摘要:

The paper will be concerned with the description of tape recorder head measuring equipment type R‐57 now in development, for checking performance standards of all professional tape recording and reproducing units. The R‐57 unit does not require galvanic contact with the tape reproducing assembly. The R‐57 permits inductive coupling to the head assembly and measures recording current, high‐frequency bias, and frequency response of the reproduce head assembly at tape speeds of 30, 15,712, and334 in.per second. No test tape with its mechanical and electrical variations is required for this standard test. Special inductive pickup coil assemblies types K10 and K11 are briefly described. Tape reproducer equalization curves follow the norm of the CCIR recommendations No. 135. Further, disk reproducing equipment type EMT 930 will be briefly described in terms of very rigid disk reproducing standards in western Europe. The paper will also briefly touch upon a musical pitch generator producing the standard toneAat 440 cycles and will describe briefly circuitry in arriving at a typical oboe pitch at 440 cycles. A brief summary will be given of an instrument in use for accurate and direct measurement of wow and flutter as frequency modulated and amplitude modulated variations in reproducing equipment.

ISSN:0001-4966    

DOI:10.1121/1.1918294

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The impact of two solids traveling with relative velocity of 3 km/sec or more, or the detonation of high explosive in contact with a solid, generates compression waves in which the magnitude of the stress can easily exceed 100 000 atmospheres while its duration may be but slightly, more than a microsecond. In this situation, which lies outside the realm of classical elastic behavior, all the classical criteria for plastic flow are greatly exceeded; it appears, however, that the strain rate is so high that the usual mechanisms of plastic flow cannot act, so nonplastic behavior is to be expected. There is a considerable body of evidence which indicates that metals, at least, behave very much like ideal fluids under these conditions. This evidence includes the hydrodynamic behavior of metal liners in hollow explosive charges, the anomalously low measured shock velocity in iron, and agreement between dynamic compressions measured by Walsh and the extrapolation of static data obtained by Bridgman. These data are reviewed and the plausibility of the hydrodynamic theory is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1918312

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A rigorous solution based on the method of L. Cagniard has been obtained for the transmission of a pulse from a point source of pressure in a fluid through a solid plate imbedded in the fluid. On the normal from the source to the plate the pressure response is given by a closed form expression requiring no integration. Numerical results on the normal agree in essential features with experiment. The formal solution on the normal can be expressed in terms of reflection and transmission coefficients for compressional and shear waves at the two boundaries. In this form the solution is easily generalized to a many layer problem. [A preliminary report was given at the American Physical Society meeting held on Febraury 26 and 27, 1954, at Austin, Texas. See Phys. Rev.94, 3, 812 (1954).]

ISSN:0001-4966    

DOI:10.1121/1.1918320

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The characteristic feature of the method is that at any point in the sound field the conservation criteria are expressed in terms of the speed of propagation and the instantaneous values of the particle velocity, the excess pressure, and the excess density. These criteria, together with the adiabatic assumption, determine explicit relations between any two of these quantities. Excess pressure and excess density are here defined as departures from the equilibrium values that exist at the instant when the particle velocity is zero. For waves of finite amplitude, these equilibrium values, as well as the speed of propagation, are found to depend on the intensity. The increment in the speed of propagation does not agree with that obtained by classical methods of analysis. The discrepancy is found to be due to the omission in the classical forms of the continuity criterion of a term that specifies the effect of the rate of change in the speed of propagation. [Supported in part by Office of Naval Research Contract N 5ori‐07861.]

ISSN:0001-4966    

DOI:10.1121/1.1918336

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A long line source has been simulated by placing a horn terminating in a slot8×14in.. between two large, rigid plane surfaces 8 inches apart. The resulting cylindrical sound field has been used for measurements of acoustic radiation forces. The force exerted on rigid spherical obstacles of up to 3 cm radius has been measured at distances within 10 cm of the source of the field. Forces of attraction have been found; their magnitude as a function of frequency, size of spherical obstacle and distance from the source is in agreement with theory [T. F. W. Embleton, J. Acoust. Soc. Am.28, 155(A) (1956) and Can. J. Phys.34, 276 (1956)]. This apparatus overcomes the difficulty of eliminating spherical waves from the sound field encountered in previous experiments with a short line source.

ISSN:0001-4966    

DOI:10.1121/1.1918342

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

An experimental setup, based on a properly designed torsion balance has been built, which allows to produce ultrasonic standing waves and to control, through the radiation pressure, the energy density of the field during the time of its application. The control of the energy density is usually difficult, when employing transducers rigidly connected with reflectors, in particular at high energies and when cavitation occurs. The standing waves produced by this device have been used to investigate the darkening of photographic plates in water and the coloration of starch plates in dilute iodine solutions. These processes have been studied with reference to their dependence on the energy density, frequency, time, cavitation, and hydrodynamic flow within the liquid. A comparison is made between the experimental results obtained with standing waves and with progressive waves at the same frequency and energy.

ISSN:0001-4966    

DOI:10.1121/1.1918358

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

When hydrogen peroxide is produced sonochemically in water containing dissolved oxygen gas, the rate of production of the hydrogen peroxide is appreciably greater than with just an inert gas such as argon to support cavitation. This gives rise to the question as to whether the oxygen gas in the cavitation bubbles actually participates in the chemical reaction or just modifies the thermal or possibly electrical conditions within the cavitation bubble so as to favor the peroxide formation. Isotopic techniques involving oxygen‐18 enriched gas have been used to prove that approximately 30% of the oxygen in the peroxide originates with gaseous oxygen in water saturated at 1 atmos. Through the use of nonequilibrated isotopically enriched gas, the following further information has been obtained. In hydrogen peroxide molecules for which the gas is the source of oxygen, both of the oxygen atoms come from a single gas molecule without the formal breakage of the O‐O bond. The significance of these results will be discussed in terms of proposed mechanisms for sonochemical reactions. [Research partially supported by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1918363

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Several branches in physics have led to the concept of walls which characterize a difference in state of adjacent regions in a medium. Examples are thenaturalBloch walls separating the Weisz domains in ferromagnetics or theartificialporous powder props which are used in the experimental technique of heliumIIfor separating ground state and excited components of the fluid. Another almost trivial example is a mirror (in empty space) intercepting an electromagnetic disturbance. All examples, whether natural or artificial, have the common feature of being impermeable for the state at either side of the wall. The constituent particles of the medium (if any) pass through on condition that they change their state. This suggests, in analogy with the well‐known semipermeable membrane in classical physics, the definition of another semipermeable membrane or wall, which is permeable for matter (if any) but impermeable for its excitations. An analysis of the dynamics of such membranes provides a coherent picture of the classical concepts of acoustic and electromagnetic momentum together with their nonclassical counterparts: phonon and photon momentum. It leads in addition to an interpretation of the photon concept in a material medium, which corresponds to Minkowski's definition of electromagnetic momentum in matter.

ISSN:0001-4966    

DOI:10.1121/1.1918377

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

An understanding of combustion resonance phenomena requires information as to the nature of the acoustic field within the combusion zone. This paper describes a probe capable of surveying such a field and tells how it can be used in the study of high amplitude sounds. The design employs a microphone which measures the sound level near one end of a very long small bore tube in which reflections may be neglected. The bulk of the work involves the measurement of the damping coefficient of high‐amplitude sounds in tubes. A convenient way to calculate the damping coefficient α was examined. This involved dividing α into two parts. Thus,α=αK+αp, where αKis Kirchoff damping coefficient due to viscous effects and αpis damping coefficient of unconfined sawtooth waves. Good agreement between calculated and measured values of α was obtained. A sample survey of pressure amplitude distribution across the flame zone of a screeching combustor is given.

ISSN:0001-4966    

DOI:10.1121/1.1918385

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

In previous publications we have discussed a series of experiments on the critical pressure for the onset of cavitation and the spectrum of the cavitation noise. The behavior of an individual cavitation bubble is of even greater interest, and has been studied in two types of experiments. (1) In the study conducted by L. Bohn, the sound of a parabolic array of magnetostrictive transducers at 22 kc/sec is picked up at the focal point by a small probe microphone, a very thin nickel wire with all but the tip shielded against the incident sound by a plastic tube (frequency range up to 1 Mc/sec). The reaction of the oscillating bubble on the tip is recorded and its spectrum is analyzed. (2) In the study conducted by E. Mundry a vibrating nickel rod (2.5 kc/sec) is used, one end of which dips into water. The bubbles originating and oscillating at the lower surface are photographed by a high speed movie camera (100 000 frames per sec) and the sound waves of the collapsing bubbles are recorded by a Schlieren‐method. The results of both studies are discussed with regard to different qualities of water and different sound amplitudes.

ISSN:0001-4966    

DOI:10.1121/1.1918391

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP