bluuebunny/crossref_metadata_2025 huggingface dataset:
The FLEXBAR™: A new transducer element with applications to low-frequency, high-power, broadband sonar projectors
Authors: Fitzgerald James W. , Parssinen Edwin J.
Published: October 2005

Conventional wisdom in the sonar community has always held that the free-free (F-F) flexure bar, unlike its hinged-hinged (H-H) counterpart (i.e., the bender bar), has no useful application as an underwater transducer, presumably because it radiates as a dipole [R. S. Woollett, “The Flexural Bar Transducer,” p. 203, NUSC (1988)]. However, a simple modification converts the F-F bar to an efficient monopole radiator, while at the same time retaining its beneficial and unique properties of nodal mounting and dynamic balance. Such a modified F-F bar, termed a “FLEXBAR™,” has profound consequences as regards sonar projector performance. Among them is the fact that the FLEXBAR™, unlike the bender bar, can be driven at high amplitudes with essentially no mechanical coupling to or reaction on its mounting, housing, or array structure. Applications of FLEXBAR™s are illustrated by designs and predicted performances of two different liquid-filled, tuned-cavity projectors. The first of these is based on a cylindrical array of piezoceramic FLEXBAR™s, 21 in. in diameter × 30 in. high, covering the band of 400–800 Hz with a source level of SL≃210 dB/μPa‖m. The second unit consists of electrodynamic FLEXBAR™s in a cylindrical array 7 ft. in diameter×7.5 ft. high, and covers the band of 100–200 Hz with a source level of SL≃220 dB/μPa‖m. The calculated responses of FLEXDUCER™s (comprised of FLEXBAR™s) from their equivalent circuit representations compare favorably with their measured responses. [Work supported in part by NUSC/NLON.]
New designs of class V flextensional transducers with ATILA
Authors: Anifrani K. , Boucher D.
Published: October 2005

The improvements sought in range and performance of sonar arrays require the use of higher acoustical powers at lower frequencies from radiators of reduced dimensions. At the present time, flextensional transducers seem to offer a good solution. Two kinds of flextensional transducers are generally employed: classes IV and V. In the first case, the motors consist of parallel stacks of ceramics, the shell providing the prestressing. In the second case, the motors are made from ceramics staves arranged to form a ring, the prestressing being achieved by wrapping the ring with glass fibers under tension. However, because it is not conventional, the application of prestress in these two cases remains delicate and imprecise. The purpose of this paper is to analyze by the finite element code ATILA [Decarpigny et al., J. Acoust. Soc. Am. 78, 1499–1507 (1985)] an original idea for a class V flextensional transducer that does not suffer from this disadvantage. This flextensional transducer is made from a segmented ring on which are mounted classical ceramic stacks arranged in the form of an inscribed polygon. Several shell configurations will be modeled and analyzed with a special emphasis on technical advantages of these new flextensional designs.
Graphing capabilities for CHIEF (combined Helmholtz integral equation formulation)
Authors: Siders C. M.
Published: October 2005

The computer program CHIEF [G. W. Benthien, D. Barach, and D. Gillette, “CHIEF Users Manual,” Naval Ocean Systems Center Report 920 (Sept. 1988)] is designed to obtain approximate solutions to exterior steady-state acoustic radiation problems for surfaces of arbitrary shapes vibrating with a prescribed normal velocity. Being unable to view the shapes defined by CHIEF can lead to many difficult debugging problems as well as incorrect solutions. DISPLAY3D provides points as though the data were locations on a three-dimensional surface on a solid and a description of how these points are connected. DISPLAY3D has several options that make it a versatile package. The code permits the user to change the orientation from which the data are viewed. DISPLAY3D also provides the option of viewing the direction of the normal velocity vector as defined by CHIEF. These options, as well as others, will be explained in detail. [Work supported by ONT.]
On the use of sympathetic resonators to improve the performance of a low-frequency underwater projector
Authors: Ellsworth John M. , Baker Steven R.
Published: October 2005

An analysis has been performed of the achievable gain in the radiation resistance and directivity of a low-frequency underwater transducer due to the nearby presence of an array of sympathetic resonators. The resonators were all taken to be air bubbles of radius a(≪ λ), equally spaced around a circle of radius R. The transducer was taken to be a sphere of radius a0 (≪ λ), located on the axis of the circle. The achievable gain was calculated for various numbers of sympathetic resonators as a function of ka0, ka, and kR, for the transducer in the plane of the resonators and out of the plane a distance of one-quarter wavelength. For the transducer in the plane, a gain in radiation resistance of almost a factor of 2 is possible with approximately six or more sympathetic resonators. For the transducer out of the plane, some amount of unidirectionality can be achieved at the expense of a slight reduction in radiation resistance. [Work sponsored by NUSC and NPS.]
Low-frequency cutoff in fluid-saturated porous piezoelectric ceramics
Authors: Besombes J. P. , Gragnolati C. , Lagier M.
Published: October 2005

Voided piezoelectric ceramics show interesting properties, particularly under hydrostatting solicitations. The 3.3 composite structure can be regarded as a porous solid frame with different scales of open porous cell (like an open cell foam). The high value of the dH piezoelectric coefficient is obtained by closing the surface cell openings to avoid external fluid entrances. The present work concerns the analysis of viscous fluid saturation effects on piezoelectric properties of porous LZT ceramics. Experimental results are presented that show a three-regime behavior of the hydrostatic sensitivity: a low-frequency regime characterized by a flat weak response that corresponds to the “local hydrostatic regime,” a high-frequency regime characterized by voided material response, and a transition regime characterized by a first-order cutoff response. This behavior can be explained in terms of competition between permeability and elasticity with an “RC” electrical filter analogy.
Computer modeling of piezoelectric transducers
Authors: Lerch Reinhard
Published: October 2005

A piezoelectric finite element modeling tool was developed to compute the complete static and dynamic behavior of piezoelectric devices. The exact differential equations governing piezoelectric media are solved numerically. Telephone transducers, ultrasonic phased array antennas, acoustical delay lines, and surface acoustic wave devices are analyzed with respect to their mechanical strains and stresses, electrical fields and displacements, as well as various integral properties, such as the electric input impedance or the electromechanical coupling coefficient. Even mass loading and radiation effects due to the surrounding media (gas or fluid) are computed by including the wave equation of the sound emitting media to the set of piezoelectric differential equations and, therewith, the interaction between piezoelectric solid and surrounding media is considered. Quantitative agreement between theoretical and experimental results is obtained for all investigated types of transducers. Examples for the optimization of piezoelectric sensors and actuators will be presented.
The shape of a spoken phrase
Authors: Liberman Mark Y.
Published: October 2005

When someone speaks, you don't just hear a string of words. Usually, you also hear how the words are grouped, and how the word groups are related; you hear where the speaker wants to focus our attention; and you hear a lot about what kind of person is talking, what the situation is like, how the speech fits into the situation, and how the speaker feels. You may hear hesitation or fluency, haste, or relaxation, a happy grin or a mouthful of chewing gum. Nothing will be said here about grins or gum, and relatively little about social setting, discourse structures, or the projection of emotions in speech. The topic is the shape of a spoken phrase, that is, the ways in which its fluent performance reflects the structure of the information it presents. Specifically, some of the ways in which the pronunciation of words in various languages reflects their grouping and their relative prominence will be examined. However, it is important to keep in mind that only a few apsects of potentially meaning-bearing variation in linguistic performance will be treated, and that most real speech will also show effects of the many phenomena that are being ignored. The study of phrasal shape in speech sheds light on the investigation of linguistic information structure, is of practical importance in the design of algorithms for speech synthesis, and is relevant to the study of musical performance as a source of comparison and contrast.
Memory for text, prosody, and melody in speech and song
Authors: Crowder Robert G.
Published: October 2005

Everyday speech is intoned through F0 contours and songs are intoned through observance of the musical score. In each case, the text is theoretically independent of the pitch variation (except in tonal languages). Whether the two streams, verbal and musical/prosodic, are remembered independently of one another is the target question here. Many experiments on memory for songs have shown that melody recognition is enhanced when the melody is presented with its original words as oppposed to when it is presented with different, but equally familiar words. New experiments have extended this finding to memory for the words and prosody of spoken sentences. Whether or not the prosody engaged different syntactic analyses, or changed the “sentence focus,” was unimportant in this experiment. The enhancement of sentence memory with unchanged prosody occurred when the verbal message comprised nonsense words (as does the enhancement of melody memory with unchanged text). Therefore, the dependence of these two streams cannot be explained by some integration of the meanings of the two streams.
Pitch in speech and music: Is there a single concept?
Authors: Houtsma Adrianus J. M.
Published: October 2005

The ANSI definition of pitch makes no distinction between conditions of speech sounds and music. Pitch behavior, on the other hand, shows numerous similarities but also peculiar differences for speech and music conditions. For both conditions the concept of virtual pitch, i.e., the holistically perceived pitch corresponding to the fundamental frequency, regardless of the physical presence of such a fundamental, plays an important role. When pitches are perceptually scaled, however, musicians tend to associate identical pitch intervals with roughly equal frequency ratios, which leads to a musical scale of equal log-frequency steps, whereas equality judgments of tonal accents in speech results in a critical-band scale, in principal similar to Stevens' and Zwicker's mel scale. When two simultaneous sounds are preceived, a paradoxical situation between speech and music is also found. Whereas it is easier to recognize two simultaneous vowels with a different fundamental (f0) than two vowels with the same f0, it is also easier to identify the pitches (f0's) of two simultaneous complex tones with overlapping spectral components than it is to recognize the virtual pitches of tones with spectral components in very different frequency regions. These perceptual findings should caution us not to treat pitch of speech and music too lightly as one and the same concept.
Space-time evolution of void fraction under a plunging breaking wave
Authors: Su Ming-Yang , Cartmill John
Published: October 2005

Bubble plumes generated by natural wave breaking in the ocean under moderate to strong wind are found to be important for acoustic reverberation near the air-sea boundary layer. The most significant underlying physical parameter is the void fraction of the bubbly medium. So far, very little quantitative data of the void fraction due to wave breaking are available. In this paper, some results shall be presented on the spatial-temporal evolution of void fraction under a plunging breaking wave. The experiment is conducted in a large wave tank (12 × 15 × 350 ft) with a programmable wave maker at the Oregon State University Wave Research Facility. The plunging breaking wave of a 3-s wave period with a maximum wave height of about 5 ft is created within a wave packet. The void fraction is measured at three depths below the wave surface at six separate stations 10 ft apart. It is found that the maximum void fraction reach of about 40% to the depth of the maximum wave height over spatial distance is close to the wavelength of 60 ft. The e-folding time for the decay of the void fraction of the initial bubble plume is less than the one-half of the wave period, but a significant void fraction (70.1%), which causes large sound-speed deficits persisting up to six wave periods, is also found. The void fraction is measured by a resistance gauge based on a theory originated by James Maxwell. [This project is funded by the Office of Naval Research Acoustic Reverberation program.]
Whitecaps and bubble clouds: Average and individual characteristics
Authors: Wu Jin
Published: October 2005

Spatially averaged results on white cap coverages of the sea surface and air bubbles in the near-surface ocean were parametrized recently (Wu 1988a,b). Both the whitecap coverage and the bubble population at the sea surface were found to vary with the cube of wind-friction velocity; in addition, the vertical distribution of bubble populations was shown to be exponential. Reported data of individual whitecaps (Snyder et al., 1983; Bortkovskii, 1987) are analyzed herewith according to the scaling of breaking waves reported by Hwang et al. (1989); their individual characteristics are then used along with global descriptions to determine the spatial density of whitecaps on the sea surface. The influence of water temperature is found to be rather significant in the production of bubbles, and therefore of whitecaps. Consequently, different distributions and coverages are proposed for bubbles and whitecaps in cold and warm waters. The vertical distribution of volumetric concentrations of spatially dispersed bubbles is subsequently obtained from that of numerical concentrations. Finally, results of whitecaps and bubbles are compared to further explore physical processes of their productions by the wind.
Music and speech: Neural substrates underlying complex auditory processing
Authors: Zatorre Robert J.
Published: October 2005

The possible role of various cerebral structures in some aspects of complex auditory processing will be discussed. Study of patients undergoing cerebral excision for the relief of epilepsy provides a good opportunity to examine the specific contribution of the primary auditory cortex to various types of tasks, including melodic discrimination, melodic memory, pitch perception, and auditory short-term memory. The results of such studies suggest that there is both lateralization and segregation of function within each temporal lobe: Certain types of processing (e.g., extracting the pitch of a complex tone) are disrupted only when the right primary auditory cortex is damaged, whereas in other cases (such as retaining a stimulus for a brief period of time) lesions to secondary associative areas are sufficient to produce a deficit. When appropriate, perception of musical sounds will be compared and contrasted with perception of speech sounds, in order to clarify the extent to which their processing may be dissociated at the neural level.
An engineering test of moving ship tomography in the Greenland Sea
Authors: Howe Bruce M. , Mercer James A. , Spindel Robert C. , Worcester Peter F. , Cornuelle Bruce D. , Munk Walter H. , Birdsall Theodore G. , Metzger Kurt
Published: October 2005

Moving ship tomography seeks to synthesize a high-resolution three-dimensional snapshot of the ocean sound speed field from a few tomographic instruments by moving them during the survey. A moored array of six acoustic transceivers was deployed in the Greenland Sea from September 1988 to August 1989 as part of the Greenland Sea Tomography Experiment. A prototype ship-deployed array of ten hydrophones was used to receive about 30 transmissions after mooring deployment and about 40 prior to recovery, distributed at locations encircling the moored sources. The positions of the sources and receivers are imperfectly known at this time, but it is possible to compare the observed arrivals with ray theory and identify many of the observed arrivals with numerical ray paths. The second survey yielded enough identified rays to produce estimates of the ocean sound-speed field in spite of the need to solve for the unknown instrument positions. The resolution of the sound-speed maps will improve as the ship and mooring positions are refined using NAVSTAR Global Positioning System data. The tests in the Greenland Sea are preparatory to a trial of moving ship tomography in the western North Atlantic in 1991. The experimental design for that experiment includes simulations examining the effects of ocean dynamics on the reconstruction process. Cases including both linear planetary wave propagation and advection by uniform barotropic currents show that the mapping can proceed in the presence of realistic dynamical evolution. [Work supported by ONR and ONT.]
Graphical method for identification of multipaths in ocean acoustic tomography
Authors: Nakano Iwao
Published: October 2005

In many cases of tomographic or long-range transmission experiments, ray identification is done by means of a simple comparison of observed and calculated arrival times of multipaths. But this is not effective in a case of strong perturbation. Now a new method is proposed which is applicable to a more complicated case. It is based on the fact that all of the multipaths are separated into several groups. Each group usually consists of four multipaths with the same number of lower turning points. Therefore, it is natural to plot the predicted arrival times in an x coordinate and to plot the measured arrival times in a y coordinate. Then some crosspoints are obtained as potential candidates of identifiable multipaths. Here, the linear relation is applied to select true crosspoints from false ones. The principle is that multipaths in the same group could have kept a good linear dependency and be in line in the figure. Finally, almost all of the measured multipaths are expected to be well identified and make a single identification curve. In the theoretical point of view, the method seems to be analogous to the least-squares method.
The dispersion equation in bounded viscothermal fluid: General formulation and applications
Authors: Bruneau M.
Published: October 2005

In the last century, G. Kirchhoff proposed a very fertile description of sound propagation in viscothermal fluid. He calculated the attenuation factors and speeds of propagation of harmonic plane waves in rigid-walled tubes, which are solutions of the dispersion equation, for the wide tube case and the upper wavelength range, making approximations to the lowest orders possible. The problem of extending these classical Kirchhoff results to the case of higher-order propagating modes was given by Beatty (1950), but the theory is not valid near the adiabatic cutoff frequency and for the evanescent modes. The initial purpose of this work is to provide an exact and unique general dispersion equation for all kinds of modes in cylindrical tubes. The main feature of this work is a new set of equations, derived from the basic classical theory of acoustic propagation in viscothermal fluid and valid not only in the frequency domain but also in the time domain. Three particular solutions of the general dispersion equation are two well-known results, i.e., the equivalent specific impedance of a rigid plane wall (equivalent to the viscosity and thermal conduction effects inside the boundary layers) and the complex resonant frequencies of the spherical acoustic resonator, and a new one, i.e., the complex propagation constant of waves for all kind of modes in a rigid-wailed circular tube. These results greatly facilitate calculations that are currently being worked on to obtain solutions to boundary problems such as the inertial mode coupling in acoustic gyros.
Influence of grain contact stresses on P- and S-wave attenuation in partially saturated Berea sandstone
Authors: Suárez-Rivera Roberto , Nihei Kurt T. , Cook Neville G. W.
Published: October 2005

It was observed that attenuation for both P and S waves is controlled by grain contact stress and the presence of fluids at the contacts. Attenuation is least for dry specimens loaded hydrostatically and greatest for water-saturated specimens loaded uniaxially. For hydrostatic loading, the difference between attenuation in dry and saturated rock is nearly constant and varies with stress only at the lowest stress levels. In the uniaxial case, the change in attenuation with stress persists at all stresses. Under uniaxial stress, only some of the grain contacts are subjected to stress whereas, under hydrostatic compression, all of the grain contacts are under stress. Interestingly, at the highest stresses, the rate of change in attenuation with stress is almost identical for saturated and dry samples loaded either hydrostatically or uniaxially. Significant differences in attenuation were not observed for saturations from 4% to 100% nor did attenuation depend upon whether the water was added before or after applying the stress.
Consequences of temporal asynchrony for modulation detection interference
Authors: Hall J. W. , Grose J. H.
Published: October 2005

Previous investigations have shown that the ability to detect the existence of amplitude modulation at a target frequency is reduced when amplitude modulation exists at a flanking frequency [Yost and Sheft, J. Acoust. Soc. Am. 85, 848–857 (1989)]. A similar modulation detection interference (MDI) effect has been demonstrated for the detection of frequency modulation [Wilson et al., J. Acoust. Soc. Am. (in press)]. Explanations for this type of interference have been proposed that are based upon channels tuned to frequency of modulation, and upon principles of auditory grouping. The present study investigated conditions where the asynchrony of temporal gating of the target and flanking frequencies was manipulated in order to make the frequencies more or less likely to be grouped by the auditory system as originating from a single putative source. Both AM and FM were investigated. By a simple channel hypothesis, such manipulations should have either no effect on MDI, or should increase the magnitude of MDI. However, by the auditory grouping hypothesis. MDI would be expected to be smaller in conditions favoring perceptual segregation of the target and flanking frequencies. Preliminary findings indicate that temporal asynchrony can reduce the magnitude of MDI effects. [Research supported by AFOSR.]
Cued envelope-correlation detection
Authors: Sheft Stanley , Yost William A.
Published: October 2005

The ability to detect coherence among simultaneously presented noise bands was examined in a cued 2IFC procedure; each trial was preceded by presentation of the synchronous target noise bands as a cue complex. Center frequencies (CFs) of the two to three target bands were either 500, 1250, or 3125 Hz, with bandwidths ranging from 12.5–200 Hz. Performance was evaluated both for the target bands presented alone and in the presence of one to two masker noise bands. The uncorrelated target and masker bands had the same bandwidth, with their CFs separated by a factor of either 2.0 or 2.5. Though performance was impaired by the maskers, there was less masking than generally observed in modulation detection experiments with narrow-band maskers. There was little effect of coherence among the bands of the nonsignal interval if these bands were asynchronous with the target bands of the cue complex. Results indicate that listeners can discriminate among synchronous patterns of noise-band fluctuation, with performance generally better at the narrower bandwidths. [Work supported by NIDCD and AFOSR.]
Interactions among cues contributing to concurrent sound segregation
Authors: Marin Cécile M. H. , McAdams Stephen
Published: October 2005

Recent research has studied the contribution of individual acoustic cues to the perceptual segregation of simultaneously presented sound sources, but few have studied the way they might interact with one another. A first series of experiments was performed to determine subjects' ability to segregate equal-amplitude, three-harmonic target sounds embedded in a harmonic background at different values of single cues such as onset asynchrony between background and target (ΔO), differences in their fundamental frequencies (ΔF0), and the frequency modulation width present on the target when the background was unmodulated (FM). The stimulus complex consisted of 14 harmonics of a nominal 240-Hz fundamental presented in quiet. Stimulus F0 was roved over ± 5% on a trial-to-trial basis and stimulus level was roved over ± 3 dB re: 65 dB SPL on a tone-to-tone basis. Two 700-ms sounds with 50-ms raised cosine attack and decay ramps were separated by a 200-ms silence. Subjects were to decide if the targets embedded in the sounds were identical or different. Targets were composed of harmonics 3–5 to 7–9. From the psychometric functions for each cue, d′ values of 0.5, 1.0, and 1.5 were determined for each subject. In the second series of experiments, matrices of stimuli combining the stimuli corresponding to these d′ values were presented for different pairs of cues: (1) ΔO plus ΔF0, and (2) ΔF0 plus FM. The same experimental paradigm used in the first series was used here to determine combined d′ as a function of the d′ values of the two cues in isolation. The three-dimensional surface defined by the input d′ values of each cue and the measured combined d′ values were highly nonmonotonic for the ΔO-ΔF0 combination, indicating that the separate cues are not combined linearly. The ΔF0-FM combination was more linear and additive in nature. The results are discussed in terms of mechanisms underlying concurrent sound segregation.
Spectral shape discrimination using three-tone complexes
Authors: Berg Bruce G. , Green David M.
Published: October 2005

Thresholds were obtained for an increment in the intensity of a 100-Hz, center component of a standard consisting of three equal intensity tones. For three conditions, the frequency separation between each tone was 80, 40, and 10 Hz, respectively. Overall intensity was varied over a 20-dB range to preclude the use of absolute intensity as a cue. Unexpectedly, thresholds when tones were separated by 80 or 40 Hz differ little from thresholds when tones are separated by more than a critical hand (e.g., profile analysis). Moreover, thresholds increase by 10 dB when the digital-to-analog conversion rate is varied randomly between 38–42 μs/sample, providing evidence that listeners use pitch cues. If we assume that listeners use a strategy of off-frequency listening, then the results are consistent with Feth's EWAIF model [Feth and Stover, in Auditory Processing of Complex Sounds, edited by W. A. Yost and C. S. Watson, pp. 76–86 (1987)]. When tones are separated by 10 Hz, thresholds increase by 5 dB but are unaffected by variation of the conversion rate. [Work supported by AFOSR and NIH.]
Detection of relative-duration changes in total sequences
Authors: Kidd Gary R. , Watson Charles S.
Published: October 2005

This series of experiments continues an investigation of listeners' abilities to detect pattern invariants in tonal sequences that undergo relative-frequency and relative-time-preserving transformations. It was previously reported that frequency transposition had a large adverse effect on the detection of relative-frequency changes in randomly generated sequences of tones, although time “transposition” (a constant proportional increase in component durations) had little or no effect [G. R. Kidd and C. S. Watson, J. Acoust. Soc. Am. Suppl. I 84, S141 (1988)]. One possible explanation for the lack of an effect of time transposition is that the dimension of the to-be-detected change was not affected by the transformation. The present experiments were designed to determine whether time transposition might have an adverse effect on the detection of changes in relative duration comparable to the effect of frequency transposition on the detection of changes in relative frequency. Subjects were tested under conditions of high stimulus uncertainty (a different random sequence of durations on every trial) and low uncertainty (the same duration sequence on every trial) using different total durations and a wide range of transposition factors. An adverse effect of time transposition was observed under some conditions, but the effect was, in general, much smaller than in previous frequency-transposition experiments. [Work supported by AFOSR and NIH.]
Experiments on active control of structurally radiated sound using multiple piezoceramic actuators
Authors: Clark Robert L. , Fuller C. R.
Published: October 2005

Active control of sound radiation from a vibrating rectangular plate excited by a steady-state harmonic point force disturbance is experimentally studied. Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the panel. Microphones were implemented as error sensors, while the control approach was based upon a filtered-X version of the adaptive lms algorithm. Both position and number of piezoceramic actuators were varied during the test to determine the effects on control authority. The influence of increasing the number of channels of control was also considered. A variety of test cases was studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that piezoceramic elements provide an efficient method for distributed modification of structural response to attenuate sound radiation. In addition, the adaptive lms algorithm is shown to be an effective narrow-band controller which, in contrast to feedback approaches, requires no system modeling. [Work supported by ONR/DARPA.]
Theory of feed-forward controlled system eigenproperties
Authors: Burdisso Ricardo A. , Fuller Chris R.
Published: October 2005

Adaptive feed-forward algorithms have been successfully applied in the active control of sound and vibration. However, the actual mechanisms of control inherent in the technique remain an area of much interest. The main objective of this research is to study the dynamic characteristics of a feed-forward controlled system. The structure is assumed to be subjected to a harmonic input excitation, and the system controlled by another force. The controller is defined by minimizing the mean-square value of an error sensor signal. The error sensor is an accelerometer mounted on the structure or a microphone placed in the acoustic field for the active control of vibration or sound radiated, respectively. An entirely new mathematical approach to predict the dynamics of the controlled system is presented, which shows that the controlled system effectively has new eigenproperties. They are a function of the control force and error sensor locations, and independent of the input disturbance. Numerical examples demonstrate the formulation. These results are also corroborated experimentally using a feed-forward controller implemented on a TMS320C20 DSP processor. [Work supported by ONR.]
Active control of sound radiation due to subsonic wave scattering from discontinuities on fluid-loaded plates
Authors: Gu Yi , Fuller Chris R.
Published: October 2005

Active control of sound radiation from a fluid-loaded infinite plate with either a line constraint or reinforced by a uniform rib is analytically studied. The incidient field is assumed to be a subsonic structural wave and sound radiation is due to wave scattering from the discontinuity. The mathematical models are based on the coupled plate vibration and sound radiation due to a line force or a line moment solved in the spectral kdomain. Feed-forward control is applied by up to two active forces located near the discontinuity. The amplitudes of the control forces are determined by the optimal solution of a cost function that integrates the farfield radiated acoustic intensity in a semicylindrical space around the discontinuity. The results show that for subsonic incident waves, high global reduction in radiated pressure due to spectral wave scattering at the discontinuities is possible with the two active control forces. The amount of sound reduction, as well as the residual directively pattern, is shown to depend upon the number and location of the control forces. The far-field directivity pattern, the transverse plate velocity, and the near-field intensity distribution are extensively studied. [Work supported by ONR.]
Active acoustical control of broadband structural disturbances
Authors: Baumann William T. , Saunders William R. , Robertshaw Harry H.
Published: October 2005

The objective is to actively suppress the acoustic power radiated from a structure that is steadily excited by narrow-band or broadband disturbances. The problem is constrained by the assumption that the far-field pressure cannot bc measured directly. Therefore, a method for estimating the total radiated power from measurements on the structure is developed. Using this estimate as a cost function and assuming knowledge of the spectrum of the disturbance, a controller is designed using the LQG theory to minimize the cost. Computer simulations of a clamped-clamped beam show that there may be significant difference in the total radiated power between a system with a vibration-suppression controller and a system with an acoustic controller that accounts for the coupling of these vibrations to the surrounding fluid. In some cases, the acoustic controller increases the system vibration in order to minimize the radiated power. Experimental verification of these theoretical results is given in the subsequent paper “An experiment in state-space acoustic control of a plate excited by steady disturbances” [J. Acoust. Soc. Am. Suppl. 1 88, S149 (1990)]. [Supported by DARPA/ONR.]
Modification of transducer characteristics using active feedback
Authors: Corsaro Robert D. , Covey Joel F. , Ng Kin W. , Young Rose M.
Published: October 2005

Active feedback in a hydrophone-projector system is used to modify the transmit or receive efficiency of the system. Hence, the output from the hydrophone layer can be used to broaden the bandwidth of the projector or, conversely, the driver can be used to correct the response of the hydrophone. The principal features of the system can be represented by a one-dimensional model resembling a four-media system, consisting of water, a receiver layer, a projector layer, and a backing impedance. Since the output of the receiver layer is amplified and applied to the projector layer, an active acoustic feedback system results. Experimental data using a large-area projector bonded to a transparent large area polymer (LAP) hydrophone are presented.
Intraspeaker variation in aerodynamic and acoustic parameters of voice production across repeated recordings
Authors: Holmberg Eva B. , Hillman Robert E. , Perkell Joseph S. , Gress Carla DeLassus
Published: October 2005

In a previous study of aerodynamic and acoustic measurements of voice production for groups of female and male speakers to establish normative data, interspeaker variation was often found to be highly correlated with SPL [Holmberg et al., J. Acoust. Soc. Am. 84, 511–529 (1988)]. In this study intraspeaker variation across three recordings is examined for each of three female and three male speakers. Measurements were made from the inverse filtered air-flow waveform, of estimated average transglottal air pressure and glottal air flow, and the amplitude difference between the two first harmonics of the acoustic spectrum for productions of syllable sequences in soft, normal, and loud voice. Although the results show different patterns across both speakers and intensity conditions, preliminary observations reveal that a small amount of SPL variation could be accompanied by large variation in other parameters. For some parameters, the variation was strongly related to SPL, for others not. Statistical analyses will be performed to compare the intraspeaker variation across recordings with interspeaker variation from normal group data, in order to help quantify normal variation. [Work supported by NIH.]
Local spatial heterogeneity of the ocean's infrasonic sound field
Authors: D'Spain G. L. , Hodgkiss W. S. , Edmonds G. L.
Published: October 2005

The energetics of the ocean's infrasonic (0.5–20 Hz) sound field have been studied using simultaneous measurements of particle velocity and pressure by freely drifting sensors. Here, observations of the reactive intensity spectrum, which is proportional to the spatial gradient of the pressure autospectrum, are discussed. Results from a recent deep-water deployment indicate that, away from the ocean boundaries, the midwater background sound field above 1.7 Hz was locally spatially homogeneous in all directions. However, the vertical spatial inhomogeneity near the ocean bottom was statistically significant in two bands, 0.6–1.4 Hz and 7–20 Hz. The direction of the reactive intensity spectrum in the lower band suggests the presence of vertically decaying, ocean-sediment interface waves. From 7 to 20 Hz, the direction of the reactive intensity spectrum is opposite that in the lower band, and is probably due to the deep sound channel's ability to trap energy at higher infrasonic frequencies. For the sound field generated by a long-range, single-tone source, the vertical spatial heterogeneity can be large, implying that the particle motion is elliptical rather than rectilinear. [Work supported by ONR.]
The nature of the inhomogeneous component of the wave-induced microseismic noise field
Authors: Kibblewhite A. C. , Wu C. Y.
Published: October 2005

Spectra of the near-field microseismic noise induced by nonlinear surface wave interactions are calculated to examine the influence of the inhomogeneous component of the wave-induced pressure field. The contribution of this component appears to be critically dependent on the thickness of the water column, the properties of the bottom structure, and the position of the observation point. Calculation for a typical six-layered bottom with an overlying unconsolidated sediment on top of a solid half-space, in a shallow-water environment (100-m water layer), shows that the microseismic spectrum inside the active wave region is dominated by the inhomogeneous component that is some 40 dB higher than the homogeneous component. However, when the bottom is a single solid basement, this component reduces by about 30 dB. Further, when the observation point moves beyond the boundary of the active region, the spectral level drops dramatically and finally approaches the level of the Rayleigh mode of the basement. Applications of these results to the estimation of the ULF noise spectra from microseismic data recorded on shore are discussed. Variation of the spectra with distance from the active region is also examined. [Work supported by ONR.]
Detection and source localization of singular arctic ice-noise producing events
Authors: Leybourne Allen E. , Mire Christine T.
Published: October 2005

Detection and localization of single noise-producing events comprising underwater arctic ice noise are difficult due to myriads of sound sources present. This paper describes a recent experience gained while processing data from several horizontally placed hydrophones, where it has been shown that source localization of relatively nearby events (5000–10 0000 m) is feasible under conditions favorable to individualization of single ice transients. Initial processing strives to isolate event ensembles comprised at most of a small number of concurrent events of magnitude well above background noise. The ensemble detector employed dynamically determines the ratio of short and long time base mean deviations. At a suitable adjustment of its time base parameters, a ratio of 10 to 20 ensures that this goal is achieved. Multichannel ensemble graphs are examined visually to select ensembles comprising the singular events required for time delay estimation and computation of source location. The procedure works well during time periods of low overall noise level, allowing nearby events to be separated in time. [Work supported by NOARL.]
Teaching architectural acoustics by clarifying goals and demonstrating sound behavior
Authors: Kellogg Richard
Published: October 2005

There are three separate, often conflicting goals in architectural acoustic design: (1) good sound distribution in rooms designed for hearing; (2) sound isolation; and (3) noise reduction within spaces. Architects often seem to confuse these goals and the means of achieving them. For example, they often tend to “treat” all types of rooms with absorptive ceilings. A teaching method is described that aims at clarifying the goals by building a conceptual framework while demonstrating the physical nature of sound; i.e., waves that travel slowly. The consequences of wave behavior and slow speed are related to the goals by showing how each characteristic becomes an asset or liability for achieving each goal. To demonstrate wave behavior, a clear plastic tray containing about 3/8 in. of water is placed on a conventional overhead projector. The image of waves generated in the water, interacting with strips of modeling clay representing reflective surfaces are thus projected onto a wall screen. With this method, one may demonstrate diffraction, focusing, flutter, reverberation, resonance, transmission, etc., but not differential absorption or wavelength-related effects. Live demonstration allows repetition and variation in response to student queries and class discussion, and vividly backs up theory.
New approach to teaching architectural acoustics
Authors: Sotiropoulou Alexandra G.
Published: October 2005

Ways of presenting technological acoustic knowledge so as to awaken artistic sensibility to architectural students are explored, with emphasis on the acoustics of auditoria. The search is based on recent examples from modern architecture, where forms express in a highly artistic way the acoustical functions being served. There are also accounted, contemporary ideas about intrinsic communalities between musical composition (musical sound effect) and the architectural space, as well as the possibilities emerging from the introduction of modern psychometric methods to the research of audio and visual environmental perception. An audio visual example is employed to demonstrate the intrinsic relationships between musical composition and its visual aesthetic context.
Form function dependence at low ka
Authors: Dragonette Louis R. , Gaumond Charles F.
Published: October 2005

The form function of an infinite cylindrical shell has been solved and previously studied as a function of ka, shell thickness, and material parameters, e.g., density, longitudinal velocity, and shear velocity. However, at values of ka below 1.5, physical intuition suggests that the principal motions involved in scattering are uniform compression and undeformed body motion, the monopole and dipole terms, respectively. The backscattered form function at a fixed value of ka was therefore computed as a function of compressibility and mass of the cylinder, with thickness and one material parameter held constant. The effects of varying the remaining constant, as well as the effect of higher-order modes, were also found.
Long-range detection and sizing of millimeter size bubbles
Authors: George G. , Koller D. , Li Y. , Shankar P. M. , Newhouse V. L.
Published: October 2005

The sizing of mm size bubbles at ranges of 1–2 m using the double-frequency technique [V. L. Newhouse and P.M. Shankar, J. Acoust. Soc. Am. 74, 1473–1477 (1984)] is described. The experiment was performed in a small swimming pool installed in the laboratory. Bubbles generated, using a number of pipettes connected to a compressed air supply, were insonified continuously by a pump field in the range of resonant frequency of the bubbles and an imaging field at 450 kHz. The imaging field was pulsed with a Gaussian envelope, generated using an IBM PC. The echo from the bubbles at the sum and difference frequency was received by a third transducer forming a crossed-beam geometry and displayed on an HP 3585 spectrum analyzer. The sizes of the bubbles were obtained from the peaks at the sum and difference frequencies. The passive oscillations of the bubbles were also recorded at short ranges so that the size estimations can be compared. The double-frequency technique was capable of measuring the sizes of bubbles with diameters 1 mm and above at ranges of up to 2 m. The sum and difference frequency signal that was used for the measurement was also demodulated using a 450-kHz carrier, recovering the resonant pump signal. This signal recovery should be useful for off-shore measurements of bubble sizes since it is easy to record and store low-frequency information on tapes. [Work supported by ONR.]
On initial stage of bubble cavitation zone dynamics in pulse rarefaction waves
Authors: Besov A. S. , Kedrinskii V. K. , Pal'chikov Ye. I.
Published: October 2005

This paper presents experimental results of studying peculiarities of the initial stage of bubble cavitation evolution in liquid near a free surface when a microsecond duration shock wave reflects from it. Use of independent diffraction and electromagnetic techniques, as well as laser beam intensity variation, allowed the threshold effect evolution to be observed with an increase in the incident shock wave amplitude and solvability of these effects to be analyzed. Correlation of dynamics of the free surface and cavitation zone, predicted earlier on the basis of numerical studies performed [V. K. Kedrinskii and S. I. Plaksin, Proc. of the 11th ISNA (1984)], is confirmed experimentally. For the experiments, a transparent small hydrodynamic shock tube filled with distilled water was used. The shock wave was generated by a membrane occupying the central tube bottom part and excited by pulse magnetic field. The system geometry was chosen in order to exclude the effect of the tube walls on the wave field structure and cavitation evolution process. The experiments showed that, with the shock amplitude increase, the following effects can be observed: (1) the jump-like increase in light intensity scattered on cavitation micronuclei, (2) considerable velocity retaining by the free surface for a long time after the rarefaction wave has passed, and (3) its complete absorption by developing cavitation zone. Attention is paid to hysteresis-type effects of the free-surface dynamics that can be due to both the structure of nuclei and peculiarities of their attaining the “visible” zone (zone of detection).
Noise generated by vortices over a cylindrical tube
Authors: Lancey Timothy W.
Published: October 2005

The sound field generated by a system of vortices, located near the outer boundary of a cylinder, with axes parallel with the cylinder's axis, was investigated. Analytical expressions for the near-field sound and the far field were derived, following the developments of earlier researchers [A. T. Conlisk and Y. G. Guezennec, Nonlinear Interaction Effects and Chaotic Motions, edited by M. M. Reischman, M.P. Paidoussis, and R. J. Hansen (The American Society of Mechanical Engineers, New York, 1988), pp. 31–51]. A formulation with the inviscid Euler equation was employed, with the flow assumed irrotational and incompressible. From the complex potential describing the vortex array external to the cylinder, the complex velocity was derived, yielding the equations for the trajectories of the vortices. The sound field radiated was compared to that of the pulsating cylindrical source.