bluuebunny/crossref_metadata_2025 huggingface dataset:
The Acoustic Significance of the Amplitude and Phase of Harmonics Present in a Source of Sound in a Room
Authors: Robbins Joseph G.
Published: September 2005

In order to obtain some further measure of the acoustic properties of a rectangular room, a brief subjective study is made of listener response to sounds having various degrees of modulation on their decay curves and to alternate sounds which differ only in the phase relation of a harmonic in the source with respect to the fundamental frequency. The data show that the average listener finds the decay of sounds pleasant in inverse proportion to the amount of modulation on the decay curves, and that a large majority of listeners cannot distinguish between two steady-state sounds, alike except that in one sound the phase of a harmonic is changed with respect to that of the fundamental frequency. Also, an objective study is made of the modulation on decay curves. A switching device is used to insure a smooth cutoff at any predetermined phase of the fundamental frequency. The data show that, if the source includes the fundamental frequency and a harmonic at equal amplitudes, the modulation of the decay curve consists of two superposed modulations. The phase relations and amplitudes of these modulations are dependent on the phase relations and amplitudes of the driving frequencies which produce them.
An Experimental Study of Speech-Wave Probability Distributions
Authors: Davenport Wilbur B.
Published: September 2005

Measurements were made of the first-probability distribution and of various conditional probability distributions of the speech wave instantaneous amplitude. Results obtained for several speakers indicate that the first-probability distribution varies exponentially with large values of amplitude and that increases in the conditional probabilities are noted for delay times of the order of magnitude of the pitch period.

Measurements were also made of the first-probability distribution of the duration of the speech-wave zero-crossing periods, and of the auto-correlation function of clipped speech.

These measurements were of the stationary, or “long-time,” speech-wave probability distributions. Most of the results are for speech waves recorded in an anechoic chamber. Some results are included for voices recorded in a live studio.
Mechanism of Acoustic Absorption in Tissue
Authors: Fry William J.
Published: September 2005

A viscous mechanism for the absorption of ultrasonic energy in tissue is considered. It is shown that the viscous forces acting between a suitably chosen distribution of suspended particles or structure elements and a suspending liquid can account for the experimentally observed linear relations between acoustic absorption coefficient and ultrasonic frequency. The frequency band over which linearity obtains is determined by the limits of the distribution of values for the parameters which describe the structure elements. Below the linear range the relation becomes quadratic, in agreement with experiment, and at “high” frequencies a limiting value is approached asymptotically.
The Masking of Tones by White Noise as a Function of the Interaural Phases of Both Components. I. 500 Cycles
Authors: Jeffress Lloyd A. , Blodgett Hugh C. , Deatherage Bruce H.
Published: September 2005

Work by Hawkins, Hirsh, Licklider, Stevens, Webster, and others has shown the considerable reduction in masking which occurs when the interaural phase of either the signal or the noise is reversed, or when the interaural phase of the signal is shifted by various amounts. The present paper extends this work by shifting the interaural phases of the masking component of the noise and of the tone by various amounts between +180° and −180°, and also by shifting the noise timewise by amounts up to 4.0 milliseconds. The interaural phases of both the noise and the 500∼ tonal signal are therefore parameters of this study.

The results are in agreement with those already published, but show in addition large reductions in threshold even when the noise and the tone differ in their interaural phase positions by amounts less than 180°. They also show a periodic fall and rise of the masked threshold as the interaural time difference for the noise is varied. Finally, they show the importance of interaural correlation in determining the extent to which the binaural threshold will be lower than the monaural.
Phonemes and Allophones in Speech Analysis
Authors: Twaddell W. F.
Published: September 2005

Phonemes are quite abstract units. The criteria for establishing them are primarily distributional and articulatory, not acoustic. A unit intermediate between a single speech-event-segment and a phoneme is the allophone. An allophone is a statistical average, with constant, identifiable acoustic characterization. For many purposes of engineering, psychology, pedagogy, and information theory, the allophone may be a more suitable unit than the phoneme.
Operational Phonemics in Reference to Linguistic Relativity
Authors: Pike Kenneth L.
Published: September 2005

The phonemes of a language are neither absolutes nor bundles of absolute characteristics, but rather are fluctuating bundles of features identified (1) relative to each other in sequences, (2) relative to a system of fluctuating bundles of characteristics, and (3) relative to structural position in a sequence of such relative elements. Detection techniques, if paralleling phonemic analysis, would need to be able to work with fluctuating relative elements rather than with absolute physical characteristics only.
The Problem of Selective Voice Control
Authors: Kock Winston E.
Published: September 2005

The development of devices which can be operated automatically from the phonetic content of speech may be viewed in terms of the more general problem of the reduction of channel capacity in communications systems. Significance has been observed in formant positions and movements as regard the identification of speech sound. The basic problems in the derivation of phonemes from the formant patterns are reviewed.
Automatic Recognition of Spoken Digits
Authors: Davis K. H. , Biddulph R. , Balashek S.
Published: September 2005

The recognizer discussed will automatically recognize telephone-quality digits spoken at normal speech rates by a single individual, with an accuracy varying between 97 and 99 percent. After some preliminary analysis of the speech of any individual, the circuit can be adjusted to deliver a similar accuracy on the speech of that individual. The circuit is not, however, in its present configuration, capable of performing equally well on the speech of a series of talkers without recourse to such adjustment.

Circuitry involves division of the speech spectrum into two frequency bands, one below and the other above 900 cps. Axis-crossing counts are then individually made of both band energies to determine the frequency of the maximum syllabic rate energy with each band. Simultaneous two-dimensional frequency portrayal is found to possess recognition significance. Standards are then determined, one for each digit of the ten-digit series, and are built into the recognizer as a form of elemental memory. By means of a series of calculations performed automatically on the spoken input digit, a best match type comparison is made with each of the ten standard digit patterns and the digit of best match selected.
Apparatus for Absolute Measurement of Analogous Impedance of Acoustic Elements
Authors: Thurston George B.
Published: September 2005

A hydrodynamical test system for absolute measurement of analogous impedance of acoustic elements is described. The test system is designed for use from dc to 700 cps, and in this frequency range it accurately measures pressure and volume flow.
The Use of Binaural Tape Recording in Automotive Noise Problems
Authors: Apps David C.
Published: September 2005

The record-playback method of making noise comparison tests provides realistic answers with a minimum of equipment and sophistication. Such a method is especially attractive in problems handled by making experimental changes which, taken individually, usually produce very small changes in level and quality of noise.

In automotive work, playback of single-channel recordings of interior car noise sensed by a single microphone sound unreal because of an emphasized bass, the cause of which is not known to the author. Directional effects also contribute to the lack of realism.

The use of a binaural magnetic tape recorder improves realism, which in turn enhances the resolution of smaller differences.
Tube Method of Measuring Sound Absorption
Authors: Taylor Hawley O.
Published: September 2005

A description of a tube method of determining the sound absorbing power of materials in which no exploring device is introduced in the path of the sound wave in the tube. The method is an extension of a research by Kennelly and Kurokawa on “Acoustic Impedance and Its Measurement,” and makes use of the motional impedance of a telephone receiver which serves as both the source of the sound wave in the tube and as the means for determining the fraction of sound absorbed by the material, a sample of which is attached to the piston which slides in the tube. Sample calculations for sound absorption are included.
Techniques for Evaluation of Noise-Reducing Piping Components
Authors: Callaway D. B. , Tyzzer F. G. , Hardy H. C.
Published: September 2005

The need for quantitative information on piping noise reduction obtainable by various devices such as flexible couplings, isolating hangers, or pipe-wall damping treatments led to the development of a test setup for making the desired measurements. The setup consisted of a long, straight length of pipe in which the test device was installed. Broad-band noise was introduced into the water or the pipe wall at one end of the system. Pipe-wall vibrations were detected by accelerometers and were analyzed by means of an octave filter set. It was found that flexible couplings could be rated in terms of the difference in vibration levels at two points on opposite sides of the coupling. Differences of 20 to 45 db were found for some couplings at high frequencies and at atmospheric pressure. The effectiveness of damping treatments which extended along a considerable length of the pipe ranged from 0.2 to 0.5 db per foot. The isolation provided by resilient hangers was measured by comparing pipe-wall and support structure vibrations, but test results must be used with caution since mounting conditions found in practical installations often vary widely from those provided by the test set-up.
Pitch Discrimination
Authors: Harris J. Donald
Published: September 2005

A new determination was made of the way in which differential sensitivity for frequency varies both with loudness level (up to 30 phons) mud with frequency (60–4000 cps). The effect of loudness level is independent of frequency, but sensitivity (in terms of cycles discriminable) improves continuously as frequency decreases. These results are in sharp contrast with those of the most widely-quoted study in the field, and call for some reinterpretation of the relation between pitch DLs and such psycho-acoustic phenomena as the pitch scale, the masking of tones by noise, and frequency localization within the auditory system.
New Types of Ear Protectors
Authors: Zwislocki Jozef
Published: September 2005

In the construction of ear plugs the chief problem is to combine the necessary sound insulation with comfort and sufficient speech intelligibility. Ear plugs are described which fulfill these requirements to a reasonable degree. They can be used for the attenuation of all audible frequencies or, with minor adaptation, as low-pass filters attenuating the more dangerous high frequencies only. For maximum speech intelligibility, both kinds of sound insulation are adequate for steady noises, whereas the low-pass filter is better for intermittent noises, detonations, and noise that can be interrupted to permit communication. Extensive experiments in industry and the armed forces have shown that low-pass filters with a cut-off frequency of 1000 cps provide sufficient hearing protection in most situations.
An Experimental Study of Single Bubble Cavitation Noise
Authors: Harrison Mark
Published: September 2005

An experimental study of the noise produced by a single cavitation bubble has been made. The noise consists principally of a transient pressure pulse associated with the collapse of the bubble. The motion of the bubble has been photographed simultaneously with the measurement of the pressure pulse.
Auditory Tests with Synthetic Vowels
Authors: Miller R. L.
Published: September 2005

The results are given for a series of phonetic evaluation tests which were made by means of synthetically produced vowel sounds. By employing synthetically produced sounds, a number of the significant parameters could be varied in an independent and systematic manner without encountering the uncertainties and limitations of the human speech mechanism. The types of parameter changes which were investigated by this means were those of fundamental frequency or pitch, formant frequency and amplitude, and, finally, the number of formants important to a sound. The results of the tests indicate that all of these parameters are important in the evaluation of the sound. In particular, there is a shift in the phonetic evaluation which can be attributed to pitch alone.
Action of Ultrasound on Nerve Tissue—a Review
Authors: Fry William J.
Published: September 2005

This review is concerned with (1) certain physiological and structural changes produced in tissues of the central nervous system caused by high level ultrasound and (2) investigations into the physical mechanisms underlying these changes.

The cell bodies of neurons in the central nervous system are particularly susceptible to change by ultrasound. The effect of irradiation is immediately evident as a loss of function which may be reversible or irreversible depending on the dosage. Irreversible changes in function are accompanied by changes in the structure of the cell. The susceptibility of neurons studied so far is graded according to size, the larger neurons exhibiting a greater susceptibility. The dose of ultrasound can be adjusted to cause irreversible changes in neurons without causing any observable damage to the vascular and supporting components of the tissue. This selective and specific effect of ultrasound is being used as a tool in neuroanatomical studies now in progress and has considerable potential value in neurosurgery. The ultrasound alters the state of the nerve cells and, therefore, affords a basis for studying intracellular structure and function.

The physical basis for the ultrasonically produced biological effects has been investigated part. The following aspects of temperature have been analyzed and rejected: (1) High average (space) level, (2) interface heating, (3) rapid time rate of change, (4) temperature changes resulting from cavitation, (5) heating at gas nuclei. The phenomenon of cavitation is also shown to play no essential direct role in producing the effects.
The Theory of Steady Rotational Flow Generated by a Sound Field
Authors: Westervelt Peter J.
Published: September 2005

Starting from the Navier-Stokes equations, general equation governing the generation of vorticity R is obtained: ∇2R = μ0−1∇ × ∇ ⋅ 〈ρ0uu〉, wherein R is the time-independent vorticity in the Eulerian frame and 〈ρ0uu〉 is the average value of Reynolds' stress dyadic. The solution to this vorticity equation, when properly transformed to the particle coordinates, is shown to be divergence free.

A specialization of the vorticity equation to the case of solenoidal first-order motion is shown to lead to the generating term employed by Rayleigh and by Schlichting; a specialization to the case of irrotational first-order motion is shown to lead to the generating term employed by Eckart. The sum of the two specialized driving terms does not equal the general term, indicating that the contributions to vorticity from rotational and compression effects are not independent of one another.

The theory is applied to find the streaming generated by a well-defined beam of sound giving results agreeing with Eckart and with Markham. However, when it is applied to a two-dimensional standing wave problem, the configuration of the streaming velocity in the boundary layer is found to differ from the results obtained by Rayleigh.

Finally, the effect on streaming of a time-dependent viscosity coefficient is examined.
Temperature Changes Produced in Tissue during Ultrasonic Irradiation
Authors: Fry William J. , Fry Ruth Baumann
Published: September 2005

This paper is concerned with the technique of temperature measurement in living tissue during irradiation by high intensity ultrasound. The interpretation of data obtained by the use of thermocouples is presented. The specific biological object used in this study is the spinal cord of rat exposed by laminectomy. This particular preparation serves to illustrate the relative importance of the heat conduction process in contributing to the temperature change as a function of the proximity of the imbedded thermocouple to bone and the time elapsed after initiation of the exposure.

The ultrasonic frequency used in these studies was 980 kc. The sound intensities incident on the cord were between 60 and 80 watts/cm2.

The experimental results presented in the paper are used to obtain values for the acoustic absorption coefficient of the tissue of the spinal cord. The range of values obtained for the intensity absorption coefficient per centimeter from measurements made on six adult rats at various positions in the spinal cord is 0.19 to 0.23 if the heat capacity of the tissue at constant pressure is 1.00 calorie/cm3.
Measurement of the Propagation of Sound in Fiberglas
Authors: Esmail-Begui Z. , Naylor Thomas K.
Published: September 2005

As an aid to acoustical designers, this paper presents some experimentally determined values of the attenuation coefficient and the speed of propagation of sound in Fiberglas. The propagation parameters α and β in the equation for a plane wave p = p0εjωt−(α+jβ)z are determined by comparing the amplitudes and phases of the sound pressures existing simultaneously at separate points in the Fiberglas. The principle of measurement is similar to that used by Beranek and Scott involving a longitudinal movable probe in a long narrow metal duct filled with rockwool. However, in the redesigned apparatus, edge effects were reduced by using a tube of larger cross section; wall vibrations were damped by laminated rubber and Masonite walls; and the shunting effect of the longitudinal probe hole was eliminated by the use of transversely inserted microphones.

Experimental data were obtained within one db for frequencies between 50 and 1000 cycles for two samples of Fiberglas with nominal weights of 9 lb/cu ft PF (hard) and 414 lb/cu ft TWF (soft). The direction of propagation of the sound was normal to the surface of the blanket. For both samples the attenuation increases almost as the square root of the frequency, but the speed of propagation is found to increase almost as the 14 and 12 root of the frequency for the hard and the soft samples, respectively.
Diffraction of Sound Waves by a Circular Aperture
Authors: Bekefi G.
Published: September 2005

Diffraction of an acoustic wave by an aperture in a plane reflecting screen has been investigated experimentally at a wavelength of about 3 cm. The pressure amplitude distribution within a circular aperture illuminated by a plane, progressive sound wave exhibits oscillations which do not conform to theoretical requirements. A possible explanation for the disagreement offered. Diffraction measurements made in the near-field of the circular hole were found to be in fair agreement with the Fresnel-Kirchhoff theory. A modified theoretical expression, valid for apertures large as compared to the wavelength, is also presented. It is concluded that this theory is capable of predicting the diffraction effects to a greater degree of accuracy and over a larger region of space than Kirchhoff's classical formula.
Absorption of Sound in Argon, Nitrogen, and Oxygen at Low Pressures
Authors: Parker J. G. , Adams C. E. , Stavseth R. M.
Published: September 2005

The amplitude absorption coefficient α for pulsed sound waves in argon, nitrogen, and oxygen has been measured over a range of pressure p from 1 to 10 mm Hg for frequencies f between 60 and 70 kc, the temperature in all cases being held nearly constant at 20°C. For the three gases used, the following experimental values of (pα/f2)107 (cgs units) were obtained: (1) for argon 1.86 with an rms deviation of 0.03, (2) for nitrogen 1.64 with an rms deviation of 0.04, and (3) for oxygen, 1.92 with an rms deviation of 0.03. The corresponding values computed from the classical absorption equation are (1) for argon, 1.87, (2) for nitrogen, 1.31, and (3) for oxygen, 1.61. Thus the absorption in argon is classical while for nitrogen and oxygen the absorption exceeds the classical value. These excesses are attributed to rotational relaxation and the associated relaxation times are calculated in accordance with the thermal relaxation theory of Herzfeld and Rice, and Kneser. For nitrogen, the relaxation time (reduced to STP conditions) is 4.85×10−10 second and for oxygen is 4.95×10−10 second. Both these values are significantly smaller than the values obtained by other workers at higher frequencies.
Effects of Sonic Vibration on the Proteolytic Activity of Pepsin
Authors: Naimark George M. , Mosher William A.
Published: September 2005

Pepsin preparations were sonically treated for various periods of time in a 9-kc magneto-striction oscillator with the temperature maintained at 13°C–16°C during treatment. After sonic treatment the residual proteolytic activity of the enzyme was determined by measuring the turbidity decrease during the digestion of an albumin substrate. It was found that dilute solutions of Merck U.S.P. pepsin were rapidly inactivated by sonic treatment whereas highly concentrated solutions were refractory to ultrasonic destruction. Sonic irradiation of a pure Armour crystalline pepsin solution yielded slight enzyme inactivation only. In no instance was enzyme activation observed in this study.
Transducers for Producing Ultrasonic Waves
Authors: Mattiat Oskar
Published: September 2005

After a short description of mechanical transducers such as the siren in air and the Pohlman Whistle in liquids, some fundamentals of electromechanical transducers using electric and magnetic fields are given, and magnetostrictive and piezoelectric transducers for the irradiation of liquids which are available on the market are mentioned.

In the second part transducers made of barium titanate (“ceramic transducers”) are described. Polycrystalline ceramic material can be shaped and thereafter polarized in such a way as to produce convergent waves, with the possibility of focusing ultrasonic energy and thus creating zones of extremely high ultrasonic intensities. Electrical and acoustic data on spherical ceramic transducers are given. Fair agreement is found between O'Neil's theory of spherical transducers and measurements of the pressure distribution in a sound field along the central axis in front of the transducer. The diagram of motional impedance for a 400 kc spherical bowl and power limitations of ceramic transducers are discussed. Finally, a tubular ceramic transducer is described which seems to offer good possibilities for efficient treatment of large liquid volumes in a continuous flow process.
Broad Band Directional Barium Titanate Transducers
Authors: Camp Leon
Published: September 2005

Transducers were constructed using thin-walled barium titanate tubes cut in short lengths. The outside walls of the tubes were covered with pressure relief material. Radial motion of the tubes developed motion along their axes in an enclosed fluid medium. If one end of the tube was closed by a heavy metal block, the tube became the equivalent of a quarter wave piston, the open end being a vibrating surface moving parallel to the axis of the tube. Various mosaic patterns were formed of these tubes to give directional transducers. Their operating characteristics were quite dependent on the kind of fluid enclosed by the tube.
Noise Control Measures for Jet Engine Test Installations
Authors: Hardy Howard C.
Published: September 2005

The various schemes currently used for controlling the noise of aircraft engine test stands and warm-up operations on the ground are briefly surveyed. The first step is to evaluate a design goal for acceptable levels in the neighborhood for the installation. The size of cross section required to handle the intake and exhaust gases is determined from the amount of air consumed, the temperature, acceptable gas velocities, and the aerodynamic pressure drops. The modern trend in size of engines is such as to require cross sections of 200 sq ft or more. Several different styles of structures have been found successful. The various types used—steel mufflers, duct splitters, and plenums and 180-degree bends—are discussed, and typical data are given for each type. Economic considerations are emphasized. The use of scale model acoustic tests for untried acoustic designs is strongly recommended.
The Effect of Insonation on the Specific Reaction Rate Constant in the Acid Hydrolysis of Ethyl Acetate
Authors: Thompson Dudley , Vilbrandt F. C. , Gray W. C.
Published: September 2005

The effect of insonation on the specific reaction rate of the hydrolysis of an aqueous solution of ethyl acetate in the presence of hydrochloric acid catalyst was studied. Three frequencies, 400, 700, and 1500 kc, were employed from the commercailly available Model 520 Ultra-Sonorator. A specially designed reactor, commercially fabricated from Pyrex, was employed to maintain approximately isothermal conditions for the tests. Insonation was for periods of 10 and 20 minutes at temperatures of 19±0.1 and 30±0.1°C. The course of the reaction was followed in such a way that the concentrations of the reacting substances were not disturbed. Samples were drawn off at intervals and titrated with sodium hydroxide using phenolphthalein as the indicator. Calculations were based on the difference of the titration at any time t and the titration at the end of 24 hours, at which time the reaction was essentially complete. Specific reaction rates were increased in the order of five percent for 20-minute insonation over the rates for 10-minute insonation.
The Pulsation Frequency of Nonspherical Gas Bubbles in Liquids
Authors: Strasberg M.
Published: September 2005

The effect of nonspherical shape on the pulsation frequency of a gas bubble in a liquid is calculated. The frequency is expressed in terms of a stiffness constant independent of shape and an inertial constant mathematically equivalent to the reciprocal of the electrostatic capacitance of a conductor having the same shape as the bubble. The calculation is carried out for an oblate spheroid, and the variation of the pulsation frequency with shape is shown to be small. The effects of a rigid wall and of a free surface on the pulsation frequency are also calculated by the same method.
Magnetic Dispersion of Sound in Electrically Conducting Plates
Authors: Robey Donald H.
Published: September 2005

It is shown theoretically that plane longitudinal sound waves traveling in an electrically conducting plate will generate complex electric currents provided there is a magnetic induction perpendicular to the particle displacement. The currents react with the induction to produce a complex mechanical force which opposes the particle motion. The impedance associated with this force effectively modifies the impedance of the medium by adding a resistance and a stiffness reactance. The induced resistance attenuates the waves while the induced stiffness increases Young's modulus and therefore increases the sound velocity.

Of all the elements, it appears that this effect is a maximum in lithium, i.e., at a given frequency and induction.
Abnormal Sound Propagation Over the Southwestern United States
Authors: Johnson C. T. , Hale F. E.
Published: September 2005

Abnormal propagation of sound in the east-to-west and west-to-east directions has been studied throughout a period of a year. Experiments were carried out over the California-Arizona desert using explosions of 1200 pounds of TNT. Returns of sound from altitudes of 30 to 50 km were consistently received to the east in winter and to the west in summer. Sounds which traveled to the high temperature region at 80 to 100 km altitude were received about one-fifth of the time. Sounds were returned from the second region somewhat better to the east ha summer and to the west in winter. An early arriving abnormal wave was received at ranges greater than 400 km.
Sonochemistry: The Production of Chemical Changes with Sound Waves
Authors: Weissler Alfred
Published: September 2005

An extensive survey is made of the chemical effects of ultrasonic waves. Increased understanding of the mechanism of these effects is sought through a consideration of the significance of certain experimental variables such as frequency, intensity, pressure, and temperature. Also considered is the role of cavitation.
Ultrasonically Induced Cavitation in Water: A Step-by-Step Process
Authors: Willard G. W.
Published: September 2005

A 2.5-Mc, barium-titanate, spherically focusing radiator was used to produce cavitation in both degassed and aerated water entirely within the restricted, high intensity focal region, remote from the water boundaries. The sonic intensity rises to 1.8 kw/cm2, and the pressure amplitude to ±70 atmos at the focus. High-intensity illumination and an unusual high speed photographic technique permit observation and timing of the step-by-step process of cavitation development.

Feather-shaped cavitation bursts are sporadically produced, being initiated in the insignificant quill portion nearest the radiator, then abruptly expanding to form the catastrophic plume portion. The plume is believed to be formed by myriads of micro-cavities, too small and close for individual observation. These two fundamental steps are identically produced, and with equal ease, both in degassed and aerated water. The whole action is over in several milliseconds, except that in the case of aerated water a third bubble step is produced. In aerated water, non-collapsing gas bubbles are generated by and concurrently with, the catastrophic step. These bubbles remain after collapse of the burst, to be blown off down stream by the sonically induced liquid streaming.

The bubble step is not generated without the presence of the catastrophic step. The latter is generated only if the initiation step reaches a definite degree of development (not always attained). This requires sonic activation for increasing lengths of time for decreasingly smaller sonic intensities. Origination of the initiation step, and hence of the whole cavitation phenomena, is believed to occur whenever a stray nucleus (weak spot) streams into the high intensity sonic field.
Design Techniques for a High Frequency Transducer with a Wide-Beam Searchlight Pattern
Authors: Lane A. L.
Published: September 2005

It is frequently essential for a transducer to have a smooth, wide-beam directivity pattern with negligible side lobes. If, in addition, this transducer must operate in the fractional megacycle frequency region, then conventional designs such as small plane radiators or curved surface mosaics are not satisfactory. As a result of an extensive investigation, it was found that a barium titanate spherical shell sector properly designed will meet these difficult wide-pattern and high frequency specifications. This paper outlines some of the design considerations required to adapt a ceramic shell into a transducer with the desired performance. The problems discussed are shell size, included angle of the spherical shell, inside diameter to thickness ratio, and the uniformity of the thickness dimension. Various baffle techniques are also examined detail. Shell arc lengths ranging from four to twenty wavelengths are considered as to their effects on the shape of the surface displacement distribution and on the directivity pattern. Though this paper presents a solution to a specific transducer problem, the design techniques discussed are applicable to transducers having other frequency and pattern requirements.
Electromechanical Response and Dielectric Loss of Prepolarized Barium Titanate under Maintained Electric Bias. Part I
Authors: Baerwald H. G. , Berlincourt D. A.
Published: September 2005

In transducer applications of ferroelectric ceramics it is standard practice to rely for the electromechanical response on retained polarization. This is practicable only for moderate driving amplitudes and sufficiently low temperature. At higher driving fields dielectric losses increase inordinately and lead to eventual depolarization and loss of response. This can be remedied by application of a comparatively modest dc bias. The quantitative loss behavior of various ceramic bodies over extended ranges of temperature, field amplitude, and for various values of aiding bias is investigated. Results are also presented on various other effects obtained with bias operation, such as increase of electromechanical coupling and shifts of thermodynamic transition points. Work on other associated phenomena—electrostriction, secular relaxation, etc.—will be reported in part II.
The Information of Elementary Auditory Displays. II
Authors: Pollack Irwin
Published: September 2005

Previous studies have shown that the amount of information transmitted with a simple one-dimensional auditory display is relatively small. This paper considers three conditions designed to increase the information transmission with elementary auditory displays. The three conditions or variables were (1) the frequency range of tones investigated; (2) the utilization of objective reference tones presented with the unknown tone; and (3) the “dimensionality” of the display—the number of independently varying stimulus aspects of the display. Little additional gain in information transmission is associated with the first factor; a moderate gain is associated with the second; and a relatively substantial gain is associated with the third.
Ultrasonic Velocities in Solutions and Mixtures
Authors: Chhapgar A. F.
Published: September 2005

In a recent paper, Maier and Mez have reported a maximum in the absorption-concentration curve for a phenol-carbon tetrachloride solution at small phenol concentrations, which was ascribed to association resulting from hydrogen bonds. The present paper investigates the behavior of the velocity-concentration curve for the same solution. The results show a departure from linearity at low concentrations, agreeing with the results of Maier and Mez.
Temperature Variation of Velocity and Absorption Coefficient of Ultrasonic Waves in Heavy Water (D2O)
Authors: Pancholy M.
Published: September 2005

The coefficient of absorption and velocity of propagation were measured in D2O at 50.22 Mc/sec as functions of temperature. Velocity values are lower than those in H2O at corresponding temperature by about 100 m/sec but measurements extended to 90° show a striking qualitative similarity between velocity vs temperature curves for D2O and H2O. The value of the frequency-free absorption coefficient 2α/ν2 varies from 124×10−17 to 27×10−17 cm−1 sec2 over the temperature range of 5° to 50°C. The mean value of the ratio of measured value to classical value is 2.87 against 3.12 for H2O.
The Sound Field of a Moving Source
Authors: Zatzkis Henry
Published: September 2005

The sound field generated by an ellipsoidal vibrator, moving with constant velocity, is examined. The solution has the form of an infinite series. The first term of the series agrees with the solution for a point source, established by previous investigators.
Propagation of Acoustic Discontinuities in an Inhomogeneous Moving Liquid Medium
Authors: Heller G. S.
Published: September 2005

It is shown that a surface in a moving inhomogeneous liquid on which the time derivatives of pressure and velocity are discontinuous must propagate according to a generalized eikonal equation. The usual assumption of infinitesimal amplitudes is not required in this treatment.
Measurements of the Acoustical Properties of Two Roman Basilicas
Authors: Raes Auguste C. , Sacerdote Gino G.
Published: September 2005

Reverberation times, pressure decay, and echo patterns were experimentally determined. Some conclusions are presented on the application of classical formulas to very large halls and on the influence of architectural elements, especially the usefulness of columns.
Wave Propagation in a Randomly Inhomogeneous Medium. II
Authors: Mintzer David
Published: September 2005

The region of validity of the single-scattering approximation used in Part I is found by considering the next higher approximation; it is valid for k02arα2≪1, where k0 is the wave number of the incident sound, r is the range from source to observer, a is the mean size of the inhomogeneities, and α is the rms value of the refractive index variations. Some approximate results are given for the case of wavelength large compared with inhomogeneity size. By consideration of the intensity variations, it is found that ray theory is valid for (k0a2/r)≫1, as has been found for plane waves.
The Absorption of Sound in Gas Mixtures
Authors: Angona F. A.
Published: September 2005

The absorption of sound has been measured in CO2, CS2, C2H4O, and in mixtures of the latter two gases with CO2 for frequencies ranging from 2 to 10 kc and for pressures ranging from 3 to 300 mm of Hg. The tube method was employed. The absorption was determined by observing the decrease in sound pressure as the path length between the speaker and the microphone was increased. A fixed condensor microphone and a movable ribbon-type speaker were used.

The measured absorption coefficient was corrected for the effect of the tube and also for the absorption due to viscosity and heat conduction of the gas. The corrected absorption coefficient was then plotted as the attenuation coefficient per wavelength against the logarithm of the ratio of frequency over pressure. These curves were then compared to those determined from Bourgin's Theory for mixtures of absorbing gases. The agreement between the observed attenuation and that predicted by the theory was within 5 percent.
Transmission of Sound Through Plates
Authors: Makinson K. Rachel
Published: September 2005

Fay's treatment of the theoretical problem of the transition of sound through a solid plate immersed in a fluid is used to deduce an additional criterion for total reflection, and some comments are made on the criteria for total transmission.
Reflection from a Statistical Array of Scatterers
Authors: Grace James C.
Published: September 2005

The average energy spectrum of the reflection from an array of randomly located point scatterers has been calculated. It is shown that this spectrum is proportional to the square of the sum of the individual scatterer amplitudes for wavelengths large compared to the extent of the array and that it is proportional to the sum of squares of the individual amplitudes for wavelengths small compared to the array extent.
A Vortex Whistle
Authors: Vonnegut Bernard
Published: September 2005

Simple whistles have been constructed that produce sound by the escape of a vortex from the open end of a tube. The whistle operates equally well on either air or water.

When the frequency that is produced by the passage of either air or water is plotted against the volume rate of fluid flow, it is found that the frequency depends almost linearly on the rate of flow and that the number of cycles produced by the flow of a unit volume of air is nearly the same as that produced by the flow of a unit volume of water. Measurements have been made relating the frequency of the sound produced to different pressures of air applied to the whistle.
Boundary Layer Flow Near a Cylindrical Obstacle in an Oscillating, Incompressible Fluid
Authors: Holtsmark J. , Johnsen I. , Sikkeland T. , Skavlem S.
Published: September 2005

1. The flow in two dimensions of an oscillating incompressible fluid near a circular cylinder with its axis normal to the direction of oscillation, is studied theoretically and experimentally. Starting from Navier-Stoke's differential equations the method of successive approximations has been used in order to get approximative solutions, when the appropriate boundary conditions are applied. The zeroth approximation gives the modified field of oscillation near the cylinder as a function of the viscosity. The first approximation also gives a stationary flow, which is found from the solution of an ordinary linear differential equation of 4th order.

2. Experiments have been carried out in air in a Kundt's tube. The velocities in the plane normal to the axis of the cylinder have been found by photographing smoke particles in air. The experimental and theoretical results agree fairly well. Comparison with corresponding data obtained by Schlichting is also made.

Some G functions, derived from Hankel functions which have been used in the theoretical solutions, have been tabulated to 6 digits.
A Linear, Passive, Nonreciprocal Transducer
Authors: Bobber Robert J. , Darner Charles L.
Published: September 2005

An underwater sound transducer which uses two different types of electromechanical coupling has been built, and its nonreciprocal nature is illustrated with directivity patterns.
On Nonspecular Reflection at a Rough Surface
Authors: Miles John W.
Published: September 2005

The reflection of a plane wave at a rough interface separating two fluid media is examined in the approximation of “small roughness,” such that second-order terms in the magnitude of the roughness may be neglected. Exact solutions are obtained when the roughness is harmonic, while asymptotic results are obtained for arbitrary distributions. The analysis deals principally with an incident wave that is harmonic in time, but the problem of the reflection of a pulse from a perfectly reflecting, sinusoidal boundary is solved. It is found that such a boundary acts as a band-pass filter of the nonspecular components of the reflected wave. Outisde of this pass band the reflection is not only specular but distortionless. Rather less generality is possible when the boundary is not perfectly reflecting, but the pass band is found to be independent of the properties of the reflecting medium.
Visual Contribution to Speech Intelligibility in Noise
Authors: Sumby W. H. , Pollack Irwin
Published: September 2005

Oral speech intelligibility tests were conducted with, and without, supplementary visual observation of the speaker's facial and lip movements. The difference between these two conditions was examined as a function of the speech-to-noise ratio and of the size of the vocabulary under test. The visual contribution to oral speech intelligibility (relative to its possible contribution) is, to a first approximation, independent of the speech-to-noise ratio under test. However, since there is a much greater opportunity for the visual contribution at low speech-to-noise ratios, its absolute contribution can be exploited most profitably under these conditions.
Determination of Absolute Sound Levels and Acoustic Absorption Coefficients by Thermocouple Probes—Theory
Authors: Fry William J. , Fry Ruth Baumann
Published: September 2005

A detailed theoretical analysis of the operation of thermocouple probes used to determine absolute sound levels or acoustic absorption coefficients is presented.

The probe consists of a thermocouple imbedded in a sound absorbing medium which closely matches in density and sound velocity the medium in which the sound level is to be determined. In use the transducer which generates the acoustic field is excited to generate sound pulses with a rectangular envelope. The initial time rate of change of the temperature at the thermocouple junction is determined. In addition to the measurement of the temperature change, the calculation of the absolute sound intensity requires only a knowledge of the absorption coefficient of the imbedding material and its heat capacity per unit volume at the temperature at which the measurements are made.

The theoretical discussion includes an analysis of the relation between the temperature rise at the junction resulting from absorption in the body of the imbedding medium and the sound level. In addition, the effects of (a) viscous forces arising from relative motion between the thermocouple and the imbedding fluid and (b) heat conduction between the thermocouple and the fluid, in contributing to the temperature change at the thermocouple junction are analyzed.

Based on the analysis, a set of design formulas is obtained which are summarized and illustrated for the convenience of other investigators who may wish to design and use such probes.
Acoustic Factors in the Design of Noise-Reducing Telephone Booths
Authors: Bishop D. E. , Hewitt F. G. , Callaway D. B.
Published: September 2005

Acoustically treated, doorless telephone booths can increase the effectiveness of telephone communication in noisy environments even though practical size and open area requirements limit the amount of noise reduction which can be achieved. The principal factors determining the noise reduction of an acoustically treated booth (where the noise reduction is considered as the decibel difference in octave band noise levels measured outside and inside the booth) have been investigated by use of full size and 13 model booths.

The principal parameters affecting the reduction of an acoustically treated telephone booth were found to be (1) the sound absorption coefficients of the wall surfaces as function of frequency; (2) the ratio of open area to the wall area of the phone booth; (3) the transmission loss of the walls of the phone booth; and (4) the size and shape of the booth.

The investigation resulted in a new triangular design of booth which is fully as effective acoustically as the rectangular booths, yet has added practical advantages.
Characteristics of Ultrasonic Delay Lines Using Quartz and Barium Titanate Ceramic Transducers
Authors: May John E.
Published: September 2005

Previous analysis of the equivalent circuit for the ultrasonic delay line was applied to quartz crystal transducers and a vitreous silica delay medium. The analysis has been extended to evaluate the use of other materials such as magnesium, aluminum, and steel, and to include BaTiO3 ceramic transducers. Calculations show the decrease in loss to be expected as the impedance of the delay medium is decreased and conversely the increase in band width to be expected as the impedance of the delay medium is increased. The increase in band width resulting from symmetrical loading of the transducers is also evaluated. Modifications to the equivalent circuits for the case of BaTiO3 ceramic transducers are considered. Theoretically losses can be reduced to 10 db or less using the ceramic transducers with a vitreous silica medium. The band width is slightly less than for quartz crystal transducers. However, by utilizing higher impedance materials, band widths approaching 100 percent should be achieved.
Thermal Relaxation of Vibrational States in Sulfur Hexafluoride
Authors: Leonard O'Connor C.
Published: September 2005

The velocity of ultrasonic waves in sulfur hexafluoride (a symmetrical molecule with fifteen vibrational degrees of freedom) has been measured at frequencies of 251.22 kc and 1001.8 kc in the range from 0.38 to 15.89 Mc sec−1 atmos−1 at 36.10°C. The observed disperison in ultrasonic velocity is ascribed to the slow rate of energy exchange between translational and vibrational states. The dispersion region involves the disappearance of the whole of molecular vibrational energy, and corresponds to a single relaxation time. The relaxation time as derived from dispersion measurements is found to be 5.89×10−7 sec at one atmosphere corresponding to 4.68×103 a collisions required for energy exchange. The relaxation time for a sulfur hexafluoride mixture with 0.066 mole fraction of helium is found to be 5.46×10−7 sec.