bluuebunny/crossref_metadata_2025 huggingface dataset:
University of Miami shallow buried OBS experiments at the Oregon Margin.
Authors: Yamamoto Tokuo , Turgut Altan
Published: October 2005

A new method of OBS burial has been successfully tested in 3000-m-deep waters of the Oregon Margin during the cruise on board R/V Wecoma in September 1991. Guralp CME-3 broadband seismometers were buried approximately 1 m below seafloor. Approximately 50 h each of continuous data were successfully collected at OM-1 (44 42.5’ N, 125 32.3’ W) and OM-8 (45 04.83’ N, 125 24.96’ W) sites. A local earthquake event at 01:36 a.m., 12 September (Oregon time) was clearly recorded in the seismic channels and pressure channel at OM-1 station. The time-averaged frequency spectra of vertical acceleration and pressure show a quiet notch at 0.04 to 0.10 Hz as well as very high coherency between channels both at the infragravity wave band (0.003 to 0.03 Hz) and at the double frequency microseism band (0.10 to 0.50 Hz). The crustal structures of compressional wave velocity, shear wave velocity, and porosity down to 10 km below seafloor are determined at a resolution of a few hundred meters using BSMP inversion of the infragravity data. [Work supported by NSF.]
Effects of base complexity in musical duplex perception.
Authors: Hall Michael D. , Pastore Richard E.
Published: October 2005

Duplex perception (DP) occurs when one stimulus or stimulus component contributes simultaneously to two distinct percepts. Most DP research has been used to loosely address the postulation of a phonetic module. The present musical DP experiments focus instead on the utility of DP in evaluating perceptual organization. The present investigation evaluated one variable which, according to Gestalt notions, could be critical to DP, base complexity (the number of frequency components in the base). In a modified AX task, two experiments used chord stimuli, dichotically presenting a fixed base and variable (major/minor chord) distinguishing tone on each trial. Fusion of contralateral distinguishing tones was frequent, but contrary to modularity conjectures, little evidence was found for triplex perception. Other unexpected results will be presented. Findings are discussed as they apply to (a) speech stimuli (stimulus dominance) and (b) attentional constructs (as an example of feature integration). [Work supported by NSF.]
Syllable internal timing: Effects of speaking rate, sentence position, and focal stress.
Authors: Behne Dawn M. , Nygaard Lynne C.
Published: October 2005

The duration of a vowel can be affected by speaking rate, sentence position, and focal stress. Having confirmed the independent effects of these factors on vowel duration, the goal of this study was twofold: (1) to describe their effects on the timing of consonants neighboring the affected vowel, and (2) to characterize the internal timing of the syllable when these factors are combined in the same sentence. Conversations were developed in which target CVCs occurred in initial or final sentence position and were either focused or nonfocused by the discourse. Twelve subjects produced each conversation at three speaking rates. The results indicate that (1) like vowels, consonant durations are affected by speaking rate, sentence position, and focal stress, and (2) when converging on a syllable, the investigated factors influence the syllable’s internal timing independently. These findings suggest that speaking rate, sentence position, and focal stress each globally affect the internal timing of a syllable, with the effects of each factor being superimposed on one another within flexible upper and lower limits.
Individual variability in the perception of natural and synthetic speech.
Authors: Hazan Valerie L. , Shi Bo
Published: October 2005

The extent of individual variability in the perception of natural and synthetic speech was examined in a group of 60 listeners, homogeneous in terms of age, language, background, hearing threshold, and exposure to synthetic speech. Listeners were tested on three types of speech material, representing different levels of contextual information: nonsense syllables (VCV), semantically unpredictable sentences (SUS), and SPIN sentences, in which test words are presented in high- and low-probability sentence contexts. All tests were presented in synthetic speech and natural speech-in-noise conditions. A large amount of variability in scores was found for all tests. Cluster analyses showed the presence of three main listener groups, differing mainly in their performance on low-redundancy sentence material. There was a strong correlation between the SUS and SPIN sentence test results but performance on synthetic speech was not strongly correlated with performance on natural speech in noise. Scores obtained for word and sentence tests were compared to the listeners’ performance on reduced-cue identification tests for place and voicing contrasts in order to ascertain whether there was a link between a listener’s use of acoustic cues and need for contextual redundancy. [Work supported by SERC.]
An improved Kirchhoff approximation for scattering from penetrable media using the operator expansion.
Authors: LePage Kevin , Tang Dajun , Schmidt Henrik
Published: October 2005

Recent work by Milder [J. Acoust. Soc. Am. 89, 529–541 (1991)] has shown that increased efficiency in evaluating the Helmholtz integral equation for scattered fields may be obtained through a method known as an operator expansion (OE). More recently Kaczkowski and Thorsos [J. Acoust. Soc. Am. 90, 2258 (A) (1991)] have validated the accuracy of the OE for a broad variety of impenetrable 1-D rough surfaces. Here the OE formalism is used to obtain results for penetrable, even acoustic–elastic interfaces. Since in penetrable problems neither the value of the scattered field nor its derivative on the interface is known, it is necessary to seek some approximation. In this work a modified Kirchhoff approximation is proposed, where the scattered field on the interface is approximated by the incident field multiplied by the local reflection coefficient, but its derivative is approximated using the operator expansion. Two-dimensional scattered field realizations computed using this procedure are compared to exact fluid–fluid results obtained by a boundary integral approach and fluid–elastic results obtained by the boundary element method of Gerstoft and Schmidt [J. Acoust. Soc. Am. 89, 1629–1642 (1991)]. Conclusions are drawn concerning the accuracy of the method and the feasibility of using it to estimate three-dimensional reverberation.
A general theory of scattering by thin interface layers, plates, and shells.
Authors: Wickham Gerry
Published: October 2005

In recent years there have been a number of attempts to model the effect of thin interface layers on the scattering and transmission of sound by bodies submerged in a continuous medium. Interface layers or coatings occur in numerous engineering acoustic applications. For example, when two solid bodies are bonded together, the adhesive or the imperfect fusion region will generally introduce an acoustic mismatch with both partners. Similarly, the use of austenitic cladding as a protection against corrosion creates an analogous problem, except that here the layer should be thought of as being fused to the surface of the material. In underwater and aeroacoustics the fluid–solid interactions with a shell or plate are often modeled using the Euler–Bernoulli thin plate theory. As far as the scattering problem here is concerned, the thin plate equation appears as an ‘‘effective boundary condition’’ relating the transverse displacement to the fluid pressure. Similarly, a thin interface layer between two solids is also modeled by some effective boundary condition. A typical approach is to assume that the layer is characterized by interfacial mass, spring, and damping constants. The latter are estimated by comparing the predictions of the model with the exact solutions to certain statical canonical problems. The difficulty with this approach is that, generally, it is not self-consistent. In other words if the spring constant is calculated so that the predictions of the model agree well with certain exact solutions at ‘‘normal incidence,’’ say, then it is usually not the case that they give agreement under different loading conditions. Similarly, in the fluid–solid interaction problem, the Euler–Bernoulli theory gives a correct approximation to the dispersion relation for leaky antisymmetric Rayleigh–Lamb waves in a fluid-loaded thin plate but incorrectly predicts the transmission and reflection of a plane wave by such a plate in the fluid! In this paper these problems are addressed by developing a rational approximation scheme for an arbitrary thin layer immersed in a contrasting matrix. a)The author is currently on leave from The Department of Mathematics, University of Manchester, Manchester M13 9PL, U.K.
A new formulation for scattering of sound by cylinders with noncircular cross section.
Authors: DiPerna Daniel T.
Published: October 2005

The problem of scattering of acoustic waves from a cylinder of noncircular cross section is treated using a plane wave expansion in Cartesian coordinates. By changing to a coordinate system in which ‘‘radial coordinate =constant’’ is the scatterer surface, series expansions for the incident and scattered field are obtained. The form of these expressions allows rigid or soft and in some cases penetrable (fluid) boundary conditions to be easily satisfied. The result is a system of equations that may be solved for the expansion coefficients of the scattered field. Numerical results for a 10:1 aspect ratio elliptic cylinder under rigid boundary conditions show excellent agreement with the exact solution. [Work supported by ONR.]
Measurements of scattering by irregularly shaped bodies.
Authors: Thorne Peter D. , Boyle Frank A. , Chotiros Nicholas P. , Waters Kendall R.
Published: October 2005

Scattering by spheres is a classical problem in underwater acoustics, and developments over the past two decades have established a detailed description of the scattering process in terms of the form function structure. More recently, interest has focused on sound scattering by spheroids and a number of studies have successfully applied the T -matrix formulation to solving the scattering problem. Currently the scattering of sound by irregular bodies is receiving increasing attention because of the application of acoustics in studying suspended sediment processes, the effect of irregular bodies on sea bottom scattering, and the use of acoustics in medical physics. In the present study a series of measurements have been taken on a number of solid irregular bodies over a broad frequency range to examine their scattering behavior. A statistical approach has been adopted to measure the ensemble average form function for the irregular bodies and these observations are compared with predictions based on a semiheuristic approach to solving the scattering problem.
Nonreciprocity of long-range reverberation in a wedged continental shelf.
Authors: Zhou Ji-xun , Zhang Xue-zhen , Guan Dinghua
Published: October 2005

The bottom scattering strength at low frequency and grazing angle in shallow water can only be extracted from long-range reverbertion (with large R/N ratio). Due to multipath effects the conventional model of boundary reverberation, based on geometric ray theory in the deep sea, is no longer suitable for calculating the long-range reverberation in shallow water. Up to date little reliable information on bottom scattering at low frequency and small grazing angle has been given in shallow water. For a frequency range of 50–2000 Hz and at a grazing angle of 0.5°–10°, it is hard to confirm the mechanism of bottom scattering and its dependence on frequency, grazing angle, and bottom type. In such a range, even the angular dependence of bottom scattering (a most basic relationship) is questionable. In this talk, using the WKB approximation to adiabatic normal mode theory, an averaged intensity expression R(r) of long-range reverberation in wedged homogeneous shallow water is derived. For two identical sources directed at each other, the monostatic reverberation intensities, obtained at two terminations with a depth of h1 or h2, would not be reciprocal. It is shown that Rh1(r)/Rh2(r) = (h1/h2)n, where n is an angular index of bottom backscattering. Based on this result, the value of n at small grazing angle can be determined from at-sea long-range reverberation data. A simulation tank experiment is suggested. [Work supported by ONR and the IAAS.]
Two-dimensional cross correlation of reverberation data.
Authors: Canales L. , Harris J. , Yoerger E. J. , Caruthers J. W.
Published: October 2005

A technique of time stretching time-series data is applied to reverberation time sequences beamformed from a multielement horizontal receiving array. For different, but nearby, array locations, beams that are scattered off a common area should be highly correlated. The correction method applied here maps each beamformed time series such that common scatterers coincide in position on a 2-D grid. The method uses an average pilot signal and 2-D cross correlations to stretch the time series in a way similar to static corrections in surface seismic processing. This process requires multiple iterations and the average pilot signal is recalculated between iterations. This method was applied to the aforementioned data from five different array locations using an average pilot signal. The results showed a high degree of correlation among the time series. The results are compared with available bathymetry to determine if scattering events can be matched with bottom features. [Work supported by ONR.]
Ocean-basin scale inversion of reverberation data.
Authors: Makris N. C. , Berkson J. M. , Kuperman W. A. , Perkins J. S.
Published: October 2005

An optimization method for numerically estimating scattering strength over large areas of the ocean floor is under development. A cost function comparing beamformed towed-array reverberation data with replica reverberation data derived from an ocean-basin scattering strength model is minimized. Data spanning a sufficient set of source locations and/or receiver orientations are inverted simultaneously. Inherent to this process is also the removal of the right-left ambiguity of the beamformed data during the inversion. The method has been successfully applied to synthetic data. It is presently being used to analyze bottom reverberation data acquired during the ONR/SRP Acoustic Reconnaissance Cruise of August 1991. In conjunction, the adiabatic mode formulation [Kuperman etal., J. Acoust. Soc. Am. 89, 125–133 (1991)] is being used to efficiently model acoustic propagation over the variety of source locations required.
Effect of levels of stimulus uncertainty and consonantal context on formant frequency discrimination.
Authors: Kewley-Port Diane
Published: October 2005

Discrimination thresholds for the second formant of vowels in consonantal context were significantly larger than for vowels in isolation in a report by Mermelstein [J. Acoust. Soc. Am. 63, 572 (1978)]. These results were not upheld in a recent report to this society [Kewley-Port and Watson, J. Acoust. Soc. Am. 89, 1996 (A) (1991)] for testing under minimal stimulus uncertainty procedures. Moreover, Mermelstein’s thresholds were a factor of 5 larger than those reported by Kewley-Port and Watson. The present experiment examines the effects of testing under higher levels of stimulus uncertainty in conditions more similar to those of Mermelstein. For well-trained subjects, most thresholds for the eight CVC stimuli tested did not change when levels changed from minimal to medium uncertainty. Further studies, using testing conditions similar to those of Mermelstein, employed untrained subjects. Results indicated that some subjects rapidly improved their ability to discriminate changes in formant frequency during just 1 h of testing. The differential effects of consonantal context, training, and levels of stimulus uncertainty will be discussed. [Research supported by NIH and AFOSR.]
Perceptual space and learning in speech perception.
Authors: Guzman Sandra J. , Nusbaum Howard C.
Published: October 2005

When listeners are given training on synthetic speech, intelligibility improves and listeners become more efficient in using cognitive resources for the perception of speech [L. Lee and H. C. Nusbaum, J. Acoust. Soc. Am. Suppl. 1 85, S125 (1989)]. The present study investigated one possible account of the connection between changes in intelligibility and changes in efficiency in using cognitive capacity: Learning may shift cognitive resources away from the analysis of acoustic properties of synthetic speech that are not informative about phonetic structure to more informative acoustic properties. If learning changes the distribution of attention to the acoustic signal, a change should occur in the structure of the perceptual space used in recognizing synthetic speech. Multidimensional scaling was performed on consonant confusions before and after training in order to determine if and how the structure of perceptual space is affected by learning. The results are consistent with the hypothesis that perceptual learning of synthetic speech changes the way listeners focus attention on the acoustic properties of the speech signal. [Work supported by NIDCD.]
Underwater polyvinylidene fluoride (PVDF) acoustic sensors.
Authors: Hughes W. Jack
Published: October 2005

Polyvinylidene fluoride (PVDF) is increasingly being used as a piezoelectric sensor in the construction of underwater hydrophones. Its desirable properties of high sensitivity, small thickness, mechanical flexibility, and variable electrode geometry, made PVDF an intriguing sensor to develop. One of the first applications of PVDF at ARL/PSU was in the measurement of the flow noise over the surface of an underwater vehicle. These data were compared with flow noise data that had been gathered by Professor Skudrzyk in the late 1960’s. Dr. Skudrzyk’s most recent interest in flow noise led to the conduction of field tests of three differently shaped PVDF sensors. These data will be presented. Also to be discussed are several of the numerous applications that PVDF has been put to at ARL/PSU: underwater intensity probes, hydrofoil pressure fluctuation monitoring, annular ring beam forming, large area/high-frequency sensors, and shaped-beam element sensors. Some of the advantages, disadvantages, and construction problems with PVDF sensors will also be addressed.
Variational analysis of thin beam excitation using asymmetric piezoelectric actuators.
Authors: Plantier Guy , Nicolas Jean
Published: October 2005

This paper presents a dynamic model as well as an experimental study of the response of a beam to excitation by a single piezoelectric ceramic glued to the structure. Such an actuator, when excited, produces both flexural and extensional motion in the structure. Based on an analytical approach using a variational method, the model takes into account the dynamic coupling between the structure and the actuator, includes the free stress conditions at the piezoelectric actuator boundaries and allows one to predict with accuracy the beam displacement and thus the extensional strain on the surface of the structure for any beam boundary condition. Although essentially devoted to the study of asymmetric piezoelectric actuators, the accurate model presented here allows one to discuss the simplifying hypothesis usually made in past studies on symmetric actuators.
Experimental measurement of structural intensity in the frequency–wave-number domain.
Authors: Padiyar S. , Cuschieri J. M.
Published: October 2005

Typical methods of structural intensity measurement involve the use of either contacting transducers or single and dual channel laser vibrometers. Because of the generally limited number of measurement locations, approximations that can limit the accuracy of the measured structural intensity data are implemented. The accuracy of the data can be compromised especially in the case of finite structures. Furthermore, if waves with different wave-number components exist, the measurement schemes used are typically tailored toward only one wave type. Using a multiple channel laser vibrometer, with more than two channels, eliminates the need for the approximations in the measurements. Additionally, by scanning the surface of the structure, the structural intensity components can be decomposed by using frequency–wave-number transforms. The result for the structural intensity in the frequency–wave-number domain will discriminate the intensity component into those associated with in-plane and out-of-plane waves. The frequency and wave-number transforms are obtained using digital signal processing techniques. One disadvantage with this approach is that inherent in discrete signal processing. In this paper, issues associated with the range of frequency and wave number(s), spatial window size, selected window type, and method of processing are discussed. A data processing scheme for frequency–wave-number measurements of structural intensity on finite structures is defined. Results showing the application of this technique using the multiple channel laser vibrometer will also be presented. [Work sponsored by ONR.]
On the detection and perception of modulation by human listeners.
Authors: Hartmann William Morris
Published: October 2005

In a series of papers, beginning in 1952, Eberhard Zwicker and his colleagues redefined the psychoacoustics of modulation detection and perception. The scope of this subject now encompasses questions of considerable generality: whether the detection of modulation is effectively a measure of difference limens, or whether the temporal variation present in the modulation introduces specific elements of neural processing; whether frequency modulation detection and amplitude modulation detection can both be understood from a single excitation-pattern model, and, whether auditory temporal processing of all kinds can be understood in terms of superposition of responses to modulated tones. Presently, there appears to be a totally satisfactory understanding of modulation detection at high modulation rates in terms of a spectral model and tone-on-tone masking. However, attempts to find a unified model for low modulation rates, where temporal processing is indicated, must cope with some difficult experimental results, including data that show awkward dependences of modulation detection and difference limens on signal parameters, evidence of selective adaptation, and recently discovered cross-channel effects. [Work supported by the NIDCD, DC00181.]
Detection of combined frequency and amplitude modulation.
Authors: Moore Brian C. J. , Sek Aleksander
Published: October 2005

Zwicker [Acustica 6, 356–381 (1956)] proposed that amplitude modulation (AM) and frequency modulation (FM) are coded by a common mechanism. To test this, the detection of simultaneously occurring AM and FM is discussed. In a two-alternative forced-choice task, thresholds for detecting AM alone were determined. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed, which can be explained by assuming that detection of modulation at high frequencies is based on detection of the lower sideband in the modulated signal’s spectrum. In a second experiment, psychometric functions were measured for the detection of AM alone and FM alone. For each type of modulation, d’ was approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms.
Modulation masking in normal-hearing listeners and in auditory brainstem implant patients.
Authors: Ahlstrom Chris , Shannon Robert V.
Published: October 2005

Recent experiments have suggested that a modulated masker can interfere with detection of a signal of similar modulation rate, in a manner analogous to the familiar critical-band concept in the frequency domain [Houtgast, J. Acoust. Soc. Am. 85, 1676–1680 (1989)]. An experiment with sinusoidally modulated maskers did not show such a critical-band effect in either normal-hearing listeners or in patients electrically stimulated on the cochlear nucleus. Maskers consisted of 500- or 1000-Hz sinusoidal carriers sinusoidally modulated at 4, 10, or 16 Hz with a modulation index of m=0.5. Thresholds for modulation depth were obtained for the same carrier modulated at signal frequencies of 1 to 32 Hz (in 1-Hz steps). Modulation masking was observed only when the masker and signal modulation frequencies were equal. The magnitude and form of the masking patterns depended strongly on the relative phase of the two modulators. Prior results might have shown critical-band type interference patterns because of the stochastic nature of the modulated maskers used. Previous and present results can be explained adequately by a short-term envelope correlation, without need to postulate a central mechanism for grouping temporal modulation patterns in the manner of a filter. [Work supported by NIH.]
Spectral transposition of envelope modulation.
Authors: Sheft Stanley , Yost William A.
Published: October 2005

Previous work [Sheft and Yost, J. Acoust. Soc. Am. Suppl. 1 85, S121 (1989)] has shown that it is often difficult to identify which component of a multicomponent complex is amplitude modulated. The role of the carrier in envelope processing was examined in the present study with a cued 2IFC envelope-discrimination procedure. The narrow-band noises of the two observation intervals differed only in terms of their pattern of envelope fluctuation, with the signal interval a repetition of the cue envelope pattern at a center frequency (CF) different from that of the cue. Cross-spectral transposition of envelope information was evaluated by varying the number of common CFs between the noise bands of the cue complex and the target bands of the observation intervals. With both the cue and observation intervals consisting of a single noise band, the ability to transpose envelope information from the cue to the observation-interval CF diminished with increasing noise bandwidth from 12.5 to 200 Hz. Results from the multiband conditions indicate that listeners are unable to integrate the envelope information across audio-frequency regions to improve performance. In fact, the added noise bands led to a significant drop in performance in many conditions. These results suggest that envelope information is not processed inde- pendent of the spectral location of the modulated carrier. [Work supported by NSF and AFOSR.]
Discrimination of tonal sequences composed of repeated temporal patterns.
Authors: Sadralodabai T. , Sorkin R. D.
Published: October 2005

The discrimination of rhythmic and nonrhythmic temporal patterns was investigated. Two sequences of 12 tones were presented successively (tone duration=25 ms, frequency=1000 Hz). The temporal pattern of each sequence was defined by the time intervals between the tones. The task was to report whether the two sequences had the same or different temporal patterns. According to the pattern correlation model [R. D. Sorkin, J. Acoust. Soc. Am. 87, 1695–1701 (1990)], listeners perform the task by computing the correlation between the two temporal patterns. In the current experiment, two aspects of these sequences were manipulated: (a) the correlation between the two 12-tone temporal patterns, and (b) the rhythmicity of the sequences, which we define as the correlation between the temporal patterns of successive 4-tone subsequences within a 12-tone sequence. Listeners’ performance increased with the rhythmicity of the sequences. Performance was above the level predicted by a simple extension of the pattern correlation model [Work supported by AFOSR.]
Development and comparisons of two cylindrical passive arrays.
Authors: Howarth Thomas R. , Pecoraro Mark L. , Walden Alan K. , Tims Allan C.
Published: October 2005

Two cylindrical, high-gain, wide-band (three octaves) passive arrays have been recently developed. Both arrays consist of 36 lead titanate elements mounted on a cylindrical structure. The elements are arranged in a 3×12 configuration with the 12 elements placed along 180° of the cylinder’s circumference. The difference between the design of the two arrays is in the backing of the individual piezoceramic elements. The elements in the first array have a steel tail mass behind them to form an acoustic hard boundary while the elements of the second array have a corprene layer backing to form an acoustic soft boundary. Other differences are that the first array has its elements in an oil-filled boot and the second array is potted in polyurethane. The presentation shall include conceptual drawings of the configuration of the elements and the arrays. Performance comparisons shall include the measured free field sensitivity, acoustic radiation patterns, and equivalent self-noise. [Work sponsored by DTRC.]
A three-parameter model for the behavior of transducers.
Authors: Ge Li-Feng
Published: October 2005

Owing to the limitation of materials and technology, it is significant to determine the behavior of a transducer as a whole by experiments. The impedance method is one of the most important methods. In previous works, a four-parameter model was established to relate the mechanical load impedance to its input electrical impedance. The characterized parameters of the transducer were then determined from the model parameters. [L.-F. Ge, J. Acoust. Soc. Am. Suppl. 1 87, S129 (1990); J. Acoust. Soc. Am. 89, 1860 (1991)]. But, results obtained by the model vary more or less with different beginning values calculated even from proper three-pair impedance data. In this paper, a three-parameter model is presented, and a complex least-squares fitting code is developed to fit the model to more than three pairs of data; thereby, a definite and more accurate solution has been obtained. The model is formulated as ZE=A*(ZL−B*)/(ZL−C*), where ZE is the electrical impedance, ZL is the load impedance, and the multiplier A*, pole point C*, and zero point B* are the three parameters to be determined. Exactly, A* is equal to the mechanically blocked electrical impedance and C* is equal and opposite to the electrically blocked mechanical impedance. The new model has been successfully used to determine the characterized parameters, motional impedance, and sensitivity of both piezoelectric and electrodynamic vibration generators, and then the sensitivity of accelerometers.
The dormant Noise Control Act and options to abate noise pollution.
Authors: Shapiro Sidney A.
Published: October 2005

In 1981, Congress ended funding for the Office of Noise Abatement and Control (ONAC) at the Environmental Protection Agency (EPA). Before the elimination of ONAC, EPA engaged in a wide variety of activities to abate noise pollution under the authority of the Noise Control Act and, after 1978, the Quiet Communities Act. Elimination of ONAC’s funding has stymied noise abatement efforts at both the federal and state level, while noise levels have probably increased. Without federal action, little governmental noise abatement activity can be expected. Although Congress has several options to abate noise pollution, funding EPA to implement the NCA is the best solution.
The role of voluntary standards in a National Noise Control Program.
Authors: Eldred Kenneth McK.
Published: October 2005

Voluntary standards can and should play a central role in a National Noise Control Program. They provide a uniform vocabulary for noise and its effects on people both in the USA and throughout the world as a result of efforts to harmonize national and international standards. They contain methods for the objective measurement of the noise characteristics of sources, evaluation of sound propagation effects, and characterization of the spatial and temporal aspects of environmental noise. Voluntary standards in acoustics in the USA are developed by several organizations, including the Acoustical Society of America, the Society of Automotive Engineers, and the American Society of Testing and Materials. They are the product of concerned professional individuals and representatives of directly concerned interests including both government and industry as well as organizations representing concerned technical and public groups.
Comparison of the speech transmission index and the modified rhyme test in simulated cockpit ambient noise.
Authors: Griffin Lisa A.
Published: October 2005

The military aircraft test and evaluation community has recently introduced a much quicker, less obtrusive method for evaluating speech intelligibility of a communication system. The method uses the Speech Transmission Index (STI) to predict intelligibility using 15 s of flight time. Previous research has developed a correlation between this method and subjective intelligibility scores for the Phonetically Balanced (PB) word test. This research has not yet shown an experimental relationship to the Modified Rhyme Test (MRT), one preferred method of the military. In addition, the research has not accounted for ambient noise with a spectrum that represents an in-flight aircraft cockpit environment. In the present study, the relationship between the STI and MRT in simulated noise was investigated. Two types of noise were used. The first type was noise with a spectrum to represent in-flight ambient cockpit noise. The second was pink noise (equal energy per octave), a commonly used representation of environmental cockpit noise. The study was two phase. Phase one measured the intelligibility of a communication channel degraded with the noise presented at different signal-to-noise ratios. The intelligibility test was the MRT. Phase two used the same communication channel and signal-to-noise ratio conditions to measure objectively the intelligibility using the STI. The findings of the study showed that the MRT scores were significantly differ ent between the different noise presentations while the MRT scores and STI yielded approximately the same values.
Effects of noise on crewmembers during Spacelab Life Sciences-1.
Authors: Koros Anton S. , Wheelwright Charles D. , Adam Susan
Published: October 2005

Excessive noise can lead to decrements in performance, impaired verbal communication, fatigue, and hearing damage. On the STS-40/SLS-1 mission noise levels were evaluated through the use of a questionnaire and two objective measures−in-flight sound level measurements and pre- and post-flight crew audiometry tests. Sound level meter measurements suggested that noise levels in Spacelab during nominal operations were approximately 70 dB (A-weighted). This is in excess of the current acoustic specification of 59 dB (A-weighted). Noise measurements conducted in the Orbiter did not exceed current Shuttle standards. Crewmembers recommended that noise levels be reduced. Post-flight audiometry tests indicated that transient decreases in hearing ability had taken place during the mission. The average decrease in hearing level of 4.34 dB was statistically significant. Crewmembers noted that sleep, concentration, and relaxation were negatively impacted by high noise levels. Communication was also hampered. The higher than desirable noise levels in Spacelab were attributed to flight specific payloads for which acoustic waivers were granted. It is recommended that current noise levels be reduced in Spacelab and the Orbiter Middeck. Levels of NC 50 are recommended in areas where speech communication is required, and NC 40 in sleep areas−in accordance with current Space Station Freedom standards. [This research was supported by the National Aeronautics and Space Administration under Contract No. NAS9-17900.]
Toward linear macrosonics.
Authors: Lucas Timothy S.
Published: October 2005

Large resonant acoustic pressure amplitudes were mechanically generated inside resonators filled with refrigerant HFC-134a. The nonlinear losses normally associated with resonant macrosonic waves were dramatically attenuated via resonators whose higher resonant modes were noninteger multiples of the fundamental. Such resonators reduced Q amplification of the fundamental’s harmonics, minimized viscous and thermal wall losses and minimized peak acoustic velocity. These noninteger resonators provided acoustic pressure amplitudes of up to 60 psi peak-to-peak for ambient pressures of 70 psi. At peak acoustic pressure amplitudes of 25% ambient, measured acoustic energy dissipation was within 34% agreement with strictly linear predictions. A high-amplitude resonator was used to construct a laboratory prototype of an oil-free resonant acoustic compressor. Compression ratios were provided via high-speed valves that converted acoustic pressure oscillations into an external discharge pressure. A 300-Hz discharge valve was tested that converted 95% of a resonator’s peak acoustic pressure amplitude into an external discharge pressure. Efficiency calculations indicate that resonant acoustic compressors could provide improved efficiency for home refrigerators. [Work conducted at Los Alamos National Laboratory in collaboration with Greg Swift and supported by DOE.]
Absorption of sound by noise in one dimension.
Authors: Larraza Andrés , Denardo Bruce
Published: October 2005

The problem of the statistical closure for one-dimensional interactions of nondispersive random waves is apparently ill posed. The problem consequently lacks an H-theorem formulation for how the system approaches thermodynamic equilibrium. Rudenko and Chirkin have, on the other hand, successfully computed the attenuation of an infinitesimal coherent wave due to the nonlinear interaction with broadband noise in one dimension [O. V. Rudenko and A. S. Chirkin, Sov. Phys. JETP 40, 945–949 (1975)]. They have shown that the attenuation coefficient is a linear function of position. This remarkable result implies that in one-dimensional acoustics, translational invariance is broken, the fluctuating forces are nonlocal, and the system is necessarily far from equilibrium. The physical implications of this result, and the connections to the fluctuation-dissipation theorem, will be discussed.
Nonlinear attenuation of 10- to 25-MHz ultrasonic waves in argon at pressures up to 10 MPa.
Authors: Bond L. J. , Dube B. , Chiang C-H. , Fortunko C. M. , McColskey J. D.
Published: October 2005

A large dynamic range (70 dB) ultrasonic measurement system has been developed to investigate the technology and the phenomonology of finite-amplitude high-frequency (10–25 MHz) acoustic waves in gases at pressures up to 10 MPa (100 bar). Transmission measurements of velocity and attenuation are made using two efficient lithium niobate transducers set onto quartz buffer rods, with variable separation from less than 1 to 25 mm. In this paper, data will be presented that show nonlinear phenomena as a gated tone burst (20 cycles) of finite amplitude acoustic waves propagated in argon. The received signals are digitized and analysis is performed in the time domain and using a Fourier transform. For low powers, linear attenuation with distance is observed. For finite amplitude waves, excess nonlinear attenuation and significant second harmonic generation are observed. The nonlinearity parameter at various combinations of pressure, temperature, and frequency is reported for argon.
Water fountains produced by intense standing waves in air.
Authors: VanDoren Thomas W. , Hamilton Mark F.
Published: October 2005

An acoustic demonstration found in several science museums involves a horizontal standing wave tube that contains a shallow layer of liquid. When the liquid is water and the sound pressure level of a standing wave in the air above the water exceeds approximately 160 dB (re: 20 μPa) at frequencies below 1 kHz, vigorous fountains occur at the nodes in the pressure field. The introduction of a surfactant in the water causes clusters of fountains to appear near the nodal planes at somewhat lower sound pressure levels. Standard quasilinear theory provides a reasonable description of the acoustic streaming and dc pressure in the air prior to the appearance of fountains. The fountains seem to result from the ejection of droplets by inner streaming vortices that are formed above the air–water interface. The water fountains and streaming patterns are discussed in relation to Andrade’s observations [Proc. R. Soc. London Ser. A 230, 413–445 (1932)] of solid particulate motion produced by intense standing waves in air. [Work supported by a Rockwell Graduate Fellowship, the ONR, and the Packard Foundation.]
Upper ocean diagnostics during rainfall.
Authors: Medwin Herman
Published: October 2005

Laboratory measurements have been made of the sound radiated by the complete size range of acoustically significant, single raindrops, falling at terminal speeds onto the surface of an anechoic water environment. This has provided the source information for the detailed analysis of many effects of light to heavy rainfall at sea. The three acoustically distinctive subranges are defined as ‘‘small’’ drops (equivalent diameter, 0.8–1.1 mm), ‘‘midsize’’ drops (1.1–2.2 mm), and ‘‘large drops’’ (≳2.2 mm). These subranges correspond to drops that are oblate ellipsoids, slightly flat-bottomed ellipsoids, and completely flat or concave-bottomed ellipsoids just before they hit the water surface. Their penetration through the air–water interface results in underwater spectra which, respectively, have peaks around 15 kHz, are very broadband, and have peaks that decrease from 10 to 2 kHz as the drop diameter increases from 2.2 to 5 mm. This knowledge of the acoustical sources at the surface has now made it possible to determine, during rainfall, such ocean parameters as: gas transfer by active microbubbles, bubble populations under the sea surface, rms ocean slope, raindrop size distribution, total rainfall rate, raindrop temperature, and even the type cloud and its base height from which the rain came. Some results will be presented. [Work supported by the ONR.]
An inversion technique to measure rain using underwater sound.
Authors: Nystuen Jeffrey A. , Ostwald Leo H.
Published: October 2005

Laboratory measurements of the sound generated by individual raindrops striking at terminal velocity show distinct spectral signatures for drop sizes from 2.2–4.6 mm diameter. These spectral signatures form a basis of a linear inversion algorithm that allows the large drop size distribution in rain to be estimated from the measured underwater sound spectrum. As large drops comprise most of the water volume, the estimate of rainfall rate should be very good. Examples of both the forward problem−estimating the underwater sound spectrum given the drop size distribution−and the inverse problem−estimating the drop size distribution given the sound spectrum−will be presented and compared to field observations. [Work supported by NOARL and NPS.] a)Lt., USN.
Distortion of bubble clouds by orbital motions in surface waves.
Authors: Longuet-Higgins Michael S.
Published: October 2005

The acoustical properties of a bubble plume, both as an emitter and as a backscatterer of underwater sound, will be strongly influenced by its geometrical shape and dimensions, and by its distance from the sea surface. In this paper the distortion of a bubble plume due to both the periodic motion in a steep, irrotational wave and the Lagrangian-mean shearing motion associated with the Stokes drift are calculated. It is shown that the bubble plume is rotated and also brought closer to the free surface on the rear face of the wave. The cloud is furthest from the surface when it is immediately below the wave crest. That is neglecting the natural buoyancy of the plume. The dynamical effects of buoyancy and mixing can also be taken into account. [Work supported by ONR.]
The dynamics and acoustics of breaking waves.
Authors: Melville W. K. , Lamarre E. , Loewen M. R.
Published: October 2005

In this presentation, recent progress is reviewed in the understanding of the relationship between the dynamics of breaking and the sound generated by breaking waves. Gently breaking waves entrain a small number of bubbles that may break up, resonate, and relax toward their equilibrium shape. Medwin and Daniel’s (1990) measurements of the sound spectrum under gently spilling waves are shown to be consistent with a simple model of the acoustics based on the resonant relaxation of individual bubbles. More energetic breaking may lead to significant air entrainment with recent laboratory and field measurements showing void fractions of O(10−1 ) or more. At these large void fractions the entrained air becomes dynamically significant and up to 50% of the energy lost from the surface wave field by breaking may be expected by entraining air against buoyancy forces. Bubble clouds of large void fraction may oscillate collectively and radiate sound at frequencies much lower that the resonant frequencies of the individual bubbles. Elsewhere at this meeting, measurements of low-frequency sound generated by 2-D and 3-D braking waves are presented, which are consistent with collective oscillation frequencies predicted from independent measurements of the void fraction. Methods are reviewed by which acoustic measurements of breaking may prove useful in indirect measurements of the dynamics of breaking and its role in processes of air–sea interaction. [Work supported by ONR (Ocean Acoustics) and NSF (Physical Oceanography).]
Nearsurface bubble density distribution due to wave breaking.
Authors: Su Ming-Yang
Published: October 2005

Several series of experiments have been conducted in the past 2 years on breaking of surface gravity waves and its subsequent air entrainment, which forms plumes of bubbles. These experiments were conducted using both electromagnetic and acoustic principles. The laboratory experiments were performed in a very large tank, in both fresh and salt water, and were used to quantify the significant effects of salinity on the production and evolution of bubbles due to wave breaking. From the open sea experiments, extensive measurements of the near-surface void fraction under moderate to high sea states yield some remarkable new studies of occurrence of breaking waves as well as the significant effect of wave age on such statistics. From both the laboratory and open ocean measurements, a universal size distribution of bubbles with radii ranging from 34 to 1200 μ due to surface gravity wave breaking has been observed.