bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration damping for rapid transit elevated structures
Authors: Curreri J. R. , Kirschner F. , Koch J. E.
Published: October 2005

It is well known that train operations on an elevated structure are much noisier than those on a grade level roadbed. For the composite type of bridge structure made up of a concrete deck on a steel box girder, theoretical and experimental studies show that the steel web plates are a major source of noise radiated from the structure. This paper will summarize some of the work done over the last 15 years to reduce this source of noise by damping the steel box girder of such structures. Both homogeneous type damping and shear type, or constrained layer damping materials have been used successfully. The noise reduction on one type of structure with homogeneous damping mateddais will be described, including scale model and full scale tests. In another type of structure, a partial damping treatment with shear type damping material was developed to reduce the very disturbing low frequency noise radiated by the steel box girder plates. Full scale field tests will be described in which noise and vibration measurements were made on damped and undamped sections of the elevated structure during train passage at several speeds. The effect of damping on the noise and vibration levels will be detailed.
Vibration and noise control at MARTA
Authors: Wilson G. P.
Published: October 2005

Control of vibration and noise has received careful and thorough consideration throughout the design of the MARTA [Metropolitan Atlanta Rapid Transit Authority] rail transit system facilities and vehicles. This has included use of sound barriers, damping of structures and resilient support, or vibration isolation supports for rails. Operations on the limited extent of the system now in service have allowed for measurements to show the effectiveness of the designs in controlling vibration and noise. Floating slab trackbed for vibration isolation of the rails from the supporting structure proved effective in reducing ground-borne vibration and noise. Sound barrier walls on aerial structures give substantial reduction of airborne noise from the transit vehicles. Damping of aerial structure girders proved effective in reducing low-frequency noise radiated from the structure. Primarily emphasizing wayside vibration and noise, design configuration details and results showing effectiveness will be presented for floating slab rail supports and aerial structure with barriers and damping.
Criteria for acceptable levels of building vibration due to rapid transit operations
Authors: Saurenman H. J.
Published: October 2005

The ground-borne noise and vibration created by rail transit operations have often resulted in intrusion inside neighboring structures. Although there are appropriate criteria available for the acceptable limits of ground-borne noise in various types of buildings, because of the lack of consistent data, criteria for acceptable limits of building vibration due to transit train operations have not been established. A starting point for vibration criteria applicable to transit train operations is the Addendum 2 to ISO Standard 2631, “Vibration and Shock Limits for Occupants in Buildings.” Based on this standard the CHABA Working Group 69 on Evaluation of Environmental Impact on Noise recommended weighted vibration acceleration levels that could be used to obtain a single number descriptor for building vibration, analogous to A-weighting for noise. Using this weighting curve, a number of measurements of building vibration due to rapid transit operations have been analyzed and compared with the perceptibility of the vibration and the annoyance expressed by the building occupants. Although this analysis is only preliminary there is a clear indication that the weighted vibration level is strongly correlated to the annoyance of building occupants.
Ground vibration from trains on concrete elevated structures
Authors: Hanson Carl E. , Towers David A.
Published: October 2005

Transmission of vibrations through the key structural elements in the path between the rails and the ground was measured on a concrete elevated structure of the Port Authority Transportation Corporation (PATCO) rail transit system in Camden County, New Jersey. Results are compared with similar, but less complete measurements taken at sites in New York City, San Francisco, and Atlanta. Generalizations of the results are applied to the new concrete elevated transit structures under design for the Metropolitan Dade County Rapid Transit System. [Work supported by Urban Mass Transportation Administration (various contracts).]
Language-universal aspects of intonation in children's first sentences
Authors: Landahl K. H.
Published: October 2005

Intonation usually segments speech into sentences. The “breath-group” theory [P. Lieberman, Intonation, Perception and Language (MIT Press, Cambridge, MA, 1967)] claims that a significant acoustic cue for delimiting sentences is the fall in fundamental frequency and amplitude at the breath-group's end. The “declination” theory [S. Maeda, “A characterization of American English Intonation,” MIT dissertation (1976)], in contrast, claims that the significant cue is a gradual, linear, fall in fundamental frequency. Both theories claim that the sentence delimiting function of intonation is language universal and probably innate. However, whereas the breath-group theory allows variation in the nonterminal fundamental frequency contour, the declination theory claims that a linear fall through the entire intonation contour is language universal. if the language-universal aspect of intonation has an innate basis we should expect it to be manifested in the initial sentences of young children. We therefore derived fundamental frequency contours using computer-implemented techniques from a corpus of one, two, and three word utterances produced by three children between 52 and 104 weeks of life. The data refute the claims of the declination theory; fundamental frequency does not fall in a gradual, linear manner through the utterance.
Intonation distinguishes tenses in Montreal French
Authors: Santerre L.
Published: October 2005

In rapid connected speech, we can observe the forms of 3 tenses reduced to the same segmental string [je ta]: (1) Il est à l'hôpital [je ta lopital] (he is at the hospital), (2) Il était à l'hôpital [je tεa …] → [je ta …] (he was at the hospital), (3) Il a été à l'hopital [jae tea …] [je ta …] (he has been at the hospital), or he went to the hospital. Even without contexts, these sentences are not ambiguous, because the intonation is falling for (1) [je ta], it is rising for (2) [je ta], and it is high on both syllables for (3). We will see that these patterns are not conditioned by the tenses, but by the placement of stress, the vocalic elision and the nature of the boundaries. The basic intonation contours are the same in slow and fast speech, but in slow speech the intonation contour is less modulated. In fast speech, where the segmental ambiguity makes the intonation contour distinctive, it is exaggerated, with greater variation in found. freq. (FF). In this paper I will describe the nature of this fast speech phenomenon and present data on the acoustic changes in duration, intensity and FF involved.
Temporal models of interarticulator programming
Authors: Tuller B. , Harris K. S.
Published: October 2005

Two basic types of explanation have been proposed for the changes in segmental timing that occur with changes in speaking rate and syllabic stress. One view is that the segmental “commands” for syllables spoken quickly and for unstressed syllables show more extensive temporal overlap than in the same syllables spoken more slowly or with greater syllabic stress (Lindblom, 1963; 0̈hman, 1967). An alternative view is that the temporal relationships among articulations remain constant over changes in stress and speaking rate and that the durations of the gestures themselves change (Kent and Moll, 1975; Kent and Netsell. 1971). The experiments described here were designed to explore the temporal relationships within and among articulatory events over these suprasegmental changes. Acoustic and electromyographic measures were taken of production of simple, disyllabic utterances with varying stress and speaking rate. Analysis of the muscle activity patterns supports the second view, that temporal relationships within and among articulations remain essentially constant over changes in syllabic stress and speaking rate. [Work supported by NINCDS and BRSG.]
The identification of prosodic information from acoustic records by phoneticians
Authors: Welin Carl Wilhelm , Lindblom Björn
Published: October 2005

Previous work [S. G. Svensson (1974). Prosody and grammar in speech perception. Monographs Instit. Ling. Univ. Stockholm] on spectrogram reading using Swedish utterances drawn from a very large corpus indicates that highly improved scores can be obtained if subjects are provided with (1) a grammar- and prosody-based decoding strategy, and (2) an error-free specification of the prosodic structure (stress and word accent information) of each test utterance spectrographically portrayed. The present study attempts to examine the realism of the assumption that the prosodic parameters can be extracted bottom-up independently of the interpretation of an utterance. Test phrases were recorded in a fixed sentence frame and the following variables were controlled: phrase length (2–4 syllables), three degrees of stress, word accent (grave versus acute), acoustic salience of syllable boundaries (sonorants versus voice-less obstruents), and semantic content (meaningful versus non-sense phrase). Subjects had considerable experience from research on the acoustic features of Swedish prosody and responded for each item to a set of displays (F0, intensity, duplex and microphone signals) by indicating: the number of syllables, syllable stress, and word accents. The aim of this paper is to report on the identification of these aspects as a function of the experimental variables.
Position and utterance-length effects on P
Authors: Flege J. E. , Brown W. S.
Published: October 2005

Previous studies have shown that supraglottal air pressure (P10) is greater for stressed than unstressed stops and for voiceless than voiced stops. The present study examined these P10 contrasts as a function of utterance length and position within the utterance. Eight subjects read nonsense utterances consisting of from one to five /bábá/s or/pápá/s (5 times each) with the intonation of an English declarative sentence (e.g., “Bábá bábá Bábá”). Peak P10 was sensed via a pressure tube inserted in the mouth and measured from osciiiographic traces. P10 in utterance-initial words increased as number of following words increased. P10 was greater for /p/ than /b/ except for stops initiating the 2- and 5-word utterances. P10 was always greater for stressed than unstressed /b/; it was also greater for stressed than unstressed /p/ except in utterance-initial words where pressure for the initial stressed Ipl was less than that of the following unstressed /p/. This reversal of the expected P10 contrast for stress appears to reflect the length of time necessary for subglottal pressure (P8) to rise to peak level at onset of phonation. Even though stressed /p/ was longer in utterance-initial than -medial positions it was probably shorter than the minimal time necessary for P8 to reach peak level at onset of phonation. It thus appears that P10 for stressed /p/ in utterance-initial position represents rising P8, while a following unstressed /p/ reflects P8 which has already reached peak level.
Time-domain response of fluid target in fluid medium
Authors: Mieras H. , Bennett C. L.
Published: October 2005

The responses of fluid targets are computed using space-time integral equations formulated in the time domain. The incident pressure wave is a “smoothed-impulse” with a Gaussian shaped time dependence whose width is of the order of a target dimension. A space-time integral equation for the pressure field on the outside of the target surface and a space-time integral equation for the pressure field on the inside of the target surface are solved simultaneously for the pressure and the pressure gradient by stepping on in time and making use of the boundary conditions (continuity of pressure and displacement). The farfield is then computed from these source fields. The technique is applicable to targets of arbitrary contour and is demonstrated for a sphere and right circular cylinder at various angles of incidence. Fluid targets support interior compression waves; sound-hard and sound-softargets are treated as limiting cases of this formulation. The technique has been verified for the case of a sphere by comparison with the response computed by classical expansions. [Work supported by NCSC.]
Standards Committee S1, Acoustics
Authors: Flynn D. R.
Published: October 2005

Working group chairpersons will report on their progress in the preparation of standards, methods of measurement and testing, and terminology in physical acoustics, electroacoustics, sonics, ultrasonics, and underwater sound. Work in progress includes measurement of noise sources, noise dosimeters, integrating sound-level meters, and revision and extension of sound-level meter specifications. Open discussion of committee reports is encouraged.
Measurement of acoustic intensity in a duct system with flow
Authors: Chung J. Y. , Blaser D. A.
Published: October 2005

A transfer-function method is described of measuring the acoustic intensity of plane waves in a duct with flow. In this method, the transfer function between two locations in the duct is used to determine the reflection coefficient. Acoustic intensity in a duct with flow is then determined from the reflection coefficient using an expression developed by Morfey. In the case of no flow, the transfer-function formulation reduces to a cross-spectral relation similar to the relation used to measure acoustic intensity in three dimensions. In contrast to the relation in three dimensions, however, the cross-spectral formulation for a duct is not limited in accuracy by the microphone spacing. Laboratory tests have been conducted in which the transfer-function method was used inside the pipe to evaluate the net sound power transmitted toward the open end of the pipe. The three-dimensional cross-spectral method of measuring acoustic intensity was used outside the pipe to evaluate the total radiated sound power. The acoustic power-loss during the radiation process was then determined by comparing the two results.
Frequency selectivity in the binaural and monaural hearing systems: Evidence from a modified two-tone masking procedure
Authors: Yama Mark F. , Small A. M.
Published: October 2005

A series of masking experiments was performed with the aim of comparing frequency selectivity of the binaural and monaural hearing systems. In these experiments, the masking stimulus contained both a sinusold, which was gated simultaneously with a 100-ms signal, and a continuous broad-band noise musket. The frequency of the tonal masker was varied while that of the signal was fixed at 500 Hz. Signal thresholds were obtained in a 3 ITFC paradigm with an updown adaptive procedure. In the first part of the experiment, the tonal musket was omitted and noise levels were selected so that signals in N0Sπ and NmSm conditions were equally detectable. When a tonal musket which was intense relative to the noise was subsequently introduced a comparison of masking functions obtained for N0M0Sπ, N0MπSπ, and NmMmSm, conditions (here “M” denotes the tonal masker) suggests that the binaural and monaural systems possess identical internal filters. However, a replication of the N0MπSπ and NmMmSm conditions with a low masker-to-noise ratio leads to a different conclusion: that the binaural system is less frequency selective than the monaural system. The implications of these results are discussed. [Work supported by the Neurobehavioral Sciences Program, University of Iowa.]
Detection of targets in clutter by an echolocating Atlantic bottlenose dolphin
Authors: Au Whitlow W. L. , Turl Charles W.
Published: October 2005

An experiment was conducted to determine the ability of an echolocating Atlantic bottlenose dolphin to detect targets located in front of a clutter screen. Forty-eight 5.1-cm-diam cork spheres spaced 15.2 cm apart and arranged in a rectangular array were used as the clutter screen. Hollow aluminum cylinders, 7.5, 10.0, and 14.0 cm in lengths were used as targets. The outer diameter and wall thickness of the cylinders were 3.81 cm and 0.32 cm, respectively. The dolphin was trained to station in a hoop, 6 m from the targets, and echolocate on command. Only one of the cylinders would be presented in a target-present trial. Data were collected on the animal's performance as a function of the relative distance between the clutter screen and the cylinders. Correct detection for the smallest cylinder varied from 91% to 55% as the distance between the screen and the targets decreased from 10 to 0 cm. The animal's performance with the larger cylinders was better. The target strengths of the clutter screen and the cylinders were measured using a broadband dolphin-like echolocation signal.
Aural discrimination of target echoes by human observers using broadband sonar pulses
Authors: Martin Douglas W. , Au Whitlow W. L.
Published: October 2005

Echo discrimination experiments were conducted with human observers, using targets employed in a dolphin echo-recognition study. Digital recordings of the target echoes were obtained using dolphin-like signals, and were played back to five subjects at 1/50 of the original sample rate. Targets included hollow cylinders of aluminum and glass having diameters of 3.81 and 7.62 cm, and a solid 7.62-cm aluminum cylinder. Echo amplitudes were adjusted so that stimulus intensity was never a cue. The subjects discriminated between (1) solid and hollow, (2) large and small aluminum cylinders with correct responses of 98% and 92%, respectively, after one session per task. The aluminum-glass discriminations were performed in five categories and after 30 sessions per subject, the correct responses varied between 73% and 97%. The dolphin discriminated between the 3.81-cm aluminum and glass cylinders, but failed to learn the task with the 7.62-cm targets. Discrimination cues were time-separation pitch associated with echo highlights, and echo duration. Duration may not have been a cue to the dolphin, while becoming apparent to the human subjects because of pulse stretching.
First data on an auditory homing method for divers
Authors: Hollien H. , Hicks J. W. , Klepper B.
Published: October 2005

Perceived movement of an acoustic signal has been found to be a powerful underwater localization cue. Moreover, in pilot research, signals of this type appeared promising as the basis for unaided homing by divers. Accordingly a full scale experiment on this underwater auditory Phi phenomenon was carried out. After some preliminary studies of preferred signal frequency, duration, rise/decay times, three experimental signals were selected: (1) 500 Hz with a duty cycle of 500 ms and a rise/decay time of 25 ms, (2) 1 kHz; 500 ms; 100 ms, and (3) band-passed noise (0.2–2 kHz); 1 s, 50 ms. Signals were presented serially via three USRD J-11 transducers placed 10 ft apart. Seven experienced divers made ten 150-m swims as follows: (1) visual, (2) compass, (3) single beacon (noise), (4–9) multiple beacon pairs (counterbalanced)—first: acoustic signal only; second: signal plus compass, and (10) visual. The obtained results demonstrated that this approach provides a reasonable diver homing technique. Further, a powerful learning effect was observed; finally, of the signals evaluated, the band-passed thermal noise was the best—indeed, in half the cases, times for the compass/noise runs were equivalent to, or better than, those for the visual. [Work supported by Sea Grant.]
Laboratory tests with acoustic intensity measurements including the effect of reverberant environment
Authors: Tichy Jiri
Published: October 2005

The purpose of the work was to find the effect of microphone type, size, distance, sensitivity, stability, mounting, and other possible effects on the precision of the intensity measurement by using the cross-spectral method. The calibration was conducted in a spherical sound field generated by a small loud-speaker baffled by a tube. The low frequency range of the measurement is limited by phase mismatch of the two channels while the microphone distance affects the upper frequency limit of usability. The paper will also discuss the intensity measurements in a reverberant environment.
Techniques for displaying noise source identification data
Authors: Larbes Terence H. , Steedman James , Brown David L.
Published: October 2005

Considerable efforts are being made to develop new techniques for noise source identification of complex machinery, such as internal combustion engines. Acoustic intensity measurements with closely spaced parallel microphones, microphone array measurements, and nearfield sound pressure contour measurements are three such techniques receiving interest at the present time. The measurement goal of such techniques is to identify and rank the contribution of individual sources, as well as to determine the total acoustic output of the system. Each of these techniques produces a relatively great number of individual measurements, and it is essential that convenient means of displaying the data be developed in order to evaluate the techniques and to make the results useful and easy to relate to. This paper describes several ways of displaying data from such measurements so that the strengths and weaknesses of the techniques can be assessed. Data are presented from simple but useful models using the three techniques. The data are presented in several formats including CRT, color displays, and contour plots.
Some observations on sound intensity measurements
Authors: Lyon Richard H.
Published: October 2005

Sound intensity is a vector that predicts sound power when integrated over a closed surface. Since only the integral is directly related to local physical constraints such as conservation of energy, the local intensity may be subject to considerable variations, depending on the acoustical environment of the radiating system. Limitations in the use of acoustical intensity data, quite apart from those that result from the accuracy of the measurement, will be discussed.
Coherence measurements of surface vibrations related to the acoustic intensity method
Authors: Hodgson Thomas H.
Published: October 2005

An important parameter in the use of the surface acoustic method for sound power measurement or sound power accounting of sources is a knowledge of the behavior of the spatial coherence or incoherence of the surface motion viewed as an acoustic source. If the machine surface can be treated as a collection of incoherent sources with some scale determined by a correlation length then considerable simplification in the power measurements may result. Measurement of the coherence of surface vibrations on a large machine are discussed with a view toward establishing a correlation length and hence the determination of the number of measurement points.
Acoustic intensity measurements in low Much number flows with moderate turbulence levels
Authors: Oswald L. J. , Donavan P. R.
Published: October 2005

Experimental investigations were conducted to determine the limitations imposed when making acoustic intensity measurements with the two-microphone cross-spectral method in situations with mean flow. An anechoic wind tunnel and grids were used to provide the desired flow conditions. The acoustic intensity probe was mounted in the flow and a small broadband noise source of known acoustic intensity was mounted outside the flow. Intensity measurements of the source were compared with and without flow. Parameters studied included: microphone diameter and spacing, noise source intensity and relative direction, airflow velocity, turbulence level, and turbulence eddy size. The investigations showed that good performance is obtained using 12.7-mm-diam microphones spaced 16 mm apart. With this probe, the flow restricts acoustic intensity measurements to sources whose intensities are -5 dB or greater than the flow-induced wind noise on either one of the microphones. Therefore, this lower limit is easy to measure before intensity measurements are made in any unknown flow. An example is presented to show how acoustic intensity measurements can be made near a truck tire onroad to help in identifying and quantifying the suspected tire noise sources.
A method for computing the sound power of machines
Authors: Koopmann G. H. , Benner H.
Published: October 2005

In this paper, a computational method for assessing the sound power characteristics of machines is presented. The method, which is based upon a Helmholtz integral formulation, requires a knowledge of the geometry and the modal characteristics of a machine's vibrating surfaces. Closed form integration of the associated surface integral is carried out in a piecewise manner over planar surface elements of simple shapes such as rectangles and triangles. This choice of element allows the grid geometries associated with the acoustic power computations to be made identical to those used in existing structural modal analysis schemes such as finite element methods or Fourier analysis methods. In this way, the sound power characteristics of a given machine can be computed in terms of the sound power radiated by each of the structural modes comprising the overall response. The structural modes can then be ranked in order of their radiation efficiency for purposes of noise control treatments.
High resolution intensity measurements using a new technique
Authors: Williams Earl G. , Maynard J. D.
Published: October 2005

Long-wavelength acoustical holography can be used to reconstruct images of sound sources which radiate into the farfield, but these images are generally assumed to be limited in resolution by the wavelength of the radiated sound. A new technique based on holographic principles has been developed with no intrinsic resolution limit. Thus, high resolution images of sound sources are obtained irregardless of the wavelength. The technique involves the recording of the sound pressure amplitude and phase with a plane array of microphones, then exactly reconstructing digitally the intensity of the sound sources with a computer and displaying the results with computer graphics. Thus, one can identify the location and intensity of multiple sound sources.
Ground effects: New analytical approximations and experimental results
Authors: Habault D. , Corsain G.
Published: October 2005

Analytical approximations for the sound field produced by a point source S in the presence of a ground have recently been developed [D. Habault, J. Sound. Vib. 68(3) (1980)]. The sound pressure at a point x can be expressed by a convergent series: p(x) = −exp(ikr)4πr +  ∑ n=0∞ Λn⋅A(θ) exp(ikR)4πR + exp(ikR)4πR  ∑ n=0∞ FnRn (R,θ), where r = SX, R the distance to X from the image source, A(θ) the plane wave reflection coefficient, and Λn a differential operator with respect to θ of order 2n. An approximation of the farfield is obtained by taking into account only the first terms of the series: the terms of the second series, called complementary terms, provide a better description of the field when R is not so large and can be neglected when R is very large because the functions Fn(R,θ) decrease exponentially with R. Measurements made in France and Canada over grassy ground show fair agreement between theory and experiment in the asymptotic region when the ground is characterized by a complex specific normal impedance. At low frequencies (∼500 Hz) prediction is not as good due to the fact that a better model for ground should be used, for instance, a finite or infinite thickness layer of porous medium.
Diffraction of a spherical wave by an absorbing plane: A general theoretical approach
Authors: Filippi Paul
Published: October 2005

In outdoor sound propagation, the ground absorption is described by various models such as a locally reacting surface or layer of porous material. For each type of absorbing plane, different authors have developed specific methods to calculate an approximation of the sound pressure. In the present paper a general method is proposed. If the absorbing plane is located at z = 0, and a point source at S(0,0,d), an exact representation of the solution shows that the diffracted field can be decomposed into the sum of (a) the radiation of an image source at S′(0,0,−d); (b) the radiation of a surface source located in the z = −d plane; (c) the z = derivative of the radiation of a surface source located in the same plane. From this exact integral representation of the solution, two series expansions can be derived. The first one, convergent for any source and receiver locations, involves the asymptotic series and a correcting series: the first two or three terms provide a sufficiently accurate approximation for distances from a few wavelengths up to infinity. The second is a Taylor-like series with respect to the vertical distance between the image source S′ and the receiver; it points out the well-known surface wave term, but gives good approximations close to the ground surface, only. Several examples are given: locally reacting surface; finite or infinite thickness layer of porous material; thin elastic plate. Numerical results show the efficiency of these approximations for engineering purposes.
Diffraction of a point source by two impedance covered half-planes
Authors: Naghieh M. R. , Hayek S. I.
Published: October 2005

An analytical solution is given to predict the propagation of noise from a point source to a point receiver over an infinite plane consisting of two half-planes, each covered by a different impedance. The solution is found by the use of function theoretic methods, and is evaluated asymptotically by the method of pole subtraction. It includes a reflected wave, three diffracted (ground) waves, and a surface wave due to each impedance in addition to a direct wave. The reflection coefficient form is different than the plane wave reflection developed for a point source over an infinite impedance covered plane given in the literature. However, it reduces to the plane wave reflection coefficient once the point source position approaches infinity representing an incoming plane wave. Out of the two reflecting waves only one contributes depending on the position of the receiver. The two surface waves correspond to the two impedance half-planes, but only one contributes depending on the location of the receiver. If the receiver is close to an impedance plane it picks up the surface wave emitting from that part of the plane, but it disappears as the receiver moves away from that surface. The diffracted (ground) waves depend on the difference of the impedances of the half-planes. [Work supported by NCHRP.]
A method of measuring the acoustic impedance of the ground by using two or more microphones
Authors: Glaretas Constantine , McDaniel O. H. , Reethof Gerhard
Published: October 2005

This paper reports the results of a new experimental method to measure the real and imaginary parts of the ground impedance assuming the validity of Thomasson's formulation. A small loudspeaker placed above the ground is fed by a sweeping pure tone and the sound field is recorded by two or more microphones. The ratio of pressures at two micrphone locations provides two equations (real and imaginary part) which are sufficient to determine the real and imaginary part of ground impedance. This method does not require knowledge of the spectrum and strength of the sound source. There are no assumptions as to the nature of ground cover except that of local reaction. For a given pair of microphones there is a frequency range of maximum excess attenuation difference where this method is most sensitive in determining ground impedance. The sensitivity can be extended by taking more than two microphone position measurements. [Work supported by FHWA.]
In-duct measurement of acoustic properties using a two-microphone technique with random and pure tone excitation
Authors: Seybert A. F. , Soenarko B.
Published: October 2005

A two-microphone technique has been used to determine acoustic properties of materials using pure tone and random excitation. Theory shows that the acoustic properties may be derived from magnitude and phase angle measurements for a pair of microphones. An alternative derivation based on four-pole theory will also be presented. Absorption measurements of glasswool samples using pure tones show discrepancies when compared with the conventional standing-wave method. These errors are traced to phase angle measurement uncertainty. It will be shown that the use of random excitation avoids these errors, and that absorption measurements using random excitation compare well with measurements using the standing-wave method. However, there are bias and random errors generated during signal processing of random data. These errors may be minimized by proper selection of signal processing parameters.
An acoustical mirage effect
Authors: Embleton T. F. W. , Piercy J. E.
Published: October 2005

Strong vertical gradients of temperature in the atmosphere in the first few centimeters above a hot ground surface, such as a roadway in the sun, are known to significantly refract light, producing optical mirages. Since the velocity of sound is 1700 times more sensitive to temperature, proportionally, than the velocity of light, powerful acoustic mirages and their associated shadow zones should appear somewhere, due to this thin layer of hot air, although they have not been reported explicitly. A measurement program using an acoustic point source was undertaken to find whether such a mirage could influence standard compliance testing of noise sources, particularly vehicular, at distances of 7.5 and 15 m. For both distances shadow zones were found which produced excess attenuations of l0 to 20 dB for frequencies of 2–10 kHz when the source and microphone were sufficiently close to the ground. These measurements throw doubt on existing measurements of tire noise from vehicles.
General losses occurring in an inhomogeneous, granular, lossy medium with energy mechanism size ordering
Authors: Akers G. R.
Published: October 2005

The energy loss mechanisms that take place as a wave propagates through a granular, inhomogeneous, lossy medium with liquid/gas/vacuum in the interstices are considered. The losses include the following: (a) frictional loss F, (b) thermodynamic loss T, (c) viscous loss V, (d) scattering loss S, (e) intrinsic attenuation in solid A, (f) intrinsic attenuation in fluid (gas/liquid) B. Over the frequency regime different losses become dominant and these mechanisms reorder themselves in magnitude. As a result of the use of these derived energy loss mechanisms, specific wavefield solutions are presentable utilizing the generalized nonlinear behavior for a dissipative medium obtained in a prior paper. The near and far fields over the frequency range are definable in terms of adjustable power series consisting of various terms. [Work supported by Navy Long-term Training Program.]
Perception of transmission-echo periodicity in bat sonar
Authors: Simmons J. A.
Published: October 2005

Echolocating bats (Eptesicus fuscus) detect displacements in the arrival times of sonar echoes as small as 500 ns. They can thus detect differences in target range or fluttering motions of prey resulting in displacements in range as small as 100–200 μm. The range-axis acoustic image of a planar target corresponds to the half-wave rectified crosscorrelation function between the bat's broadband, FM sonar transmissions and echoes. The bat perceives an intersignal periodicity histogram for the sounds. The FM sweep is rapid enough that the signal frequency is within the tuning curve of any given primary auditory neuron for a few periods at most. Thus, to the auditory system of Eptesicus, the sonar sound is a set of impulses with center frequencies distributed across the echolocation bandwidth. Only the first or “on” discharge of each primary neuron needs to be locked to individual stimulus waves for the neural representation of the signal to preserve transmission-echo phase or period. These bats model sonar targets as acoustic “glints” in the nervous system, and they discriminate among target features with a time-domain sonar receiver.
Evidence for separate echolocation and communication processing areas in the inferior colliculus of bats
Authors: Marsh D. S. , Pollak G. D. , Bodenhamer R.
Published: October 2005

Although acoustic signals are used by bats for both echolocation and for communication little is known about how communication signals are represented in the bat's brain. Recently we have obtained data which strongly suggest that the inferior colliculus of Mexican free-tailed bats (Tadarida brasiliensis mexicana) is functionally partitioned into two major subdivisions: a medial region having neurons specialized for processing echolocation signals and a lateral region having neurons that appear to be well suited for analyzing communication sounds. The features which distinguish the two regions are marked differences in tonotopic organization as well as in tuning and discharge properties. The tonotopic organization of the medial region is mammalian in design. The characteristic frequencies (CF) of neurons in this region increase in an orderly manner with depth and encompass the full compliment of frequencies in the echolocation sounds emitted by this species. The neurons in the medial region are very sensitive to brief frequency-modulated (FM) signals which mimic the natural orientation cries and exhibit fast recovery. In striking contrast, the tonotopy of the lateral portion of the colliculus is characterized by a relative constancy of CFs with depth. The CFs of neurons situated dorsally are 20-22 kHz and only increase to 24-26 kHz in the deepest parts of the lateral region. In addition, the majority of neurons are either unresponsive to brief FM signals or have very high thresholds for responding to these stimuli. A final feature is that many neurons have two frequencies of maximal sensitivity in their tuning curves. Such multiply tuned neurons were only found in the lateral region. Many of the communication sounds emitted by Mexican free-tailed bats have long constant frequency portions. The fundamental frequencies range from about 20-25 kHz and are rich in harmonics, features which correlate closely with the tuning features of neurons in the lateral region. [Supported by NIH Grants NS13276 and NS00367.]
Studies of the middle ear in birds: Anatomical and physiological aspects
Authors: Saunders James C. , Kuhn Angelika
Published: October 2005

The structural organization of the middle ear in adult parakeets and neonatal chicks was examined using light and scanning microscopy. The areas of the tympanic membrane (TM) and columella footplate were ascertained, as was the columella length and angle of incidence between columella and TM. The ligaments of the TM and columella were identified, and the angular relations between the shaft of the columella, its footplate and the oval window were measured. Transmission electron microscopy was used to examine the layers of the TM. A capacative probe was further used to describe the response characteristics of the TM (measured at the tip of the extracolumella) when stimulated at 100 dB SPL between 0.2 and 10.0 kHz. The unique response properties of the TM are considered with regard to the structures of the middle ear. [Work supported by Heinrich-Hertz Foundation, West Germany.
Backward solution of a two-dimensional cochlear model
Authors: Neely S. T.
Published: October 2005

A traditional linear approach to modeling the mechanics of the cochlea has as its end result the mechanical response of the cochlear partition to sinusoidal excitation of the stapes and assumes that the mechanical point impedance of the cochlear partition is known in advance. A backward modeling approach has been found which starts with any specified cochlear partition response (i.e., amplitude and phase of partition motion as a function of place) and uses the traditional modeling assumptions to obtain the unique mechanical impedance function implied by such a response. The backward approach makes it possible to avoid the labor and uncertainties of trying to match responses by trial-and-error choice of impedance functions; furthermore, it can be used as an inverse operator to check the validity of traditional forward solutions (and vice versa). The partition impedance obtained by the backward approach is a complex function of position with no particular functional form and has a real part (damping term) that is not always positive. [Supported by NIH grants NS07498 and GM01827.]
Low-frequency biasing of the basilar membrane and its effect on some responses of auditory-nerve fibers
Authors: Schmiedt R. A.
Published: October 2005

Rate-level functions of auditory-nerve fibers were obtained in the Mongolian gerbil to tone bursts alone and superimposed on a low-frequency biasing signal. The bias was a triangular sound-pressure waveform with a fundamental frequency of 10 Hz. Cochlear microphonics (CM) recorded in scala media of the basal and second turns of the cochlea in response to the triangular stimulus were trapezoidal in shape. Assuming CM waveforms reflect basilar-membrane (BM) displacement at low frequencies, the trapezoidal CM pattern implies a cochlear input impedance that is largely resistive even at 10 Hz. The rate-level functions indicate that characteristic-frequency (CF) tones associated with scala-tympani (ST) displacement of the CM trapezoid had thresholds typically 10 dB lower than those associated with scala-vestibuli (SV) displacements in all fibers tested. Tone-alone thresholds were generally between those obtained under the two biased conditions. Threshold differences of tones associated with ST and SV displacements were reduced when the frequency of the tone was placed off, especially below, CF. [Work supported in part by SC Biomedical Research Grant.]
Changes in EP and K+ in the inner ear fluids following loop diuretics
Authors: Morizono Tetsuo , Rybak L. P. , Sikora Michael A.
Published: October 2005

Pathogenesis of inner ear deafness are thought to be due largely to imbalance of potassium and sodium ions in the inner ear fluids. Such imbalance can occur with renal diseases, vascular insufficiencies, and ototoxic drugs. An ion-specific micro-electrode was applied to the peri- or endo-lymph in chinchilla's cochlea. Simultaneous measurements of endocochlear dc potentials (EP) and K-ion concentration were made over a period of a few hours and their changes following temporary asphyxia, following various loop diuretics, following permanent anoxia were studied. The reduction of endolymph potassium concentration was accompanied by the elevation of perilymph concentration of this cation following loop diuretics. Normal values for K+ in the inner ear fluids and potassium conductance following various doses of loop diuretics will be discussed in detail.
Unspecific ion channels in guinea pig cochlear hair cells
Authors: Marcus D. C. , Thalman R.
Published: October 2005

It has been proposed that the cochlear microphonic (CM) is produced by a modulated potassium-current through channels in the apical membrane of the hair cells. In support of this concept, Salt and Konishi [J. Acoust. Soc. Am. 66, S47 (1979)] have found that electrophoretically applied tetraethylammonium (TEA; a blocker of K channels of excitable membranes) reduces the CM while raising the endocochlear potential. However, two lines of evidence suggest that these pathways might not be K-selective: (1) Cory and Hudspeth [Nature (in press)] have shown in an in vitro lower-vertebrate hair cell system that the microprohie-producing ion channels are not K selective, since numerous ions can be accommodated. (2) We have observed that injections into scala media of about 50 nl each of phentolamine (1 mM), serotoxin (5 mM), or EGTA (1 mM) in artificial endolymph produce effects similar to those reported for TEA. Control injections produced no effect. The diversity of the known primary actions of each of these agents (alpha-adrenergic blocker, neurotransmitter, and calcium chelating agent, respectively) suggests that TEA may not be acting on a strictly K-selective channel. [Supported by NSF and NIH.]
Organ of Corti-specific polypeptides: OCP-I and OCP-II
Authors: Thalmann I. , Rosenthal H. L. , Moore B. W. , Thalmann R.
Published: October 2005

Proteins associated with the specific functions of differentiated cells have been found in numerous systems. By means of two-dimensional polyacrylamide gel electrophoresis, we have identified two polypeptides, apparently specific to the organ of Corti and tentatively named OCP-I and OCP-II. These polypeptides comprise a substantial proportion of the total protein of the organ of Corti of the guinea pig and rat, the only species studied to date. They are not present in other inner ear structures (macula sacculi, tectorial membrane, stria vascularis, etc.), nor in other tissues (brain, liver, retina, etc.). The molecular weights of OCP-I and OCP-II are 37 000 and 22 500 daltons, respectively. The corresponding pI values are 4.9 and 5.1. At this preliminary stage we can only speculate about the functions of OCP-I and OCP-II; it is conceivable that they are involved in auditory transduction and/or transmission. [Supported by NIH.]
Audiologic performance of young deaf adults
Authors: Bode Daniel L. , McFarland William H. , Bricca Barry , Holum-Hardegen Laura
Published: October 2005

Deaf students entering Gallaudet College routinely are evaluated audiologically. Data for 330 new students enrolled during Fall semester 1978 were analyzed. The primary purpose was to obtain descriptive statistics for 118 assessment variables. Clinical test variables included pure tone and speech audiometric responses, immitence measures, aided and unaided hearing aid performance, history of hearing aid use, speechreading scores with and without audition. auditory speech reception measures with and without hearing aids, speech intelligibility ratings, and reported information regarding onset, etiology, and family history of hearing loss. Summary descriptive data and intercorrelations among major clinical variables will be reported and discussed.
Effects of some acoustic-cue modifications on the perception of voiced and unvoiced final stop consonants for hearing-impaired listeners
Authors: Revoile Sally , Pickett J. M. , Holden Lisa , Talkin David
Published: October 2005

Various acoustic cues to voicing were modified systematically in a corpus of ten utterances each of dap, dak, dat, dab, dag, and dad spoken by a male. The acoustic cues, modified separately and/or simultaneously, were: vowel duration, closure duration, murmur presence, final stop-burst presence, and vowel offset. The modifications were accomplished by either deleting, iterating, or transposing segments of digital representations of the utterances, using waveform manipulations via computer. The digital stimuli, with and without acoustic-cue modifications, were presented to 23 hearing-impaired listeners for identification of the final consonant within the closed set of six stimuli. In general, different acoustic-cue modifications degraded the perception of voicing among the listeners. Burst and/or murmur absence greatly affected performance for some listeners, but not for others. Alterations to vowel duration degraded voicing perception for a few listeners. The elimination of the last ten vowel pitch periods, with burst and murmur also absent, degraded voicing perception for most listeners. Adjustments to closure duration had little effect.