bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Effects of Clipping in Array Processing
Authors: Remley Winslow R.
Published: September 2005

The operation of amplitude clipping in array processing is examined to determine (1) the fidelity of the system, (2) the improvement in system performance resulting from a post beam-forming filter, and (3) the effects of non-Gaussian noise. It is found that, under suitable conditions, the system fidelity is quite good. The over-all process is statistically equivalent to passing the signal waveform through a soft amplitude limiter with characteristics determined by the noise statistics and the signal-to-noise ratio. It is shown that a post beam-forming filter can improve the output signal-to-noise ratio by nearly 1 dB for narrow-band signals. For non-Gaussian noise, the clipping loss can be relatively large. For sinusoidal interference, the clipping loss is between 6 and 7 dB.
Masking and Discrimination
Authors: Bos C. E. , de Boer E.
Published: September 2005

With the same experimental technique, two sets of related experiments have been performed. In one, a band of random noise is used to mask a pure tone. In the other experiment, the intensity difference limen for the band of noise has been determined. Thresholds for masking and discrimination were obtained with help of a Békésy audiometer. A large range of bandwidths (5–12 000 cps) and five central frequencies (500, 1000, 2000, 4000, and 8000 cps) have been employed. Both sets of data agree qualitatively with data appearing in the literature. From the discrimination data, it appears that, for small bandwidths, inherent intensity fluctuations of bands of noise determine the maximum intensity discrimination. These fluctuations should influence the masking situation to the same degree. The similarity of masking and discrimination thresholds in the region of small bandwidth lends support to this prediction. Thus, it is argued why masking data should not be judged in terms of a fixed standard (as Fletcher has done) in order to arrive at values for the critical bandwidth. If one judges masking data in terms of the discriminatory power that the ear exhibits for the masking noise employed, one arrives at critical-bandwidth data much more in line with generally accepted data. The accuracy with which these can be determined is so poor that one should consider masking experiments of this kind as totally unsuited to measure the critical bandwidth.
Oscillation of a Bar Magnetostrictor
Authors: Witting James M.
Published: September 2005

The response of a uniform magnetostrictive bar to electrical excitation is calculated for two sets of boundary conditions. Either both ends are coupled to a resistive load, or one end is coupled and the other clamped rigidly. First-order terms involving dissipative forces are retained in the equation of motion. An expression relating displacement to excitation current is derived. A new equivalent circuit for the magnetostrictor is found and analyzed. It is shown that it can be used to evaluate the important constants of the magnetostrictor from simple measurements that do not change the magnetic properties of the sample.
Fifty Years of Physical Ultrasonics
Authors: Herzfeld Karl F.
Published: September 2005

The experimental investigations that first showed excess of sound absorption in gases above the classical value are described, and the theoretical ideas that lead to their explanation by relaxation processes are discussed. A survey is then given of later progress, which is closely connected with the rapid development of electronics, and of the parallel refinement of the theory. The work in liquids started somewhat later. The theoretical situation is more complex, but, for that very reason, ultrasonic measurements in liquids give information about problems absent in gases. The consideration of viscous liquids led to a connection with the behavior in glasses, in accordance with Simon's theory. In metals, the starting point, the methods, and the important frequency range for loss measurements were originally different; but here, too, the investigations and theoretical viewpoints have been multiplied and diversified.
Impedance of Tapered Structures
Authors: Young Frederick J.
Published: September 2005

The exact solution for the impedance of a manifold of differing but uniform transmission lines is derived. The number of uniform structures contained in the manifold is arbitrary and can be increased without bound. The exact solution to the manifold is used to obtain the impedance of a continuously tapered structure having a characteristic impedance and a velocity of propagation that varies along the length of the structure. This solution to the continuously tapered structure can be made as accurate as desired. An approximation to the continuous solution is derived that is valid provided the maximum value of the product of the internal reflection coefficient and the wavelength is much less than unity. The application at this approximate solution to the synthesis of tapered structures is discussed.
Frequency Equations for Wave Propagation in an Initially Stressed Circular Cylinder
Authors: Chen W. T. , Wright T. W.
Published: September 2005

This paper describes the derivation of frequency equations for the propagation of small sinusoidal waves in an infinitely long isotropic elastic cylinder that has been initially stressed.
Coupled Thickness Shear and Flexure Displacements in Rectangular AT Quartz Plates
Authors: Spencer W. J. , Hunt R. M.
Published: September 2005

The length variation of the thickness-shear and thickness-flexure modes in rectangular AT quartz plates are computed from Mindlin's first order theory, which assumes particular thickness variation. These curves are compared with the mode shapes determined experimentally by measuring the x-ray intensity diffracted from vibrating quartz plates. The diffracted x-ray intensity is proportional to the curvature, a combination of strain-gradient terms of the Bragg planes, which may be approximated from the first-order theory. The approximation for the curvature is quite good for modes that are essentially thickness shear. When the mode has a large flexure component, the approximation used to determine the curvature of the Bragg planes is not as accurate.
Use of Thermosensitive Paper in Sound-Spectrum Analysis
Authors: Abramovitz Arnold
Published: September 2005

The use of thermosensitive paper is mooted in the design of an all-purpose sound-spectrum analyzer that would instantaneously and continuously provide both display and permanent graphic record. Some applications and extensions of the technique are suggested.
Laser Interferometric Technique for Measuring Small-Order Vibration Displacements
Authors: Deferrari Harry A. , Andrews Frank A.
Published: September 2005

A Michelson interferometer using a CW laser-light source has been used to measure the amplitude of small-order vibrational displacements. Measurements over the surface of a vibrating plate at points 12 mm in diameter are reported. Magnitudes of 0.1–5000 Å at frequencies of 100 Hz–20 kHz have been measured with higher and lower limits possible. The advantages of the technique are discussed.
Amplitude Variability of Explosion Waves at Long Ranges
Authors: Reed Jack W.
Published: September 2005

Microbarograms, made at long range from three 106-g high explosives fired at few-minute intervals, were compared in show atmospheric propagation variability. Records made at 40–250-km ranges gave amplitude repeatability with a logarithmic-normal standard deviation of 0.49.
Interactions between Synchronous Neural Responses to Paired Acoustic Signals
Authors: Teas Donald C.
Published: September 2005

Brief tone pips were used as stimuli in two-signal interference experiments to provide a basis for interpretation of intensity functions. Whole nerve action-potential responses were recorded from the cochlea (guinea pig). Stimulation by a 6-kcps pip interferes with the response to a 2-kcps pip only when the latter reaches a magnitude (baseline peak measure) of 30–40μV, about 18 dB above a just detectable response. Interference depends more upon the strength of the 2 kcps pip than upon the strength of the 6-kcps pip. The form of intensity functions for low-frequency signals is dominated by a basal extension of excitatory region. Intensity functions for high-frequency signals show less spatial change. The data suggest that there are two response modes for neural activity elicited by acoustic signals. For high-frequency signals, synchrony of excitation depends upon envelope and there is little change in location of excitatory region along the cochlear partition with signal strength. For low-frequency signals, synchrony depends upon the locations along the cochlear partition that exceed a critical amplitude, i.e., upon the velocity of the traveling wave. Broad-band transient signals, such as clicks, may elicit neural activity in both response modes.
Logarithmic Frequency Systems
Authors: Pikler A. G.
Published: September 2005

Logarithmic calibration of the range of audible frequencies serves both physical and musical acoustics. Logarithmic assessment of frequency intervals leaves open the choice for a log base, for divisive multipliers, and for some reference frequency serving tabulations of “acoustical logarithms.” Euler's binary-log measure describes intervals in terms of fractions of an octave; the characteristic counts the octaves re the frequency standard and the mantissas are invariant with the tonal species. Different forms of binary systems, their transforms (especially duodecimal), and other log systems (common, natural, commatic, etc.) are discussed. The angular transform of 2x, representable as an exponential spiral (helix), portrays the periodic properties of frequencies as perceived by the musical ear in the octave system. Huygens used common logs and antilogs to compute cycles of 12 and 31; Mercator proved the merits of the cycle of 53 by natural logs; Sauveur invented the first acoustical log step scale. Lambert, DeProny, and Drobisch elaborated binary measures, while Ellis, Hornbostel, Young, and Husmann constructed tabulations.
Intensity-Decay Laws for Sound Propagation in Shallow Water of Variable Depth
Authors: Denham R. N.
Published: September 2005

Normal-mode theory is applied to the problem of finding the variation of acoustic intensity with range in shallow water of variable depth. A solution of the wave equation is obtained by neglecting the coupling of normal modes produced by the horizontal variation of depth. Relatively simple formulas for the intensity as a function of range are obtained in the case of isovelocity water by averaging the expression for intensity over source and receiver positions and replacing a Summation over all the allowed modes by an integration at intermediate ranges. At long ranges, only the first mode is effective and a modified cylindrical spreading law is obtained.
Note on the Data Logging of Audiometric Measurements
Authors: Atherley G. R. C. , Lord P. , Power J.
Published: September 2005

Modifications to a Rudmose ARJ-4 are described that permit thresholds to be presented as a binary decimal code on punched tape suitable for processing by a digital computer.
Absorption of Sound in Air versus Humidity and Temperature
Authors: Harris Cyril M.
Published: September 2005

Measurements have been made of the absorption of sound in air at 13-octave frequency intervals from 2000 to 12 500 Hz, as a function of humidity, at six temperatures in the range from −0.5° to 25.1°C at normal atmospheric pressure. The results of the new study are presented and compared with those of past investigations. Then a “best fit” is obtained to existing data. The resulting information is presented in both tabular and graphical form, useful for the solutions to problems of the calculation of attenuation of sound propagated in the atmosphere and the computation of the effects of air absorption in problems of room acoustics. These results have been extrapolated downward in frequency to 125 Hz and extrapolated to cover the temperature range from −10° to 30°C at normal atmospheric pressure.
Changes in Velocity of an Elastic Pulse owing to Geometrical Diffraction
Authors: Lord Arthur Edson
Published: September 2005

The mathematical theory of geometric diffraction with a circular elastic-wave source and receiver in a fluid half-space shows that the phase at maximum received amplitude does not correspond to the plane-wave value, i.e., ωl−kz. The excess phase 〈φ〉 plays the rôle of phase shift in an electrical network. Therefore, the value of −d〈φ〉/dω can be used to estimate the delay, due to geometrical diffraction in arrival of the bulk of a pulse. Under usual pulse echo measurement conditions, the velocity measured will seldom be 0.01% smaller than v0, the true plane-wave phase velocity. It is assumed here that measurements are made to parts of the pulse where steady-state geometrical diffraction is occurring. It is further assumed that transient diffraction effects exist for only a small fraction of the pulse. The possibility of diffraction contributing to changes in velocity caused by an external parameter (strain, magnetic field, etc.) is discussed.
Heat Transfer across a Solid-Liquid Interface in the Presence of Acoustic Streaming
Authors: Gould Robert K.
Published: September 2005

Experiments are described in which heat flow from a metal into a bathing liquid is measured in the absence and in the presence of acoustic streaming. The streaming is produced by a resonant vibrating air bubble resting on a solid plane, of which the heated metal forms a part. The temperature difference between the heated metal and the main body of surrounding fluid is kept constant. In these experiments, the heat flow rate is found to increase approximately linearly with the first-order sonic amplitude when the liquid is water. Increases up to 10-fold over the nonstreaming values of heat flow are obtained. When more-viscous liquids (glycerin-water mixtures) are used, the relationship between heat flow and sonic amplitude is non-linear. In the latter situation, a region appears in which the flow rate decreases with increasing sonic amplitude. It is found that the decrease is associated with a reversal in direction of the streaming above the vibrating bubble. An order-of-magnitude theory is presented that gives rough numerical agreement with experiment and that predicts a linear relationship between heat flow and sonic amplitude.
Air-Blast Suppression as a Function of Explosive-Charge Burial Depth
Authors: Vortman L. J.
Published: September 2005

The blast wave from buried explosions consists primarily of a pulse induced by the ground shock followed by another pulse when the explosive gases are vented to the atmosphere. The latter pulse provides the dominant contribution for the shallower burial depths. Air-blast measurements made along the ground surface for 46 chemical explosive and 7 nuclear explosive detonations have shown the peak overpressure of the ground-shock-induced pulse to be about the same for chemical and nuclear explosions in basal rock as for chemical explosions in alluvial soil. The ground-shock-induced pulse has not been observed for nuclear explosions in soil. The peak overpressure from venting gases is about equal for chemical explosives in basalt rock and alluvial soil. Peak overpressures are higher for nuclear explosions in soil, in part because the cavity pressures at the time of venting are higher; peak overpressures are lower for nuclear explosions in rock, presumably because less gas is formed and because the pulse from venting gas coincides with the negative phase following the ground-shock-induced pulse, thus reducing overpressure amplitude. Measurements have been made over a sufficiently large range of charge burial depths that a pattern of air-blast suppression with charge burial can be presented.
Masked DL for Pitch Memory
Authors: Harris J. D.
Published: September 2005

This paper reports differential sensitivity for pitch memory of pure tones as frequencies from 0.125 to 2 kcps are progressively raised above white noise adjusted to a 50% masking effect at the 45-dB sensation level of the tone. The Weber fraction (DF/F) improves with some negative acceleration through 2 kcps both in favorable and in unfavorable masking levels, but below about 0.5 kcps the sensitivity progressively deteriorates. The Weber fraction is related linearly to loudness, the loudness of tones in noise being specified by balancing to a 1-kcps tone in quiet. However, tones in noise exhibit poorer Weber fractions than tones at the same loudness but with no mask. Thus, the noise introduces a brake on sensitivity not only by loudness reduction but by an additional mechanism. The number of distinguishable pitches between 0.125–2 kcps is reduced from 548 for tones in quiet at 45 dB sensation level, to only 170 for tones in noise at a very unfavorable (signal-to-noise) S/N ratio (tones 5 db over the 50% masking point.)
Reexamination of a Model of the Cochlea
Authors: Klatt Dennis H. , Peterson Gordon E.
Published: September 2005

A model of cochlear mechanics is specified by a set of differential equations that relate pressures and displacements in the inner ear. The assumptions implicit in the equations are considered in this paper. The equations are solved by a straightforward difference-equation approximation on a digital computer. An equivalent electronic circuit was constructed in order to examine certain of the characteristics of the model. The response of the model is compared to physical data from a number of experiments.
Residue Pitch: A Remaining Paradox and a Possible Explanation
Authors: Schroeder M. R.
Published: September 2005

The residue pitch of an amplitude-modulated carrier wave with fixed carrier frequency decreases for small increases modulation frequency. This surprising experimental finding can be accounted for by considering the effect of phase modulation, synchronous and antiphasic with the amplitude modulation, on the temporal fine structure of the signal or its spectrum. Some conversion of amplitude modulation into phase modulation is known to occur in the mechanical response of the basilar membrane. However, for phase modulation to account fully for the pitch matches reported in the literature, additional amplitude-to phase conversion must occur either in the mechanical-to-neural transduction or in the neural processing.
Segmentation of Speech Sounds
Authors: Reddy D. R.
Published: September 2005

A program for segmentation of an acoustical continuum of speech sounds into discrete parts suitable for further analyses is described. The speech wave is read into the computer using an A-D converter. Analysis is performed directly on the acoustic waveform, using an IBM-7090. The pattern-recognition techniques used to segment the acoustic waveform into sustained and transitional parts are discussed. Some results obtained by the computer program are given.
Long-Wavelength Scattering by Hard Spheroids
Authors: Burke James E.
Published: September 2005

The exact series solution for the scattering of a plane wave by hard spheroids is used to obtain explicit long-wavelength approximations in powers of k = 2π/λ, where λ is the wavelength. The far field scattering amplitude is given to the sixth power of k and the nearfield is given to the second power. The results are valid for prolate and oblate spheroids and arbitrary angles of incidence and observation.
Propagation of Harmonic Flexural Waves in an Infinite Elastic Rod of Elliptical Cross Section
Authors: Wong P. K. , Miklowitz J. , Scott R. A.
Published: September 2005

The potential equations of motion of a linear elastic solid are employed to study the propagation of a class of harmonic flexural waves in an infinite rod of elliptical cross section with a stressfree surface. Using the separation solutions to these equations, a frequency equation is obtained in the form of an infinite determinant set equal to zero, the elements of which involve Mathieu functions and their derivatives. When the eccentricity goes to zero, this determinant can be written in diagonal form, the terms of which, when set equal to zero, describe the propagation of flexural and circumferential modes of odd order in a circular rod.
Measured Structure of Harmonics Self-Generated in an Acoustic Beam
Authors: Gould Robert K. , Smith C. W. , Williams A. O. , Ryan R. P.
Published: September 2005

The acoustic beam from a circular plane piston 1.01 cm in radius, driven sinusoidally to finite amplitudes in water, at 2.58 Mc/sec, has been mapped with two quite different small probes about 2 mm in diameter. Equivalent acoustic pressures at the source ranged from 0.2 to 6.0 atm. The fundamental component and the self-generated second and third harmonics were filtered separately, and beam patterns were photographed on a CRO screen. Fine structure down to the size of the probes was recorded. Reliability was demonstrated both by agreement of the two different probes and by measurements on theoretically known patterns at very low amplitude; maxima and minima were, respectively, lowered and raised in the records, but approximate analytical corrections are available. Rough estimates (±30%) of sensitivity showed that both probes were substantially linear and stable. The second-harmonic component of the beam was found to be more nearly cylindrically collimated than was the fundamental. Fine structure in second and third harmonics was rather less complex than in the fundamental, and different in detail, yet the higher harmonics were not much nearer than the fundamental to being collimated plane waves.
Evaluation of Acoustic Properties of Enclosures by Means of Digital Computers
Authors: Atal B. S. , Schroeder M. R. , Sessler G. M. , West J. E.
Published: September 2005

A method employing a digital computer for evaluating the acoustic properties of enclosures is described. Specially shaped tone bursts, generated on the computer, are radiated into the enclosure under study. The sound-pressure responses at different locations in the enclosure are recorded on a magnetic tape. The data are converted into digital form by an analog-to-digital converter and are processed by the digital computer. The processing by the computer includes filtering (to improve signal-to-noise ratio), envelope detection, and evaluation of different quantities having subjective or physical significance. A microfilm plotter attached to the computer is used to plot the results. Among the quantities evaluated are reverberation times based on different portions of the decay; direct, early, and reverberant energies; and directional distribution of sound-energy flux (diffusion). The different quantities are evaluated both as a function of frequency and location in the enclosure. Spatial and frequency averages of the different quantities are also evaluated.
Instrumental Method for Improved Intensity Discrimination Data
Authors: Campbell Richard A. , Lasky Elaine Z.
Published: September 2005

When investigating the ability of humans to detect intensity changes of acoustic stimuli, the fluctuations of typical psychoacoustic laboratory apparatus and the limitations of measuring instruments can easily yield random intensity errors (±0.1 dB) that are of the same order of magnitude as the difference limens obtainable (0.2–0.3 dB). In the proposed method, the required small intensity changes in the variable stimulus are obtained by combining two waveforms with only one waveform constituting the standard. The intensity difference between the two stimuli, or the increment in the variable stimulus owing to the addition of the second signal, can then be calculated from the voltage or sound-pressure ratio in decibels of the two waveforms. As an example of the improvement of precision, if this ratio is maintained within 0.1 dB, the precision of the resulting increment can be 0.002 dB for an intensity increment of 0.2 dB. Tables and formulas for calculating both the increments or decrements resulting from the in-phase or 180° out-of-phase combination of identical waveforms and the increments from the combination of independent waveforms are outlined.
Intensity Discrimination of Fluctuating Signals
Authors: de Boer E.
Published: September 2005

In this paper, the theoretical aspects of the fluctuations inherent in random noise are discussed, insofar as these influence detection of random signals. Brief elucidations of the fundamentals of statistical detection theory and of sampling theory are given. The model developed for the detection process closely follows a proposal by Green, but with the major exception that a kind of internal noise is supposed to be involved in the process. The auditory mechanism is assumed to measure the average intensity of the signal presented over a certain time T. In doing so, the evaluation is hampered by random activity so that the measurement is carried out less accurately than possible. The detection finally involves a likelihood-ratio decision procedure. The theory explains experimental thresholds of random-noise signals very well. Agreement with data on thresholds of very short noise bursts is less convincing. Finally, the theory explains very elegantly why experimental psychometric functions for wide-band signals have the same slope as those for narrow-band signals. Instances in which higher slopes are reported for experimental psychometric functions for wide-band signals can most likely be traced down to having involved experimental procedures that leave too much uncertainty in the listener's observations.
Growth of Distortion in a Finite-Amplitude Sound Wave in Air
Authors: Cruikshank Donald B.
Published: September 2005

Distortion components in an intense sound wave within a plane-wave tube have been measured. Excellent agreement with theory (wall effects included) has been obtained for the growth of second and third harmonics of a single, pure tone as well as for the growth of sum and difference frequencies resulting from the combination of two pure tones.
Inverse Design for Flexural Vibrators
Authors: Eisner E.
Published: September 2005

It is shown how flexural vibrators with prescribed vibrational characteristics can be designed by an inverse method. An illustration of the algebraic procedure is given.
Pitch Shifts of Tones in Wide-Band Noise
Authors: Steiner Sylvia J. , Small Arnold M.
Published: September 2005

Pitch shifts of pure tones occuring in wide-band noise were measured for five frequencies (250, 500, 1000, 3000, and 6000 Hz) at four levels (5, 15, 25, and 35 Db] above quiet and masked thresholds for each of 11 subjects. Amount of noise employed was sufficient to shift threshold of a 1000-Hz tone by 35 dB. Alternate monaural presentation of 500 msec standard and variable signals was employed. The amount of pitch shift expressed in Hertz was found to increase with frequency. Relative pitch shift (absolute shift/standard frequency) increased with frequency between 250 and 3000 Hz but was less for 6000 than for 3000 Hz. The data suggested that the relative amount of pitch shift may decrease with signal level for frequencies less than 3600 Hz, increase with signal level for 6000 Hz, and be independent of signal level for 3000 Hz. All observed pitch shifts were in all upward direction, except for the two lowest frequencies.
Energy Dissipation Associated with Gas-Pumping in Structural Joints
Authors: Maidanik G.
Published: September 2005

Recent experimental work dealing with the vibratory energy dissipation of plates with beams riveted to them has indicated that the dominant damping mechanism is associated with “gas-pumping” in the space between the plate and the beam. Based on this deduction a semiphenomenological theory is developed that predicts satisfactorily not only the order of magnitude of the loss factors, but also their dependence on frequency and on gas pressure. This theory attributes the damping to viscous forces associated with gas motion tangential to the plane of the plate, resulting from the relative flexural motion between the adjacent plate and beam surfaces.
Influence of Rise-Fall Time upon Short-Tone Threshold
Authors: Dallos Peter J. , Johnson Kenneth R.
Published: September 2005

Thresholds for short-duration 1000-Hz tones were obtained from eight listeners. The rise-fall times of the trapezoid-shape tone pips were varied between 0–40 msec, while the equivalent duration was held constant at a number of values. It was demonstrated that, as long as the equivalent duration was unchanged, the rise-fall time had no effect upon auditory threshold.
Pitch of a Periodically Interrupted Tone
Authors: Swigart Elca
Published: September 2005

A series of tone pulses was produced by periodically interrupting a 1000-Hz tone (carrier frequency). Each interruption was 1 msec (one wavelength of the carrier frequency). The duration of the tone pulses was varied by increasing or decreasing the interruption rate. Listeners matched continuous tones to the interrupted tones under three conditions: (1) binaurally at a low intensity, (2) monaurally at a low intensity, and (3) monaurally at a high intensity. Results show that the stimuli that elicited responses corresponding to the carrier frequency contained individual pulses of longer duration than those stimuli which elicited matches to the interruption rate. Comparison of the duration of individual pulses of interrupted tones with the duration of tone “pips” in studies relating pitch to tonal duration revealed similarities in the stimulus duration necessary to detect the pitch of the carrier frequency. Order of presentation of stimuli significantly affected responses. Listeners receiving the stimuli in an ascending order (tone pulses of shorter to longer duration) required pulses of longer duration to respond to the carrier frequency than did listeners receiving the stimuli in a descending order.
Time-Frequency Analysis in the Hearing Process
Authors: Gambardella G. , Trautteur G.
Published: September 2005

The hypothesis that a temporal waveform analysis is performed along the basilar membrane is considered and proved wrong, on the basis of a comparison between the uncertainty principle in Fourier analysis and the time-frequency relations in the cochlea, obtainable from experimental data. A suggestion is introduced in the conclusions for an appropriate electrical model of the cochlea, which could prove useful for both Fourier and waveform analyses of speech.
Interim Bone-Conduction Thresholds for Audiometry
Authors: Lybarger Samuel F.
Published: September 2005

An interim method of calibration for bone-conduction audiometry, using an existing type of artificial mastoid and currently available bone vibrators, has been recently established by the Hearing Aid Industry Conference. The method and calibration values are described.
Comments on “Acoustic Response of a Rectangular Receiver to a Rectangular Source” [Y. Fujii and K. Yamada, J. Acoust. Soc. Am. 40, 249–251 (1966)]
Authors: Arase Elizabeth M.
Published: September 2005

The results obtained in the paper by Y. Fujii and K. Yamada [J. Acoust. Soc. Am. 40, 249–251 (1966)] may also be obtained by the method that was used previously to compute the mutual radiation impedance of rectangular pistons [E. M. Arase, J. Acoust. Soc. Am. 36, 1521–1525, (1964)]. This is shown for the case of an aligned square aperture and source of identical dimensions.
Recent Results from the Straits-of-Florida Underwater-Sound-Propagation Study
Authors: Clark J. G. , Dann R. , Yarnall J. R.
Published: September 2005

The phase-versus-time patterns of acoustic signals transmitted across the Straits of Florida in March 1966 show close similarities with corresponding patterns presented recently by Steinberg and Birdsall [J. C. Steinberg and T. G. Birdsall, J. Acoust. Soc. Am. 39, 301–315 (1966)], which were obtained 14 months earlier. Both diurnal and tidal periodicities appear in the patterns, and the phases of the tides were approximately the same during the two test intervals. The phase patterns at recently installed hydrophones located two to three miles from the sound source also show the characteristic periodicities observed at locations across the Straits. All data obtained from this program thus far lead to the conclusion that signal phase, in sharp contrast to amplitude, is basically very stable, and that many of the fluctuations that do occur may be associated with large-scale environmental events.
Near Field of a Dipole for Measurements in Shallow Lakes
Authors: Bobber Robert J.
Published: September 2005

Acoustic measurements in shallow lakes are subject to interference caused by reflections from the lake surface and bottom. This interference is particularly serious at frequencies below about 2 kHz. If a dipole (two out-of-phase simple sources) is used as a projector, substantial sound-pressure level is available in the near Field, regardless of the well-known inefficiency of such a projector. At the same time, interference caused by lateral reflection is virtually eliminated by the farfield directivity characteristics of the dipole. The optimum relationships among dipole size, test distance, boundary geometry, and frequency are analyzed and verified by experiment.
Experiment on Sound Propagation in Shallow Water under Isovelocity Conditions
Authors: Kibblewhite A. C. , Denham R. N.
Published: September 2005

An investigation into the long-range propagation of sound in shallow, isovelocity water was carried out using an extensive area of the continental shelf off the west coast of New Zealand. The results obtained showed that a classic example of normal-mode propagation in shallow water was involved. The values of attenuation obtained and the general behavior of the attenuation as a function of frequency are comparable with other shallow-water areas. Other characteristics of the propagation mechanism can be explained in terms of depth variation and layering of the bottom.
Foil-Electret Microphones
Authors: Sessler G. M. , West J. E.
Published: September 2005

Electrostatic microphones with foil electrets are described. Foil electrets are solid dielectric materials, such as fluorocarbon, prepolarized in an electrostatic field at an elevated temperature. The use of electrets eliminates the need for an external dc bias. The sensitivity of these microphones depends largely on the surface charge of the electret and is typically between −50 and −60 dBV for a sound-pressure level of 1 μbar. The sensitivity of fluorocarbon electret microphones does not decay over periods of the order of years at room temperature. Extrapolation tn room temperature of results obtained at elevated temperatures indicates the time constant of the sensitivity of fluorocarbon microphones to be between 30 and 103 years, depending on the preconditioning (temperature cycling) of the systems. The relative humidity is of little influence on the time constant. Even at 80°C and high relative humidity, the time constant is still of the order of 100 days. The capacitance per unit area of electret microphones (about 60 pF/cm2) is three times greater than that of air-gap systems. Because resonance frequency and sensitivity do not depend on the diameter of the system, a capacitance much higher than that of air-gap systems can be achieved for a given bandwidth. The free-field frequency response is within ±1.5 dB from 50 to 14 000 Hz when the microphone is terminated by a few megohms.
Steady-State Wave Propagation in Infinite Bars of Noncircular Cross Section
Authors: Nigro Nicholas J.
Published: September 2005

An approximate solution to the equations of elasticity is obtained for the problems of steady-state longitudinal, flexural, and torsional wave propagation in isotropic bars of infinite length and rectangular cross section. Results were obtained for sections with various ratios of width to depth. These results indicate that, in a phase-velocity versus wavenumber plot, the higher branches exhibit a certain minimum feature; i.e., these branches approach their limiting value at bγ = ∞ from below. This feature has not been reported in the case of bars with a circular cross section.
Vibrations of Plates Bounded by Parts of Elliptical and Hyperbolic Cylinders
Authors: Krishnappa Ebenezer N. , Callahan W. R.
Published: September 2005

The partial differential equations governing the motion of plates, when transverse shear and rotary inertia are considered, are solved for plates bounded by elliptical and hyperbolic cylinders. By assuming product solutions for the partial differential equations (in elliptical coordinates) Mathieu's equations and Mathieu's modified equations are obtained. The resulting solutions satisfy all of eight different boundary conditions entering into the theory. The elimination of the arbitrary constants in each boundary problem leads to the frequency equation for the normal modes of vibration.
Frequency Dependence of Amplitudes of Scattered Elastic Waves
Authors: Knopoff L. , Hudson J. A.
Published: September 2005

The problem of the scattering of elastic waves by a random set of inhomogeneities is extended to high frequencies. As in the case of scattering of scalar waves at high frequencies, the mean-square scattered amplitudes for elastic waves vary as the square of the frequency. The scattering process P-S, important at low frequencies, is vanishingly small at high frequencies; the ratio of the amplitudes of the scattering processes S-S to P-P, although still large, is significantly reduced as one proceeds from low frequencies to high.
Calculations of Eigenvalues for Uniform Fluid Waveguides with Complicated Cross Sections
Authors: Laura Patricio A.
Published: September 2005

This paper deals with the calculation of eigenvalues of acoustical waveguides with arbitrary cross section. The method presented herein makes use of conformal mapping techniques and Galerkin's method to solve the transformed wave equation. Numerical calculations are presented for two types of boundary conditions: (a) zero velocity, and (b) zero pressure at the walls.
Rhyming Minimal Contrasts: A Simplified Diagnostic Articulation Test
Authors: Griffiths John D.
Published: September 2005

The diagnostic approach to articulation testing examines the phonemic confusions in the responses made by an articulation test crew. Since a phoneme may be regarded as a sum of its essentially independent features or attributes (either the distinctive features or the conventional articulatory classifications of manner, place, and voicing), a phonemic confusion, or error in identification, may be regarded as a confusion in one or more of its independent attributes. A pair of phonemes which differ from each other in only a single feature or attribute is a minimal feature contrast, and an error in the identification of one of the phonemes for the other is a minimal feature confusion. Any phonemic confusion can be seen to be the sum of one or a number of minimal feature confusions. A test which includes all the minimal feature contrasts in a language can then estimate speech system performance for an input sample from the natural language. A previously reported test [A. S. House, C. E. Williams, M. H. L. Hecker, and K. D. Kryter, J. Acoust. Soc. Am. 37, 158–166 (1955)] has been modified to include all the minimal feature contrasts for initial and terminal consonants. This modification is an easily interpreted tool for diagnostic research, and in addition, retains the desirable characteristics of the original test: case of administration and scoring, stable responses without learning effect, and use of of naïve listeners.
Analytic Description of the Low-Frequency Attenuation Coefficient
Authors: Thorp William H.
Published: September 2005

A simple practical expression is given for determining frequency-dependent sound attenuation coefficients. The expression is an extension of Horton's equation to lower frequencies and represents a fit to experimental data covering the band below 50 kHz.
Negative Dispersion and Brillouin Scattering
Authors: Mountain Raymond D. , Litovitz T. A.
Published: September 2005

The fluctuations in density observed in Brillouin scattering may be represented as temporally absorbed waves. Negative dispersion occurs for these waves although it may be masked by positive dispersion due to relaxation processes. Numerical estimates of velocity and of negative dispersion are made for CCl4 at 20°C. The importance of measuring both the position and the width of the Brillouin peaks in order to obtain the elastic modulus of the liquid is stressed.
Binaural Release From Masking for Speech and Gain in Intelligibility
Authors: Levitt H. , Rabiner L. R.
Published: September 2005

Relative importance of different frequency regions in binaural release from masking (for detection) and binaural gain in intelligibility was investigated. Experiments showed that the release from masking (SπN0 case) for single words in high-level, broad-band Gaussian noise is roughly 13 dB and is determined primarily by interaural phase opposition in the low-frequency (<500 Hz) region. The binaural gain in intelligibility at the 50% level was on the order of 6 dB and only partly dependent on interaural phase opposition in the low-frequency region. Interaural amplitude differences were not considered in the investigation. Subjecting the speech to a large interaural time dealy with the noise binaurally in phase resulted in a relatively constant masking level difference approaching 13 dB over the measured range from 0.5 to 10 msec. The corresponding binaural gain in intelligibility at the 50% level was on the order of 3 dB.
Use of a Sequential Strategy in Intelligibility Testing
Authors: Levitt H. , Rabiner L. R.
Published: September 2005

In a recent experiment involving intelligibility testing, the response curve (intelligibility function) was found to flatten off sharply at moderately high intelligibilities. A sequential strategy of the up-down-transformed-response (UDTR) type was used in order to concentrate observations in the symmetric region of the curve. The transformed-response curve showed the departure from symmetry at a much higher intelligibility level. Precision of estimation for the 50% level was found to be higher than for the simple up-and-down procedure. The technique is designed for situations in which it is difficult or impossible to vary the step size.
Using the Ocean Surface as a Reflector for a Self-Reciprocity Calibration of a Transducer
Authors: Patterson Robert B.
Published: September 2005

Though the self-reciprocity technique provides a simple means of obtaining absolute calibrations of electroacoustic transducers, it does not seem to have found wide acceptance. While the acoustic impedance of water and air differ sufficiently to make the loss of acoustic energy through a water-air interface negligible, the ocean surfaces is generally not a plane, and hence, would not seem to be a suitable reflector for use with the self-reciprocity technique. However, by using the mean of the returns from a number of pulses, it is possible to use the ocean surface. The accuracy of the technique is a function of the number of pulses, and possibly, variations in wind and sea conditions. With this technique one can make free-field calibrations of large, low-frequency transducers at high hydrostatic pressures and determine any variation as a function of pressure.
Acoustic Wave Generation by Entropy Discontinuities Flowing Past an Area Change
Authors: Cuadra Elizabeth
Published: September 2005

A solution is presented for the strengths of the two weak pressure waves produced by an entropy wave of finite strength being convected (in a subsonic flow) past an infinitestimal area change. Such an entropy wave may be either a temperature discontinuity in a single gas or an interface between two different gases. The strengths of the generated pressure waves according to this nonlinear solution are compared with previous (unpublished) results for an infinitesimal temperature discontinuity, and the sensitivity of the wave strengths to the physical parameters of the problem is given. This solution has been combined with other (existing) interaction solutions required to construct a computer program for prediction of the sound produced by the passage of a “bubble” (composed of two such interfaces) in an infinite pipe. A deck of program cards is available from the author upon request.
Matching Functions and Equal-Sensation Contours for Loudness
Authors: Ross Strange
Published: September 2005

Loudness balances were collected from three subjects, employing 57 combinations of 13 frequencies extending from 20 to 5000 cps. Determinations were made from levels close to threshold to the highest levels tolerable by the subjects, with 5-dB intervals. Stimuli were applied by an earphone through individually moulded ear inserts, and were measured in decibels sound-pressure level a few millimeters from the eardrum. For each subject, a symmetric and transitive subset of the data was employed for constructing a set of matching functions and a set of equal-loudness contours. Matching functions generally were linear, or showed a double inflection (in log-log coordinates). Equal-loudness contours generally agree with previous determinations, but show a steeper rise towards low frequencies; below 300 cps, and at medium levels, the contours approach straight lines with a slope of −40 dB/decade. Obtained matching functions are compared to three sets of theoretical functions, favoring the matching functions derived from loudness theories developed by Zwicker and by Zwislocki.
Calculation of the Acoustic Power Radiated by a Monopole in a Reverberation Chamber
Authors: Maling G. C.
Published: September 2005

The acoustic power W radiated by a harmonic monopole of strength Q located in a rectangular reverberation chamber has been calculated by using an eigenfunction expansion of the Green's function. An expression for the sound intensity valid for small normal admittance β has been integrated over the chamber surfaces to determine the power output. The results are within approximately ±2 dB of the results obtained by Waterhouse and Cook when the source is near one or more reflecting surfaces. At low frequencies, the ratio of W to the free-space output W0 varies with source position within the chamber, and has been treated statistically. The space-averaged value of W/W0 is generally less than unity, but values in the range 0.1–10.0 occur for particular values of frequency and β. The normalized standard deviation of W/W0 lies in the range 0.3–0.4 for β=0.05, and increases as β decreases. The results are applicable to the choice of an optimum absorption characteristic for low-frequency pure-tone power-level measurements.
Evaluation of Robey's First Reactance Integral for Small ka
Authors: Thompson William
Published: September 2005

The first of two integrals representing the self-radiation reactance loading on a finite-length uniformly vibrating cylinder bracketed by two semi-infinite-length rigid cylindrical baffles is evaluated for small ka where k is the acoustic wavenumber, and a the cylinder radius.
Acoustic Properties of Sediments
Authors: Hampton Loyd D.
Published: September 2005

This is a summary of an experimental study to measure the acoustic properties of water-saturated sediments. The sediments used were laboratory prepared to allow control of physical parameters (such as grain size, volume concentration, compressibility, etc.) and to approximate natural sediments. Acoustic velocity and attenuation in the sediments were measured over the frequency range 4–600 kHz. Acoustic measurements were made at high frequencies by means of two probes inserted in the sediments, and at low frequencies by means of a specially constructed rigid-wall standing-wave tube. The data presented show the frequency dependence of attenuation and velocity in the laboratory-prepared sediments and the change in this frequency dependence with changes in physical parameters of the sediments. Sediments composed of pure kaolinite, or kaolinite and sand up to 15% (by weight), show an f1.37 frequency dependence of attenuation. Sediments with greater than 30% sand (by weight), including pure sand, exhibit an f0.5 frequency dependence of attenuation. The measured velocity dispersion approximately 2% over the frequency range 4–200 kHz. Velocity increases with frequency. All measurements reported are for sediments free of entrapped gas.