and results are presented both for a Fourier series method and a Fourier integral method.
Method for solving eigenvalue problems of the Helmholtz equation with an arbitrarily shaped outer boundary and a number of eccentric inner boundaries of arbitrary shape
Authors: Nagaya Kosuke , Yamaguchi Toshizumi
Published: October 2005

This paper presents a method for solving eigenvalue problems of various phenomena that are governed by the Helmholtz equation with an arbitrarily shaped outer boundary and a number of eccentric boundaries of arbitrary shape. In the analysis, the outer boundary condition is satisfied by means of the Fourier expansion collocation method using the exact solution of the equation of motion. To satisfy the inner boundary conditions, the point restraints are added to the equation of motion, and the inner boundary conditions are satisfied by making use of a point matching procedure. The equation for finding the eigenvalues are derived, and numerical calculations are carried out for cases of elliptical outer and inner boundaries and polygonal outer and inner boundaries.
Transfer matrix modeling of hyperbolic and parabolic ducts with incompressible mean flow
Authors: Easwaran V. , Munjal M. L.
Published: October 2005

A general differential equation for the propagation of sound in a variable area duct or nozzle carrying incompressible mean flow (of low Mach number) is derived and solved for hyperbolic and parabolic shapes. Expressions for the state variables of acoustic pressure and acoustic mass velocity of the shapes are derived. Self-consistent expressions for the four-pole parameters are developed. The conical, exponential, catenoidal, sine, and cosine ducts are shown to be special cases of hyperbolic ducts. Finally, it is shown that if the mean flow in computing the transmission loss of the mufflers involving hyperbolic and parabolic shapes was not neglected, little practical benefit would be derived.
Vibrational modes of a noncircular bell with a church bell profile
Authors: Brelay Hervé , Rossing Thomas D.
Published: October 2005

The vibrational modes of an almond-shape bell, having the profile of a church bell, were studied using holographic interferometry. The noncircular shape results in mode pairs, one pair member having a node at the end of the bell, the other an antinode. Frequency ratios between the mode pairs range from 0.94 to 1.21.
Correlation dimension of woodwind multiphonic tones
Authors: Keefe Douglas H. , Laden Bernice
Published: October 2005

A multiphonic is a regime of oscillation of woodwind musical instruments that is perceived as two or more simultaneously sounding pitches. The frequencies fl,m of the line spectral components of a measured woodwind multiphonic tone fit a biperiodic spectrum at low- to mid-playing levels. For the saxophone and clarinet multiphonics investigated, the two basis frequencies of the biperiodic spectrum are phase locked, that is, their ratio is equal to a ratio of small integers. A broadband spectrum is present in multiphonic spectra that exceeds instrumentation noise and window leakage associated with signal processing. The correlation dimension D of P. Grassberger and I. Procaccia [Physica D 9, 189–208 (1983)] is measured by embedding a single measured time series in a higher-dimensional space, so as to reconstruct the phase space of the dynamical system. The time delay used in the dimensional reconstruction is chosen using information theory. For the particular multiphonics analyzed, the correlation dimension ranges from 2.5 to 2.9 for the saxophone and from 1.3 to 2.2 for the clarinet. One clarinet multiphonic shows possible additional dynamical complexity at small length scales in the embedding space, with a correlation dimension of 3.3. These results give quantitative evidence that some, but not all, multiphonic tones possess a strange attractor.
Perception of the English /s/–/∫/ distinction relies on fricative noises and transitions, not on brief spectral slices
Authors: Whalen D. H.
Published: October 2005

A series of experiments compared two approaches to fricative identification, spectral template matching and articulatory dynamics. Natural-speech /s/ and /1/ noises from fricative-vowel or vowel-fricative syllables were cross spliced so that ‘‘hybrid’’ noises started out as either /s/ or /1/ and ended up with the other fricative noise in varying proportions. With both initial and final fricatives, listener judgments most often agreed with the longer part of the noise even when spectral templates would predict the other category. Also, the vocalic formant transitions contributed to the judgment. In another experiment, open transcriptions by four expert listeners similarly showed that all the cues were used; there were also some instances of nonspeech percepts that would be predicted by gestural models. One further experiment had subjects identify two fricatives from hybrid noises between two vocalic segments. When the order of the noises differed from the order of the transitions, the perceived ordering of the fricatives was often the reverse of the order of the noise segments. Taken together with previous results, these experiments indicate that listeners take the whole fricative noise, as well as the transitions, into account in fricative identification.
Methods for estimating infant thresholds
Authors: Werner Lynne A. , Marean G. Cameron
Published: October 2005

Detection thresholds for 1000-Hz, 16-ms tone bursts were estimated for 3- and 6-month-old infants and for young adults. The test procedure used was the observer-based psychoacoustic procedure. Thresholds were estimated using two different adaptive procedures and the method of constant stimuli. There was little difference among the average thresholds determined by any of these techniques. The least variable thresholds were obtained in the method of constant stimuli. In addition, 10 infants at each age completed two 30-trial blocks of trials in the method of constant stimuli; 22 adults completed 8 blocks of 30 trials. For 3- and 6-month-olds and for adults, there was no significant change in average threshold between blocks. Individual 6-month-olds’ thresholds rarely changed by more than 5 dB between blocks, and the correlation between the thresholds obtained in the two blocks was significant. Individual 3-month-olds’ thresholds, however, sometimes changed by as much as 10 dB between blocks, and the correlation between first and second block threshold was not significant. The effects of response bias on threshold were assessed by examining receiver operating characteristic plots of hit and false alarm rates at threshold and the correlation between false alarm rate and threshold. Although there was some variability in response bias, infant/observer teams tended to respond in an unbiased fashion. In one of the adaptive procedures only, false alarm rate was significantly correlated with threshold. In all procedures, the exclusion of infants with high false alarm rates changed the average thresholds obtained by less than 5 dB. About half of the infants with high false alarm rates appeared to perform no better than would be expected by chance. Finally, the difference between infant and adult thresholds for these short duration stimuli was about 10 dB greater than the difference previously reported for long duration stimuli.
Hearing loss in the chinchilla from impact and continuous noise exposure
Authors: Dunn Derek E. , Davis Rickie R. , Merry Carol J. , Franks John R.
Published: October 2005

The relative hazard posed to the peripheral auditory system by impact/impulse and continuous noise of the same power spectrum was determined. Impact noise was generated by striking a nail with a hammer and was digitally recorded. The acoustical power spectrum of the impact was determined and pink noise was filtered to produce a continuous noise stimulus with the same acoustic power spectrum. Pre-exposure auditory evoked response (AER) thresholds were obtained at 1, 2, 4, and 8 kHz on 16 adult chinchillas. The pool of animals was divided into two equal groups based upon pre-exposure AER thresholds. One group was exposed to impact noise and the other group to the filtered pink noise. Exposures were 4 h/day for 5 days. Thirty days following the exposure, auditory evoked response thresholds were remeasured. Changes in auditory sensitivity were determined by subtracting the pre-exposure thresholds from the post-exposure thresholds. Hearing threshold shifts of the impact noise group were significantly greater (p<0.0001) than the hearing threshold shifts of the continuous noise group. These data indicate a need to more closely examine the parameters and effects of impact noise. There may be a need to develop expanded damage–risk criteria for occupational exposure to impulse/impact noise.
Computation of the equivalent modal impedance matrix of a multiple degree of freedom electroelastic structure using antiresonance modes
Authors: Decarpigny Jean N. , Hamonic Bernard F. , Debus Jean C.
Published: October 2005

In a recent paper [M. P. Johnson, J. Acoust. Soc. Am. 88, 1–6 (1990)], Johnson presented an interesting approach for connecting a finite-element model and a multiport network model of a piezoelectric transducer. Thus using one of the several simple numerical tools designed to analyze the electromechanical behavior of a transducer described by a multiport network model, it remains possible to obtain the accuracy otherwise provided by a finite element model. To do this, Johnson built up a modal impedance matrix representation of the transducer structure, starting from finite-element equations, but the diagonal modal stiffness part of the matrix obtained is perturbed by additional piezoelectric stiffness terms that can induce a more or less complex coupling between modes. The aim of this paper is to demonstrate that, starting with antiresonance modes instead of resonance modes provided by the finite-element modeling to build up the impedance matrix, avoids the occurrence of these complex coupling terms and, thus, gives the desired simple formulation to the approach.
Edge-less short-pulse piezoelectric transducers
Authors: Hazony Dov
Published: October 2005

The behavior of a thin transducer is analyzed when the electroded section constitutes a small part of the available areas. The principal signals are relatively short stress pulses. It will be seen that these pulses may travel close to or at the speed of sound in an unbounded medium and that circuit models may be associated with these transducers. The results also apply to the analysis of elastic properties of thin plates when the aperture of the probing beam is wider than the thickness of the plate.
Nonuniform beams with harmonically related overtones for use in percussion instruments
Authors: Orduña-Bustamante Felipe
Published: October 2005

Beams used in certain percussion instruments with definite pitch such as marimba, xylophone, and vibraphone are undercut in order to bring the frequencies of the first few overtones into a harmonic relationship with the fundamental frequency. This paper addresses the problem of determining the optimal dimensions of the undercut so that the frequencies of modes 2 and 3 of transverse motion are harmonically related with that of the fundamental (mode 1). The undercut is assumed to have a parabolic shape described by two variable parameters related to its depth and width. The rest of the beam on each side of the undercut is assumed to be uniform. Seven pairs of optimal undercut parameters are found that bring the frequencies of the first three transverse modes into the harmonic (integer) ratios 1:3:6, 1:4:8–9, and 1:5:10–13. Calculations performed with and without taking into account the effects of rotary inertia and shear stress are compared against measurements taken from a set of experimental beams. The comparison shows that including the effects of rotary inertia and shear stress results in a better prediction of the optimal parameters of the undercut.
The effects of auditory feedback on the regulation of intraoral air pressure during speech
Authors: Moon Jerald B. , Folkins John W.
Published: October 2005

Previous experimental evidence has been interpreted as support for regulation of both acoustics and aerodynamics during speech production. One recent perspective is that although speech acoustics may be manipulated, regulation of aerodynamics is a central component of the processes that produce speech. From this perspective, it has been suggested that aerodynamic regulation is given priority over perceptual accuracy. The experiment attempted to test this hypothesis by forcing speakers into a choice between aerodynamic and acoustic regulation. The intensity level of frication (embedded in a carrier phrase) was selectively amplified or attenuated and fed back to the speaker on line. Intraoral air pressure was recorded in order to assess whether or not perturbed auditory feedback would result in aerodynamic compensation. Although compensatory changes in peak intraoral air pressure, pressure duration, and pressure curve area were seen in response to 30-dB alterations of frication, no systematic effects were seen for smaller auditory manipulations. Further, the compensations were less than what one might expect from a system controlling auditory output. Explanations of these findings and their implications for the control of speech production are offered.
Different phase-stable relationships of the upper lip and jaw for production of vowels and diphthongs
Authors: Shaiman Susan , Porter Robert J.
Published: October 2005

Relational invariants have been reported in the timing of articulatory gestures across suprasegmental changes, such as rate and stress. In the current study, the relative timing of the upper lip and jaw was investigated across changes in both suprasegmental and segmental characteristics of speech. The onset of upper lip movement relative to the vowel-to-vowel jaw cycle during intervocalic bilabial production was represented as a phase angle, and analyzed across changes in stress, vowel height, and vowel/diphthong identity. Results indicated that the relative timing of the upper lip and jaw varied systematically with changes in stress and vowel/diphthong identity, while remaining constant across changes in vowel height. It appears that modifications in relative timing may be due to adjustments in the jaw cycle as a result of the compound nature of jaw movement for diphthongs as compared to vowels, with further modifications due to the effect of stress on these compound movements.
Decrement detection in normal and impaired ears
Authors: Plack Christopher J. , Moore Brian C. J.
Published: October 2005

The smallest detectable duration of a brief decrement in the intensity of wideband noise was measured as a function of the depth of the decrement. In the first experiment, conditions were tested in which the noise before the decrement was more intense than the noise after the decrement, and vice-versa. These data were used to estimate the shape of an intensity-weighting function, or temporal window, describing the temporal resolution of the ear. The equivalent rectangular durations (ERDs) of the temporal windows measured in this way had values of about 5.5, 4.6, and 6.6 ms for noise spectrum levels of 10, 30, and 50 dB, respectively. In a second experiment, decrement detection was measured in subjects with unilateral sensorineural hearing loss. One set of thresholds was measured in the impaired ear, and two sets of thresholds were measured in the normal ear; one with the noise level at equal SPL to the level in the impaired ear, and one with the noise at equal SL. Temporal window shapes were also estimated from these data. Only one of the subjects showed reduced temporal resolution in the impaired ear, the other two subjects having similar ERD values for all three conditions.
An artificial neural network for range and depth discrimination in matched field processing
Authors: Ozard John M. , Zakarauskas Pierre , Ko Peter
Published: October 2005

Associative feedforward neural networks with no hidden layers were applied to the problem of localizing a source in range and depth using the acoustic signal arriving at a vertical array of sensors. A highly processed form of the signal (excitations of an orthogonal basis) was used as input in order to increase the robustness of the trained network. The output layer consisted of one unit for each possible range and one unit for each possible depth of the source. The networks were trained with a signal-to-noise ratio (S/N) at the hydrophone of 50 dB, and then their performance was evaluated with S/Ns of 50 and 0 dB. Network weights were found for narrow and broad target shapes that correspond to narrow and broad beamshapes. The narrow target produced the beamformer with the lowest sidelobes and highest gains with acceptable but somewhat higher sensitivity to noise. Performance in the region for which the network was trained compared favorably with minimum variance beamforming.
Model study of sound propagation over ground of finite impedance
Authors: Pirinchieva R. K.
Published: October 2005

Experimental results are presented for the sound level distribution at different distances from the source when the sound waves propagate over ground with finite impedance. The measurements have been carried out in an anechoic chamber using a point source and using materials that can be used to model both reflecting and absorbing surfaces. The results from the measurements are compared with the theoretically calculated ones. The latter are obtained making use of a one-parameter ground model to allow for the presence of the finite impedance of the ground.
Shear wave diffraction loss for circular plane-polarized source and receiver
Authors: Green Douglas H. , Wang Herbert F.
Published: October 2005

An integral expression is derived which gives the shear wave magnitude received by a circular plane-polarized receiver that is identical to and coaxial with a source on the surface of an isotropic solid half-space. Numerical evaluation of the expression shows that the shear wave diffraction profile (i.e., the received magnitude as a function of source/receiver separation) is very similar to that for compressional waves in a solid and acoustic waves in a fluid in the Kirchoff limit of large ka, where k is the wave number and a is the source and receiver radius. Under such conditions, simplified acoustic diffraction formulas may be applied to shear wave data with little loss of rigor. In the opposite limit of small ka, the shear diffraction profile differs significantly from that of compressional or acoustic waves and the shear wave diffraction formula presented herein should be employed.
Technique for detecting the presence of finite sample-size effects in transmitted-wave measurements made on multilayer underwater acoustic panels
Authors: Piquette Jean C.
Published: October 2005

An experimental technique for detecting the presence (and magnitude) of finite sample-size effects in transmitted-wave measurements made on multilayer underwater acoustic panels is described. The technique is illustrated by presenting measurements made on several different sample panels. The measurements presented were made in the frequency range 2–12 kHz. Measurements are also presented which suggest that finite sample-size effects in transmitted-wave measurements may be reduced by replacing the standard steel backing plate with a plastic backing plate.
Microprocessor-based apparatus for direct evaluation of environmental impulsive sounds
Authors: Cannelli Giovanni B. , Santoboni Silvio
Published: October 2005

A new apparatus for direct evaluation of environmental impulse sounds was designed and realized on the basis of an improved formulation of the noise disturbance level LDI and by a suitable digital technique. The noise disturbance meter is equipped with a microprocessor and 32 kbyte of RAM, enabling it to perform uninterrupted measurements for time intervals from seconds to hours. Since the apparatus can be tuned to different time constants, this allows fast, average, or low-noise fluctuations to be detected, covering a wide range of environmental impulse noise situations. Some experimental tests carried out on a few impulsive noise samples of different origin showed that the noise disturbance level can give suitably greater weight to the fast fluctuation component of noises, in comparison with the conventional indices. Also, results indicated that the time constant is a critical parameter in measuring the impulse component of a sound. This stimulates further investigations to find the ‘‘optimum’’ time constant in measurements involving impulse sound evaluation and suggests that the study should be extended toward the investigation of a subjective ‘‘cutoff frequency’’ related to the noise fluctuation sensitivity.
Active control of noise transmission through a panel into a cavity. III: Effect of the actuator location
Authors: Pan Jie , Hansen Colin H.
Published: October 2005

The effect of the location of a point force used to control sound transmission through a panel backed by a cavity has been theoretically analyzed for a single frequency plane-wave incident sound field. Although the simple quadratic relationship between the point force phase and amplitude and the resulting interior noise level is well known, there is no such quadratic relationship between point force location and the resulting minimum achievable sound energy in the cavity. Results obtained here demonstrate that for a particular type of incident sound field, the optimum locations for the actuator producing the point force can be obtained by a global evaluation of the total sound energy in the cavity as a function of actuator location. It is demonstrated that a controller that drives an actuator placed at the optimum location will always produce a better attenuation performance than one that drives a randomly located actuator. It is shown that there might be more than one location at which a single actuator may achieve a similar minimum sound energy level in the cavity. However, the best actuator location is determined by considering other constraints, such as control force amplitude and the structural vibration level.
Scattering matrix and boundary integral equation methods for long-range propagation in an acoustic waveguide with repeated boundary deformations
Authors: Dawson Trevor W.
Published: October 2005

Boundary integral equation methods (BIEM) provide an accurate model for predicting the scattering of acoustic radiation from compact deformations of the walls of a waveguide. In numerical implementation, however, the denseness of the resulting coefficient matrix inhibits the modeling of scattering over very extensive deformations. It is shown how scattering matrix methods can be used to extend BIEM to allow for long-range propagation in a two-dimensional range-dependent waveguide. The extension to three-dimensional sources is also indicated.
An analytical approximation of strong nonlinear effects in bounded sound beams
Authors: Coulouvrat François Y.
Published: October 2005

The propagation of large nonlinear bounded sound beams in inviscid fluids is studied by means of the method of renormalization. Starting from a nonuniform quasilinear expansion of a solution of the Khokhlov–Zabolotskaya equation for a Gaussian source, a straining of the retarded time is introduced, which leads to a uniform approximation. The main point is the choice of a nonlinear phase shift, which yields a single smooth continuous representation for the wave, both before and beyond the shock formation point. A computation of the harmonics shows the asymmetrical distortion of the wave profile due to the coupling between nonlinearity and diffraction. A comparison with the results of a finite-difference numerical algorithm turns out favorable. The method is then extended to general plane sources.
A weighted residual formulation for the CHIEF method in acoustics
Authors: Wu T. W. , Seybert A. F.
Published: October 2005

In this article, the combined Helmholtz integral equation formulation (CHIEF) proposed by Schenck is greatly improved so that it will alleviate the annoying nodal surface problem. The constraint provided by each CHIEF equation and its first-order derivatives is enforced in a weighted residual sense over a small interior region rather than only at a single point. Consequently, ‘‘CHIEF blocks’’ rather than CHIEF points are used in the numerical implementation. Although the corresponding interior problem may have nodal surfaces at characteristic frequencies, it has no such things as ‘‘nodal blocks.’’ Therefore, the ‘‘CHIEF-block’’ (CHIEF-B) method is expected to work even if all of the CHIEF blocks fall on the intersection of several nodal surfaces. This new formulation is implemented in an isoparametric element environment. Numerical examples in spherical radiation and scattering at intermediate frequencies are given to test the new formulation.
Spherical-wave expansions of piston-radiator fields
Authors: Wittmann Ronald C. , Yaghjian Arthur D.
Published: October 2005

Simple spherical-wave expansions of the continuous-wave fields of a circular piston radiator in a rigid baffle are derived. These expansions are valid throughout the illuminated half-space and are useful for efficient numerical computation in the near-field region. Multipole coefficients are given by closed-form expressions which can be evaluated recursively.
Measurements of underwater sounds from a concrete island drilling structure located in the Alaskan sector of the Beaufort Sea
Authors: Hall John D. , Francine Jon
Published: October 2005

Underwater sounds produced by a concrete island drilling structure (CIDS) located in the Camden Bay region of the Alaskan sector of the Beaufort Sea were measured during idle and drilling operations, by use of both Nagra model IV-SJ and TEAC digital audio tape model RD101T recording systems. The wideband sound-pressure level at 1370 m recorded by the Nagra system, with a low-frequency recording limit of about 20 Hz, was 89.7 dB re:1μPa. The TEAC DAT system, with a low-frequency recording limit of 0.2 Hz set by Brüel & Kjaer type 2635 charge amplifier, at 1370 m recorded a sound-pressure level of 111.9 dB re: 1μPa. At a distance of 22 km the underwater, wideband sound exposure level of a single report of the airgun on the geophysical survey vessel Western Aleutian was 142.8 dB re: (1μPa)2s.
Analytic and synthetic pitch of two-tone complexes
Authors: Houtsma A. J. M. , Fleuren J. F. M.
Published: October 2005

An experiment was performed in which subjects had to judge whether the pitch of two sequential sounds went up or down. The sounds were harmonic two-tone complexes. They were constructed in such a way that the frequency of one harmonic remained fixed, the frequency of the other went up or down, and the missing fundamental moved in the opposite direction. Results show that, for partials of low harmonic order, most subjects tend to follow the frequency of the moving partial, whereas for partials of order 6 or higher, responses are divided more or less equally between tracking of the moving partial and tracking of the missing fundamental.
Coherent and diffusive fields of underwater acoustic ambient noise
Authors: Shchurov V. A.
Published: October 2005

In this paper, results of investigations of underwater ambient noise are presented based on statistical analysis of the acoustic pressure and three orthogonal components of particle velocity of a medium P(t), Vx(t), Vy(t), Vz(t). The mathematical analysis used includes cross-spectral characteristics, simple coherence functions, phase spectra, and an algorithm to split the noise field into anisotropic and isotropic fields. The above approach is applied to study the anisotropic and isotropic fields of ambient noise in the deep open ocean and in a coastal area. A fundamental feature of the anisotropic field that has been revealed is that the direction of the horizontal component of dynamic noise energy flux is similar to the surface roughness propagation direction.
Optimizing the performance of piezoelectric drivers that use stepped horns
Authors: Bangviwat Athikom , Ponnekanti Hari K. , Finch Robert D.
Published: October 2005

An analysis is presented for the design of piezoelectric transducers in a sandwich configuration using a stepped horn as a particle velocity amplifier. The condition for maximum power delivery to the load impedance is established in terms of the parameters of the horn and the piezoelectric material. As an example, the method of false position is used to find solutions numerically for the dimensions of a horn suitable for radiating into steam.
Optimum design of a piezoelectric diaphragm for telephone transducers
Authors: Ichinose Yutaka
Published: October 2005

The optimum design of a piezoelectric diaphragm consisting of a piezoelectric plate and a base plate and used in telephone transducers is described. First, the relationship between the microphone and earphone sensitivities and the dimension ratios (a thickness ratio and a radius ratio) of the piezoelectric plate to the base plate is determined. Then the relationships between the maximum sensitivities, the optimum dimension ratios where the maximum sensitivities are obtained, and the material constant ratios (Young’s modulus ratio and a density ratio) are examined. The base plate material should be harder and lighter than that for the piezoelectric plate to achieve high sensitivities. A diaphragm designed for an earphone or sounder can be used in a microphone as well. Experimental results agree well with the calculated values.
Evaluation of simple models of auditory profile analysis using random reference spectra
Authors: Kidd Gerald , Mason Christine R. , Uchanski Rosalie M. , Brantley Merry A. , Shah Phalguni
Published: October 2005

This article describes further study of the finding reported by Green et al. [J. Acoust. Soc. Am. 73, 639–643 (1983)] and others that, in certain conditions, the threshold of detectability for an intensity increment to the center tone of a multitone reference spectrum decreased as the number of nonsignal tones increased. That result was considered remarkable since critical-band theory would predict that these nonsignal tones, spaced outside the ‘‘critical band’’ containing the signal, would have no effect on or, at most, slightly decrease within-band detectability—and certainly could not account for the result of improved detectability found in the study cited above. Recently, Henn and Turner [J. Acoust. Soc. Am. 88, 126–131 (1990)] were unable to replicate the result described above, concluding that the phenomenon exists only in ‘‘limited conditions’’ and that it is ‘‘highly individual’’ in nature. Further, they speculated that the most likely reason for the discrepancy between their study and previous studies was the selection and/or training of the observers. The present study addressed the effects of the amount of subject training on the finding of Green et al. while controlling the potential effects of stimulus order. Specifically, for a group of three ‘‘naive’’ listeners, thresholds were measured for 3-, 7-, and 21-tone inharmonic complexes as a function of the amount of practice in a mixed-block design.

In all cases the group mean thresholds decreased as the number of nonsignal tones increased both initially and after extensive practice for both fixed- and roving-level conditions. Thus the effect does not appear to be an artifact of the amount or order of training subjects receive. The possible role of subject sample size and the magnitude of individual differences in obtaining the effect remains an open question. Two hypotheses suggested to account for the improvement in threshold with increasing number of nonsignal tones were evaluated. The hypotheses were represented by simple mathematical models, referred to as the ‘‘multiple-comparison’’ and ‘‘pitch-cue’’ models. The predictions of both models were compared with the results of a series of detection experiments in which the independent variables were the number of nonsignal tones and amount of random, within-trial ‘‘amplitude perturbation’’ [cf. Kidd et al., J. Acoust. Soc. Am. 79, 1045–1053 (1986)] of the nonsignal tones. Neither model, as applied, provided a satisfactory account of the effects of the main variables of number of tones and amount of perturbation. Finally, the results provided qualified support for the explanation offered by Kidd et al. [J. Acoust. Soc. Am. 86, 1310–1317 (1989)] that the lack of improvement in signal threshold with increasing noise bandwidth found in a tone-in-noise paradigm resulted from limits on performance imposed by the spectral variability of the random noise.
Effects of relative starting phase and frequency separation of two-tone stimuli on the brain-stem auditory-evoked response
Authors: Sammeth Carol A. , Burkard Robert F. , Hecox Kurt E.
Published: October 2005

Brain-stem auditory-evoked responses (BAERs) were obtained in six normal-hearing adults using single-tone and two-tone stimuli arithmetically centered around 4000 Hz. Two-tone stimuli varied in frequency separation from 200 to 3200 Hz, and started in-phase (homophasic) or 180 deg out-of-phase (antiphasic) with each other. Responses to each of the single-tone components of the two-tone stimuli were elicited and then summed for comparison with responses to the two-tone stimuli. Results indicated no significant difference in wave V latency between homophasic or antiphasic two-tone conditions, and summed single-tone conditions. Under the homophasic condition, the mean latency for the widest frequency separation of the tones was significantly longer than those for narrower separations. A significant difference in wave V amplitude between two-tone phase conditions was found for frequency separations of 200, 400, and 3200 Hz only. Summed single-tone BAERs demonstrated a significantly larger wave V amplitude than responses from either two-tone phase condition at all frequency separations.
Optimum estimation of the mean of non-normal populations
Authors: Sheehy Jerome J.
Published: October 2005

The purpose of this paper is to analyze and to verify, via computer simulation, the performance of a new method for obtaining an optimum estimate of the mean when dealing with non-normal populations. It is shown that optimum estimation of the mean of a population with a known, but not necessarily normal probability density function (pdf), requires the use of nonlinear operations on the sampled data and that these operations are completely specified by the pdf of the population. For the special case where the population is normal, the proposed estimators reduce to the conditional mean when a priori knowledge regarding the mean is available or to the conventional arithmetic average when no such knowledge is available. With regard to performance, theoretical predictions are verified using a computer simulation, and it is shown that the proposed estimator achieves the Cramer–Rao lower bound for a particular non-normal pdf. These results are significant because they offer an alternative to conventional linear estimation theory, which for non-normal populations can result in very suboptimum performance, and to suboptimum ‘‘robust’’ estimation techniques which may not employ, in an optimum way, all the information available about a particular population. It is believed that the findings should be of interest in any field where non-Normal populations are encountered and improving the efficiency of statistical testing procedures is important. Investigators in the field of underwater acoustics, where a number of experiments have indicated that signals and noise do not always exhibit Gaussian behavior, should find these results of particular interest.
Near-field identification of vibration sources, resonant cavities, and diffraction using acoustic intensity measurements
Authors: Mann J. Adin , Tichy Jiri
Published: October 2005

Near-field acoustic intensity measurements are a powerful analysis and diagnostic tool when all available measured quantities are utilized. The advantage of considering the reactive intensity and complex specific acoustic impedance along with the active intensity is stressed. An added feature to the data presentation is the pressure phase that is reconstructed from the time-independent measured data. The active intensity plots are thus enhanced by superimposing the lines of constant phase so that the wave-front propagation is visualized. In the first measurement configuration, an active source absorbing power is differentiated from a resonant cavity absorbing power and diffraction is localized. In the second configuration, the mode shape of a vibrating plate is identified.