bluuebunny/crossref_metadata_2025 huggingface dataset:
Attenuation of Sound in Lined Air Ducts
Authors: King A. J.
Published: September 2005

Theoretical predictions of the performance of silencers are apt to be difficult and unreliable so experimental results are often very valuable. A previous paper contained curves giving the attenuation of sound with frequency in lined ducts of various widths and thicknesses of lining of rock wool. Subsequent experience has shown the need for an extension of these curves to cover thicker linings and splitters and advantage has been taken of an opportunity to obtain further data on 16-in. splitters and air channels. New curves including these data are given for 50% space factor, together with an extrapolation to 32-in. splitters. Thicknesses greater than 16 in. are unlikely to be used unless frequencies lower than 100 cps are important. For covering very wide frequency bands two stage filters are recommended.
Some Observations on Reproduced Sound in an Automobile
Authors: Schwarz B. A. , Brinkerhoff D. E.
Published: September 2005

Some of the physical and psychological factors of reproduced sound in an automobile, are discussed. The environmental conditions, such as: ambient noise as it affects audible frequency and dynamic range; “listening room” size, audience seating arrangement, and acoustical properties, are compared with these conditions in a living room or concert hall. The transducer efficiency, size, loadings, required power handling, frequency balance, frequency and dynamic range, and the effects of its location on the distribution and delivery to the listeners are considered. Psychological factors affecting the desirability of many experimental loudspeaker locations tested, are presented.
Stereophonic Sound Reproduction in the Home
Authors: Olson Harry F.
Published: September 2005

To achieve realism in a sound reproducing system three fundamental conditions must be satisfied, namely: first, the frequency range must be such as to include all the audible components of the various sounds to be reproduced; second, the volume range must be such as to permit noiseless and distortionless reproduction of the entire range of intensity associated with the sounds; third, the reverberation and spatial characteristic of the original sound must be preserved. This paper describes experiments and tests conducted over a period of a decade with the object of determining the factors which play a major role in establishing realism in reproduced sound under practical operating conditions in the home. The subjects investigated include the following: acoustic frequency preference; nonlinear distortion; stereophonic frequency preference; noise; localization (lateral and depth); reverberation.
Bigradient Uniaxial Microphone
Authors: Olson Harry F. , Preston John , Bleazey John C.
Published: September 2005

A second-order unidirectional microphone has been developed consisting of two uniaxial microphones connected in series opposition. This system has been termed the bigradient uniaxial microphone. The directional efficiency, that is, the energy response to random sounds is one-ninth. The high discrimination which this microphone exhibits to sounds which originate from the sides and rear makes it particularly suitable for long distance sound pickup in radio, television, sound motion pictures, phonograph recording, and sound reinforcing systems.
Propagation of Sound across Audience Seating
Authors: Schultz Theodore J. , Watters B. G.
Published: September 2005

Measurements have been made in four concert halls, and on scale models of the seats alone, of the attenuation of sound passing at grazing incidence over the seating area. For low-frequency sound, we find attenuation in excess of inverse-square loss, which amounts typically to 15–20 dB; the attenuation is considerably less at frequencies lower and higher than about 150 cps, the frequency of maximum attenuation. This attenuation attains its maximum severity after about 12 seat rows, beyond which little further degradation occurs. It appears to be an interference effect and does not depend markedly on the absorptive properties of the seats. The frequency of maximum attenuation is related primarily to the height of the seats and only secondarily to the row-to-row spacing. This low-frequency loss occurs in all the halls that we have measured, and we believe it to be typical of the main-floor sound of all concert halls.
Perception of Music Heard via Interfering Paths
Authors: Schultz Theodore J. , Watters B. G.
Published: September 2005

In most instances, the transmission of music from instrument to listener involves multiple paths with relative time delays. The measured sound pressure due to sound waves arriving via these several paths will be reinforced at some frequencies and will be partially cancelled at others. We have found one particular set of circumstances where, contrary to earlier opinion, the hearing mechanism is not able by virtue of some precedence effect to disregard the cancellation of two complex, narrow-band, out-of-phase sound waves. We believe that the case reported here has elements in common with many typical music-listening situations.
Intracardiac Acoustics
Authors: Wallace John D. , Brown James R. , Lewis David H. , Deitz George W. , Ertugrul Ali
Published: September 2005

The authors have previously described the development of the intracardiac phonocatheter. These phonocatheters have been used routinely for the past year at the Heart Station of the Philadelphia General Hospital. This paper reports the findings of studies on dogs as well as one hundred human patients including children as young as eleven weeks. Preliminary measurements have been made of the transmission loss from chamber to chamber in the heart as well as from the various chambers to the chest wall. Spectrograms have been used in the studies of the several heart sounds, and frequency-time-intensity contours have been derived. The nature and origin of the sounds have been investigated in respect to the diagnosis of specific heart defects which in several cases have been subsequently confirmed by surgery.
Seattle Opera House—Acoustical Design
Authors: Veneklasen Paul S. , Christoff Jerry P.
Published: September 2005

The new Seattle Opera House is a multipurpose auditorium having a sealing capacity of 3100, a volume of 778 000 ft3, and a nominal reverberation time of 2.0 sec. The acoustical properties of the hall have won approval for a wide variety of performances. Interesting features of the hall include wall louvers to adjust the reverberation time and a fully adjustable, movable orchestra enclosure. The paper describes the acoustical performance in terms of the acoustical features integrated in architectural design. The achievement of clarity with reverberance is especially stressed, also the verification of structural absorption and correction of faulty seat-absorption versus frequency characteristics. The use of acoustical modeling is stressed in the achievement of sound projection over the audience surface and under balconies, as well as for the avoidance of echoes. The economic efficiency of maximizing reverberation as a function of volume is illustrated.
Temporal Summation and Backward Masking
Authors: Wright H. N.
Published: September 2005

Appropriate transformations based on the theory of temporal summation were used to determine backward masking as a function of the time interval between the onset of a 1000-cps tone and the onset of 40-, 60-, and 80-dB narrow-band noise bursts that partially masked the tone. It was shown that under these experimental conditions backward masking consists of at least three phases: (1) a short phase immediately preceding the onset of the masking sound in which threshold is determined by the level of the masker; (2) a long phase in which threshold is independent of the level of the masker; and (3) a transition phase that lies between the short and long phases. The short phase and the transition phase each last about 25 msec, while the long phase extends from 50 to about 200 msec ahead of the masking sound. It was also shown that the theory of temporal summation is sufficient to predict threshold differences during the long phase of backward masking, and probably during the short phase also. During the transition phase, however, the threshold for tones does not vary as a function of their duration.
Acoustical Techniques for the Study of Electrochemical Processes
Authors: Yeager Ernest , Hovorka Frank
Published: September 2005

At relatively low frequencies, sound waves produce an alternating component in the potential of a reversible electrode in accord with the thermodynamic dependence of the potential on pressure and temperature. With increasing frequency, the ac response of the electrode decreases until at sufficiently high frequencies only the alternating components associated with the variation of the electrode-solution interface capacity and the ionic vibration potentials remain. The departure of the response from thermodynamic expectations occurs because the electrode processes responsible for the establishment of the potential are too slow for instantaneous equilibrium to be maintained in the sound field. The situation is analogous to the relaxation effects associated with the excess sound absorption in polyvalent electrolytes such as magnesium sulfate. From the frequency dependence of the alternating potentials at various electrolyte concentrations and temperature, information can be obtained as to the orders, rate constants, and energy barriers for various electrode processes, e.g., electron transfer from a metallic electrode to an ion. Since most electrochemical systems involve several consecutive steps, a spectrum of relaxation frequencies is anticipated. The measurement of these acoustically produced alternating potentials offers considerable promise for the study of electrode processes which are too rapid for conventional electrochemical techniques. (This paper is based on research sponsored by the Office of Naval Research.)
Message Probability and Message Reception
Authors: Pollack Irwin
Published: September 2005

It has been shown repeatedly that high-probability words are associated with higher intelligibility scores than are low-probability words. Conventional intelligibility measures are, however, biased with respect to differential response probability. The initial finding is, nevertheless, verified under the typical conditions of of intelligibility testing against noise with small, known word sets with relatively unbiased measures of intelligibility.
Absorption and Velocity Measurements in Castor Oil
Authors: Hunter Joseph L. , Bruening Leonard F.
Published: September 2005

Velocity and absorption in castor oil have been measured over a frequency range from 3 to 15 mc, and over a temperature range from 0° to 90°C. The velocity measurements indicate that dispersion, if present at all, is extremely small, and probably beyond the experimental accuracy. On the other hand, the change of velocity with temperature is extremely large, varying from 1570 msec−1 at 0°C, to 1320 msec−1 at 90°C. The measured absorption coefficient is definitely below the Stokes low-frequency value in all cases where the absorption coefficient is large, and definitely above where the absorption coefficient is small. Although the temperature at which the crossover point occurs varies greatly with frequency, (from 25°C at 3 mc to 90° at 15 mc) an interesting feature of the results is that the value of the coefficient at the crossover point is always approximately the same. This fact makes it appear that absorption in castor oil is entirely a viscosity phenomenon, in spite of the fact that there are marked departures from the simple frequency-squared law.
Sonic Drying
Authors: Soloff Robert S.
Published: September 2005

This paper deals with the application of airborne sonic energy in the drying process. Particular emphasis is placed on the development of the Hartmann-type sound generator for this application. The mechanism of the drying of solids is shown to be a complicated process influenced by many factors. How a sound field can influence these factors and increase the rate of drying is discussed. A description of a typical sonic dryer is given in conjunction with actual applications.
Cocktail Party Effect
Authors: Pollack Irwin , Pickett J. M.
Published: September 2005

Acousticians have long recognized that the cocktail party is a stimulating environment for inquiry into the basic problem of acoustics. The cocktail party provides a critical test of listening to a talker against extraneous sound sources. The “cocktail party effect” hence has been identified with situations which require selective directional listening in a multitalker environment. After appropriate operational research of cocktail parties, we brought the problem to the laboratory. Unfortunately, we were forced to reduce the problem to more sober proportions. We tested the intelligibility of recorded monosyllabic PB words against a babble of 1, 2, 4, or 7 independent talkers reading newspaper text. Two test conditions were examined: (1) test words were introduced stereophonically with one set of background talkers presented over one earphone and another set of talkers presented over the other earphone; and (2) test words were introduced with a single set of background talkers presented over a single earphone. The cocktail party effect was identified with the difference between the speech-to-background ratios required for 50% intelligibility under the two conditions. The effect ranged from 12 db with one back-ground voice to 6 db with seven background voices (in each ear).
Generation of Circularly Polarized Transverse Elastic Waves
Authors: Einspruch Norman G.
Published: September 2005

A technique for generating a circularly polarized traverse elastic wave is proposed. The circularly polarized wave is converted from a linearly polarized wave in a suitably oriented buffer rod prepared from an anisotropic material. Design considerations for a practical experiment, using tungsten buffers, are presented.
One-Syllable Words
Authors: Moser Henry M.
Published: September 2005

A systematic listing of the monosyllabic words in American English is made according to sound. An empirical approach is followed in which sounds are produced alone or in combinations. If the auditory signal is recognized as a word, it is listed in conventional spelling. A number of words not included in dictionaries are identified by this method. While the list was prepared to supply additional single syllable words to supplement those already used in radiotelephone communication, it can be utilized in language studies to show the frequency of occurrence of vowels, consonants, and consonant combinations at the beginning and endings of words. Frequency of occurrence of the speech sounds in various combinations are presented in tabular form. [Done in connection with contract AF 19(604)-1577, Operational Applications Laboratory, AFCRC.]
Airborne Sonic Emissions of Tursiops truncatus (M)
Authors: Lilly John C.
Published: September 2005

The generation of airborne sonic emissions by Tursiops was described by Aristotle (384 to 322 BC). In modern times, only passing notes are found in the literature (Tomilin, etc.). The first sonic spectrograms are published [Proc. Am. Phil. Soc. 106, 520 (1962)]. During the first few days in confinement, the usual large underwater sonic repertoire of Tursiops can be recorded; airborne emissions are rare [Science 134, 1873 (1961); Handbook of Physiology, p. 741; Am. Physiol Soc. (1964)]. (During the first day or two of confinement, some individuals (3 out of 40 observed) produce in air sounds usually heard under water, and then become “air-silent.” In many cases, after 8 to 24 weeks in confinement, the airborne emissions start. These complex sounds in air are specified by their amplitude patterns, basic repetition rates, frequency spectra, time courses, and relations to underwater sounds produced concurrently and/or alternatively. Oscillograms and spectrograms are presented. Some recorded evidence for some degree of apparent time-course coupling of trains of some of these emissions to similar missions from other sources is presented. [Work supported in part by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, by the U. S. Air Force Office of Scientific Research, and by the National Aeronautics and Space Administration.]
Acoustic Impedance in a Rigid-Walled Cylindrical Sound Channel Terminated at Both Ends with Active Transducers
Authors: Beatty Louis G.
Published: September 2005

When two transducers are coupled together by a sound channel such as a water-filled steel tube and independently driven at a common frequency, dynamic control may be exerted over the acoustic impedance presented by the channel to either of the transducers. The determination of this load in the practical case, however, presents considerable experimental difficulty. For the ideal rigid-walled channel excited by symmetrically mounted piston sources, the load impedances may be expressed in terms either of the ratio of the source velocities or of their blocked driving forces. At frequencies below those for which radial mode propagation occurs within the channel medium, the load impedances may be also related to the standing-wave ratio of the longitudinal mode. This latter relationship seems better suited to practical measurements. Of particular interest for underwater acoustic calibration is the use of the active-load technique to produce plane progressive waves inside a practical water-filled steel tube.
Long Wavelengths in Stratified Media: Comparisons between Theory and Experiment
Authors: Tolstoy I.
Published: September 2005

A principal characteristic of propagation in a medium of rapidly varying properties is its strong dispersion. For a transient source this means a rapidly changing form of the traveling wave. For simple harmonic excitation it results in different rates of energy transport for different frequencies and thus in resonant and antiresonant excitation frequencies. Both types of phenomena have been studied experimentally, although most of the past work has been limited to the dispersion of pulses, and in particular to the concept of “arrival time” of the various Fourier components. This concept, although not rigorous, has been very useful and has found many applications and verifications in geophysics and acoustics. In the last five years successful efforts have been made to obtain more detailed agreement between theory and experiment, with particular reference to the quantitative prediction of sound fields and wave forms. Several such experiments will be discussed here. One of these is a model experiment with a transient source, designed around Pekeris' treatment of the two-layered haft-space. Another is a simple harmonic experiment carried out in shallow water at sea. In both cases detailed and quantitative agreement has been secured within quite acceptable limits of error.
Excitation of a Resonant Cavity by Ducts of Small Cross-Sectional Dimensions
Authors: Van Bladel J.
Published: September 2005

Two basic configurations are considered in this paper: (1) a resonant cavity with a single-input waveguide of vanishingly small cross-sectional dimensions, in which the pressure in the resonator and the reflection coefficient in the waveguide are investigated. Particular emphasis is laid on the behavior around a resonant frequency of the cavity; (2) a cavity with an input and an output waveguide (a “filter”), in which the the transmission properties are investigated around resonance.
Absorption of Sound in Mixtures of Oxygen and Water Vapor
Authors: Harlow R. George , Kitching Ronald
Published: September 2005

The attenuation of sound waves in mixtures of oxygen and water vapor contained in a tube has been measured at frequencies between 90 and 1200 cps. The tube was terminated at one end by a fixed reflector and at the other by a plane diaphragm producing the sound waves. The impedance of the diaphragm/gas-column system was investigated near natural modes of the tube and analyzed by means of a circle diagram to yield the attenuation coefficient. The frequency of maximum absorption of sound was found to be a quadratic function of the water-vapor concentration. The value of the vibrational specific heat for oxygen was found to be (0.0332+0.0015) R.
Noise Produced by Boundary Layer Turbulence of a Rotating Cylinder
Authors: Skudrzyk Eugen , Haddle Gillian P.
Published: September 2005

A rotating cylinder was equipped with hydrophones and immersed in water. Measurements of the velocity distribution and the noise level were performed. The results have been used as a guide line to derive a general theory of the noise production by plane or curved, smooth, and rough surfaces and to estimate the admissible size of surface roughnesses under given conditions.
Transmission of Sound through a Stretched Ideal Membrane
Authors: Romilly Nicholas
Published: September 2005

The exact solution, in infinite series form, is given to the problem of the transmission of an axially symmetric sound wave through an ideal stretched membrane in a rigid circular tube. Certain simple exact results are deduced, and the exact equations for the resonance and antiresonance frequencies are considered. It is shown that, for an incident plane wave, above a certain frequency there are no exact resonances or antiresonances. Below this frequency, the resonances and antiresonances differ from those predicted by approximate methods, and, contrary to the simple results, their frequencies depend on the density of the medium surrounding the membrane. The same analysis, which involves the inversion of an infinite matrix, applies also to the parallel-plate guide and to transmission through a thin elastic plate. Numerical results are given for a particular case.
Arrays for the Investigation of Ambient Noise in the Ocean
Authors: Anderson V. C.
Published: September 2005

A discussion of the important parameters to be considered in the use of directional arrays for the study of noise fields in the ocean leads to specialized array designs. Some properties of circular and spherical arrays composed of omnidirectional elements are presented. The calculation of directivity index for a spherical array is carried out by the use of the space-correlation functions of an isotropic noise field. The measured, broad-band directivity pattern of a circular plane array as a function of frequency is also shown. (This work represents one of the results of research carried out under contract NObsr 72512, NE 120221-4-5-6 with the Bureau of Ships, Navy Department.)
Method of Perturbation Applied to the Vibration Problem of a Circular Membrane of Varying Density
Authors: Sen Gupta Ratneswar , Ghosh Ranjit
Published: September 2005

In this paper, a treatment for determining the eigenfunctions and eigenvalues for the vibration of a circular membrane with fixed boundary and density varying as exp[− εγ2] is made by the method of perturbation, and the expressions for perturbed eigenvalues and eigenfunctions are obtained up to second-order terms. The first-order perturbed term of the eigenvalue is effected by numerical integration.
Several General Purpose Transducer and Reflector Combinations for Underwater Sound Work
Authors: Mechler M. V. , McKinney C. M. , Anderson C. D. , Collins F. A.
Published: September 2005

Several transducer and reflector combinations are described which are useful over a fairly wide range of frequencies. One form consists of a right-angle conical reflector with a line transducer mounted on the principle axis of the cone. The units described have aperatures ranging from 6 in. to 48 in. Frequencies covered are from 25 kc to 0.5 mc. One arrangement allows simultaneous operation of the unit as a projector and as a hydrophone. Another transducer, designed to be used in the fractional megacycle region, uses a conventional parabolic reflector with a probe at the focus. Means are shown for rapidly changing the beam width, shading, and focus. Several other experimental transducers are described briefly. Calibration data in the form of directivity patterns, sensitivity, and impedance are shown.
Analysis of Echoes from a Hollow Metallic Sphere in Water
Authors: Hickling Robert
Published: September 2005

The nature of sonar echoes from a hollow metallic sphere in water is investigated theoretically in relation to the thickness of the shell and the contents of the hollow region. Steady-state solutions are presented for iron and aluminum spheres filled with water and for iron spheres with a vacuum inside. Calculated results for pulsed sound suggest that part of the echo originates from a type of flexural wave moving around the shell, which changes into a surface wave as the shell thickness increases. Significant differences in echo structure occur when the interior region is changed from water to a vacuum.
Underwater Noise Produced by Bullet Entry
Authors: Leslie Charles B.
Published: September 2005

Investigations of the underwater sound produced by shooting bullets into water indicated that the principal mechanism of sound production might be the oscillatory collapse of an air bubble near the surface. High-speed motion pictures taken of a .38-caliber-pistol bullet's entry into a tank confirmed this idea. The main features of the acoustic signature can be explained and correlated with the motion pictures. On the order of 1% of the available kinetic energy was converted to acoustic energy. Most of the energy was transferred to a single bubble during the first 2 ft of travel in the water.
Effects of Extraneous Tasks on Auditory Fatigue
Authors: Bell Donald W. , Stern Hervey W.
Published: September 2005

Nine subjects with normal hearing were exposed for 3 min to 50- and 100-dB-SPL, 4-kc/sec tones during the performance of a task. Three tasks were used: long division, light tracking, and reverie. Each subject received 3 replications of every task/level-of-exposure combination. Performance of task during exposure was found to have no significant effect on the magnitude of TTS. Repeat-reliability measures showed the subjects to be reasonably consistant in their responses.
Temporary Hearing Losses following Exposure to Pronounced Single-Frequency Components in Broad-Band Noise
Authors: Cohen Alexander , Baumann Karl C.
Published: September 2005

Temporary hearing losses were observed for 20-min exposures to pure-tone frequencies (500, 1000, 2000, 4000 cps), which were independently mixed in various strengths with a broad-band noise to create different exposure conditions involving a strong tonal component in a noise field. The over-all (combined pure-tone/noise) SPL for all conditions was fixed at 105 dB and the resultant losses were compared to those caused by equivalent exposures to just the broad band noise (referred to as the continuous-spectrum-noise condition). The pure-tone/noise combinations produced greater threshold losses than the continuous-spectrum noise primarily when the pure tone was of low frequency (below 2000 cps) and contained most of the available energy in the sound field. These more prominent pure-tone exposures exceeded the criteria set forth by the U. S. Air Force 160-3 Noise Regulation for identifying those conditions of strong pure-tone energy in noise that are believed more hazardous to hearing. However, other pronounced pure-tone conditions in this study also met these criteria even though they gave no evidence for increased hazard to hearing when their postexposure losses were compared with those of the continuous-spectrum noise. The findings were discussed with regard to the action of the acoustic reflex that has been proposed to account for the differences in the ability of pure tones and noise to cause hearing loss.
Effect of Repeated Exposure to High-Intensity Sound
Authors: Riach W. D. , Elliott D. N. , Frazier L.
Published: September 2005

Auditory fatigue was experimentally induced in eight subjects over a period of several weeks so that a systematic study could be made of the alteration in hearing that might occur as a result of such repeated exposures. Temporary threshold shifts and intensity-difference thresholds were obtained from each of these subjects as indices of fatigue. In general, there were only chance variations in the TTS and the IDT over the period studied. It was concluded that within the limits of this study repeatedly exposing subjects does not basically alter the hearing mechanisms. However, as the sessions progressed, a trend toward a smaller TTS at the 1-min postexposure point was noted. This change resulted in an accentuation of the “bounce” phenomenon, which did not disappear when the contralateral ear, not previously exposed, was fatigued. Thus, the data suggest that the change in the R-1 recovery function was the result of a factor common to both ears.
Detection of Tone Pulse of Various Durations in Noise of Various Bandwidths
Authors: van den Brink G.
Published: September 2005

Noise-masked hearing-threshold measurements for tone pulses of 800 cps over a wide range of pulse durations and bandwidths of the masking noise show that the slope of the threshold versus bandwidth curve of 3 dB per factor 2 in bandwidth, as predicted by Fletcher [Rev. Mod. Phys. 12, 47 (1940)] occurs only for bandwidths of 10 cps and smaller. This is due to a criterion change for bandwidths between 10 and 100 cps. In this range of bandwidths, the average slope is about half of that expected by Fletcher. In the present experiments, the slope of the threshold versus pulse-duration curve turned out to be 3 dB per factor 2 in time when white-masking noise is used, and often even less when bands of masking noise are used. These measurements indicate the existence of a mechanism that adjusts the width of the critical band in such a way that detection of the stimulus occurs more efficiently than it would in the case of a fixed width of the critical band.
Experiment on Cochlear Summation
Authors: van den Brink G.
Published: September 2005

A new method for measuring cochlear summation is introduced. This method is an analog of the method earlier applied for measuring retinal summation. The probability of hearing pulses of two small noise bands presented simultaneously is measured as a function of the frequency difference between these noise bands. Within the experimental error, the result of the present experiment shows a remarkable agreement with the results of the similar visual experiments.
Use of High-Strength Ceramics in Vibration Transducers
Authors: Jones Earle
Published: September 2005

Some advantages of high-strength ceramics over other materials are given for use in vibration pickups and shakers.
Backscatter of Sound from the Sea Bottom
Authors: Eaglesfield C. C.
Published: September 2005

Recently published measurements of backscatter from the sea bottom seem to be explained by an inverse-square probability density of surface inclinations.
Arctic Ocean Ambient Noise
Authors: Greene Charles R. , Buck Beaumont M.
Published: September 2005

Directional, spectral, and statistical properties of the under-ice noise in the arctic are presented. The measurements were made during a 15-day period on an ice floe in the Beaufort Basin in April 1963.
Derivative of Travel Time with Respect to Source Angle for a Layer of Constant-Velocity Gradient
Authors: Novick Arnold W.
Published: September 2005

An expression is developed for the rate of change of travel time with source angle for a ray in a layer with a constant-velocity gradient. This expression is then shown to be simply related to another ray-tracing quantity, which is generally calculated in existing computer programs.
Acoustics of Philharmonic Hall, New York, during Its First Season
Authors: Beranek Leo L. , Johnson F. R. , Schultz Theodore J. , Watters B. G.
Published: September 2005

Acousticians, musicians, and the community at large have taken a lively interest in Philharmonic Hall, the first building to be completed at Lincoln Center for the Performing Arts in New York, N.Y. This interest derives in part from the fact that Philharmonic Hall is the first major hall in nearly 30 years to be built principally for concert uses in this country, but also because the acoustics of the Hall have excited a wide range of opinion since the opening, despite considerable effort to assure fine sound on the part of all who participated in the design. This paper presents the original design goals for Philharmonic Hall and, with reference to the goals, evaluates the Hall's history, during the first year of use.
Solion Infrasonic Microphone
Authors: Collins Joseph L. , Richie William C. , English G. Earle
Published: September 2005

The solion infrasonic microphone is an electrochemical pressure transducer designed for the measurement of atmospheric-pressure variations. An over-all transducer frequency response from 0.003–50 cps and a dynamic range from 0.1–1000 dyn/cm2 has been obtained with the design described. Stability, sensitivity, low power consumption, and remote-operation capability are the inherent features of this new acoustic tool. Descriptions of the solion transducer, the infrasonic microphone, and the over-all response of the system are presented.
Sound Radiation from Vibrating Surfaces
Authors: Chertock George
Published: September 2005

The radiation field of a body vibrating with a specified distribution of velocity on the surface may be computed from the Helmholtz integral if the pressure distribution on the surface is known. In special cases of low frequency, high frequency, or particular surface shapes, it is possible to estimate the surface pressures with sufficient accuracy and thus reduce the calculation of the field pressure to a simple quadrature over the surface. In more-general cases, the surface pressure may be calculated by numerical solution of a Fredholm integral equation. This solution is described in detail for the special case of a surface of revolution with an arbitrary velocity distribution and frequency. The numerical solutions are illustrated by particular examples and compared with exact analyses.
Investigations on the Vibrations of Grillages and Other Simple Beam Structures
Authors: Heckl Manfred A.
Published: September 2005

In the first part of this paper, the transmission of bending and torsional waves on beams forming + or T-shaped systems is investigated. Then, the propagation of two different wave types, such as bending and longitudinal or torsional waves, on beams with periodic discontinuities is studied theoretically. Finally, the results are applied to the vibrations of grillages.
Random Vibration of Connected Structures
Authors: Lyon Richard H. , Eichler Ewald
Published: September 2005

The sharing of energy by connected, randomly vibrating structures can be estimated, using a statistical approach. Modal energy is taken as the primary variable; the structures are described statistically by their modal densities, masses, and loss factors. Average response levels are computed. In addition, response variations are calculated to establish confidence coefficients for estimates related to these average levels. The method is applied to two cases: a single resonator attached to a plate and two plates attached together. Experimental studies are reported that support the methods.
Free Vibration of Rotationally Symmetric Shells
Authors: Kalnins A.
Published: September 2005

This paper is concerned with a theoretical investigation of the free vibration of arbitrary shells of revolution by means of the classical bending theory of shells. A method is developed that is applicable to rotationally symmetric shells with meridional variations (including discontinuities) in Young's modulus, Poisson's ratio, radii of curvature, and thickness. By means of the method of this paper, the natural frequencies and the corresponding mode shapes of axisymmetric or nonsymmetric free vibration of rotationally symmetric shells can be obtained without a limitation on the length of the meridian of the shell. To illustrate the application of the method given in this paper to particular shells, stone results of free vibration of spherical and conical shells obtained earlier by means of the bending theory are reproduced by the general method of this paper, and a detailed comparison is made. In addition, paraboloidal shells and a sphere cone shell combination are considered, which have been previously analyzed by means of the inextensional theory of shells, and natural frequencies and mode shapes predicted by the bending theory are given.
Intelligibility of Frequency-Modulated Speech
Authors: Darnall W. H. , Birch J. N.
Published: September 2005

An electronic system has been developed that allows a speech spectrum, initially confined to a band of frequencies from 300–3300 cps, to be deviated from its normal spectral location. The perturbation is sinusoidal in nature and controls both the amount of deviation and the rate of deviation eft the spectrum about its normal position. This system, in conjunction with an appropriate psychoacoustical test, provides a functional relationship between intelligibility and the independent variables, deviation and rate of deviation.
Lateralizing Effects of Interaural Phase Differences
Authors: Elpern Barry S. , Naunton Ralph F.
Published: September 2005

A discrepancy between experimental observation and theoretical construct is pointed out with reference to the lateralizing effects of interaural phase differences. In essence, the observation that a phase difference of 90° produces maximal sound lateralization appears less amenable to physiological explanation than a theoretical relationship in which lateralizing effect is proportional to the magnitude of interaural phase difference, at least up to an area of uncertainty near 180°.
Acoustic Properties of Fluid-Filled Chambers at Infrasonic Frequencies in the Absence of Convection
Authors: Gerber Henry
Published: September 2005

The general equation of heat conduction inside a fluid-filled chamber takes two forms, which correspond to zero and infinite acoustic impedance of the driving source, respectively. By means of a simple transformation, it is possible to convert this equation to the standard diffusion equation with simple initial and boundary conditions. Special solutions to this equation are used to derive transfer functions E, which relate the impressed temperature to the resultant average temperature. The equation of state of the fluid is then used to determine the relationships between pressure and volume changes in terms of E. These relationships take the form of two different acoustic impedances Zp and Zv which correspond to zero and infinite source impedance, respectively. In general, the chamber impedance is a function of Zp, Zv, and the external impedances. The above results can be used to extend the validity of acoustic circuit diagrams to zero frequency. The infrasonic acoustic impedance is an R C network, and numerical values of the components can be calculated in a simple manner.
Calculation of Dynamic-Pressure Changes in the Presence of Free Convection
Authors: Gerber Henry
Published: September 2005

If a piston compresses and heats gas in a chamber that is larger than a few cubic inches, then the heat exchange between the gas and the wall is governed by convection. The simultaneous, nonlinear partial-differential equations of free convection are given. Application of dimensional analysis to these equations indicates that the convection process can be described in terms of three dimensionless variables: the Grash of number, the Prandtl number, and the thermal-diffusion number. A simplified model of the process of free convection is derived and it is shown that the geometrical constants of the model can be expressed in terms of the Grashof and Prandtl numbers. The chamber length l and the boundary-layer thickness lb play a key role. Mathematical solutions for the chamber pressure that follows a step piston displacement are derived and they agree within 1% with the measured pressure.
Determination of the Propagation Constants for Ultrasonic Waves in Melting and Molten Polyethylene
Authors: Eby R. K.
Published: September 2005

An extension of McSkimin's technique to polymer melts and soft amorphous polymers is reported. For 12-Mc/sec longitudinal waves, the modulus and internal friction are presented for the melting, super-cooling, and annealing or recrystallization of polyethylene. Maxima of internal friction are observed in the solid at −52°, 60°, and 100°–130°C. The last is associated with the presence of crystals, decreases sharply near the melting temperature, and is not present in the supercooled melt. At 129.5°C, the modulus increases linearly with the logarithm of recrystallization time and the internal friction decreases. Correlation of the modulus and lamellar thickness during recrystallization indicates that the effects above 100°C are related to recrystallization. For the melt between 140° and 290°C, the internal friction exhibits a low, nearly constant value. In this temperature range, the ratio of the thermal coefficient of velocity change to the thermal coefficient of volume expansion is −2.6. A decrease of modulus and increase of internal friction above 300°C is believed to be associated with thermal degradation of the polymer.
Ambient-Noise Directivity Measurements
Authors: Fox George R.
Published: September 2005

Measurements have been made from which the vertical directivity of ambient sea noise near the ocean bottom in water 14 500 ft deep has been computed. A vertical linear array of 40 hydrophones was used, with delay lines, to form 28 beams in directions from horizontal to vertically upward. Measurements were made at four fixed frequencies, 200, 400, 750, and 1500 cps, in a variety of weather conditions. The directional distribution of the noise is shown as a function of angle for three sea states at each frequency. It is found that at low sea state the noise distribution has a peak in the horizontal direction. As the sea state increases, the vertical and near-vertical contributions increase more rapidly than do the horizontal contributions.
Ambient-Sea-Noise Model
Authors: Talham Robert J.
Published: September 2005

A model of ambient sea noise is developed under the assumption of a surface distribution of noise sources. Volume absorption and the effects of refraction and reflection over long-range paths are included. The derived directional noise field is expressed as a function of vertical arrival angle, with the parameters being velocity profile, surface distribution, bottom-reflection coefficient, surface-reflection coefficient, and frequency. Several forms of surface source directionality are considered. In an example representative of deep-water and low-sea-state conditions, the model predicts that most of the low frequency acoustic energy at the ocean bottom should arrive over nearly horizontal paths. This is in agreement with reported measurements. Methods of incorporating the effects of sea state into the model are discussed.
Underwater Backscattering Strengths of Arctic Pack Ice
Authors: Milne A. R.
Published: September 2005

The backscattering strengths under Arctic sea ice for octave bands between 12 cps and 4 kc/sec were measured, using explosive sound sources. The measurements were made from a camp established in April 1962 on broken and pressure-packed one-year ice over the Canada Deep. For grazing angles between 5° and 14°, results show a dependence of scattering strengths both on grazing angle and on frequency. The dependence on grazing angle is small in frequencies above the 0.5- to 1-kc/sec band and large in the 12- to 25-cps band.
Underwater-Sound-Transducer Calibration from Nearfield Data
Authors: Trott W. James
Published: September 2005

Farfield transmitting response, freefield sensitivity, and directivity of large audiofrequency transducers can be obtained directly from measurements made in the near field (Fresnel zone) of a transducer array especially designed to radiate a plane wave of constant amplitude within a portion of the Fresnel zone. The theory of the measurements and of the design of the special measuring array are supported by experimental data. Design data for building suitable measuring arrays are given.
Solid-Core Probe Hydrophone
Authors: Barger James E. , Hunt F. V.
Published: September 2005

Analysis and experiment have shown that the sensitivity of small probe hydrophones using a ceramic tube as the active element can be substantially improved by properly proportioning the cylinder and mounting it on a solid metallic core. The solid core raises the resonance frequency of the hydrophone by more than an octave, thereby extending also the frequency range of uniform response.
Sound Absorption and Velocity in Water Vapor
Authors: Lewis James W. L. , Shields F. Douglas
Published: September 2005

Kirchhoff'f tube-wall corrections and virial real-gas corrections adequately account for experimental values for the unsaturated vapor at 100° and 250°C.
Transducer-Thickness Effects in Measuring Ultrasonic Velocities
Authors: Kammer E. W.
Published: September 2005

A series of transit-time measurements was made on a silica block, using X-cut quartz transducers of thicknesses ranging from 0.011–0.125 in. The corresponding transit times for the same specimen pathlength of transmission varied from 6.86–7.92 μsec. Since the variation in transit time with transducer thickness was linear, it is suggested that the zero-thickness extrapolated intercept is a more realistic value from which to compute velocity, especially for materials having acoustic impedances nearly the same as the piezoelectric component in the transducer.
Pitch of Frequency-Modulated Signals
Authors: Ritsma Roelof J. , Engel Frederik L.
Published: September 2005

This study deals with measurements carried out to determine the pitch of a quasi frequency-modulated signal consisting of only three frequency components. Such a signal was generated by modulating a sinusoid of center frequency f with a second sinusoid of frequency g and shifting the phase of the center-frequency component over 90 deg. Listening experiments showed that, with a ratio n = f/g ⩾ 9 and a modulation index m = 2, a better tonality was achieved for odd values of n than for even values. Moreover, the frequency values for pitch were found to vary as a function of the modulation index m. This was investigated at a center frequency of 2000 cps. The pitch values found are in good agreement with those calculated from the hypothesis that the distance between two positive peaks in the fine structure near two adjacent crests of the envelope of the signal constitutes a measure of the pitch of the complex. Finally, an explanation is given for the experimental evidence of a purely frequency-modulated signal giving rise to a low pitch sensation.
Feedback Vibrometer
Authors: Fleming Lawrence
Published: September 2005

A seismic-type vibration pickup is described having its natural frequency in the middle of the operating range; the response is made flat by means of electromechanical feedback. Advantages over conventional velocity pickups are ruggedness and stability. A typical instrument covers 5–1000 cps within ±10%. Output is proportional to acceleration.
Note on Buzz-Hiss Detection
Authors: Gold Bernard
Published: September 2005

Speech sounds can be approximately divided into two categories: buzz or periodic sounds and hiss or aperiodic sounds. The usual vocoder buzz-hiss detector, which discriminates on the basis of spectral-energy distribution, is not adequate when close-talking microphones (which often produce large amounts of noiselike low-frequency energy) are used. This paper describes the rules of operation of a periodicity meter that can discriminate between voiced and unvoiced sounds regardless of the spectral-energy distribution. These rules are derived from a previously developed pitch extractor. Since this pitch extractor makes use of the simultaneous operation of six individual pitch detectors, a buzz-hiss decision can be based on the degree of agreement among these six detectors. Preliminary tests show that accuracy of buzz-hiss detection is noticeably improved for both carbon-button microphones and moving-coil microphones when used in ordinary telephone handsets.