bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater Sounds of Biological Origin
Authors: Small Arnold M.
Published: September 2005

This paper will report the progress of a study which is directed toward determining adequate descriptive terminology and making spectral analyses of all available underwater sounds ascribed to biological sources. A program of recording and collecting such sounds is underway. Sample recordings of typical sounds from marine life will be presented, and the audience will be given an opportunity to actively participate in selection of descriptive terms. The preferences of all listeners systematically studied to date will also be reported.
Theoretical and Observed Absorption of Sound in Suspensions
Authors: Urick R. J.
Published: September 2005

A theory is outlined which attributes the absorption of sound in suspensions of small, rigid, spherical particles to the viscous drag exerted by the fluid upon the particles. The absorption is found to depend on the magnitude of the drag coefficient and the velocity difference between particles and fluid in the sound field.

By use of a pulse reflection technique, the absorption of 15-megacycle sound has been measured in aqueous suspensions of finely divided silica and kaolin. The absorption is found to vary linearly with concentration, and in the range of particle size 1 to 10 microns is approximately proportional to the total area of particles in suspension. The observed variation of absorption with particle size, concentration, and viscosity of the suspending liquid is in agreement with the theory, although the computed values are larger than those observed.
The Acoustical Performance of Rooms
Authors: Rudmose H. Wayne
Published: September 2005

It is appreciated that the reverberation characteristic is only one measure representing the acoustical performance of a room. Measurements have been made on a number of average size studios and rooms using techniques other than reverberation measurement. Equipment has been constructed to produce an audio signal varying continuously in frequency and in band width. The band width can be varied continuously from 15 c.p.s. to 150 c.p.s., and the upper frequency limit is 15,000 c.p.s. Measurements show the effect on the response of the room as the band width is increased. Preliminary measurements demonstrate that the band width required to give a smooth response for a polycylindrical (plywood) studio is very much less than required for a rectangular studio with conventional acoustical treatment. The minimum band width for smooth response may be a useful figure in evaluating the diffusion of a room. The space variations of sound pressure within studios have also been made as a function of band width and frequency of the exciting signal. The minimum band width for smooth space response also appears to be a useful measure of the room's performance.
Interaction between a Plate and a Sound Field in a Fluid Medium
Authors: Fay R. D.
Published: September 2005

When underwater sound impinges on a steel plate at an oblique angle of incidence, there have been observed strong reflections directed toward the source. An analysis of the interchange of energy between a sound field in a liquid medium and flexural vibrations in a plate immersed in the field indicates the mechanism involved in this type of non-specular reflection. It has been found that for a plate and a liquid of specified properties, the behavior of the system depends on the product of plate thickness and frequency. For a steel plate b inches thick in water at a frequency of f kilocycles per second, the forces exerted by the water on the plate become negligible for values of bf exceeding about 20. For values of bf less than about unity, the effect of the plate in the sound field becomes negligible. It is therefore in the range of values between 1 and 20 for which the results are of particular interest. The velocity of phase propagation and the attenuation of flexural waves having origin in the plate have been calculated as a function of bf. There has also been found the angle between the plate and the wave fronts generated in the liquid. This angle, for the upper range of bf, is substantially equal to the angle of incidence for maximum non-specular reflection. The calculated values are in good agreement with measurements made by W. J. Finney.
Ultrasonic Radiation from Constrained Piston Sources and Rings
Authors: Williams A. O. , Heller G. S. , Hellens R. L.
Published: September 2005

Quantitative knowledge of the ultrasonic field near a circular piezoelectric source radiating into a fluid is desirable for some uses (interferometry, absorption, and diffraction measurements). The exact theoretical solutions available for numerical calculations assume an ideal piston source, which is not necessarily correct in practice. Two studies of a non-ideal piston source are reported here: (1) If the piston is assumed to be partially constrained in its outer portions, the axial sound field can still be computed by the Rayleigh method. It does not differ markedly from the ideal case, in the region of greatest practical interest. Certain experiments which have been quoted as substantiating the ideal piston may therefore not be significant. (2) A circular ring source can be treated by King's method, in integrals of Bessel functions. Some non-ideal pistons are equivalent to assemblies of such rings. The narrow ring source has interesting properties: at moderate and large distances it produces a beam more highly directive than that from the circular source. The ring source also produces an axial intensity following the inverse square law, at short ranges, more closely than that of the circular source
A Discussion of Some of the Factors which Determine the Effective Noise Level in Magnetic Recording
Authors: Gratian J. Warren
Published: September 2005

In this paper the causes of noise generated by the conventional supersonic biasing and erasing fields used in magnetic recording systems are discussed. The data to be presented emphasize the manner in which this noise varies with the wave form and frequency of an applied supersonic field. The importance of these two factors is shown to be a function of the characteristics of the erase and recording heads and of the inherent frequency response and modulation noise characteristics of the medium. By proper control of the wave form and frequency of the supersonic signal, noise may be reduced to such an extent that the effective noise level of a given recording medium with bias and erase signals applied will be equal to or less than the noise level of a virgin sample of the medium. Under these conditions, values of saturated signal to noise exceeding 80 db may be obtained.
Distortion in Magnetic Recording
Authors: Erikson Walter H.
Published: September 2005

This paper reviews most of the distortion-measuring techniques which have been suggested and evaluates their application to magnetic recording systems. A description is given of a harmonic-distortion measuring technique which provides a significant comparison of the low frequency non-linear distortion of different magnetic recording media. Methods for evaluating high frequency non-linear distortion are also presented. Distortion curves which are representative of the large number of distortion measurements taken on about forty samples of magnetic recording media will be shown.
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. Calibration data was secured from both dynamic and static measurements, the agreement of which is indicated.
The Calibration of Phonograph Reproducers
Authors: Wathen-Dunn Weiant
Published: September 2005

The application of the techniques used in microphone calibration to the calibration of phonograph reproducers will be discussed with particular emphasis on the significance of the relation between the mechanical driving point impedance and the physical properties of the source of known vibration, which may be a test record or an electromechanical vibrator rigidly coupled to the stylus. The particular methods used at the Naval Research Laboratory will be described, and typical calibrations of some of the newer reproducers will be given.
Preliminary Report on Absorption in Air From 10 to 100 kc, Measured by Pulse Techniques
Authors: Rothenberg H. C. , Pielemeier W. H.
Published: September 2005

A study is being made, using a pulsed carrier technique, of the absorption and dispersion of ultrasonic waves in air in the frequency range of 10 to 100 kc. The other parameters considered are pressure, humidity, and, to some extent, temperature. A tank 15 feet long and 22 inches in diameter, thermally insulated and with temperature control, is used for the work. A pulsed amplifier applies the variable frequency carrier signal to a ribbon transducer, acting as a source, in the tank. An indentical transducer, used as a receiver, is mounted on a movable carriage whose distance from the source can be changed an accurately known amount by means of a Selsyn motor. Measurements are made by observing the received pulse on a cathode-ray oscilloscope. The pulse repetition rate and the cathode-ray sweep frequency are crystal-controlled for purposes of accurate velocity measurements. The measurements reported are on the classical absorption as a function of pressure.
Ultrasonic Investigation of Molecular Properties of Liquids, Cyclic Compounds
Authors: Weissler Alfred
Published: September 2005

The velocity of sound in a pure liquid depends on the chemical structure of the molecules. In order to study this dependence further, the velocity of sound in twenty cyclic compounds at 30°C was measured by means of a three-mega-cycle ultrasonic interferometer which requires only 10 cm3 of liquid. These molecules consist fundamentally of rings of carbon atoms having hydrogens attached, in some cases with atoms of nitrogen, oxygen, or sulfur replacing one or two of the carbons. The values obtained lie between 1100 and 1550 meters/second; the accuracy is estimated as ±0.03 percent. Correlation of the results is facilitated by the use of the molar sound velocity R = v13M/d, where v is sound velocity, M molecular weight, and d density. This quantity may alternatively be calculated as the summation of the R increments for each of the chemical bonds in the molecule. In the present work, the average agreement between the observed and the summation values of molar sound velocity was about 1 percent. Therefore, one can predict the velocity of sound in a pure liquid with an accuracy of a few percent, simply from a knowledge of the molecular structure. The adiabatic compressibility, 1/v2d, is another property of interest in the study of chemical structure by ultrasonics. For example, a compound which contains two rings has a smaller compressibility than that associated with either of the constituent rings.
Dispersion of Compressional Waves in Isotropic Rods of Rectangular Cross Section
Authors: Morse R. W.
Published: September 2005

The compressional wave velocity in rectangular metal rods is measured as a function of frequency by means of standing wave patterns made visible by the use of lycopodium powder. An x-cut quartz crystal is used as a driver at frequencies between 300 and 700 kilocycles per second. Results are obtained on brass rods of different width-to-thickness ratios, the thickness being the same in each case. The dispersion curves display the same general behavior found in circular rods by other investigators, although the slope of the curves is found to depend on the width-to-thickness ratio. Theoretical calculations have been made for the case in which the width is much larger than the thickness. The general elastic equations lead to the dispersion relation necessary to satisfy the surface conditions. An equivalent relation was found by Rayleigh and the general character of the dispersion curves was investigated further by Lamb. Lamb's calculations are here extended by finding numerical solutions for the dispersion curves of the first symmetrical longitudinal mode for different values of Poisson's ratio. Calculated values are in good agreement with measured values when the cross section dimensions are in the ratio of 8:1.
Ultrasonic Investigations of Substances under High Pressures
Authors: Holton Gerald J.
Published: September 2005

The various techniques used in the investigation of substances under pressure by velocity and absorption measurements of sound will be reviewed briefly, including the multiple echo-method currently employed by this writer in conjunction with Professor Bridgman's high pressure techniques. After a summary of recent results of a study on the structure of water at pressures to 6000 atmos. and at various temperatures, other promising problems in the theory of liquid and solid states will be discussed and suggested instrumentation will be described.
Measurement of Ultrasonic Bulk-Wave Propagation in High Polymers
Authors: Nolle A. W.
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 in length 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 in 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.
Reduction of Reverberation in a Water-Filled Steel Test Vessel By Use of a Porous Material
Authors: English Bruce V. , Darner Charles L.
Published: September 2005

A porous material has been used in a steel test tank at the Underwater Sound Reference Laboratory to decrease the reverberation time of the tank. Data will be presented showing the effects of frequency and pressure on the underwater sound absorption coefficient of the material. Measurements of performance characteristics of underwater electroacoustic transducers are made in the test tank under hydrostatic pressures up to 300 pounds p.s.i. Calibration work in this tank requires the use of the pulse method. For present research projects, the reverberation level in the tank must be at least 40 db below the level of the directly received pulse. Before using the porous material, the reverberation level at the time of the received pulse was down only 5–30 db in the frequency range 10–150 kc. Use of the absorbing material in the tank has reduced this level by as much as 40 db, thus affecting the present margin of 40–70 db.
Acoustic Filters for Supercharged Diesels
Authors: Voelker Ch. H.
Published: September 2005

This paper considers railroad Diesels supercharged with Roots-Connersville Blowers and power plant Diesels supercharged with Elliott-Buschi turbochargers, and describes intake acoustic filters which have attenuations approaching ambient noise levels which have been applied to the intake in combination with the air cleaners.
Acoustical Laboratory Facilities at the U.S. Naval Engineering Experiment Station
Authors: Wohlberg George
Published: September 2005

The Acoustical Laboratory facilities for engineering research and development work at the U. S. Naval Engineering Experiment Station are described. Particular reference is made to a new laboratory, to be completed in 1948, designed specifically for sound and vibration investigations of Naval machinery. Three large free-field test rooms, an underwater sound tank, quiet ventilation systems, isolated foundations, steam, and electrical power will render this facility particularly suitable for acoustical work on large machinery. A Diesel engine driven boat, equipped as a floating laboratory, is also available. Descriptions are included covering the facilities of related activities devoted to noise reduction through use of isolating devices, to mechanical shock testing and to outdoor atmospheric and underwater acoustical work. The instrumentation available for implementing acoustical and vibration work is briefly described.
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.
The Chemical Effects of Ultrasonic Irradiation: Reaction between Carbon Tetrachloride and Water
Authors: Weissler Alfred , Cooper Herbert W. , Snyder Stuart
Published: September 2005

Intense ultrasonic waves produce interesting physical and chemical effects, such as emulsification, luminescence, and chemical transformations. In an attempt to clarify the mechanism by which ultrasonic irradiation causes chemical reactions in liquid mixtures, a quantitative study was undertaken of the ultrasonic production of iodine in aqueous solutions of potassium iodide which contain some carbon tetrachloride. It was found that the amount of iodine liberated depends greatly on the dimensions and material of the container, but only slightly on the concentrations of potassium iodide and carbon tetrachloride. Frequencies of 400, 700, 1000, and 1500 kc gave varying results, but this is attributed to varying transparency of the test tube rather than to intrinsic frequency-sensitivity of the process. Although earlier investigators believed that dissolved oxygen is essential, the present work shows that nitrogen or helium serves nearly as well. As the power input is increased, no iodine is produced until cavitation occurs; then the yield increases almost linearly if the volume of solution is large enough, but for smaller volumes the yield first increases and then decreases sharply. The fundamental reaction is apparently that between water and dissolved carbon tetrachloride, caused by the large mechanical or electrical forces generated at the collapse of cavitation bubbles; the potassium iodide is primarily an indicator of the oxidizing chlorine set free. Rate studies suggest that the reaction takes place in two steps, each of which liberates two chlorines per CCl4 molecule; the first step is about ten times faster than the second.
Radiation Characteristics of Ultrasonic Focusing Radiators
Authors: Willard G. W.
Published: September 2005

An experimental study has been made of the complete radiation pattern of a 5 mc, spherical, concave, focusing quartz radiator. This is the same radiator as elsewhere described with regard to its quality of focusing and power of concentrating ultrasonic energy. Because of the curvature of the radiator, the radiator thickness direction varies relative to the crystallographic axes from truly x cut at the center of the radiator to about 13° off x axis at the edge of the radiation region (18° off at the mounting boundary). Hence the effective electromechanical coupling and frequency constant, relative to the respective thickness directions, differ over the radiator surface. Their difference from that at the center varies differently in different directions, but in general, increases on receding from the center. The result is that the radiation efficiency also decreases on receding from the center. Radiation patterns showing these effects in different planes through the axis of the radiator will be shown. Since the elastic and electrical constants of quartz are well known, it was possible to calculate the variation of electromechanical coupling, frequency constant, and radiation efficiency variations over the surface of the radiator. The experimental results above check the theory excellently. There is a plane, parallel to the x axis and inclined about −22° to the z axis (toward parallelism with the major cap face) in which the frequency constant is nearly constant with recession from the x axis and the electromechanical coupling nearly as good as in the best plane. Therefore a preferred orientation for an x-cut, cylindrical focusing radiator is that in which the cylindrical axis of the radiator is normal to this plane. Further, even with spherical focusing radiators the off-resonance effects, due to frequency constant variations, may be compensated for by varying the thickness proportionally to the frequency constant. The result of such thickness shaping is to produce a radiator of improved radiation efficiency and greater concentrating power. Theoretical curves will be presented.
Effects of High Intensity Ultrasonic Radiation
Authors: Muller J. F. , Willard G. W.
Published: September 2005

The sharpness of focus of a concave focusing radiator has been shown by G. W. Willard to be limited by wave diffraction in the same manner as in the equivalent optical case. Using a 5-mc x-cut, quartz radiator of focal length 63.5 mm and effective diameter 28.6 mm, the effective diameter of the intense core of the diffraction pattern in the focal plane is less than 1.6 mm. By radiation pressure measurements it was found that over three-fourths of the energy passed through this core region (optical case theory gives 86 percent). Thus, with 90 watts electrical input to the radiator an ultrasonic intensity of about 5000 watts per cm2 has been obtained in water at the focus of this radiator. This corresponds to particle acceleration amplitudes of ±25 million times gravity, and to hydrostatic pressure amplitudes of ±120 atmospheres. Even with this level of intensity and its corresponding hundred atmospheres of tension in the liquid it has been impossible to obtain any evidence of cavitation in water, at this frequency of 5 mc. Using the same radiator at 15 mc (its third harmonic), but at lower powers, it has also been impossible to produce cavitation, as would be expected from the above. Also at somewhat lower intensities, it has been impossible to produce cavitation in carbonated water. Little is known about the dependence of cavitation power on frequency. However, H. B. Briggs, J. B. Johnson, W. P. Mason have produced cavitation in water at 25 kc with an intensity of only one-half watt/cm2. Other interesting fountain, fog, and local heating effects will be mentioned.
Onset of Acoustical Cavitation in Fluids
Authors: Blake F. G.
Published: September 2005

Apparatus built for a study of the factors affecting the onset of cavitation in the body of a fluid has been described and since then improved. Pressure concentrations in a region remote from any boundary surfaces are produced by convergence of several sound beams to a common focus. Pressures are directly measured by means of a miniature magnetostriction hydrophone. The probe sensitivity is measured by a reciprocity method using short pulses to permit free-field calibration in a small tank. Qualitative observations and results of preliminary measurements on water will be presented.
An Ultrasonic Materials Tester
Authors: Van Valkenburg H. E.
Published: September 2005

For either production tests or investigational projects, the technique of ultrasonic transmission measurement has the desirable feature that the required electronic equipment can be versatile without being complex or costly. To utilize this technique for industrial non-destructive testing, an instrument has been developed which is operable from 200 kc to 2 mc and consists essentially of a frequency-modulated generator and a wide band receiver. Average ultrasonic transmission through a specimen for a sweep-frequency range of several hundred kc is indicated by a panel instrument, while the frequency response pattern may be shown simultaneously by a conventional oscilloscope. Discontinuities which attenuate the ultrasonic signal or physical changes which alter the frequency can therefore be detected. Transducers may be placed either on the same or the opposite surfaces depending upon the application. A group of samples can be rapidly inspected by comparison with a standard specimen, while a regularly shaped object can be inspected by scanning about an axis of symmetry.
An Ultrasonic Underwater “Point-Source” Probe
Authors: Fein Louis
Published: September 2005

A conically shaped piezoelectric probe of ammonium dihydrogen phosphate is described. Its sensitivity over a frequency range from 1235 kc–1280 kc was obtained by means of a reciprocity calibration. The average value is about 0.12 microvolt per dyne per square centimeter. Since the measured pattern of the probe as a receiver was the same at various points in the acoustic field, it may be concluded that the probe is a “point source.”
A Pulse Method for Measuring Small Changes in Ultrasonic Velocity in Solids with Temperature
Authors: Holbrook Richard D.
Published: September 2005

A pulse-modulated, 10- to 30-mc oscillator is used to apply pulses of r-f voltage to piezoelectric crystals attached to solid samples. The transmitted pulse is amplified, detected, and returned to the pulsed oscillator as a trigger voltage. The number of pulses occurring per second is then a function of the electrical and acoustic delay. Since the latter is a function of temperature, small changes in sound velocity can be determined from observed differences in the repetition frequency of the pulsed oscillator after correcting for changes in acoustic path length caused by linear expansion. Repetition frequencies in the region 50,000 to 100,000 per second are used.
Crystal Pick-Up for the Detection of Ultrasonic Standing Waves in Rods
Authors: Bakanowski A. E. , Lindsay R. B.
Published: September 2005

The powder pattern method of measuring standing waves in solid rods, though very useful, has certain disadvantages, notably in the difficulty of securing good patterns on rods which are not highly polished and very smooth. In the present work a Rochelle salt pick-up has been constructed which can travel along the rod by means of a calibrated screw. An x cut 45° crystal with a wedge-shaped edge is used. By means of a suitable counterbalance this edge rests very lightly on the rod and the piezoelectric voltage proportional to the magnitude of the oscillation at the point of contact is delivered to and measured by an R.C.A. Chanalyst. Detection of the nodes for any particular pattern is readily accomplished. The resonant modes can also be detected by the pick-up. The estimated accuracy of the use of pick-up in measuring the velocity of the waves in the rod is about 1 percent. The method is not successfully applicable to wave-lengths of less than 2 mm. On smooth rods the pick-up yields values agreeing with those obtained by the powder method to within 2 percent, which is considered within the limits of experimental error.
The Interpretation of Loudness, Pitch, and Masking Phenomena with Regard to the Two-Canal Theory of Cochlea Mechanics
Authors: deRosa L. A.
Published: September 2005

A theory as to the operation of the cochlea and with consideration as to the role of the scala tympani, has been proposed: This “two-canal” theory offers a possible explanation for a number of auditory effects. The variation in loudness level with intensity level at different frequencies may be due to the appearance of “repeat points” both at the low and high frequency portions of the acoustical spectrum. For steady-state tones, the phenomenon of masking can be attributed to the appearance of these “repeat points,” without requiring marked departures from linearity in the auditory transmission links to the cochlea. Certain phase effects encountered for steady-state stimuli require that the cochlea, following the Helmholtz resonant theory, should display low damping. On the other hand, observational data on the masking effects of clicks and other transient stimuli both on steady tones and on other impulsive stimuli require that the cochlea response be highly damped. The “two-canal” theory provides an explanation for this apparent inconsistency by providing for a highly damped but sharply frequency-selective mechanism.
The Importance of Different Frequency Regions for Speech Intelligibility
Authors: Galt Rogers H.
Published: September 2005

Published studies of the results of speech intelligibility tests have described the derivation of an empirical function which expresses the relative importance for intelligibility of the various parts of the audible frequency spectrum. The integral of this function with respect to frequency, between 0 c.p.s. and any chosen upper limit, f, gives the total importance of all frequencies from 0 to f. When this integral of importance is plotted against f, the resulting curve is found to be closely related to the curve showing the total number of nerve endings on the basilar membrane passed over by the region of maximum stimulation as the frequency is changed from 0 c.p.s. to f. Thus it is found that the importance of any frequency region for intelligibility is, within certain frequency limits, directly proportional to the number of nerves or of nerve patches stimulated. This proportionality and the departures from it together determine a new function which measures the importance of each frequency interval as a building block of speech sounds.
Determination of the Loudness of Noise from Simple Measurements
Authors: Beranek Leo L. , Peterson Arnold P. G.
Published: September 2005

This paper extends earlier methods for the calculation of the loudness of continuous spectra noises and proposes an apparatus for the simple measurement of that loudness. Fletcher and Munson outlined a procedure for calculating the loudness of a sound from its masking audiogram. Also a simple relationship exists between masking and the sound pressure level of critical bands of noise above the threshold for pure tones. As a consequence it would seem that we might calculate loudness if we know the r.m.s. pressure spectrum of the noise. However, we find that calculations on this basis frequently give loudness levels which differ from recent data by 10 to 20 db. Greater accuracy can be achieved by taking into account the difference between covered-ear and open-ear thresholds and by avoiding the use of masking contours. Not unlike Fletcher and Munson, we assume that the loudness contributed by equal pitch intervals (approximately equal lengths of the basilar membrane) are linearly additive. Next, we establish by trial a relationship between loudness and sound pressure level for a 300-mel frequency band in the vicinity of 1000 c.p.s. (860–1330 c.p.s.). Similar curves for 300-mel bands at other frequencies are derived from equal-loudness contours for random noise (unpublished data). The loudness and the loudness level of a continuous spectrum noise extending over the audible range are therefore easily determined from measurements made with a sound analyzer incorporating ten filter bands, each 300 mels wide.
The Influence of Interaural Phase on Interaural Summation and Inhibition
Authors: Hirsh Ira J.
Published: September 2005

The difference between the binaural and monaural thresholds varies within fairly large limits. Although this binaural-monaural difference may not vary systematically as a function of frequency when pure-tone thresholds are measured in the quiet, the difference varies greatly, as does frequency, when pure tones are presented against a background of noise. Binaural summation, a term which has been used in the past to refer to the phenomenon in which the binaural threshold is lower than the monaural, obtains for masked thresholds only when the phase angles between the two earphones are opposite for the tones and the noise. If the tones and the noise have the same interaural phase angle the binaural threshold is higher than the monaural. This phenomenon, called interaural inhibition, as well as its antipode, interaural summation, is most marked at low frequencies and increases as the intensity of the masking noise is increased. The discussion considers some implications of these findings for the theory of masking and of interaural summation.
The Loudness and Monaural Loudness Matching of Short Tones
Authors: Garner W. R.
Published: September 2005

Differential sensitivity to the intensity of tones as a function of tone duration can be studied in a variety of ways. In these experiments a monaural loudness-matching technique was used, and the standard deviation (SD) in db of the matching scores was used as the measure of precision. With one technique a standard tone of 500 msec. duration was followed by a tone of variable duration (10–500 msec.) after a silent interval of 50, 100, or 500 msec. In another technique, both standard and comparison tones were of the same duration (10–500 msec.) with the same silent periods between tones. (1) When the standard tone was always 500 msec., the SD of the loudness matches increased with a decrease in the duration of the comparison tone from approximately 1 to 3 db, and the length of the silent interval had no effect on the function. (2) When both standard and comparison tones were of the same duration, the SD again increased as the duration was decreased; in this case, however, a silent interval of 50 msec. caused an increase from approximately 1 to 4 db while a silent interval of 500 msec. caused an increase of approximately 1 to 1.5 db throughout the range of durations employed. (3) When a standard tone of a constant duration is used to obtain loudness matchings, a measure of the loudness of tones as a function of duration is also obtained. These measures showed a clear distinction between the 6 observers used. For 3 observers, the change in duration caused practically no change in loudness. For the other 3 observers, changes in loudness level as great as 9 db were recorded. It appears that some observers make a loudness match of this sort in terms of intensity, while others tend to match in terms of total energy.
Masking by Interrupted Random Noise
Authors: Miller George A. , Garner W. R.
Published: September 2005

Most of our knowledge of masking is derived from experiments that used one continuous sound to mask another continuous sound. In practical situations, however, masking noises are often intermittent. The present experiments were designed to explore the effect of interruptions upon the masking effectiveness of random noise. In the first experiment, tones were masked by continuous and by interrupted noise. The noise intensity, the proportion of the time the interrupted noise was on, and the rate of interruption were varied. The principal effect of interruption is to lower the masking effectiveness. The extent to which the masking is decreased depends principally upon the duration of the silent interval and secondarily upon the frequency of the masked tone and the intensity of the noise. A computational scheme is possible which will permit a rough approximation of the masked threshold in the presence of interrupted noise. In a second experiment, articulation tests were conducted to determine the effect of interrupted noise upon the intelligibility of speech. The results of this second experiment can be predicted on the basis of the data obtained for pure tones.
The Intelligibility of Interrupted Speech
Authors: Licklider J. C. R. , Miller G. A.
Published: September 2005

The paper concerns the effect of intermittent interruptions of the speech wave upon intelligibility as measured by word articulation tests. The principal experimental variables are: the interruption rate (the number of on-off cycles per second) and the speech-time fraction (the fraction of the time that the communication circuit is turned on). When the interruption rate is very low (on and off once in ten seconds), the percentage of the words heard correctly is, of course, equal approximately to the product of (a) the percentage understood in the absence of interruptions and (b) the speech-time fraction. At the other extreme, when the interruption rate is very high (on and off 5000 times a second), intelligibility is essentially unimpaired regardless of the speech-time fraction. In the intermediate range, each curve of the family relating intelligibility to interruption rate for various speech-time fractions rises to a maximum at about 15 interruptions per second, then falls to a minimum in the neighborhood of 300 interruptions per second. With a sound-time fraction of 0.50 and 15 interruptions per second, the listeners hear almost all of the words despite the fact that the speech is, and sounds, intermittent. A curious effect is produced when, with the same speech-time fraction and the same interruption rate, the speechless intervals are filled with white noise. No longer does the speech sound intermittent; instead, it is as though the speech were the scene behind a picket fence, viewed by a moving observer. The speech sounds continuous, and the words are understood just as well as they were before the noise was introduced. In the experiments just described, the interruptions occurred at regular intervals and the speech was turned on and off abruptly. Other experiments were conducted with iterruptions at irregular intervals and with gradual transition from “on” to “off” and vice versa. The disturbance produced by irregular interruption sounded very much like static and was therefore readily distinguishable from the effect produced by regular interruption. (At high rates, the latter has a tonal quality.) The intelligibility scores, however, were approximately the same with irregular as with regular interruptions. Changing from abrupt to gradual modulation (holding constant the speech-time fraction as measured at a level corresponding to one-half the peak speech amplitude) improved both the quality and the intelligibility of the interrupted speech.
The Representation of Vowels and their Movements
Authors: Potter Ralph K. , Peterson Gordon E.
Published: September 2005

It is shown that movement of the major resonances in the voiced sounds of speech may be represented by traces in a three-dimensional graph. Apparently, a great deal can be learned about speech through investigation of such traces, and they suggest a new method for vowel designation that is particularly adaptable to quantitative analysis.
Lamination Design for Magnetostrictive Electromechanical Transducers
Authors: Camp Leon
Published: September 2005

Theory is presented for the design of laminations used in the construction of a transducer having a plane, piston-like radiating face. Data are presented to show to what extent the simplifying assumptions made are justifiable.
Optimum Directivity Patterns for Linear Arrays
Authors: Pritchard R. L. , Rosenberg M. D.
Published: September 2005

The “sharpest” major lobe of a directivity pattern is obtained when the elements of the source are excited in such a way that all minor lobes have the same relative amplitude. Dolph's treatment of linear arrays that produce equal minor-lobe patterns has been extended for all useful spacings in acoustical arrays in a manner suggested by Riblet. The required distribution of excitation to produce such patterns has been computed explicitly for linear, equally-spaced arrays of simple sources containing odd numbers of elements up to 13. The results are exhibited by curves showing the relationships among angular width of the major lobe, relative amplitude of the equal minor lobes, directivity index, and the number and spacing of the elements of the array.
A Small High Frequency Microphone
Authors: Rudnick I. , Rothenberg H. C.
Published: September 2005

A small rochelle-salt crystal probe microphone and preamplifier have been developed for use in air, or water, at frequencies up to 100 kc. The microphone response is reasonably flat up to 50 kc in air, with a sensitivity of approximately −100-db re 1 volt per dyne per cm2. Beyond this frequency the response varies, but is satisfactory and usable up to 100 kc at least. In water the sensitivity is about −100 db and is relatively flat to 100 kc. At 100 kc there is a variation in response of about 5 db as the microphone is rotated through 360°. This variation is less than 2 db at 20 kc. The crystal ensemble is coated with Glyptal, and has two copper shields, insulated from each other, plated over it. Its dimensions are 14″×516″×38″, and it is mounted on tubing 7″ long and 18″ diameter. The preamplifier was designed to have very high input impedance so as to be independent of capacity changes in the crystal, and a low output impedance. This is accomplished by using two stages—a cathode-follower input and a pentode output with 500-ohm output impedance. The use of a double shield and a high impedance load on the cathode follower results in a gain of 2.5 db, flat within 0.5 db from 2 kc to 200 kc, the lower limit being imposed by coupling-condenser size rather than input impedance. The microphone has had considerable use in air and water media during the past year and has stood up well.
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, more useful analog is that of a transmission line containing a discontinuity. Experiments with woven and perforated screens of different geometric forms have been performed and the results evaluated.
The Acoustical Performance of Rooms
Authors: Rudmose H. Wayne R.
Published: September 2005

In an earlier paper, two methods of measuring the acoustical performance of rooms based on physical measurements were presented. More data have been taken using these two schemes. Also, another method, using psycho-physical techniques, has been used. Articulation scores have been obtained by placing the room under a constant acoustical stress of noise while varying the signal level of the speech material. The steepness of the articulation function correlates with the results obtained by using physical methods for measuring the performance of the rooms. When polycylindrical studios and rectangular studios are compared, polycylindrical studios show more diffusion and a steeper articulation function than rectangular studios.
Measurement of Sound Absorption of Highly Absorbent Acoustic Structures
Authors: Chrzanowski Peter
Published: September 2005

Reverberation chamber measurements of sound absorption by sound absorbent structures of the type used in treating “dead” rooms show a curious anomaly. When the structures are placed in an enclosure so that only the top of the enclosure is exposed to the reverberant sound, the apparent absorption of the structure is less than for a highly sound absorbent layer of material placed on the floor of the chamber. Measurements which confirm this effect are presented and an attempt is made to explain the discrepancy.
Some Randomizing Experiments in Reverberant Sound Fields
Authors: Edelman S. , London A.
Published: September 2005

In the measurement of sound-transmission loss and sound-absorption coefficients it is necessary to randomize the sound field to the greatest extent possible so as to validate the reverberant sound field statistics upon which such measurements are based. One difficulty that is often experienced is the lack of excitation of a sufficient number of normal modes of the test rooms. For this reason a new type of warble oscillator that generates a continuous band of frequencies, in which the band width and band center are capable of continuous variation, has been investigated. In addition, some experiments will be described in which averaging of sound levels is accomplished by the use of a large number of microphones, as many as 18, in series-parallel combinations.
Considerations Concerning a Standard for the Measuring of Impact Sound
Authors: Jordan Vilhelm Lassen
Published: September 2005

So far no general agreement has been reached concerning the definition and measuring of impact sound. Noise-level measurements have been replaced by frequency analysis, but the fundamental question, whether a transmission loss definition should be preferred to a level definition, remains unsolved. The analogy between the insulation of airborn sound and that of impact sound should be taken into account when considering this question. Another important question which has received very little attention is the question of the sound damping value of a floor construction in regard to the noise level arising in the room in which the floor is located. Any floor construction should be judged according to its insulation value as well as to its damping value. Definitions and methods of measurement for both cases mentioned are offered.
Calculations on a Short-Tube Method for Measurement of Impedance
Authors: Cook Richard K.
Published: September 2005

The precision measurement of the impedance of acoustic materials is an important problem for which a number of techniques have been devised. The possibility of using a short-tube technique to measure such impedances has been examined mathematically. The basic idea is that the sound pressure within the tube, because of a source of known volume velocity, is dependent on the impedance of the walls of the tube. It appears from the results of the calculations that the short-tube method can be used successfully for measurement of impedance of both isotropic and anisotropic materials, even though the source of sound has a diaphragm, which is constrained to move in a non-piston-like way, and whose mechanical impedance is not very large. The analysis shows how well such a source can be represented by a mechanomotive force in series with a mechanical impedance, and hence how accurately Flanders' method can be used.