Index of content:
Volume 29, Issue 4, April 1957
Effect of Pressure between Tool Tip and Workpiece on the Rate of Ultrasonic Machining in Ketos Tool Steel29(1957); http://dx.doi.org/10.1121/1.1908914View Description Hide Description
Data are presented for the ultrasonicmachining rate in Ketos tool steel obtained by using rectangular tool tips having different perimeters and circular tool tips having different radii. It is shown that the pressure rather than the force maintained between the tool tip and the workpiece is pertinent in the ultrasonicmachining process, and that the ratio C/A of the tool tip perimeter C to the tool tip area A is of importance. It is also shown that for rectangular and circular tool tips a critical machining rate V 0 and a critical pressureP 0 exists, the values of which are related to the ratio C/A by the two simple expressions and , where 2ξ and ν are the peak to peak amplitude and the frequency of vibration respectively, d is the abrasive particle diameter, and M and L are parameters independent of 2ξ, ν, d, C or A. On the basis of the above two equations a phenomenological expression is derived which for circular and rectangular tool tips relates the machining rate in general to the pressure in general.
29(1957); http://dx.doi.org/10.1121/1.1908916View Description Hide Description
The dynamic magnetostrictive properties of Ni‐Fe alloys containing from 35% to 67.5% nickel were investigated to determine their suitability for use in electromechanical transducers. The material, in the form of toroids made from ring laminations, was evaluated by the motional impedance method. Annealing temperatures were varied from 600°C to 1220°C, and the effect of various annealing techniques was investigated. Measured values of the electromechanical coupling coefficient, the reversible permeability, the dynamic magnetostrictive constant, and other parameters are given.
The electromechanical coupling coefficient for alloys containing from 40% to 52.5% nickel was greater than 0.31. A maximum value of 0.37 was found for the 40% nickel alloy. The product of the magnetostrictive constant and the reversible permeability for the above range of alloys was greater than 95×104 (dynes/oersted‐cm2) and reached a maximum value of approximately 130×104 for the alloy containing approximately 40% nickel.
29(1957); http://dx.doi.org/10.1121/1.1908918View Description Hide Description
The reflection and transmission process is analyzed for plane sound waves originating in air at rest and impinging obliquely on a plane interface with a moving stream. Use of a moving reference frame provides transformation to an equivalent aerodynamic problem of flows past a wavy wall—the rippled interface. The angles of incidence, reflection, and refraction are identified with the Mach angles. The angular relations and the amplitude relations (coefficients of reflection and transmission) are evaluated in closed form. In a graph three zones can be distinguished the plane of angle of incidence v.Mach number of the moving medium: ordinary reflection and transmission, total reflection, and amplified reflection and transmission. Included are three loci of infinite reflection: i.e., serf‐excited waves. The energy balance is examined, and the source of amplification is concluded to be the energy of the moving stream. In appendices the results are generalized (1) for the case of two moving media and (2) for differing density and speed of sound in the two media.
29(1957); http://dx.doi.org/10.1121/1.1908920View Description Hide Description
The acoustic amplitude attenuation constant has been measured in air for pressures from 2.3 to 0.18 atmos in a cylindrical tube of 5.16 cm diameter and in cylindrical capillary tubes of 0.10 and 0.15 cm diameter. In the first series of measurements the amplitude of stationary waves in the wide tube is measured as a function of the distance from the end, and the attenuation constant calculated. In the second series of measurements the measuring tube is dosed by a sample of capillary tubes; the absorption coefficient and the phase difference at the input of the samples are measured and from that the attenuation in the capillary tubes is calculated. In both cases it is found that the theoretical values of Kirchhoff‐Helmholtz are about 13% lower than the mean experimental ones.
Variation of Elastic Constants and Static Strains with Hydrostatic Pressure: A Method for Calculation from Ultrasonic Measurements29(1957); http://dx.doi.org/10.1121/1.1908922View Description Hide Description
The elastic constants and static strains of a solid subjected to large hydrostaticpressures can be deduced from measurements of resonant frequencies (or transit times) for ultrasonicwaves in specimens of suitable crystallographic orientations. The pressure changes the specimen's size, shape, and density as well as the elastic constants, and all of the effects influence the resonant frequencies. An algorithm for separating out the effects due to variations in elastic constants from the effects due to static strains is presented and applied to cubic crystals and hexagonal crystals, these structures being of immediate interest to investigators concerned with the properties of metals. The results apply also to isotropic and transversely isotropic solids. The only measurements needed while the specimen is under hydrostaticpressure are resonant frequencies (or transit times). Also required are the size and density at zero pressure, or the elastic constants at zero pressure.
29(1957); http://dx.doi.org/10.1121/1.1908924View Description Hide Description
Sound absorption and velocity measurements have been made in carbon dioxide between 0 and 200°C. The relaxation absorption was isolated by subtracting the tube and classical absorptions from the measured absorption. The Kirchhoff equations, which had been justified previously by measurements in A and N 2 were used to make these corrections. From the relaxation absorption were determined the temperature variation of the thermal relaxation time, the transition probability, and the collision efficiency. The results indicate that for the frequencies and pressures here employed the relaxation absorption and velocity effects are a function of f/p. This means that only binary collisions are effective in transferring energy between the vibrational and translational modes. The relaxation theory with a single relaxation time for all the vibrational modes adequately predicts the observed absorption and velocity. It is estimated that a separation in the relaxation times of the two lowest modes by a factor of more than two could not have gone undetected at 100°C. The temperature variation of the collision efficiency was adequately predicted by the Landau‐Teller equation.
29(1957); http://dx.doi.org/10.1121/1.1908928View Description Hide Description
Observations have been made on the sound radiated by a self‐excited underwater jet‐edge system, in which a flat jet of water impinges on the sharp edge of a wedge or blade. Comparison made between the sound (edge tones) generated when a rigid wedge is used, and that when a fixed‐free vibrating blade is employed. A characteristic kind of “resonance” is found, similar to that reported by others for analogous systems in air.
29(1957); http://dx.doi.org/10.1121/1.1908930View Description Hide Description
Underwater sound signals from the deep atomic explosion of Operation Wigwam in May, 1955, were recorded on bottom‐mounted hydrophones at Point Sur and Point Arena, California, and Kaneohe Bay, Oahu. Reflected signals were recorded for two hours at Kaneohe and nearly four hours at Point Sur, and many reflectors were tentatively identified. Values for the attenuation of 20–200 cps sound in the sea were obtained from an analysis of the change in spectra of the reflected signals with travel distance. These values, plus earlier work at higher frequencies, indicate that the attenuation in db per kiloyard (kyd) over the frequency range 20 cps to 60 kc is equal to , f being in kc per sec.
29(1957); http://dx.doi.org/10.1121/1.1908932View Description Hide Description
The absorption and velocity of sound in argon, nitrogen, and carbon dioxide have been investigated over a range of frequency, pressure, and temperature conditions. Use was made of a movable sound source and a stationary microphone, both employing the principle of the ribbon microphone, located inside glass tubing 1.73 cm in diameter. It was found that Kirchhoff's equations correctly predicted the absorption and velocity as the temperature was varied from 0 to 200°C in the case of argon and from 0 to 150°C for . Not only did the tube absorption vary as a function of , but the factor incorporating the physical properties also appears to be valid. Certain earlier experiments have not agreed with the Kirchhoff predictions of the magnitude of the factor which depends on the physical properties, and the success in checking the theory is attributed to the use of improved data for the properties and to the use of precision bore tubing the apparatus.
29(1957); http://dx.doi.org/10.1121/1.1908934View Description Hide Description
An unequal temperament is described in which the fifths and fourths of the tuning chain have the same beat rate. No Wolf intervals are produced and all intervals can be described by ratios of integers. The equal heating chromatic scale is an excellent approximation to equal temperament; moreover it may well represent a closer approximation to Bach's “well‐tempered tuning” than does equal temperament. Circulation of a kind is complete and this tends to restore in some degree the feature of key color. Inasmuch as there is only one beat rate to observe (very nearly one per second) the procedure for tuning keyboard instruments to this temperament is simpler than that nominally required for equal temperament. Tuning notes are appended.
29(1957); http://dx.doi.org/10.1121/1.1908936View Description Hide Description
Some communication situations involve several noisy channels, and only certain ones of these carry relevant information to a given communication operator. The operator must receive and identify a restricted number of different messages, and he must ignore others. The performance of the listener in this situation will depend both on the discriminability of the messages and on the listener's criterion for accepting his response as correct or rejecting it as incorrect. The present paper gives a quantitative description of the monitor's behavior in terms of the operating characteristic and the articulation‐criterion function. The results of two experiments are reported. In one of these, the confusion matrices for the various sets of messages were also determined.
29(1957); http://dx.doi.org/10.1121/1.1908938View Description Hide Description
A mechanical model of the cochlea in which the skin of the arm is used as a senseorgan was compared with the organ of Corti. Three phenomena were investigated: (1) directional hearing, (2) heats, and (3) harmonics. For directional hearing almost no differences were found between hearing and the sensation produced by the model. In the case of beats it was possible to confirm the earlier observations of Helmholtz by improving the frequency resolution of the model ear. Concerning the harmonics it was found that the method of best beats does not permit the measurement of overtones of the ear.
29(1957); http://dx.doi.org/10.1121/1.1908940View Description Hide Description
Pulsed pure‐tone audiograms were obtained in quiet and in the presence of narrow bands of noise centered at 500, 1000, 2000, and 4000 cps and at several levels. The masking produced at lower frequencies was of particular interest: The bands of noise at about 75 db/cy SPL produced from 12 to 24 db of masking at 100 cps and from 25 to 40 db of masking at frequencies between about 200 cps and the lower effective limit of the band of noise. This phenomenon contrasts with the fact (briefly reaffirmed in this paper) that a single pure tone of comparable frequency and intensity does not produce appreciable masking at these lower frequencies.
It is hypothesized that a band of noise is functionally somewhat equivalent to a bunch of pure tones which when passed through a nonlinear transducer (the ear), produce aural difference tones which elevate the threshold for signals of lower frequency, while a single tone masker would not have this effect. It was found that two pure tones at a spectrum level and at frequencies comparable to the bands of noise do produce aural difference tones (as measured by best beats) of a level which correspond well with the level of lower frequency masking effects in question.
29(1957); http://dx.doi.org/10.1121/1.1908942View Description Hide Description
Noise masked thresholds for 800 cps tonal pulses 25 to 400 msec long were measured in masking noise bands from 19 to 1100 cps wide. It was found that the threshold remained constant for equal values of band width, pulse‐length product. The threshold varied according to a formula proposed on the basis of limited data in an earlier report (T. H. Schafer and C. A. Shewmaker, U. S. Navy Electronics Laboratory Report 372, 1953): , where S is the signal power, N is the noise power in the pass band of the filter, B is the band width, T is the pulse length, and m is a constant.
29(1957); http://dx.doi.org/10.1121/1.1908944View Description Hide Description
Masked audiograms for six different masking stimuli were obtained from five observers. The audiograms show that remote masking can be controlled with respect to frequency region by controlling the envelope of the masking sound. Regular variations in the envelope at, say, 500 cps produce remote masking in the 500‐cps region; while irregular, “random,” variations produce equal amounts of masking everywhere outside the frequency region corresponding to the masking band or tone. It is argued that the constant masking seen in remote masking is related to the fact that signal frequencies are differentially attenuated in their transmission from the tympanum to the cochlear partition, while the masking frequencies are not since they are actually generated at the cochlear partition itself.
29(1957); http://dx.doi.org/10.1121/1.1908946View Description Hide Description
The frequency separation between two simultaneously sounding tones necessary to give perception of two pitches has been investigated. Frequency levels of 200, 1000, 4000, 6000, and 10 000 cps were used. For the two‐ear condition (where one tone was led to one ear, the other tone to the other ear), no striking differences were found between results at sensation levels of 10, 30, and 50 db. When both tones were led to the same ear, results tended to approach the two‐ear situation when masking and interaction effects were minimized.
The relation of the two‐ear results to localization is discussed. Finally special phenomena are described which arise when two low frequencies, related by simple multiples, are used in the two‐ear situation.
29(1957); http://dx.doi.org/10.1121/1.1908948View Description Hide Description
Frequency difference limens (DL) were measured for Gaussian noise having band widths of to 64 cps centered at 800 cps and for a pure tone, also at 800 cps. Six listeners were used, and the DL's were defined as the probable errors of the fitted transition curves. For band widths wider than 8 cps, the DL rises regularly. Between to 8 cps the threshold changes are small, having a minimum at about 8 cps. None of the DL's for noise approach that of the pure tone, all being at least twice as large. It is suggested that the failure of ΔF for narrow bands of noise to converge on ΔF for a pure tone is due to the dependence of frequency discrimination on intensity discrimination. In narrow bands of noise, the auditory system follows the amplitude fluctuations, which increases the uncertainty of judgments of intensitive differences. For the bands of noise wider than 8 cps, ΔF increases directly with band width. A linear increase in ΔF with band width is predicted for a limited range of band width and was found to fit the data.
29(1957); http://dx.doi.org/10.1121/1.1908951View Description Hide Description
The object of this study was to determine how signal amplitude and duration effect the detectability of a pure tone partially masked by random noise. If signal duration and amplitude are considered two dimensions in a space, the study attempted to determine the surface of detectability in this space. To accomplish this task three experiments were conducted with the same observers in each experiment. In the first experiment signal duration was held constant while amplitude was varied. In the second experiment signal energy was held constant while various pairs of values of signal duration and amplitude were tested. Finally, signal amplitude was held constant while signal duration was varied. A three parameter equation was determined which provided a reasonable fit to this surface of detectability in the plane of signal amplitude and duration. The equations are consistent with the data of previous research in this area. Finally, a comparison of the results and the predictions generated by a simple filter model is discussed.