bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reciprocity Calibration of Electroacoustic Transducers in the Time Domain
Authors: Niemoeller Arthur F. 
Published: September 2005

A method of directly evaluating the impulse response of a reciprocal electroacoustic transducer is presented. The method is essentially the time-domain analog of the conventional (frequency-domain) reciprocity method. The transient response of a coupled pair of identical transducers is used to compute the impulse response of either of the pair. A numerical method of obtaining solution is presented and is shown to be equivalent to the numerical solution of a real convolution integral equation. First, an approximate solution for one member of the pair of identical transducers is obtained. Then, a more precise solution is generated by minimizing the squared error between the actual response of the coupled pair and the one obtained by convolving the approximate impulse response with itself.
The method was tried on two pairs of condenser microphones, the microphones within each pair being very nearly identical. A pair of Western Electric 640-AA microphones were tested with the grids both on and off, and a pair of Bruel and Kjaer type 4131 microphones were tested with the grids on an off and with grids equivalent to those on the W.E. 640-AA both on and off.
Two unsatisfactory solutions resulted when W.E. 640-AA grids were used on the transducers. Three solutions were satisfactory, even though each contained slight negative drift for large values of time. One solution contained no appreciable error in its entire time course.
Electronic Binary Selection System for Phoneme Classification
Authors: Wiren Jacob , Stubbs Harold L. 
Published: September 2005

A successive-binary-selection system for automatic classification of spoken English into several groups of phonemes is described. The first step separates voiced from unvoiced by measuring the filtered output in the range of the pitch frequency. The next step separates turbulent (noise-like) from nonturbulent by measuring the filtered output in the range of the first formant.
Nonturbulent sounds are classified into 6 groups of 2 or 3 phonemes each in successive selections based on spectrum measurements. For each of the two groups of phonemes being separated in a given step, a frequency band is chosen where phonemes of that group have large amounts of energy compared to those of the other group. The polarity of the weighted difference of the corresponding band-pass-filter outputs determines the classification.
Unvoiced turbulent sounds are separated into stops and fricatives by means of the amplitude information contained the onsets of these sounds. Two of the fricatives, |s| (see) and |∫| (she), are separated by means of their zero-crossing-density levels.
Determination of the Speech Spectrum through Measurements of Superposed Samples
Authors: Tarnózy T. H. 
Published: September 2005

By recording on one magnetic tape the simultaneous utterances of several speakers saying unrelated things, we have obtained noise which is essentially time-invariant, has a continuous spectrum, and displays the average spectral properties of speech much more readily than methods employed heretofore. Spectral analysis of this speech noise has been performed.
The advantages of the method are (1) the integration time needed for determining the long-time spectrum of speech can be reduced to a few seconds; (2) the combination of speech wave forms can be treated as a statistical noise constant in time; (3) this noise does not contain any line spectrum elements; (4) with normal speaking levels, better signal-to-noise ratios are obtained.
The experiments suggest that different languages may be characterized by differences in the long-time average spectra. Spectra obtained by the present method were used to compute the average loudness level of a single speaker. The method is adaptable to measurement of the spectrum of a speech sound or of an individual mode of pronunciation.
Disk-Loaded Torsional Wave Delay Line. II. Theoretical Interpretation of Results and Design Information
Authors: Thurston R. N. 
Published: September 2005

In order to account for the magnitude of the delays reported in Part I, the effects of distributed mass and elasticity in the disk must be included in the analysis. Formulas for the torsional impedance at the inner circle of a thin annular elastic disk with a free outer boundary were first derived by H. T. O'Neil. One finds from these formulas that the structure can properly be represented by lumped electrical elements over a relatively wide frequency range. This electrical analog is a tandem arrangement of identical low-pass filter sections for which formulas are conveniently available.
Complicated elastic effects near the sudden change of diameter are not included in the theory, and these effects may account for the discrepancy between theory, and experiment. Relatively simple empirical corrections should be possible after a sufficient number of tests.
The design of disk-loaded delay lines is discussed in the light of the aforementioned analysis.
Ultrasonic Doppler Method for the Inspection of Cardiac Functions
Authors: Satomura Shigeo 
Published: September 2005

When the continuous ultrasonic wave is sent forth towards the heart from the surface of the chest wall, the cardiac motion causes the Doppler effect upon the partial wave reflected from it. Therefore, an apparatus suitably constructed for sending and receiving ultrasounds is quite useful for the investigation of the movements of theatrium, ventricle, or valves, etc., through the analysis of the particular Doppler signals developed from the motion of the respective part.
The author developed a method for the inspection of cardiac functions by recording these Doppler signals simultaneously with the electro- and phonocardiographs the oscillograph paper. This method made it possible not only to obtain direct informations for the valvular movement which could not have been ascertained up to present, but also to examine the transitional aspects of the myocardial excitation which is utterly uudetectable by the electrocardiograph alone.
Field of a Spatially Extended Moving Sound Source
Authors: Oestreicher Hans L. 
Published: September 2005

The rigorous determination of the field of a spatially extended sound source moving with subsonic speed in a viscous compressible gas is formulated as an initial-boundary value problem of a system of linear partial differential equations. This system reduces to a single equation of the second order with variable coefficients if the medium is a perfect gas and the motion of the gas around the source a potential flow. For steady motions and harmonic sources the equation becomes elliptic if time is eliminated.
Generalizations of Green's identity and Helmholtz's formula for this partial differential equation allow the representation of the sound field as a series of generalized multipoles. The field of a sufficiently small source of arbitrary shape with boundary conditions appropriate for the acoustic case and its relation to the concept of a moving simple source, dipole, etc., is investigated.
Effects of Ambient Noise on Speaker Intelligibility for Words and Phrases
Authors: Dreher John J. , O'Neill John 
Published: September 2005

The Lombard, or voice reflex, effect results in speech with characteristics different from those of speech that is normally produced. This change of characteristics can be demonstrated as an effective way to combat noise interference during reception. It also demonstrates the advisability of control of the production of speech by the speaker himself, in addition to that offered by equipment, during audiological evaluations.
Fifteen naive speakers read words and sentences while noise was being delivered to their headsets. There were five noise conditions. Their speech was recorded, with the noise being kept out of the recording channel, and then limited. Noise was then added to the recording in such a way as to produce a constant speech-to-noise ratio. The result was played to 200 American listeners. Results indicate that at a constant speech-to-noise ratio of reception speech produced by a talker with masking noise in his cars becomes more intelligible as the masking level rises to a given value. The change in intelligibility throughout the range investigated suggests an application to audiological testing as well as a device for use in voice communication.
Ultrasonic Attenuation in Water Containing Brine Shrimp in Suspension
Authors: Gruber George J. , Meister Robert 
Published: September 2005

A study is made to determine the frequency and concentration dependence of the ultrasonic attenuation in aqueous suspensions of hatched and unhatched brine shrimp in the frequency range 1–45 Mc. In both types of suspensions a linear relationship is found to exist between the excess attenuation and concentration at each frequency. The attenuation caused by hatched brine shrimp is found to be the same when the organisms are either living or dead.
For both types of suspensions the major cause of the excess attenuation is attributed to a scattering mechanism. Over the range of frequencies studied, while the excess attenuation in a hatched brine shrimp suspension varies as the 1.35 power of frequency, the attenuation caused by unhatched brine shrimp exhibits a maximum. The fact that the unhatched brine shrimp can be considered as small spherical particles allows calculation of the scattering loss, which, when subtracted from the measured values, results in a resonance type loss. The measured loss maximum associated with this resonance occurs at a frequency coincident with the principle mode of oscillation calculated assuming the eggs to be spherical cavity oscillators. A simple theory of geometric scattering from unhatched brine shrimp gives attenuation values which agree exactly with those measured above 20 Mc.
Calculations of Random Fatigue of Hard-Spring Resonators
Authors: Smith P. W. 
Published: September 2005

Computations have been made for the effect of a nonlinearity of the hard spring type upon the fatigue damage ensuing on excitation of a resonator by a stationary, broad-band, random Gaussian force. The fatigue theory used assumes simple accumulation of damage in proportion to a power of the peak values of response strain, without interactions between peaks. Two cases are distinguished: (a) strain proportional to displacement; (b) strain nonlinearly dependent on displacement, as is the surface fiber strain in a bar with pinned ends, responding in a single mode.
Numerical results are presented that indicate for case (a) a continuous decrease, with increasing nonlinearity, of the rate of accumulation of damage, while for case (b) this damage rate increases to a maximum as large as 3.4 times the linear estimate, and then falls below the value for linear response. Probability density (in response amplitude) of damage is greater at small amplitudes, and less at large, than for the linear case. The value of response amplitude of maximum damage density is also affected by nonlinearity.
Laboratory Standard Ceramic Microphone
Authors: Newitt William 
Published: September 2005

Microphones using barium titanate disk ceramics in conjunction with a split-tube diaphragm have been designed and constructed. Frequency response measurements were obtained by use of reciprocity techniques and by comparison with a known standard.
Sensitivities from −86 to −88 db referred to one volt per dyne per square centimeter, were obtained with a frequency response of plus or minus one db from 10 cycles to 30 kilocycles. The rugged construction and high stiffness of the microphone make it adaptable for use in high sound pressures, and for sound measurement in liquids.
The paper discusses theoretical relations pertinent to the development, describes the construction, and presents performance data of the microphone and associated electronic equipment.
Propagation of Nonaxially Symmetric Waves in Elastic Cylindrical Shells
Authors: Cooper R. M. , Naghdi P. M. 
Published: September 2005

In a previous paper two general systems of equations of motion, designated as (I) and (II) for thin elastic cylindrical shells (which include the effects of both transverse shear deformation and rotatory inertia) were derived and employed in a study of the torsionless axisymmetric wave propagation in an infinite cylindrical shell. The character of the two systems of equations is such that, upon the neglect of transverse shear deformation and rotatory inertia, Eqs. (I) will reduce to those known as Love's first approximation, while Eqs. (II) will correspond to those given by Donnell.
This paper, again employing the systems of Eqs. (I) and (II), is concerned with the predictions of phase velocities and amplitude ratios, for nonaxially symmetric as well as purely torsional propagation of elastic waves in an infinite cylindrical shell. As in the previous case of axisymmetric propagation, comparison is made between the predictions of the two systems of equations and the conclusions are specified.
The Computation of Far-Field Radiation Patterns from Measurements Made near the Source
Authors: Horton C. W. , Innis G. S. 
Published: September 2005

An analysis is made of two methods of predicting the far-field radiation pattern from pressure measurements made over a closed surface S, containing the source. One of these methods involves the use of Green's functions and yields two subcases according to the particular Green's function that is used. The Helmholtz formula, which results when one uses a Green's function of the form exp(ikR)/R, requires the knowledge of the normal gradient of the pressure ∂p/∂n over S in addition to the pressure p, but it leads to a formula that is relatively easy to evaluate. An approximation to ∂p/∂n is discussed. If, instead, one uses the Green's function which vanishes over the surface S, one can evaluate the pressure in the far field, in terms of measurements over S, of p only. The resulting formula is somewhat more complicated than the Helmholtz formula, but it does not require a knowledge of ∂p/∂n.
The second method is based on a proposal recently made by Pachner. It is shown, for the case of prolate spheroidal coordinates, that Pachner's method is completely equivalent to the second approach mentioned above. The applicability of these formulas is demonstrated with experimental data for a line hydrophone. Good agreement is obtained between the experimental radiation pattern and the theoretical patterns predicted by the formulas.
Ear-Insert Microphone
Authors: Black Raymond D. 
Published: September 2005

It has been observed by several different technical groups that an acoustic transducer placed at the ear can be used as a microphone to pick up the voice of the wearer. This paper presents the results of an investigation to determine the various factors which make possible the use of a microphone in the ear.
The investigation, using a laboratory model dynamic ear-insert microphone and a protective headset, determined the relative importance of the two principal paths that conduct sound pressure from the mouth to the outer ear canal: (1) The air path around the head, and (2) the path through the head. The voice spectrum in the outer ear canal, contributed by the path through the head, was also obtained.
It appears that the ear-insert microphone could compete with a conventional microphone in front of the lips only in an application where it is difficult to use the conventional microphone because of its size or its interference with other equipment. The investigation forms a basis for further study to determine whether the ear insert microphone has a future as a practical communications device.
Improved Nickel-Base Alloys for Magnetostrictive Transducers
Authors: Clark C. A. 
Published: September 2005

Dynamic magnetostrictive properties have been measured for nickel-base alloys containing up to 10% cobalt, with from 0 to 6% chromium. The maximum value of electromechanical coupling coefficient 0.51 occurs in a binary alloy containing 4.5% cobalt, balance nickel, for which the magnetocrystalline-anisotropy constant is zero. The maximum value of potential electroacoustic efficiency for resonance frequencies below 100 kc/sec is found, however, in a ternary alloy containing 1.4% cobalt, 2.3% chromium, balance nickel.
It is concluded that the binary alloy is the most suitable material for the magnetostrictive element of receivers, such as hydrophones, particularly where a reasonably flat response is sought. The ternary alloy, because of its lower eddy-current losses, is to be preferred for generating high-frequency acoustic power.
Generation of Intense Audio Sound Fields Utilizing Arrays of Multiple-Driver Horns
Authors: Levy Sidney E. , Carlisle Richard W. 
Published: September 2005

There are several major applications for intense audio sound fields: the outdoor propagation of speech and of warning signals, and the sonic fatigue testing of missile and aircraft components. In these applications, several factors combine to make it necessary to limit the portion of the frequency spectrum covered by any one loudspeaker unit. In order to provide adequate power capacity, selection is required between the alternatives of (a) using a large number of identical drivers, (b) using a plurality of drivers each especially designed for a selected portion of the frequency range, and (c) using combinations of these arrangements.
In an array currently being used for sonic-fatigue testing, a plurality of large open cone loudspeakers is used for low frequencies, and a plurality of horns is used for middle and high frequencies. Each horn is driven by several drivers.
The driver voice coil and diaphragm proportions have been optimized to withstand fatigue stresses under the thermal conditions encountered. The driver is rated at 50-w input for program material.
Horn assemblies are available having throat arrays for mounting 6, 12, or 24 drivers. Various applications will be illustrated.
Information in Simple Multidimensional Speech Messages
Authors: Webster John C. 
Published: September 2005

Simultaneous pairs of four-bit messages were presented to listeners at rates of two pairs every 4 sec (4 bits/sec), three pairs every 4 sec (6 bits/sec), four pairs every 4 sec (8 bits/sec), and six pairs every 4 sec (12 bits/sec). Each message of the pair was either [a] or [i], said by a male or a female, as a question (rising inflection) or a statement (falling inflection), and heard in either the right or the left ear.
Sequences were made that were balanced (1) between ears, (2) between male and female voices, (3) between [a]'s and [i]'s and (4) between questions and statements. The subject sometimes listened to both messages but usually listened only for the messages (1) in one ear, (2) of one voice, (3) of one vowel sound, or (4) of one inflection.
The best subject could receive correctly about 6 bits/sec whether this was one of two messages at the 12 bits/sec rate or both of two at the 6 bits/sec rate.
Masking of Speech by Line-Spectrum Interference
Authors: Licklider J. C. R. , Guttman Newman 
Published: September 2005

Two series of intelligibility tests were conducted. In the tests, speech was presented against a background of interference. The line-spectrum interference consisted of from 4 to 256 sinusoids, superposed in a linear adder. Three different spacings of the components in frequency, and several different distributions of power among the components, were studied. Tests with continuous-spectrum random noise were made for comparison.
The over-all interference power required to reduce intelligibility to a given level decreases as the number of components in the interference increase. The drop is about 10 db in the decade from 4 to 40 components. Beyond 40, there is much less change. Even 256 components, however, mask measurably less effectively than random noise of equivalent power in the band 200–6100 cps. For a given number of components, the line-spectrum interference most detrimental to intelligibility has the same number of components in each frequency band of equal contribution to intelligibility, and its components are uniform in amplitude. The bearing of these findings on the theory of intelligibility and on procedures for predicting intelligibility from physical parameters is discussed.
On the Relation between the Intelligibility and Frequency of Occurrence of English Words
Authors: Howes Davis 
Published: September 2005

The threshold of intelligibility for a word in a wide-spectrum noise is shown to be a decreasing function of the frequency with which the word occurs in general linguistic usage (word frequency). The drop in threshold is about 4.5 db per logarithmic unit of word frequency. This rate is independent of the length of the word, although the thresholds for words of given frequency of occurrence are lower for long words.
The effect of restricting the listener's alternatives in an intelligibility test to a specified number of words is calculated from this relationship. These calculations come within 1 db of published experimental data. Theoretical functions relating intelligibility threshold to word length are also calculated from the word-frequency effect, on the assumption that listeners can discriminate the length of a word at levels too low for it to be identified. These functions are in general agreement with the experimental results.
Implications for intelligibility testing procedures are discussed.
Acoustical Time Regulator
Authors: Springer Anton M. 
Published: September 2005

The paper describes a device for altering the speed of reproduction of tape recordings, by mechanical means, without altering the frequency and therefore the pitch.
The playback time can be changed within a range of 50–200% of the recording time. Although there are no technical limits to the range of time-change, certain loss of quality begins to become apparent if the time-change is increased beyond ±30%.
The possibilities of application are also discussed.
Structural Fatigue under Combined Sinusoidal and Random Vibration
Authors: Spence H. R. , Luhrs H. N. 
Published: September 2005

Structural fatigue caused by combined sinusoidal and random vibration is of concern in flight proofing of electronic equipment, since such excitation is required by many current ballistic missile equipment specifications. How to predict the fatigue under this vibratory excitation is discussed with particular reference to the relationship of combined vibration to a single sinusoidal substitute.
Equations and curves for obtaining the sinusoidal substitute are presented and their application illustrated on a single resonator system.
Application of the Theory of Signal Detectability to Amplitude Discrimination
Authors: Tanner Wilson P. 
Published: September 2005

The fact that Weber's law appears to apply in the same way both to intensity discrimination for pure tones and to intensity discrimination for white noise poses a theoretical paradox: in the case of pure tones, the human observer becomes less efficient as the intensity of the tone is increased, while in the case of white noise he exhibits a constant efficiency independent of intensity.
An inventory of the various possible noise sources which may exist is made, and the way in which these may be expected to effect the detectability of a signal leads to the equation (d′)2=η2E&Dgr;NG+NE+kV02, where η is the individual observer's efficiency, NG is the noise introduced by the experimenter, NE is the uncontrolled noise present in the experimental situation, and k is a constant indicating that small amplitude variation in the oscillator constitutes a noise source proportional to the power of the lower of two signals to be discriminated.
Data for three observers over four noise levels is described by this equation sufficiently well to suggest that the hypothesis that Weber's law is merely a reflection of the oscillator noise (kV02) is plausible.