bluuebunny/crossref_metadata_2025 huggingface dataset:
Sea surface reverberation
Authors: McDaniel Suzanne T.
Published: October 2005

Reflection and scattering from the sea surface have been extensively studied both experimentally and from a theoretical standpoint. This paper focuses on reverberation processes because, due to the relative ease of measurement, a vast store of experimental data has been amassed. Measurements have been performed to study the dependence of the strength and Doppler spread of monostatic backscatter on acoustic frequency, incidence angle, sea state, windspeed, and heading with respect to the mean wind direction. In this paper, reverberation measurements and the accompanying development of theories to explain the experimental results are reviewed from a historical perspective. The theoretical effort is traced from the application of the Kirchhoff approximation in the geometrical optics limit, to the use of composite-roughness theory along with a treatment of scattering from the layer of wind generated microbubbles that exist below the surface. Our present ability to characterize sea surface reverberation is demonstrated using recent measurements of ocean wave spectra and bubble densities as inputs to the theory. [Research supported by NORDA.]
Diffraction of pulsed ultrasonic waves in lossless and absorbing media
Authors: Guyomar Daniel , Powers John
Published: October 2005

A theoretical model is presented for computing the transient acoustical field radiated by a baffled transducer in a lossless or absorbing medium. Attenuation is introduced by the addition of a term to the wave equation, simulating the absorption of biological tissue. The method is based on a time generalization of the angular spectrum theory. It shows that diffraction of the pulse is equivalent to the time-varying spatial filter that reduces the high spatial frequency components. The effect of attenuation is to enhance the low-frequency components even more than in the lossless case, while exponentially attenuating the wave amplitude. The method is valid for any planar velocity souce distribution with arbitrary time excitation. Neither the Fresnel nor the Fraunhofer approximations are used, consequently no restrictions on the propagation distance are required. The effects of a finite receiver are easily incorporated in the formulation as an additional spatial filter. Computer simulations of results both with and without attenuation are included.
Computer-aided backscattering measurement of ultrasonic waves
Authors: Csakany Antal , Wang Shiao , Adler Laszlo
Published: October 2005

A system based on two microcomputers was developed to increase the precision and repeatibility of ultrasonic measurements. The first micro-computer controls the mechanical movements (resolution: 40 μm in linear distance; 1/40° in angle) and data collection, the second one is used for data processing and interactive data presentation. The system was applied to measure leaky Rayleigh and leaky Lamb wave velocities from critical angles with an increased precision in different materials. A method was also developed to measure the loss of leaky Rayleigh waves from several materials in water. This system has been especially advantageously used where a large number of inhomogeneities are the sources of the ultrasonic scattering, i.e., grains, pores. Examples will be given to present the various displays of complex measured data.
Numerical implementation of the orthonormalization method for acoustic scattering from a rigid prolate ellipsoid
Authors: Gaumond C. F. , Dallas Allan
Published: October 2005

The orthonormalization method was used to derive the solution for a smooth rigid body. The scattering from a prolate ellipsoid was described using spherical harmonics on basis functions. The form function was found for low values of ka, where a is the semi-major axis, and for various length/width ratios. The effects of including various numbers of basis functions will be shown.
Resonance scattering of acoustic waves from air-filled cylinders in water
Authors: Delsanto P. P. , Alemar J. D. , Rosario E. , Nagl A. , Überall H.
Published: October 2005

A general theory for the scattering of plane elastic waves obliquely incident on an infinite cylindrical solid obstacle has been developed. In the present paper, this is specialized to the acoustic case for the example of an air-filled cylinder in water. We study the resonances of the scattering amplitudes, and determine their poles in the complex frequency plane (SEM poles) and mode number plane (Regge poles). The motion of the poles upon variation of the angle of incidence is investigated. The pole diagrams lead to a determination of the dispersion curves of helical surface waves generated by the incident wave, as well as their refraction and attenuation, all as a function of the angle of incidence. This includes both external (Franz type) and internal surface waves propagating in the water and air medium, respectively. [Work at Puerto Rico supported by the U.S. Army Research Office.]
Pulse response and the pole structure of elastic-body scattering amplitudes
Authors: Numrich S. K. , Howell W. E. , Überall H.
Published: October 2005

The interference features appearing in acoustic scattering amplitudes of elastic targets, when plotted versus frequency, are largely governed by the complex-frequency poles of the amplitudes. Unitarity entails the existence of a zero accompanying each pole. The dependence of interference features on the pole and zero structure of the scattering amplitude S can be strikingly visualized by plotting contour maps of |S| over the complex frequency plane. We further studied the influence of the pole structure on the scattering of long sinusoidal wave trains for tungsten carbide, aluminum, and lucite spheres and cylinders. Both quasi-stationary and transient portions of the echo are affected, as physically explained by the phase relationships between specularly reflected and circumferential pulses. [H.Ü. was partly supported by ONR.]
Measurement of energy flow and acoustic absorption
Authors: Rasmussen Gunnar
Published: October 2005

The measurement of energy flow in rooms may be conveniently carried out using a real time intensity analyzer allowing one to plot the flow in the planes of interest. Supplemented with absorption measurements carried out with the same setup, a thorough knowledge of the important parameters, such as local absorption, controlling the acoustics of a room may be obtained over a wide frequency band in a very short time. Comparison with data obtained by conventional methods will be reported.
Forward masking by two sequential sinusoidal maskers
Authors: Neff Donna L.
Published: October 2005

Two temporally distinct maskers of 300 and 30 ms were used to forward mask a 10-ms signal. The signal was a 1000-Hz sinusoid. The maskers were either 900- or 1000-Hz sinusoids and all four combinations of the masker frequencies were tested. From growth-of masking functions for individual maskers, levels were chosen to produce 5, 10, or 15 dB of masking for the first masker and 5, 10, 15, or 20 dB of masking for the second masker. When the two maskers were combined, the amount of additional masking, relative to that produced by the more effective masker, ranged from 0–24 dB across listeners and conditions. The smallest amount of additional masking was observed when both maskers were 1000 Hz. The remaining frequency combinations produced roughly similar amounts of additional masking. The results will be discussed in terms of models of additional masking. [Work supported by NIH.]
Signaling along elastic plates with wideband acoustic pulses
Authors: Barger James E.
Published: October 2005

High data-rate signaling with acoustic pulses along an elastic plate must contend with resolution of the launching pulse into many component pulses that arrive separately over a time span that is longer than the travel time of the first component to arrive. Computations of travel times (group velocities) and amplitudes (transfer admittances) for the first 12 modes are presented as functions of frequency. At frequencies below the cutoff frequency of about the fourth propagating mode, it is shown that a single mode can dominate the propagating signal. At higher frequencies, up to the cutoff frequency of about the ninth mode, there are always at least four important modes that cluster between both faster and slower modes having low amplitudes. At higher frequencies the dominant modes cluster to form the Rayleigh wave, which travels at a speed intermediate to the remaining low-amplitude mode speeds. Measurements made in each of the three frequency regimes are presented to illustrate the propagation of third-octave-band pulses in a steel plate.
Effects of filtering and hearing impairment on sensitivity to cues to initial stop voicing
Authors: Summerfield Quentin , Barker Brendan , Gatehouse Stewart , Browning George G.
Published: October 2005

The perception of stop voicing is relatively resistant to noise, filtering, and hearing impairment, partly because voicing cues are subsumed by robust amplitude patterning at low frequencies, but possibly also because listeners can compensate when listening is difficult by increasing the weight given to those cues that are audible. We measured the amount by which changes in F1, F0, aspiration amplitude, and syllable duration shifted the VOT boundary on a ‘dole-toll’ series bandlimited to 0–4250 Hz. Where σij and mgr;ij are the mean and standard deviation underlying the sigmoidal best fit to the identification function with value i of cue j, sensitivity was defined as (1/σij) to VOT and otherwise as [(μ1j − μ2j)/(σ1j2 − σ2j2)1/2]. Compared to normal broadband performance, listeners with normal hearing (n = 12) showed increased sensitivity to F0 and F1 following abrupt low-pass filtering at 1600 Hz, demonstrating that compensation can occur. In contrast, overall, listeners with high-frequency sensorineural losses (n = 10) showed a reduction in sensitivity to VOT, but no change in sensitivity to the secondary cues. For some impaired listeners, reduced sensitivity to VOT allowed secondary cues to surpass the effect of VOT, demonstrating their potential for maintaining stable performance when cues co-vary naturally.
Perception of vowels produced by the hearing impaired
Authors: Rubin-Spitz Judith
Published: October 2005

Hearing and hearing-impaired talkers were compared with respect to the information used by listeners in decoding their vowels. Each vowel was produced in a fixed consonant context (/bVb/) within a carrier phrase. Experienced and inexperienced listeners were asked to identify the vowel and the hearing status of the talker when provided with the entire sentence, with the /bVb/ word only, or with a gated steady state vowel segment. Although there were no significant differences between sentences and words, there were between words and gated vowels. Results suggest, however, that listeners use the same acoustic sources of information in decoding vowels produced by the two groups of talkers. While the ability to identify the hearing status of the talker decreased as a function of condition, performance in the gated vowel condition was significantly above chance. There were no significant differences between experienced and inexperienced listeners in any perceptual task. Results are discussed in terms of current theories regarding the underlying deviant nature of speech production by the hearing impaired. [Work supported in part by NIH Grants NS-17764, NS-13617 and HD-01994, and also by C. U. N. Y.]
Suppression within frequency regions of normal and impaired hearing
Authors: Weber Daniel L.
Published: October 2005

In psychophysical experiments, the reduction in the effect of one stimulus (the masker) due to the addition of a second stimulus (the suppressor) is attributed to the suppression of the masker by the suppressor. Kramer [reported by F. L. Wightman, T. McGee, and M. Kramer, in Psychophysics and Physiology of Hearing, edited by E. F. Evans and J. P. Wilson Academic, London, 1977)] measured “unmasking patterns” (signal threshold as a function of suppressor frequency) in listeners with high-frequency hearing loss. Although he observed normal suppression effects in a region of normal hearing, he found no evidence of suppression in regions of impaired heating. One factor which might have contributed to this failure was an unlucky selection of the suppressor level. This experiment compares the effect of suppressor level in normal and hearing-impaired frequency regions. Thresholds for 10-ms signals (10-ms, cosine-squared ramps with no steady state) were obtained for signals at 1 and 4 kHz forward masked by 300-ms, narrow-band (50-Hz-wide) noise maskers centered at the signal frequencies. Masker levels were 50 and 70 dB (total noise power), respectively. Suppressor levels varied from 30 to 90 dB SPL; suppressor frequencies were 0.7 kHz for the 1-kHz masker and 2.8 and 5.0 kHz for the 4-kHz masker. As observed by Kramer, suppression effects appear to be absent in regions of hearing impairment. However, in this experiment, this absence does not appear to be correlated with an absence of a difference between simultaneous and forward masking. [Research supported by grants from NSF and NIH.]
Objective speech quality measures based on human audition
Authors: Clements Mark A.
Published: October 2005

To accurately assess the quality of a speech transmission or coding system generally requires subjective ratings obtained by experiment. An alternative measurement procedure which would be highly desirable would involve an objective assessment automatically performed by computer. Using a large data-base consisting of many distortions as well as the corresponding quality ratings, we have attempted to predict subjective quality based on psychoacoustic models. Such properties as intensity perception, frequency resolution, and time integration were incorporated. One of the most interesting results involves the fact that quality of distortions involving waveform coding and additive noise were well modeled by psychoacoustic parameters. However, the quality of more complex distortions, such as those produced by linear predictive coding, was best predicted using parameters (e.g., growth of loudness) at substantial variance with psychoacoustic test results. One conclusion is that complex distortions are not well characterized by simple measures. However, many of our measures outperformed more traditional measures by a large margin. [Work supported by the Defense Communications Agency.]
Properties of the beam noise distribution function for horizontal arrays in ship-induced noise fields
Authors: Heitmeyer Richard M.
Published: October 2005

An analysis is presented of the environmental and array system factors governing the fluctuations in the beam noise of a horizontal array in a ship-induced noise field. A model is used that relates the cumulative distribution function to the directivity and side-lobe characteristics of the system and the strength and anisotropy of the shipping distribution. The results are threefold. First, for a given environment, an increase in the array length results in a large increase in the prevalance of low noise periods at the expense of a modest increase of high noise periods. Second, for sufficiently large apertures, a “noise floor” develops in that noise values larger than the noise floor occur with high probability, whereas values less than the noise floor occur only rarely. Finally, the noise floor level is essentially independent of the noise anisotropy and of further increases in aperture length, and it increases with degradation in side-lobe level.
The theoretical response of a vertical array to wind noise in shallow water
Authors: Hamson Rachel M.
Published: October 2005

A wave theory model for the propagation of noise from a surface source layer has been used to investigate the response of a vertical array to shallow water wind noise. The model assumes an infinite layer of sources radiating sound with pressure directionality of the form costm α, where m> 1 and α is an angle measured from the downward vertical. The field incident on the array is inhomogeneous and directional responses have been calculated from the (non-Toeplitz) spatial correlation matrix for various bottom types, sound-speed profiles, and values of m up to 3. Results show that both components of the noise field, the discrete normal modes and the continuous spectrum, can contribute significantly to the array response. Furthermore the mode arrivals give much higher responses for near-horizontal steered directions than those predicted by a simple correlation model for a semi-infinite medium. Finally calculations using an approximated Toeplitz matrix result in large errors under certain conditions, and demonstrate that a one-dimensional correlation function is not a sufficient descriptor of noise in shallow water.
Effects of intensity and filtering on identification of nonsense syllables
Authors: Studebaker Gerald A. , Goshorn Edward L.
Published: October 2005

The identification of nonsense syllables was investigated under various conditions of filtering, noise, and intensity level. The syllables were filtered and recorded simultaneously as two separate bands in a background of speech spectrum noise. The low-pass band (200–400 Hz) was recorded at a nominal signal to noise ratio of 20 dB, the high-pass band (1–5 kHz) at 7 dB. The low-pass band was presented at 60, 80, and 96 dB SPL, the high-pass band at 60 and 80 dB SPL (nominal levels represent coupler level prior to filterings. Each band was presented alone and in every possible combination of intensity level with the other band to four normal hearing subjects. The best performance resulted when both bands were at 60 dB. Increasing the level of the high-pass band by 20 dB and of the low-pass band by 20 and 36 dB relative to the best condition resulted in a reduction in performance. Poorest performance resulted when the low-pass band was at the highest level (96 dB) and the high-pass band was at the lowest level (60 dB).
Trading relations in nonspeech
Authors: Parker Ellen M. , Kluender Keith R. , Diehl Randy L.
Published: October 2005

Two acoustic features shown to be sufficient in specifying the distinction between intervocalic /b/ and /p/ are closure duration and the presence or absence of a low-frequency voicing pulse during the closure interval. These features of the signal can be considered to exhibit a trading relation [B. Repp, Psych. Bull. 92, 81–110 (1982)] to the extent that a longer closure is required to perceive the consonant as voiceless when the pulse is present than when it is not. This study addressed the issue of whether a trading relation of the type found in speech can be demonstrated for nonspeech as well. Two types of square wave analogs, modeled after a speech series ranging from “rabid” to “rapid,” were constructed. One set of nonspeech stimuli contained frequency transitions into and out of the silent interval while frequency for the other nonspeech stimuli remained constant. Preliminary (AXB) identification results indicate that in the speech condition, the presence of the pulse affects a shift in the ID boundary between “rabid” and “rapid” relative to the no-pulse condition. A comparable shift is observed between the pulse and no-pulse series in the nonspeech transition condition; no shift is apparent for the nonspeech no-transition condition. The implications of these results for the notion that speech perception requires a “special” mode of processing will be discussed. [Work supported by NINCDS.]
Detuning a large turbine generator statur endwinding
Authors: Humphries Ben T.
Published: October 2005

From experience with similar steam turbine generators it was predicted that the stator coil endwinding, a truncated cone shaped structure attached to the stator core, would have an elliptical mode natural frequency near, 120 Hz, its excitation frequency. A new support bracket was designed to lower this natural frequency 15 Hz. The turbine generator was built in its original form, and was excited using impact and random noise shakers. The impact tests were quick and excited all modes while the diametrical shaker tests were designed to simulate actual excitation forces and tended to accentuate the problem mode. The new support bracket was installed and the natural frequencies were measured again. Natural frequencies were then rechecked under simulated operating temperatures and decreased as expected. The new support bracket detuned the coil endwinding as expected.
Putative amino acid neurotransmitters in cochlear (CN) and vestibular (VN) nuclei of guinea pig
Authors: Thalmann Ruediger , Comegys Thomas H.
Published: October 2005

We reported that aspartate (asp) and glummate (glu) are significantly reduced in the ventral CN after surgical destruction of the organ of Corti, corresponding to the pattern of primary innervation [Thaimann et al., J. Acoust. Soc. Am. Suppl. 1 67, S77 (1980)]. More recently, we confirmed and extended Wenthold's finding [Brain Res. 143, 544 (1978)] that these substances decline similarly, although on a faster time scale, after VIIIth nerve section–no decline in molecular and fusiform layers of dorsal CN, but significant declines (p < 0.001) in deep dorsal CN (asp 29%, glu 24%) and in posteroventral CN (asp 48%, glu 45%). Analogous declines occurred in the phylogenetically older VN following VIIIth nerve section. In the heavily innervated central part of superior VN asp and glu decreased by 21% and 37%, respectively (p < 0.001), with no decline in the sparsely supplied peripheral part. In lateral VN, asp and glu declined significantly (35% and 21%, respectively) in the heavily innervated ventral portion, while in the sparsely innervated dorsal part, only asp declined (26%). The behavior of asp and glu after lesion (as well as their resting distribution) is consistent with the involvement of either or both in neurotransmission at the primary auditory and vestibular terminals. [Supported by NIH.]
Model for threshold shift following intense exposures
Authors: Price G. Richard
Published: October 2005

Hearing loss experiments with impulse noises at high intensities typically produce threshold shifts that have an extremely high variability. Price [Hearing and Other Senses: Presentations in Honor of E. G. Weber, edited by Fay and Gourevitch (Amphora, Groton, 1983), Chap. 20, pp. 335–346] proposed that at high intensities, loss was essentially mechanical in origin and that its growth might be a function of the number of stress cycles times the mechanical stress raised to a power. A model was constructed to embody this relationship as well as a normally distributed threshold of sensitivity to damage. Given a standard deviation of about 8 dB for the sensitivity and a power of 2 for the stress exponent, the model produces threshold shifts that look like those seen with both human and animal subjects exposed to intense impulses.
Acoustic scattering from a pair of rigid spheres
Authors: Seybert A. F. , Soenarko B.
Published: October 2005

Scattering of a plane acoustic wave from a pair of rigid spheres is considered for the case where the spheres lie on a line perpendicular to the incident wave. Our primary interest is in the effect the second sphere has on the scattered field in the vicinity of the first sphere. The scattered field is computed by two methods. The first method is based on a numerical solution of the Helmholtz integral formula. The second method is an approximate solution formed by adding the scattered field of each sphere without the presence of the other. Comparison data are presented for the two methods as a function of frequency, distance between the spheres and the ratio of the spheres' radii.
The structural and acoustic response of a submerged infinite cylindrical shell in the presence of hydrostatic pressure fields
Authors: Keltie Richard F.
Published: October 2005

The dynamic response of an infinite circular cylindrical shell submerged in an acoustic medium was formulated using Flugge's thin shell theory. The effects of a uniform hydrostatic pressure field were modeled by including constant initial stress terms in the shell equations of motion. The driving point impedance of the shell was examined and characterized in terms of the in-vacuo shell impedance and the additional fluid impedance. The effects of the hydrostatic pressure on both were determined and examined as a function of frequency. The surface acoustic intensity field resulting from a localized harmonic driving force was formulated and integrated numerically over the surface of the shell in order to determine the radiated acoustic power. The relative effects of the fluid loading and the hydrostatic pressure field on the acoustic response were subsequently examined as a function of the frequency of the excitation.
Experimental studies of acoustic radiation for unbaffled complex planar sources with nearfield acoustic holography
Authors: Lee Yongchun , Maynard J. D.
Published: October 2005

Design data for the evaluation of the acoustic radiation coupling loss factor for complex planar sources, such as ribbed plates, nonuniform plates, damped plates, and aircraft panels, etc. is still fairly scarce. This work presents a broad survey of complex vibrating planar sources. These results were obtained using nearfield acoustic holography (NAH) to illuminate the effects of stiffness, mass, and damping on radiation loss factor. [Work supported by ONR and NASA.]
An assessment of second-order perturbation theory as applied to the scattering of sound by statistically rough surfaces
Authors: Tolstoy A. , Berman D. , Diachok O. , Tolstoy I.
Published: October 2005

Second-order perturbation theory is one of few theories presently capable of describing scattering of low-frequency acoustic plane waves by statistically rough surfaces. In order to assess this theory we have compared its predictions of the magnitude of the reflection coefficient |R| with known near exact solutions, in particular, for surfaces which consist of identical, hard, ellipsoidal bosses sparsely and independently distributed on a hard plane by means of a uniform probability law. In order to apply perturbation theory to such a surface we needed to compute its correlation function, operate on that function, and compute an effective boundary admittance. Finally we compared that admittance with (farfield) near-exact results for spherical and oblate ellipsoidal bosses with eccentricity e. Calculations of |R| are presented showing that discrepancies decrease as grazing angle increases and are less than 10% for e>0.99, and approximately 70% for e≈0. We conclude that perturbation theory is excellent in the case of oblate spheroids and not to be used for prolate spheroids. [This work was supported by ONR and NRL.]
Determination of the ocean wave directional spectrum from acoustic backscatter
Authors: Clifford Steven F. , Lataitis Richard J.
Published: October 2005

We describe a technique for extracting the ocean wave height directional spectrum (OWHDS) from underwater acoustic backscatter measurements. Our technique requires a bottom-mounted acoustic transceiver consisting of a quasi-isotropic source of sound and a receiver array designed to measure the mutual coherence function (MCF) of the surface scattered and reflected fields. The MCF is shown to be directly related to the OWHDS which can then be extracted using a simple inversion scheme. Our results are applicable for all relative values of the rms surface wave height to acoustic wavelength provided the rms surface wave slope s < 1.
Pattern recognition applications in underwater acoustics
Authors: Chen C. H.
Published: October 2005

Pattern recognition application to underwater acoustics is a relatively less explored area, even though much study has been made of sonar signal detection. Recently, significant effort has been made of submarine transient signal analysis and classification. Various spectral and time domain features are considered for detection and event classification. Effective recognition requires signal segmentation. The use of entropy distance measure for waveform segmentation is then examined. The next pattern recognition application is the target motion analysis by using pattern matching idea in the estimation of target range, velocity, and bearing. Another application is in multipath ranging. An image processing technique is used to extract the significant tracks from the correlograms to provide a continuous estimate of time delay or range under a multipath environment. Major computer results reported earlier [C. H. Chen, Pattern Recog. J. 16 (6) (1983)] along with further results on transient signal analysis are presented. Other applications such as sonar recognition in fisheries are also examined. While the trend continues to be digital processing and system integration, the basic recognition issue remains to be the extraction of effective features from the preprocessed underwater acoustical data. [Work partially supported by NUSC at Newport, RI.]
Pattern recognition in acoustic signature inspection of railroad wheels
Authors: Haran Shivan , Finch R. D.
Published: October 2005

There is a need for an automatic testing system for railroad wheels in service. Earlier work established the feasibility of using acoustic signatures for this purpose, to the extent that such a system has now been installed and is under test. An important conclusion from previous work was that the best detection method was a comparison of sounds from the two members of a wheel set. Pattern recognition techniques were used to detect the difference in the sounds of these two wheels. Preliminary results indicate that these techniques are adequate to discriminate good wheels from flawed ones. Various comparison schemes can be used depending on the features selected. Among features considered are spectral cross correlation, and the number of resonances common to the signals of both wheels. Linear decision functions and a least-squares procedure are used in the classification. The results obtained are encouraging. [Work supported by the Association of American Railroads.]
Stability analysis of a Stokes boundary layer in a waveguide having slowly varying height
Authors: Thompson Charles
Published: October 2005

The stability of an acoustic disturbance in a two-dimensional waveguide having slowly varying height will be investigated. The enclosed fluid is assumed to be both viscous and compressible. It is shown that the dynamic behavior of the enclosed fluid can be parameterized by three small parameters, ε, 1/R, and 1/S, where ε is the ratio of the typical duct height H0 to the wall wavelength L0, 1/S is the ratio of the oscillatory particle displacement U0/ω to the typical duct height H0, and 1/R is the ratio of the oscillatory boundary layer thickness lv to the typical duct height H0. Special attention will be paid to waveguides with cross sections that are small compared to an acoustic and/or wall wavelengths. A stability analysis will be presented in the amplitude range where ε2R/S2 = 0(R).
Interface wave mode propagation in clad rod acoustic waveguides
Authors: Hanna Susan J. , Claus Richard O.
Published: October 2005

The propagation of acoustic waves on the cylindrical boundary between the core and cladding materials of a clad rod waveguide is described. Typically, axisymmetric torsional, axisymmetric radial-longitudinal, and core-guided shear modes may propagate within a rod of cylindrical cross section if the velocity of plane shear waves in the cladding material exceeds the velocity in the material of the core [R. N. Thurston, J. Acoust. Soc. Am. 64, 1 (1978)]. If instead the elastic constants of the core and cladding materials of the rod are reversed so the material with the slower shear wave speed is on the outside, no modes are supported within the core but an interface wave can exist on the core-cladding boundary. In this paper the transmission properties of an all glass clad rod with a suitable core-cladding elastic constant relationship to support non-attenuating interface waves are discussed. The resulting improved freedom from spurious responses allowed by this single mode operation is discussed. [Work supported by NASA.]
Tangential component of an acoustic surface pulse
Authors: Claus Richard O.
Published: October 2005

Measurements of the in-plane components of the surface particle displacement caused by a simulated Heavyside step function load source on the same surface of a large glass block are described and compared with theory. These components were measured by attaching a small rectangular solid crystal with reflecting surfaces to the block and observing the tangential motions of the normal surfaces of the crystal using stabilized optical interferometry. Although the bandwidth of the detected signals is limited by the length of the crystal compared to an acoustic wavelength, and the observable motions are influenced by the mass loading of the surface by the crystal, good agreement between theory and measurements is obtained. These data combined with similar optical measurements of the normal component [F. R. Brekenridge, C. E. Tschiegg, and M. Greenspan, J. Acoust. Soc. Am. 57, 626 (1975)] yield full localized three-dimensional displacement information. [Work supported by NASA.]
Coupled aerodynamic and acoustic predictions for turboprops
Authors: Clark Bruce J. , Scott James R.
Published: October 2005

To predict the noise fields for proposed turboprop airplanes, an existing turboprop noise code by Farassat has been modified to accept blade pressure inputs from a 3-D aerodynamic code. A Euler-type code written by Denton can handle the nonlinear transonic flow of these high-speed, highly swept blades. This turbofan code of Denton was modified to allow the calculation mesh to extend to about twice the blade radius and to apply circumferential periodicity rather than solid-wall boundary conditions on the blade in the region between the blade tip and the outer shroud. Outputs were added for input to the noise prediction program and for color contour plots of various flow variables. The input subroutines were modified to read files of blade coordinates and predicted surface pressures. Aerodynamic and acoustic results are shown for the SR-3 model blade and are compared to various measured data.
The role of induced vibrations in helicopter noise annoyance
Authors: Schomer Paul D.
Published: October 2005

Community reaction to helicopter noise remains only a partially answered question. While the A-weighting appears to work out of doors and at modest noise levels, and the community response in terms of percent of population highly annoyed can be correlated with respect to the DNL (day/night level) descriptor, questions remain as to the role of perceived building vibrations in the response of people to helicopter noise. Does hearing windows rattle, or ceiling tiles rattle, objects in the room rattle, or the general perception of building vibration increase the public's adverse response to helicopter noise? The purpose of this study was to examine the growth in human response to helicopter noise as the noise levels grow from modest levels to fairly high levels. At the higher levels the noise will excite vibrations in building elements and objects within the structure. The purpose of this study was to discover a shift in the growth in human response (if any) to increasing noise which can be related to these vibrations. This study used a UH-IH helicopter in conjunction with an old farm house, a new mobile home, and outdoors in a tent as a live “laboratory.” This paper reports on the test execution and initial results. [This was a joint U.S. Army/FAA study.]
Reduction and discrimination of wind noise in outdoor blast noise measurement
Authors: Walker Douglas R.
Published: October 2005

It is difficult to distinguish between wind-induced noise and blast noise under field conditions, since the spectral content of both is concentrated below 50 Hz. As one solution, an omnidirectional, low-frequency, outdoor microphone windscreening system was designed and tested. An empirical data base of approximately 600 measurements characterizing outdoor blast noise was collected with the system. It employed a layered, low-porosity foam, mechanical windscreen which was optimized for rejection of low-frequency wind noise. This windscreen attenuated the A-weighted wind noise by up to 26 dB overall. Additionally, a two-microphone array was used and it was found that blast events could be distinguished reliably from wind by comparison of selected features of the two signals.
Enhancing spectral contrast in the auditory representation of speech
Authors: Sidwell Andrew , Summerfield Quentin
Published: October 2005

The intelligibility of many classes of speech sounds requires the preservation of spectral amplitude patterning in the auditory representation of the signal. In hearing impairment of cochlear origin contrast in spectral amplitude may be reduced: first, suppression may be less effective; second, auditory filters may be more broadly tuned. It is possible in principle to compensate for a reduction of contrast in the auditory spectrum by increasing contrast in the physical spectrum, e.g., by processing the signal to reduce formant bandwidths. Two steady-state noise-excited vowel sounds were synthesized, one similar to a naturally produced whispered vowel, the other with formant bandwidth reduced to 50 Hz. The auditory spectra of both sounds were measured using simultaneous and forward masking, to assess the enhancement due to suppression, in three normal-hearing and three sensorineurally impaired listeners. Little structure was preserved in the auditory spectrum of the vowel with conventional bandwidths above 2.5 kHz. Reducing formant bandwidths increased spectral contrast in both groups of listeners. Where contrast was preserved, it was enhanced by suppression, again in both groups. The ability to enhance the auditory spectrum in the impaired group may have implications for the design of signal-processing hearing aids.
Comparison of objective and subjective measures of communication difficulty
Authors: Hodge David C. , Garinther Georges R.
Published: October 2005

Speech intelligibility was determined for subjects wearing the M25 gas mask at various distances using the PB Monosyllabic Word Intelligibility Test. The subjects also rated communication difficulty at each distance, and specified the maximum distance at which short commands could easily be given and understood. The intelligibility tests were conducted outdoors at distances ranging from 1 to 32 m, using nine subjects serving as both talkers and listeners. The talkers were instructed to use that voice level which they felt was appropriate for each distance. Mean intelligibility ranged from 70% at 1 m, to 20% at 32 m. Voice level measured at 1 m increased from 66 to 74 dB(A) as communication distance increased. Subjects' ranging of communication difficulty were highly correlated with the intelligibility data. The subjects indicated an average maximum comfortable communication distance of 8.5 m, corresponding to about 49% PB intelligibility. An upward shift in voice spectrum was found as the subjects spoke at greater distances.
The role of nasalization in the perception of synthesized speech
Authors: Thomas John C. , Nartey Jonas N. A. , Rosson Mary Beth , Klavans Judy
Published: October 2005

Thus far synthesized speech has been reported by phonetically naive listeners as sounding “metallic” or “as if the speaker had a cold.” One of the explanations for the above is that the simulation of nasal coupling is not close enough to natural speech. We report on research on diphone synthesized utterances (Dixon and Maxey, 1968). In order to simulate a better set of nasalized vowels in synthesized speech, a new set of diphones was created to replace the original ones in those cases in which there is a nasal consonant in the immediate vicinity. These new diphones were the result of hand-painting single nasal formants in addition to the regular formant frequencies found in the original diphones. Utterances made of both the new and old sets of diphones were played to phonetically naive listeners. Results on naturalness judgments and on intelligibility will be presented.
Model of human sound localization based on spectral pattern recognition
Authors: Perkins Mark E. , Kistler Doris J. , Wightman Frederic L.
Published: October 2005

In the course of our research on sound localization we have measured direction-dependent pinna transfer functions of eight observers. The magnitudes of these functions have peaks and valleys that vary in spectral locus across subject and across source location. We addressed the question of whether these spectral patterns contain sufficient information for accurate localization of sounds in space. We used standard multivariate statistical techniques to develop a model of sound localization based on pattern recognition principles. A Bayesian classification procedure is employed to make a decision as to the most probable source location. The errors made by this procedure are compared to the errors made by subjects when judging source location in free-field listening conditions. Preliminary results are extremely encouraging. The source positions for which the model makes errors match quite well those for which the subjects make errors. [Work supported by NSF and NIH.]
Azimuthal localization of sounds with a single early reflection
Authors: Rakerd Brad , Hartmann W. M.
Published: October 2005

When localizing sounds in a room, listeners must overcome interference from numerous echoes. We created a simple limiting case of this situation by conducting experiments in an anechoic chamber in which a heavy 4 × 8 ft panel provided a single early reflection. The panel alternatively served as a left wall, right wall, floor, or ceiling. Localization accuracy was assessed with the source identification method [W. M. Hartmann, J. Acoust. Soc. Am. 74, 1380–1391 (1983)] for eight loudspeakers separated in azimuth by three degrees of arc. The stimuli were 500-Hz tones which were either pulsed for 50 ms or turned on with a slow (7 s) envelope and left on to deprive the listener of any transient information. For pulses, performance was significantly poorer with side wall reflections than with reflections from the floor or ceiling, or with no reflections at all. There was no evidence that responses systematically deviated to the left or right of targets in any condition. Together, these findings indicate that the precedence effect [H. Wallach et al., Am. J. Psychol. 62, 315–336 (1949)] can break down over short intervals and that when it does so the result is simply increased uncertainty in localization. For tones with no transients, performance was very much poorer for side walls and ceiling than for the floor and no-wall conditions. Physical measurements indicate that these judgments were determined jointly by the binaural time and intensity differences that resulted from interference between the source and its reflection. [Work partially supported by NIH and the Department of Audiology and Speech Sciences, Michigan State University.]
Simulation of vocal fold tissue movement
Authors: Alipour Fariborz , Titze Ingo R.
Published: October 2005

A computer simulation for two-dimensional vibration of the vocal folds is presented. Free and forced oscillations are studied by imposing an impulse and time varying surface force. The solution is obtained by a semi-discrete numerical method. A finite element technique is used for the space-dependent solution and a Crank-Nicholson finite difference method is used for time integration. Horizontal and vertical displacements as a function of time, as well as x-y trajectories, are calculated for some points at the tip of fold. In addition, the response of the system due to a sinusoidally varying force was obtained and compared with experimental results of an excised larynx of similar loading. [Work supported by NINCDS.]
Some relations between voice quality judgments and derived acoustic measurements
Authors: Prosek Robert A. , Montgomery Allen A. , Walden Brian E. , Hawkins David B.
Published: October 2005

The use of extracted acoustic features as descriptors of abnormal voice quality was explored by correlating voice quality ratings with the measurements. Sixteen talkers with no history of speech problems and 52 talkers with documented laryngeal pathologies recorded the vowel /ɑ/ using their typical pitch and loudness. Estimates of the excitation for each vowel were obtained using the linear prediction technique of inverse filtering, and the acoustic measurements, known as residue features, were calculated from this waveform. Voice quality estimates were obtained from a panel of judges who rated each vowel on 11 voice quality scales that have been described in the literature. The residue features were used as predictors of average voice quality rating in multiple linear regression analyses. The results are discussed in terms of the voice quality scales that were used most reliably by the judges and the ability of the features to distinguish among various voice quality categories.
Revised noise criteria for design and rating of HVAC systems
Authors: Blazier Warren E.
Published: October 2005

This paper reviews current methods of rating the noise produced by HVAC systems and explains why these ratings fail to be correlated with subjective opinion in many cases. An entirely new method of assigning noise ratings is proposed which is expected to provide a significantly better correlation between objective measurements and subjective response. The proposed new rating method makes use of a revised set of noise criterion curves (RC curves) which appeared for the first time in Chap. 35 of the 1980 Systems Volume of the ASHRAE Handbook. This paper also discusses the technical considerations leading to the development of the RC curves as a replacement for the NC curves which have been used in the past.
Predicting sound pressure levels in furnished dwellings and offices
Authors: Schultz Theodore John
Published: October 2005

The Diffuse Field Theory of sound propagation indoors, embodied in the formula, [Lp = Lw + 10 log(Q/4πr2 + 4/A)], does not work well for typical furnished rooms in dwellings and offices. An alternative simple empirical relationship has been found that predicts with considerable accuracy the sound pressure level in such rooms, based on the sound power level of the source, the room volume, the frequency, and the distance from the source: Lp = Lw − 10 log r(ft) − 5 log V(cu ft) − 3 log f(Hz) + 25 (dB). If this new relationship is accepted, there are serious implications for our current standard test procedures for field measurements in occupied buildings. Since the room absorption A does not appear explicitly in the formula, the customary normalization with terms like 10 log A in transmission loss and impact noise field tests is probably incorrect. In addition, since no uniform reverberant sound field occurs in normally furnished dwelling and office spaces, it is not clear what one ought to measure for the receiving-room sound pressure level in field tests of transmission loss, noise reduction, and impact noise. [Work supported by ASHRAE.]
An experimental investigation of active noise control in ducts
Authors: Smith C. D. , Silcox R. J.
Published: October 2005

This study was directed to gaining an understanding of the physical mechanism of active noise suppression in ducts for both plane waves and higher order modes. Previous work has indicated large suppressions are attainable using active control concepts for plane progressive wave propagation. However, there is little evidence suggesting the mechanism of suppression. Furthermore, it was of interest to determine whether this concept could be applied to sound carried by higher order modes in ducts. This work utilized NASA Langley's Spinning Mode Synthesizer duct facility to provide the number of control points necessary for higher order mode propagation. Pressure measurement probes were installed between the noise source and control point to provide data to define the suppression mechanism. Results indicated that for all modes suppressions of 25 dB or greater were attainable over a broad frequency range. The mechanism of suppression appeared to be a pressure minimum being forced at the control plane which caused a near perfect reflection to occur, This was true for both primary and control sources, as little net acoustic energy was actually developed.