Showing papers in "Journal of the Acoustical Society of America in 1956"

Theory of Propagation of Elastic Waves in a Fluid‐Saturated Porous Solid. I. Low‐Frequency Range

Abstract: A theory is developed for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid. The emphasis of the present treatment is on materials where fluid and solid are of comparable densities as for instance in the case of water‐saturated rock. The paper denoted here as Part I is restricted to the lower frequency range where the assumption of Poiseuille flow is valid. The extension to the higher frequencies will be treated in Part II. It is found that the material may be described by four nondimensional parameters and a characteristic frequency. There are two dilatational waves and one rotational wave. The physical interpretation of the result is clarified by treating first the case where the fluid is frictionless. The case of a material containing viscous fluid is then developed and discussed numerically. Phase velocity dispersion curves and attenuation coefficients for the three types of waves are plotted as a function of the frequency for various combinations of the characteristic parameters.

Theory of Propagation of Elastic Waves in a Fluid-Saturated Porous Solid. II. Higher Frequency Range

Abstract: The theory of propagation of stress waves in a porous elastic solid developed in Part I for the low‐frequency range is extended to higher frequencies. The breakdown of Poiseuille flow beyond the critical frequency is discussed for pores of flat and circular shapes. As in Part I the emphasis of the treatment is on cases where fluid and solids are of comparable densities. Dispersion curves for phase and group velocities along with attenuation factors are plotted versus frequency for the rotational and the two dilational waves and for six numerical combinations of the characteristic parameters of the porous systems. Asymptotic behavior at high frequency is also discussed.

Physical Acoustics and the Properties of Solids

Abstract: The techniques of physical acoustics have been applied in determining the elastic properties and internal friction of polycrystal and single crystal metals, glasses, nonmetallic crystals, high polymer materials, and ceramics. They have been used as tools in investigating such solid state phenomena as grain and domain boundary effects in metals and ferromagnetic and ferroelectric materials, in the diffusion of atoms, molecules and vacancies through a solid, in the motion of imperfections such as dislocations and have even detected an interaction between the lattice sound vibrations and free electrons in metals at low temperatures.These effects are studied by techniques varying from the vibrations of torsional pendulums at frequencies below 1 cy to frequencies as high as 300 Mc by ultrasonic pulsing methods and have employed strain values from 10−8 to 10−2. Four examples of these techniques are discussed in the present paper. These include diffusions of nitrogen and carbon atoms in iron, the motion of domai...

Some Measurements of Interaural Time Difference Thresholds

Abstract: Thresholds for the detection of interaural time difference were determined by ten listeners (1) for band‐limited random noise (150–1700 cps), (2) for a 1000‐cps tone, and (3) for a 1‐millisecond click. The average interaural time differences corresponding to 75% correct detection in the symmetrical two‐alternative tests were (1) 9 microseconds, (2) 11 microseconds, and (3) 28 microseconds. Ranges of individual thresholds and group psychometric functions are presented.

Pressure Fluctuations in Turbulent Flow over a Flat Plate

Abstract: The pressure fluctuations exerted on a flat plate by a turbulent boundary layer flow are investigated. The approximate dependence of the mean‐square intensity, spatial scale, and frequency scale on Mach number and distance from transition point are estimated through the use of similarity arguments. The wave number spectrum of the pressure fluctuation distribution over the surface of the plate is expressed in terms of transforms of two‐point velocity correlations and expressions are derived for the driving force exerted on a rectangular piston set in the surface of the plate. It is found that the integral over the boundary surface of the two‐point quadratic correlation function of the pressure fluctuation should vanish, with the result that the mean‐square force per unit area exerted on a large area of the surface should tend to zero as the area increases indefinitely. An idealized model of turbulent boundary layer flow is constructed and used to relate the spectrum and correlation function of the surface ...

Just Noticeable Differences in Dichotic Phase

Abstract: The just noticeable difference in dichotic phase, as a function of sensation level and of frequency, has been determined on a number of listeners with normal hearing. The test tones were transmitted by earphones, and the phase difference between the ears was varied by means of an electronic phase shifter. The psychophysical method used combined paired comparisons and forced choice. The first tone pulse of each pair presented was kept at a constant phase difference at which the subject localized the sound source as equidistant from his ears. The dichotic phase difference of the second pulse was varied irregularly (“randomly”). The results show that the sensitivity to dichotic phase difference is highest (2° of phase) at medium sensation levels, and that the jnd increases with positive acceleration as the sound frequency increases. Around 1300 cps the jnd becomes so great that it cannot be measured. The dichotic time difference calculated from the measured jnd in phase has a minimum near 800 cps.

Diffraction Effects in the Ultrasonic Field of a Piston Source and Their Importance in the Accurate Measurement of Attenuation

Abstract: A study is made of the ultrasonic field produced by a circular quartz crystal transducer and the integrated response of a quartz crystal receiver with the same dimensions as the transducer. The transducer and receiver are taken to be coaxial, and it is assumed that the transducer behaves as a piston source while the integrated response is proportional to the average pressure over the receiver area. Computations are made for cases of interest in the megacycle frequency range (ka=50 to 1000; a=piston radius; λ=wavelength; k=2π/λ). The results contain features of use in identifying and correcting for diffraction errors. These features which apparently have been missed in previous investigations are compared with available experimental data. Finally correction formulas to account for diffraction effects in the accurate measurement of attenuation are discussed. It is shown that the order of magnitude of the diffraction attenuation is given by one decibel per a2/λ.

Spectral Properties of Fricative Consonants

Abstract: Energy density spectra of gated segments of fricative consonants were measured. The spectral data were used as a basis for developing objective identification criteria which yielded fair results when tested. As a further check gated segments of fricatives were presented for identification to a group of listeners and their responses evaluated in terms of the objective identification criteria.

Gas Bubbles as Sources of Sound in Liquids

Abstract: Gas bubbles, when entrained in water or other liquid, can generate high sound pressures in the liquid. Significant sound pressures are associated only with volume pulsations of the bubble, whereas oscillations in the shape of the bubble do not result in appreciable sound. Calculations have been made of the sound pressures resulting from excitation of volume pulsations by the following mechanisms: by bubble formation, coalescence, or division; by the motion of a free stream of liquid containing entrained bubbles past an obstacle; and by the flow of liquid containing entrained bubbles through a pipe past a constriction. The calculation of the sound pressure generated by bubble formation has been verified by measurements with bubbles formed at a nozzle.

Theory of recognition.

Abstract: The theory of statistical decision has previously been applied to the problem of sensory detection of signals. In this paper, the theory is expanded to treat a simple recognition problem. While the data supporting the expansion have been collected in auditory experiments, the theory applies generally to all human sensory behavior.

Tabular Data of the Velocity and Absorption of High‐Frequency Sound in Mammalian Tissues

Abstract: This report is a condensed presentation of currently available data on the velocity and absorption of high‐frequency sound in mammalian tissues.

Propagation of Sound in Five Monatomic Gases

Abstract: The speed and attenuation of sound at 11 Mc were measured in He, Ne, A, Kr, and Xe at various pressures between atmospheric and a few mm Hg, and the results were compared with existing theories.

On the Resonant Vibrations of Thick Barium Titanate Disks

Abstract: An optical interference technique employing illuminated multiple beam Fizeau fringes has been used to study the surface motion of barium titanate disks. In a properly polarized, accurately shaped cylindrical disk only normal modes having symmetry with respect to the axis and to the central plane are observed. A particular disk having radius/semithickness ratio (a/l) of 3.86 has been studied in some detail, and the displacement patterns for three important modes in the thickness resonance region have been accurately measured. Stress distributions for these three modes have been calculated from theory and these show that the wave motion is of a complex character in all three cases; this question is discussed in the light of elementary conceptions of thickness resonance. A more comprehensive experimental survey covering 25 different values of a/l within the range 1.14 to 6.63 has now been completed, and vibration patterns of 12 modes are given together with graphs of resonance frequency and values of electro...

Elastic, Piezoelectric, and Dielectric Constants of Polarized Barium Titanate Ceramics and Some Applications of the Piezoelectric Equations

Abstract: A complete set of the elastic, piezoelectric, and dielectric constants of polarized barium titanate ceramics is presented. The various electromechanical coupling factors, as derived from the piezoelectric equations, and their numerical values are also given. The determination of the elastic and piezoelectric constants using the resonant method applied to small bars, square plates, and disks is discussed.

Hydrophone for Measuring Particle Velocity

Abstract: Mathematical expressions are derived for the motion of a rigid, uniform sphere in an underwater sound field. The results show that at low frequencies a neutrally buoyant sphere of this type has a velocity equal to the particle velocity of the water at the same location when the sphere is removed. A velocity pickup may be mounted inside such a sphere to form a hydrophone sensitive to particle velocity. Two practical design applications are presented. A low‐frequency hydrophone with a diameter of five inches was constructed having an essentially flat response between 15 and 700 cps with a sensitivity of 0.18 volt/cm/sec working into a 500‐ohm load. A higher frequency design with a 2.5‐inch diameter operated from 70 to 7000 cps with somewhat lower sensitivity and impedance level. Velocity hydrophones of this type are easy to build, easily calibrated, stable, and possess good directionality.

Onset of Ultrasonic Cavitation in Tap Water

Abstract: The conditions influencing the onset of acoustically‐induced cavitation in tap water have been investigated, with special attention to the role of air‐filled nuclei. Cavitation was induced by exciting the water, contained in a spherical flask, at the resonant frequency of a radial mode near 25 kc/sec. Air‐filled nuclei were detected by observing the reverberation decay of sound in the sphere at frequencies from 150 to 700 kc/sec, the presence of undissolved air cavities causing an increase in the decay rate. The results indicate that tap water standing undisturbed for several hours contains no air nuclei with radii larger than 5 × 10−4 cm, even when the water is supersaturated with dissolved air. The smaller nuclei (not detectable by reverberation decay) seem to become progressively smaller, for the measured threshold sound pressure at the onset of cavitation increases several‐fold as the water stands undisturbed for several days. The observed influence of the air content on the threshold peak sound press...

Calculation of the Loudness of Complex Noise

Abstract: Charts and formulas are presented for the calculation of the loudness of noises having approximately continuous spectra. By means of direct loudness matches it is shown that the loudnesses in octave bands can be combined according to the formula St = Sm+0.3(ΣS − Sm), where St is the loudness (in sones) of the total noise, Sm is the loudness of the loudest band, and ΣS is the sum of the loudnesses of all the bands. The loudnesses of the octave bands can be determined from measurements of their sound pressure levels by means of a chart based upon a new determination of the equal loudness contours for bands of noise. Other charts and formulas are presented for half‐ and third‐octave band widths.Measurements were also made of the dependence of loudness on such factors as (a) separation between noncontiguous bands, (b) width of very narrow bands, and (c) rate and level of square wave modulation.

Nature of the Vocal Cord Wave

Abstract: The shape of the vocal cord wave or glottal puff is an important parameter in any analog representation of the vocal mechanism, since the final speech wave is a function of both the generator wave shape and the transmission characteristic of the vocal tract. The shape of this wave has been determined by two independent methods: (1) by measuring the area of the vocal cord opening as a function of time through the use of motion picture studies, and (2) by the use of a network having a characteristic which is the inverse of the first vocal resonance. Harmonic analysis of some of the typical shapes indicates that a uniform distribution of harmonic amplitudes is a rarity; instead there is a tendency for the distribution to have a cyclical variation of the form (sin kn + c)/n2. The use of the inverse network method has also served to bring out several other interesting aspects of speech production such as the relation of the onset and amplitude of excitation of the higher resonances with respect to the vocal co...

Contour Vibrations of Isotropic Circular Plates

Abstract: A mathematical analysis has been done according to Love's theory. The results are: (a) The coefficients of the dilatation and the rotation are equal in amount regardless of Poisson's ratio only for the modes whose circumferential order is one. (b) The first mode whose order is two has the lowest natural frequency. This mode is practically equivoluminal, while the second mode is dilatational. (c) Locations of nodes are considered. Circular nodal lines can exist only for the radial and the tangential modes. (d) Frequencies and displacements of the most important modes are calculated.Applying the above results to barium titanate vibrators, we find that only the radial modes can be excited with full electrodes and the compound modes with split or partial electrodes, while the tangential modes can never be excited. Such an excitation of compound modes provides a convenient means for measuring Poisson's ratio of the material. Equivalent series inductances of the radial modes are calculated.Vibrations of thick c...

Wave propagation through fluid contained in a cylindrical, elastic shell

Abstract: A study is presented of the propagation of axisymmetric waves through compressible, inviscid fluid contained in a cylindrical, elastic shell. The dependence of the phase velocity as a function of frequency on four dimensionless parameters of the system is discussed and illustrated graphically.

Masking of Tonal Signals

Abstract: Many of the phenomena of masking can be explained on the basis of two models, one for monaural listening, and the other for binaural. The monaural model is the familiar narrow band‐pass filter followed by a detector responsive to changes in output level. The binaural model is a series of coincidence detectors associated with a delay‐network capable of matching delay in the stimulus with a delay in the neural path.The two models have proved helpful in understanding the phenomena of tonal masking, and have led to a number of predictions which have been subsequently verified by experiments reported here. Some of the new findings are related to monaural masking and some to binaural. Among the latter are the fact that masking‐level differences can be observed in the masking of one pure tone by another when a short signal is employed, and that a binaural signal can be heard in the presence of uncorrelated noise at the two ears better than a monaural signal can be heard against noise presented monaurally, again ...

Electronic Control of Noise, Vibration, and Reverberation

Abstract: Existing passive materials are inadequate to cope with many problems in the control of noise, vibration and reverberation. It is only within quite recent times that active systems have been given consideration for the control of sound. The electronic sound absorber is an example of an active‐type sound absorber. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected in an inverse feedback manner. The electronic system reduces the effective acoustical impedance in the vicinity of the absorber. As a consequence, the electronic sound absorber may be used in the manner of a conventional sound absorber or as a zone‐type sound reducer. The electronic vibration reducer consists of a sensor, amplifier, and driver connected either in negative or positive feedback fashion. The electronic vibration reducer may be used to isolate vibrating machines or to reduce the vibration of machines.

Propagation of Elastic Waves in Cylindrical Shells, Including the Effects of Transverse Shear and Rotatory Inertia

Abstract: Two systems of equations of motion, designated as (I) and (II), for thin elastic cylindrical shells are derived which include the effects of both transverse shear deformation and rotatory inertia. The character of the two systems of equations is such that, upon the neglect of transverse shear deformation and rotatory inertia, Eqs. (I) will reduce to those known as Love's first approximation, while (II), which enjoys a considerable mathematical simplicity as compared to (I), will correspond to those given by Donnell. Both systems of Eqs. (I) and (II) are employed in a study for propagation of axisymmetric waves in an infinite cylindrical shell. The agreement between the predictions of the two systems of equations, in all modes of motion, for phase velocities of propagated waves in the complete range of wavelengths is found to be excellent. The results, with reference to the nature of the modes of motion according to both (I) and (II), are further examined and the relative merit of the present paper to the work of other authors is discussed.

Effect of Visual Factors on the Intelligibility of Speech

Abstract: Research has indicated the important role that vision plays in face‐to‐face voice communication. This study was an attempt to quantify further the visual contribution to speech intelligibility in a high intensity noise environment in terms of the angle and distance from the listener to the speaker.Results indicated that (1) visual cues resulted in a significant increase in listener‐intelligibility scores, (2) the angle at which the listeners observed the speaker influenced their listener‐intelligibility scores, and (3) the distance of the listener from the speaker did not have a significant effect on listener‐intelligibility scores within three to nine‐foot limits.The importance of speech‐reading training and the use of visual cues is evident where face‐to‐face voice communication has to be conducted in high intensity noise environment.

Ultrasonic Attenuation at Low Temperatures for Metals in the Normal and Superconducting States

Abstract: At very low temperatures the mean free paths of electrons in metals become so large with respect to their values at room temperature that they can acquire momentum from collisions with lattice vibrations which result in ultrasonic attenuation when the electrons are in the normal state. This attenuation drops to zero in the superconducting state. Original measurements in impure lead, tin, and copper showed an attenuation proportional to the square of the frequency which could be directly related to the electron viscosity calculated from the number N, the mass m, the mean free path l and the mean velocity 0 of the electrons.Recently some very pure tin samples have been obtained and much larger effects have been measured due to the increased conductivity at low temperatures. Six oriented samples have been measured and from the measurements the six elastic constants and six viscosity coefficients have been obtained. These correspond to those for a tetragonal crystal. As the mean free path becomes longer than the acoustic wavelength, the loss is determined by a scattering process and the loss for a given frequency approaches a limiting value in agreement with a theoretical prediction of Pippard. The loss for longitudinal waves is from 2.5 to 7.5 times the predicted value while that for shear waves is about 1.5 times the theoretical value of Pippard's.Measurements of the elastic constants have been made through the super conducting range and the only discontinuity that occurs is that due to the thermodynamically predicted value. The change for a longitudinal wave is less than that predicted for a volume change in agreement with a theoretical derivation. No relaxation effect occurs for the measured velocity even for very pure tin.

Pressure Field within Homogeneous Anisotropic Turbulence

Abstract: Integral expressions are derived for the mean‐square fluctuation pressure, pressure correlation, and certain moments of the pressure correlation within general anisotropic, homogeneous turbulence. Application is made to idealized flow models exhibiting certain anisotropy characteristics similar to those observed in boundary layer turbulence. Pressure fluctuations arising from the turbulence itself and from interaction of the turbulence with a mean flow exhibiting constant shear are compared with the isotropic case. It is found that, in contrast to the completely isotropic case, the anisotropic pressure correlation is negative for some difference coordinate values and exhibits a “tail” which falls off with distance x as x−3 at separations for which the velocity correlations have fallen essentially to zero. It is concluded that in general the principal normalized moments of the pressure correlation will tend to be less than the corresponding velocity correlation moments. For isotropic turbulence this implie...

Internal Friction and Fatigue in Metals at Large Strain Amplitudes

Abstract: A barium titanate transducer coupled to an exponential horn can produce large strains in metals. By using a final horn with a necked down section, it is possible to concentrate the strains in a small specimen. Measurements of the impressed voltage and a voltage from a pick up electrode on the titanate make it possible to calibrate the device so that the internal friction, change in elastic constant, and the strain in the sample are all determined.The measured internal friction can be divided into three strain regions. From 10−6 to 10−5 the internal friction is approximately independent of the strain. For strains from 10−5 to from 2 × 10−4 to 2 × 10−3, depending on the material, the internal friction increases with strain in a reversible anelastic manner. Above this range the internal friction increases very rapidly and for strains twice as large as those for the initial rise, the metal fatigues in a very short time.It appears that the anelastic range is caused by the reversible production of unstable Frank‐Read loops. The shape of the internal friction curve allows one to evaluate the dislocation distribution with results in accord with etch pit methods. The final phase appears to be due to irreversible production of Frank‐Read loops caused by dislocations cutting through other dislocations. This process produces jogs in the dislocations and vacancies in the metal. These vacancies accumulate to produce fatigue cracks in accord with a theory of Mott's. Temperature and time effects result from the lowering of the activation energy by the applied stress. At liquid nitrogen temperature, the fatigue stress increases until the activation energy for diffusion is nearly zero.

Effects of Vocal Force on the Intelligibility of Speech Sounds

Abstract: Measurements were made of the intelligibility of speech heard in noise and produced by different amounts of vocal force. Vocal force ranged from the weakest voiced whisper to a very heavy shout. The results show less than 5% deterioration in intelligibility over the range from a moderately low voice to a very loud voice (55 to 78 db in a free field at one m from the lips). Beyond these points intelligibility decreases abruptly and in a linear relation to decibel change in vocal intensity. Listeners' errors are analyzed to determine the effects of the extremes of vocal force on the intelligibility of different parts of the syllable and of different vowels.

Small‐Scale Acoustic Streaming in Liquids

Abstract: By using special acoustical and optical arrangements, vortex motions are discovered in the vicinity of small vibrating sources in liquids. Of particular importance is the vigorous eddying that typically takes place near a vibrating gas bubble when it rests on a boundary. This bubble‐associated streaming has been observed under a variety of circumstances, and apparently occurs quite generally. Especially violent and chaotic motions appear near bubbles of resonant size. The attendant highly localized convection and viscous stresses are probably very important as intermediate physical mechanisms for sonic irradiation effects.

Low Sound Velocities in High‐Porosity Sediments

Abstract: Recent in situ and laboratory determinations of density and velocity of sound in fine‐grained, high‐porosity sediments of the sea floor off San Diego, California, reveal several stations at which the velocity of sound in the sediment was 2% to 3% less than the velocity of sound in the water just above the bottom. Comparison of the compressibility of the sediment computed in two ways and of the ratio: velocity in sediment/velocity in water computed and actually measured indicates that these high porosity sediments are approximately described acoustically by the velocity formula which applies to a suspension. The theoretical explanation for this phenomena was apparently made by R. J. Urick, [J. Appl. Phys. 18, 983 (1947); J. Acoust. Soc. Am. 20, 283 (1948)] and R. J. Urick and W. S. Ament [J. Acoust. Soc. Am. 21, 115 (1949)].