bluuebunny/crossref_metadata_2025 huggingface dataset:
Individual Differences in Noise Masked Thresholds
Authors: Webster J. C. , Lichtenstein Malcolm , Gales Robert S.
Published: September 2005

Absolute thresholds and thresholds of pure tones masked by thermal noise were obtained for 3666 persons attending the 1948 San Diego County Fair. The masked hearing losses as well as the absolute hearing losses (1) increased with an individual's age, (2) were positively correlated with his awareness of hearing difficulty, and (3) were inversely related to his musical training. Masked losses, however, were less dependent upon one's sex and upon one's past noise environment than were absolute losses.

When groups of individuals were equated as to their absolute losses on 880 c.p.s. and 3520 c.p.s. (the frequencies which were masked), that part of each group that had the lower absolute thresholds on 440 c.p.s. also had the lower masked thresholds.

The signal to noise ratio (noise expressed as spectrum level) at masked threshold for those with no absolute loss was 20 db at 880 c.p.s. and 21 db at 3520 c.p.s. This is equivalent to saying that the noise bands which were effective in masking these frequencies were 100 and 128 cycles wide, respectively.
The Frequency Selectivity of the Ear as Determined by Masking Experiments
Authors: Schafer T. H. , Gales R. S. , Shewmaker C. A. , Thompson P. O.
Published: September 2005

The results of experiments on masking of tones by narrow bands of noise at 200, 800, and 3200 c.p.s. are presented. These are interpreted in terms of the critical band hypothesis. Assuming a simple resonant characteristic for the aural frequency selectivity the shape of the masking vs. frequency function is computed and gives a reasonably good fit in the narrow regions studied. The critical band widths are determined at frequencies 200, 800, and 3200 c.p.s., and the corresponding values of Q of the equivalent tuned circuit are given. Data are presented for masking of tones slightly removed from the masking noise band, and are shown in fair agreement with the computed values. The selectivity curves are shown to be consistent with available data on differential sensitivity to frequency.
The Effect of a 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.
Response Peaks in Finite Horns
Authors: Molloy C. T.
Published: September 2005

In this paper the term hyperbolic horn is used to designate those horns whose area law is given by: S(x) = πR02[coshax+T sinhax]2. Where S(x) is the cross-sectional area of the horn at distance (x) from the throat, (a) is the flare constant; (T) is the shape parameter and (R0) is the throat radius.

The pressure on the axis due to a circular mouth, unbaffled horn loudspeaker is derived. In this calculation use is made of the recent results of Levine and Schwinger [Phys. Rev. 73, 383 (1948)] and some useful additional functions are computed from their data and presented here in graphical form.

It is shown how to calculate the frequencies at which peaks occur in hyperbolic horn type loudspeaker frequency response curves.

It is shown how to calculate the parameters of hyperbolic and exponential horn type loudspeakers having pre-determined peaks in their frequency response curves.

Some experimental confirmation of the theory is presented.
On the Propagation of Sound Waves in a Cylindrical Conduit
Authors: Daniels Fred B.
Published: September 2005

The characteristic impedance and propagation constant of a cylindrical conduit are calculated on the basis of an equivalent electrical T-section. Numerical values of the results are plotted for air at 20°C, for a range of values of the independent variable which includes the region of transition from isothermal to adiabatic conditions.
A Method for Measuring Source Impedance and Tube Attenuation
Authors: White J. E.
Published: September 2005

If the active face, or acoustic output terminal, of a sinusoidal sound source moves as a plane piston, then the source can be characterized by a blocked pressure and an acoustic output impedance. If this piston is coupled to a microphone by means of a closed air column, the pressure at the microphone depends on the acoustic impedance of the microphone, on the impedance of the source, and on the air column. An expression for this pressure as a function of the length of the air column is developed, and data are presented which show how source impedance, tube attenuation and other quantities may be obtained.
Propagation of Sound in Rarefied Helium
Authors: Greenspan Martin
Published: September 2005

The velocity and attenuation of sound at 1 mc/sec. were measured in helium at pressures as low as 0.1 mm Hg (sound frequency about twice mean collision rate). The observed dispersions are very large and agree well with those predicted by existing theories except at very low pressures where uncertainties are introduced by lack of gas purity.
Piezoelectric Equations of State and Their Application to Thickness-Vibration Transducers
Authors: Cady Walter G.
Published: September 2005

The electromechanical equations of state are written in a number of forms, extending from Voigt's formulation to the recently introduced formulation with g and h as the piezoelectric constants. Those equations that are most appropriate in the theoretical treatment of the two chief types of crystal transducer are pointed out. A detailed treatment of the thickness-vibration transducer is then given, leading to expressions for the electrical characteristics and for the acoustic vibrational amplitude and intensity. Some special cases are also considered.
A Second-Order Gradient Noise Canceling Microphone Using a Single Diaphragm
Authors: Beaverson W. A. , Wiggins A. M.
Published: September 2005

A close talking, noise canceling microphone has been developed which responds to the second order of the pressure gradient and which has only one diaphragm. Since there are four sound pressures involved in a second-order gradient microphone it has been deemed necessary in the past to have four surfaces for the four pressures to act upon. This microphone has sound entrances to the two surfaces of a single diaphragm spaced and oriented in such a manner as to produce the second-order effect, thereby increasing the signal-to-noise ratio over that obtained in a first-order gradient microphone. Mathematical analyses are made of the microphone first as a purely theoretical microphone with infinitesimal spacing of the sound entrances, then as a microphone with dimensions between sound entrances which are practical for use in a microphone of this type.
On the Masking Pattern of a Simple Auditory Stimulus
Authors: Egan James P. , Hake Harold W.
Published: September 2005

The masking audiogram of a pure tone is complicated by phenomena that arise from the interaction of the test tone with the masking stimulus. The production of beats and of difference tones results in a masking audiogram that does not represent the pattern of activity in the cochlea or nerve due to a simple masking stimulus. In the present experiments a narrow band of noise was used to mask pure tones. The “beat” heard in the immediate vicinity of the masking noise is not prominent, and a test tone higher in frequency than the band of noise is detected in terms of the characteristic pitch of that tone rather than by means of a difference tone.

With a band of noise slightly wider than a critical band (Fletcher), the amount by which the test signal at the center of the band exceeds the level/cycle of the noise is less than that obtained with a considerably wider band of noise. This smaller signal-to-noise ratio obtained with the narrow band of noise is probably due to “beats,” since the test tone is heard as a “buzz” or “rattle.” For purposes of deriving excitation or loudness patterns, a better estimate of the maximum amount of masking is obtained by using a wide band of noise whose pressure spectrum level is the same as that of the narrow band.
The Masking of Clicks by Pure Tones and Bands of Noise
Authors: Hirsh I. J. , Rosenblith W. A. , Ward W. D.
Published: September 2005

Pure tones and various bands of noise were used to mask impulsive acoustic stimuli (clicks) that were produced by electrical square pulses through a moving-coil type earphone. Results indicate that it is difficult to generalize about the masking of clicks by pure tones from observations on only a few observers because of sizeable individual differences. The masking of clicks by noise, however, is related unambiguously to the intensity and the spectral distribution of the noise. Both pure tones and narrow bands of noise provide maximum masking in the region between 1000 and 3000 c.p.s. Generally speaking, noise is a more efficient masker of clicks than are single pure tones. Although the present measurements were made with masking frequencies below 6500 c.p.s., there is some preliminary evidence to suggest that the audibility of certain clicks in noise is markedly dependent on frequencies above 6500 c.p.s. The linear (slope = 1) relation between the masking of speech or pure tones by noise and the intensity of the noise does not apply here. Rather a trimodal function indicates that the masking of unfiltered clicks by “pinkish-white” noise does not change over a 30-db range of moderate intensities. Below and above this range masking increases with the intensity of noise, sometimes at a slope greater than one.
The Information Theory Point of View in Speech Communication
Authors: Fano R. M.
Published: September 2005

This paper presents a nonmathetical discussion of the Wiener-Shannon theory of information. The results of this theory are used to estimate the rate of transmission of information in speech communication.
Typology of Languages
Authors: Menzerath Paul
Published: September 2005

Phonemics having been atomistic, it is now completed by typology, or integral phonemics. Encoding, entropy, spelling reform. Criteria for classifying given vocabulary. Monosyllabics-parallelogram. Phonetic nets. Frequency distribution of vowels in monosyllabic words (French, English, German).
Description of Language Design
Authors: Joos Martin
Published: September 2005

Physicists describe speech with continuous mathematics, such as Fourier analysis or the autocorrelation function. Linguists describe language instead, using a discontinuous or discrete mathematics called “linguistics.” The nature of this odd calculus is outlined and justified here. It treats speech communication as having a telegraphic structure. (Non-linguists normally fail to orient themselves in this field because they treat speech as analogous to telephony.) The telegraph-code structure of language is examined from top to bottom, and at each of its several levels of complexity (compared to the two levels of Morse code) its structure is shown to be defined by possibilities and impossibilities of combination among the units of that level. Above the highest level we find, instead of such absolute restrictions, conditional probabilities of occurrence: this is the semantic field, outside linguistics, where sociologists can work. Below the lowest level we find, instead of such absolute restrictions, conditional probabilities of phonetic quality: this is the phonetic field, outside linguistics, where physicists can work. Thus linguistics is peculiar among mathematical systems in that it abuts upon reality in two places instead of one. This statement is equivalent to defining a language as a symbolic system; that is, as a code.
The Relation of Phonetics and Linguistics to Communication Theory
Authors: Straus Oliver H.
Published: September 2005

An attempt is made by means of communication theory to build a single conceptual scheme that describes the transmission of messages from one man's brain through the medium of speech into another man's brain. It emphasizes the resemblance of speech production to an encoding process, and the resemblance of the hearing and interpreting of speech sounds to a cryptanalytic procedure that depends on the known conditional probabilities of the language. It is pointed out that speech sounds, or phones, form an infinite, continuous set, while phonemes, the smallest significant units of the cipher, are a discrete small set. It is felt that a logical method of decoding can be set up only through the convergent behavior of language as a statistical process.
An Apparatus for Speech Compression and Expansion and for Replaying Visible Speech Records
Authors: Vilbig F.
Published: September 2005

In speechband compression or expansion all the frequencies of the band are divided or multiplied in a certain ratio, but without changing the time dimension. This last requirement makes the problem very difficult because, if we could neglect the time aspect, we could record speech and simply play it back at slower or faster speeds.

I have tried to solve this problem by three different methods: (1) by transformation of the speech frequencies into an optical spectrum and retransformation by light modulation disk and photo-tube; (2) by use of a string filter; and (3) by use of an ultrasonic cell as a storage device.
System-Function Analysis of Speech Sounds
Authors: Huggins W. H.
Published: September 2005

The analysis of speech sound is facilitated if the sound is considered to be the response of a slow-time-varying linear system to appropriate excitations. The linear system is characterized by one or more system functions which may be represented most naturally as the sum of complex exponential terms having complex frequencies corresponding to the various formants. Thus, a generalized frequency analysis is made not of the speech wave itself but rather of the system function that shaped that wave. On the other hand, the excitation is best analyzed by autocorrelation methods.
Binaural Localization and Masking
Authors: Kock W. E.
Published: September 2005

Binaural experiments are described which indicate that the ability of the brain to localize a desired sound and to suppress undesired sounds coming from other directions can be traced in part to the different times of arrival of a sound at the two ears. It is suggested that the brain inserts a time delay in one of the two nerve paths associated with the ears so as to be able to compare, and thus concentrate on, those sounds arriving at the ears with this particular time of arrival distance.

The ability to perceive weak sounds binaurally in the presence of noise is shown to be a simple function of the direction of the desired sound and noise. An explanation is given for the effect reported by Koenig that front and rear confusion is avoided by head movements.
The Intelligibility of Amplitude-Dichotomized, Time-Quantized Speech Waves
Authors: Licklider J. C. R.
Published: September 2005

This paper describes two ways of reducing the normally very complicated speech wave to simple geometrical form without destroying intelligibility, reports the results of articulation tests of the simplified speech, and gives two illustrations of things that can be done more simply with the simplified than with the normal wave. Both methods of simplification involve dichotomization of the amplitude scale and then quantization of the time scale. The first step is achieved by subjecting the speech wave to infinite peak clipping, the second by generating a rectangular wave whose switchings from one amplitude level to the other are related to the switchings of the clipped speech wave by one or the other of two rules. One of the rules yields marginal intelligibility with quanta 0.2 millisecond in length; the other requires slightly shorter quanta. The relative merits of the two methods are accounted for by an elementary application of information theory. Autocorrelation functions, which are especially easy to compute for the simplified waves, are shown.
Loudness Balance Methods for Earphone Response Measurements
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 method 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 response under circumstances where the first method is virtually impossible. However, the interpretation of the 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.
Calibration of Audiometers
Authors: Corliss E. L. R. , Snyder W. F.
Published: September 2005

A general description is given of the procedure developed at the National Bureau of Standards for calibrating audiometers. The sources of calibration standards are presented, and there is a discussion of the physics underlying the present technique. Limitations on the validity of the threshold data are pointed out. A method for determining the calibration of audiometer earphones is described. Data on earphone response can be used to gain some insight into the malfunctioning of an audiometer, and the way in which this can be done is indicated.
The Electrical and Acoustical Performance of Some Commercial Audiometers
Authors: Morrical Keron C. , Benson Robert W. , Davis Hallowell
Published: September 2005

The electrical and acoustical performance of a number of commercially available audiometers has been examined in the light of requirements for pure tone diagnostic audiometers recently issued by the American Medical Association and now under consideration by the American Standards Association, Inc. Performance has been judged to be satisfactory except for discrepancies at 8000 c.p.s. in the case of several audiometers. Likewise, it is concluded that the specifications themselves are reasonable.
A Tuning Fork Filter
Authors: Wulfsberg Karl N.
Published: September 2005

An audiofrequency electromechanical filter using a tuning fork as the resonant element is described. Q's ranging from 1000 to 20,000 were attained. Typical response curves have been plotted and the factors that affect the Q, insertion loss and stability are discussed.
The Dependence of Shadow Zone Sound on the Surface Sound Velocity Gradient
Authors: Morse R. W.
Published: September 2005

Consideration is given to the direct sound which is observed to penetrate the so-called “shadow zone” of ocean acoustics. It is shown by ray theory that the assumption that the sound velocity gradient approaches zero in the top few feet of the oceans predicts sound levels in the “shadow” which are of the same order of magnitude as those which are measured at a frequency of 24 kc/sec.
The Piston Source at High Frequencies
Authors: Williams A. O.
Published: September 2005

For a circular plane piston of radius a, producing an ultrasonic beam with propagation constant k (or 2π/λ), an expression is derived for the velocity potential or the acoustic pressure, averaged with respect to magnitude and phase over a “measurement circle” equal in area to the piston and centered in the beam. The expression should be highly accurate for ka ⩾ 100, at distances z from the source governed by (z/a)3 ⩾ ka. It agrees well with results computed, in another way, by Huntington, Emslie, and Hughes. The assumption that relatively near the source there is a collimated beam of plane waves is shown to be not very accurate; the averaged pressure falls off monotonically over all distances considered. The velocity potential at the rim of the “measurement circle” is also computed, and compared with the plane wave assumption.
The Voicing of Organ Flue Pipes
Authors: Mercer Derwent M. A.
Published: September 2005

The art of “voicing” an organ pipe, that is, treating it in order to produce a satisfactory musical tone, is highly developed, but on an entirely empirical foundation. Flue pipes only are dealt with here, chiefly the open diapason, an open metal cylindrical pipe. The several tone-producing mechanisms in it are described, and some two dozen different variables, each of which can affect the tone, are described with reference to the stage in manufacture in which they occur. Some account is given of the interrelationship of the various adjustments. Finally mention is made of the place of any one pipe in the tonal structure of a complete organ.
Experimental Determination of Acoustic Wave Fronts
Authors: Tamarkin Paul , Boyer George L. , Beyer Robert T.
Published: September 2005

An apparatus is described for measuring acoustic wave fronts in water at frequencies in the vicinity of 1 mc. The sound waves are radiated by a piezoelectric crystal and are picked up by a movable microphone. The voltage output from the microphone is compared in phase with the voltage feeding the piezoelectric source, by means of a phase discriminator. The signal at the microphone is due both to the transmitted acoustic wave and a stray electric signal. These two are combined in the microphone in such a way as to produce a full wavelength modulation in the resultant electric signal. A wave front in the sound wave is then traced by moving the microphone along such a line or surface as will cause the phase discriminator to indicate constant phase difference. A mathematical analysis of the problem is given and the method of measuring the shape of acoustic wave fronts in water is described. The apparatus and method which are described reduce the time required for measuring wave fronts to about one-third that previously needed. Typical experimental results are given.
Ultrasonography
Authors: Ernst Paul J.
Published: September 2005

It is shown that with or even without ultrasonic lenses or other devices for the concentration of ultrasonic energy, by ultrasonics, images can be made on photo-sensitive emulsions. Several of the first ultra-sonographs, as these images are called, are reproduced and some potential fields of application of the new technique are mentioned.
Improved Methods for Measuring Ultrasonic Velocity
Authors: Willard G. W.
Published: September 2005

Some improved sound wave interference methods for measuring the longitudinal and transverse ultrasonic velocity in opaque as well as transparent solids may be simply carried out by using the ultrasonic light-diffraction system (as arranged for making sound beams visible on a screen). The sonic unit of the system is arranged to produce two individual traveling-wave sound beams, by use of two generators by splitting a single beam. Three simple arrangements are described in detail. In Case A one beam travels entirely in a reference liquid, while the other beam travels a parallel path in an immersed transparent test specimen. In Case B one beam travels entirely in a reference liquid, while the other beam travels an adjacent course through an immersed, transparent or opaque test prism, and on into the liquid at an angle to the first beam. In Case C the two beams are generated at the equal edge faces of a transparent or opaque isosceles test prism (only the base edge face contacting the liquid). The two beams traverse the prism to the base, where they are refracted into the test liquid as confluent beams.

In Cases A and B, simulated interference (by optical integration), and in Case C true interference, each give a light and dark band interference pattern on the screen, whose band spacing is used in calculating the velocity of sound in the test solid. The other required factors are the optical image magnification, the frequency of the sound, the angular disposition of the one or more acoustic surfaces of the test solid relative to the incident sound beams, and in Cases A and B the velocity of sound in the reference medium. Other variations of arrangement are suggested.

Advantages of the improved methods are simple preparation of test specimen, directness and simplicity of measurement and calculation, good accuracy, low sonic power requirements. A table of measured velocities (and attenuations) in two metals and in numerous plastics and polymers show the wide range of materials that may be measured by the new interference methods.
Variable Resonant Frequency Crystal Systems
Authors: Fry William J. , Baumann Fry Ruth , Hall Wayne
Published: September 2005

A general analysis of variable resonant frequency crystal systems which utilize liquid media as backing is presented. Formulas are obtained for evaluating the effect of different geometries of backing on the resonant frequencies of the system. The various loss factors associated with such a system are related to the measurable quantity, the quality factor.

The observed operating characteristics of a variable resonant system which covers a two-to-one frequency band (40 kc to 80 kc) are presented. The results of an experimental comparison of such a system with fixed resonant frequency systems for generation of ultrasound in liquid media are given. The theory is used to correlate the experimental observations.
Determination of the Effects of Dissipation in the Cochlear Partition by Means of a Network Representing the Basilar Membrane
Authors: Bogert B. P.
Published: September 2005

Results are given of measurements made on a 175-section network representing the basilar membrane, which was modified to include the effects of dissipation in the cochlear partition. The results show that the dynamical theory of the cochlea, when dissipation is considered, is in good agreement with experimental evidence.
Electrical Excitation of Nerves in the Skin at Audiofrequencies
Authors: Anderson Attell B. , Munson W. A.
Published: September 2005

This is a report of results obtained in preliminary tests of perception of signals applied directly to the skin in the form of electrical potentials. The lowest signal level that could be felt and the highest level that could be applied without extreme discomfort to the observers were determined for sine wave potentials ranging from 100 to 10,000 cps. The difference between the lowest and highest levels was about 25 db over this frequency range.

Difference limen measurements for intensity and frequency showed that intensity discrimination is not greatly different from what it is for hearing, but the ear is vastly superior in the matter of frequency discrimination.
An Ultrasonic Method for Outlining the Cerebral Ventricles
Authors: Hueter T. F. , Bolt R. H.
Published: September 2005

This paper discusses the general physical problems underlying the portrayal of ventricular geometry by ultrasonic techniques. This offers another means somewhat analogous to x-ray ventriculography for the detection of brain tumors. Progress is reported on studies of ultra-sound propagation properties in the tissues involved. Preliminary conclusions on safety thresholds of pain and damage are discussed. The most promising method to date is straight-through transcranial transmission (not echo ranging) utilizing changes in attenuation owing to differing amounts of ventricle along the transmission path. The optimum compromise frequency appears to be about 2.5 megacycles for which frequency results are reported on studies of receiver sensitivity and dynamic range, resolution, shielding, transducers, and presentation problems.
Ultrasonic Velocities in Gases at Low Pressures
Authors: Boyer Robert A.
Published: September 2005

An ultrasonic interferometer with high sensitivity is used to measure acoustic velocities at 0°C in gases, as the wavelength approaches the mean free path of the molecules. Measurements are made of velocity as a function of pressure down to about 2 mm of Hg, the frequency being kept constant at approximately 970 kc. The following increases in velocity (at the lowest pressures) over that at standard conditions were observed: argon 27 percent, nitrogen 16 percent, oxygen 20 percent, and dry CO2-free air 7 percent.
On the Acoustical Radiation of an Emitter Vibrating in an Infinite Wall
Authors: Pachner Jaroslav
Published: September 2005

The velocity potential distribution of a circular emitter vibrating in an infinite wall is calculated by the King method for the points immediately before the wall. It is showed on the close connection between the Rayleigh formula and the expression for the velocity potential which follows from the King method. The equation for the space distribution of the velocity potential expanded in spherical wave functions is transcribed into an abstract form by means of the Dirac bra-vector, ket-vector, and linear operator represented by the corresponding matrices. The space distribution of the velocity potential is then computed from the known values in the plane immediately before the emitter by the well-known method of undetermined coefficients written in its matrix form. Thereafter the space distribution of the velocity potential is determined by another, new method due to H. Stenzel. In both methods explicit expressions are given for the case of a vibrating rigid disk, membrane, and plate.
A Barium Titanate Transducer Capable of Large Motion at an Ultrasonic Frequency
Authors: Mason W. P. , Wick R. F.
Published: September 2005

By using a barium titanate cylinder poled radially a lengthwise motion can be excited in the cylinder whose resonant frequency is controlled by the length of the cylinder. By using a 4 percent lead titanate-barium titanate combination, stresses up to 1000 pounds per square inch of cross-sectional dimension and motions up to 50 parts in 106 times the length of the cylinder are available for static or slowly varying voltages of 15,000 volts per centimeter along the radial dimension. When such a cylinder is driven at its resonant frequency, the maximum strain appears to be limited to 10−4 by heating considerations if no cooling is used. For a cylinder 12 centimeters long, which resonates at 18 kilocycles, this corresponds to a displacement on each end of 3.9 × 10−4 cm, a particle velocity of 44 cm/sec and an acceleration of 5 × 10−6 cm/sec/sec. All of these quantities can be enhanced by a factor of 10 by soldering a solid brass “horn,” tapered exponential, to the end of the barium titanate cylinder. If the large end of the horn, which is soldered to the cylinder, is 10 times the diameter of the small end, the horn acts as a transformer to increase the particle motion by a factor of 10. Hence, a 1.5-mil motion is possible with this combination at 18 kilocycles. This structure has been made the basis of several instruments used for testing wear, for measuring magnetic flux, for testing adhesion of films, and for boring odd-shaped holes. A feedback amplifier system with a diode limiting element is used to keep the amplitude constant.
Analysis of Multiple-Echo Effect Arising from the Release of a Stored Wave Train
Authors: Gold Louis
Published: September 2005

A generalized theoretical treatment is presented of a problem which has direct application tothe phenomenon of multiple-echo patterns as employed for propagational studies of high frequency sound waves in various media. An analysis is made of the functional dependence of the number of observable echoes N in terms of a prescribed threshold sensitivity db* of a detecting device, and the storage medium parameters, which are the effective absorption coefficient a and the boundary reflection coefficient R. The equation derived is: N = {db*/10+logR − log(1 − R )}/{logR − αd loge}, where d is the length of the storage system. This relation has values Ropt for which N is a maximum, and it is shown that Nmax = 1/1 − Ropt. The solutions for Nmax are actually difficult to express explicitly since Ropt must be evaluated from the condition for a maximum Ropt1 − Ropt logRopt+log(1 − Ropt) −αd loge1 − Ropt=db*10. Asymptotic solutions are discussed, and detailed examination of the case of zero loss is given in the form of several graphical results.
Some Effects of Cavitation near 30 cps
Authors: Pielemeier W. H.
Published: September 2005

Publications by other investigators on the production of cavitation in liquids and its effects are discussed. Several points in favor of low frequency cavitation studies are listed. Two methods were used by the author to feed power at about 30 cycles/sec into the liquids. In one method a thick-walled Lucite tube containing the liquid was attached to the vibrating element of a Sonntag Universal Fatigue Machine. Similar results were obtained with a modified paint spraying compressor which had a vibrating diaphragm instead of a metal piston. Photographs show both methods. Emulsions and suspensions were made in a few minutes, the cleansing effect on cloth soiled in a standard manner was tested and the oxide coating on aluminum foil was removed. Probably greater corrosive effects could be obtained with the same power at higher frequencies.
On Multiple Excitation of an Elastic System
Authors: Bennett G. S.
Published: September 2005

The possibility of excitation of nonlinear elastic system by the combination frequencies produced when two forces of different frequencies act on the system is investigated, using the approximate method of Rayleigh. Experimental evidence is cited to support the results of the calculations, namely, that the combination frequencies need not be considered as potential sources of excitation.
Some Recent Work on Auditory Adaptation and its Relationship to the Loudness Recruitment Phenomenon
Authors: Hallpike C. S. , Hood J. D.
Published: September 2005

In the course of previous investigations, Dix, Hallpike, and Hood have concluded that the phenomenon of loudness recruitment is attributable to disordered function resulting from injury or disease of the hair cells of Corti's organ.

In the present paper, an account is given of an experimental study of certain loudness changes caused by adaptation of the hair cell responses to pure tone stimulation.

Two outstanding characteristics of the adapted state are defined: “on-effect normality” and “relapse.” Both resemble very closely those described by Matthews in the case of adaptation occurring the muscle stretch receptors of the frog.

Further studies in a number of human subjects show that both of these characteristics are exhibited regularly by the unadapted hair cell responses of individuals suffering from degenerative changes of the hair cells.

These studies appear to establish a very close similarity between “on-effect normality” occurring in the case of the adapted normal sense organ and the phenomenon of loudness recruitment, as demonstrated by the alternate binaural loudness balance procedure of Fowler in the case of the unadapted but diseased sense organ.

The experimental findings are considered to favor the view that loudness recruitment is one element of a complex disturbance of cochlear function due to disease or injury of specific elements of the cochlear sensory apparatus, namely the hair cells of Corti's organ.
Some Remarks on the Modern Status of Auditory Theory
Authors: Wever Ernest Glen
Published: September 2005

A discussion is made of two lines of evidence that bear upon the problem of the relative importance of place and frequency principles in auditory theory. The first line of evidence has to do with the relation between pitch discrimination and the degree of specificity of action in the cochlea and brings us to an evaluation of the principle of maximum stimulation. A consideration of loudness discrimination data discloses a serious limitation on our ability to appreciate the point of maximum in the cochlear activity and, in general, to make use of a spatial pattern. We must conclude that for the low tones whose patterns are broad the place principle contributes little or nothing to pitch discrimination, and the frequency principle has to serve this function alone.

A study of the evolution of the ear brings out still more clearly the relative roles of place and frequency principles. Hearing in some degree is present throughout the vertebrate series, and even the lowest forms have frequency ranges of several octaves and exhibit a fair degree of tonal discrimination. Yet, these lower forms possess an ear of exceeding simplicity, an otic sac in which there is little evidence of mechanical differentiation. It follows that these primitive ears must operate as frequency receptors, with ranges and discriminative abilities that depend simply upon the patterns of impulses conveyed by the auditory nerve. It appears, therefore, that in the history of the ear the frequency principle came first as the basis of tonal reception, and only sometime later in the course of evolutionary development was it joined by the place principle.
The Theory of Steady Forces Caused by Sound Waves
Authors: Westervelt P. J.
Published: September 2005

A general expression is derived for the force owing to radiation pressure acting on an object of any shape and having an arbitrary normal boundary impedance. It is shown that boundary layer losses may lead to forces that are several orders of magnitude greater than the forces owing to classical radiation pressure. Steady forces arising from an asymmetric wave form are compared with the other forces. A sound wave, consisting of equal parts of fundamental and second harmonic components, can cause forces ten or more orders of magnitude greater than the forces owing to radiation pressure to be exerted on small particles.
Scattering and Absorption by an Acoustic Strip
Authors: Levitas Alfred , Lax Melvin
Published: September 2005

A method for treating the scattering and absorption of sound in the presence of non-uniform boundary conditions is applied to the case of an infinite strip of material (of given width) placed on an infinite, otherwise hard, wall. The strip is assumed to be characterized by a normal acoustic impedance that may possess a resistive component.

The wave equation is reformulated as an integral equation over the strip. A variational expression is found for the amplitude of sound scattered by the strip in any direction. The total cross section for scattering plus absorption is determined from the amplitude of specular reflection according to a well-known cross-section theorem. Comparison with Pellam's results for absorption by such a strip shows that the methods used have an accuracy better than 2 percent over the entire frequency range.
On the Nonspecular Reflection of Sound from Planes with Absorbent Bosses
Authors: Twersky Victor
Published: September 2005

The nonspecular reflection of plane waves of sound from certain surfaces composed of absorbent bosses (semicylinders or hemispheres of arbitrary impedance) on an infinite plane of ∞ or 0 impedance is considered. Exact solutions are obtained for the problem of the single boss and then extended, subject to the single-scattering hypothesis, to obtain far field solutions for certain planar distributions of bosses of radii small compared with the wavelength. The results are compared with those obtained previously for non-absorbent bosses, and it is shown that the effects of the finite impedance are most pronounced in the simple source terms of the scattered components and may lead to either a decrease or an increase in the radiation reflected at the specular angle. Another effect of the finite impedance (for the small finite distributions) is to shift the critical value of the angle of incidence for which the reflection at the specular angle consists only of the specular component—below this value the reflection at the specular angle being a minimum and above it a maximum. For the infinite uniform random distributions it is found that the effect of the bosses is essentially but to change the impedance of the plane—these effective impedances being functions of the angle of incidence and the parameters and distribution of the bosses. The effect of the finite impedance of the bosses is most pronounced for these distributions yielding terms much lager than those previously retained for the nonabsorbent bosses. The results for the analogous distributions of cylinders and spheres are also given.
Transmission of Sound through Steel Plates Immersed in Water
Authors: Fay R. D. , Fortier O. V.
Published: September 2005

The measured transmittivity of a steel plate in water is presented as a function of the angle of incidence and the product of frequency and plate thickness over wide ranges.

The normal velocity of the plate surface can attain an amplitude necessary for good transmission only by constructive interference among internal reflections. It is shown that the ideal conditions can be met in a plate of finite width in only a few cases. In general, the conditions for a transmission maximum are the conditions for the existence of appropriate types of stable traveling waves in a plate of infinite extent; these conditions, however, are modified by edge effects. An apparent effect of this modification is to produce changes in the divergence of the transmitted beam and hence in the observed transmittivity.
Acoustical Impedance in Terms of Energy Functions
Authors: Westervelt P. J.
Published: September 2005

The acoustical impedance is expressed in terms of energy functions, and this procedure is applied to interpret the observed decrease in kinetic mass of circular apertures at large amplitudes.
Random Noise in an Attenuating Fluid Medium
Authors: Roberson Robert E.
Published: September 2005

It is assumed that acoustic background noise is caused by a distribution of random “white” noise sources whose physical mechanism is unspecified. A law expressing the amplitude-distance attenuation characteristic of the medium is also assumed. Several distributions of noise sources are considered: uniform volume distributions, uniform surface dipole distributions, and two mixed cases. The noise drop-off with frequency at a point below the surface is found for each case. For an infinite volume of noise sources, this drop-off is 6 db/octave at all frequencies. It is shown how this simple model can be generalized to other attenuation laws and other spatial and amplitude distributions of noise sources.
Physical Factors Involved in Ultrasonically Induced Changes in Living Systems: II. Amplitude Duration Relations and the Effect of Hydrostatic Pressure for Nerve Tissue
Authors: Fry W. J. , Tucker D. , Fry F. J. , Wulff V. J.
Published: September 2005

The results of experiments with frogs under a hydrostatic pressure demonstrate that cavitation is not an important factor in the mechanism of production of paralysis of the hind legs of frog by ultrasonic (frequency one megacycle) irradiation over the lumbar enlargement region of the spinal cord. Experimental results indicate that a linear relation exists between the reciprocal of the minimum exposure time for paralysis and the acoustic amplitude. This result is readily described in terms of a one factor rate process. On the basis of this experimentally determined relation, it is shown that time rate of change of temperature cannot be correlated with the observations. It is concluded on the basis of a theoretical calculation that absorption of ultrasound at interfaces in the spinal cord does not result in minute hot regions.

Further work on summation of subparalytic doses, spaced apart at various time intervals, indicates that the recovery process following exposure to a subparalytic dose of ultrasonic radiation may not be a monotonic function of time.
The Growth of Subharmonic Oscillations
Authors: Cunningham W. J.
Published: September 2005

Subharmonic oscillations at one-half the frequency of excitation may appear in certain types of oscillating systems, among which is the direct-radiator loudspeaker. These oscillations occur at very nearly the resonant frequency of the system when the parameters of the system are made to vary at twice this frequency. The rate of growth of the subharmonic depends upon the amount of variation of the parameters relative to the dissipation in the system. If the dissipation is small, the rate of growth may be large. In the loudspeaker, conditions are such that the rate of growth is usually small for typical conditions of operation.
Levels and Spectra of Traffic, Industrial, and Residential Area Noise
Authors: Bonvallet G. L.
Published: September 2005

A survey of city noise in the Chicago area was initiated in 1947. This report describes traffic, industrial, and residential area noise which was investigated as a part of the work. Levels of traffic noise were 35 to 45 db, 45 to 65 db, and 65 to 75 db in the 400–800-cps band for light, average, and heavy traffic conditions, respectively. Industrial noise ranged from 50 to 60 db in the same band for fifty percent of the cases measured. Ninety percent were below 65 db. A limiting spectrum for noise which is considered not objectionable is presented. Residential area noise ranged from 38 to 47 db in the mentioned band for fifty percent of the cases measured. At night and for winter conditions, traffic noise was 10 db lower in the mentioned band than in the daytime. At night, industrial area noise dropped to levels of existing traffic conditions, and in winter it was lower by about 5 db in octave bands mainly because factory windows were closed. At night, residential area noise was 5 to 10 db less in octave bands than during the day, and for winter conditions there was a drop of 6 to 8 db in octave bands due to the modified character of distant traffic.
A Phoneme Detector
Authors: Smith Caldwell P.
Published: September 2005

A speech analyzer is described which measures the degree of fit between the energy distribution of any speech signal and a set of “standard” energy distribution patterns stored in the machine. This technique is based on the assumption that a phoneme can be characterized, at least for a single speaker, by specifying the points of energy concentration in the frequency spectrum and by specifying the energy envelope, i.e., energy vs time characteristic, of selected portions of the spectrum. A set of contiguous band filters covering the frequency range 100–7000 cycles/sec are used in combination with rectifiers and integrators to produce polarized signals which are functions of the energy distribution of the speech input signal. Improved selectivity and discrimination against noise and noise-like signals are obtained by combining the outputs from adjacent filters to measure the difference between signal levels, and further combining signals to measure the second difference between signals in adjacent filter bands. “Optimum filters” for phonemes are constructed by adding output signals corresponding to frequencies of energy concentration and subtracting signals corresponding to energy minima; this summation generates a signal proportional to the degree of “fit” between the speech signal and the specified pattern. Separate summations of the low and high frequency filter outputs provide measures of intensity, voiced-unvoiced detection, and pitch extraction signals. Some results are presented.