Volume 29, Issue 10, October 1957
Index of content:
29(1957); http://dx.doi.org/10.1121/1.1908698View Description Hide Description
Some similarities and differences between skin sensations and hearing have been investigated. The sensation of pitch on the skin has little similarity to the pitch sensation in hearing. The pitch sensation on the skin changes very much with changes in loudness, and there is a strong diplacusis between different parts of the skin. But the rotating skin sensations and rotating tones (Drehton) have many aspects in common. It was further found that the apparent size of the sensation on the skin and in the ear vary similarly as the stimulus changes. From a neurophysiological point of view, it seems to be important that it is possible to find a situation on the skin where two stimuli of different frequencies cancel each other completely. In this case, one sensation is inhibited by another, but the inhibiting sensation is felt no more. In order to be able to extrapolate from the skin to the cochlea, for several phenomena on the skin, the changes are plotted which occur when the vibrator is moved from an insensitive spot on the skin to a more sensitive one.
29(1957); http://dx.doi.org/10.1121/1.1908700View Description Hide Description
The problem of computing sound power from measurements of average rectified sound pressure is reviewed, particularly in relation to “Absolute Amplitudes and Spectra of Certain Musical Instruments and Orchestras” published by Sivian, Dunn, and White in 1931. Experimental data on the distribution of instantaneous pressure amplitudes of music in a wide band and relations between rms and average pressure in octave and half‐octave bands for speech are introduced; these data suggest, for example, that in a half‐octave band in the vicinity of 1000 cps the rms sound‐pressure level during a 15‐sec interval of music exceeds the average pressure level by 9 db. Means are described for converting the old data based on “pressure per cycle” to a form that would be obtained with the modern octave band analyzer and sound level meter. In place of the steeply sloping spectra suggested by the original figures, the two kinds of corrections lead to an average sound power spectrum, for the 15‐piece orchestra, having a broad peak between 100 and 4000 cps.
29(1957); http://dx.doi.org/10.1121/1.1908702View Description Hide Description
The velocity and absorption of ultrasound in dry have been measured along the 50.8° isotherm with a Hubbard‐type, variable path, recording acoustic interferometer at six frequencies from 300 kc to 7 mc and from 0.3 to 250 atmos, i.e., up to liquid densities. Velocity dispersion is clearly shown in addition to the change in velocity attributable to the nonideality of the gas. The values of the frequency/density ratio f/ρ, at which the transition from to is half‐completed as the pressure is lowered, and at which the maximum absorption per wavelength occurs, were measured wherever possible. From these determinations the relaxation time of the gas has been determined as a function of the density. It proves to be inversely proportional to the density up to the highest density reached (0.8 g/ml), indicating that ternary collisions have not become important and that the number of binary collisions required to excite the internal vibrations does not vary with density. At 50.8° and one atmosphere the relaxation frequency 1/2πτ is about 26 kc and the number of collisions required to excite the molecule is 48 500. The extra absorption (in excess of the classical) remains a consequence of thermal relaxation up to liquid densities, and no new mechanism need be postulated to explain it. Further work at higher densities and other temperatures is in progress.
29(1957); http://dx.doi.org/10.1121/1.1908704View Description Hide Description
Observations have been made of the absorption of ultrasound in castor oil at 3 Mc over the temperature range from 10° to 45°C. An improved interferometer system which utilizes a liquid‐to‐air reflecting interface was employed, together with a simplified electrical detection circuit. The observed absorption is less than the classical values below 25°C, but greater at higher temperatures. In general, the results compare well with those obtained by other observers using different measuring techniques.
29(1957); http://dx.doi.org/10.1121/1.1908706View Description Hide Description
The time‐average forces and torques exerted by a plane sound wave upon fixed rigid disks of various shapes are calculated. Results are given for disks bounded by smooth closed convex curves. These results are then specialized to ellipses and circles. Results are also given for infinitely long thin strips. The results are all valid for ka large, where k = 2π/λ, λ being the wavelength and a being a typical dimension of the disk. The oscillatory behavior of the torque as a function of ka and the occurrence of numerous equilibrium positions are interesting consequences of these calculations.
29(1957); http://dx.doi.org/10.1121/1.1908708View Description Hide Description
The transmission of a spherical sound wave through a homogeneous stretched membrane of infinite extent is investigated theoretically. An integral representation of the transmitted sound field is initially derived. The path of integration is then transformed into the complex plane and the integration carried out in an approximate manner by the method of stationary phase.
The transmitted sound field is found to be composed of two parts, an outgoing spherical wave modified by an amplitude factor containing angular dependence and a surface wave. The surface wave, which results from the free flexural vibration of the membrane itself, exhibits an interesting “zone of silence” in the transmitted sound field.
29(1957); http://dx.doi.org/10.1121/1.1908710View Description Hide Description
The use of piezoresistivematerials as strain gauges and in the measurement of displacement, force, and torque is discussed generally. A torsional transducer which has been constructed from n‐type germanium is described, and the experimentally obtained voltage‐torque characteristic given.
29(1957); http://dx.doi.org/10.1121/1.1908712View Description Hide Description
Two semi‐infinite isotropic media (porous or nonporous) are separated by a plane interface. A simple point source of sound is imbedded in either of the media. Expressions for the resultant wave function are obtained by the method of steepest descents as modified by Banos and Wesley. In particular, two different asymptotic solutions are presented. The first solution is valid in the vicinity of the interface. The expansions, calculated out to three terms, yield the wave solution as a continuous function of the parameters of the two media and the space coordinates for horizontal ranges beginning at small distances from the source and extending to infinity. It is shown that a surface wave exists and that this wave gradually disappears when the horizontal range becomes sufficiently large. The second solution consists of a simple three term asymptotic expansion valid in the vicinity of the vertical axis. The mathematical treatment uses a new path of integration not found in the literature on this problem.
29(1957); http://dx.doi.org/10.1121/1.1908714View Description Hide Description
A response spectrum (shock spectrum) is the response of a series of single‐degree‐of‐freedom systems of given damping to a shock or vibratory motion, as a function of the frequencies of the simple systems. An oscillographic galvanometer is a single‐degree‐of‐freedom system having a rotational response to an exciting current. If the exciting current is made proportional to the amplitude of the motion, the response of the galvanometer to the current will be proportional to that of a single‐degree‐of‐freedom system to the motion, provided their natural frequencies and damping properties are the same. A commercial galvanometer‐type oscillograph has been obtained having twelve undamped galvanometer elements with natural frequencies in the range between 10 and 2500 cps. Damping, by electrical means, has been made adjustable between about 3 and 50% of critical. Associated circuitry has been constructed so that electrical playback of recordings of shock and vibratory motions can be conveniently analyzed.Calibration techniques are described and examples are given for analysis of simple and complex shock motions.
29(1957); http://dx.doi.org/10.1121/1.1908716View Description Hide Description
A Timoshenko‐type theory of cylindrical shells, developed by the authors in a previous paper [G. Herrmann and I. Mirsky, J. Appl. Mech. 23, 563–568 (1956)] for the case of axial symmetry, is generalized presently to include nonaxially symmetric motions. As an application, the propagation of free harmonic waves in the axial direction of a shell of infinite extent is studied and discussed in the light of previous work on this problem.
29(1957); http://dx.doi.org/10.1121/1.1908718View Description Hide Description
Scattering measurements are compared with the predictions of the existing theories. The agreement is satisfactory. Measurements of the temperature microstructure, however, lead to unexpected results, showing that the patch sizes or scales of patch sizes are continuously distributed and that the temperaturefluctuation increases continuously with range. There seems to be almost perfect agreement with the results of the theory of homogeneous turbulence and the temperaturefluctuations in water. This would appear to invalidate the present theories, since a correlation function as defined in the usual sense does not exist. If, however, the correlation function is replaced by a new function in connection with a suitably defined temperature distribution, practically all the results of the current theory can be shown to remain valid, and it becomes possible to explain other items as, for instance, the independence of acoustical scattering with depth, and acoustical predominance of certain patch sizes, which hitherto had not been understood. The acoustically effective patches turn out to be a function of the frequency and range rather than of the particular conditions of the sea.
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