Index of content:
Volume 27, Issue 1, January 1955
27(1955); http://dx.doi.org/10.1121/1.1907489View Description Hide Description
The ultrasonicabsorption coefficient has been measured in toluene by means of the spherical resonator method of Leonard and Wilson. Measurements were made in the temperature range 6°–40°C and in the frequency range 50–400 kc. The existence of a relaxation peak in this region, previously reported by Moen, has been confirmed, and a second peak has been identified at a lower frequency. The temperature dependence of the first peak indicates heat of reaction of 5.2 kcal/mole and an activation energy of 8.5 kcal/mole. This result is inconsistent with the hypothesis of a stretching vibration of the C–H bond, and suggests some sort of structural source for the absorption.
27(1955); http://dx.doi.org/10.1121/1.1907497View Description Hide Description
Effect of Ultrasonic Energy Applied During the After‐Ripening Stage of Photographic Emulsion Preparation27(1955); http://dx.doi.org/10.1121/1.1907503View Description Hide Description
When a photographic emulsion of the boiled type is treated with 800 kc ultrasonic energy at an energy level of 5 w/sq cm during the after‐ripening or digestion period, an increase the photographic sensitivity of that emulsion occurs. No significant change in the gamma or the grain size distribution of the emulsion results from this treatment. The mechanism appears to be a transport phenomenon which disrupts grain‐sensitizing‐agent concentration gradients in the intergrain gelatin matrix.
27(1955); http://dx.doi.org/10.1121/1.1907475View Description Hide Description
Characteristics of spectra from relatively thick orifices differ from those from relatively thin. In a given range of Reynolds number, in many cases the jet may exist in any one of several reproducible jet‐tone states (metastable states) characteristic of the orifice. The dependence of the component frequencies of the jet‐tone spectra (expressed in terms of the orifice‐number on Reynolds number is shown, where d is diameter of orifice; f, frequency; Δp, pressure difference across orifice; ρ, density; and μ, viscosity of gas. The orifice numbers of the components of the jet‐tone spectra generally tend to fall on a single array of equally spaced orifice‐number levels. Jet‐tones from the same orifice plate, characteristic of both thin as well as thick orifice plates, are found to coexist over a small transition range of orifice thickness‐diameter ratio. If the orifice number of the head of the most probable spectral mode for a given orifice thickness‐diameter ratio is noted, the same will be found again for the head of the most probable mode at approximate orifice thicknesses t±nd, where n is a small integer.
On the Contribution of a Contained Viscous Liquid to the Acoustic Impedance of a Radially Vibrating Tube27(1955); http://dx.doi.org/10.1121/1.1907490View Description Hide Description
The impedance presented to the inside surface of a hollow, liquid filled, radial cylinder of finite length has been determined theoretically. It was assumed that the liquid was retained by pressure‐release caps or one pressure‐release cap and one rigid cap at each end. For a loss‐free liquid it is shown that the reactance presented to the cylinder wall becomes infinite whenever the liquid has a longitudinal or coupled radial resonance.
A sizeable resistance may appear when a viscous liquid is used. This is because the geometry of the arrangement is ideal for creating large shear losses. Exceptions to this occur for high frequencies where the wavelength is small in comparison to the cylinder length.
27(1955); http://dx.doi.org/10.1121/1.1907491View Description Hide Description
This paper gives a theoretical study of the two‐dimensional flow of an incompressible, viscous fluid enclosed between two coaxial cylinders, one of which is oscillating. The Reynolds number is assumed to be small, and the Navier‐Stokes differential equations are solved by means of the method of successive proximations. Both for the first and second order solution the proper boundary conditions are applied. We have shown that there exist two stationary circulation systems in every quadrant, and that the direction of circulation is opposite in these two systems. The circulation velocities are calculated in detail, and the results are compared with experimental results referred to in an earlier paper. Some new experimental results, which are not published yet, are briefly mentioned. The agreement between theoretical and experimental results is excellent.
In a discussion at the end of the paper we give the explanation of the remarkable fact that in some experiments the direction of circulation seems to reverse when the oscillation amplitude increases and exceeds a certain critical value.
27(1955); http://dx.doi.org/10.1121/1.1907492View Description Hide Description
The time‐average forces exerted by the constraints of a vibrating system (radiation pressure, mean tension in a vibrating string, etc.) are easily computed from the adiabatic principle of Boltzmann and Ehrenfest (BE principle). The usual derivation from the “principle of varying action” is difficult.
Here an equivalent principle (which gives in addition the time dependence of the forces) is derived from Lagrange's equations. It is also shown how similar results can be got from the solution of a linear differential equation with slightly variable coefficients.
Sound Propagation into the Shadow Zone in a Temperature‐Stratified Atmosphere above a Plane Boundary27(1955); http://dx.doi.org/10.1121/1.1907493View Description Hide Description
The sound field in the “shadow zone” (diffraction region) formed over a plane boundary in an atmosphere with a constant vertical temperature gradient is analyzed both theoretically and experimentally. The boundary condition at the plane is given by a normal acoustic impedance independent of the angle of incidence. As in the corresponding problem of underwater sound where the boundary is a pressure release surface, it is found that the major portion of the sound pressure in the shadow zone decays exponentially with distance at a rate proportional to the one‐third power of frequency and two‐thirds power of temperature gradient. The effect of boundary impedance enters mainly through its resistive component. The rate of sound decay for a pressure release boundary (zero impedance) is found to be 2.3 times that for a rigid boundary (infinite impedance).
Sound pressure measurements in the shadow zone in a laboratory chamber in which a large temperature gradient was created were made for both hard and absorbing boundaries, and the results were found in essential agreement with theory.
27(1955); http://dx.doi.org/10.1121/1.1907494View Description Hide Description
Flexural waves generated in a thin plate by a spark source are used to investigate properties of air‐coupled surface waves. Both ground shots and air shots are simulated in the model. Effects of source elevation, fetch of air pulse, and cancellation by destructive interference are studied.
27(1955); http://dx.doi.org/10.1121/1.1907495View Description Hide Description
The problem of spherically symmetric wave propagation in homogeneous, isotropic elastic media of infinite extent has been examined frequently in recent years, and a number of analytical solutions have been reported in the literature for various initial conditions. Some interest has also been exhibited in the application of these relations to the transient phenomena occurring in metals when subjected to contact explosions. Under these conditions, an actual wave system can be approximated by postulating the existence of a spherical cavity in the interior of the medium and applying as the initial condition a pulse of exponentially decaying character. While no difficulty is encountered here in an analytic expression of the displacements, velocities and stresses occurring at each point of the medium as a function of location and time, it has been found highly desirable to represent these terms in pictorial form to permit a rapid evaluation of the nature of the disturbances in the region of interest. Consequently, numerical calculations have been performed on an IBM machine and the resultant data have been employed in a space‐time representation of these parameters.
27(1955); http://dx.doi.org/10.1121/1.1907496View Description Hide Description
A vibratory gyroscope or Gyrotron has been under development at the Sperry Gyroscope Company for the Bureau of Aeronautics as an instrument for measuring rate of turn. The instrument utilizes a tuning fork which undergoes a torsional vibration due to Coriolis forces when a rate of turn is applied. Thus, a familiar acoustical device is applied to the problem of control of aircraft. The absence of bearings gives it virtues of low electrical noise level, ruggedness, and long life. This paper presents a simplified analysis of the response of the instrument to steady rates of turn, with special emphasis on linearity considerations.
27(1955); http://dx.doi.org/10.1121/1.1907498View Description Hide Description
The response of a tuning fork rate Gyrotron or vibratory gyroscope to steady rates of turn was discussed in a previous paper [J. Acoust. Soc. Am. 26, 56(1955)]. The treatment is now extended to yield the amplitude and phase response of the instrument to impressed oscillation about the sensitive axis. The results can be used in calculating the stability of a servo loop incorporating Gyrotron as an element.
27(1955); http://dx.doi.org/10.1121/1.1907499View Description Hide Description
Instantaneous indication of the beginnings of individual pitch periods of a voice‐sound speech wave is often desirable in speech analysis. With conventional means, such as linear filtering and subsequent waveform shaping, this instantaneous indication is very hard to achieve because of the considerable time delay involved.
In the “instantaneous” pitch‐period indicator the problem is solved by using nonlinear techniques and a variable time‐gating circuit; a pitch‐period beginning is indicated by a marker pulse having a maximum delay of the order of five percent of the pitch‐period duration. The application of the device to certain problems of speech analysis is indicated.
27(1955); http://dx.doi.org/10.1121/1.1907500View Description Hide Description
Bariumtitanateceramics show an aging effect during which the dielectric constant and electromechanical coupling factor decrease while the elastic constants and Q increase. At room temperature, this process takes over a year to stabilize. By heating the ceramic up to 70°C the process is considerably shortened. A comparison of the rates of aging at 70°C and 25°C shows that an activation energy of about 19 kilocalories per mole is involved the aging process. The experiments and calculations made show that the cause of the aging is a reduction in the effective polarization caused by a slow temperature‐induced motion of the domain walls of the ceramic. This motion is biased by the residual strains stored up when the crystal becomes ferroelectric and also by strains induced by the poling process. It appears likely that the high activation energy measured arises from the simultaneous motion of a number of unit cells in a bordered wall. Due to this high activation energy, aging can be speeded up by a heat treatment process.
27(1955); http://dx.doi.org/10.1121/1.1907501View Description Hide Description
To reduce an intense noise with frequency components extending from 5 to 10 000 cps due to the burning of a jet engine in the test section of a supersonic wind tunnel, a special muffler was built having an open cross‐sectional area of 600 square feet. For frequencies below 11 cps, large Helmholtz type resonators were used. Between 11 and 20‐cps intermediate‐sized Helmholtz resonators were employed. Between 20 and 800 cps a tuned set of six Fiberglas lined square ducts, were constructed. At higher frequencies two lined bends were employed to reduce the noise. Performance data measured in models and in the full scale wind‐tunnel are presented. The result is a wind tunnel that is so quiet that nearby listeners are unaware of its operation.
27(1955); http://dx.doi.org/10.1121/1.1907502View Description Hide Description
The method described in this paper attempts to measure the transmission loss of any wall independently of the surrounding elements of the building. The extreme case of a wall without any surrounding elements, i.e., the first wall in a building under construction, is included in the problem.
27(1955); http://dx.doi.org/10.1121/1.1907469View Description Hide Description
Perstimulatory fatigue, or adaptation, is measured by a simultaneous loudness balance or median plane localization of a dichotically presented acoustic stimulus. After one ear has been stimulated for a period of time, it is usually found that the variable or comparison stimulus must be reduced below the prefatiguing intensity in order to maintain the loudness match or localization balance.
Five observers made median plane localizations of a continuous 100–5000 cps band‐pass noise before, during and after a seven‐minute fatiguing period. The fatiguing stimuli were continuous noises at 30, 60, 87, and 100 db SPL, and noises interrupted at 1, 2, 5, 9, and 12.5 ips with both burst level and noise‐time fractions held constant at 90 db SPL and 0.5, respectively.
It was found that (a) the time required for fatigue to reach an apparent asymptote is at least seven minutes, about twice that required for pure tones; (b) the maximum fatigue increases with the intensity of the fatiguing stimulus and the function is positively accelerated; (c) for a fixed intensity of fatiguing noise, the maximum fatigue for the highest rate of interruption used (12.5 ips) is less than that obtained with a continuous noise having the same over‐all level (87 db).
During the course of fatigue, the between‐observer variations (standard deviations) of the balances tend to be greater than the within‐observer variations; the reverse is true for the post‐fatigue period.
27(1955); http://dx.doi.org/10.1121/1.1907470View Description Hide Description
Perstimulatory fatigue is the decrease in loudness of a steady auditory stimulus during its presentation. In the past it has been measured by requiring a simultaneous dichotic loudness balance between two pure tones of the same frequency, one in each ear. Under these conditions the listener hears a single phantom sound whose localization depends upon the relative intensities of the two tones. The present investigation shows that the process of localizing the soundimage in making the loudness balance is not critical to the occurrence of perstimulatory fatigue.
Two principal conditions were compared. In the first, the frequency of the comparison stimulus was the same as that of the fatiguing stimulus. In the second, the comparison and fatiguing stimuli differed sufficiently in frequency so that the listener always heard two pure tones which he could correctly localize in the two ears. It is concluded that the amount of perstimulatory fatigue is very nearly the same under these two conditions.
In the early phases of the present research it was suspected that the loudness balances were influenced by absolute judgments of loudness. A procedure is developed which precludes the formation of a single absolute standard of loudness. This method results in greater measured fatigue than the usual procedure.
27(1955); http://dx.doi.org/10.1121/1.1907471View Description Hide Description
Comparison of the threshold shifts for 500, 50, and 5 millisecond short tones following a two‐minute exposure to thermal noise at an over‐all SPL of 110 db re 0.0002 microbar revealed disturbance of the pre‐exposure time‐intensity relationship for threshold during the post‐exposure period. The pattern of this disturbance was similar to that which has been described by other investigators in the ear with Organ‐of‐Corti‐type hearing loss. Thirty seconds after the termination of the noise the pre‐exposure intensity differential among these three short tone durations was markedly reduced. As post‐exposure time increased, the decline in the degree of temporary hearing loss was accompanied by a gradual return to the pre‐exposure time‐intensity relationship.
27(1955); http://dx.doi.org/10.1121/1.1907472View Description Hide Description
Pitch discrimination was studied in 4 normal hearing subjects monaurally, binaurally, and in a variety of other channels of reception. No difference exists in sensitivity between the two normal earn of a subject, nor is there a difference between the sensitivity of the monaural channels and the binaural channel if all are matched for loudness. Also bone conduction was found to yield essentially equal pitch DL's after loudness was matched. All channels, except successive interaural, are equivalent under matched conditions. Successive interaural channels (standard in the right, variable in the left, and vice versa) show some deterioration of sensitivity and some increase in variance which can be attributed to the monetary fluctuations of diplacusis. Similar fluctuations were found also with respect to a channel utilizing a monaural standard and a binaural variable stimulus, the two ears matched in loudness. Under these conditions, furthermore, a third pitch is sensed, a phenomenon we term “triplacusis.” The authors suggest an interpretation of diplacusis and triplacusis as interaural interactions.
In cases of perceptive hearing loss, however, the channels are not usually equivalent in pitch discrimination even if matched for loudness. Evidently other principles must be sought for the pathological case.