bluuebunny/crossref_metadata_2025 huggingface dataset:
Difference Limen for Pure Tone Diminution
Authors: Kirk Roger E.
Published: September 2005

The difference limen for linear pure tone diminution was investigated with diminution rate and fundamental frequency as parameters. Electronic means provided two tone diminution rates which were independently adjustable. The two tones were automatically recycled five times each. The initial loudness level of the tones was 80 phons. The terminal loudness level of the tones was randomized. This was accomplished by randomizing the duration of the tones. The tones were presented to subjects over PDR-8 earphones. The method of constant stimuli was used to determine the difference limen. An analysis of the results indicates that the difference limen for tone diminution is of the order of 412 to 512% over the range of diminution rates investigated. The difference limen is relatively independent of the fundamental frequency of the tone. The relationship between the difference limen and diminution rate is described by an equation of the form Y=0.048X where Y and X are measured in db/sec.
Sound Absorption Coefficients of Acoustical Materials Backed by Large Depth Air Spaces
Authors: Jack W. A.
Published: September 2005

The Johns-Manville reverberation chamber technique uses a sample area 8 by 8 ft. A deep pit, beneath the sample, fillable with water to the height desired, provides a ready means for investigating any air space up to 46 in. in depth. Below 600 cps strong depth dependencies were found. The results on a variety of materials are presented.
Development of Acoustic Attenuators for Air-Conditioning Ducts
Authors: Becker Carl
Published: September 2005

The air-borne noise path along ducts is important for frequencies above approximately 150 cps. While long, tortuous ducts often provide inherent attenuation, special treatment can be necessary for short ducts. Treatment effectiveness is judged in terms of air flow resistance in relation to minimum acoustic attenuation which will be provided for a range of installation conditions. Design of acoustic duct attenuators involves selection of suitable means for providing sound absorptive surfaces, effective over the wide frequency range involved, and their arrangement in the air stream. Methods are discussed for measuring acoustic attenuation in relation to air-flow resistance. Attenuation measurements without air flow permit detailed examination of acoustic effectiveness of attenuator components and their arrangement. Subsequent attenuation measurements under rated air-flow conditions are used to determine any potential source of self-noise from turbulence.
Measurement of Noise Inside Ducts
Authors: Dyer Ira
Published: September 2005

Recently Kerka, and earlier Beranek, Reynolds, and Wilson, discussed the measurement of sound power radiated by a fan in a straight duct, by measurements of the sound pressure inside the duct. One of the difficulties associated with this technique is that above the first cutoff frequency the sound pressure varies markedly across a transverse section of the duct and the relation between mean square pressure and power is not simple. The transverse variation can be understood by application of mode theory to propagation of noise in the duct; this theory is in good agreement with measurements reported by others. Furthermore, in given frequency ranges, it is possible to select a measurement position inside the duct such that the mean square pressure is related to the power flow by the usual free-field equation.
Ambient Noise under Arctic-Sea Ice
Authors: Milne A. R. , Ganton J. H.
Published: September 2005

Underwater ambient-noise spectra and amplitude distributions are described for data acquired during field experiments made in the spring, late summer, and winter within the Canadian Arctic Archipelago. Measurements in each case were made using a bottom-mounted hydrophone. The ice cover was fast to the shore during the spring and winter experiments. In the summer experiment, the ice cover, although 10/10, was free to move. The ambient noise was generally impulsive and at times highly non-Gaussian. The significant noise was the result of mechanical activity associated with the ice cover. For shore-fast spring and winter ice, surface cracks as a result of thermal stresses were important; for late summer ice, relative motion of the floes was important.
Miniature Loudspeakers for Personal Radio Receivers
Authors: Bleazey John C. , Preston John , May Everett G.
Published: September 2005

This paper presents two small experimental loudspeakers of the same general design, suitable for use in personal radio receivers. The design of the magnetic structure is unconventional in that the loudspeaker cone housing and the magnet occupy the same space, and the over-all loudspeaker depth is thereby reduced. The vibrating system of the loudspeaker is conventional so that the directional characteristics, distortion, and frequency response are, in general, similar to a completely conventional loudspeaker of the same diameter. Some general design considerations applicable to this type loudspeaker are discussed, together with a chart summarizing these design considerations.
Flow Excitation of Cylindrical Shells and Associated Coincidence Effects
Authors: Rattayya J. V. , Junger M. C.
Published: September 2005

The purpose of this analysis to predict the vibration level of a pipe conducting a turbulently flowing fluid. First, recent data on the correlation function describing the random pressures in the turbulent boundary layer are reviewed. The Strouhal-number dependence displayed by the cross-spectral density (in both the downstream and transverse direction), is equivalent to a complex vectorial wavenumber proportional to ω/V, where ω is the circular frequency and V is the convection velocity. The components in the transverse and downstream directions are, respectively, imaginary and complex. Starting from the formal solution for the response of an elastic structure to random excitation, published by Powell, the vibration level of the pipe wall is computed, use being made of the correlation function obtained from narrow-band measurements performed at the U.S. Navy Underwater Sound Laboratory. The average spectrum level that would be obtained from vibration measurements made with finite-bandwidth filters is then computed. The maximum frequency at which individual resonance peaks can be observed is expressed in terms of the filter bandwidth. Amplification of the pipe-wall response by coincidence effects in pipes conducting high-speed air or steam flow is examined. Spatial coincidence occurs when the longitudinal wavenumber of a shell mode matches the real component ω/V of the pressure cross-spectral-density wavenumber. Because of the exponential dependence of the cross-spectral density on the transverse Strouhal number, enhancement by coincidence is limited to modes whose circumferential wavelength exceeds approximately one-third of their axial wavelength.
Precise Automatic Method for Measuring Hearing Aid Response
Authors: Jensen Thelma H. , Burnett Edwin D. , Corliss Edith L. R. , Burkhard Mahlon D.
Published: September 2005

This paper describes equipment used at the National Bureau of Standards for rapid, precise measurement of hearing aid properties. By using an insert technique, allowance can be made for variations in the measuring system. A compression circuit which is relatively fast acting serves to stabilize the source. Logarithmic amplifiers and a differencing circuit make possible the direct recording of gain. A Panoramic analyzer serves as a swept wave analyzer for distortion measurements. The system has proved satisfactory for free-field measurements as well as cavity pressure measurements. This work was supported by the Department of Medicine and Surgery of the Veterans Administration.
Word Intelligibility and Position in Sentence
Authors: Rubenstein Herbert , Pickett J. M.
Published: September 2005

There is evidence that the manner in which context is distributed affects its constraint on verbal responses. For example, it has been demonstrated that a bilaterally distributed context is most effective in reducing the number of acceptable meanings for a given word. Another investigation has shown that nouns are most predictable at the end of a sentence and least predictable at the beginning of a sentence. In these investigations the contexts were presented visually; the present experiment was undertaken to ascertain whether similar results would be obtained with speech presented against a background of noise. Complete declarative sentences, all of the same length, were constructed in pairs; e.g., for each sentence containing the test noun in initial position, there was a semantically equivalent sentence made up of the same words but with the test noun in medial or final position. The members of a pair were presented at different experimental sessions in such a way that each experimental condition was equally represented at each session. The results indicate that, when the signal is compressed so that all words are approximately equal in intensity, intelligibility is lowest in initial position and highest in final position.
Attenuation of Guided Waves in Isotropic Viscoelastic Materials
Authors: Coquin G. A.
Published: September 2005

Wave propagation in an infinite isotropic elastic plate with tractionfree faces is governed by the Rayleigh-Lamb frequency equation. As is well-known, an analysis of the equivalent viscoelastic problem shows that the frequency equation for an isotropic viscoelastic plate may be obtained from the Rayleigh-Lamb equation by replacing the two independent elastic constants with complex functions of frequency. The propagation wavenumbers corresponding to modes that propagate unattenuated in an elastic plate are complex in a viscoelastic plate, the imaginary parts being attenuation constants. In this paper, an approximate method is developed for obtaining roots of the viscoelastic-frequency equation from known roots of the Rayleigh-Lamb equation with comparatively little additional calculation. The approximate method is applicable when the attenuation per wavelength is small. Calculations have been carried out for the lowest three longitudinal and flexural modes in plates with Poisson's ratios of 0.17 and 0.35, and curves are presented that show the contributions to the over-all attenuation owing to dissipation associated with dilatational and shear deformations separately. As an example, the variation of attenuation with frequency in a Voigt solid has been calculated and plotted for two ratios of dilatational to shear losses. The same procedure can be used to calculate the attenuation in an isotropic viscoelastic cylinder, using the Pochhammer-Chree equation, and numerical results are given for the longitudinal modes of a cylinder.
Sounds Produced by the Unsteady Flow of Water
Authors: Strasberg M.
Published: September 2005

The production of sound by the unsteady flow of a homogeneous fluid is discussed, with special attention given to those phenomena of practical concern as sources of underwater noise. Brief reviews are given of recent experimental and theoretical investigations of the sound associated with the following flow phenomena: (1) unsteady flow within an unbounded fluid, related to the noise from turbulent jets and wakes; (2) fluctuating hydrodynamic forces due to unsteady flow about a rigid body, related to “aeolian tones” and the rotation sound from a propeller; and (3) excitation of the vibration of an elastic body by the flow. A short motion picture produced by L. Prandtl will be shown to illustrate several kinds of unsteady flow.
Sound Propagation in Layered Media with a Rough Interface
Authors: Eby R. K. , Williams A. O.
Published: September 2005

When sound propagates in a fluid layer of suitable thickness, overlying a much thicker layer of greater density and sound velocity, the normal-mode propagation expected ideally [C. L. Pekeris, “Theory of propagation of explosive sound in the sea,” in Memoir 27 of the Geological Society of America (1948)] is a result of total internal reflection. Anything preventing such reflection, such as a rough interface, should cause attenuation of the sound. A qualitative explanation is that some diffusely reflected sound strikes the interface at less than critical angles and escapes. Such attenuations have been studied with the apparatus of the accompanying paper by Ryan, Eby, and Williams. Small solid spheres were spread on the rubber-water interface; the extra attenuation caused by them was measured in the water layer as a function of frequency, water depth, sphere size, and area density of spheres. This attenuation is roughly proportional to area density of spheres, and to their acoustic scattering cross sections, and varies additionally with sphere size, water depth, and frequency, Frequencies were 100–250 kc; sphere radii 0.07–0.23 cm; water depths 0.5–2.0 cm. Glass, lead, and steel spheres behaved alike. (Supported in part by the Office of Naval Research.)
Evaluation of Surface Reverberation in Sonar
Authors: Horton J. W.
Published: September 2005

Several measures have been devised for evaluating those characteristics of an acoustic medium, or of its boundaries, which determine the level of reverberation following the transmission of a pulse of acoustic energy. Of those measures which are applicable to surface reverberation, the coefficient giving the rate per unit area at which acoustic energy reaching a scattering surface along a given ray path is returned toward the source is particularly useful in computing the equivalent plane wave level of reverberation as a function of time. The present paper discusses the relations between this coefficient and other factors which must be taken into account in computing the total transmission loss suffered by acoustic energy returned in the form of reverberation. The significance of these relations with respect to practical problems is discussed briefly. A simple and accurate method for measuring the value of the backscattering coefficient in any given situation is described.
Propagation of Explosive Sound in a Layered Liquid
Authors: Mitra M.
Published: September 2005

The transient pressure produced by explosive sources in a two-layered liquid half space has been evaluated in terms of definite integrals, using Cagniard's method of inversion of the Laplace transforms involved.
Self- and Mutual-Radiation Impedance and Beam Patterns for Flexural Disks in a Rigid Plane
Authors: Porter David T.
Published: September 2005

Expressions are given for the nearfield pressure on a flexural disk in an infinite, rigid, plane baffle. This pressure is then integrated over the disk to obtain finite series expressions for self-radiation impedance, which is referred to average surface velocity, as are all impedances in this article. Expressions are derived for the far field directionality factor of a flexural disk. The Bouwkamp integral method is used to obtain infinite series expressions for mutual radiation impedance between flexural disks by integrating the farfield directionality factor of two identical flexural disks, vibrating in phase, over a set of complex angles. It is shown that as the relative radius (ka) of the disk approaches zero and the element spacing becomes large as compared to the radius of the disk, the equations for mutual-radiation resistance and reactance and self-radiation resistance for flexural disks are the same as for circular pistons. However, as ka → 0, the self-radiation reactance is larger for disks than pistons, being 0.849 ka for pistons, 1.060 ka for supported-edge disks, and 1.204 ka for clamped-edge disks.
On the Theory of Segmented Electromechanical Systems
Authors: Martin Gordon E.
Published: September 2005

Many applications in the field of underwater acoustics utilize an electromechanical system consisting of identical segments. The theory of such a system is derived and the behavior of all segments is described in terms of any two boundary conditions at the ends of the system. An electromechanical equivalent circuit is derived that substantially facilitates the analysis of segmented systems. The use of the theory is illustrated by the consideration of a system of coaxially segmented, longitudinally polarized ferroelectric tubes.
Errata: Method for the Calculation and Use of the Articulation Index [J. Acoust. Soc. Am. 34, 1689–1697 (1962)]
Authors: Kryter K. D.
Published: September 2005

Two Figures in my paper cited above contained errors: In Fig. 10, the vertical ordinate should be shifted downward by 0.1 unit (this ordinate should start at 0.1 rather 0). In Fig. 15, the word “sentences” in the upper left-hand corners of the Figure is misspelled; also the phrase “skill of talkers and listeners” should be added to the legend in the lower left-hand corner of the Figure.
Effect of Noise Crosscorrelation on Binaural Signal Detection
Authors: Langford Ted L. , Jeffress Lloyd A.
Published: September 2005

The effects of varying the crosscorrelation of a noise masker upon the detection of a 500-cps tonal signal were investigated. The correlation was varied by introducing a time delay into the channel to one ear. Ten delays yielding various positive and negative correlations and nine delays yielding zero correlations were employed with in-phase and reversed-in-phase signals. A two-interval forced-choice procedure was used to obtain MLD's relative to the diotic condition. The function relating MLD's to delay is periodic, the largest values occurring for the antiphasic conditions and the smallest for the homophasic. The function for zero correlations is not periodic, but decreases regularly to a value near that found for uncorrelated noise. No difference is apparent between the two conditions of signal phase for zero correlations. The temporal interval over which the binaural system is able to effect a correlation between events occurring at the two ears is estimated to be at least 9 msec.
Vibrations of Coaxially Segmented, Longitudinally Polarized Ferroelectric Tubes
Authors: Martin Gordon E.
Published: September 2005

Ferroelectric ceramic materials are often used in underwater sound transducers by stacking a number of identical pieces together. In this paper, the theoretical behavior is derived for a ferroelectric, cylindrical tube consisting of any number of longitudinally polarized coaxial segments. The effects due to lateral dimensions, which may not be negligible, are included. Electromechanical equivalent circuits are developed that greatly simplify and improve the analysis of composite resonators in transducer design. The theoretical parameters are related simply to experimentally measured quantities so that the parameters can be evaluated even though the lateral dimensions are large relative to the length of each individual segment. The dielectric, piezoelectric, and elastic losses are included in the general theory but losses are not considered explicitly.
Mutual Radiation Impedance of Square and Rectangular Pistons in a Rigid Infinite Baffle
Authors: Arase Elizabeth M.
Published: September 2005

An integral solution has been obtained for the mutual radiation impedance of two identical rectangular or square pistons vibrating in an infinite rigid plane. These expressions are relatively easy to evaluate by machine computations. Numerical values of the radiation impedance are given for square pistons of dimension ka = 12, 1, and 2, separated by 12⩽kd⩽18. For larger pistons, the orientation of the pistons with respect to each other becomes important. This is demonstrated for the case ka = 5.
Loudness Function of a 1000-cps Tone in the Presence of a Masking Noise
Authors: Hellman Rhona P. , Zwislocki J.
Published: September 2005

Loudness levels of a partially masked 1060-cps tone are determined by loudness-balance procedures and, indirectly, by the methods of magnitude estimation and production. It is shown that loudness balances obtained by the method of adjustment are consistent with the loudness judgments obtained by the combined method of magnitude estimation and production, called method of numerical magnitude balance. The final results are in good agreement with those of other investigations in which balanced procedures were followed.
Radiation Properties of Cylindrical Shells
Authors: Manning Jerome E. , Maidanik Gideon
Published: September 2005

A theoretical method, similar to that applied recently to flat panels, is developed for estimating the radiation efficiency of a cylindrical shell. The radiation efficiency of the cylinder is significantly greater than that of a flat panel of equal dimensions at and about the ring frequency where the longitudinal wavelength is equal to the circumference of the cylinder. This peak in the radiation efficiency is shown to be associated with the increase in flexural-wave speed due to curvature. A series of measurements of radiation efficiency of cylinders was conducted. The agreement between theory and experiment is satisfactory.
Some Factors in the Recognition of Timbre
Authors: Berger Kenneth W.
Published: September 2005

Listeners' recognition of wind-instrument tones was investigated for the tone concert F on the treble staff (frequency approximately 349 cps). Tones of a flute, oboe, B-flat clarinet, tenor saxophone, alto saxophone, cornet, trumpet, French horn, trombone, and baritone were recorded, equated for duration and sound level as well as frequency. Thirty university band members listened to these tones played back: unaltered, backward, with the rise and decay removed, and through a 480-cps low-pass filter. Recognition of wind-instrument tone quality was best for the unaltered playback, next best under the backward condition, next in the absence of rise and decay, and poorest under the filtered condition.
Time Requirements for the Tonal Function
Authors: Boomsliter Paul C. , Creel Warren , Powers Samuel R.
Published: September 2005

Use of short pure-tone bursts to test perception of tone rather than click in cases of disturbed blood Supply to the brain stem in humans has shown that the threshold of tonal processing provides an approach to measurement of neural processes in pitch perception.
Axisymmetric Vibrations of Orthotropic Cylinders
Authors: Mirsky I.
Published: September 2005

An exact solution is obtained for the axisymmetric vibrations of orthotropic cylinders by the application of the Frobenius series method. Numerical results are given for the two orthotropic materials barytes and topaz.
Ambient Sea Noise at Low Frequencies in Shallow Water of the Scotian Shelf
Authors: Piggott C. L.
Published: September 2005

Ambient sea-noise data in the frequency range 8.4-3100 cps were collected for a one-year period, using two bottomed hydrophones in 20- and 28-f (fathom) water depths on the Scotian Shelf. The relative spectral-energy distribution of the sea noise is presented for a number of wind speeds. Linear relations between the sea-noise spectrum levels and the logarithm of wind speed were found over the entire frequency region, but the slopes were markedly frequency-dependent. A seasonal variation of noise level that was independent of frequency was observed, the noise levels at the same wind speeds being higher during the winter months. There were no significant differences in the results from the two hydrophones, except below 43.7 cps where the sea-noise levels were 2–3 dB higher at the 20-f hydrophone. The results are compared with those of other studies of sea noise.
Psychophysical Comparison of Just Tuning with Equal Temperament in Sequences of Individual Tones
Authors: Ward W. D. , Martin D. W.
Published: September 2005

The alleged merits of “just” musical scales are frequently recommended to designers and manufacturers of keyboard musical instruments employing the equally tempered scale. Consequently it is a matter of practical interest to determine the conditions under which the two types of scales are discriminable. Two experiments were performed investigating one facet of the question: discriminability of melodic sequences. First an ABX test was given to 20 listeners, using prerecorded ascending diatonic scales of each type. Two widely different timbres were used, one flutelike and the other spectrally complex. Only three subjects gave results significantly different from chance. A second experiment employed scales deviating from equal temperament in a manner similar to the just scale, but varying in amount from −6 to −30 cents on the third, sixth and seventh steps (mi, la and ti). These were compared to equally tempered scales by both ABX and AX procedures. Results showed that the maximum difference between the just and equally tempered scales (16 cents) lies just below the “ABX threshold,” but above the “AX threshold,” for most of these relatively well-trained observers. It is significant that music students used here (admittedly well conditioned to equal temperament) said that when they were certain of a discrimination, it was because one of the scales contained tones which were “too flat.”
Subjective Evaluation of Musical Scale Temperament in Pianos
Authors: Martin D. W. , Ward W. D.
Published: September 2005

Piano tuners normally “stretch” the tuning, adjusting the upper strings of a piano sharp, and the lower strings flat, relative to the equally tempered scale. The desirability of this stretch (largely a natural consequence of tuning by beats) has apparently not been demonstrated formally, although there is anecdotal evidence that a piano tuned to strict equal temperament sounds less pleasant than one tuned with the typical stretch. The question assumes practical importance because of the relative simplicity of a device that would permit tuning to equal temperament by comparatively untrained personnel, in contrast to the much greater complexity of a similar device incorporating the stretch. Therefore, recorded tonal and chordal sequences from a small upright piano, tuned to an empirical average “stretched” scale by means of a visual device, were compared with similar sequences in which the same piano was tuned (1) to strict equal temperament (again using the visual device), and (2) by the conventional auditory method. The stretched scale was definitely preferred to strict equal temperament, both by Baldwin research engineers and by music students. No consistent preference for the auditory method of tuning was found.
Ultrasonic Attenuation and Velocity Measurements in Fused Silica at Low Temperature
Authors: Bömmel H. E.
Published: September 2005

Recently measurements have been published on the temperature dependence of the attenuation and velocity of ultrasonic shear waves in fused silica, at frequencies of 66 and 201 kc/sec1 and also at 10 mc/sec.2 They show a very pronounced peak in attenuation which lies at approximately 35°K and a flat minimum in velocity at about 65°K for the frequencies 66 and 201 kc/sec. The measurements of McSkimin at 10 mc/sec have a gap in the temperature range between 4.2°K–77.3°K, thus preventing the exact location of the extrema. To complete this, measurements were made at 20 mc/sec in the temperature range from 1.6°K–80°K. The results show a peak in attenuation at about 45°K and a minimum in velocity at about 75°K. This shift with frequency indicates a relaxation phenomenon as the cause for the very high increase in attenuation between 30° to 50°K. This may be due to sidewise vibrations of the oxygens in the Si–O–Si bonds. These vibrations should not occur for quartz crystals for which the oxygens are in minimum energy positions.
Experimental Studies on the Nature of Acoustic Radiation Pressure
Authors: Herrey Erna M. J.
Published: September 2005

Measurements have been made of the normal and of the shearing component of the force of radiation pressure exerted by an ultrasonic beam in water on an absorbing surface intercepting the beam. It is found that the magnitude of the resultant force is independent of the angle of incidence and that its direction is always parallel to the direction of the beam. This result confirms the theory first proposed by Brillouin, and later further developed by Borgnis, that radiation pressure is not an isotropic pressure like hydrostatic pressure but rather due to a state of unidirectional stress in the region of a plane progressive wave. This stress is represented by the tensor |−(p + E)000−p000−p|, where p is the hydrostatic pressure in the undisturbed medium, and E the energy density in the wave. Based on the experimental results a simple method is developed to establish for any given sample of material approximately what fraction of the incident ultrasonic power is reflected, absorbed, or transmitted, respectively, at various angles of incidence.
Monitoring and Controlling the Motion of a Sound Source
Authors: Corliss Edith L. R. , Burkhard Mahlon D. , Koidan Walter
Published: September 2005

The vibration of a sound source gives rise to changes in electrical reactance between its fixed and moving elements which are detected by means of an auxiliary carrier signal that differs substantially in frequency from the driving signal. In many cases the carrier signal can be introduced at the same terminals at which the driving signal is applied. Use of the carrier signal makes it possible to monitor the mechanical motion. It thus provides a motion-detecting signal which can be made more sensitive to changes in source motion than can the usual feedback signal derived from changes of electrical impedance in the driving circuit. This method has been applied to controlling the motion of a capacitance-type driver designed for use in ear-impedance measurements. The behavior of a sound source under varying conditions of load has been observed. In some applications a sound field can be stabilized without the use of an auxiliary microphone. (The application of the method to microphone calibration is described elsewhere in this program.)
On the Propagation of Noise in Pipes. II
Authors: Young J. E. , Mawardi O. K.
Published: September 2005

A noise field propagated in a pipe is discussed in terms of a continuous space correlation function for the noise pressure and appropriate boundary conditions. This formulation does not take into account the presence of noise sources. The statistics of the noise pressure and the correlation function are not explicitly discussed in this approach. The pipe cutoff frequencies as defined by the single frequency analysis appear naturally in the formalism. As is to be expected the disposition of such frequencies is important in the transmission of a given noise spectrum. The relation between the present point of view and that of I is discussed. It is concluded that the source-function approach will be more useful for a large class of physical problems.
Variation in Sound Pressure Produced in Guinea Pig Ears Due to Normal and Abnormal Ear-Drums
Authors: Benson R. W. , Eldredge D. H.
Published: September 2005

Sound pressures measured with a probe-tube microphone in front of the tympanic membrane of the guinea pig have been compared at 100 cps intervals in the frequency range 50 to 8000 cps to the sound pressures similarly measured in a speculum coupling an acoustic source to the ear canal. Rather different functions were obtained for each of five conditions: (1) normal, (2) hair-line slit in the tympanic membrane, (3) rupture of tympanic membrane, (4) fluid behind tympanic membrane, and (5) bulla open. The variability in each of the categories will be presented. The correlation between the physical measurements and the physiological response as indicated by the cochlear microphonic will be discussed.
Neural Responses to Clicks: an Analysis of Masked and Unmasked Intensity Functions
Authors: Frishkopf Lawrence S. , Rosenblith Walter A.
Published: September 2005

Wire electrodes located near the round window of anesthetized cats record electrical activity in response to clicks. The amplitude of the earliest neural component (N1) of these click responses was measured for click and noise stimuli varying over an intensity range of 90 db. The intensity function for unmasked clicks is obtained by plotting the amplitude of N1 vs stimulus intensity; this function increases monotonically for low and high intensities with a plateau in the middle of the range. The presence of masking noise decreases the amplitude of N1; for a given click intensity the effect is more pronounced for higher intensities of the noise. These data yield by inference something akin to an intensity function for neural responses to noise. The shape of this function resembles that exhibited by the click intensity function. N1 represents electrical activity evoked after stimulation of receptor cells and peripheral auditory neurones. Present evidence suggests (a) that there are two populations of such receptor-neurone elements whose mean sensitivities differ by about 40 db; (b) that the threshold of a single element in the sensitive population fluctuates rapidly.
A Two-Projector Method of Absolute Calibration at Low Audio and Infrasonic Frequencies
Authors: Trott W. J.
Published: September 2005

An absolute method is described for calibration of hydrophones which, unlike other absolute methods, depends on a frequency-independent factor that is easily measured statically. One projector is equipped with a displacement measuring circuit. The factor 0.1 Bl/Area plus voltage and current measurements yield the hydrophone receiving response.
On the Radiation Impedance of the Liquid-Filled Squirting Cylinder
Authors: Robey Donald H.
Published: September 2005

The impedance presented to the inside surface of a hollow radially vibrating cylinder of finite length has been determined theoretically. Two cases were considered; in the first, the cylinder was filled with a viscous liquid which was retained by pressure-release caps at each end, while in the second, the cylinder was squirting from both ends into an infinite liquid medium. In the first, curves showing how the impedance was affected by viscosity are presented. In the second, viscosity was not included, but the radiation resistance contributed a real term to the impedance. It is shown that for some length to diameter ratios, the reactive part of the impedance can become negative. Also for each particular ratio there is a frequency for which the radiation resistance is a maximum.
The Dynamical Analysis of Speech Sounds
Authors: Wente E. C.
Published: September 2005

Crandall and Sacia in 1924 first made an analytical study of speech sounds by means of frequency selective networks. They, in effect, simultaneously impressed speech current on a set of tuned circuits, having resonant frequencies distributed more or less uniformly over the speech frequency range, and measured the long-time average power output of each of the tuned circuits. By this means they obtained a power-frequency spectrum for each of thirteen sustained vowel sounds. The objective in this study was the translation of the time pattern of the sound wave into a frequency pattern, for the ear, in so far as it obeys Ohm's law of hearing, makes a translation of this type and presumably uses such frequency patterns in the identification of the speech sounds. This general method of study, improved and modified to meet special requirements, has since been used for obtaining a great variety of useful speech data. In this paper apparatus will be described by which, in effect, short-time average output power levels of a set of frequency-selective networks are graphically recorded in synchronism when speech current is applied to the set. The problems of selecting the optimum number and type of networks and of designing a suitable recorder for producing the most useful data on both vowels and consonants will be discussed. Samples of records obtained with the apparatus will be shown.
Prediction of Speech Intelligibility in Noise
Authors: Pickett J. M. , Kryter Karl D.
Published: September 2005

PB word and sentence intelligibility tests were presented over earphones and loudspeakers to a crew of five listeners. Tests were conducted in four noises of different spectra. The results were compared with scores predicted by five current methods proposed for this purpose. The method of French and Steinberg, employing twenty articulation bands, predicted test results obtained in “flat” noise but failed to give satisfactory results for the other noise spectra; the shorter methods which employ a few octave bands underestimated the speech levels required to obtain specified test scores by 1 to 24 decibels. In general, the results obtained with speech presented over a loudspeaker in an anechoic room were closer to predicted values than were the results from the tests using earphones. It is concluded that existing methods of predicting speech intelligibility are not suitable for use with noise spectra deviating significantly from “flat.” Required speech levels (RSL) for satisfactory speech communication in noises of various spectra are proposed.
Vibration of Circular Plates
Authors: Wah Thein
Published: September 2005

The vibration of circular plates with a large initial tension (or compression) is studied for the case of (a) simply supported and (b) clamped edges. The basic equation used is that of the Poisson-Kirchhoff theory. Numerical results are given.
Frequency Analysis of Vowels Produced in a Helium-Rich Atmosphere
Authors: Beil Ralph G.
Published: September 2005

Frequency analysis was made of vowel sounds produced after inhaling a high concentration of helium. Comparison of helium vowels with normal vowels shows an increase in the component frequencies. The formant ratios are found to remain nearly constant. A slight increase in fundamental frequency was observed, but this is postulated to be due to physiological rather than acoustic effects. The effective change in the velocity of sound in the vocal cavity during a helium utterance is considered.
Scattering of Sound by Sound
Authors: Bellin J. L. S. , Beyer R. T.
Published: September 2005

An experimental attempt is made to determine the presence of scattering resulting from the nonlinear interaction of two finite amplitude sources, operating in water. The two beams cross each other at right angles. A detector crystal, tuned to the summation frequency of the two sources (13.4 Mc), and pivoted about a point above the interaction region, is used to investigate the scattered field. This crystal feeds into an RAO-7 receiver, equipped with a calibrated s meter. The results of these investigations indicate no scattered sound above the noise level of the detection system. Therefore, any scattering present would be several orders of magnitude below that predicted by the theory of Ingard and Pridmore-Brown. The lack of scattered sound is in agreement with the theoretical considerations recently presented by Westervelt. (This work was supported in part by the Office of Naval Research.)
Rotational Relaxation in Nitrogen
Authors: Greenspan Martin
Published: September 2005

The attenuation and speed of sound at 11 Mc were measured in pure N2 over the pressure range 760 to 1 mm Hg using apparatus previously described. The excess attenuation in the nondispersive (low-frequency/pressure) region as obtained from 70 measurements made between 80 and 760 mm Hg is (35.88 ± 0.04%) corresponding to a relaxation number of 5.26 collisions. The results will be compared with those of other investigators.
On Sequential Decisions by Human Observers in a Signal Detection Problem
Authors: Swets John A. , McKey Mary , Green David M.
Published: September 2005

In a sequential test of statistical hypotheses, a sample is taken, and one of three decisions is made: accept H0, accept H1, or take another sample. Samples are taken successively until the resulting sequence of samples is sufficiently persuading in favor of one or the other terminal decision. The criteria which are to be met before making a terminal decision are stated in terms of the error probabilities that lead to maximizing the expected value of a decision. These error probabilities, and hence the average number of samples preceding a terminal decision, are functions of the a priori probabilities of H0 and H1, the values associated with the four possible outcomes of a terminal decision, the cost of taking a sample, and the divergence between the distributions of sample values expected under H0 and under H1. The optimum sequential test generally requires less time on the average than a test of fixed length that yields the same error probabilities.

This paper deals with an experimental application of the theory of sequential testing to the human observer making decisions concerning the presence of signals in noise. Our observers made as many observations as they chose before asserting the existence of noise alone or of signal plus noise. They knew, in each of several experiments which varied in these respects, the values of the situational parameters that ideally govern the choice of the decision criteria. Their performance is compared to optimum performance in terms of error probabilities and average number of observations. A comparison is also made of their relative efficiency in sequential tests and tests of fixed length. [This study was supported by the Operational Applications Laboratory of the Cambridge Research Center under Contract AF19(604)-1728.]
Information Transmission with Elementary Auditory Displays
Authors: Sumby William H. , Chambliss Davis , Pollack Irwin
Published: September 2005

A procedure for transmitting the letters of the alphabet by tone-coded signals was examined in quiet and against a noise background. The procedure employed successive selections, each from among a small number of alternatives, in order to transmit a target-vocabulary of 25 letters. Four stimulus variables: tonal frequency, sound level, location, and duration were examined, one at a time. Successive selections were made among two, three, and five alternatives per variable. With less than 1 min of practice at slow rates of presentation with the two-alternative frequency code, naive listeners were able to receive the entire vocabulary with insignificant error. The highest transmission rate was obtained with a three-alternative, frequency-coded display, at only about 1.5 bits per sec. Transmission of tone-coded signals in noise was nearly equivalent to that in the quiet, when the tonal signals were about 3 db above masked threshold.
Measurement of High Intensity Noise
Authors: Kamperman George W.
Published: September 2005

The problems of fatigue and malfunction due to high intensity noise have become increasingly important in recent years. Accurate and meaningful measurements of the high intensity noise fields present at aircraft and missile structures and electronic components are necessary to understand these problems. This paper discusses characteristics of available microphones for the measurement of high intensity noise. It points out the difficulties frequently encountered with acoustical measuring systems in the presence of intense noise fields. Techniques for calibrating acoustical measuring systems are also described.
Lead-Zirconium-Titanite Microphones for Measurement of High Noise Levels
Authors: Fitzgerald James W. , Leydorf Glenn E.
Published: September 2005

A series of small lead-zirconium-titanite microphones has been developed for the measurement of random air-borne noise fields of sound pressure levels in the range of 45 to 200 db (rc 0.0002 μb) and higher. With a capacitance 1000 μμf and a sensitivity of 93 db (rclv/μl), special preamplifiers are unnecessary for many applications. A substantially spherical beam pattern, even at the higher frequencies (± 3 db @ 35 bc), and a wide-frequency response (1 cps–40 bcps) make these units exceptionally suitable for high noise-level studies. The design is based on the use of ferroelectric cylinder, coaxially mounted on, but electrically and mechanically isolated from, a center aluminum spindle. The whole acoustic head assembly is molded in a Neoprene or silicone rubber jacket resulting in a water-tight, rugged construction. In order to minimize vibration pickup, the acoustic head and stem assembly are mounted in a modified vibration mount with a counter-balancing weight. The acoustic head is also covered with a flexible conductive coating to minimize electrostatic pickup. These and other design features result in a microphone which is truly capable of measuring airborne noise fields, while at the same time discriminating against structure borne vibration, as well as electrostatic and magnetic pickup.
Acoustical Resonances Produced by Combustion of a Fuel-Air Mixture in a Two-Dimensional Duct. I.
Authors: Elias
Published: September 2005

To better understand the mechanisms which initiate and maintain high-frequency combustion pressure oscillations in the air-breathing engine (commonly referred to as “screech”), an experimental program was conducted with a 212-in. by 10-in. model ramjet combustor. Results show that pressure oscillations characteristic of transverse acoustic modes occur as fuel-air mixtures approach stoichiometric values. The particular mode excited is related to orientation of the flame fronts in the duct, which in turn are functions of the particular flame holder geometry. It is shown that heat release associated with the flame fronts occurs in high impedance zones for the modes excited. High-speed motion pictures of the combustion zone during screech show that the flame fronts are serrated, the number of serrations being proportional to screech frequency. The serrations are interpreted to be related to vortex shedding from the flame holder lips. High amplitude oscillations corresponding to the fundamental longitudinal mode occurred when conditions of intense screech were achieved. This mode transference is attributed to increased heat addition in the forward portion of the duct, a position favorable for driving longitudinal modes. Preliminary results show that high turbulence levels produce screech at lower values of fuel-air mixture. (This work was performed under Contract AF 33(616)-2951.)
Free Radicals in the Production of Hydrogen Peroxide by Ultrasound
Authors: Weissler Alfred
Published: September 2005

Further information on the fundamental processes through which ultrasound causes chemical changes has been obtained by a quantitative study of the yield of hydrogen peroxide in irradiated aqueous solutions of “radical scavengers” (formic acid, acrylamide, and allylthiourea, over a wide range of concentrations) saturated with either oxygen or argon. The results are consistent with the view that electrical discharges during cavitation decompose water molecules into H and OH free radicals, which may recombine in like pairs to give H2 and H2O2. In the presence of a substance which quickly reacts with these primary molecular fragments, the yield of peroxide decreases in approximate accordance with the prediction of a radical-diffusion theory. Previous workers have pointed out a certain resemblance between the chemical effects of ultrasound and those of ionizing radiations (α, β, and γ rays); but, as this study shows, there also are substantial differences.
Studies of Sonic Rust Removal
Authors: Fitzgerald James W. , Cook Edward J.
Published: September 2005

The efficacy of sonic fields in the removal of rust from 1020 cold-rolled steel samples is described. Comparative descaling rates with and without the use of a sonic field in various liquid media such as tap water, tap water and detergents, tap water and abrasive grits, acid pickling solutions, chlorinated hydrocarbons, and commercial rust removers are given. In general for chemical rust-removing solution, the time required to descale a rusted specimen without the use of an applied sonic field was 10 to 100 times or more greater than the time required with sonically produced cavitation. Furthermore, much lower concentrations of descaling bath agents were necessary when the sonic field was utilized. Ultrasonic cavitation in other liquid vehicles had little or no effect.