摘要:

The inharmonicity of plain wire stringsin situhas been measured in six pianos of various styles and makes. By inharmonicity is meant the departure in frequency from the harmonic modes of vibration expected of an ideal flexible string. It is shown from the theory of stiff strings that the basic inharmonicity cents (hundredths of a semitone) is given by3.4×1013n2d2/v02l4, wherenis the mode number,dis the diameter of the wire in cm,lis the vibrating length in cm, andv0is the fundamental frequency. A value ofQ/ρ = 25.5 × 1010 (cm/sec)2was assumed for the steel wire, whereQis Young's modulus and ρ is the density. The observations are entirely compatible with the relationship given. In general terms the inharmonicity of the plain steel strings is about the same in all the pianos tested, being about 1.2 cents for the second mode of vibration of the middleCstring. Above this point every eight semitones it is doubled. Below middleCthe inharmonicity is consistently less in large pianos than in small ones.

ISSN:0001-4966    

DOI:10.1121/1.1906888

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Continuing the theoretical work of Strehlke, Seebeck, and Lord Rayleigh, the transverse vibrations of uniform thin bars subject to the following end conditions are considered: (a) both ends free; (b) both ends fixed; (c) one end free, the other fixed. Accurate values for the position of the nodes, antinodes, and points of inflection and of maximum curvature are calculated for the first few principal modes of vibration, several errors of long standing are rectified, and the amplitudes at the antinodes are computed (Tables I and II). Approximate expressions, valid for the modes of higher order, are given for the node and antinode positions (Tables III and IV) as well as for the amplitudes at the antinodes (Sec. 6).

ISSN:0001-4966    

DOI:10.1121/1.1906889

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The Kirchhoff integral is applied to obtain an approximate solution for the pulse reflected from the surface of a sphere to a receiver near the source. The solution shows that for a reflection path of minimum time (in the sense of Fermat's principle) the reflected pulse should develop a “coda” and that for a path of maximum time, a “prelude.” The approximations are such that the coda and prelude should have an amplitude greater than that predicted by the integral. It was found experimentally that a prelude did result from a reflection over a path of maximum time. The information from reflections over paths of minimum time was less definite, but it can be safely inferred that a coda developed as well. In addition, the pulse diffracted from the edge of an open reflector was examined and found to have the sign predicted by the integral. It can be concluded that the Kirchhoff integral can be used to give a good description of pulse reflection.

ISSN:0001-4966    

DOI:10.1121/1.1906890

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In past studies of the interaction of an ultrasonic beam with a solid plate immersed in water, the general practice has been to assume that a narrow radiation pattern is a sufficiently close approximation to a plane wave to permit the use of plane wave theory to predict the results. Reflection measurements made in water with a three‐degree radiation pattern at a frequency of 3.35 megacycles per second, using both air‐backed aluminum plates of thicknesses ranging from 0.250 to 0.025 inch and a two‐inch aluminum slab to approximate a semi‐infinite medium, indicate that under certain conditions this assumption is not valid. Experimentally, the excess pressure of the reflected wave is considerably lower than that predicted by plane wave theory when the angle of incidence is such that the change of phase of the wave upon reflection varies greatly with a small change of the angle of incidence. It is apparent that at these angles of incidence a divergent beam which is several degrees wide cannot be used to approximate a plane wave. The nature of the phenomenon indicates that it should be of equal importance in the study of transmission phenomena.

ISSN:0001-4966    

DOI:10.1121/1.1906891

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

This paper presents a series of curves of acoustic reactance and resistance ratios for partial waves emitted by cylindrical and spherical sound radiating sources whose dynamic configuration is expressible by infinite series. This information permits the calculation of sound pressure at the radiating surface, power of sound emitted, and accession to inertia for wavelengths and sound radiators in the range 0⩽ka⩽10.

ISSN:0001-4966    

DOI:10.1121/1.1906892

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

With an eye to application in the investigation of sound scattering by marine life, the reflectivity of a spherical elastic shell containing a fluid is studied. It is found that for incident wavelengths of the order of magnitude of the sphere, the behavior for thin shells is similar to that of the fluid sphere alone. For longer wavelengths a correction is computed, good to terms in the first power of the thickness: diameter ratio of the shell.

ISSN:0001-4966    

DOI:10.1121/1.1906893

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A jet‐edge (JE) system is an arrangement whereby a thin blade of fluid impinges on an edge and thus, under appropriate circumstances, gives rise to tones which are called edge tones. Experimental results are presented for JE systems such as might be employed in jet‐edge‐resonator type whistles. Operating ranges of parameters are mapped out for various possible stages of self‐oscillation. Edge tone fields are described as functions of parameters, particular emphasis being given to magnitudes and distributions‐in‐space of stage 1 edge tone sound fields. Examination is also made of sound fields generated by a JE system coupled to a resonator; characteristic interaction pattern is described.

ISSN:0001-4966    

DOI:10.1121/1.1906894

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Beranek developed in 1942 a relatively simple and easily applicable theory of the acoustic impedance of porous materials. This paper presents a modification of his theory which avoids two approximations used formerly. It is found that the specific dynamic frictional resistance and the effective density of the material are functions of frequency. Their values may be computed from experimental values of the flow resistance, porosity, and certain area ratios which have to do with the structure of the material. A method of determining the area ratios in the isotropic case is presented. Acoustic impedances may then be computed. The modified theory is applied to two common acoustic materials, and it appears to be quite adequate for materials of large porosity and small flow resistance. It is less adequate for other materials. Possible reasons for the latter case are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1906896

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The effect of perforated facings of a small percent open area on the specific acoustic resistance of backing materials of appreciable thickness was investigated for several backing materials. The resistance was found to increase by factors of 2 to 7 depending on the percent open area of the facing and the resistance of the backing material. The increase was considerably less in all cases than 1/p, wherepis the open area ratio of the facing. It was found that the specific acoustic resistance of a resonant absorber can be varied considerably above and below the resistance of the uncovered backing by means of an air space between the facing and the porous backing.

ISSN:0001-4966    

DOI:10.1121/1.1906897

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Recent experimental data show that some error in concentration dependence is involved in Liebermann's application of his theory of sound propagation in chemically active media to the case ofMgSO4solutions. Therefore a more careful analysis made of the concentration dependence of some of the factors involved the theory. The proper concentration dependence is shown to be consistent with experimental results. Present experimental data are insufficient for determining whether a unimolecular reaction or a dissociation reaction is causing the observed anomalous absorption inMgSO4solutions.

ISSN:0001-4966    

DOI:10.1121/1.1906898

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP