bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering and diffraction from random surfaces with multiple roughness scales
Authors: Moritz Elan
Published: October 2005

Previous studies of reflections from random surfaces have emphasized single scales of roughness. In some instances, single-scale theories encounter difficulties in explaining low grazing angle underwater acoustic phenomena such as bottom backscattering. Often variability is ascribed to different bottom types and environmental conditions. An additional mechanism which can allow the observed variability is that of interactions with multiple roughness scales. Results are presented of investigations of scattering and diffraction from fractal surfaces containing multiple roughness scales. In contrast with the exponential (time) decay of average power reflected by a “smooth” surface, surfaces with multiple scales possess three regimes dependent on the grazing angle with the mean surface plane. In the near normal case there's a power law dependence for the average power decay. In the low-grazing angle case the power dependence is strongly modulated by the grazing angle as shadowing effects become more prominent. The intermediate region displays a weak dependence on grazing angle. In underwater acoustics the multiplicity of scales enters through geometric features of the interfaces and density variations near the interfaces. Incident signal bandwidth is significant since it may allow simultaneous multiple scale interactions.
Spatial coherence of sea surface reverberation
Authors: Jackson D. R. , Moravan K. Y.
Published: October 2005

Experimental results are given for the dependence of horizontal spatial coherence properties of sea-surface reverberation on transverse separation and signal bandwidth. These results are compared with predictions of a point scatterer model in which the correlation is found to factorize into the product of functions of transverse and longitudinal separation (equivalently, lag time). The transverse coherence is due to the finiteness of the insonified patch, is calculable in terms of array geometry, and vanishes for separations greater than the horizontal array dimension. The longitudinal function is simply the autocorrelation of the reverberation signal. We find that this model is in substantial agreement with experimental results obtained by Frazer [M. E. Frazer, ARL-TR-74-16 (1974)] and Wilson [G. R. Wilson, ARL-TR-81-23 (1981)] as well as with our own experimental results. Our experiments employed a receiving array with transverse separations up to 23 cm. Some departures from the predictions of the simple point scatterer model have been found. These reflect intrinsic properties of reverberation rather than array geometry and deserve further study. [Work supported by NAVSEA 63R.]
Doppler spectra of sea surface backscatter at high acoustic frequencies
Authors: Mellen R. H. , Konrad W. L. , Browning D. G.
Published: October 2005

The initial transfer of energy from atmospheric wind to the ocean surface, which would be a significant factor in ambient noise, may occur via the so-called Cat's Paw phenomena. To study this effect an experiment was conducted at Seneca Lake for a moderately disturbed (no whitecaps) air-water interface. Doppler spectrum measurements of high-frequency acoustic waves backscattered from the wind-driven water surface indicate the presence of small-scale roughness that is convected downwind by surface drift. For a slightly rippled surface there is a sharp resonant peak corresponding to a convection velocity approximately 0.4 m/s which is nearly independent of windspeed. The spectrum is broadened by phase modulation due to the orbital motion of larger scale gravity waves but remains skewed in the downwind direction. [Work supported by DARPA.]
REVSPEC—A reverberation spectrum numerical model
Authors: Chamberlain Stanley G.
Published: October 2005

The REVSPEC model provides a numerical evaluation of the reverberation spectrum for a general set of sonar system parameters and environmental conditions. The model is a numerical evaluation scheme based on the discretization approach of Ackerman for a general formulation of reverberation as developed by Fauer, Ol'shevskii, and Middleton. The model produces surface, volume, and/or bottom reverberation spectra and power levels as functions of the sonar system (transmit signal waveform and power level, sampling rate, transmit/receive and horizontal/vertical beampatterns), environment (spreading and absorption propagation losses, backscattering strengths, wind speed and direction, scatterer motion), and sonar platform (motion, depth, direction). The reverberation spectra at the receiver input and at the receiver output for a range-gated and waveform-weighted receiver are generated. The reverberation is nonstationary in that the spectra vary with time (and range) both in their spectral shape and power levels. Intrinsic assumptions include: primary scattering only (no secondary scattering), isovelocity ocean (straight line propagation paths), direct path (no boundary forward reflections), quasistationary narrowband transmit signals, backscattering from a large number of randomly distributed, weak, discrete scatterers, and radial velocity distributions of boundary and volume scatterers are uniform in space. The model formulation is presented and examples which illustrate its applicability for sonar systems analysis are given.
Acoustical characterization of woods for guitars
Authors: Haines Daniel W.
Published: October 2005

The top and back plates of a guitar are among its most important components for producing the desired quality of sound from the instrument. Spruce, cedar, and redwood are wood species commonly selected by luthiers for guitar tops. Top woods have very similar acoustical characteristics which set them apart from back woods. Yet there exist subtle differences between these top woods that have interesting musical implications. Likewise back woods, e.g., rosewood, mahogany, and maple, are similar but not identical in acoustical character. Five fundamental properties of these wood plates that hold the key to much of their musical qualities are (1) density, (2) Young's modulus, and (3) low-frequency damping along-the-grain, and (4) Young's modulus and (5) low-frequency damping across-the-grain. Undesirable plate characteristics from the luthier's view, e.g., runout and skewed grain, can be correlated with measurable deviations from the normal values of these properties. A loudness index is proposed which combines the five properties into a single unit to characterize generally the plate's suitability for guitar construction. [Work supported by the National Science Foundation.]
Applied mechanics and the modern string instrument—Classical guitar
Authors: Kasha Michael , Kasha Nicolas
Published: October 2005

The design of string instruments is approached formally as a problem of three coupled oscillators: (a) the vibrating plate with appropriate boundary conditions, (b) the real string with characteristic anharmonicity and end-stiffness, and (c) the cavity resonance spectra with their body-form determined complexities. Instrument models are then constructed based on the fundamental approach, with all of the compromises required by classical dimension and form limitations, as well as the draftsman's working methods and materials. Acoustical measurements are made to demonstrate the effectiveness of the designs, and finally, concert musician acceptance in concert hall conditions is evaluated. The collaboration of Richard Schneider, luthier, and Dr. E. E. Watson, acoustician, is gratefully acknowledged.
Modes of vibration of guitar plates with and without bracing
Authors: Rossing Thomas D.
Published: October 2005

An earlier study [R. E. Ross and T. D. Rossing, J. Acoust. Soc. Am. Suppl. 1 65, S72 (1979)] indicates that the bracing pattern of the top plate, through its influence on the modes of vibration of the top plate, has a substantial influence on the acoustical properties of a guitar. We therefore tested six guitar top plates of identical shape (but varying in thickness and type of wood) in the raw state and again after various patterns of bracing had been applied and a sound hole cut. The modes of vibration were observed with both free and clamped edges. The vibrational modes of the unbraced plates resemble those of a rectangular plate, but the modes of the braced plates are considerably less predictable. Special thanks are due to luthiers Jim Williams, Gerard Gilet, and Robin Moyes, who supplied the plates used in these studies. [Work supported in part by the U.S.-Australia Cooperative Science Program while the author was at the University of New England.]
The craftsman's and the concert performer's evaluations of new classical guitar designs
Authors: Schneider Richard , Van Jeffrey , Kasha Michael
Published: October 2005

The luthier must set standards of construction based on both the choices of woods available for guitar construction and the criteria of instrumental mechanical integrity in coping with a new guitar design. The concert musician must re-evaluate his own approach to guitar dynamics in performance, as well as instrumental balance, when a new instrument is used in ensemble and concert hall performance. A demonstration of the characteristics of a new classical guitar with and without internal microphone amplification will be given.
Cabin noise reduction experiments in single engine aircraft
Authors: Campsnells Angelo J.
Published: October 2005

The in-flight noise cabin noise level of several types of single-engine propeller driven aircraft was found to be about 88 to 93 dBA at the pilot's ear position during cruise. Third-octave and narrow-band FFT spectra of these cabin sounds and interior surface vibrations were studied to identify noise sources and infiltration paths. With such single-channel techniques, it was not generally possible to separate structure-driven vibrations from those caused by sound entering or exiting the cabin space. Exhaust noise identification was achieved with a remote exhaust outlet in conjunction with narrow-band FFT analysis. The cabin's A-weighted sound level coming from the propeller was found to be dominant only during takeoff and climb. Specific identification of sound spectral components led to the rank-ordering of cruise noise sources as exhaust resonances (loudest), propeller noise, and motor-driven vibrations, respectively. Some reduction of the A-weighted SPL at the pilot's ear positions was achieved by exhaust system treatment.
The design of siren systems for evacuation notification
Authors: Allen Frank R. , Bradley Wayne E. , Letty Richard M.
Published: October 2005

The Federal Emergency Management Agency (FEMA) issued in 1980 a requirement that all operating nuclear power plants must have an alerting system to notify the population with a 10 mile radius of any plant emergency. This paper describes an approach for designing large scale siren systems for public alerting utilizing a sound propagation computer model to aid in siren placement. Siren audibility is a function of siren sound power output and frequency, atmospheric propagation, ambient sound levels, and dwelling insertion loss. Siren audibility criteria are selected for a site based upon measured exterior sound levels, expected interior sound levels and FEMA guidelines. Historical weather records of the site are analyzed to determine temperature, humidity, and wind conditions to input to a computer model. The computer model is then used to predict siren sound level contours taking into consideration site topography from USGS tapes, hemispherical divergence, atmospheric absorption, wind shadows, ground reflections, and vegetation. The results of a typical siren system design will be presented and discussed.
An analysis of community complaints to Army aircraft and weapons noise
Authors: Luz George , Raspet Richard , Schomer Paul
Published: October 2005

Noise complaints received Army-wide for a one-year period were analyzed (a) to determine the relationship between the nature of the complaint and the type of noise and (b) to determine the relationship between complaints and the day-night average noise level (DNL). For blast noise, 77% of complaints mentioned vibration or physical damage or both, thus confirming the validity of the C-weighted DNL as a better measure of blast noise than the A-weighted DNL. The relationship between DNL and complaints, however, was a very weak one. Instead, the data confirmed an independent finding of a recent study of Air Force noise complaints—that complaints are generated by unusual rather than typical noise levels. To deal with the wide variability in the emotional tone of the complaints, a psychological model was developed and tested. The implications of this model for how an installation should deal with complaints are discussed.
Aerosound from corner flow with application to the flap noise problem
Authors: Meecham W. C.
Published: October 2005

Recent correlation measurements have indicated that the major jetplane airframe noise source is located at the outboard edge of deployed flaps. The surface noise generated there is apparently due to separation and disruption of the spanwise flow at the underside edge of the flap. We model this using incompressible potential flow around a corner, with a series of vortices moving about the corner, imbedded in the flow. The model surface pressures, sound pressures (using Curle's theory) and Mach number dependencies agree well with wind tunnel experiments. A double pressure peak is found in the model (credited to image action) which is qualitatively similar to measured sound correlations. We discuss incompressible-flow aerosound calculations. Corrections are applied for the diffraction effect of the wing on the dipole surface sound (the effect enhances the forward-radiated field). We suggest that a possible explanation of the typically small Strouhal numbers seen in these experiments, is the retarding effect of the vortex image, on the motion of the vortex in the flow. [Work supported by NASA-AMES Research Center.]
Experimental investigation of the rise time of N waves
Authors: Orenstein Lori B. , Blackstock David T.
Published: October 2005

The rise time of spark-produced N waves in air has been measured with a condenser microphone of very wide bandwidth. The N waves had pressure amplitudes in the range 0.15 to 15 mbar, half-durations 7.5 to 41.5 μs, and risetimes 0.5 to 6 μs. The observed rise times are in only limited agreement with standard theoretical predictions for a weak shock in a thermoviscous gas (Taylor theory of shock thickness) and in a relaxing gas. There is some question, however, about the applicability of these predictions, which are for a step wave, to our N waves, which are relatively short. Our data indicate a weak dependence of rise time on half-duration. An alternative theoretical prediction was obtained by using a computer algorithm to predict the waveform of a propagating N wave. Included in the algorithm were finite-amplitude distortion, spherical spreading, absorption based on the ANSI standard for still air, and dispersion appropriate for oxygen relaxation. The predicted waveforms, including amplitude, half-duration, and rise time, were in good agreement with the measured waveforms. [Work supported by ONR.]
Morphogenesis of the cochlea and cochlear nucleus: Studies of normal and experimentally altered avion embryos
Authors: Whitehead Mark C.
Published: October 2005

Cochlear ganglion cells form foot-shaped synaptic endings on hair cells and large axonal end bulbs on adendritic neurons in nuc. magnocellularis (cochlear nuc.). These two distinctive types of endings, despite their separate locations, develop synchronously and their morphogenesis correlates with structural changes in their respective target cells. For example, immature synapses appear simultaneously in the cochlea and nuc. magnocellularis, contemporaneous with the differentiation of hair cells. The differentiation of end bulbs parallels the transformative loss of dendrites from their post-synaptic neurons [Jhaveri and Morest, Neurosci. (in press, 1982)]. Hair cells, ganglion cells, and magnocellular neurons may influence one another trophically to greater or lesser degrees. The survival of cochlear ganglion cells, in vitro, is depressed by excluding the receptor epithelium [Ard and Morest, Neurosci. Abstr. 7, 168 (1981)]. In nuc. magnocellularis fewer and smaller neurons survive when deprived of cochlear axons. Remarkably, however, the remaining magnocellular neurons, although contacted by abnormal boutonal endings, exhibit several normal features. Similarly, hair cells differentiate after ganglion cells are removed; in other experiments, normal synapses form between hair cells and ganglion cells even when the latter cells lack a central connection. These studies suggest that for auditory cells, some developmental events result from trophic influences while certain morphological processes may occur autonomously. [Supported by NIH grants NS 14354 and NS 16993.]
Numerical results for axisymmetric confined sound beams at finite amplitudes
Authors: Ginsberg Jerry H.
Published: October 2005

A recent investigation [J. H. Ginsberg, “A singular perturbation analysis of axisymmetric, finite amplitude sound beams,” 9th Int. Symp. Nonlinear Acoustics, Leeds, England, 20–24 July 1981] derived an analytical expression for the pressure signal in an intense confined beam. That result consistently described the phenomena of nonlinear distortion, diffraction, and spherical spreading. The present paper develops that analytical result into an efficient computational algorithm using Gauss-Chebyshev numerical integration. Results for assorted transducer vibratory patterns are given. The responses are displayed both as temporal waveforms, and as frequency spectra exhibiting the amplitudes and phase shifts of the fundamental and higher harmonics. [Work supported by the National Science Foundation, grant MEA-8101106.]
Pulsed parametric array
Authors: Trivett D. H. , Rogers Peter H.
Published: October 2005

In a previous paper [J. Acoust. Soc. Am. Suppl 1 70, S89 (1981)] on the scattering of a cw plane wave by a pulse, the frequency of the scattered signal was found to be fs = fcw[(1 − cos θ)/(1 − cos φ)], where fs is the frequency of the scattered signal, fcw is the frequency of the cw plane wave, θ is the angle between the pulse wave vector and the cw wave vector, and φ is the observation angle with respect to the pulse wave vector. This result yields no off-axis scattered signal when the pulse propagates in the same direction as the cw plane wave, as in the pulsed parametric array. We have extended this analysis to the case of a pulsed parametric array and found that while the interaction region has a stationary boundary (i.e., during the time the pulse exits the transducer) a sum and difference frequency signal is produced. However, once the pulse leaves the transducer (so that both boundaries are moving at the sound speed) no scattered signal is produced. The off-axis beam pattern is the same as that obtained by Westervelt [J. Acoust. Soc. Am. 35, 535 (1963)] in his cw calculation. The received difference frequency pulse however, appears as if radiated directly from the transducer. The pulse length is independent of observation angle, identical in length to the high frequency pulse, and has the arrival time appropriate for radiation from the transducer. This would not be the case if the entire volume were radiating. Thus the high directivity of the parametric array cannot properly be considered a volume effect, as previously thought. We present experimental evidence to support these results.
Scattering from crossed ultrasonic beams in the presence of turbulence
Authors: Korman M. S. , Beyer R. T.
Published: October 2005

Experimental results on the mutual scattering from two perpendicularly directed, continuous ultrasonic beams interacting in the presence of turbulence in water have been shown to produce a sum-frequency component that radiates outside the interaction region. Measurements of spectral broadening and Doppler shift have been reported by the authors [10th ICA, Vol. 1, p. 164, Sydney (1980)]. An investigation of the scattering mechanisms suggests that scattering to lowest order is from the cubic quadrupole source term in the wave equation (the Reynolds stress tensor ρuiuj). This mechanism allows an excess acoustic density ρ = ρ1 + ρ2 to interact nonlinearly with acoustic particle velocities uiL1 + uiL1 and turbulent velocity fluctuations uiT. The theoretical results for the temporal spectrum density of the scattered sum frequency are compared with single beam scattering. The Doppler shifts of the two scattered primary waves, when added together, equal the Doppler shift of the sum frequency for each scattering angie. The prediction for the angular dependence of the sum's broadening is Δf+ ∼ sin (θ − 45°)/2. These results are in good agreement with experiment.
Theory of resolution improvement in a focused acoustic imaging system using high intensities
Authors: Rugar Daniel
Published: October 2005

At the focus of a scanning acoustic microscope operating at 2.6 GHz, acoustic intensities in excess of 104 W/cm2 can be generated in a variety of liquids (e.g., water, liquid nitrogen, liquid argon). One consequence of operating at such high intensities is that the resolution of imaging is observed to significantly improve. This effect can be explained by considering the propagation of a finite amplitude focused Gaussian beam in a nonlinear medium. It is found that significant harmonic generation occurs in the converging portion of the beam and that the second harmonic beam focuses to a diffraction limited spot size which is smaller than the spot size of the fundamental beam by a factor of √. Upon passage through the focal region, the phase relationship of the second harmonic and fundamental changes such that a significant portion of the second harmonic power is converted back to the fundamental frequency. In this way, the high resolution information sensed by the second harmonic beam is communicated to the fundamental frequency, which propagates with lower absorption. [Work supported by ONR and F.V. Hunt Postdoctoral Research Fellowship.]
Air bubble growth in guinea pig tissue by rectified diffusion
Authors: Hansen Gary M. , Crum Lawrence A.
Published: October 2005

It has been previously shown [E. ter Haar and S. Daniels, Phys. Med. Biol. 26, 1145–1149 (1981)] that guinea pigs that are exposed to therapeutic ultrasound of intensities in the range of 80 mW/cm2 to 680 mW/cm2 (spatial average) develop air bubbles of observable size within the exposed tissue. We present evidence that air bubble growth in guinea pig tissue during ultrasonic irradiation is due to rectified diffusion. Through numerical integration of existing rectified diffusion equations, for the frequency and intensities used by ter Haar and Daniels in their recent work, we have found that small “undetectable” bubbles grow during irradiation to a “detectable” size. The number of bubbles growing and the final sizes predicted closely resembles the results obtained experimentally. [Work supported by the ONR and the NSF.]
Control of vorticity by sound
Authors: Vaidya P. G.
Published: October 2005

It is well known that a sound wave interacts with and modifies a vorticity wave. Usually such interactions are quite weak and, therefore, not of much practical importance. However, as the author has shown previously, under certain circumstances strong interactions are possible. In this paper these strong interactions are analyzed further. A resonance expansion technique has been used to arrive at numerical solutions to the interaction equations. Practical applications of modifying the vorticity wave to problems such as the laminar flow control are discussed.
Advances in the use of alternating magnetic fields to track articulatory movements
Authors: Perkell J. S.
Published: October 2005

We have reported on a prototype device for simultaneous tracking of movements of several points on articulatory structures inside and outside the vocal tract [J. S. Perkell and D. Oka, J. Acoust, Soc. Am. Suppl. I 67, S92 (1980)]. Alternating magnetic fields are generated by two fixed transmitter coils. The midsaggital plane locations of small, movable probe coils (transducers) can be computed from the amplitude of signals induced in the transducers, as long as the axes of the transmitter and probe coils are parallel to one another. Initial recordings of movements of transducers mounted on the tongue suggested that some tongue movements caused enough tilting of the transducers to produce significantly inaccurate location measurements. In conjunction with Piconics, Inc. (Tyngsboro, MA), we have devised a miniature biaxial transducer containing two orthogonally oriented sets of windings. Signals from the two windings are used to compute separation between a transmitter coil and the transducer, independent of the amount of tilt of the transducer with respect to the transmitter. Bench tests of the transducer indicate that the system may be used to track articulatory movements with an accuracy better than 0.5 mm regardless of transducer tilt. [Research supported by N.I.H. Grant No. NSO4332.]
Analytic methods in the articulatory interpretation of the aero-dynamic events accompanying consonant production
Authors: Bekey George A. , Müller Eric
Published: October 2005

The utility of a biophysically based model of consonant aerodynamics has been shown to be a considerable heuristic tool in the articulatory interpretation of the oral pressure and air flow events accompanying consonant production. Our current modeling work in this area has expanded into a number of diverse, though complementary, directions. Topics to be discussed include sensitivity analysis, the inclusion of stochastic processes in the model, hypotheses concerning an optimal adaptive controller, and the application of the model to the evaluation of dysarthric speech. While these avenues of inquiry may represent significant analytic inroads for understanding speech production, they are at best limited, as the nature of the speech motor control process cannot be elucidated by analysis of a limited aspect of the “speech chain” and without regard to performance criteria. Thus we conclude that systems modeling, on a global level will become an increasingly important aspect of speech research. [Research supported by NINCDS grant.]
Perioral biomechanics and its relation to labial motor control
Authors: Müller Eric , MacLeod Gary
Published: October 2005

Data summarizing the biomechanical nature of the labial system will be presented. The following topics will be discussed: the transfer function of the perioral tissue; spectral analysis of muscle fatigue; isometric and isotonic analysis of the contractal properties of muscle Obicularis Oris (mOO); and the describing function relating EMG and the contractile dynamics of mOO. The data will be discussed with regard to their implications for motor control of the labial system of speech production. [Research supported by NINCDS grant.]
The temporal sampling problem in electromyographic studies of speech musculature
Authors: Cooper Donald S. , Folkins John W.
Published: October 2005

Electromyographic signals are often averaged on the assumption that they represent a sum of a stable biological signal plus random noise. A muscle may be said to do the same thing on two occasions if the activity of all motor units involved is the same on both occasions. Since the activity of all units in a muscle cannot be monitored simultaneously [Cooper and Folkins, J. Acoust. Soc. Am. Suppl. I 70, S77 (1981)], we rely on the interference pattern to provide a signal representative of the activity of many units. The simultaneous monitoring of activity at multiple electrode sites allows the observation of a larger proportion of the occurring bioelectric activity than does the customary use of one derivation per muscle. Signals from three bipolar fine wire derivations high, medium, and low in the same palatoglossus muscle of speakers of American English were amplified, rectified, and integrated. The degree of similarity between pairs of simultaneous signals varied significantly across tokens of the same word, although it did not vary as greatly across tokens as it did across words. Consequently the pattern of muscle activity is not always constant across tokens of the same word, an effect which would be overlooked by averaging of tokens. [Work supported in part by NIDR.]
Compensatory response capabilities of the labial system in relation to variation in the onset of unanticipated loads
Authors: Gracco Vincent L. , Abbs James H.
Published: October 2005

Loads were applied to the lower lip during production of bilabial consonants at several selected intervals prior to and following the onset of Orbicularis Oris Inferior (OOI) EMG associated with bilabial closure to determine (1) if patterns of compensation differed as a function of when the “error” was introduced, and (2) the critical time after which “corrections” to the closing gesture could no longer be accomplished. EMG signals were recorded from OOI, Orbicularis Oris Superior (OOS), Mentalis (MTL), and Depressor Labii Inferior (DLI), and Depressor Angulis Oris (DAO) muscles to discern lower and upper lip compensation patterns. Results indicated that feedback and feedforward compensations (i.e., upper and lower lip muscle changes) both operated for early loads, while feedforward compensations (upper lip muscle compensations) were more predominant for later loads. These observations are consistent with findings in the oculomotor system and engineering analyses that suggest that feedforward is more flexible than feedback in its compensatory capabilities and also may suggest differential access to the labial muscles depending upon the compensatory pathways involved. Regarding critical correction time, it appeared that compensations could be accomplished even if unanticipated disturbances were introduced as much as 40–50 ms after the onset of OOI EMG. [Research supported in part by NINCDS grant.]
Barriers and ground effects: practice, model experiments, and theories
Authors: Embleton T. F. W. , Piercy J. E. , Daigle G.
Published: October 2005

The sound field behind a barrier is usually determined by both diffraction and interference. This interference is dependent on the acoustic impedance of the ground surface, and is significant when predicting insertion loss (as opposed to attenuation) of barriers in many typical locations. Field measurements behind a highway barrier show small but systematic deviations from expected results that suggest scattering above about 4 kHz and the need for more precise diffraction theory at all frequencies. Controlled experiments outdoors using a pure-tone sound source, and simultaneously measuring the temperature and velocity structure constants CT2 and CV2 of the turbulent atmosphere, show reasonable agreement between predicted and measured effects of scattering by turbulence into the shadow region behind a barrier. Scale model experiments indoors (no turbulence) show, with greater precision, similar discrepancies between measured results and those predicted by Kirchhoff-Fresnel and related diffraction theories—from 2 to 10 dB depending on geometrical configuration. These discrepancies can be eliminated using predictions based on either layer-potential theory [e.g., P. Filippi, J. Sound Vib. 54, 473–500 (1977)] or direct and accurate evaluation of the diffraction integral [W. J. Hadden and A.D. Pierce, J. Acoust. Soc. Am. 69, 1266–1276 (1981)].
Highway traffic noise prediction with and without barriers—Some results and observations
Authors: Lawther J. M.
Published: October 2005

Although the past decade has been a time of rapid increase in sophistication of models for predicting highway traffic noise levels including the effects of barriers, several important questions remain unanswered. This paper describes some barrier and near-ground propagation modeling work recently completed and nearing completion at Penn State, and discusses questions arising therefrom. A point of view looking towards the needs of the utlimate users of traffic noise prediction models is attempted. Experiences in both indoor and outdoor barrier testing and with both controlled sources and free-flowing traffic sources will be drawn upon in the presentation.
Sound propagation over an impedance plane
Authors: Nobile Matthew A. , Hayek Sabih I.
Published: October 2005

A comprehensive model developed by ARL/PSU [J. Acoust. Soc. Am. Suppl. I 68, S54 (1980)] is currently being used to predict sound levels behind a vertical highway noise barrier. An integral part of the theoretical problem involves the propagation of sound above an impedance plane (as is modeled the ground on either side of the noise barrier), to which a modified version of Lawhead and Rudnick's solution [J. Acoust. Soc. Am. 23, 546–549 (1951)] has been adapted. This solution, however, relies heavily on an approximation that greatly simplifies and reduces the field integral to the complementary error function form. As an alternative, a transformation of variables on a similar integral allows a direct evaluation in terms of two asymptotic series in inverse powers of kr, one of which is multiplied by the complementary error function. The first term in the overall solution is identical to Thomasson's solution [J. Acoust. Soc. Am. 61, 659–674 (1977)], and further terms should afford an improvement in accuracy. The importance of the higher-order terms relative to kr, ground impedance, and angle of incidence is explored.
Discrimination of formant frequency, intensity, and bandwidth in natural speech
Authors: Ghitza Oded , Goldstein Julius L.
Published: October 2005

Psychoacoustical discrimination limits described the ability of the human observer to perceive changes in an acoustic stimulus; sounds differing by less than a “Just Noticeable Difference” (JND) are similarly heard. Flanagan and his associates [J. Acoust. Soc. Am. 27, 613 (1955); 27, 1223 (1955); 30, 435 (1958)] studied steady-state synthetic speech sounds and measured various spectrally defined JND's. Klatt [J. Acoust. Soc. Am. 53, 8 (1973)] reexamined the JND for F0 using synthetic speech sounds that modeled the time varying features of F0 in natural speech and found it about an order of magnitude larger than reported earlier. We consider perceptually equivalent speech sounds, when all the JND's described by Flanagan are taken into account. To simplify the task of finding the JND's appropriate for natural speech we assume they all have a similar dependence upon frequency and that they are similar multiples of the steady-state JND's; the detailed dependence upon spectral frequency was taken from studies of periodicity pitch [Goldstein, J. Acoust. Soc. Am. 54, 1496 (1973)]. Speech that was anlyzed and resynthesized using a Residual Adaptive Predictive Coder was studied psychoacoustically. The quantization precision of the coder coefficients was chosen so that the resynthesized speech would not differ from the original by more than a given JND. A distance measure based upon formant JND's was formulated, and a quantization table with which to quantize the coder coefficients was constructed. Synthetic speech samples were prepared assuming various different increases of the JND's over their steady-state values and listeners scored the speech quality. Experiments indicate that the JND's are about five times greater than the values measured earlier by Flanagan.
On the just-detectable modulation of the spectral envelope on a log-∫ scale
Authors: Houtgast T. , van Veen T. M.
Published: October 2005

The interesting aspect of this study is the use of a spectral ripple on a log-f scale. The computer-generated stimuli consist, basically, of 160 frequency components added in random phase, separated by 1/40-octave intervals and covering the range of 250 to 4000 Hz. In a forced choice procedure, the reference stimulus had a flat spectral envelope (level of each component Lf = const.), whereas the spectral envelope of the target stimulus was slightly modulated according to Lf = const. + d sin (2π n log f/log 2). The parameter n indicates the number of ripples per octave, whereas d was treated as the dependent variable in an adaptive 2-AFC measuring procedure. It is found that the just-detectible peak-to-valley ratio shows a distinct minimum for about two ripples per octave. This result agrees well with the concept of an auditory filter shape with a suppression area which is located about a factor 1.2 above the filter's nominal frequency.
A masking-level difference in time (MLDT)
Authors: Patterson Roy D. , Milroy Robert
Published: October 2005

A sample of wideband noise 0.05, 0.1, 0.2, or 0.4 s in duration was digitized and then played cyclically to produce a repeated-noise masker. The signal was a tone burst (0.4 or 1.6 kHz) and it was half the duration of the noise sample. The signal was centered in the noise temporally and was repeated at the same point in each repetition of the noise. In the antiphasic conditions of the experiment, either the noise sample or the signal was inverted in alternate repetitions of the masker; in the homphasic conditions both signal and noise, or neither, were inverted in alternate repetitions. If the auditory system were capable of making a high resolution record of these signals, alternate repetitions could be added or subtracted and, by analogy with the BMLD, we could expect a release from masking in the antiphasic conditions—a release that would be larger for the lower signal frequency. The results show a small but highly significant advantage for the antiphasic conditions with the 0.4-kHz signal, and no difference at 1.6 kHz. However, in total, the data suggest a low-resolution memory and a different mechanism than that which underlies the BMLD.
Discrimination of intensity increments to components of multitone complexes
Authors: Kidd Gerald , Green David M.
Published: October 2005

The ability of listeners to discriminate between two multitone complexes having identical frequency components, but differing in the intensity of one or more of the components, is reported. The sitmulus manipulations include varying the number and spacing of the components, and varying the interstimulus interval. An experimental procedure is used where the overall level of the multitone complex and signal [intensity increment(s)] varies randomly from interval to interval for each 2IFC trial. This “within-trial” level variation forces the listener to compare simultaneously the outputs of more-than-one critical band, rather than successively comparing the output of a single critical band centered on a signal frequency. The change in detectability as a function of interstimulus interval clearly supports this simultaneous spectral analysis we refer to as “profile analysis.” Profile analysis appears to be based on simultaneous comparison of the level of components remote from the signal frequency with the level at a signal frequency. The comparison process is most sensitive when the profile is composed of many components spaced over a wide frequency range. [Work supported by NIH.]
Using the on-effect to investigate an input-dependent critical bandwidth
Authors: Daniel Jane E. , Kubovy Michael
Published: October 2005

The on-effect is the perceptual enhancement of one pure-tone component of a multitone stimulus, created by an “amplitude notch” (abrupt reduction and restoration of amplitude) in the tone. Below a critical frequency separation (CFS) of components, the on-effect is lost. This study investigated the relationship between the CFS for the on-effect and the critical bandwidth (CBW) established in masking experiments. Subjects identified the direction of a series of amplitude notches in ascending or descending components of a multitone stimulus. Tones were spaced at fifteen levels of percent of CBW (65%–100%). When stimuli were adjusted for equal loudness, the CFS for on-effect detection was a constant percentage of CBW in the range tested (100–4000 Hz). Furthermore, the CFS varied directly with loudness, i.e., the louder the stimulus the greater the CFS. These results suggest that the CBW depends on input intensity as well as input frequency. Whitfield [I. C. Whitfield, “The Neural Code,” in Handbook of Perception, edited by E. C. Carterette and M.P. Friedman (Academic Press, New York, 1978), Vol. IV] proposed a physiological model of pitch and intensity encoding consistent with these data.
Context coding in auditory memory for pitch
Authors: Boggs George J. , Sorkin R. D.
Published: October 2005

Observers performed a two-alternative forced choice high-low pitch discrimination task. Memory for pitch was studied as a function of the gap duration between a standard tone and the first following tone, and the frequency range of tones preceding and following the standard. The results are discussed within the framework of a memory model derived from the theory of single detectability [N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372–383 (1969)]. The model posits two different memory coding modes. In trace coding mode, memory resolution is subject to temporal decay and retroactive interference. In context coding mode, memory resolution is a function of the frequency range of the tonal sequence. The obtained results are contrasted with predictions of stage models that incorporate automatic erasure mechanisms; such models are unable to satisfactorily account for the data. [Work supported by NSF.]
Subjective rating of sound insulation: A pilot study
Authors: Bradley J. S.
Published: October 2005

A pilot field study of the subjective rating of the sound insulation of party walls was carried out on 98 subjects. Twenty-four hour background noise measurements were made in each home and the sound transmission loss of the party walls were measured in 1/3-octave bands. Significant relationships were obtained between annoyance responses and both STC and A-weighted transmission loss values. Measured noise levels in the neighbor's home also related significantly to measured annoyance, but no reduction of annoyance was observed due to noise levels in the subject's own home. The various annoyance responses were less homogeneous, more personal, and more unique than those commonly found in traffic noise studies.
The development of fm broadcast studios as performance spaces
Authors: Queen Daniel
Published: October 2005

The design of the recently completed studio complex for fine-arts station WFMT utilized measurement and analysis of desirable existing spaces to determine desired characteristics, such as early-late sound ratios, optimization of room dimensions for uniform mode spacing, and manipulation of reflections to improve diffusion. The main studio is designed to produce microphone pickup as in the chosen existing spaces, while maintaining a comfortable environment for performers ranging from chamber musicians to folk artists. Similarly, the secondary studio is designed for interviews and theatrical productions. Since all control rooms are used for voice announcements, the sound field perception in all such rooms regardless of size matches that in the secondary studio. Similarly, the sound of monitor speakers is uniform from room to room. To achieve these objectives, the sound fields of existing and planned rooms were computer modeled also assuring that changes required during architectural design and construction could be monitored. [A tour of the facility will follow paper presentation; see tour announcements.]
Comparison of findings from three different test methods on the violin
Authors: Hutchins Carleen M.
Published: October 2005

Three different tests of a violin in playing condition are made in the 100- to 150-Hz range: (1) bridge drive to air pickup via a microphone one body length off the back (2) air drive to microphone pickup, both inside the box near the tail end; and (3) musician bowing the violin at a constant microphone distance with the strong fundamental resonance frequencies located via two sound level meters, one with a 5-Hz bandwidth filtered signal displayed on an oscilloscope. Results of the three tests are compared and their implications discussed.
Spectral and perceptual features of a violin ensemble versus solo violin
Authors: Dolson Mark
Published: October 2005

A violin section playing in unison sounds very different from a solo violin. This is true even when the comparison is carried out with a low-fidelity monaural sound reproduction system. Electronic instruments attempt to simulate this ensemble effect by summing several slightly detuned solo waveforms or by adding together several replicas of the solo waveform with a continuously varying random time delay. In this study, recordings were made of solo violins and violin ensembles playing both isolated and connected notes. The resulting waveforms were analyzed with a phase vocoder to extract the amplitude and frequency versus time for each harmonic. A variety of simulated ensemble sounds were also subjected to the same analysis. Those sounds which were perceived to be associated with an ensemble were then examined to identify the common features in terms of the phase vocoder analysis. This work is seen as a first step toward improved understanding and simulation of ensemble sounds in general.
K-space formulation of the scattering problem in the time domain
Authors: Bojarski Norbert N.
Published: October 2005

The arbitrary direct scattering problem is solved numerically in closed form in the time domain and spatial Fourier transform space. This solution consists of casting the general basic global laws (i.e., the second-order partial differential wave equation or its integral representation) as a local algebraic equation in the spatial Fourier transform space, and leaving the specific local constitutive equations (i.e., the algebraic boundary conditions, which specify a given structure, which are conventionally imposed on the differential or integral representation of the general basic global wave equation) as a local algebraic equation in real space, thereby reducing the scattering problem to a statement of two simultaneous local algebraic equations in two unknowns (the fields and the induced sources) in two spaces connected by the spatial Fourier transform. A temporally local representation in both spaces is obtained with the aid of an introduced auxilliary field and two propagators. By virtue of causality, a numerically efficient closed form solution to this set of equations is obtained that utilizes the fast Fourier transform algorithm as the transformations between the two spaces. By virtue of the numerically efficient fast Fourier transform algorithm and the local algebraic representations, the number of required complex multiply-added operations and storage allocation is of the order of N log2 N and N per temporal discretization, respectively (where N is the number of spatial cells into which the scattering problem is discretized). It is shown that the solution is only of the order of log2 N slower than an ideal solution. The solution is thus practical for very large one-, two-, and three-dimensional scattering problems. Numerico-experimental results for a variety of refrective index profiles, including perfect reflectors, are presented, thus verifying the presented algorithm.
A novel lining for an anechoic water tank
Authors: Burton Thomas E.
Published: October 2005

A novel method for achieving excellent reflection loss and transmission loss in a layer was presented at the previous meeting [T. E. Burton, J. Acoust. Soc. Am. Suppl. 1 70, S72 (1981)]. This theoretical concept is now applied to the design of an anechoic water tank. The previous paper considers only coherent reflection and assumes convenient but unrealistic properties for the layer's materials. The present paper assumes more realistic properties, contends with both coherent and incoherent reflections, and also treats the effects of curvature of the wavefronts.