bluuebunny/crossref_metadata_2025 huggingface dataset:
Problem of localization in the median plane: effect of pinnae cavity occlusion
Authors: Gardner Mark B. , Gardner Robert S.
Published: October 2005

Localization of sound sources outside the median plane is influenced primarily by differences in head shadow and arrival time of the signal at the two ears of the observer. For sources located within this plane, localization is influenced primarily by the irregularities of the pinna. By progressively occluding these cavities, it is shown that localization ability decreases with increasing occlusion, that it is better for signals in the anterior than in the posterior sector of the median plane, and that high-frequency signal content is more important than the low. A number of hypotheses regarding localization in the median plane are noted.
Acoustic propagation in waveguides with sinusoidal walls
Authors: Salant Richard F.
Published: October 2005

The propagation of acoustic waves through a plane waveguide consisting of two rigid sinusoidal walls is examined analytically. It is found that the phase difference between the walls, the wall wavenumber, and the mode number strongly influence both the form of the disturbances generated by the walls, and the conditions under which these disturbances become very large.
Statistics of distant shipping noise
Authors: Dyer Ira
Published: October 2005

Distant shipping noise is modeled analytically as phase-random line components arriving from a number of independent sources. Three cases are distinguished as (a) all noise arrivals having the same intensity, (b) all having different intensity, and (c) mixtures of (a) and (b). The statistical distributions of the received noise, measured in decibels, are shown to be skewed and to be similar for all three cases, provided the number of ships is the same. Computation of the standard deviation for a location near Bermuda, based on available traffic data and for a 13-oct band analysis of an omnidirectional receiver, compares well with measurements by Perrone. Bandwidth and beamwidth are included implicitly in the analytical model via the number of line components, and are related through the mean frequency spacing between lines to the number of ships and their geographic locations.
Ray acoustical model of the ocean incorporating a sound-velocity profile with a continuous second derivative
Authors: Mezzino Michael J.
Published: October 2005

This paper presents the mathematical forms necessary for the calculation of ray-theory intensities for a layered, curvilinear velocity-depth profile for which the continuity of the second derivative is preserved. In doing this, one can generally ensure that intensity as a function of range is a smooth curve. Furthermore, the principal difficulty in applying correction factors at caustics is removed. Also included is a discussion of the curve-fitting technique applied to the velocity-depth profile.
Sound directivity pattern radiated from small airfoils
Authors: Hersh A. S. , Meecham W. C.
Published: October 2005

In a recent paper, Clark and Ribner [J. Acoust. Soc. Amer. 46, 802–805 (1969)] show that the instantaneous sound radiated by a small airfoil (in comparison with a typical wavelength) and its fluctuating lift are connected by Curle's point dipole equation which describes sound radiated from rigid surfaces in flow. In the present investigation, we provide an additional check on Curle's theory by measuring and comparing with his predictions the sound directivity pattern radiated by a small airfoil in flow. The results of the investigation provide some evidence that, indeed, small airfoils in flow radiate like point dipoles in apparent support of that aspect of Curle's treatment.
Dichotic speech perception: An interpretation of right-ear advantage and temporal offset effects
Authors: Berlin Charles I. , Lowe-Bell Sena S. , Cullen John K. , Thompson Carl L. , Loovis Carl F.
Published: October 2005

In two experiments on normals we presented CV nonsense syllables both dichotically and monotically, with onsets of the syllables separated by 0, 15, 30, 60, and 90 msec (first experiment) and 0, 90, 180, 250, and 500 msec (second experiment). We found that when one of the CV's trailed the other by 30–60 msec, the trailing CV became more intelligible than when it was given simultaneously; the leading syllable's intelligibility dropped from its “simultaneous” level when leading by 15 and 30 msec. The leading message was more intelligible between 15 and 250 msec when the two channels were mixed monotically. In the dichotic simultaneous conditon, voiceless consonants were more intelligible than voiced, especially in voiced-voiceless pairs. When the voiced CV trailed the voiceless CV, the former became almost as intelligible as its voiceless counterpart. A left hemisphere “speech processor” was postulated, with suppression of information from ipsilateral sources during contralateral stimulation. The postulated “speech processor” may be involved in acoustic-signal-vocal-tract control functions.
Scattering from a periodic corrugated surface: semi-infinite alternately filled plates
Authors: DeSanto John A.
Published: October 2005

An incident scalar plane wave is scattered from a surface, corrugated in one dimension, and given by an infinite number of periodically spaced semi-infinite parallel plates of zero thickness (thin plates). The surface is a parallel-plate grating. An additional plate is placed between two adjacent (in period) plates, thus dividing the periodicity interval into two regions, one of which has the same (constant) density and wavenumber properties as the material above the plates, while the second (inhomogeneous) region is filled with a material which has a different (constant) wavenumber and density from the surrounding media. The solutions of the Helmholtz equation are assumed to be upgoing plane waves above the plates and, between the plates, standing waves along the periodicity direction for either soft (Dirichlet) or hard (Neumann) boundary conditions, and downgoing waves down the slots between the plates. Continuity of pressure and velocity across the common boundary yield linear equations relating the wave amplitudes in the various regions. The equations are shown to be similar to the residue series of integrals of certain metamorphic functions. The amplitudes are expressed as values or residues of these functions, which are explicitly constructed from properties of the linear equations. Two examples are done in detail: (1) no inhomogeneity structure with arbitrary incident angle, and (2) arbitrary inhomogeneity values at normal incidence. Numerical results are presented for backscatter (specular) reflection coefficients R0 for normal incidence as a function of frequency for various values of the inhomogeneity parameters. The Rayleigh anomaly and the wavenumber threshold effects for the modes between the plates are the most prominent effects.
Mapping the underside of arctic sea ice by backscattered sound
Authors: Berkson J. M. , Clay C. S. , Kan T. K.
Published: October 2005

A narrow-beam scanning sonar was used to measure the relative backscattering strengths at 48 kHz of the undersurface of arctic sea ice. The graphic records displaying the range and relative scattering levels were assembled into a sonar map that displays the location and shape of under-ice features. The data indicate that there are two distinct types of backscattering: (1) very high level backscattering from well-defined under-ice ridges and (2) very low level backscattering from between the ridges. The higher scattering the ridges is probably due to the increase in roughness and the tilting of the average plane of the scattering surface. Comparison of the sonar map and the aerial photograph shows that most surface features have subsurface expressions and that their relationship can be complex.
Reverberation at 75 kHz to a depth of 1 km in the Pacific Ocean—a negligible factor in attenuation
Authors: Bezdek H. F.
Published: October 2005

Using the results of an acoustic reverberation experiment at 75 kHz, in which the active volume was localized to the vicinity of the source and receiver, the volume scattering coefficient is calculated and compared to the attenuation coefficient. Assuming isotropic scattering, the conclusion is reached that scattering does not significantly affect the pressure dependence of acoustic attenuation in the ocean at this frequency.
Forward and specular scattering from a rough surface: theory and experiment
Authors: Boyd M. L. , Deavenport R. L.
Published: October 2005

A heuristic rough-surface scattering model is given and compared with experimental results obtained from model rough surfaces. The theoretical model is developed from separate calculations of the coherent and incoherent parts of the scattered field. This allows a direct comparison between theoretical and experimental coherent and incoherent scattering coefficients to be made. The model is consistent in that the correct limiting forms for zero roughness and for large-scale roughness are obtained. Non-Gaussian surface statistics are incorporated in the model and the resulting theoretical predictions agree closely with specular- and forward-scattering experimental data.
Refracted, bottom-reflected ray propagation in a channel with time-dependent linear stratification
Authors: Clark J. G. , Weinberg N. L. , Jacobson M. J.
Published: October 2005

A model study has been undertaken of refracted, bottom-reflected (RBR) ray propagation in a time-dependent, linearly stratified acoustic channel. The analysis is relevant to the acoustic propagation effects of large-scale variations in the channel and pertains to the influence of these variations upon sound-speed stratification. Such ocean phenomena as surface tides, low-frequency internal waves, and advected intermediate and large-scale inhomogeneities—all of which may have scales comparable to or larger than representative acoustic path lengths of a few kilometers to a few hundred kilometers—are included. For numerical work, a measure of the influence of large-scale variations upon sound-speed stratification is provided by a thermistor string installation in the Straits of Florida. The analysis shows that any refracted, bottom-reflected ray contributes a signal that is very nearly constant in spreading loss, but phase modulated at the frequency of the environmental variation in the channel. Thus, for a simple harmonically time-dependent channel the signal at the receiver is a sum of constant amplitude, but sinusoidally phase modulated signals. Comparisons with data from a 7-NM propagation multipath in the Straits of Florida demonstrate qualitative agreement between theory and experiment.
Focusing properties of solid ultrasonic cylindrical lenses
Authors: Folds D. L.
Published: October 2005

The sound velocity, thermal coefficient of sound velocity, and attenuation coefficients of 20 common plastics were measured and used as a basis for the design of several lenses. Materials selected were polyethylene, nylon, polystyrene, polyphenylene oxide, and a low-sound-velocity silicone rubber compound. Using common geometrical optical techniques, lenses were designed to minimize off-axis aberrations for focal-length-to-aperture ratios ranging from 1 to 3 and aperture-to-wavelength ratios up to 150. Using methods analogous to chromatic aberration correction in optics, lenses were designed for constant focal length over a temperature range of 0° to 30°C. Two- and four-element lens systems with apertures up to 30 cm were fabricated from the selected materials. Measurements were made in the frequency range 600 kHz to 1.2 MHz and good agreement with theoretical predictions of focal length and directional response was observed. The effects of shear waves were not evident. The theoretical model used to evaluate lens performance was based on the numerical evaluation of the Fresnel-Kirchhoff diffraction integral. This work shows that it is possible, using established optical design methods and commonly available solid materials, to fabricate athermal acoustic lenses with good performance characteristics at aperture-to-wavelength ratios up to 150.
Measurements of mode attenuation coefficients in shallow water
Authors: Ingenito Frank
Published: October 2005

As part of an experimental study of sound transmission in shallow water, the attenuation coefficients of acoustic normal modes in a shallow area of the Gulf of Mexico were determined directly by separating and measuring the individual normal modes. The modes were separated by two methods, a temporal method depending on the differing group velocities of the modes and a spatial filtering method depending on their vertical pressure distributions. Data were taken at source frequencies of 400 and 750 Hz for a variety of sound-speed profiles. With two exceptions, only the first two modes could be identified and measured. The mode attenuation coefficients depend on the prevailing sound-speed profile, but the most reliable experiment yielded attenuation coefficients of 0.61 and 1.58 dB/km for the first and second modes, respectively, at 400 Hz, and 0.30 and 1.06 dB/km for the first and second modes, respectively, at 750 Hz. Assuming that the mode attenuation could be accounted for by bottom attenuation represented by a complex propagation constant, the above results require bottom attenuation coefficients of 126 dB/km at 400 Hz and 378 dB/km at 750 Hz. The latter imply an f1.75 frequency dependence of the bottom attenuation, a result which is supported by the remaining data.
Normal-mode propagation in water layers having linear gradients of sound speed
Authors: Ryder R. D. , Williams A. O.
Published: October 2005

The normal-mode eigenfunctions and eigenvalues are given for sound propagation in a water layer of constant depth, with a negative linear gradient of sound speed. The bottom is taken as an absorptive fluid. The analysis, extending that of R. N. Denham [J. Acoust. Soc. Am. 45, 365 (1969)], examines the mode attenuation coefficients αn. We prove that αn is at least for the mode having its horizontal component of phase speed somewhat less than the sound speed at the water surface, in approximate agreement with Denham's assumption. This result is independent of source and receiver depth. The problem of a positive linear gradient of sound speed is also solved. For this case, αn increases monotonically, from the lowest to the highest mode. Numerical examples are given for both negative and positive gradients.
Quantizer functions and their use in the analyses of digital beamformer performance
Authors: Wang H. S. C.
Published: October 2005

The formulation of output autocorrelation function of a digital beamformer into an infinite series leads naturally to the introduction of “quantizer functions” of various orders as a convenient vehicle in the evaluation of beamformer performance corresponding to different input quantizer designs. For arrays operating in a Gaussian ambient noise field, the quantizer function of a general nonuniform quantizer is defined and evaluated in terms of “reduced Hermite polynomials,” which facilitate less costly machine computation via their unique recursion formulae. A rigorous proof of the convergence of the series of quantizer functions is given to ensure confidence in numerical results. Examples of the use of quantizer functions given are (i) determination of optimum step sizes of 2-, 3-, and 4-bit uniform quantizers which yield maximum array gain for a typical array, (ii) calculation of directivity patterns of digital beamformer with input signals of arbitrary bandwidth, and (iii) evaluation of the effect of post filtering on the directivity patterns of digital beamformers. The special case of 1 bit per channel quantization (DIMUS) was especially discussed in detail with respect to both array gain and directivity patterns. The use of quantizer functions can also be extended to the solution of active-sonar problems involving sine-wave signals, and a brief example was given to illustrate the partial recovering of clipping loss in DIMUS by post filtering.
Backscatter measurements of acoustic waves scattered from a known irregular layer
Authors: Leovaris A. , Fung A. K.
Published: October 2005

Backscatter measurements were taken from an irregular rubber layer of uniform thickness, 3 mm, at five discrete frequencies (0.33, 0.54, 0.78, 1.0, and 1.5 MHz). Comparisons were made with data taken from a much thicker rubber target (mean thickness 38 mm) of the same surface roughness. It was found that there were no significant differences in the angular behavior of the return signals at the three lower frequencies. However, at higher frequencies, an oscillatory component appeared in the return from the layer. This implies that at least for the case studied (a rough layer with rms roughness of its interfaces comparable to its mean thickness), a layer must be more than about two wavelengths thick before it can be detected. It also follows that a multifrequency sensor is essential for exploring unknown terrains with possible subsurfaces.
Comparison of single- and double-chamber models of the cochlea
Authors: Berkley D. A. , Lesser M. B.
Published: October 2005

Using previously developed theoretical results we show the relationship between cochlear models with both chambers fluid filled and those with tympanic chamber empty. Numerical solutions of the equations show significant quantitative differences, between the two cases, in both amplitude and place of the basilar membrane displacement patterns.
A comparative study of S/N and E/N
Authors: Reed Charlotte M. , Bilger Robert C.
Published: October 2005

Masked thresholds were obtained for ten frequencies between 125 and 8000 Hz at three different noise levels on five subjects. Threshold procedure was 4IFC, in which duration of the tone was 300 msec. Values of both S/N0 and E/N0 (where S is power of tone at MT, E is energy of tone at MT, and N0 is spectrum level of the noise) were calculated from this set of data. The results of the present study were compared to those of Hawkins and Stevens (1950) and those of Green, McKey, and Licklider (1959). The problem of converting a signal-to-noise ratio measurement into an indirect estimate of critical bandwidth is discussed.
Normal modes, virtual modes, and alternative representations in the theory of surface-duct sound propagation
Authors: Labianca Frank M.
Published: October 2005

This paper presents a theoretical study of sound propagation in an ocean-surface duct. It deals with several aspects of the theory from a point of view which has not heretofore been taken in the analyses of this problem. The model used to describe a duct assumes the ocean surface to be smooth and the square of the refractive index to be bilinear. Alternative representations of the sound field excited by a point source are derived, the two playing the most significant role in this paper being the residue series and the normal-mode representation. It is shown that the depth functions of the residue series do not form a complete set, as those of a normal-mode representation must, and that the normal-mode spectrum is continuous, rather than discrete. The completeness properties of the normal-mode functions are then utilized in a study of the energy-trapping capabilities of the duct. In this connection, virtual modes are introduced and shown to lead naturally to the derivation of a leakage coefficient characteristic of the exponential leakage of energy out of the duct with increasing range. In addition, a cutoff-frequency criterion, useful in determining when a surface duct can trap energy, is derived.
Observations of cylindrical waves reflected from a plane interface
Authors: Newman Dennis R.
Published: October 2005

Interesting reflected and re-radiated ultrasonic waves from a plane liquid-solid interface have been observed using a cylindrical transducer and a pulsed schlieren system. The reflected cylindrical waves show variations in amplitudes as a function of angle. Plane waves, apparently re-radiated into the liquid by surface waves propagating along the interface, have also been observed by an optical technique.
Transducer Measurements: Use of the Current Probe
Authors: Greenspan Martin
Published: October 2005

It has been found that various measurements commonly made on piezoelectric transducers are simplified by use of the current probe, a commercially available instrument. Examples are impedance, ultrasonic interferometry, and power.
Some comments on “Impairment to hearing from exposure to noise” by K. D. Kryter
Authors: Davis Hallowell
Published: October 2005

Dr. Kryter's arguments and proposals are good in principle but faulty in detail. Confusion could have been avoided by a clear separation of the concept of impairment (any change for the worse in structure or function) from handicap (a loss of efficiency in social communication). The AAOO rule deals with handicap, not impairment. Also its “high fence” recognizes that “everyday speech” is not only speech at 65 dB SPL but includes some speech that is much louder. The AAOO rule was deliberately simplified to promote its use. The “Social Adequacy Index for Hearing” of 1948 is valid in prinicple but is numerically inaccurate because of poor enunciation of the recorded test material that was employed. For predicting handicap in speech communication the hearing threshold level at 2000 Hz is critical. More studies of speech discrimination in subjects who have typical noise-induced hearing loss involving this frequency are badly needed.
Technical aspects of Dr. Kryter's paper “Impairment to hearing from exposure to noise” with respect to the NIOSH statistics
Authors: Lempert Barry L.
Published: October 2005

National Institute for Occupational Safety and Health (NIOSH) statistics indicate that a 26-dB fence of hearing impairment for comparing hearing levels averaged at 0.5, 1, and 2 kHz vs 1, 2, and 3 kHz yield essentially equal risk values for noise-exposed populations at retirement age. On the other hand, Kryter, using a 16-dB fence for the averaging at 0.5, 1, and 2 kHz, found risk values comparable to those found using a 26-dB fence for the averaging at 1, 2, and 3 kHz. The data “baseline” inequality between the “non-noise”-exposed and noise-exposed populations used by Kryter in the development of his SIR table raises questions as to the compatibility of his different populations. If indicated baseline corrections are used, Kryter's risk values compare favorably with NIOSH data.
Reply to the critiques of A. Cohen, H. Davis, B. L. Lempert, and W. D. Ward of the paper “Impairment to hearing from exposure to noise”
Authors: Kryter Karl D.
Published: October 2005

Critiques by A. Cohen, H. Davis, B. L. Lempert, and W. D. Ward of my paper “Impairment to Hearing from Exposure to Noise” are treated individually. Questions raised by the reviewers are discussed and areas for further discussion are noted.
Design and construction of a reverberation chamber for high-intensity acoustic testing
Authors: Slusser Ronald A.
Published: October 2005

A high-intensity acoustic test facility was constructed at the Jet Propulsion Laboratory (JPL) to support the Mariner Mars 1971 project. For ease of construction, the reverberation chamber itself is rectangular, which resulted in very little sacrifice in acoustic performance. Levels as high as 156 dB can be achieved with the chamber empty and test levels of 150 dB have been used with a Mariner Mars spacecraft model (full size) in the chamber. Levels as high as this must be generated using electropneumatic transducers, which modulate gaseous nitrogen to this facility.
Intensity perception. IV. Resolution in roving-level discrimination
Authors: Berliner J. E. , Durlach N. I.
Published: October 2005

This paper reports the results of some preliminary two-interval roving-level discrimination experiments designed to test certain predictions of the preliminary theory of intensity resolution presented in the first paper of this series [N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372–383 (1969)]. Discrimination performance was measured for roving-level ranges in the interval 0 to 54 dB and intersignal durations in the interval 0 to 9 sec. Although the results, when averaged over levels, are roughly consistent with the theory, there is a substantial dependence of sensitivity on level that is inconsistent with the theory. Much of this dependence appears to be similar to that found previously in one-interval experiments [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483–502 (1972)], and to be interpretable in terms of deviations from Weber's law and the edge effect (caused by the use of the extreme intensities in the stimulus set as perceptual anchors).
The logistic distribution as an approximation to the normal curve
Authors: Jeffress Lloyd A.
Published: October 2005

The logistic distribution yields an approximation to the normal probability function that is satisfactory for most psychophysical work. Probability is an explicit function of x or d′ and is easy to compute.
Damage-risk criteria: The trading relation between intensity and the number of nonreverberant impulses
Authors: McRobert H. , Ward W. D.
Published: October 2005

Normal listeners were exposed on separate occasions to nonreverberant impulses presented at various peak levels. During each exposure the total energy presented to the ear remained constant. The resulting temporary threshold shifts indicated that longer exposures to this type of impulse noise can be tolerated for a given decrease in peak level than is predicted by either the equal-energy concept (which permits only a 10-dB decrease in intensity per tenfold increase in the number of impulses N) or recent proposals which require even greater reductions in level. The 1968 CHABA proposal (5-dB decrease per tenfold increase in N) is found to be in reasonable agreement with the present data. These results and those from studies involving more reverberant impact noise suggest that the correct trading relation for exposures involving noise of impulsive character will be a function of the degree of reverberation associated with the exposure. The absurdity of damage-risk criteria that are expressed only in terms of pulse peak level is emphasized.
Interaction between forward and backward masking: a measure of the integrating period of the auditory system
Authors: Robinson Charles E. , Pollack Irwin
Published: October 2005

Combined forward and backward masking of a click by preceding and following noise bursts was investigated for the region of gaps (between the two noise bursts) of 50 msec or less in duration. An interaction between the two modes of masking was found and was qualitatively explained in terms of the hypothesis of the temporal integrating period, or running average.
Internal processes in speech perception
Authors: McNeill David , Repp Bruno
Published: October 2005

We estimate the amount of time taken by listeners to perceive artificial stop consonants to be in the vicinity of 120 msec. The duration of the formant transitions in the syllables we employ, on the other hand, is 50 msec (followed by a nondistinctive vowel). Processing thus outlasts relevant input by some 70 msec. Moreover, forward masking develops as consonant processing takes place, which could lead to masking within a single syllable and block further-input. These results suggest that, for a significant fraction of the time, normal speech perception takes place in the absence of input. A view of speech perception compatible with such a limitation ascribes most of the perceptual structure of speech to largely autonomous internal processes, rather than to the acoustic structure of the speech signal. This signal serves primarily to trigger the process of speech perception in this view.
Acoustic effects on gas bubbles in the flows of viscous fluids and whole blood
Authors: Macedo I. C. , Yang Wen-Jei
Published: October 2005

Gas-bubble behavior in a liquid flowing inside a circular tube subjected to an acoustic pressure field is studied analytically and experimentally. Consideration is given to both viscous fluids and whole blood, with the effects of acoustic radiation and viscosity taken into account. Slug flow and laminar parabolic flow cases are treated. Analytical solutions are obtained which predict the trajectory of bubble motion and the location where the bubble can be brought to a standstill on the tube wall by the acoustic force. It is disclosed that the trajectory is strongly dependent upon the acoustic pressure amplitude, flow velocity, and liquid viscosity. By either increasing the acoustic pressure amplitude or decreasing the flow velocity or liquid viscosity, the bubble can be brought to a standstill in the first half-wavelength from the tube entrance, at the node or antinode depending upon its size. The theory is in good agreement with experiments performed in water and SEPARAN AP30 polymer solutions. The latter fluids resemble whole blood in rheological properties.
Arrays of parametric receiving arrays
Authors: Berktay H. O. , Muir T. G.
Published: October 2005

Theory is presented to describe the response of arrays whose elements consist of parametric end-fire receivers. The results of measurements on arrays containing up to four elements are presented in support of the theory. Electronic steering of this type of array is also addressed. The use of very small transducers in the formation of narrow receiver beams at low frequencies is demonstrated.
Determination of the farfield radiation of a noise source from nearfield measurements made with a Trott array
Authors: Rudgers Anthony J.
Published: October 2005

It is demonstrated theoretically that a Trott nearfield array can be used to measure the farfield-radiation characteristics of a finite source radiating partially coherent noise. Radiated noise signals of finite duration are considered and an integral equation analogous to the Helmholtz-Kirchhoff theorem is used to describe the mutual-coherence function of the noise field. The farfield form of this mutual-coherence function can be determined from measurements made in the nearfield because the Trott array is able to measure the farfield characteristics of a strictly coherent source located within its planewave region.
Level and zero crossings in volume reverberation signals
Authors: Spindel R. C. , McElroy P. T.
Published: October 2005

A point scatterer model is used to formulate expressions for the expected number of level crossings of backscattered volume reverberation signals. Results are obtained for both narrow-band and wide-band insonification of regions of high and moderate scatterer density. For narrow-band signals it is shown that level crossing data can yield quantitative estimates of scattering strength, and estimates of scatterer density. For wide-band signals level crossing information provides quantitative relationships between scatterer Q and resonant frequency and therefore is useful in characterizing the reverberation process. A narrow-band experiment east of Bermuda gives scatterer density as a function of depth through a scattering layer.
Validity criteria for filters matched to delayed, Doppler-shifted signals
Authors: Hageman D. H.
Published: October 2005

The response of a filter matched to a delayed, Doppler-shifted version of a narrow-band transmitted signal in white noise is considered. Conditions under which the response is the one expected are arrived at by (1) setting up the response to a more accurate representation of the echo waveform, (2) applying Taylor's theorem, with the response considered a function of v/c (range rate over the speed of propagation), and (3) requiring that the remainder be small relative to the leading term (expected response). The resulting validity criteria differ from that put forward by several authors, namely, 2(|v|/c)B T ≪ 1 (one also sees <), where B is a signal bandwidth, and T is the signal duration. It is shown that, to good approximation, the old criterion implies the new, and that modulations exist such that one of the new criteria is satisfied but the old is not.
Moving-frame analysis of jet noise
Authors: Chu W. T.
Published: October 2005

By means of the spectral representation, a simple mathematical procedure is possible in deriving the moving frame formulation of jet noise.
Response of a towed thin flexible cylinder in a viscous fluid
Authors: Pao H. P. , Tran Q.
Published: October 2005

A study is made of the forced oscillations of a thin flexible cylinder towed in a viscous fluid. It is shown that the forcing frequency has a dominating influence on the modal-shape amplitude of the towed cylinder. A study of the movement of the free end of the towed cylinder reveals that the phenomenon of “whipping” can occur during a severe resonance.
Macromolecular interaction in the absorption of ultrasound in fixed erythrocytes
Authors: Kremkau F. W. , Carstensen E. L. , Aldridge W. G.
Published: October 2005

Whereas it has been recognized for some time that the absorption of sound in suspensions of erythrocytes is primarily a macromolecular phenomenon, recent observations have led us to believe that interactions between macromolecules may play a significant role as well. Two tests of the interaction postulate are reported: (i) Acrolein or glutaraldehyde fixing of bovine erythrocytes, which cross-links macromolecular hydrophobic groups, causes an increase in specific absorption by as much as a factor of five at 30 MHz. The absorption increase is greatest at 30 MHz and above. (ii) Suspension of fixed erythrocytes in low-dielectric constant liquids (ethylene glycol and ethanol), thus increasing forces between ionic groups, further increases the specific absorption by as much as a factor of four at 10 MHz. The absorption increase associated with solvent changes is greatest at 10 MHz and below. Scattering, viscous relative motion, and thermal absorption have been ruled out as explanations for the observations. The explanation is more apt to lie in some forms of chemical or structural relaxations.
Effect of cavity absorption and multiple layers of wallboard on the sound-transmission loss of steel-stud partitions
Authors: Loney Wayne
Published: October 2005

Sound-transmission-loss tests in accordance with ASTM E90-70 were conducted using steel-stud partitions with a single or double layer of gypsum wallboard on each face of the studs. These test results were used to investigate the effect on the acoustical performance due to number of layers of gypsum wallboard, the installation of cavity absorption of different types and thicknesses, the size of stud, and the thickness of wallboard used. These test results have been summarized in two ways. First, to offer a method of calculating the change in STC due to changes in the components of a partition of known STC ratings. Secondly, a table showing the effect on the TL values due to each of the changes.
Acoustical privacy in the landscaped office
Authors: Warnock A. C. C.
Published: October 2005

Two landscaped offices were used for field studies of the acoustical isolation value of masking noise, absorptive ceilings and partial-height screens. The occupants of one of the offices were recruited for a subjective study of the relative acceptability of various masking noises. The study showed that this group consistently preferred less noise — a conclusion that contradicts some previous experience. Interviews indicated that the acceptability of masking noise is closely linked to the occupants' activities and the resulting need for privacy. Propagation measurements were made under a flat lay-in ceiling configuration to determine the effectiveness of screens, ceiling materials and ceiling baffles. The ceiling baffles were not found to be a practical means of ensuring a low ceiling reflection coefficient. The results of the measurements are analyzed in terms of changes in articulation index. Consideration of the area disturbed by a hypothetical speaker emphasizes the importance of small relative changes in articulation index caused by small changes in physical parameters.
Suprathreshold loudness adaptation
Authors: Morgan Donald E. , Dirks Donald D.
Published: October 2005

Experiments were performed to measure suprathreshold loudness adaptation at 500 Hz using a heterophonic listening condition in order to reduce binaural interaction. The adapting stimulus was presented at 70 dB SPL for 7 min. A long (3000 msec) and a short (300 msec) comparison stimulus were chosen to delineate the possible influence of the duration of the comparison stimulus itself on the magnitude of the loudness change measured. No loudness adaptation was observed during these experimental conditions. We interpret these results as corroborating similar findings in another laboratory indicating essentially no loudness change under perstimulatory test conditions in which binaural interaction is reduced. During the initial experiment an apparent “enhancement” of loudness was observed during the adapting period when a train of short pulses (300 msec each) was used as the comparison stimulus. In a second experiment, results suggested that, in fact, there is a loudness disparity between a pulse train and a continuous signal. For conditions where the loudness of a single short pulse is compared to a continuous signal, however, no loudness disparity was observed.
The effects of relative phase and the number of components on residue pitch
Authors: Patterson R. D.
Published: October 2005

The pitch of the residue produced by 6- and 12-component waves whose components were either in cosine or random phase was measured as a function of the frequency region of the components. The components were all of equal amplitude and the frequency spacing between them was 200 Hz. Waves with the same lowest component were found to produce the same pitch: neither the number of components nor the relative phase of the components was important in determining the pitch of the residue. If every component in a wave was a multiple of 200 Hz, the wave produced a 200 Hz pitch; if such a set of components was shifted in frequency by a small amount, there was a corresponding linear shift in the pitch of the residue. When the lowest component in the wave was below about 900 Hz, the slope values associated with the lines relating the pitch shift to the frequency shift varied little from their average value of 0.21. As the lowest component increased from 900 to 2580 Hz the slope values decreased to about 0.08. These findings are in good agreement with the current model of pitch perception based on interpeak durations.
Some determinants of localization-adaptation effects for successive auditory stimuli
Authors: Thurlow Willard R. , Jack Charles E.
Published: October 2005

Evidence is presented which shows that localization aftereffects can be produced not only by an adapting stimulus which has only an intensity differential at the two ears, but also by one which has only a time-delay differential at the two ears. In general, the displacement of the test stimulus is away from the perceived location of the adapting stimulus. However, exceptions to this rule have been found. It is concluded that the mechanism of these localization aftereffects is not in some final central location corresponding to perceptual space.
Introduction to electrets
Authors: Wintle H. J.
Published: October 2005

A short review will be given of the types of electret in terms of their electrostatic configuration: dipolar, internal space charge (heteroplar), injected space charge (homopolar), and deposited charge (monopolar). The methods used to make thermo-, photo-, electro-, and surface electrets will be described. The internal fields, short-circuiting effect, stability, limitation due to air breakdown, charge measurement, charge storage, and trapping levels will be discussed.
Electrets in miniature microphones
Authors: Fraim Freeman W. , Murphy Preston V. , Ferran Robert J.
Published: October 2005

The electret capacitive microphone element is ideally suited for miniature applications. However, because these miniature elements represent very high impedances at audio frequencies, a complete microphone will almost always incorporate a high input impedance preamplifier, which is a source of noise in the microphone. Proper design of both the preamplifier and electret element is required in order to avoid poor signal-to-noise ratio. The electret element and accompanying preamplifier are electrically modeled to indicate the important parameters for minimizing the noise. This model is then coupled with the performance equations for two simple electret element geometries to indicate the effects of a noisy preamplifier on the optimum element design. The results indicate that the best signal-to-noise level is not obtained at the design point which yields the maximum acoustic sensitivity, but at conditions which maximize the electret element capacitance. The characteristics of two typical wide-band electret microphones are given to indicate the type of performance actually possible from very small microphones.
Electronic simulation of violin resonances
Authors: Mathews M. V. , Kohut J.
Published: October 2005

A study of the resonances of the violin is described. Magnetic pickups attached to the bridge of a violin (sans body) responded to the lateral motion of the strings to produce a signal used to excite a set of electrical resonances. The parameters, such as center frequency, bandwidth, and attenuation of the resonances were adjustable and by means of these variables a variety of tones were produced and presented to experienced subjects from the music world. Subjective evaluation of the various tones indicates that the preferred violin tone is produced when the resonance frequencies are irregularly spaced with respect to the harmonics of the string vibration and the bandwidths have values which achieve a 12-dB peak-to-valley differential in the resonance response curve. A theory of enhancement of tone quality by resonant filters is presented and the construction of an electronic violin is discussed.
A new inverse-filtering technique for deriving the glottal air flow waveform during voicing
Authors: Rothenberg Martin
Published: October 2005

A method is described for deriving the volume velocity waveform at the glottis during voiced speech by inverse-filtering the volume velocity waveform at the mouth. Unlike the previously used technique of inverse-filtering radiated acoustic pressure, this method provides a signal that is accurate down to zero frequency, not susceptible to low-frequency noise, and easily calibrated in amplitude by a constant air flow. The primary limitation is the need for a transducer that will measure volume velocity at the mouth with adequate fidelity. In this work, volume velocity was recorded from a specially designed circumferentially vented wire screen pneumotachograph mask which provided a time resolution of 1/2 msec, without serious speech distortion. Inverse-filtered volume velocity was recorded with two adult male subjects for voicing in the modal register. Typical results are shown which indicate the way in which the glottal waveform varied with changes of fundamental frequency, subglottal pressure, and a dimension of voice quality related to the degree of compression of the vocal folds. Also considered are the effects of glottal-supraglottal acoustic interaction, and the effect on the glottal waveform of air displaced by the movements of the vocal folds.
Electrostatic ultrasonic transducers and their utilization with foil electrets
Authors: Legros D. , Lewiner J.
Published: October 2005

Electrostatic ultrasonic transducers are very attractive when considered from the point of view of simplicity. They are constituted by a condenser, the ultrasonic wave being directly excited on the electrodes. These transducers are currently used at low frequencies (microphones) and sometimes at higher frequencies (up to a few megahertz). At higher frequencies the bias voltage applied across the condenser has to be quite large and electrification of the central dielectric layer can appear. This paper describes such effects and presents the experimental conditions allowing the transducer to operate. The electrification of the dielectric layer is studied and the problems related to the conservation of the deposited charges are considered for Mylar and polypropylene foils of about 10-μ thickness. In the present work the ultrasonic waves generated or received by these transducers have frequencies ranging from 10 to 200 MHz.
Resonance generation of ultrasonic second harmonic in elastic solids
Authors: Peters R. D.
Published: October 2005

Second harmonic and fundamental standing-wave amplitudes have been measured to see if nonlinearity parameters (combinations of third-order elastic constants) can be determined from measurements made on samples driven at resonance. A model for the resonance is formulated by considering the process of overlap for a sample-applied pulse whose length is extended to many overlap orders. Attenuation is included in the model, and the nonlinearity parameters obtained from the application of the model to experimental data are compared with values from other experiments.
Specularly scattered sound and the probability density function of a rough surface
Authors: Clay Clarence S. , Medwin Herman , Wright Wayne M.
Published: October 2005

The coherent component of specularly scattered underwater sound is sensitive to the probability density function (PDF) of displacements of the rough surface. For the specular reflection of diverging waves, the coherent component and the PDF are shown to be related by the Fourier transformation. Laboratory measurements of sound scattered at a partially shadowed nearly Gaussian model sea surface show the coherent component is much larger than would be expected for a Gaussian PDF. Fourier transformations of the measured PDF, on inclusion of a shadowing correction, gave the coherent component. Fourier transformation of the coherent component yields a surface PDF similar to the measured PDF with shadowing correction.
Short-range transmission loss and the evidence for bottom-refracted energy
Authors: Hanna J. S.
Published: October 2005

Transmission loss over the range of the direct arrival is examined for a receiver lying on a deep, sedimentary ocean bottom and is found to exhibit interference structure not explained by water-borne paths alone. It is suggested that this structure can be understood in terms of energy refracted through the sediments back to the receiver. The velocity structure in the sediments required to account for the interference is quite consistent with the velocity structure inferred from seismic profiling the vicinity of the receivers.
CW beacon system for hydrophone motion determination
Authors: Porter R. P. , Spindel R. C. , Jaffee R. J.
Published: October 2005

A system consisting of three bottom-moored 12 000-Hz CW beacons, each separated in frequency by 40 Hz, and separated in space by about 8 km, has been used to track the motion of ship-suspended, ship-mounted, sonobuoy-deployed, and bottom-moored hydrophones to an accuracy of 4 cm. The system uses Doppler tracking of the beacon signals to provide real-time estimation of hydrophone velocity and displacement. Factors that might compromise system performance, such as surface, bottom or forward volume scattering, or multipath effects, were found to be negligible. Random phase fluctuations in beacon signals due to these phenomena are small compared with those due to hydrophone motion. Two tests of the system, near Eleuthera Island and near Bermuda, were made in September–October 1972. [This work was performed under U.S. Office of Naval Research Contract No. N00014-72-C-0205.].