bluuebunny/crossref_metadata_2025 huggingface dataset:
A-weighting and the rating of auditory hazard
Authors: Price G. Richard
Published: October 2005

Considering the complexity of the alternatives, it is easy to understand the reasons that evaluation procedures using A-weighting have gained acceptance. On the other hand, it may seem suprising that this specific weighting, not originally intended for rating hazard, should have proved so useful in that role. From a theoretical viewpoint it can be argued that the shape of the curve is a function of physiological mechanisms that also underlie hearing loss. This paper will discuss these mechanisms as they are becoming known and the implications they have for the use of A-weighting with special emphasis on the noise research conducted in the last decade.
Nasal vowel identification using LPC-based formant analysis
Authors: Hamada Masahiro
Published: October 2005

An experiment was carried out to determine the problems associated with the identification of nasal vowels in English in the context of vowel recognition using LPC-based formant analysis. A number of tokens of three pairs of oral/nasal vowels [æ, ɛ, ɪ,] produced in similar phonetic contexts (such as in camp versus camp) were obtained from three male speakers. The first and second formant frequencies obtained as LPC spectral peaks from these pairs of vowels showed significant differences in distribution on the F1−F2 plane. The first formant frequencies of nasal vowels especially had apparent overlap with those of other nasal vowels, while oral vowels had no overlap with each other. The LPC spectra corresponding to the shifted formants and the pole-zero pairs introduced by the nasal cavity coupling showed substantial individual differences in shape in the first formant region, including different bandwidths and number of peaks. These facts suggest the difficulty of vowel identification in (1) using the same template for both oral and nasal vowels and (2) identifying an unknown vowel even if one knows it is nasalized.
On the effects of varying filter bank parameters on isolated word recognition
Authors: Dautrich B. A. , Rabiner L. R. , Martin T. B.
Published: October 2005

The vast majority of commercially available isolated word recognizers use a filter bank analysis as the front end processing for recognition. It is not well understood how the parameters of different filter banks (e.g., number of filters, types of filters, filter spacing, etc.) affect recognizer performance. In this talk we present results of performance evaluation of several types of filter bank analyzer in a speaker trained, isolated word recognition test using dialed-up telephone line recordings. We have studied both DFT (discrete Fourier transform) and direct form implementations of the filter banks. We have also considered uniform and nonuniform filter spacings. The results indicate that the best performance (highest word accuracy) is obtained by both a 15-channel uniform filter bank and a 13-channel nonuniform filter bank (with channels spaced along a critical band scale). In comparison to a conventional linear predictive coding (LPC) word recognizer, the performance of the best filter bank recognizers was, on average, several percent worse than that of an eighth order LPC-based recognizer.
Alignment classification method to facilitate automatic acoustic-phonetic statistics collection
Authors: Baker Janet M.
Published: October 2005

Automatic labeling methods have been developed which allow speech recognition systems to be trained and tested on very large data bases (up to 140 000 word tokens). But are these automatic labeling methods accurate enough to collect statistics of direct value to speech science? Despite the success of automatic methods in effectively training speech recognition systems, the alignment routines still make a small percentage of gross phone alignment errors—in sharp contrast to human spectrogram or waveform experts. Automatic training procedures seem, nonetheless, to be tolerant of this small percentage of misaligned sounds provided they are given a sufficiently large number of correctly aligned instances of each sound. In this paper, a new method is proposed to directly address the following classification problem: is a particular putative phone alignment correct or is it an alignment error? Applying this classification method to a large data base previously labeled by a conventional automatic routine, acoustic-phonetic statistics for each sound may be obtained for all instances of that sound which are classified as correctly labeled.
Frequency response considerations in the acoustic coupling of hearing aids and telephones
Authors: Stoker Richard G. , French-St. George Marilyn , Holmes Alice E.
Published: October 2005

Four types of signal processing (high-frequency emphasis, low-frequency emphasis, bimodal emphasis centered at 900 Hz, and flat gain) were evaluated for their effects upon the perception of speech over the telephone when used with a hearing aid microphone. The telephone receiver and hearing aid microphone were acoustically coupled and recordings made using a dummy head. These recordings were later presented to three subject groups (normally hearing, moderately impaired, and severely impaired). The data suggest that the frequency response of conventional hearing aids may be inappropriate for the acoustic coupling of hearing aids and telephone receivers, especially in backgrounds of noise. Additionally, it was demonstrated that subjects do not reliably select the test conditions which give them maximum objective scores when given the opportunity to personally manipulate frequency response and signal level.
An acoustic bottom microprofiler and its application to high-frequency acoustic scattering
Authors: Igarashi Y. , Allman R. L.
Published: October 2005

Small-scale bottom roughness data are required for evaluation of high-frequency scattering models. A shipboard-launched acoustic microprofiler has been designed for obtaining detailed traces of bottom contours over 6-ft horizontal line scans in random orientations. The system consists of a 5.75-MHz, downward-looking transducer and electronic instrumentation package mounted on a cable-lowered frame, which is set on the sea floor. A roughness scale of approximately 1 cm–1 m is measured. Estimated vertical and horizontal resolutions are 1 and 8 mm, respectively. Measurements were made in two bottom areas that are nominally flat but have contrasting small-scale features. Computed roughness height power spectral density functions showed that the magnitude of the spectral functions differed by about 15 dB, but the slopes of the spectra both exhibited a power-law decay of approximately 2.50. These results are directly applicable to many theoretical scattering formulations with regard to the magnitude and frequency dependence of scattering functions. [Work supported by the Naval Sea Systems Command.]
Sound-channel effects on ambient noise spectra
Authors: Diachok Orest , Gauss Roger
Published: October 2005

Possible causes of the observed site dependence of deep ocean noise spectra below 100 Hz are examined through a coherent ambient noise prediction scheme due to Ingentio and Kuperman. The model accounts for propagation from a random distribution of surface dipoles in a range-independent, compressional sound-velocity structure; hence data-theory comparisons were limited to deep ocean abyssal plain environments. A variety of environments from open ocean (with varying wind speeds) to noisy ice-edge configurations were considered. Results below 100 Hz reveal a frequency-dependent, sound-channel-controlled amplification of the noise-source spectra which is sensitive to bottom sound-speed profile/attenuation coefficient and sea-surface scattering loss. Below 5 Hz the computed amplification accurately accounts for the apparent discrepancy between theoretical and measured noise due to nonlinear interaction of surface waves. Above about 50 Hz the computed noise-source spectral shapes in the open ocean and at the ice edge were nearly identical, suggesting that the same mechanism (possibly subsurface bubble cavitation) is responsible. Estimated sound-channel effects on the frequency and wind-speed dependence of the noise spectra between 5 and 50 Hz, where a different mechanism(s) predominates, will also be presented. [Work supported by 425AR, NAVELEX 612.]
Sonar array measurement facility
Authors: Reitz Frederick , Main Melvin
Published: October 2005

DED has developed a facility for the accurate calibration of towed line sonar arrays which is small and noise immune enough that it can be installed at any site requiring such measurements. The facility consists of a series of cylindrical transducers submerged in a water tank. The array under test is pushed through the transducers and the free field voltage sensitivity of each channel is measured one-at-a-time by comparison against some of the transducers. The remaining transducers project acoustical energy into the water. This facility is an outgrowth of a concept developed by NRL/USRD [J. F. Zalesak and W. J. Trott, J. Acoust. Soc. Am. 62, 91–101 (1977)]. Within limits, the accuracy of this facility meets the requirements of the Navy's towed line arrays. Typically, between 20 Hz and 2 kHz, measurements are repeatable within ±0.7 dB and correlate with the Navy's measurements within ±0.7 dB. During the past three years, the facility has performed over 3000 measurements and is presently under development as a product line.
Very accurate production oriented hydrophone calibration systems
Authors: Reitz Frederick , Main Melvin
Published: October 2005

DED produces towed line sonar arrays for a large number of U.S. Navy applications. The fact that the performance of these arrays is very tightly specified and that DED produces hydrophones for these arrays by the tens of thousands each year has forced the development of production oriented hydrophone calibration systems meeting the following requirements: parameters measured—free field voltage sensitivity, relative phase; frequency range—1 Hz to 2 kHz; measurement repeatability—±0.2 dB max., ±0.5 dB degrees max.; measurement correlation with Navy's standard facility (NRL/USRD)—±0.2 dB max.; temperature/pressure—ambient. Automated measurement systems have been developed where the above hydrophone parameters are measured within closed, rigid air chambers. Measurements are made by comparison against acoustical standards which are built into each chamber. These systems provide a well behaved, repeatable measurement over a wide frequency range. These measurement systems meet or exceed the above requirements and have been in use for approximately ten years.
A sonic tour of symphonic concert halls
Authors: Ashley J. Robert
Published: October 2005

The Koss CM-1030 speakers designed by the author will be described to justify their choice for the demonstration at the 104th meeting. The 100-liter bass section was synthesized to a 30-Hz BB4 alignment. Dual closed-box 800 ml mid-range systems are crossed over at 300 Hz. Dome tweeters cover the spectral ranges of 2 to 6 to 15 kHz. These speakers have much lower intermodulation distortion than most commercially marketed speakers. Telarc® digitally mastered recordings will be used for most of the sonic examples. These recordings have been made with three omni-directional microphones and little equalization. A recording from the current best concert hall in the world, Powell Hall in St. Louis, will illustrate the accuracy of the recording and playback process. Another good hall, Symphony Hall in Boston, will show why the musicians prefer halls such as these. The cold, steely string quality of many modern halls will be sonically illustrated by the Atlanta Symphony. Slides will illustrate the physical causes of sonic differences.
Finite-amplitude waveforms produced by a circular piston projector
Authors: Moffett Mark B. , Ginsberg Jerry H.
Published: October 2005

Measurements were made of the waveforms produced at six different locations on the axis of a 0.51-m-diam projector driven at 60 kHz in the NUSC/Newport large acoustic tank facility. The locations were at the last three pressure maxima in the nearfield, a quasifarfield point at 5 m, and two farfield positions at 10 m and 15 m. The projector was driven at several levels, and yielded waveforms ranging from sinusoidal at the lowest levels and shortest ranges to shock formation at the highest levels and longer ranges. Two different hydrophones were used, but neither had a flat enough response to avoid ringing when shocks were present. The waveforms exhibit the asymmetry (sharp pressure peaks and rounded pressure troughs) previously observed by Browning and Mellen [J. Acoust. Soc. 44, 644–646 (1968)] and predicted by recent work of Ginsberg which accounts for diffraction as well as nonlinear propagation effects. [Work supported by ONR Code 425 UA.]
The field of a focused nonlinear source
Authors: Muir T. G. , Lucas B. G.
Published: October 2005

Theoretical and experimental results on focused, nonlinear radiations are presented. The theory is developed with a parabolic approximation to an inhomogeneous Helmholtz wave equation, and accounts for both diffractive and nonlinear effects. Solutions are obtained for harmonic and difference frequency generation, under conditions (1) large ka, (2) small aperture angles, and (3) quasilinear interaction (strong shocks precluded). The solutions furnish computations on the phase and amplitude of both primary and secondary components in propagation along the acoustic axis and in the focal plane. Of particular interest are the phase shifts that are observed in passing through the region of geometrical focus. In general, focal phase shifts for difference frequency sound are not usually observed, while focal phase shifts for harmonic radiations are less pronounced that that experienced by linear radiations. Experimental results are presented on underwater measurements conducted with an f/2 lens coupled to a dual, interleaved primary array operating at 373 and 403 kHz. The measured data support the utility and validity of the analytical model. In particular it is shown that both diffractive and nonlinear effects are important in the focal region, especially for the harmonic radiations. The measurements also confirm the effective focusing of the difference frequency radiation for the present configuration, in that the width of the beam in the focal plane becomes quite narrow (approximately 1/3 of a difference frequency wavelength). [Work supported by the Office of Naval Research.]
Echo sensitivity as a function of target range: Automatic gain control in echolocating bats
Authors: Kick S. A.
Published: October 2005

The sensitivity of the echolocating bat, Eptesicus fuscus, for detecting sonar echoes at different delays (corresponding to ranges of less than 3 m) was measured in a two-choice psychophysical task. The stimuli were either electronically reproduced, delayed replicas of the bat's own sonar sounds or were tone-bursts triggered by the bat's sounds. The threshold for echo detection at delays for ranges of 3 m or more is about 0 dB SPL, but it rises for shorter delays, for example, to 35 dB SPL at the delay for 25 cm. The bat's middle-ear muscles contract during vocalization and are still relaxing when echoes return from targets at close ranges, accounting for most of the elevation of thresholds. The threshold shift at different ranges corresponds to the change in echo strength from a target at different ranges due to spreading losses and atmospheric attenuation. The bat thus regulates its sensitivity to echoes to a constant echo strength above threshold as it approaches targets. The mechanism is a delay- or range-related change in threshold.
Directional hearing in the Atlantic bottlenose dolphin (Tursiops truncatus)
Authors: Au Whitlow W. L. , Moore Patrick W. B.
Published: October 2005

The directional hearing sensitivity of an Atlantic bottlenose dolphin was measured behaviorally in the vertical and horizontal planes for puretone frequencies of 30, 60, and 120 Khz. The vertical beam-pattern results were reported previously [Moore and Au, J. Acoust. Soc. Am. Suppl. 1 70, S85 (1981)]. Measurements in the horizontal plane were performed with the dolphin stationing in a bite plate and with two noise sources located ± 20° on either side of the bite plate, 3.5 m away. The levels of the noise sources were held constant and the masked thresholds were determined by varying the level of the signal source at different azimuths. The horizontal beam patterns, which were directed forward, were fairly symmetrical about the major axis and became narrower as the frequency increased. Using the beam patterns measured in the vertical and horizontal planes, the receiving directivity index was calculated and found to be approximately 10, 15, and 21 Db for frequencies of 30, 60, and 120 Khz, respectively. A two-element rectangular transducer array was used to model the dolphin's directivity index; each element having an effective area of 8.1 cm2. The frequency dependency of the doiphin's directivity index was found to be very similar to the linear array model.
An acoustic approach to diver navigation: Parameter selection and training effects
Authors: Hicks J. W. , Hollien H. , Klepper B.
Published: October 2005

Recently Hollien, Hicks, and Klepper (1981) presented data concerned with the development of an underwater diver navigation system based on the projection of an acoustic signal through an underwater range. It was found that a multiple beacon source, energized sequentially in a linear fashion, generates an Underwater Auditory Phi Phenomenon (UAPP). This multiple beacon configuration, when used in combination with a thermal noise source, produces an acoustic field which divers can localize and swim to from a distance of 150 m. As part of a coordinated research program designed to develop and refine this acoustic navigation system, further investigations were carried out to (1) delineate more precisely the types of signals that were best suited for the production of the UAPP percept in divers, and (2) determine the effects of training on divers' abilities to navigate through the markerless space that is characteristic of the underwater environment. The results of this investigation demonstrate that divers improve their navigational skills quite rapidly, and even previously uninitiated divers learn to accurately home on the target within five or six trials. Furthermore, it appears that a band-limited thermal noise source provides the best acoustic navigation signal. [Work supported by Florida Sea Grant award R/OE-12.]
Melodic octave tuning; separable dimensions of perception
Authors: Makeig Scott , Balzano Gerald
Published: October 2005

Ascending and descending digitally synthesized pure-tone melodic octaves in the range 250–1500 Hz, varying width from 1180¢ to 1220¢ were presented to nine highly musical subjects who were asked to judge (1) degree of octave mistuning, and (2) whether the second tone of the pair was sharp or flat. Results confirm the existence of so-called “octave stretch” previously reported in the literature. However, the two tasks were found to be perceptually dissimilar in degree of octave stretch, variability, and dependence on register. Consistent with results of Lindqvist and Sandberg (VIIth Int. Congr. Acoust., 1971] preferred “octave stretch” for the “sense of mistuning” judgments was very small (about 2.5¢) for low register octaves. An additional significant finding was that melodic octaves whose second tone was flat relative to an adjudged “in tune” octave were called more “mistuned” than octaves whose second tone was equally sharp. Together, these results imply that perception of octave tuning does not amount to a one-dimensional judgment of log frequency difference, but is multidimensional in nature.
Administering a “noise budget” for a civil airport
Authors: Bishop Dwight E.
Published: October 2005

“Noise budgets” offer air carrier airports a means for achieving noise control without imposing rigid restrictions of numbers of operations or types of aircraft. This paper describes the application of noise budget concepts to actual administration of operations at a medium size air carrier airport. The airport's noise budget is based upon consideration of the noise-incompatible land use areas within a specified community noise equivalent level (CNEL) contour. However, budget controls for air carriers are expressed in terms of the “equivalent numbers of operations” where the equivalent number is based upon the number of opertions per day, evening, and night periods and the relative noise levels produced by different aircraft. The relative noise levels are derived from data from the airport's permanent noise monitoring system. Samples of the budget analyses that are undertaken to evaluate changes in air carrier schedules will be presented.
Outdoor sound propagation over ground with several impedance discontinuities
Authors: Bassiouni M. Reada
Published: October 2005

Extensive studies have been made on the outdoor propagation of sound over a surface of finite impedance as well as over a surface with an impedance discontinuity. Under realistic field conditions, the ground surface over which sound is propagating has several discontinuities. This paper deals with the propagation of sound from a well-defined sound source over a surface characterized by a finite number of infinitely long parallel regions of ground with homogeneous impedance within each region, but the impedance varies from one region to another. The sound source itself generates one tone at considerably higher levels than the higher order harmonics. The analytical results are presented in comparison to experimental measurements obtained from testing conducted under actual field conditions. Factors such as topography and meteorology, which would otherwise contribute to the excessive attenuation, have been omitted in order to isolate the effects of a finite number of impedance discontinuities. Because the analytical study has been validated by field results the findings will improve prediction methods of environmental noise from sources of discrete tones (e.g., high power transformers, I.D. and F.D. fans, etc.) propagating over realistic outdoor ground conditions.
Mathematical models of glottal area and vocal fold contact area
Authors: Titze Ingo R.
Published: October 2005

The glottal area function and the vocal fold contact area are computed as a function of a dynamically changing glottal configuration. Parameters are prephonatory widths and amplitudes of vibration of the upper and lower margins of the vocal folds, and the phase angle between the two. The computed waveforms are compared with measured photoglottographic (PGG) and electroglottographic (EGG) waveforms. The basic PGG and EGG waveform shapes are confirmed by modeling, although a simple relationship between vocal fold contact area and EGG may not always exist. It is demonstrated that symmetries in these glottographic waveforms are related to the shape of the medial surface contour of the vocal fold and should not be confused with asymmetries in the glottal volume flow [Rothenberg, Vocal Fold Physiology, edited by Stevens and Hirano (1981), pp. 305–323].
The national noise control program: needs and strategies; motor vehicle noise: the industry viewpoint
Authors: Pataky Paul P.
Published: October 2005

This presentation briefly describes the history of the motor vehicle industry's involvement in the understanding and control of transportation noise and, specifically, the impact of motor vehicle noise on overall community noise levels. Recognizing the need for valid noise regulations, the presentation then discusses industry's requirement for harmonized vehicle noise standards and test procedures in order to facilitate compliance to those regulations in the most cost-effective manner possible. The paper then presents industry's recommendations for future strategies that can be implemented to meet the objective of achieving a quieter environment at the least cost to society. These strategies include the use of computer mathematical models to determine the environmental impact of new vehicle noise regulations and to assess other, perhaps more viable and more cost-effective alternatives to vehicle noise regulations. Also discussed are strategies that can be pursued jointly by industry, the voluntary standards associations and the motor vehicle regulators to achieve harmonization of motor vehicle noise standards and compliance test procedures, not only on a national, but on a worldwide basis.
Classroom exercise programs for numerically predicting and graphically displaying propagation characteristics of sound
Authors: Clark Joseph A.
Published: October 2005

Several computer programs will be described which were developed for an introductory graduate course in underwater acoustics that was offered at a government laboratory (DTNSRDC) where Tektronix or H.P. graphics computers were available to most of the students. One program numerically solves the acoustic field equations in one dimension by a finite difference method. This program has been used to illustrate the reflection of sound at boundaries and effects of transmission into a second (or third) medium where the acoustic impedance and sound speed might differ. A second program numerically solves the acoustic field equations in two spatial dimensions. A ray tracing program will be described which illustrates the major features of sound propagation in inhomogeneous media and a program which plots beam patterns for an array with an arbitrary number of elements spaced at arbitrary distances apart will also be presented. The programs are written in BASIC and include interactive features which allow the students to explore a variety of propagation and radiation conditions on their own. The programs were found to provide a third useful way to develop a physical intuition for sound propagation characterstics when they were used in conjunction with studies of approximate analytical solutions of the field equations and laboratory demonstrations.
Development of standards on vibration effects on buildings
Authors: Coonan G. R. , Siskind D. E. , Ying S. P.
Published: October 2005

One of the Working Groups of the American National Standards Institute S2 Committee on Mechanical Shock and Vibration is S2-78 on Measurement and Evaluation of Structural Vibration. This working Group is currently participating in the development of a standard for building vibration with the corresponding Working Group of the International Standards Organization TC 108/SC2/WG3. Consensus standards of this type provide technical guidelines to the Government agencies responsible for establishing regulations for environmental conditions as well as occupational health and safety. The proposed standards on building vibration specify the basic principles of performing vibration measurement and processing data, in regard to using the results of measurements for evaluating vibration effects on buildings. The evaluation is primarily directed toward structural response, but appropriate analytical methods are also included. The response as affected by vibration frequency, duration, and amplitudes as induced by any source is examined. The status of the proposed international standards and the available empirical data on damage from various sources are reviewed.
Vehicle vibration standards: From the ground up
Authors: Barton J. C.
Published: October 2005

ANSI S2-67 includes the measurement and evaluation of mechanical vibration and shock in land vehicles. The starting point of the work is the ground, or roadway, as a principal source of vehicle vibration. The end point is vibration and shock data relevant to vehicle or component service life, and/or to the occupants of the vehicle. The standards work of ANSI S2-67 ranges from test instrumentation, through test methods and data analysis, to the form of the final report. Through its liaisons with other USA standards organizations, ANSI S2-67 coordinates the USA position on ISO proposals for standards and provides the USA input to the corresponding ISO working group. Hence, ANSI S2-67 insures that USA views are represented in the development of international standards. The international standards have as their objective the removal of technical barriers to trade and the facilitation of international trade, hence are important for the export of USA products and are beneficial to the USA economy.
Doubly asymptotic approximations for vibration analysis of submerged structures
Authors: Geers Thomas L. , Felippa Carlos A.
Published: October 2005

Doubly Asymptotic Approximations (DAA's) are differential equations for boundary-element analysis of the dynamic interaction between a complex structure and a surrounding infinite medium [T. L. Geers, J. Acoust. Soc. Am. 64, 1500–1508 (1978); P. G. Underwood and T. L. Geers, Int. J. Solids Struct. 17, 687–697 (1981)]. In this paper, the use of first- and second-order DAA's for vibration analysis of submerged structures is examined. First, the governing discrete-element equations for the general problem are set down and discussed. Then the accuracy of three DAA forms is studied through the generation of numerical results for a submerged spherical shell. Although the first-order DAA is found to be inadequate, the two second-order forms show considerable promise. [Work supported by the David W. Taylor Naval Ship R & D Center.]
The entrapped elasticity of a fluid-loaded plate
Authors: Stuart Alan D.
Published: October 2005

It is basic knowledge that the wave equation for an acoustic fluid represents a force balance between an inertia and an elastic-restoring component in much the same way a balance exists between the mass and spring forces of a simple oscillator. It is also commonly known that only the mass component contributes to sound radiation from a simple pulsating convex source like a pulsating sphere, cylinder, or circular piston in a baffle. (By simple source one usually means a source whose dimensions a, are small compared to the acoustic wavelength, that ka < 1.) This paper will explore the situations under which the elastic component of an acoustic field arise, and specifically, consider how both the mass and elastic components of the acoustic field contributes to the vibratory response of a fluid-loaded plate.
Acoustic sensitivity to sound-speed profile selection in the deep ocean
Authors: Bilazarian P. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

The effect of the selection of a deep-ocean sound-speed profile on the sensitivity of acoustic receptions is examined. In our initial study [J. Acoust. Soc. Am. Suppl. 69, S34 (1981)], the fixed sound source and receiver were positioned on the ocean boundaries. In this work, a variety of locations of submerged source and receiver, with separations of less than 50 km, is considered so that different types of ray propagation must be examined. Given a particular profile, procedures are prescribed for constructing a simpler profile for which all significant ray geometric and acoustic quantities, such as ray types, numbers, phase, and amplitudes, are either identical or virtually so. Also, the sensitivity of performance measures for horizontal linear receiving arrays to profile selection is studied. Conditions on array length and source-receiver range and orientation are developed for which a simpler profile may replace a given profile, and still maintain essentially equivalent array performance. [Work supported by ONR.]
Model experiments on the spatial altering of modes
Authors: Wang Yunyu , Zhou Ji-xun , Li Hong-hai , Zhang Zhen-zhong , Jiang Shen-li , Shang Er-chang , Bao Qing-hua , Zu Long-jiang , Yan Guo-guang
Published: October 2005

The spatial filtering of modes is very important both for theoretical and practical purposes. Spatial filtering of modes can verify the normal-mode theory and is also a way to match the waveguide fields. It will have an important application in the investigation of the interaction between the sound wave and environmental factors such as the acoustic characteristics of ocean bottom, internal wave,…etc., because it is easier to study separate modes. In this paper, the model experiments include the following: (1) The spatial filtering of modes in a long water tank without absorbers on the side wall. (2) The suppression of the near interference point source by means of selected mode. (3) The effects of surface waves on each individual mode and the sum of all modes at a point receiver.
Normal mode filtering in shallow water
Authors: Lo En-cen , Zhou Ji-xun , Shang Er-Chang
Published: October 2005

The filtering of mode 1 and mode 2 by using a vertical array of nine hydrophones has been realized in the frequency range of 250–800 Hz in the shallow water of the Yellow Sea with a near-perfect isovelocity condition. The eigenfunctions of the mode were calculated by using two parameters (P, Q) to describe the characteristics of the bottom reflections approximately at small grazing angles. The results of the mode filtering were quite good: (1) The group delay measurements of mode 1 and mode 2 agree well with the theoretical value calculated by using the bottom reflection phase shift parameter P; (2) The parameter Q of the bottom reflection loss can be extracted from the amplitude ratio of mode 1 and mode 2. The extracted values of Q were quite near to the values of Q obtained by other approaches.
An improved numerical ordinary-differential-equation solution to the parabolic wave equation
Authors: Lee Ding , Jackson Kenneth
Published: October 2005

The solution of the parabolic wave equation can be approximated by the solution of a stiff Initial Value Problem (IVP) associated with a system of Ordinary Differential Equations. The Generalized Adams Methods (GAM) based upon a stable rational approximation to the matrix exponential has been shown to be an effective method for solving this problem. However, previous implementations of the GAM suffered from severe storage limitations because of the use of an explicit rational approximation to the matrix exponential. In this presentation, we describe a new implementation of the GAM that is based upon an implicit use of a “Restricted-Pade” approximation to the matrix exponential. This implementation is particularly effective for problems for which the associated matrix is banded, as is the case for the IVP approximating the parabolic wave equation. A problem of propagation in a wedge shaped region is presented to illustrate the strong limitation of the previous implementation and how this limitation is removed in the new implementation. [Work is supported by ONR.]
Signal statistics near a caustic in the presence of fluctuations
Authors: Clarke Thomas L.
Published: October 2005

Signal fluctuations in the field near a caustic produced by random inhomogeneities in sound speed are examined. Statistics are calculated by Monte-Carlo simulation based on a phase-screen approximation. The diffraction parameter for the phase-screen approximation serves to generalize the Λ parameter. The statistics are found to depend on the strength of the fluctuations in a complicated way when the generalized diffraction parameter is near unity. In particular, the scintillation index is large at intensity minima even for weak fluctuations.
Propagation in a random medium: An experiment using heating and cooling in a large water tank
Authors: Posey Joe W. , Levenson Coleman
Published: October 2005

One millisecond tone bursts in the frequency range 0.8 to 2.0 MHz were propagated to a range of 10 m through a water tank having a 3.7×3.7 m cross section. Sound speed distribution along the propagation path was randomized by either heating or cooling. The heating technique has been used by several previous investigators. This method has been criticized because degassification bubbles rise through the propagation path and may act as resonant scatterers. The cooling approach does not produce bubbles. A three-dimensional, fast response thermistor array was used to measure temporal and spatial statistics of the temperature fluctuations. Variations in the complex amplitude of received acoustic signals are compared with Wenzel's theory [AIAA paper 75–546 (1975)]. He defines the coherent wave as having the mean complex amplitude of the total wave and derives a conservation relation for the sum of coherent and incoherent wave energy. He predicts that coherent energy will decay exponentially with characteristic length and mean-square amplitude of sound speed fluctuation as well as with range and signal frequency squared.
Microelectrode arrays for neurostimulation fabricated by integrated circuit technology
Authors: White R. L. , Roberts L. A. , Kwon O.-H.
Published: October 2005

We are engaged at Stanford University in the development of an auditory prosthesis which works by direct electrical stimulation of the auditory nerve. This project must confront many questions on the nature of speech processing, speech comprehension, and the representation of speech as electrical stimulation patterns on the auditory nerve. It is also necessary to develop a microelectrode array for delivery of the appropriate electrical stimulation pattern onto the auditory nerve. While it is possible both in principle and practice to fabricate such arrays using fine wire bundles, it is clearly attractive to utilize the high-resolution high-precision photolithographic technology common to integrated circuit fabrication to achieve arrays which are electrically and mechanically optimal and are reproducible and stable. For the cochlear prosthesis we have developed rigid electrode arrays using a sapphire substrate, tantalum conductors, platinum electrodes and tantalum pentoxide and silicon nitride insulation. We have also developed a flexible electrode array using a liquid polymer and platinum conductors. Comments will be made on problems solved in developing these fabrication techniques and on their extensibility to electrodes for other biostimulation applications.
Acoustic response of a twisted nematic liquid crystal cell
Authors: Hamidzada W. , Letcher S. V.
Published: October 2005

A thin layer of liquid crystal can be used as a simple two-dimensional detector of ultrasound. The acoustic beam disturbs the molecular alignment of the liquid crystal, which allows changes in light transmission when the cell is placed between crossed polarizers. Most studies have concentrated on nematic liquid crystals with optic axis along the layer normal. We have studied the acoustic response of a new type of cell developed for electro-optic displays [D. Berreman and W. Heffner, J. Appl. Phys. 52, 3032–3039 (1981)], which is a twisted nematic with oblique attachment angle at the layer surfaces. We find that this cell is generally more sensitive than the homeotropic nematic and has a faster response time. The cell has the additional feature of having two stable molecular configurations that satisfy the same boundary conditions. Under certain conditions the acoustic beam can drive the system from one state to the other, providing a memory feature for the detector.
Detection of broadband acoustic pulses in liquids using wideband differential interferometry
Authors: Garg Avinash O. , Claus Richard O. , Dockery George D.
Published: October 2005

Several authors have reported the detection of continuous ultrasonic waves in transparent media by interferometric transmission techniques [C. H. Palmer, R. O. Claus, and S. E. Fick, Appl. Opt. 16, 1849 (1977); D. P. Jablonowski, Appl. Opt. 17, 2064 (1978)]. In this paper, the measurement of broadband acoustic pulses in a water tank by a wideband differential optical system is discussed. The two coherent light beams in this system are narrowly collimated and propagated through the tank along lines parallel to the generated ultrasonic wavefronts and normal to their direction of propagation. A change in the index of refraction of the water caused by the acoustic field at the location of one optical beam alters the optical phase difference between the beams and is interferometrically detected. Since the optical beams are separated, the acoustic pulse modulates them at different times and two detected differential signals of opposite sign are observed. Beam separation determines the lower frequency response limit of the system; upper frequency response is limited to approximately 100 MHz by the diameter of the optical beams. Applications in the scanning of three-dimensional acoustic fields is indicated. [Work supported in part by NASA and NSF.]
Volume perturbers as possible sound field randomizers in room-average spectrum measurement procedures
Authors: Lindeveld I. M. , Benade A. H.
Published: October 2005

The use of moving volumes (people) instead of rotating vanes for sound field randomization has been proposed as a plausible and convenient technique. A perturbing volume Vp in a room of volume V0 shifts the frequency of the lmn mode by an amount (Δf/f)lmn = ∫vp(U − K)lmndV/∫v0(U + K)lmndV, where U and K are the modal potential and kinetic energy densities of the sound field. Computer experiments confirm that when Vp is moved throughout a room, the rms frequency shift is given by (Δf/f)rms = 3(Vp/V0)H(ka). For a cube of side a, H≃1 for ka⩽1, falling basically as (1/ka) above this. For Vp a thin square of side a, or bar of length a, the same asymptotic relations hold, but the transition to (1/ka) behavior is much less abrupt. If (Δf/f)rms⩾ the mean intermode frequency spacing (c3/4πV0f3), one expects adequate randomization of the room modes for frequencies above fp = c/(12πVp)1/3 provided Vp is displaced sufficiently between recordings of the spectral samples. Measurements of spectra using fixed source and microphone but moving Vp as outlined show however that the observed mean spectrum has a variance only slightly less than the ± 5.2 dB value associated with a single reading. That is, the expected randomization due to moving Vp hardly takes place. Other types of experiment confirm this. Possible reasons will be discussed. [Assisted by NSF.]
Aerodynamic/timing factors related to the intelligibility of deaf speakers
Authors: Brown W. S. , Goldberg Donald , Rothman Howard
Published: October 2005

The literature describing the speech of the deaf indicates that the inability to learn timing characteristics of consonant and vowel productions is a major cause of reduced intelligibility in oral communication. This study measured several timing gestures for consonant and vowel combinations which have been shown to be essential for intelligibility. The subjects included three groups of speakers between the ages of 12 to 14 years. Group I, which served as the control, consisted of 15 normal hearing school children with normal speech. Group II consisted of 15 prelingual deaf children who were trained predominately in manual communication. Group III consisted of 15 prelingual deaf children who were trained predominately in oral communication. The three groups were compared for differences and similarities in (1) consonant duration, (2) vowel duration, and (3) VOT associated with productions of CV, VCV, and VC syllables spoken in a carrier phrase. The results will be discussed in terms of the deviations of the deaf speech from the normal speech and their relationship to intelligibility.
Acoustical design considerations for two air-supported structures
Authors: Curtis John A. , Hirtle Parker W. , Horrall Thomas R.
Published: October 2005

This paper presents information on the acoustical design of the Hubert H. Humphrey Metrodome in Minneapolis, Minnesota and the Dalhousie University Athletics Complex (Dalplex) in Halifax, Nova Scotia. The Hubert H. Humphrey Metrodome seats up to 63 000 people under an air-supported fabric roof. Major concerns that are discussed were reverberation control and the design of a system of loudspeaker clusters that are suspended from the roof membrane and maintain proper orientation when the structure is moved by changes in wind loading. The main feature of Dalplex, which is located in a residential neighborhood, is a 300 ft by 240 ft stainless steel air-supported roof over the field house and running track. This 116-in.-thick stainless steel membrane presented some unique acoustical problems that had to be addressed, including control of reverberation in the fieldhouse, reduction of the noise of rain on the metal roof to acceptable levels, and reduction of crowd noise transmitted through the roof to nearby houses. These and other acoustical considerations are discussed.
Ear-canal acoustic emissions as frequency-specific indicators of cochlear function
Authors: Schmiedt Richard A. , Addy Cheryl L.
Published: October 2005

Acoustic emissions in the form of distortion products (2f1-f2) can be measured in the external ear canal. Previous work has shown that the nonlinearities generating these emissions reside in the cochlea and disappear with metabolic disruption. Distortion products measured in the cochlear microphonic and in the responses of auditory-nerve fibers have been shown to be generated largely at the cochlear location associated with the primary tones. If cochlear emissions behave similarly, it should be possible to generate an “acoustic-emission audiogram” with appropriately placed primary pairs; i.e., low-frequency pairs could be used to test the cochlear apex, high-frequency pairs to test the base. We have obtained acoustic-emission and whole-nerve action potential audiograms in Mongolian gerbils and cats both before and after exposure to narrow-band noise sufficient to cause a temporary threshold shift. Our results indicate that emssions produced by lower-level primaries (70 db SPL) seem to reflect the recovery of the whole-nerve response over time better than higher-level primaries (80 dB SPL). Further, acoustic emissions can be used on a frequency-specific basis to monitor the condition of the mid and basal regions of the cochlea. [Work supported in part by a South Carolina Biomedical Research Grant.]
Acoustical properties of “FABRASORB” acoustical fabrics
Authors: Effenberger John
Published: October 2005

“FABRASORD” acoustical fabric was developed by CHEMFAB about six years ago to provide a solution to the poor acoustics (U. S. Patent No. 4,152,474) within fabric structures. Based on woven fiberglass and polytetrafluoreotylene (PTFE) resins, it is a natural companion to “SHEERFILL” architectural fabrics which have enabled fabric structures to meet all applicable codes for permanent construction by virtue of the durable and fire-safe properties inherent to fiberglass and PTFE. Key to the successful behavior of a FABRASORB acoustical liner to such construction is close control of the acoustical absorption. This in turn is achieved primarily through control of the porosity of the coated fabric. Data are presented showing sound absorption coefficients over a broad range of frequencies as a function of porosity along with specifications for the noise reduction coefficient achievable.
Underwater target echo analysis facility
Authors: Coble G. P.
Published: October 2005

A versatile, minicomputer-based acoustic data acquisition and analysis system has been installed at the ARL:UT Lake Travis Test Station. This system differs from analog systems used in the past to measure target strength in that the entire echo is digitized and recorded on 9-track digital magnetic tape, thus retaining both amplitude and phase information. Data recorded on tape are read back into the data acquisition computer for analysis. Data stored in this form are also easily disseminated to other investigators. The echo analysis facility became operational in 1979 and has since been used to study echo characteristics of targets of interest to the U.S. Navy. The system has recently been upgraded to accommodate multiple receiver channel experiments. [Work supported by NAVSEA.]