摘要:

From the equation for propagation of acoustic plane waves through a solid medium, expressions are derived for the vibrational amplitude, radiated power, and electrical admittance of a plane‐wave crystal transducer. The transducer consists of crystals, backing, and diaphragm, radiating into any medium. The crystals may be an assemblage of flat bars vibrating lengthwise, or there may be a single flat crystal plate, or mosaic of plates, in thickness vibration. The equations take account of attenuation in the diaphragm, but not of attenuation in crystals and backing, nor of the effects of cement layers and lateral stresses between crystals.The general equations, which are valid at all frequencies and for all thicknesses of backing, crystal assemblage, and diaphragm, are specialized to the case in which the backing is air. Special attention is given to those frequencies at which the crystals, or diaphragm, or both, are in resonance. Some typical theoretical curves are shown, and a graphical method is described for the rapid plotting of curves.

ISSN:0001-4966    

DOI:10.1121/1.1906483

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

In this paper the causes of noise generated by the conventional supersonic biasing and erasing fields used in magnetic recording systems are discussed. The data to be presented emphasize the manner in which this noise varies with the wave form and frequency of an applied supersonic field. The importance of these two factors is shown to be a function of the characteristics of the erase and recording heads and of the inherent frequency response and modulation noise characteristics of the medium. By proper control of the wave form and frequency of the supersonic signal, noise may be reduced to such an extent that the effective noise level of a given recording medium with bias and erase signals applied will be equal to or less than the noise level of a virgin sample of the medium. Under these conditions, values of saturated signal to noise exceeding 80 db may be obtained.

ISSN:0001-4966    

DOI:10.1121/1.1906484

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

In listener tests of sound reproducing equipment there are many variable factors that contribute to the validity of the result. Among these factors are the program material, associated acoustical and electronic equipment, the size and nature of the audience, the method used in reporting audience response, and the statistical analysis of the audience response. This paper discusses these variables and proposes a definitive method for recording and presenting the data in a simple and thorough manner.

ISSN:0001-4966    

DOI:10.1121/1.1906485

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

In this paper a method is described of measuring the acoustic impedance of a sample of material forming one boundary of a shallow cylindrical cavity, by determining the sound pressure produced when a known volume current is injected into the cavity from a high impedance source. The volume current is effectively determined by observing the pressure when the cavity is rigidly terminated. The use of a ring source suppresses the first radial mode of the cavity and extends the frequency limit set by uniformity of pressure by at least an octave.Secondary effects due to the finite impedance of the source and microphone and heat losses at the walls have been evaluated. The method appears to be simple, rapid, and precise.

ISSN:0001-4966    

DOI:10.1121/1.1906486

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A high speed level recorder of the “potentiometer type” which is useful both for laboratory and field measurements is described. The recording system consists of a moving coil with translational motion, the speed of which can be varied with a maximum value of about 1000 db/sec. Recording is made by a steel stylus on waxed paper of the same kind as that in the usual Neumann recorder.

ISSN:0001-4966    

DOI:10.1121/1.1906487

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A precise experimental study of the reactive component of the complex impedance of small circular orifices has been made for a number of orifices varying in diameter from 2 cm down to 0.357 cm, with diameter/thickness ratios from 4 to 40, over the frequency range from 200 to 1000 c.p.s. The measurement of the impedance is performed with a precision impedance tube.A theoretical correction for the influence of the tube walls is applied by considering the orifice to act as a plane piston and taking into account the influence of all possible higher order modes of the tube in the neighborhood of the orifice. Comparison between calculated and measured values of reactance shows that, as far as this quantity is concerned, the assumption that the orifice acts like a plane piston appears valid for radii equal to or greater than 1 cm for “thin” orifices within the range of variables specified above. For orifices of radii less than 1 cm, however, a modification of the radius is necessary to make the classical theoretical equation for orifice reactance fit the measured data. The observations and analyses reported here are restricted to wave‐lengths much greater than the hole diameter and to the low velocity region where reactance is independent of particle velocity.

ISSN:0001-4966    

DOI:10.1121/1.1906488

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

This note compares the predictions of the Kirchhoff approximation with those of the exact theory for the problem of diffraction by a circular aperture.

ISSN:0001-4966    

DOI:10.1121/1.1906489

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Thenormalor common type of ultrasonic light diffraction occurs when traveling sound waves act like a phase grating. The spacing and intensities of the respective orders of spectra are given by the Raman‐Nath theory. Experimentally and theoretically, this type of diffraction is obtained when the product of (width of sound beam) × (frequency)2× (sound amplitude) is sufficientlylow. When the light beam is maintained parallel to the sound wave fronts, the right and left spectra of the same order are of equal intensity.Anabnormalor uncommon type of ultrasonic light diffraction occurs when the sound waves diffract the light in a manner satisfying the Bragg reflection law, well known in x‐rays. The spacing of the spectra is essentially the same as before but right and left spectra do not appear simultaneously. Strong intensity in a given portion of the spectra is obtained only when the glancing angles of incidence φ and of reflection θ are equal, as in mirror reflection, and when λ, Λ, and θ satisfy the Bragg lawnλ = 2Λ sinθ, (λ and Λ are the light and sound wave‐lengths, respectively, andnis the order of spectra). This type of diffraction is obtained only when the single product (width of sound beam) × (frequency)2is sufficientlylarge.Experiments and theory indicate the above criteria for these two types of light diffraction. Theory also indicates the possibility of other types ofabnormaldiffraction, such as mirror reflection, diffraction satisfying ruled grating theory,nλ = Λ(sinφ + sinθ), where φ does not necessarily equal θ, and others.

ISSN:0001-4966    

DOI:10.1121/1.1906472

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A procedure was devised for determining the air blast pressures of the A‐bomb at Bikini. In such a disturbance the air particles move with large and finite amplitudes; hence, the propagated waves do not obey the ordinary laws of acoustics. By measuring the ratio of the air shock wave velocity to normal acoustic velocity, an indication may be obtained as to the peak pressure of the explosion. Blast waves in water, on the other hand, follow substantially the familiar acoustic laws and are propagated at a well‐known velocity. Measurements were made of transit times at identical positions for the air and the water blast waves. These yielded immediately the desired air blast velocity in terms of the known velocity of sound in water. This procedure eliminated the need for simultaneous measurement of the continually shifting distances between buoys which carried observational equipments. However, careful positioning of the buoys was necessary in order to avoid their destruction and yet record the maximum possible air blast. These positions were calculated on the basis of an equivalent explosion from 20,000 tons of TNT. Since the measurements had to be made automatically and without human observers, special timing and recording systems were provided. All requirements for gathering the data were successfully met in the assembly of apparatus described herein.

ISSN:0001-4966    

DOI:10.1121/1.1906473

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A theory is outlined for the propagation constant in media containing numerous small spherical particles. Using expressions derived by Lamb for the zero and first‐order scattering coefficients of a particle free to move in a sound field, an expression for the complex propagation constant is derived whose real part yields a velocity which reduces to the homogeneous case for extremely small particles, and whose imaginary part yields an absorption coefficient identical with that derivable from the viscous‐drag theory outlined in a previous paper.Using both an interferometer and a pulse‐reflection method, measurements of sound velocity and absorption at megacycle frequencies have been made on mercury‐in‐water and bromo‐form‐in‐water emulsions of non‐uniform particle size, up to a volume concentration of about 50 percent of emulsified liquid. These materials, though showing considerable deviation from a homogeneous behavior, are found to have a velocity and absorption in good agreement with the theory up to concentration of about 25 percent by volume.

ISSN:0001-4966    

DOI:10.1121/1.1906474

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP