bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustical Characteristics of Noise Produced by Snapping Shrimp
Authors: Everest F. Alton , Young Robert W. , Johnson Martin W.
Published: September 2005

Some marine animals produce sounds which, under certain conditions, completely dominate the ambient noise in the sea. The snapping shrimp (not to be confused with the edible shrimp) are the most widely distributed of these animals; they are frequently less than 3 cm in length and produces the sound by snapping of the claw. Shrimp noise is likely to be found around the world in tropical and subtropical waters less than 55 meters deep wherever rock, coral, or other material on the bottom provides interstices in which shrimp thrive. This paper describing the acoustic output of the snapping shrimp (Crangon and Synalpheus) is based upon measurements made off the Southwestern and Southeastern coasts of the United States, the Hawaiian Islands, and several islands in the Southwest Pacific. Over a shrimp bed, the noise spectrum is found to be roughly independent of frequency from 2 to 24 kc (the upper limit of measurement), whereas the ambient noise normally present in the deep sea decreases with frequency. There is a broad peak in the shrimp spectrum somewhere between 2 and 15 kc. Over a shrimp bed the noise at 20 kc is about 25 db above the ambient noise which accompanies a sea state of 2 (waves less than a meter high, not including swell). For low sea states, shrimp noise is appreciable a mile or more from the boundary of the bed. The maximum diurnal variation of shrimp noise is from 3 to 6 db, the noise being greater at night. Single snaps from isolated specimens have been subjected to a Fourier integral analysis which indicates a spectrum comparable to that measured over shrimp beds where the underwater sound consists of a multitude of snaps. A typical peak sound pressure at the distance of a meter from a single shrimp is of the order of 200 dynes/cm2.
The Atonal Interval
Authors: Pollack Irwin
Published: September 2005

Thresholds for the detection of the presence of a sinusoidal signal (thresholds of audibility) and thresholds for the perception of the tonal character of the signal (thresholds of tonality) were determined by three listeners over a wide range of audible frequencies. At each of the frequencies tested, the threshold of audibility was found to be significantly lower than the threshold of tonality. The difference between the two thresholds—the atonal interval—ranged from about 2.5 db at 500 c.p.s. to about 6.5 db at 4000 c.p.s. Little difference was found between the variabilities of the two thresholds.

Preliminary measurements indicated that acuity of frequency discrimination changes quite abruptly at the threshold of tonality. Below the threshold of tonality, frequency discrimination is very poor; above the threshold of tonality, frequency discrimination is markedly more acute.
The Influence of Interaural Phase Relations upon the Masking of Speech by White Noise
Authors: Licklider J. C. R.
Published: September 2005

If a communication engineer, confronted with a sound wave consisting of speech mixed with audible random noise, were requested to build a device to separate the speech from the noise, he would be hard pressed to produce a mechanism as effective as the human auditory system. But if he were given two waves, one a sample of speech plus a sample of random noise, the other the same speech minus the noise, he would invoke the elementary mathematical (or electronic) processes of addition and subtraction and oblige in short order with noise-free speech and with speech-free noise.

This paper examines the performance of the (binaural) human auditory system in handling the two-wave problem. The effectiveness of the solution is judged in terms of the intelligibility of speech heard against a background of white noise. If monaural intelligibility is taken as a standard of comparison, it is found that the advantage of binaural presentation of the speech and the noise depends upon the interaural phase relations. The auditory system handles best the problems that are easiest for the engineer, though not as effectively as the engineer would handle them. Intelligibility is highest with noise plus speech in one ear, noise minus speech (i.e., the noise wave plus the inverted speech wave) in the other. Words are understood almost, but not exactly, as well with speech plus noise in one ear, speech minus noise (i.e., the speech wave plus the inverted noise wave) in the other.

These modes of presentation, in which either the speech waves or the noise waves in the two ears are 180 degrees out of phase, yield word articulation scores as much as 25 percentage units higher than the more conventional mode of presentation in which both the speech waves and the noise waves in the two ears are in phase. Observations with other interaural phase relations and with monaural-binaural presentation of speech and noise are also described.

The results suggest a means of providing a small but probably significant improvement in reception whenever speech is heard through earphones in the presence of ambient noise. The scheme is simply to reverse the connections of one of the earphones.

The significance of the results for the theory of masking is discussed.
The Perception of Short Bursts of Noise
Authors: Miller George A.
Published: September 2005

Short bursts of random noise were used to study the perceptual growth and decay of the noise experience. Noise, unlike sinusoidal tones, does not change materially in spectrum as the duration of the sound is varied.

A short burst of noise must be more intense in order to be equal in effectiveness to a longer noise. Thus the threshold of hearing is lowered by increasing the duration of the noise up to durations at least as long as 1 sec. The loudness of an intense noise, however, depends upon its duration up to durations of only 65 msec. Judgments of the slowest rate of decay of a noise which sounded indistinguishable from an abrupt termination also led to the concept of a critical time of approximately 65 msec. for the sensation to decay to threshold from any steady magnitude of stimulation.

From these data it is inferred that the auditory system acts as if the growth and decay periods of the noise perception depend upon differences in latencies among the various neural paths in transmitting the cochlear activity to the higher centers in the brain. According to this hypothesis, the activity in the slowest pathways arrives at the higher center 65 msec. after the activity of the fastest pathways. By means of this hypothesis it was possible to predict the judgments of time of termination of noises in the two ears when the intensity of the noise differed between the ears.
The Perception of Repeated Bursts of Noise
Authors: Miller George A. , Taylor Walter G.
Published: September 2005

Noise interrupted at a steady rate has essentially the same spectrum over the range of frequencies transduced by the earphone as does continuous noise. The frequency corresponding to the rate of interruption is not intensified in the spectrum. Consequently, the ability of listeners to respond differentially to the rate of interruption cannot be explained on the basis of a simple resonance theory of hearing. The point at which an interrupted noise becomes indistinguishable from a continuous noise depends upon the rate of interruption, the sound-time fraction, and the intensity of the noise. For a sound-time fraction of 0.5, the presence of interruptions can be detected at rates well above 1000 per second. Differential sensitivity to changes in the rate of interruption (with a sound-time fraction of 0.5) is poor above 250 interruptions per second. Also at these high rates the listener loses his ability to match the frequency of a pure tone to the rate of interruption. Presumably the ability to perceive interruptions in a random noise depends upon the synchronous firing of the fibers in the auditory nerve. This hypothesis is supported by the correspondence between auditory sensitivity to changes in the rate of interruption of a noise and the tactual sensitivity to changes in the frequency of a vibrating pressure applied to the skin.
A Study of Ultrasonic Velocity and Absorption in Liquid Mixtures
Authors: Burton Charles J.
Published: September 2005

The absorption and velocity of sound in binary mixtures of water with alcohols, glycols, and glycol ethers have been measured at frequencies in the range of 5–25 megacycles, using the optical diffraction method originally developed by Debye, Sears, Lucas, and Biquard. However, the method of absorption measurement has been improved by utilization of a high gain, secondary multiplier-type photo-tube viewing the first-order diffraction spectrum, the change in intensity of this spectrum being an index of the sound absorption in the liquid. This method has proved more rapid and precise than other diffraction techniques described in the literature.

Ultrasonic absorption peaks at intermediate concentrations have been found in mixtures containing acetone, ethanol, propanol, isopropanol, and tertiary butanol and in the monoethyl and monobutyl glycol ethers. In both series, the magnitude of the peaks increases as one progresses from the ethyl to the butyl derivative, and there is a simultaneous shift of the peak toward higher water concentration. No absorption peaks were found in mixtures containing methanol, glycol, monomethyl glycol ether, or dioxane. Velocity peaks at intermediate concentrations have been found in all of the mixtures listed. Mixtures of tertiary butanol and methanol show neither absorption nor velocity peaks.

The observed absorptions are considerably greater than would be expected from classical theory. Consequently, the experimental data appear to require a new, or at least modified, theoretical approach. The problem is discussed briefly in the light of modern theories of molecular association, liquid crystal formation, etc.
The Analysis of Acoustic Signals by Means of the Self-Consistent Spectrum
Authors: Markham Jordan J.
Published: September 2005

The problem of analyzing the spectrum of acoustic signals is discussed for various types of filters. The problem is straightforward for narrow filters but requires, in general, a self-consistent assumption for broad filters. The necessary assumption is made, and two examples are given to show the nature of the problem.
On the Elasticity of the Cochlear Partition
Authors: v. Békésy Georg
Published: September 2005

A number of special techniques are described which are necessary in preparing the cochlea. Using these, the elasticity of the cochlear partition is determined as a function of locus along the canal. It is demonstrated that the production of undertones is very improbable because of the form of vibration in the cochlear partition and because the basilar membrane possesses no inherent stress.
Effects of High Pass and Low Pass Filtering on the Intelligibility of Speech in Noise
Authors: Pollack Irwin
Published: September 2005

The effect on intelligibility of eliminating either the high frequency speech sounds or the low frequency speech sounds was determined by standardized articulation testing procedures under the special circumstance of a background of white masking noise. In general, it was found that intelligibility increased as the frequency range and the intensity level of the speech signal were increased. Contours are presented which describe the interrelations among (1) the frequency range of the speech signal, (2) the intensity level of the speech signal, and (3) articulation efficiency.

For each of the experimental conditions, the articulation index—a measure developed by the Bell Telephone Laboratories—was computed. It was found that the scatter of the computed indices, when plotted against the scores actually obtained, was of the same order of magnitude as the intrinsic variability of typical articulation scores. This result indicates that the computational procedures are an acceptable substitute for time-consuming articulation testing when an approximate assessment of the relative efficiencies of a series of communication systems is required and when a background noise is encountered like the white noise of this study.

It was found that the relative contribution of the various speech frequencies was not constant, but rather was a function of the intensity of the speech signal relative to the constant white noise masking signal. More specifically, as the intensity level of the speech signal was increased, the relative contribution to intelligibility of the higher speech frequencies increased.
Absorption-Frequency Characteristics of Plywood Panels
Authors: Sabine Paul E. , Ramer L. G.
Published: September 2005

This paper gives the results of measurements of the absorption coefficients of panels made from birch plywood, using the standardized test procedure of the Acoustical Materials Association. In the range from 128 to 512 cycles measurements were made at interoctave frequencies in order to take account of the marked resonances shown. Effects of thickness of the plywood, of the air space back of the panels, and of absorbent backing were investigated, as well as that of damping material applied to the plywood. Measurements were also made on splayed assemblies of panels placed vertically against the wall of the reverberation chamber. The measurements showed that prefabricated portable panels of the type investigated afford an easily applied means of varying the absorption-frequency characteristics of rooms of moderate size.
Secondary Pressure Pulses Due to Gas Globe Oscillation in Underwater Explosions. I. Experimental Data
Authors: Arons A. B. , Slifko J. P. , Carter A.
Published: September 2005

Pressure waves emitted by the oscillating gas globe in underwater explosions of T.N.T. have been recorded at depths great enough to render small the perturbation effects due to migration of the bubbles under the influence of gravity. The first eight periods of oscillation have been measured and the pressure-time curves analyzed in order to obtain peak pressure, positive impulse, and energy flux resulting from the first two pulses. The scaling of pressure pulse parameters with charge size is examined.
The Absorption of Sound in Suspensions of Irregular Particles
Authors: Urick R. J.
Published: September 2005

The greater part of the absorption of sound in aqueous suspensions of small spherical particles can be attributed to the viscous drag between the fluid and the particles in the sound field. The absorption resulting from this process is found to agree with that obtained by Lamb in another manner. The applicability of the theoretical result to suspensions of irregular particles is examined by means of measurements on sand and kaolin suspensions, using a pulse-reflection method at megacycle frequencies. Approximate agreement with the idealized theory is found as the particle size, viscosity, and frequency are varied.
The Magnetostrictive Radial Vibrator
Authors: Camp Leon
Published: September 2005

A description is given of a radial vibrator used in underwater sound signaling. A technique is presented for providing a plastic cast to protect the windings which serves to improve rather than decrease the potential efficiency. Data are presented to show the operating characteristics of these sound sources.
Reflection and Transmission of Sound by a Spherical Shell
Authors: Keller Joseph B. , Keller Herbert B.
Published: September 2005

A periodic point source in medium 1 is at the center of a spherical shell of medium 2 which is surrounded by medium 3. The densities, sound speeds, and shell radii are arbitrary. For this case an exact, explicit expression for the sound pressure is obtained. If the shell radii become infinite but the thickness remains constant, and if media 1 and 3 are the same, the solution reduces to that of Rayleigh for plane waves normally incident on a flat plate. If the shell radii become infinite and if media 2 and 3 are the same, the solution yields the acoustic Fresnel formulae for normal incidence of a plane wave on a plane interface between two half-infinite media. For finite radii, with media 1 and 3 identical and the shell thickness small compared to a wave-length, a simpler form for the solution is obtained. This solution is found to agree with the approximate solution of H. Primakoff and J. B. Keller for the sound fields reflected and transmitted by a thin shell of any shape, when their result is specialized to the present case.
Notes on Sound Diffraction by Rigid Circular Cones
Authors: Wiener Francis M.
Published: September 2005

A stationary right circular cone was exposed to an essentially plane progressive wave, and the sound pressure p at various points on the surface was determined relative to the free-field pressure p0 in the undisturbed incident wave. Measurements were made in the frequency range of 14 < ka < 8, where k is the wave number of the incident wave and a the radius of the base of the cone which had a generating angle of 30°. In particular, the diffraction effect |p/p0| was determined at the center of the base for various angles of incidence θ, measured with respect to the axis of the cone. The results are generally similar to those obtained for other obstacles with the same circular face, e.g., a disk. As might be expected, the greatest differences are exhibited in the region θ>90°. A “bright” spot appears at the center of the base when the vertex points directly towards the source (θ = 180°). For incidence normal to the base, pressure measurements have been made at several other points on the surface of the cone. The data, represented as a function of frequency and position by a surface, given an approximate picture of the pressure distribution over the whole surface of the cone.
The Diffraction of a Sound Wave by an Infinite Set of Plates
Authors: Miles John W.
Published: September 2005

It is pointed out that a certain class of diffraction problems can be formulated as Wiener-Hopf integral equations [R. E. A. C. Paley and N. Wiener, “The Fourier transform in the complex domain,” Am. Math. Soc. Colloq. Pub. 19 (1934), Ch. IV] and solved exactly, an observation due to Schwinger [J. F. Carlson and A. E. Heins, Q. App. Math. 4, 313 (1947)]. Following the analysis of the equivalent electromagnetic problem by Carlson and Heins [Q. App. Math. 5, 82 (1947)], the diffraction of a plane wave of sound by an infinite set of parallel equally spaced semi-infinite plates is calculated. The conditions for plane wave propagation within the plates, for a single reflected wave, and expressions for the reflection and transmission coefficients are given. Except for the limitations by the requirements that only a plane wave be propagated and that there be only a single reflected wave, the reflection and transmission coefficients are found to be independent of wave-length or the spacing between the plates. Other problems which may be solved by the same techniques are cited.
Theoretical Analysis of the Mercury Delay Line
Authors: McSkimin H. J.
Published: September 2005

A mathematical expression for the pressure distribution in a circular mercury delay line is derived. It is found that many waves having slightly different phase velocities can exist, and under certain circumstances may interfere with each other to produce distortion effects.

An analysis is made of the voltage developed by the piezoelectric pick-up crystal, and of the distortion that might result when the carrier is pulse modulated.
Measurement of Ultrasonic Bulk-Wave Propagation in High Polymers
Authors: Nolle A. W. , Mowry S. C.
Published: September 2005

The velocity and attenuation of bulk waves (longitudinal waves of dilatation) in solid samples of high polymers are measured by an acoustic pulse technique in the frequency range 10 to 30 mc. An ultrasonic pulse of about 2 microseconds' duration is transmitted by a crystal into the liquid contained in a tank about 5 cm long, and returns as an echo to the crystal transducer. The velocity of bulk waves in the polymeric material is found from the change in echo arrival time which occurs when a flat sample is introduced into the sound path, and the attenuation is found from the reduction of echo intensity. Measurements for several rubbers and plastics are reported over various portions of the temperature range −60°C to 100°C. The attenuation generally shows at least one maximum with respect to temperature in this range. Maximum attenuation values for various rubbers at 10 mc range from 200 to 400 db/cm.
A Single Shear Plate Crystal Phonograph Pick-Up
Authors: Wiggins A. M. , Lewis F. S.
Published: September 2005

A method of driving a single shear plate crystal through a mechanical transformer is described. Particular attention is paid to the application of this drive to a phonograph pick-up. The advantages of this method of drive over previous methods are discussed.
Example of Propagation of Underwater Sound by Bottom Reflection
Authors: Young Robert W.
Published: September 2005

From data obtained in an extended program for the study of underwater sound propagation, eight examples at 200 c.p.s. have been selected to illustrate long-range propagation involving reflection from the ocean bottom. Essentially continuous sound measurements were made while the sending vessel moved from 100 meters to 60 kilometers or more away from the receiver. The source was at a depth of 4.3 meters, the receiver usually at 5, 15, or 90 meters. For the examples given the water depths were 3600, 1800, and 95 meters respectively, and with some variety of thermal conditions. There is some evidence of interference extrema. In 3600-meter water the bottom-reflected signals were roughly constant to 10 kilometers, partly because in water of this depth the distance to and from the reflecting bottom does not change rapidly with increasing horizontal range. In an extreme case the bottom-reflected signal was about the same at ranges of 3 and 60 kilometers, and it was about 15 decibels higher than this value at a range of 10 kilometers.
Reaction of Small Enclosures on the Human Voice
Authors: Morrow Charles T.
Published: September 2005

A peculiar problem in communication arises when a talker is wearing an oxygen mask or a gas mask, in that both react on the vocal mechanism and distort the voice at its source. Thus, the loss of intelligibility when a gas mask is worn is much greater than would be predicted from the amount of muffling, and, even when the oxygen mask contains a microphone, the talker's enunciation is not, in general, clear. The reaction on the voice is in part mechanical, by constraining the facial muscles and obstructing the flow of the breath, and in part acoustical, by adding a new cavity onto the vocal system so that the talker has less control over the character of the sound. The requirements for good intelligibility during the use of such enclosures have been discussed in some detail in a previous paper (see reference 1).

The present paper concerns itself with an experimental analysis of the distortion produced by some small enclosures, and an evaluation of present theories of vowel production by comparing their predictions with the experimental results. Such a comparison is probably as severe a test of the theory of vowels as can be devised.

In general predictions from the present state of the theory of vowels give a useful qualitative picture of the nature of distortion by small enclosures, but are not in quantitative agreement with experiment. A criticism is given of the assumptions involved in the present theory, and some suggestions are made toward the future improvement of our knowledge of speech.
Voice Measurements with an Audio Spectrometer
Authors: Rudmose H. W. , Clark K. C. , Carlson F. D. , Eisenstein J. C. , Walker R. A.
Published: September 2005

The distribution of average power in various speech sounds as a function of frequency has been measured with an integrating audio spectrometer. This instrument divides the electrical signal into 14 frequency bands and simultaneously records the integrated square of the amplitude in each band over a measured time interval, usually 30 seconds. From these data and the known over-all calibration of the spectrometer channels one can compute the spectral distribution of average acoustic power at the location of the input microphone. The operation of the instrument and the procedure of measurement are described. Speech spectra are given which are average results for a trained crew of seven men, speaking into a condenser microphone in an anechoic chamber.
The Loudness of Repeated Short Tones
Authors: Garner W. R.
Published: September 2005

The relation between loudness and the repetition rate of short tones was experimentally determined. The effects of intensity, frequency, and tone duration on this relation were also studied. The results can be summarized as follows. (1) A series of repeated short tones can be louder than a steady tone of the same peak intensity. (2) The difference between the loudness of repeated tones and a steady tone of the same intensity is dependent on both frequency and intensity. (3) Two series of repeated tones, of the same frequency and intensity, will not have the same loudness unless their repetition rates and durations are the same. At high intensities, the tones with the faster repetition rate and shorter duration are louder, and conversely at low intensities. (4) The rate at which loudness increases with repetition rate is dependent on the duration. The shorter the duration, the greater the change in loudness with a change in repetition rate; and conversely, the slower the repetition rate, the greater the change in loudness with a change in duration.

All of the relations shown are understandable in terms of the shape of the loudness function, and the complex spectra of repeated short tones. Calculated loudness levels, according to the method of Fletcher and Munson for calculating the loudness of multicomponent tones, agree very well with the observed loudness levels.
Some Background History of Ultrasonics
Authors: Klein Elias
Published: September 2005

Ultrasonics was conceived and came into being in France in a wartime academic atmosphere. Its physical principles were explored in England and in this country during World War I. Piezoelectric quartz was the primary, and for many years the only, active transducer element which was utilized in Europe. However, as soon as the work was started in this country, vigorous innovations were introduced. Synthetic Rochelle salt crystals were investigated and applied. Some theoretical work and several experimental techniques were developed in the United States concerning transducers. Of the number of outstanding physicists identified with this effort in America, most returned to their universities as soon as the emergency was over, and the subject of ultrasonics become dormant during the twenties. The Navy maintained an interest in ultrasonics and sponsored classified projects in the field. The subject of piezoelectricity was advanced, new synthetic crystals were brought forth, and large-scale processing, cutting, grinding, and lapping of crystals were started and pursued by the Navy. An American version of the steel sandwich was produced for operational tests. The Pierce magnetostrictive devices were incorporated in sonar systems. Similarly, the electrodynamic principle was implemented into a useful transducer. A variety of absolute and secondary standards were developed.
Biological and Psychological Effects of Ultrasonics
Authors: Davis Hallowell
Published: September 2005

Ultrasonic and also sonic waves of high intensity may produce discomfort and even injury. The dominant biological effects of various parts of the frequency spectrum are summarized. “Discomfort” implies that some sense organ is affected; but some combinations of intensity, frequency, and duration of exposure may possibly injure without the usual warning of discomfort. For the benefit of personnel working in high intensity sonic or ultrasonic fields we should establish both discomfort and danger contours, and there are wide gaps in our present knowledge. The Ultrasonics Panel of the Aeronautical Board desires particularly to receive any relevant well-authenticated observations, either positive or negative, particularly concerning the effects of high-intensity sound or ultrasonics on the sense organs and the nervous system. Casual publication of isolated, uncontrolled but spectacular “observations” may cause widespread popular apprehension and hinder the adoption of methods and instruments that involve ultrasonics of any sort.
A 100 kc Underwater Magnetostrictive Transducer
Authors: Camp Leon , Vincent Richard , du Breuil Felix
Published: September 2005

A description of the design and construction of a 100 kc underwater magnetostrictive transducer having beam width 20° wide 6 db down. Operating remanence, it may be driven with 40 watts at 50 percent efficiency.
Interactions between a Plate and a Sound Field
Authors: Fay R. D.
Published: September 2005

The paper deals with phenomena associated with the interactions between flexural vibrations in a plate and the sound field in an ambient fluid medium. An equation is developed in tractable form which determines the propagation function of the free and forced flexural waves which can exist under stated assumptions. It is found that the reaction of the fluid on the plate makes possible a wave which cannot exist in the free plate in steady state. For a steel plate in water, the potential effect of the additional wave is relatively great when the product of frequency and plate thickness lies between 6 and 20 kilocycle-inches.
Reciprocity Calibration of Primary Vibration Standards
Authors: Thompson Sanford P.
Published: September 2005

The reciprocity method for the absolute calibration of vibration transducers is reviewed, and the design and calibration of a set of primary standard transducers is described. Resulting calibrations are shown to be both reliable and accurate up to at least 700 cycles per second.
The Lumping of Distributed Mass
Authors: Hudson G. E. , Specht R. D.
Published: September 2005

The natural frequencies of longitudinal vibration of a rod fixed at one end and carrying a concentrated mass at the other end can be found by solving the transcendental frequency equation. Rayleigh showed that a good approximation to the fundamental frequency is got by replacing the distributed system by a simple harmonic oscillator having one degree of freedom, whose stiffness equals the original stiffness of the rod and whose mass equals the end-mass increased by one-third the mass of the rod alone. The factor one-third may be replaced by some other “lumping coefficient” λ. It is shown that Rayleigh's lumping coefficient λ = 13 is the best possible one when the end mass is large compared with the mass of the rod alone, and leads to a maximum error in the frequency of 10.3 percent. This maximum error takes a minimum value of 1.68 percent when a lumping coefficient λ0 = 0.3919974 is used; this “best” coefficient yields a better approximation to the fundamental frequency than does the Rayleigh coefficient when the end mass is less than 0.511 times the mass of the rod alone. The variable lumping coefficient, which is a function of the masses involved, is discussed.
The Masking of Tones by Repeated Bursts of Noise
Authors: Miller George A. , Garner W. R.
Published: September 2005

The masking of tones by continuous and interrupted noise was determined for three noise intensities, three noise-time fractions, and rates of interruption varying from 0.5 to 512 interruptions per second. The decrease in masking effectiveness as a result of the discontinuity of the masking noise depends principally upon the duration of the silent interruption, and secondarily upon the frequency of the masked tone and the intensity of the noise. A computational device is presented which will permit a first approximation of the masking produced by interrupted noises.
The Role of Interaural Phase in Loudness
Authors: Hirsh Ira J. , Pollack Irwin
Published: September 2005

Recent experiments have shown that the interaural phase angle is a critical factor in the masking of pure tones and speech by white noise. The present study extends these findings to the role of interaural phase in loudness. It is found that the reduction in loudness which is effected by noise under several conditions of interaural phase parallels the masking that is produced under similar conditions. These effects are marked, however, only at signal-to-noise ratios in the region of the masked threshold. At higher signal-to-noise ratios, approximating listening in the quiet, the effect of interaural phase on loudness is nil. A convenient basis for discussion is provided by considering the masked and masking signals in terms of the figure-ground relation between them.
A Comparison of Artificial Ear Couplers
Authors: Glaser Joan L. , Morrical Keron C.
Published: September 2005

Comparison made of the response of several earphones measured on two different types of earphone couplers. Points of difference are noted and explained. In addition, the existence of certain characteristics which might influence the design and use of such couplers is brought out and proposed for further investigation.
Amplitude Cross-Section Representation with the Sound Spectrograph
Authors: Kersta L. G.
Published: September 2005

Spectrograms as normally produced by the “sound spectrograph” are three dimensional. Time is portrayed along the length of the spectrogram paper, frequency across it, and amplitude by the blackness of the marking. The time and frequency scales thus provided are adequate for most analysis purposes. The amplitude scale, however, is poorly defined, first because inherent characteristics of the spectrogram paper limit the amplitude portrayal to a highly non-linear and limited range, secondly, because reading degrees of blackness by eye is inaccurate. This inadequacy in determining amplitude led to the development of a method for portraying amplitude which was independent of the characteristics of the paper or of the ability of the eyes to delineate grades of blackness of marking.

The device developed and herein described provides an auxiliary presentation which portrays, at any preselected point in time, a two-dimensional spectrogram with axes of amplitude and frequency. This device delineates a 35-db amplitude range with the scale in uniform logarithmic steps.
Acoustic Impedance Matching by Means of Screens
Authors: Slaymaker Frank H. , Hawley Mones E.
Published: September 2005

The acoustic impedance of a transducer may be matched to that of the surrounding medium by means of a metal screen. When operating in air, transmission increases of nine decibels have been obtained by placing correctly selected and positioned screens in front of a crystal transducer. The device narrows the response curve of a sharply resonant transducer only slightly, while the directional characteristics are not measurably altered. The situation is somewhat analogous to the non-reflection coating of optics. For purposes of analysis, a more useful analogue is that of a transmission line containing discontinuity. Experiments with woven and perforated screens of different geometric form have been performed and the results evaluated.
Instrumentation for the Measurement of Sound Pressure Level with the Western Electric 640AA Condenser Microphone
Authors: Veneklasen Paul S.
Published: September 2005

Given the pressure calibration of the W.E. 640AA microphone, certain instrumentation and complementary calibrations are needed for the convenient use of this microphone under the various conditions encountered during research work. The following aspects of this subject are discussed: (1) Considerations regarding the effect of preamplifier input impedance on the frequency response and noise threshold of a condenser microphone. (2) An a.c. operated, cathode follower type preamplifier and associated circuits. (3) A flexible extension for use with the preamplifier. (4) The use of small probe tubes. (5) Random incidence calibration and collected free field calibrations. (6) A “supercharged” cathode follower circuit and its application as a preamplifier.
Reciprocity Calibration of Vibration Probes
Authors: Morrow Charles T.
Published: September 2005

Apparatus has been developed for calibration of vibration probes, analogous to that for reciprocity calibration of condenser microphones, except that a metallic rod instead of an air cavity couples the two transducers. The rod is assumed to act as a mechanical open circuit, whereas the air cavity is assumed to be an acoustic short circuit. The product of the sensitivities of the two transducers can be obtained from the current to the driving probe (A), the mass of the coupler, and the open circuit voltage of the pick-up probe (B). The ratio of the sensitivities of A and B can be obtained as the ratio of their open-circuit voltages when the coupler is driven by an auxiliary drive. From the product and the ratio, the two individual sensitivities can be calculated.
Vibrators for Measurement of Response and Compliance of Phonograph Pick-Ups
Authors: Pearson H. A. , Carlisle R. W. , Cravis H.
Published: September 2005

Two vibration instruments are described. The first is a vibrator having substantially constant amplitude over a wide frequency range. A small reed is milled from a solid block of steel and driven with a conventional magnetic system. A light platform with a grooved Nylon pad is attached to the end of the reed. A phonograph pick-up is laid on this platform in the same manner as on a record, and the response from 30 to 10,000 cycles may be measured. The second is a vibrator having an armature with considerable mass and negligible stiffness. The armature is pivoted and retained by magnetic attraction with no restoring spring. A platform is provided on this armature on which to rest a pick-up. From the frequency of resonance of the armature with the stiffness of any pick-up or other vibrator, the stiffness of such a vibrator may be readily ascertained, as in the case of B. B. Bauer's vibrator [J. Acous. Soc. Am. 19, 319 (1947)]. Calibration data were secured from both dynamic and static measurements, the agreement of which is indicated.
The Scattering of Ultrasonic Waves in Water by Cylindrical Obstacles
Authors: Bauer Louis , Tamarkin Paul , Lindsay R. B.
Published: September 2005

An ultrasonic beam produced in water by an oscillating quartz crystal (frequency, 1145 kc; wave-length, 1.3 mm) is scattered by cylindrical obstacles. Three different obstacles are used: (i) a 14″ steel rod, (ii) a 12″ steel rod, and (iii) 58″ hollow polystyrene tube. Lateral pressure amplitude distribution curves are obtained at different points along the axis of the beam for various positions of the obstacles on the axis. The effect of lateral displacements of the obstacles is studied. Wave-front determinations are made with and without obstacles. The conclusion is reached that transmission through and reflection by the obstacles play an insignificant role compared with diffraction around them.
Objectives for Sound Portrayal
Authors: Potter Ralph K.
Published: September 2005

Translation of sound into visible patterns is discussed in terms of broad objectives. It is suggested that no single design can be optimum and that perhaps the most useful standard of reference is the human ear. Special interests and complexity generally affect final design requirements.
The Laplace Transform Solution of Beams
Authors: Thomson William T.
Published: September 2005

The application of the Laplace transform to the general problem of the beam is discussed. The method requires no knowledge of normal modes often employed in the classical solution. A solution in closed form is given for the forced vibration of a hinged beam excited by a concentrated harmonic force. The result converges to the correct static curve for zero frequency. The method is extended to the problem of finding the natural frequencies of beams with concentrated mass and spring. The analysis for beams with several masses and springs is outlined.
Abnormal Audibility Zones in Long Distance Propagation through the Atmosphere
Authors: Cox Everett F.
Published: September 2005

Five thousand tons of high explosives detonated on Helgoland, April 18, 1947, created air pressure perturbations recorded on microbarographs between 66 and 1000 km SSE from the blast. Instruments responded to frequencies 0.05–5 c.p.s. Arrival times of abnormal signals at six stations more distant than 220 km, supplemented by high altitude meteorological data and the assumption of negligible winds above 30 km, permit upper atmosphere temperature calculations. Temperatures agree with N.A.C.A. values up to 42 km, but show a reduced gradient above that altitude, and a maximum value 294°K in the temperature hump between 30 and 70 km. This temperature maximum establishes critical ray which is refracted to infinity. A new explanation for observed outer boundaries of abnormal zones is therefore proposed, and substantiated by recorded evidence of dispersion near the temperature maximum. In the signal received near the abnormal zone outer boundary, high frequency content predominates.
Criteria for Normal and Abnormal Ultrasonic Light Diffraction Effects
Authors: Willard G. W.
Published: September 2005

The normal or common type of ultrasonic light diffraction occurs when traveling sound waves act like a phase grating. The spacing and intensities of the respective orders of spectra are given by the Raman-Nath theory. Experimentally and theoretically, this type of diffraction is obtained when the product of (width of sound beam) × (frequency)2 × (sound amplitude) is sufficiently low. When the light beam is maintained parallel to the sound wave fronts, the right and left spectra of the same order are of equal intensity.

An abnormal or uncommon type of ultrasonic light diffraction occurs when the sound waves diffract the light in a manner satisfying the Bragg reflection law, well known in x-rays. The spacing of the spectra is essentially the same as before but right and left spectra do not appear simultaneously. Strong intensity in a given portion of the spectra is obtained only when the glancing angles of incidence φ and of reflection θ are equal, as in mirror reflection, and when λ, Λ, and θ satisfy the Bragg law nλ = 2Λ sinθ, (λ and Λ are the light and sound wave-lengths, respectively, and n is the order of spectra). This type of diffraction is obtained only when the single product (width of sound beam) × (frequency)2 is sufficiently large.

Experiments and theory indicate the above criteria for these two types of light diffraction. Theory also indicates the possibility of other types of abnormal diffraction, such as mirror reflection, diffraction satisfying ruled grating theory, nλ = Λ(sinφ + sinθ), where φ does not necessarily equal θ, and others.
The Patterns of Response in the Cochlea
Authors: Wever Ernest Glen , Lawrence Merle
Published: September 2005

The general form of the intensity function for the electrical responses of the cochlea is now well known. As we raise the intensity of a sound applied to the ear, the cochlear potentials rise at first in simple proportion to the intensity, and then at a high level, as the stimulus is elevated further, they cease to follow this simple relation and give a bending curve. From the first departure from linearity onward the responses rise more and more slowly in relation to the stimulus until at last they reach a maximum value, a value beyond which they actually diminish as the intensity is raised.

So much of the form of the function is established on the basis of numerous experiments (see reference 2), yet there still are many details not yet worked out with exactness. The present study seeks in a measure to supply this lack. We have been concerned especially with the initial departure from linearity and the maximum value of the response for various frequencies over the tonal range. This information, as we shall show, has a pertinent application to the problems of the locus and spread of response over the basilar membrane.
Adaptation of the Ear to Sound Stimuli
Authors: Lüscher E. , Zwislocki J.
Published: September 2005

The most important results of the determinations previously published on the adaptation of the ear to sound stimuli are briefly recapitulated. Adaptation is defined as the elevation of the auditory threshold by a previous sound stimulus. It may be determined by means of a short tone impulse (testing impulse) which follows the sound stimulus (stimulating impulse) causing the adaptation. The testing impulse is adjusted to the threshold value. By altering the interval between the stimulating and testing impulses, the curve of return adaptation, i.e., the return to normal sensitivity, may be ascertained. When plotted on a logarithmic db scale, this curve is approximately a straight line.

New experiments have shown that the entire process of adaptation requires less than 0.4 sec. The return adaptation is complete within a few tenths of a second. After stimulation by a tone of 80 db above threshold intensity, return adaptation is complete after 250 μsec.

The increase in adaptation is approximately proportional to the intensity of the stimulating tone when both magnitudes are expressed in db. With a sound impulse of 80 db above the auditory threshold, the adaptation reaches a value of 40 to 50 db.

Binaural determination of adaptation, by leading the stimulating impulse to one ear and the testing impulse to the other, shows that adaptation is a monaural and therefore a peripheral process.

A pure tone induces an elevation of the auditory threshold not only for its own frequency but also for neighboring ones. The adaptation spreads chiefly to higher frequencies than that of the stimulating tone at which it reaches a maximum. The maximum is more pronounced at high frequencies of the stimulating tone than at low ones.

Comparative experiments between adaptation and masking demonstrate a far-reaching similarity between the two processes. These show a similar behavior with respect to intensity and frequency. A quantitative comparison leads to the conclusion that masking depends chiefly upon the adaptation of the ear to sound stimuli.
A Theory of the Crystal Transducer for Plane Waves
Authors: Cady Walter G.
Published: September 2005

From the equation for propagation of acoustic plane waves through a solid medium, expressions are derived for the vibrational amplitude, radiated power, and electrical admittance of a plane-wave crystal transducer. The transducer consists of crystals, backing, and diaphragm, radiating into any medium. The crystals may be an assemblage of flat bars vibrating lengthwise, or there may be a single flat crystal plate, or mosaic of plates, in thickness vibration. The equations take account of attenuation in the diaphragm, but not of attenuation in crystals and backing, nor of the effects of cement layers and lateral stresses between crystals.

The general equations, which are valid at all frequencies and for all thicknesses of backing, crystal assemblage, and diaphragm, are specialized to the case in which the backing is air. Special attention is given to those frequencies at which the crystals, or diaphragm, or both, are in resonance. Some typical theoretical curves are shown, and a graphical method is described for the rapid plotting of curves.
Measurement of Acoustic Impedance
Authors: Mawardi Osman K.
Published: September 2005

In this paper a method is described of measuring the acoustic impedance of a sample of material forming one boundary of a shallow cylindrical cavity, by determining the sound pressure produced when a known volume current is injected into the cavity from a high impedance source. The volume current is effectively determined by observing the pressure when the cavity is rigidly terminated. The use of a ring source suppresses the first radial mode of the cavity and extends the frequency limit set by uniformity of pressure by at least an octave.

Secondary effects due to the finite impedance of the source and microphone and heat losses at the walls have been evaluated. The method appears to be simple, rapid, and precise.
A Note on the Kirchhoff Approximation in Diffraction Theory
Authors: Spence R. D.
Published: September 2005

This note compares the predictions of the Kirchhoff approximation with those of the exact theory for the problem of diffraction by a circular aperture.