bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Detection of Structural Failure of Mechanical Cables
Authors: Laura Patricio A. , Vanderveldt Hendrikus , Gaffney Paul
Published: September 2005

The mechanical cable is one of the most important components in many ocean engineering systems. The present letter describes preliminary research on suitable methods to detect internal failure of the cable prior to complete breakage.
Effect of Duration on Amplitude Discrimination in Noise
Authors: Henning G. Bruce , Psotka Joseph
Published: September 2005

Amplitude-discrimination performance is found to be independent of the duration of the signals to be discriminated for durations ranging from 20 to 200 msec provided that the ratio of signal energy to noise-power density is kept constant. If the ratio of signal energy to noise-power density is manipulated by altering either the noise-power density or the signal duration, then discrimination performance is also independent of that ratio once it exceeds 20 dB. The implication of these findings is discussed.
Multiple Ratings of Sound Stimuli
Authors: Kerrick Jean S. , Nagel David C. , Bennett Ricarda L.
Published: September 2005

Sixteen brief sounds (music, vehicle sounds, and artificial sounds) were judged on each of 15 bipolar scales by 20 subjects. Without instructions, subjects use the descriptors “loud” and “noisy” as synonomous. On the other hand, subjects do not equate either loudness or noisiness with acceptability, although there appears to be a moderate relationship when only vehicle or aircraft sounds are rated by subjects. The implications of these findings for instructions in psychoacoustic research are discussed.
SUBMISCROSECOND AUDITORY JITTER DISCRIMINATION THRESHOLDS
Authors: Pollack Irwin
Published: September 2005

Thresholds of temporal uncertainty, or jitter, were obtained for auditory pulse trains by computer control of real-time clocks. For high-frequency pulse trains, auditory jitter thresholds below 0.1 μsec (100 nsec) are obtainable.
On Estimating Noisiness of Aircraft Sounds
Authors: Young Robert W. , Peterson Arnold
Published: September 2005

Results of judgment tests on the noisiness of aircraft sounds published during the past decade [and cited by K. D. Kryter, J. Acoust. Soc. Amer. 43, 344–361 (1968)] have been analyzed collectively to find the relative precision with which the judgments are explained by calculated perceived noise level, calculated loudness level, and Sound Levels A, B, C, and D (formerly N). For consistency, all levels have been recalculated, in accordance with current rules, from published noise spectra. Application of standard statistical procedures to the available data indicates that differences among the first three levels and the sixth, in their correlation with judged noisiness, are not statistically significant; only the B and C levels are clearly inferior as predictors of noisiness. A new weighting derived simply from two cascaded RC circuits, with corner frequencies at 2 and 8 kHz, leads to levels of better precision than any of the others, but adoption of this new weighting is not proposed without further study. Since Sound Level A predicted the judged noisiness of the aircraft sounds as precisely as did calculated loudness level or perceived noise level, this readily measured sound level may well be applied to the rating of aircraft noise along with other noises in the community.
Character of Pseudo Surface Waves on Anisotropic Crystals
Authors: Lim T. C. , Farnell G. W.
Published: September 2005

When the free surface is anisotropic, mode of elastic surface-wave propagation can arise that has many of the properties of a normal surface wave but has a phase velocity higher than that of the transverse bulk waves in the corresponding direction. The pseudo surface wave is a coupled mode involving terms decaying rapidly beneath the free surface and a term representing a bulk wave radiating into the solid. For many choices of crystal and plane of propagation, the contribution of the bulk term over a range of directions is small enough that the energy of the wave is essentially concentrated within a few wavelengths of the free surface and flows parallel to the surface as with the normal elastic surface waves. Moreover, in certain specific directions, the bulk term disappears completely and the pseudo-surface wave has all the properties of a normal surface wave. The method of computation of the characteristics of the pseudo surface waves is outlined here and typical results of velocity, displacements and energy flow are given for an assortment of anisotropic crystals and planes of propagation.
Thickness-Twist Vibrations in Beveled
AT
-Cut Quartz Plates
Authors: Pearman G. T.
Published: September 2005

Frequencies and mode shapes of thickness-twist vibrations in beveled, rectangular AT-cut quartz plates have been determined from an infinite-strip model. In addition, the possible use of beveling for mode suppression has been studied. Experimental results from beveled plates verify the theoretical predictions. Descriptions of the calculations and comparisons with the experimental results are included. Thickness-shear frequencies and mode shapes were also calculated using a similar model and are compared with thickness-twist results.
Theoretical Analysis of the Performance of an Air-Modulated Speaker
Authors: Meyer Warren A.
Published: September 2005

A theory is developed that predicts the performance of the air-modulated speaker by assuming that the pneumatic energy is converted to acoustic energy by a mixing process similar to that which takes place in the jet pump. To derive these relationships, it is necessary to assume, for certain portions of the flow that the effect of the nonsteady terms is negligible. Owing to the high intensity of the sound waves generated, it is not possible to use the usual small-disturbance approximations normally employed in acoustic problems. The nature of the assumptions used requires that the results be limited to a frequency range that is above the rolloff frequency of the horn and below 100-500 Hz, depending on the slot geometry. The analytical results agree well with the available experimental data both for sound-pressure level and efficiency; they should thus be useful for design purposes.
Mach Bands in Hearing
Authors: Carterette Edward C. , Friedman Morton P. , Lovell John D.
Published: September 2005

It is difficult to explain the extraordinary capacity of the ear in discriminating pitch without assuming the existence of laterally inhibitory neural nets fed by cochlear potentials. On such an assumption, we have sought to show edge effects in direct auditory masking analogous to Mach bands found in vision. Noise bands having theoretically infinite attenuation rates outside the passband were generated by computer from 56 sinusoids spaced randomly by frequency. Monaural pure-tone-masked audiograms were obtained for each of four subjects for each of two such noise bands (480–580 Hz and 960–1160 Hz) at sensation levels of 20, 30, 40, 50, and 60 dB. Edge effects, as measured by contours of threshold shift, were revealed for all subjects, at every loudness, and were similar for both noise bands. Sharpening was greater at the low frequency end of a band and grew nonlinearly with loudness, as did upward spread of masking. Sharpening was greater for an interrupted than for a continuous masked tone and may be maximal for relatively low interruption rates. The data are consistent with the existence of laterally inhibiting neural nets and are discussed in relation to their neural basis and to other phenomena such as the pitch of noise bands and the regions of increased sensitivity often found in abrupt hearing loss.
Large-Amplitude Damped Free Vibration of a Stretched String
Authors: Anand G. V.
Published: September 2005

The equations of motion of a vibrating string are derive, and it is shown that a coupling exists between the longitudinal and transverse modes of vibration. Free transverse vibration of small order, under sinusoidal initial conditions, is analyzed. Under these conditions, the equations are separable. The time-dependent parts of the equations are solved by the method of variable amplitude and phase. It is seen that, when the vibration is nonplanar, part of the energy oscillates between the mutually perpendicular transverse components with a frequency proportional to the nonlinearity parameter α. The path of any point on the string is shown to be an ellipse with slowly rotating and shrinking axes.
Theory of Holographic Interferometry
Authors: Brown G. M. , Grant R. M. , Stroke G. W.
Published: September 2005

A simple theory of three forms of holographic interferometry “time-average,” multiple-exposure, and “real-time” (live) interferometry is presented, based on a new development in holographic “image synthesis” (complex amplitude addition and subtraction), introduced in 1965 by D. Gabor and G. W. Stroke et al. They demonstrated the remarkable property of holography: Interference can occur between two or more light beams that are not superimposed either in time or in space, if the holographic intensities corresponding to the beams are obtained with the aid of a coherent reference-background beam of the same spatial shape and if these intensities are successively added in the same hologram. Following the independent discovery of holographic interferometry, in 1965, by J. M. Burch; by R. L. Powell and K. A. Stetson; and by L. O. Heflinger, R. F. Wuerker, and R. E. Brooks, among others, it was found that two or more successive photographic additions of the hologram intensities (corresponding to two or more sequential positions or shapes of a given object) would thus indeed permit one to “synthesize,” in the form of an interferogram, the complex sum of the spatial-electric-field vectors, corresponding to each object-point position, as if the different object-point positions had all existed simultaneously rather than sequentially, as they do during the hologram recording (for instance in the case of multiple holographic-image recording of a vibrating object). The rigorous equations we present, notably in vector form, for the general cases of practical interest bear out the equations previously derived by a number of authors, for some special cases, frequently in heuristic form.
Dichotic Summation of Loudness
Authors: Scharf Bertram
Published: September 2005

The over-all loudness of a pair of equally loud tones presented dichotically, a different frequency to each ear, is independent of the frequency separation between the two tones. This rule applies over the whole range of frequency separations tested, from 0 Hz to several thousand hertz; hence, dichotic tone pairs are just as loud as a binaural pair (same frequency to each ear). Both binaural and dichotic pairs, however, are generally less than twice as loud as a component presented by itself. The over-all loudness is invariant even though at narrow frequency separations the components of a dichotic pair interfere with each other so that each component is softer when heard in the presence of the other than when heard by itself. At wide separations, where two distinct auditory images are reported, the loudness of a component is the same whether presented with or without the contralateral tone.
Elastic Wave Propagations and Acoustical Birefringence in Stressed Crystals
Authors: Tokuoka Tatsuo , Saito Masakatsu
Published: September 2005

The elastic wave propagations in deformed crystals with any symmetry are investigated theoretically. The rotationless acoustical tensor, which specifies the propagation condition, consists of the tensor based on the natural unstressed state and the perturbation term being proportional to the stress. The perturbation theory is applied to nondegenerate and degenerate cases with respect to the quasitransverse wave velocities. The perturbed wave velocities and the polarization directions are formulated by the stress suppressed on the crystals, and then the general formulas for the acoustical birefringence depending on the second- and third-order elastic constants are reduced. The difference of the quasitransverse wave velocities is expressed by the sum of two terms: the difference of these in unstressed crystals due to the intrinsic anisotropy and the perturbation term due to the stress. In the cases of the cubic system and of the isotropic material, the explicit relations are calculated. For the isotropic material, the so-called stress-acoustical law holds.
Consonance Theory Part II: Consonance of Complex Tones and Its Calculation Method
Authors: Kameoka Akio , Kuriyagawa Mamoru
Published: September 2005

A theory for calculating subjective dissonance of static complex tones has been established. The theory proposes a dissonance perception model that assumes that the mutual interactions between two components constitute an essential additive unit contributing to the dissonance. The model introduces a new concept of “dissonance intensity” in a certain process of dissonance perception and extends the “power law” to the dissonance sensation, which is not clearly related to a certain physical value. Practical calculation procedures are described according to the experimental results of dyads in Part I. Theoretical calculation for various kinds of complex tones showed good agreements with psychological experiments. An application to chords of synthesized harmonic complex tones predicted great dependence of consonance characteristics on the harmonic structures, which are not taken into account in the conventional theory of harmony. It became clear that the fifth (2:3) is not always a consonant interval. A chord of two tones that consists of only odd harmonics, for example, shows much worse consonance at the fifth (2:3) than at the major sixth (3:5) or some other frequency ratios. This was proved true by psychological experiments carried out in an other institute (Sensory Inspection Committee in the Japan Union of Scientists and Engineers) with a different method of scaling. Thus, the fact warns against making a mistake in appling the conventional theory of harmony to synthetic musical tones that can take variety in the harmonic structure. The theory next explains difference in quality reduction of reproduced sounds through a nonlinear audio instrument by the physical characteristics of input sources, and it provides a measure of evaluating nonlinear distortion.
Some Effects of the Nonuniform Atmosphere on the Propagation of Sonic Booms
Authors: Kane E. J.
Published: September 2005

A recent theoretical development to describe the propagation of weak shock waves through a nonuniform media has been used to investigate the effect of stratified atmospheric models on the sonic boom generated by an airplane in steady level flight. Effects of variations in temperature, pressure, and winds with altitude on the strength, lateral distribution, and extent of the shock waves on the ground are discussed. Comparisons of theoretical results with flight-test data are presented.
Effects of Sonic Boom on People: Review and Outlook
Authors: von Gierke Henning E.
Published: September 2005

This introduction to the second part of the Sonic-Boom Symposium reviews the history of observations on human reactions to the sonic boom from the time when the boom was a demonstration curiosity to the present day where reaction of the population to the sonic boom is a scientific problem of technical, economic, social, and political consequences at the national and international level. The field programs conducted by the USAF and NASA over the last 15 years and over the last 5 years by the FAA were all of limited scope with respect to exploring direct and indirect physiological and psychological human reactions to sonic booms of different intensity and exposure frequency. Although the data accumulated might be adequate to decide on preliminary stopgap exposure criteria, it is obvious that a broader approach to the problem is required. Laboratory work in support of these questions has hardly been started. Neither conventional acoustic and vibration generators for boom-type stimulation nor special equipment for high-fidelity sonic-boom simulation have been fully utilized. Some of the open questions and possible approaches are discussed as part of a broad, long-range research program required to come up with scientific data as bases for operational sonic-boom exposure criteria.
The Determination of Reverberant Sound Absorption Coefficients from Acoustic Impedance Measurements
Authors: London Albert
Published: September 2005

A procedure is outlined whereby acoustic impedance measurements may be utilized to predict reverberant sound absorption coefficients. The average of coefficients for the six standard frequencies so determined agrees closely with the average reverberant coefficient, for cases where the material may be said to obey the normal impedance assumption. A method of utilizing acoustic impedance tube measurements in the field, for acceptance testing, is indicated which should be applicable even in cases where the normal impedance assumption is violated. On the theoretical side, best agreement with experiment was obtained by utilizing a new kind of statistics which associates, with each wave packet in a random field, a scalar quantity equal to the square of the absolute value of the sound pressure in each packet, instead of the customary energy flow treatment. On the other hand, it was found necessary to utilize a semi-empirical concept of equivalent impedance as distinguished from the usual complex impedance treatment.
Pulse Statistics, Analysis of Room Acoustics
Authors: Bolt R. H. , Doak P. E. , Westervelt P. J.
Published: September 2005

Many sounds of speech and music more nearly resemble pulsed wave trains than continuous sounds abruptly terminated as used in classical reverberation measurement. It is therefore not surprising to find that two rooms can differ markedly in acoustical quality even if they appear identical under reverberation analysis which ignores details of short transients. This paper introduces a pulse statistics point of view which takes immediate account of the pulse-like nature of common sounds. Fundamentally, the method consists in examining the response of the room to a short pulse. The walls are replaced by an array of image sources (simple images if the walls are hard, or appropriately modified if there is absorption). These image arrays are then considered statistically. From this approach one can derive such classical quantities as reverberation time and mean free path. One can also analyze the detailed nature of discrete reflections including interference effects and thus obtain an average correlation between room geometry and the character of its pulse response. Idealized experiments in a hard-walled rectangular room are employed to illustrate the essential features of this approach. A point source emits an exponentially damped 3000-c.p.s. wave train of about 2-milliseconds duration. The received signals are recorded logarithmically on an oscillograph and the system is calibrated for quantitative results. Several dozen discrete reflections can be measured and correlated with calculation. The pulses merge into a more or less continuous background after a time which is calculated and confirmed experimentally. Detailed differences arise according to the positions of the source and microphone in the room. This approach appears useful for studying auditoriums by scale models and for investigating speech intelligibility in rooms.
Sound in the Theater II
Authors: Burris-Meyer Harold , Mallory Vincent
Published: September 2005

The application of electronic facilities to the control of sound in the legitimate theater has been subject of a long term research project subsidized by the Rockefeller Foundation. Progress reports have been made from time to time before the Acoustical Society. Complete control of the auditory component of the show was achieved immediately prior to the war. However, general acceptance of the technique has been delayed because equipment was too elaborate to be carried on the budgets of any but the largest shows. This paper reports the development, also under Rockefeller Foundation subsidy, of a modular sound control system which appears to be suitable to all needs of the legitimate theater and specialized needs in other entertainment forms.
Vibration: The Engineer's Viewpoint
Authors: Roberts H. C.
Published: September 2005

A description of some vibration problems faced by the structural engineer, with comments on the magnitudes requiring measurement, and the basic methods of measurement and of vibration analysis.
A Strain-Gauge Type Artificial Mastoid
Authors: Carlisle R. W. , Pearson H. A.
Published: September 2005

An artificial mastoid for testing bone conduction receivers is described. It consists essentially of a stiff metal bar having a fundamental resonant frequency above the measurement range, with a strain-sensitive translating element fastened to the under side and a compliant pad on top. The translating element is a slab of activated ceramic, which is essentially invariant to humidity and temperature variations. The compliant pad generally used is Koroseal ♯74, which simulates the flesh over the mastoid prominence reasonably well. Koroseal ♯15 simulates flesh better but is less rugged. Calibration methods are discussed.
Supplementary Paper No. 1. Force Equations of Motion
Authors: Roberson R. E.
Published: September 2005

In the usual formulation of the equations of motion for dynamical systems, position and velocity coordinates are chosen as dependent variables. In some problems, however, the forces in the system may be of greater interest than the configuration coordinates. This paper concerns the problem of writing equations of motion in which forces are dependent variables. It is shown that such equations arise from a “loop analysis” of the mechanical schematic diagrams, as contrasted with the “nodal analysis” which leads to the ordinary equations of motion. The analytic treatment of certain classes of mechanical systems, without reference to schematic diagrams, can lead to these “force equations of motion” under conditions which are discussed. Some of the considerations which are required in extending this analytic treatment to more general systems are indicated.
Impressions of Audiology in Europe
Authors: Silverman S. R.
Published: September 2005

The author will discuss his impressions of audiological activities which he observed in England, Holland, Sweden, Switzerland, and France on a recent speaking and inspection tour of these countries. Particular attention will be paid to clinical and research programs as they relate to disorders of communication through speech and hearing. In general there is a good deal of constructive activity directed by capable personnel, but in some countries lack of facilities slows up progress.
The Calculation of Vowel Resonances
Authors: Dunn H. K.
Published: September 2005

X-ray photographs taken during vowel phonation indicate that for many vowels the vocal tract may be approximated by a series of cylindrical sections. This makes possible the use of distributed impedance theory in the calculation of the transmission through the tract, yielding multiple resonances. Several vowels have been calculated, from dimensions based on the x-rays, and in each case three resonances have been found in the right range. Several conclusions can be drawn about the origin of the first three vowel formants. The theory has been supplemented by the use of an equivalent electrical network, by means of which understandable vowels can be produced artificially, when supplied with energy from a suitable complex source.
Perceptibility of Frequency Modulation (“Flutter”) in Pure Tones
Authors: Schecter Harry
Published: September 2005

The minimum perceptible peak-to-peak frequency deviation in a frequency-modulated tone, which is a form of the difference-limen (DL) for frequency, was measured monaurally over a wide range of modulation rates (0.5 to 1000 c.p.s., sinusoidal modulation) for tones of three frequencies (333, 1000, and 3000 c.p.s.) and three sensation levels (40, 60, and 80 db). Several psychophysical methods were investigated; the method of constant stimuli appears best suited for extensive measurements of this threshold. As a matter of expediency, however, most of the results were obtained by the method of adjustment which, though somewhat more difficult, will also yield consistent results. The DLs obtained agree with the values reported by Shower & Biddulph at a modulation rate of 2 c.p.s., but the variation with rate differs from that obtained by them. At low rates (4 to 75 c.p.s.) the DL is approximately proportional to the square root of the rate but independent of sensation level. The DL reaches a maximum at a rate in the vicinity of 100 c.p.s.; at higher rates the decrease is slight at a sensation level of 40 db and progressively more pronounced at higher sensation levels (60 and 80 db). A few exploratory measurements at rates below 2 c.p.s. indicate a minimum in the vicinity of 2 c.p.s. The values obtained at high rates can be correlated with pure-tone masking data. The results at low rates suggest that a re-examination of the concept of differential frequency sensitivity may be in order. It is tentatively proposed that the DL be defined as the minimum perceptible frequency change for single transitions, and measured as a function of transition time as well as frequency and sensation level.
Loudness Balance Methods for Earphone Response Measurement
Authors: Martin Daniel W. , Touger Martin L.
Published: September 2005

Simple procedures are given for the subjective measurement of earphone response by two methods. The first method, which is rather widely recognized, requires the subject to match the loudness of an earphone tone to the loudness of a free-field reference tone of the same frequency. Interpretation of the data from this test is direct, but the facilities, technique, and time required are considerable. A second method, less widely used, involves the loudness balancing of an earphone tone of variable frequency to that of an earphone reference tone of fixed frequency and level. This method is much simpler, and can be used to measure earphone performance under circumstances where the first method is virtually impossible. However, the interpretation of the test data is less direct. This paper is an analysis of the two methods which attempts to develop a correspondence between the data obtained by the two methods.
Sound Measurements for Psychophysical Tests
Authors: Munson W. A. , Wiener Francis M.
Published: September 2005

The results of psychophysical tests on the auditory sensory system usually show much more variability than experiments involving only physical measurements of sound waves. This has resulted in the general impression that the variance of thresholds of acuity and other hearing measurements is largely due to the inability of the observers to give consistent responses. This paper reports the results of a series of threshold measurements made under carefully controlled conditions and accompanied by search tube measurements of sound pressures in the ear canals of the observers. The small variances obtained suggest that the large variability usually experienced in psychophysical work may be partly due to inadequate techniques for measuring the levels of the stimuli that activate the sensory system.
The Effect of Thermal Masking Noise on the Pitch of a Pure Tone
Authors: Schubert Earl D.
Published: September 2005

When a pure tone and a masking noise are fed into the same ear simultaneously, the pitch of the pure tone is raised. The effect is more pronounced at low loudness levels and is progressively greater as the frequency of the tone rises. Apparently the phenomenon is not present if the pure tone is 20 db or more above its masked threshold. Nineteen graduate music students served as subjects in the experiment. Control measurements were made to estimate the effects of diplacusis and of the difference in intensity between the masked and the unmasked pure tone when they were matched in loudness.
Free-Field Thresholds Versus Pressure Thresholds at Low Frequencies
Authors: Rudmose Wayne
Published: September 2005

In 1933 Sivian and White closed their paper in the Journal of the Acoustical Society with the statement that at low frequencies the difference between the thresholds for minimum audible field and minimum audible pressure could not be explained. To investigate this problem further monaural field thresholds and monaural pressure thresholds have been obtained, the latter for cavities varying from 6 cc to over 800 cc. A probe tube, attached to a W.E. 640-AA condenser microphone, was inserted near the ear drum and the sound pressure determined with the probe remained invariant under transformations of volume. Similarly the same probe was used to determine the pressure for free field. When sufficient care is taken to eliminate muscle noises, breathing noises, etc., and to insure monaural listening, there appears to be no significant difference between minimum audible field and minimum audible pressure at low frequencies. This result is based on measurements made with a limited number of subjects; however, to secure more representative data measurements are being continued with a larger number of subjects.
Preferred Rate and Extent of the Frequency Vibrato
Authors: Corso John F. , Lewis Don
Published: September 2005

The purposes of this study were, first, to determine listener preferences for rate and extent in the frequency vibrato of a complex tone at each of five octave levels in the equal-tempered scale; and, second, to discover the manner in which preferences varied with the listeners' musical training or auditory capacity. The complex tone employed at each level was generated by a multivibrator unit. This tone was electronically modulated with rates of 5.5, 6.0, 6.5, and 7.0 pulsations per second; the extents of modulation were 0, 0.10, 0.25, and 0.40 of a step. By combining each rate with each extent, twelve vibrato tones and one “straight” tone were obtained. These tones were presented for preference judgments by the method of paired comparisons. The subjects were divided into two categories: (1) individuals with little or no formal musical training as determined by answers on a personal questionnaire (N = 331), and (2) individuals with sufficient musical training and ability to be members of the University of Iowa symphony orchestra or chorus (N = 54). Rank order scales of vibrato preference were obtained for these two groups. In addition, preference scales were obtained for untrained subjects according to their ability to discriminate pitch, time, and timber as determined by tests from the Seashore battery. A comparison of the preference scales for untrained individuals indicated that (a) an extent of 0.25 step was preferred over a wide portion of the equal-tempered scale, (b) rates of 6.0, 6.5, and 7.0 pulsations per second were about equally preferred over the same range, and (c) native auditory ability had little effect on vibrato preference. The trained musicians tended to prefer the same rates of 6.0 and 6.5 pulsations per second as did non-musicians, but the musicians favored a narrower extent (0.10 of a step).
A Recorded Word Test for Auditory Discrimination
Authors: Davis H. , Keaster J. , Hartwig W. , Harrison C. E.
Published: September 2005

The phonetically-balanced monosyllabic word lists of the Psycho-Acoustic Laboratory have proved clinically useful for assessing practical auditory discrimination. A new set of recordings has been prepared that provides (1) short intervals between items, (2) accurate monitoring of intensity, and (3) uniformity of a given item as it occurs in different scramblings. The uniformity was obtained by dubbing the original material (spoken by Dr. Ira Hirsh) to magnetic tape, cutting the tape, reassembling the pieces in random order, dubbing to a disk, scrambling the same pieces again for another dubbing, etc. Four scramblings each of six 50-word lists have been used to determine the properties of the new recordings. For a team of twelve trained normal listeners, the articulation curve rises from zero at an intensity just above the threshold of detectability. Its initial slope is about 4 percent per db and its shape is convex upward throughout, rather than sigmoid. Its shape is convex upward throughout, rather than sigmoid. At 35 db re: 0.002 microbar it has reached 85 percent. From there the increase is quite steady at 0.5 percent per db, but the score does not reach 98 percent until 60 db re: 0.0002 microbar. Masking with white noise at successive signal-to-noise ratios yields approximately the same curve. An S/N ratio of 24 db lowers the articulation score to 90 percent. The most difficult words are in each case those containing weak sibilants among their terminal consonants. On the basis of an item analysis of the errors and with elimination of some of the less familiar words we are preparing for clinical use several shorter lists that will be closely comparable with one another in all scramblings and that will have the same distribution of difficulty as the original 50-word lists.
On the Mechanism of Auditory Frequency Selectivity
Authors: Licklider J. C. R.
Published: September 2005

One of the principal problems of audition is to explain how, in psychophysical experiments, the ear can display a high degree of frequency selectivity when, under direct observation, the cochlea is seen to have a broad selectivity curve. Evidently, the neural part of the auditory system sharpens the cochlear frequency analysis. Two neural operations are hypothesized. First, groups of neurons perform, upon the output of the cochlea, a double differentiation with respect to place. Second, other groups behave as autocorrelators, responding preferentially to periodic excitation. With the aid of these hypotheses, a number of auditory phenomena can be explained. Of particular interest is the relation of the double-differentiation hypothesis to the electrophysiological observations of Galambos and Davis: an inhibitory process of the kind they observed is implicit in the hypothesis.
The Effect of Exposure to Loud Sounds Upon the Response to Clicks
Authors: Rosenblith Walter A. , Galambos Robert
Published: September 2005

The normal click response recorded at the round window of a cat consists, as is well known, of so-called microphonic and neural components. When the ear has been exposed to loud sounds this click response is modified. The neural components are reduced in size for time intervals whose duration depends upon the intensity and the spectrum characteristics of the exposure sound and the duration of the exposure. The microphonic components are, if at all, much less affected. The recovery cycle of the neural components and their behavior at levels well above threshold will be discussed in the light of previously reported findings on temporary deafness in man.
A Dynamical Theory of the Cochlea
Authors: Peterson L. C. , Bogert B. P.
Published: September 2005

A hydrodynamical theory is given for a model of the cochlea. The model consists of two channels of varying but equal cross sections. The channels are separated by an elastic membrane with variable dynamical constants. The two channels are interconnected at one end, and the entire structure is rigidly enclosed except for two accessible areas corresponding to the round and oval windows. The equations of motion, continuity including the effect of the membrane, and appropriate boundary conditions are formulated. As a first step towards a complete analysis the non-dissipative case is considered. Numerical solutions are found using experimental data obtained by G. v. Békésy. Localization phenomena and phase velocities are found to be in broad agreement with experimental data.
The Anatomy of the Ear
Authors: Covell Walter P.
Published: September 2005

Several features of the gross and microscopic anatomy of the ear will be discussed and illustrated, particularly some features that frequently enter into mathematical and physical theories of the action of the ear. Anatomical dissections and microscopic preparations will be on exhibition after the presentation.
Supplementary Paper No. 3. Masking of Tones by Narrow Bands of Noise
Authors: Shewmaker C. A. , Schafer T. H. , Gales R. S.
Published: September 2005

The concept of the aural critical band introduced by Fletcher has proved to be very useful in interpreting masking phenomena in many Naval applications, as well as others. The validity of this concept rests in a large measure on the behavior of the masked threshold for pure tones masked by bands of noise narrower than the width of the critical band. In order to gather additional data in this region, narrow bands of noise having perfectly sharp edges were synthesized by superposition of single-frequency tones spaced approximately one c.p.s. apart. These bands of widths 8, 16, 32, 48, and 96 c.p.s. were used to mask pure tones centered in the band. All five band-widths were studied at 200, 800, and 3200 c.p.s. for 20 observers. The results support Fletcher's finding that, for noise bands narrower than the critical band, a pure tone at the center of the band becomes audible when its intensity equals that of the noise.
The Electrical and Acoustical Performance of Some Commercial Audiometers
Authors: Morrical K. C. , Benson R. W. , Davis H.
Published: September 2005

The American Medical Association and the American Standards Association have prepared proposed specifications covering the performance of audiometers for clinical and diagnostic purposes. The electrical and acoustical performance of a number of commercially available audiometers has been examined to determine how closely the proposed specifications have been met in these instruments.
The Loudspeaker Problem
Authors: Mawardi Osman K.
Published: September 2005

Most analyses of loudspeaker performances are based primarily on the consideration of details of the electromechanical coupling. This approach has proved too inadequate to handle the problem of explaining the phase response of typical loudspeakers or the response to transients. An attempt has been made to set up a general expression relating the free-field sound pressure at a remote point to the electric signal applied to the loudspeaker terminals. The formulation is in integral form and utilizes Green's functions. No solutions of the integral equations have yet been found for loudspeakers of arbitrary shapes, but it appears possible to apply to this problem the same electric circuit analysis techniques which represent the transfer function of the system in terms of the location of poles and zeros in the complex plane.
Electrostatic Loudspeakers
Authors: Janszen Arthur A.
Published: September 2005

New materials and techniques have made possible the design of useful electrostatic loudspeakers. High polarizing and signal potentials across air gaps which are large enough to permit diaphragm excursions of a magnitude necessary for the production of low frequencies, together with an acoustically transparent stationary electrode and a diaphragm which is light compared with the mass of the entrained air, result in unusually good pressure response and phase response characteristics as well as a useful amount of power from relatively small areas. The only resonances are those which arise between the compliance of the diaphragm material and the mass of the entrained air, and these can be made to occur below the useful range of audiofrequencies. The active radiating area is made to retract with frequency to preserve good polar response and to improve the impedance characteristic, by making the distributed capacitance of the loudspeaker part of a resistance-capacitance network. The extremely smooth pressure response resulting from the absence of resonances makes the loudspeaker suitable for the production of transient acoustic signals. Response curves and design data are presented.
Ultrasonic Study of Rubber at Low Temperatures
Authors: Nolle A. W.
Published: September 2005

A method is described for measuring velocity and attenuation of ultrasonic waves in a rubber lamina in a solid ultrasonic transmission line. The method is less convenient than liquid-path techniques previously described but has the advantages (a) that measurements are made possible at low temperatures where the large viscosity of liquids creates difficulty; (b) that transverse (shear) waves can be studied provided the sample is rigidly bonded into the transmission line. Pulse techniques are used. A buna-N (Hycar OR-15) vulcanizate is studied at frequencies of 2, 5, and 10 Mc, and at temperatures from −90°C to 75°C. At constant frequency the attenuation for bulk (longitudinal) waves becomes relatively temperature-insensitive below the range of appreciable dispersion (e.g., below −30°C at 10 Mc). Complementary shear-wave measurements indicate that compressional viscosity is always much less important than shear losses as a cause of bulk-wave attenuation; the relatively constant low temperature bulk-wave attenuation appears to result from a shear “viscosity” which is not strongly temperature-dependent but which decreases with increasing frequency. Numerical values for compressional viscosity are not given by present results because sample-to-solid bonds employed in shear-wave measurements introduce uncertainty in the data. The compressional modulus is found to be nearly independent of temperature.
The Generation of Harmonics by Small Circular Orifices
Authors: Westervelt P. J.
Published: September 2005

A spectral analysis was made of the sound field emanating from a small orifice set flush in the top of a table which acted as an infinite baffle. The orifice was driven at a single frequency at various intensities by an electromagnetic horn exciter, coupling through a small cavity below the baffle. At high intensities all harmonics up to the fortieth have been detected. Starting at a distance of one radius from the center of the orifice, the fundamental component of the sound pressure is observed to decrease at a rate of six decibels per distance doubled, indicating that the orifice acts as a spherical source whose radius is that of the orifice. The higher harmonic components decay at the same rate as the fundamental indicating that, for the levels considered, essentially no integrative interactions occur between the harmonics while progagating away from the orifice. Thus it appears that harmonic generation occurs locally at the orifice. The successive odd harmonics are invariably stronger than the immediately preceding even harmonics. Even at moderate levels, the third harmonic may lie less than five decibels below the fundamental component. A theory based upon the non-linear wave equation in spherical coordinates has been developed which accounts for the first two harmonics semiquantitatively. No account is taken of turbulence or rotational terms in the theory.
A Small Crystal Probe Transducer for Ultrasonic Studies
Authors: Cooper Herbert W.
Published: September 2005

To facilitate the exploration of complex sound fields at frequencies up to 400 kc, a small probe transducer has been constructed which utilizes a pair of lithium sulfate crystals as the sensitive element. These are one millimeter in diameter and one-half millimeter thick and are cemented, back to back, to an electrode formed from the inner conductor of a small transmission line. The outer conductor is a brass tube ten centimeters long and one and one-half millimeters in diameter. A conventional preamplifier permits proper impedance matching and insertion of a calibrating voltage. A free-field reciprocity calibration indicates a sensitivity of 155 db below one volt/dyne/cm2, at 400 kc. Directivity patterns indicate that improvement in non-directionality can be expected by the use of a single crystal.
Stage I Modes of a Rectangular Whistle
Authors: Nyborg W. L. , Woodbridge C. L.
Published: September 2005

It has been shown that a whistle, like an organ pipe, consists essentially of two components, (1) a jet-edge (JE) system and (2) a resonator, or cavity. Several whistles, with different rectangular cross-section dimensions, have been constructed. The JE system of each whistle has been duplicated separately so that the operation of each whistle could be compared with the operation of the corresponding independent JE system. Some properties of JE systems alone were discussed at a previous meeting. This paper is concerned with whistles themselves, and particularly with the numerous modes of self-oscillation that may arise when a whistle is blown. The discussion is restricted to those modes for which the JE system of the whistle is believed to be operating in Stage I. The modes of whistle self-oscillation are closely related to the normal modes of vibration of the air in the whistle cavity. These latter may be determined approximately by considering the cavity to be a rectangular room with five rigid walls and one “soft” wall of small acoustic impedance. In general, a given mode, say N, of whistle operation will be excited when the frequency of the edge tone, to which the JE system by itself would give rise, is approximately equal to the characteristic frequency fN, of the calculated cavity mode N. This has been found to be true for tangential as well as axial cavity modes. When operation is in mode N, the whistle frequency may lie anywhere in a small frequency interval whose upper limit is fN.
Recent Methods for the Measurement of Sound Transmission in the Ocean
Authors: Urick R. J.
Published: September 2005

The transmission of sound in the ocean has recently been investigated by two methods. In one, a transducer mounted on a submarine served as a sound source of controllable depth, range, and frequency. A string of six hydrophones suspended from a surface vessel enabled the sound field to be measured at six different depths. Measurements at eight and sixteen kilocycles were obtained on a cruise in Caribbean waters and have been plotted as transmission anomaly cross sections showing contours of equal sound level after the removal of spherical divergence. In the other method, the submarine was replaced by a surface vessel from which a sound projector could be lowered to specified depths. This method, employed on a cruise in Middle Atlantic waters, permits longer ranges to be reached, but yields a density of data insufficient for contouring. A second method of lucidly representing the sound field is given.
Speech Interference Levels as Criteria for Rating Background Noise in Offices
Authors: Beranek L. L. , Newman R. B.
Published: September 2005

On the basis of a number of surveys in commercial offices, criteria for tolerable office background noise levels are proposed. Questions were asked of people working in these offices regarding their ability to telephone, to confer and to perform their work under the existing noise conditions. The speech interference levels of the background noises were determined in each case. The results are presented in a chart, which rates the noise conditions as a function of speech interference levels in each of three general types of offices, (a) executive offices, (b) general clerical offices, and (c) business machines offices.