bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Radiation of Sound from a Piston in a Nonrigid Baffle
Authors: Mangulis V.
Published: September 2005

The pressure in the far field and the radiation resistance of a piston in an infinite plane baffle are derived when the baffle is almost rigid and the piston dimensions are either very large or very small as compared to a wavelength.
On Axial Vibrations of a Whirling Bar
Authors: Bhuta Pravin G. , Jones John P.
Published: September 2005

Axial vibrations of whirling bars are studied by using undeformed or Lagrangian coordinates. In general, whirling lowers the natural frequencies of the bars. In the static case, an interesting and previously unreported result is obtained as a special case of the dynamic problem. When the angular velocity of the bar approaches certain critical values, “static resonances” or instabilities occur, and the axial displacements everywhere in the bar tend to become unboundedly large. These resonances are explained physically. The same problem is also solved by using deformed or Eulerian coordinates, and it is shown that the static resonances are concealed in such an analysis.
Sound Reflection and Scattering from the Sea Surface
Authors: Marsh H. W.
Published: September 2005

A quantitative theory for backscattering or reverberation caused by the irregular sea surface is developed and compared with experimental results. Experimental results for forwardscattering or surface loss are also presented to compare with earlier theory.
Determination of the Power Radiated by a Piston-like Underwater Sound Transducer from Near-Field Axial-Pressure Measurements
Authors: Stumpf F. B. , Kendig P. M.
Published: September 2005

This letter describes a method for obtaining the acoustic power radiated from a pistonlike underwater sound transducer, where only near-field measurements are possible due to boundaries. This method can be applied, for example, in the determination of the power radiated from underwater sound transducers being calibrated in small pressure tanks. It involves measurements of the acoustic pressure along the axis of the source.
Long-Range SOFAR Studies in the South Atlantic Ocean
Authors: Bryan George M. , Truchan Marek , Ewing John I.
Published: September 2005

A study was made of the accuracy to be expected from long-range SOFAR measurements and of some of the factors which limit that accuracy. Depth charges were fired along a track across the South Atlantic and into the Indian Ocean. The signals were received on Fernando de Noronha and Ascension Island. Distances ranged from 75 to 4700 nautical miles.

The results show that it should be possible to obtain an accuracy of about 50 m in 1000 miles from a 20-shot sample. Off-axis shooting seriously affects the accuracy. Large topographic features, which do not extend into the sound channel axis itself, cut off the front of the signal, without impairing arrival-time accuracy, while continental land masses block the signal entirely. Attenuation of the peak-signal intensity with increasing range along an unimpeded path is consistent with cylindrical spreading.
Use of a High-Intensity Siren in Fatigue Testing of Structures Subjected to Acoustic Forcing
Authors: Belcher P. M.
Published: September 2005

The problem of aircraft structural fatigue under acoustic forcing has led to a need for economical high-speed destructive testing techniques. One such method, employing a high-intensity siren, is described here. A unit presently in use and one now under construction are discussed. A method for using data from this discrete tone test in fatigue design for structure subjected to random sound is outlined.
A Summation Formula for Use in Determining the Reflection from Irregular Bodies
Authors: Neubauer Werner G.
Published: September 2005

The solution to the approximate integral form of the reflection in the “far field” has been developed, as well as a graphical, or numerical, method for the case of a rigid, finite plane rotated about an edge, and for a wedge shape. The Kirchhoff approximation is used. The reflection may be conveniently presented in diagrams in the complex plane. Extension of the method has been made to the case for the magnitude of the reflection at any orientation of a reflector. Physically measurable quantities are required in the evaluation of this sum. Although the evaluation is not exact, rapid, or inclusive of all reflection mechanisms, it does make possible the derivation from shapes which are not analytically describable.
Some Comparisons of the Response of Simple Panels to Random and Discrete Noise
Authors: Hubbard Harvey H. , Hess Robert W.
Published: September 2005

This paper will deal with the response of simple aircraft type skin panel specimens which were forced to vibrate by random and discrete noise in the laboratory. These two techniques of testing are first discussed and are illustrated by means of a short moving picture. The moving picture also shows the nature of initial fatigue damage as well as fatigue crack growth resulting from noise. Finally, some comparisons of stress levels and fatigue life are presented for a panel configuration exposed to both random and discrete noise.
Light Diffraction by Ultrasonic Waves—Fresnel Region
Authors: Colbert H. M. , Zankel K. L.
Published: September 2005

The time dependence of the intensity of the light in the Fresnel region diffracted by a progressive wave is measured directly. The measurements are compared to the theory of a periodic moving grating. Suggestions are made for measuring the harmonic content of the wave and the fundamental wavelength of the grating. Examples are given of the available periodic intensity fluctuations, and a method for determining relative pressures is suggested. This paper gives the details of work that was reported at the Fourth International Congress on Acoustics (K. L. Zankel and H. M. Colbert, Fourth International Congress on Acoustics, Copenhagen, 21–28 August 1962).
Determination of the Geometry of Hidden Defects by Ultrasonic Pulse Analysis Testing
Authors: Gericke O. R.
Published: September 2005

Current methods for ultrasonic inspection of metals and other solid materials are limited by their inability to determine the geometry of concealed defects if these defects are comparable in size, or smaller than the width of the ultrasonic search beam. Whenever such relatively small flaws are involved, ultrasonic pulse echo testing, if conducted at a single frequency, will yield the flaw location only, but no information on the flaw geometry. It is therefore very difficult to interpret the test results. The difficulty can be overcome by introducing the novel ultrasonic test method described in this paper. In this procedure, ultrasonic signals are utilized which contain a broad band of frequencies, and in analogy to optics, can therefore be considered as “white” ultrasonic pulses. The form and spectral energy distribution, or “color,” of such ultrasonic pulses is influenced by the geometry of a defect from which they are reflected. Hence, an analysis of the defect echo yields information on the defect configuration. The successful application of the ultrasonic pulse analysis method for differentiating between flaws of various configurations is illustrated By a number of test examples.
Some Useful Measurements in Room Acoustics
Authors: Lane R. N.
Published: September 2005

Several measurements which have proven useful in the engineering aspects of architectural acoustics are described in this paper. Data obtained in measurements of various sized auditoriums and large coliseums are presented showing the engineering use of reverberation time measurements, articulation tests using practiced or naive listeners, pulse measurements for isolation of echoes, and noise measurements. Some preliminary results and possible use of definition measurements in schoolrooms and some auditoriums also will be discussed.
Acoustic Radiation Damping of Vibrating Structures
Authors: Mangiarotty R. A.
Published: September 2005

Existing theories for predicting the acoustic radiation damping of structures are reviewed. A uniform pressure approximate theory for predicting the acoustic radiation damping of a single flexible panel, forming part of an otherwise rigid plane baffle, formulated by D. J. Mead [“The Effect of a Damping Compound on Jet Efflux Excited Vibrations,” Aircraft. Eng. 32, 374 (1960)], is developed into an exact theory, taking into account the nonuniform pressure distribution over a vibrating surface; a general expression is also developed to include any form of panel boundary support. The equations developed have been evaluated numerically by computer, for ease in predicting the acoustic damping factor for a wide range of panel sizes. The acoustic damping of a single panel forming part of a flat baffle and also of a cylindrical baffle has been measured experimentally by three methods.
Field Experiences and Experiments with Music Practice Rooms
Authors: Fitzroy Dariel
Published: September 2005

Establishment of satisfactory room environment for music rooms used for practice purposes has been a problem of considerable difficulty for some time. Presently established criteria seem to be almost unanimously unsatisfactory. Part of this difficulty seems to be the failure of the directors to make themselves clear as to their requirements. Another obstructive factor seems to be ambiguity in the presently accepted room environment optima. Through extensive experience in this field, discussing such rooms with many directors and instructors, and in planning and testing such rooms, new viewpoints will be suggested which may be found helpful in achieving more satisfactory results.
Bending Wave Propagation in Rods and Plates
Authors: Lange James N.
Published: September 2005

Rods exhibit some very complex vibrational characteristics. The ends behave like cavity resonators in a narrow frequency band and vibrate with amplitudes as much as 80 times the amplitude of the incident wave. At low frequencies, bending vibrations of rods are described by the complex Young's modulus, and the Bernoulli theory of bending leads to the same result as the exact theory. At high frequencies, bending vibrations are described by the shear modulus, and the loss factor approaches or becomes equal to that of shear waves.

Plates exhibit a behavior similar to bending vibrations in rods. At low frequencies, Young's modulus and its loss factor describe the vibrational behavior of a thin plate. As the frequency increases, the modulus approaches the shear modulus, and the loss factor approaches the loss factor for shear waves after fluctuating in a periodic manner between the loss associated with Young's modulus and that of the shear modulus. The measurement, of the loss factor by bandwidth and decay methods agree, provided a narrow bandpass filter is used so that the low-frequency modes, which are always excited by a point force, are suppressed.
Steady-State and Transient Behavior of Two- and Three-Element Isolation Mountings
Authors: Snowdon J. C.
Published: September 2005

The response of two- and three-element isolation mountings to sinusoidal, steplike, and pulselike input displacements has been determined theoretically. In contrast to the two-element or simple mounting, the transmissibility of the three-element mounting at resonance can be made small without reducing the rate at which transmissibility decreases at high frequencies (12 dB per octave). The transient response of the mountings has been described in terms of the dependence upon a parameter γ of the suitably normalized maximum values of displacement (SDR), relative displacement (RDR), and acceleration (SAR) of the mounted item. The parameter γ is the ratio of the half-period of natural vibration of the mounting system to a time τ, which represents either the step rise time or the duration of the pulse. Shock spectra have been computed for input transients defined by three widely different values of γ. In two well-defined regions, the resiliently mounted and unmounted shock spectra are shown to differ in level by a factor that is given by the SDR or the SAR. At the higher values of γ, it is apparent that the three-element mounting can reduce the displacement of the mounted item in the manner of a heavily damped simple mounting, while reducing the acceleration of the mounted item more effectively.
Effective Absorption Coefficient of Rectanguar Areas of Absorbent Material
Authors: Daniel Eric D.
Published: September 2005

Extensive measurements of the variation of effective absorption coefficient with sample area have been made by Chrisler [J. Research Natl. Bur. Standards 13 (August, 1934)]. There is some indication that the measured variation follows a simple law based upon a very elementary consideration of diffraction effects. An attempt is made to deduce such a law from a more detailed consideration of diffraction effects at (a) the single edge of a semi-infinite, absorbent sheet and (b) the two edges of an absorbent strip. An explicit result is obtained in case (a) which leads to a calculated “area effect” of the type observed by Chrisler. The result is, however, of limited validity and cannot be applied to sound striking the absorbent material near grazing incidence. It is shown that case (b) would lead to a result valid for all angles of incidence.
Mechanical Dissipation and Breaking Stress of Butt-Joined ADP Crystal Plates
Authors: Faraday B. J. , Gregan D. J. G.
Published: September 2005

Butt-joined ammonium dihydrogen phosphate (ADP) crystals to be used for low-frequency underwater sound generation previously have been investigated from the point of view of mechanical dissipation. It was experimentally found that the dissipation factor (the reciprocal of the mechanical Q) for crystals bonded by epoxide adhesives increased linearly with the thickness of the glue line up to large bond thicknesses. Of importance in the determination of the maximum acoustic intensity radiated from a piezoelectric crystal operating at resonance is the mechanical breaking stress. Experiments performed on adherends of equal length bonded at right angles to the edges of the component crystals show that the breaking stress decreases for increasing bond thickness. In addition to keeping the bond thickness at a minimum, two further approaches are available for improving the value of the breaking stress. First, lengthening the glue line by changing the bond angle increases the mechanical strength although the mechanical Q is correspondingly reduced. Second, as the position of the right-angled bond is shifted away from the antinode of stress, i.e., the velocity node, the mechanical strength gradually increases and is accompanied by a simultaneous decrease in the dissipation factor.
A Simple and Inexpensive Method for Calibration of Earphones
Authors: Nickerson James F.
Published: September 2005

Since the small laboratory or field installation often has difficulty justifying an expensive coupler system for earphone calibration, a simple method was sought which would employ more common laboratory equipment in making the necessary calibration. To this end a coupler system employing a Permoflux PDR-8 earphone driven as a microphone was devised. Outputs from a series of phones tested by the “PDR-8 coupler system” were compared with outputs of the same phones tested by means of a Western Electric 640 AA 6-cc coupler system. The observed errors between the two systems were plotted and a line of best fit drawn. This line of best fit was accepted as the plot of constant errors introduced by the PDR-8 coupler system when used to measure output of other PDR-8's, and appropriate corrections were applied to readings of the PDR-8 coupler system. Comparison data of three test phones calibrated by means of the PDR-8 coupler system and a Western Electric 640 AA 6-cc coupler system revealed Σd/n = −0.04 db and d = 1.35 db, an error considered quite acceptable for earphone test for many laboratory or field installation purposes. To apply this method one needs to secure the constant error curve for a particular phone to be used as the calibration coupler system and apply these corrections to output readings as calibration of other phones is attempted. Correction curves are specific to the particular kind of phone under test as well as to the phone used in the coupler system. (Data collected by author at U. S. Navy Electronics Laboratory, Human Factors Division, San Diego.)
Absolute Calibration of a Displacement Detector from 10 cps to 30 000 cps.
Authors: Koidan Walter
Published: September 2005

Using the diaphragm of a condenser microphone as a reference vibrating surface, a technique has been developed for obtaining the absolute response of a probe-type capacitance vibration detector from 10 cps to 30 000 cps. The probe is fitted into the front end of the reference microphone to detect the average motion of the diaphragm when driven by applying an electrical signal between the diaphragm and the back plate. The ratio of the driving voltage to the output voltage of the vibration detector is used to compute the response of the detector in two ways. One computation, based on the linear transducer equations, is made from the response and capacitance of the reference microphone. A second method depends upon the average motion of the reference microphone diaphragm per unit driving voltage obtained from a measurement in an acoustic coupler with an auxiliary microphone; this calculation is made from the coupler impedance and the response of the auxiliary microphone. The results of the two methods of computation agree closely. As an independent check, the calibration of an accelerometer, performed optically from 150 to 500 cps, was compared with a calibration performed with the capacitance probe. Agreement was within 3%.
Calibration of 21BR Type Microphones over Wide Range of Temperature and Barometric Pressure
Authors: Hilliard J. K. , Fiala Walter
Published: September 2005

This paper reports observations of the variation in sensitivity of the 21BR type microphones when subjected to changes in temperature from −50°F to +200°F and pressure equivalent to altitudes up to 87 000 ft. An electrostatic actuator was constructed to apply force independent of ambient conditions. Certain other calibration and use accessories are described.
Origin of the Knudsen Spectra
Authors: Marsh H. W.
Published: September 2005

A theory is presented, ascribing the ambient noise spectra of Knudsen to the generation of sound by surface waves. A quantitative formula, based on Longuet-Higgins theory of surface waves in heavy, compressible fluids and the sea-surface spectra of Neumann-Pierson, Burling, and Marsh, is given, which accounts rather well for the numerical values in the Knudsen curves.
Piezo-Resistive Semiconductor Microphones
Authors: Burns Fred P.
Published: September 2005

A microphone using the piezo-resistive effect of n-type germanium has been designed and constructed with a cantilever beam arrangement. Frequency response curves were taken in a sound field of 10 microbars with the microphone in a bridge-type circuit and biased with 9 and 18 milliamperes. The microphone produces 10−11 watts in the flat low-frequency range and peaks to 10−9 watts at a resonance at 2570 cps with a total bias of 18 ma in a bridge-type circuit. Other designs of transducers and different types of semiconductor material are discussed. The performance of an ideal germanium rod microphone is compared with a standard carbon button transmitter. The construction and performance of an actual rod microphone is described. Sound pressures are applied by means of a diaphragm to a single crystal germanium rod with a cross-sectional area of 10−4 cm2.
Foreign Accent and Speech Distortion
Authors: Lane Harlan
Published: September 2005

Speech distortion is defined broadly as any operation that evokes inappropriate behavior by a listener in response to speech. Two categories of distorting operations are distinguished: (1) response-independent, in which the transfer function applied to the original speech signal is not determined by the probable response of the listener (e.g., masking, filtering); and (2) response-dependent, in which the distorting operation is related to the probable response of the listener during undistorted transmission and therefore may be specified in linguistic terms (e.g., foreign accent). Two experiments examine the effects and interactions of these two types of distortion. Twenty-four Midwest Americans listened to recorded articulation lists rendered by one American and three foreign-born speakers under eight conditions of masking and filtering. Reducing the speech to noise ratio to 20 dB or the transmission bandwidth to 500 cps yields approximately 50% reduction in word articulation for both native and foreign accent speech. The latter was approximately 40% less intelligible than native speech under all experimental conditions.
Electromechanical Analogies for Continuous Systems
Authors: Skudrzyk Eugen
Published: September 2005

The electromechanical analogies can be generalized for continuous systems including the effects of internal frictions such as hysteresis, elastic lags, and plastic flow. The methods presented are exact and correspond to a space-time Fourier analysis of the system. Every natural mode is represented by a simple tuned circuit with the proper Q, and the resultant diagram is a canonic network. The definition of a general impedance makes it possible to transform the current one-dimensional analogies into exact three-dimensional expressions which can be handled with the same ease. The theory is used to determine the effects of the resonances of a loudspeaker membrane on the frequency curve and also can be used to show up certain limits in reciprocity calibrations and to compute the vibration of a rigid tube closed by a membrane and filled with water, taking account of the resonances of the membrane and the water, the hysteresis and friction of the membrane, and the attenuation in the water.
Improved Equipment for Sound Analysis
Authors: Sherwood R. M. , Zimmerman J. K.
Published: September 2005

In many acoustical measurements one often desires to use statistical treatment of large quantities of data. A nearly automatic instrument that analyzes and digitally records signal spectra has been built to facilitate such treatment. Filters, rectifiers, and integrators are operated continuously in parallel from a signal source, and the averaged values read out intermittently to a short-term storage. Stored data are then serially sampled, expressed as decibels by a high-speed, linear-log converter and are recorded on Teletype tape after insertion of sensitivity constants. From the tape directly, or via punched cards, machines perform selecting, averaging, and other statistical processes. The system described is but one of many combinations possible. An example of its performance will be presented. Significant features are its speed, calibration flexibility, and digital read-out.
Electromyographic and Acoustic Study of the Production of Certain Final Clusters
Authors: MacNeilage Peter F.
Published: September 2005

The possibility that speech may be perceived with reference to articulation prompted this preliminary study of muscle action during speech production. The question investigated was: what is the difference, if any, in the acoustic and articulatory characteristics of /f/ in utterance final position and /f/ embedded in final consonant clusters. The acoustic duration of /f/ friction, measured spectographically, was about twice as great in final position as in any other position. On the other hand, electromyograms were similar for all positions of /f/. The change in /f/ friction duration from final to prefinal position is therefore a contextual effect on acoustical properties of production alone. The motor gesture is more independent of context.
Analysis-Synthesis of Connected Speech in Terms of Orthogonalized Exponentially Damped Sinusoids
Authors: Manley Harold J.
Published: September 2005

A continuous speech sample of six seconds' duration is pitch synchronously analyzed and resynthesized in terms of a series of orthonormal functions. The series used is obtained from a set of sixteen exponentially damped sinusoidal base functions with fixed frequencies and fixed damping at each frequency. Both the computations of the orthonormal function set and the speech analysis-synthesis operations were carried out using digital computers. The results are compared by means of listening tests, curve plots, and sound spectrograms. The major difference between the input and resynthesized speech that is evidenced in all three comparisons due to discontinuities in the resynthesized waveform at the boundaries between pitch periods.
Acoustic Relaxation in Gases
Authors: Lukasik Stephen J.
Published: September 2005

Theoretical calculations of acoustic relaxation times are reviewed. The physical principles involved in such calculations are outlined, and the quantum mechanical approximations indicated. Illustrative numerical examples are presented. Finally, directions for further work are suggested.
Sound Propagation in Viscous Liquids
Authors: Litovitz T. A.
Published: September 2005

A review of longitudinal velocity dispersion and absorption measurements will be given. New data on shear relaxation will be presented which will allow a consideration of the relationship of shear and compressional viscous processes in these liquids. The origin of the volume viscosity will be discussed, using concepts of the glassy state.
Acoustic Properties of Steel Wool
Authors: Bies David Alan
Published: September 2005

An experimental investigation of the acoustic properties of grade 00 and 000 steel wool has been carried out over a wide frequency range from zero to 10 kcps. Packing densities ranged from 0.063–0.489 gm/cm3. Various gases have been used, with ratios of specific heats ranging from 1.11–1.41, and kinematic coefficients of viscosity ranging from 0.0318–1.056 cm2/sec. The results indicate that the work of Zwikker and Kosten for a porous material made of cylinders may be generalized. The pore radius of these authors becomes a characteristic length to be associated with the fibrous material.
Effect of Humidity on the Absorption of Sound in Air
Authors: Deinken H. P. , Watson R. B.
Published: September 2005

The absorption of sound in air as a function of humidity has been measured over the frequency range from 1400 to 17 000 cps. The reverberation chamber method was used with one chamber of dimensions 26 by 16 by 12 inches. The wall absorption and classical air absorption of the chamber were determined by calibration measurements using dry air. The study was conducted using broad-band noise as a sound source. The absorption was determined for certain frequency bands by the use of band-pass filters in the receiving system. The resultant curves of the air absorption coefficient versus percentage of water molecules follow the same general shape previously calculated and measured by others, but the maximum value is somewhat lower and the curves exhibit minor maxima in addition to the usual major maximum.
Shock-Wave Propagation in Solid and Compactible Media
Authors: Payton R. G.
Published: September 2005

The equations of motion for a hydrodynamic solid are studied for a pressure-density relation appropriate to pulse propagation in solid and compactible media. After collapse of the compactible material, the pressure-density relation is assumed to have the form P = A[(ρ/ρ0)γ−1]. A semianalytical method of solution is used on the resulting one-dimensional set of nonlinear partial differential equations. By using characteristic variables, the nonlinear differential equations are transformed to a set of linear partial differential equations whose solution is then obtained numerically. Applications are made to aluminum, for which the constants A and γ are known, and to compactible materials using an assumed value for γ. This investigation serves to define the various types of phenomena that can occur in a semi-infinite compactible material that is shocked by a rectangular pressure pulse. In particular, the analysis shows that the shock-wave penetration depth at the end of the first shock-rarefaction interaction has a minimum when regarded as a function of the material porosity.
Shock and Vibration from an Acoustical Viewpoint
Authors: Morrow Charles T.
Published: September 2005

The basic problem in the field of shock and vibration is that of making hardware survive and function. For example, in the case of a missile, the airframe must not be damaged by the conditions of transportation, handling, or flight. Likewise, the various electronic, electromechanical, hydraulic, and other components associated with guidance, control, and propulsion must be reliable and be within reasonable limits of performance. Related to this basic problem are procedures for interpreting the actual service shock and vibration conditions, driving specifications for design or test, developing hardware resistant to the service conditions or the specified conditions, calculation of responses to shock and vibration, and the design isolation mounts and shipping container cushions. The approach used on these problems is still primarily empirical with a large measure of cut and try. Several recent developments promise a more systematic approach, but it will be partly empirical and partly a matter of cut and try for some years to come, for many of the more obvious exact solutions cannot be used in consideration of time and instrumentation limitations. This influences the nature of many of the more urgent problems. These various aspects are discussed from an acoustical viewpoint.
Estimating the Effectiveness of Isolation Mounts
Authors: Sykes Alan O.
Published: September 2005

Mechanical network theory is applied to the problem of estimating the effectiveness of mounts isolating nonrigid machines from nonrigid foundations. The spring-dashpot mount is treated first, the continuous mount second. Effectiveness curves are presented for a variety of machine, mount, and foundation conditions, and the application of these curves to practical isolation problems is discussed.
Measurement of Underwater Sound Scattered from a Fluid Sphere
Authors: Hartog J. J. , Knollman G. C.
Published: September 2005

Experimental procedures and techniques are described for measuring, in an oceanographic tank, the scattering of underwater acoustical radiation from submerged, isolated liquid-filled spheres. Of interest are sphere diameters of the order of or larger than the acoustic wavelength and acoustic impedance contrasts of as much as 20%. A novel dual-hydrophone detecting scheme is presented which enables extraction of the scattered signal from the total (incident plus scattered) signal arriving at the receiver. Since the scattering sphere is mobile, azimuthal radiation patterns can be determined. A few typical scattering diagrams are displayed and are found to agree favorably with those derived from theoretical treatments available in the standard literature. Density and speed of sound variations (between the liquid within the sphere and the surrounding water medium) are obtained by employing various mixtures of liquids as the internal constituent. A brief survey is given of the results derived from scattering measurements with liquid spheres of various diameters and impedance contrasts.
Variation of Elastic Constants and Static Strains with Hydrostatic Pressure; a Method for Calculation from Ultrasonic Measurements
Authors: Cook Rickard K.
Published: September 2005

The elastic constants and static strains of a solid subjected to large hydrostatic pressures can be deduced from measurements of resonant frequencies (or transit times) for ultrasonic waves in specimens of suitable crystallographic orientations. The pressure changes the specimen's size, shape, and density as well as the elastic constants, and all of the effects influence the resonant frequencies. An algorithm for separating out the effects due to variations in elastic constants from the effects due to static strains is presented and applied to cubic crystals and hexagonal crystals, these structures being of immediate interest to investigators concerned with the properties of metals. The results apply also to isotropic and transversely isotropic solids. The only measurements needed while the specimen is under hydrostatic pressure are resonant frequencies (or transit times). Also required are the size and density at zero pressure, or the elastic constants at zero pressure.
Zener Effect in Metal Bars in Transverse Vibration
Authors: Brewster John L. , Rudnick Isadore
Published: September 2005

When a metal is stressed, the temperature in the compressed parts rises, and in the stretched parts it falls. This gives rise to thermal conduction currents which, Zener showed, lead to losses of a relaxation type which are especially important in transversally vibrating bars. An apparatus is described in which nodally supported bars are excited electrostatically and their amplitude detected electrostatically. The driving prove and the vibrating metal bar are used as the plates of tank circuit of an FM oscillator which is in turn coupled to an amplifier and ratio detector. This permits simultaneous electrostatic drive and independent detection, which greatly facilitates precise tuning of the driving generator to the resonant frequencies of the bar. Decay measurements are taken with a level recorder to determine the “Q” of the bars at the several frequencies. Measurements on several different metals show substantial agreement with the Zener theory especially as regards the relaxation frequency and the shape of the absorption vs frequency curve.
On the Dependence of Absorption Coefficients upon the Area of the Absorbent Material
Authors: Daniel Eric D.
Published: September 2005

The sound-absorption coefficient for a small area of an acoustical material is much greater than for a very large (or infinite) area. Measurements of the distribution of sound pressure at the surface for diffusely incident sound suggest that the additional absorption should be proportional to 1/A12, where A is the area of the material. Experimental data on absorption coefficients are presented which confirm this deduction.
An Experiment in Magnetoelasticity
Authors: Willett Robert A. , Leonard Robert W.
Published: September 2005

Small increases in the resonant frequency and rate of decay of free vibrations of a cylindrical aluminum rod in a longitudinal mode, caused by the presence of a transverse magnetic field, have been analyzed and measured. The motion of a conducting body in the presence of a magnetic field induces circulating currents. Part of these currents are distributed in the interior of the body, and part (the skin current) is concentrated near the surface. The currents and the applied magnetic field lead to a force on the medium which in the present case modifies the resonant frequency and the rate of decay of vibrations. The measured frequency shift resulting from an applied field of 1.7 webers/m2 was an increase 0.25±0.02 cps for a rod vibrating at 20 kc. The measured value of the increase in the rate of decay of vibrations was 1.86±0.06 db/sec for a rod whose normal decay rate was 2.41 db/sec. The values predicted by the theory are a frequency shift of 0.208 cps and an increase in the decay rate of 1.79 db/sec. (This work was supported by the Office of Naval Research.)
Perception of Temporal Order and Loudness Judgments for Dichotic Clicks
Authors: Babkoff Harvey , Sutton Samuel
Published: September 2005

The effect of a loudness cue on the perception of the temporal order of dichotically presented clicks was investigated. It was shown that one can find a range of temporal intervals between dichotically presented clicks for which increasing temporal separation results in a decrease in the correct judgment of temporal order.
Tonal Thresholds for Short-Duration Stimuli as Related to Subject Hearing Level
Authors: Elliott Lois L.
Published: September 2005

The loudness threshold for pure tones varying in duration from 3–1000 msec was studied among subjects with hearing levels ranging from “normal” to severe sensorineural loss. Results showed a negative relationship between slope of the short-duration/threshold function and hearing acuity.
Method for Measuring Fine Details of Differences in the Structure of Various Speech Sound Spectrums
Authors: Vilbig Friedrich
Published: September 2005

Fine details in the spectral differences of various speech sounds can be distinguished by comparing envelope curves. In a Scanvocoder the differences can be found instantaneously if the envelope signal is distributed to (for example) 100 equal condensers by a switching arm that rotates synchronously with the analyzer switching arm. If the envelope curve does not change between two consecutive rotations, no difference charges have flowed to or from the condensers during the second rotation. If the envelope curve does change, its difference in direction and size corresponds to the difference in charge of the several condensers. A small pulse transformer in the link to the distributing switching arm picks up pulse voltages corresponding to the difference charges. Smoothed in a low-pass filter, these voltages are linked to the y deflection plates of an oscilloscope. If the electron beam is also deflected in the x axis synchronously with the rotating switch, the difference between consecutive envelopes appears as a difference curve. Because the condensers have a long discharge time, it is possible (by special switching arrangements) to compare the envelope curves of sounds spoken by the same person or by different persons. Variations of such difference curves with time also can be measured.
Résumé of Hearing Tests Conducted on Individuals Working in the Vicinity of Magnetostrictive Ultrasonic Generators
Authors: Vaughan E. M. , Schaeffer Lester
Published: September 2005

The noise from magnetostrictive ultrasonic generators and its physiological effects on employees working in an area where these units are operating is included in the projects that the Science Departments of St. Ambrose College have been investigating for Pioneer-Central Division, Bendix Aviation Corporation. Periodic checks have been made since January 30, 1956, using a Maico Model F1 audiometer operated by Professor Lester Schaeffer, St. Ambrose College Speech Department, on a group of 36 individuals associated with the Engineering Section of Pioneer-Central. These individuals are divided into three groups: (1) constantly exposed to ultrasonics during working hours (engineers and technicians working in ultrasonics laboratories); (2) occasionally exposed to ultrasonics during working hours (sales engineers and drafting personnel in ultrasonics department); (3) never exposed to ultrasonics (engineers and management personnel in other sections of engineering). The report submitted is in the form of a chart comparison of the hearing ability found for these various groups.
Build-Up Event of Cochlear Vibrations
Authors: Tonndorf Juergen
Published: September 2005

Vibratory displacement of the cochlear partition in response to transients or to sustained vibrations differs in one detail, according to Bekesy's classical descriptions. Whereas in the first case wave motion progresses along the entire cochlea at an almost constant amplitude, in the latter case it is confined to a smaller limiting envelope with a characteristic amplitude peak. Therefore, a transition (from the first to the second pattern) may be assumed to occur during the onset of cochlear vibrations. High-speed motion picture photography (equipment on loan from the Office of Naval Research under contract number 140112) was employed for the study of this postulated build-up event. In general, the foregoing hypothesis was confirmed. Some of the original motion pictures will be shown for demonstration of certain details. Simultaneous observation of cochlear fluid motion was not possible. However, the similarity of the onset event to that of surf permitted making certain complementary assumptions. Earlier [J. Tonndorf, J. Acoust. Soc. Am. 27, 1009(A) (1955) and 28, 756(A) (1956)], two dissipative forces had been recognized concerning cochlear vibrations. It appears now that, of these two, friction is the primary factor causing slowdown of wave propagation, whereas shearing motion within Bekesy's eddy is responsible for formation of the amplitude peak. The eddy, caused by reflection, is formed secondarily during the build-up period.
“Off”-Responses in the Auditory Nervous System of Anesthetized Cats
Authors: Sandel T. T. , Kiang N. Y. S.
Published: September 2005

When acoustic stimuli of duration longer than 0.1 sec are turned off, one frequently records electrical responses at cortical and cochlear locations. Several observations suggest that these “off”-responses are related to acoustic transients. Certain conditions under which cortical off-responses to transients occur have been determined. The stimuli were mostly bursts of tone (about 30 db above threshold) whose frequencies at each location of the recording electrode were specifically not those to which the cortical point was most sensitive. The large “off”-responses obtained are sensitive to decay time, duration, and intensity of the tonal stimulus; they can be masked by noise and they resemble in wave form the responses evoked by clicks at the same cortical location. When the stimuli were bursts of noise, no “off”-responses were observed. These results may be interpreted in terms of the refractory characteristics of groups of neurones. Throughout the period of tonal stimulation, a large proportion of the available cortical neurones is inactive; stimulation with noise, on the other hand, activates many of these neurones. “Off”-responses become detectable when numerous nonrefractory cortical neurones are available to fire synchronously. Recordings from cochlear locations support this interpretation. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Are Loudness Judgments Based on Distance Estimates?
Authors: Warren Richard M.
Published: September 2005

Stevens and Guirao recently confirmed an earlier study demonstrating that judgments of half loudness were the same as estimates of doubling the apparent distance of the source. The explanation they offered for this equivalence is disputed, and it is suggested rather that the manner in which sound varies with distance from the source serves as the basis for loudness judgments.
Hydrogen Retention System for Pressure Calibration of Microphones in Small Couplers
Authors: Koidan Walter
Published: September 2005

The pressure calibration of microphones using small hydrogen-filled couplers can be facilitated by connecting relatively large containers of hydrogen to the capillary tubes of the coupler and using additional capillary tubes to vent the large containers to the atmosphere.
Use of the Analog Computer in the Design of Directional Arrays
Authors: Kendig Paul M. , Binstock Leonard
Published: September 2005

The usefulness of the analog computer in the design of radiation patterns produced by various arrays of radiating elements is discussed. The analog computer provides an easy and rapid method of continuously plotting the entire pattern from known parameters, such as relative strengths of the elements, element spacing, frequency, and relative phases among the elements. Modifications of any or all of these parameters are easily made and the effects quickly determined. It may be used for a wide variety of arrays, among which are linear and plane arrays with uniform or nonuniform spacing, tapered arrays, and steered arrays in which phase lags readily may be introduced into any number of elements. Although several of the so-called optimum design techniques provide the optimum pattern in only one or two planes, the analog computer quickly provides the patterns for other planes. Also, the sum and difference patterns of two halves of an array may be drawn simultaneously. One such curve presents the locus of the vector amplitude and phase of the signal from one-half of the array.
Theory of the Quincke Tube
Authors: Herrenden Harker G. F.
Published: September 2005

Corrections are made to the theory of the Quincke tube given in G. W. Stewart and R. B. Lindsay's Acoustics (D. Van Nostrand Company, Inc., New York, 1930) and in the original paper by G. W. Stewart [Phys. Rev. 31, 696–698 (1928)]. Appended is an expression for the power-transmission ratio for the more general system in which the inlet tube is of cross-sectional area S1; the branch tubes are of cross-sectional areas S2,S3 and of lengths l2,l3, respectively; and the outlet tube is of cross-sectional area S4, instead of S1.
Theoretical and Experimental Studies of Pressure Profiles in Ultrasonic Waveguides
Authors: Carome E. F. , Lastovka J. B.
Published: September 2005

An attempt has been made to confirm the results of recent attenuation vs pathlength studies in liquid-filled ultrasonic waveguides. These had indicated that the modes propagated in such guides were those characteristic of solid guides of the same configuration. To investigate this effect further, the pressure profiles within waveguides consisting of water-filled cylindrical columns excited by circular piston sources were studied. Theoretical profiles were computed for the two ideal cases of columns with pressure-free walls and with rigid walls. As in the earlier attenuation studies, it was found that the experimental profiles, obtained at 1 Mc/sec in a number of different configurations, fit quite closely those predicted theoretically for guides with pressure-free walls.
Acoustic-Wave-Theory Interpretation of Surface and Bottom Reverberation
Authors: Toulis W. J.
Published: September 2005

The scattering of sound by the ocean surface or bottom is generally assumed to be proportional to sin φ, where φ, is the grazing angle at incidence and n may have a value from zero to two with the latter corresponding to Lambert's law. Wave theory indicates that the scattering form is not as simple and requires a space-directivity factor to account for the scattering from an insonified strip on a surface. Plane-wave theory is satisfactory for short pulses and also for long pulses at small grazing angles. At intermediate angles, the curvature of the wavefront for long pulses and the scattering due to random specular reflections may influence the form of the directivity space factors. However, from the limited number of generally available measurements, distribution of random specular reflectors near normal incidence with an equivalent angular aperture of about 27 degrees seen as to be the principal source of reverberation. Thus, a scattering coefficient near unity rather than the 10−3 value from empirical formulation is necessary to satisfy the observed reverberation as well as the acoustic-scattering loss that is observed on reflection at the ocean surface. Moreover, a distinction ought to be made between reverberation decay, scattering decay, and scattering strength.
Excitation of Cavity Resonance by Air Flow
Authors: Harrington Marshall C.
Published: September 2005

The excitation of cavity resonance by air flow past the aperture has been experimentally investigated. Rectangular apertures of different aspect ratios were located in the ceiling of a wind tunnel. A large wooden box whose volume could be changed was mounted above to provide the cavity. Intensity levels and frequency spectra were observed as a function of air speed. For any one aperture and volume, several regimes of sharp oscillation appeared in turn as the air speed was increased. Each began at an air speed conforming to nearly the same Strouhal number, S = Nd/iU, where N is the natural frequency of one of the modes of resonance (Helmholtz or organ-pipe type of resonance), U is the free stream velocity, d is the width of aperture in direction of flow, and i is an integer taking the values 1 or 2. For each regime the natural frequency of oscillation shifted upward as the air speed was increased because of a decrease in the equivalent mass reactance of the air in the opening. The oscillation died out abruptly with further increase in air speed, reaching a final frequency asymptotically. There appeared to be a strong interaction between fluctuations in the flow past the edges of the aperture and oscillations of the cavity.