Index of content:
Volume 27, Issue 4, July 1955
Relaxations in the Attenuation of Single Crystal Lead at Low Temperatures and Their Relation to Dislocation Theory27(1955); http://dx.doi.org/10.1121/1.1907985View Description Hide Description
Measurements of the attenuations of face‐centered metals by Bordoni have shown attenuation peaks at low temperatures. By using the measurements of Bömmel on single crystallead it can be verified that this is a relaxation and values can be obtained for activation energies and frequency terms. It is shown that the measured results correlate well with a relaxation due to the displacement of a dislocation from one atomic line to an adjacent one against the limiting shearing stress of the crystal. The limiting shearing stress measured for four face‐centered metals is in good agreement with theoretical calculations of Cottrell.
A higher temperature loss is also measured which increases exponentially with the temperature. It is shown that this term is due to breakaway of the dislocation from its impurity pinning points due to thermal agitation. This breakaway abstracts energy from the vibration and produces a loss independent of the frequency but increasing with temperature since more breakaways occur at higher temperatures. The activation energy of breakaways correlates well with the binding energy of impurity atoms.
27(1955); http://dx.doi.org/10.1121/1.1907987View Description Hide Description
Quantitative measurements have been performed on some fundamental phenomena caused by ultrasoniccavitation, i.e., the synthesis of hydrogen peroxide, the oxidation of potassium iodide, the decomposition of carbon tetrachloride, the degassing action, and the evolution of heat in connection with the cavitation process. The experiments were made under controlled and defined acoustic conditions (standing waves, progressive waves, and non‐resonance) and the influences by various important factors (acoustic intensity, gas content) have been evaluated.
Tentative theories of the cavitation process and allied phenomena are evaluated on the basis of the experimental results. Cavitation chemistry is found to be similar to gamma radiation chemistry (pH‐dependence of the yield of hydrogen peroxide, oxidation of solutes, necessity of oxygen). Cavitation is assumed to be preceded by a homogeneous nucleation process in which a germ or gas nucleus is being formed by rupture of the liquid around this germ. Ionization of some of the gas molecules entrained in the cavity will take place in order to establish the electric charge of the surface of the cavity. Two hydrogen peroxide molecules are formed for every ionized oxygen molecule. It is supposed that in the case of oxygen a cluster is formed by the combination of two water molecules and a positive oxygen ion. This cluster yields on decomposition at the neutralization two hydroxyl radicals and one excited hydrogen perioxide molecule.
The rate of cavitation seems to be independent of (1) the gas concentration (above the threshold concentration), (2) the pressure amplitude (above the threshold amplitude and within the region of cavitation), and (3) the nature of the dissolved gas (provided the gas may initiate homogeneous cavitation at all). These features indicate that properties of the liquid are rate determining when the various threshold requirements are fulfilled. A tentative picture of the nucleation process is presented, which seems to satisfy these conditions.
The degassing action in an ultrasonic field proceeds to half saturation practically independent of the intensity.
A method for cavitation dosimetry is described.
27(1955); http://dx.doi.org/10.1121/1.1907989View Description Hide Description
In the described instrument ten‐microsecond, 30‐Mc carrier pulses reflected from a resonant layer allow a theoretical precision of 0.1 percent in making velocity determinations while using less than 0.1 cc of test liquid. By the same technique, ultrasonic absorption can be measured in highly dissipative liquids using layers about 0.1 mm thick. Water velocities observed at 30 Mc are presented along with values by others in the range of 0° to 93°C. is proposed as the best empirical parabola to accommodate the available data, and an additional cubic correction formula is suggested.
27(1955); http://dx.doi.org/10.1121/1.1907991View Description Hide Description
Measurements have been made of the ultrasonic velocities in polarized bariumtitanateceramic blocks for both compressional and transverse waves, parallel and perpendicular to the axis of polarization. Some variation in compressional velocity with the degree of binding was evident. The largest variation between the velocities for transverse waves causing shear amounted to nearly 12 percent and proved to be accounted for by electromechanical coupling. The compressional velocity parallel to the axis of polarization ran some four percent higher than that at right angles. Here again it appeared that the effect was caused principally by differences in electrical boundary conditions and that the constant field elastic constants varied only slightly with polarization.
27(1955); http://dx.doi.org/10.1121/1.1907993View Description Hide Description
Acoustical velocities were measured at 500 kc in a number of organic liquids and binary solutions prepared therefrom. A precision ultrasonicinterferometer was employed. For the most part sound velocities were found to vary linearly with temperature. Densities were determined at 20°C. Adiabatic compressibilities at 20°C were calculated and some conclusions drawn concerning the cohesive properties of certain of the solutions. The molecular sound velocity in a binary liquidsolution is the sum of the products of the respective molecular sound velocities in the pure liquids by their corresponding mole fractions all at the same temperature. Where practicable, effective molecular radii were calculated from the data. The usefulness of the molecular weight of a liquid in predicting values of the temperature coefficient of velocity is discussed. Apparently many more experimental data are needed before an adequate theoretical analysis is possible.
27(1955); http://dx.doi.org/10.1121/1.1907995View Description Hide Description
The attenuation of normal modes in a two‐layered fluid medium due to absorption in the lower semi‐infinite layer is calculated under the assumption that this absorption is small. The result obtained gives the attenuation coefficient for each mode as the product of the absorption coefficient for plane waves in the absorbing layer and a dimensionless function of wavelength and layer depth. Curves of this dimensionless function are plotted for the first five modes in cases typical of propagation in shallow water over a sand and a mud bottom. The results indicate a very rapid decrease in attenuation as the frequency rises above the cut‐off frequency, where it is just equal to the bottom absorption. At higher frequencies the attenuation varies as (n 2λ3/H 3)α, where n is the mode number, λ the wavelength, H the water depth, and α the absorption coefficient in the bottom (α may itself be a function of frequency). The latter result is also derived by a less rigorous method.
27(1955); http://dx.doi.org/10.1121/1.1907997View Description Hide Description
An anechoic lining for underwater sound use can be made from waterproofed, rubberized, horsehair batting. It decreases the reflectivity 20 db below that obtained from a steel wall over a frequency range from 100 kc to 400 kc and for a wide range of angles of incidence. It is inexpensive, easily installed, and can be used for several 8‐hour periods before additional waterproofing is necessary.
27(1955); http://dx.doi.org/10.1121/1.1907999View Description Hide Description
The acoustical radiation scattered from a sinusoidal surface of zero pressure insonified by an obliquely incident plane wave of sound is obtained as an infinite series of waves whose coefficients may be determined by means of a recurrence relation. The corresponding analysis is presented for the case of a spherical source of radiation. At points sufficiently remote from the surface only a finite number of terms need be included. Each coefficient in the series is itself an infinite series which converges most rapidly when the height of the surface corrugations is small compared to the wavelength of the incident sound. Application is made to determine the average intensity and fluctuation of the sound reflected from a travelling sinusoidal boundary. The degree of roughness required to destroy the effect of Lloyd mirror fringes is discussed in terms of the ratio of the surface height and wavelength to the wavelength of the incident sound.
27(1955); http://dx.doi.org/10.1121/1.1908001View Description Hide Description
A general expression for the radiation impedance of the qth source in an array of n sources has been obtained in terms of Green's functions. It is applicable to finite sources or to sources which are mounted in finite baffles provided the Green's function can be found. The theory is applied to an array of finite cylinders which form part of an infinitely long rigid cylindrical baffle. If ka≪1, the radiation resistance of each member can easily be expressed in terms of sine integrals. Curves showing the radiation resistance of each member of an array of five cylinders are given. The effect of varying the separation is also shown.
27(1955); http://dx.doi.org/10.1121/1.1908003View Description Hide Description
The impedance presented to the inside surface of a hollow, radially vibrating, liquid‐filled cylinder of length l which is mounted in the aperture of a rigid wall of thickness l has been determined. It was assumed that radiation from the ends of the cylinder into the infinite liquid media (water) takes place symmetrically with respect to the plane midway between the ends of the cylinder. The liquid within the cylinder need not be the same as the liquid outside the cylinder. Although the impedance at any frequency can be obtained from the results, an approximation is introduced which is valid when the wavelength in the liquid within the cylinder is such that ka⩽π/2 (k being the wavelength constant and a the inside radius of the cylinder). Under these circumstances it is found that the output power drops to zero whenever the length of the cylinder equals nλ, where n is an integer and λ is the wavelength of sound in the contained liquid.
27(1955); http://dx.doi.org/10.1121/1.1908005View Description Hide Description
A theoretical analysis of the propagation of pressure waves through elastic tubes filled with streaming incompressible viscous liquid is presented. The limiting results for the case of vanishing viscosity are compared with those for an inviscid liquid. The influence of the steady stream upon which waves are superposed, of wall inertia, and of Poisson's ratio are discussed. The analysis is restricted to tubes with thin walls, to waves whose amplitude is small and whose wavelength is large compared to the radius of the tube, and to liquids with sufficiently small viscosity.
27(1955); http://dx.doi.org/10.1121/1.1908007View Description Hide Description
A wave equation for the sound propagation through tubes is derived by means of Hamilton's variational principle. It is assumed that the wave fronts can be approximated by surfaces of constant stream potential; this is the only assumption made. The variational principle ensures that the best equation that is compatible with this assumption will be obtained. The equation has the form of Webster's horn equation, however its coefficients are defined differently.
27(1955); http://dx.doi.org/10.1121/1.1908009View Description Hide Description
This paper describes cemented bariumtitanate accelerometers of two simple types, an electromagnetic shaker with a symmetrically mounted shake table, a set of bariumtitanate shakers, and two optical methods of accelerometer calibration, one using a microscope with a stroboscope of wide frequency range and one using a Fizeau type interferometer.Calibration results from 50 to 11 000 cps are given.
27(1955); http://dx.doi.org/10.1121/1.1908011View Description Hide Description
27(1955); http://dx.doi.org/10.1121/1.1908012View Description Hide Description
The loudness of a steady auditory stimulus declines during the first few minutes of the application of that stimulus. This decrease in loudness is so great that it is important to know whether or not the masked threshold also changes during the initial period of stimulation. In the present investigation the degree of perstimulatory fatigue and the amount of masking were both determined for the same stimulus. It is shown that the masked threshold is essentially independent of the duration of the masking stimulus.
27(1955); http://dx.doi.org/10.1121/1.1908014View Description Hide Description
When a fatiguing tone is presented to one ear of an observer, and, after a period of time, a comparison tone of the same frequency is also presented to the other ear, the intensity of an equally‐loud comparison tone is considerably less than the intensity of the fatiguing tone. This phenomenon has been referred to as perstimulatory fatigue. The present investigation was designed to determine the extent to which the perstimulatory fatigue induced by a pure tone spreads to neighboring frequencies.
Perstimulatory fatigue was measured by means of a series of simultaneous dichotic loudness balances made prior to, during, and subsequent to stimulation by a fatiguing tone of 1000 cps at a SPL of 80 db. Test tones were the same in sound pressure as the fatiguing stimulus. When measuring fatigue at a frequency other than that of the fatiguing tone, the fatiguing stimulus was turned off for a 15‐second interval. During this interval, a loudness balance was made at the frequency of the test tone.
The findings demonstrate that maximum fatigue is produced at the frequency of the fatiguing stimulus. Fatigue falls off rapidly on both sides of this frequency at a negatively accelerated rate until at 100 cps and at 2500 cps little or no effect is evident. The gradients of perstimulatory fatigue are nearly symmetrical when plotted on a log‐frequency scale.
27(1955); http://dx.doi.org/10.1121/1.1908016View Description Hide Description
27(1955); http://dx.doi.org/10.1121/1.1908018View Description Hide Description
The rise‐fall time, duty cycle, and carrier frequency of a pulsed tone were systematically varied. Listeners matched the pitch of this signal to that of a sinusoidal comparison tone. Low SPL was used throughout. Two pitches were identified, one corresponding to the repetition rate (periodicity pitch), and the other to the carrier frequency (carrier pitch). The periodicity pitch decreased in audibility with the increase of any of the experimental variables. These variables had the opposite effect on the perception of the carrier pitch, which in general was audible only at the longer duty cycles. Individual listeners varied considerably in their ability to match the pitch of the pulsed tones. Comparison of the results obtained with pulsed sinusoids to those of pulsed noise suggest that the perception of a periodicity pitch depends upon the band width and spectral location of the pulsed signal's frequency components as well as envelope wave form fluctuation.
27(1955); http://dx.doi.org/10.1121/1.1908020View Description Hide Description
This paper describes an investigation of the effect of sound duration on the perception of a linguistic characteristic, the recognition of phonemes. A pair of single syllable words was selected which consisted of identical phoneme sequences, except for the final phoneme which was either the voiced or unvoiced version of the same articulation. Different versions of these words were synthesized with all possible combinations of four different vowel durations and five different final consonant durations. In all cases the sound wave corresponding to the final consonant was inharmonic and identical except for duration. These synthesized words were recorded and presented to a group of 33 listeners who had to judge whether they heard the final consonant as a voiced or as an unvoiced sound. The results clearly show that the relative durations of vowel and final consonant can be used as a cue for hearing the final sound as voiced or unvoiced. This demonstrates that, in certain circumstances, nonspectral characteristics such as duration can serve as the basis for phoneme recognition. It also gives an example of a cue for sound recognition which, due to its relative nature, can be perceived only when it appears in a sequence of phonemes and not when the sound is pronounced in isolation.
27(1955); http://dx.doi.org/10.1121/1.1908022View Description Hide Description
The experiments reported in this paper are an attempt to explore the influence of certain physical cues on the perception of linguistic stress patterns. The material chosen was a group of English words in which a change of function from noun to verb is commonly associated with a shift of stress from the first to the second syllable. Spectrograms were used to determine the vowel duration and intensity ratios which occur in these words and this information was applied in making up a test in which listeners' judgments of stress could be correlated with variations in the duration and intensity ratios. The results of the experiments show that duration and intensity ratios are both cues for judgments of stress and that, in the material studied, duration ratio is a more effective cue than intensity ratio.