摘要:

Absorption and scattering from resonators in a free field as well as in walls are discussed. The effect of different aperture geometries on the resonance frequency of resonators is considered and illustrated by examples. Considering losses due to viscosity, heat conduction, and radiation, the optimum design for maximum resonance absorption is analyzed, and the results are expressed in terms of design charts. Nonlinear effects on the absorption and resonance frequency are also included, and a discussion of the onset of turbulence is presented.

ISSN:0001-4966    

DOI:10.1121/1.1907235

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The near field of a spherical Helmholtz resonator exposed to a plane wave is computed and shown to be in good agreement with measurements. Comparison is made with the near field of a resonator terminating a cylindrical tube. A discussion of the calculation of the dissipation in the resonators is included.

ISSN:0001-4966    

DOI:10.1121/1.1907236

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

This paper presents a systematic study of experimentally significant losses contributing to the damping of an acoustical cavity resonator. Absorption measurements in air on the 0, 1 wave of a round cavity were made by a resonance response method employing a transverse particle velocity pickup device. This study reveals that mechanical losses due to the vibrations of the walls are experimentally significant. Empirical relaxation time formulas are established for air at 24 and 27°C. The thermal and viscous boundary‐layer loss formula is fitted to these data by choosing the thermodynamic ratio νρ0/μ equal to 1.31.

ISSN:0001-4966    

DOI:10.1121/1.1907237

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

An experimental investigation of the attenuation of sound in two air‐filled tubes of 0.238 and 0.0292 cm inside radius in the frequency range from 3.8 to 20 kc was conducted, and the results were compared with values of attenuation calculated from the Kirchhoff theory for rigid walled tubes. Agreement of experimental with theoretical values was found within the accuracy of the experiment, provided that the comparison made only with the portion of attenuation proportional to square root of frequency, as suggested by Fay. The attenuation was determined by a method which was different, in some respects, from those previously employed. The variable length, closed tube was driven with a high‐impedance source, and the input pressure was sampled with a high‐impedance microphone probe. The input pressure was recorded as a function of closed tube length. Since the input pressure can be assumed to be proportional to input impedance for these conditions, the attenuation can readily be determined from the ratio of the pressure maxima or minima.

ISSN:0001-4966    

DOI:10.1121/1.1907238

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The original work of Rayleigh on scattering and radiation of harmonic disturbances by small cylinders is extended to transient disturbances. The analysis is closely related to Ward's treatment of the aerodynamics of slender bodies in supersonic flow.

ISSN:0001-4966    

DOI:10.1121/1.1907239

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

This paper is a report of a theoretical investigation of sound scattering from liquid cylindrical obstacles immersed in water following closely the conditions prevailing in the previous experimental work of Tamarkin, Bauer, and others. An incident plane wave being assumed, series solution was found for the total scattered wave. Numerical calculations were carried out using parameters approximating those of Tamarkin's experiments (radius of obstacle, 0.635 cm; sound frequency, 1.145 mc/sec; wavelength, 0.13 cm). A series of scattering patterns, confined principally to the forward direction for an angular spread of about 14° (with the obstacle at the vertex) were calculated for eight liquids, chosen to give a spread ofkiavalues (kithe wave parameter inside the liquid andathe radius) between 26.0 and 41.0. The results of this theoretical investigation confirm the experimental findings that for the liquids examined the scattering is diffractive and lies in the zone between the geometrical region and the region of Rayleigh scattering. Quantitative comparisons are made between the theoretical and experimentally plotted results with special emphasis on the experimental resonance curve and its theoretically computed counterpart.

ISSN:0001-4966    

DOI:10.1121/1.1907240

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The scattering of a sound wave in a medium undergoing shear flow confined to a finite region is investigated under the assumption that the total velocity field is everywhere small compared to the velocity of sound. Formulas are obtained for the angular distribution and frequency distribution of the scattered wave in terms of the four‐dimensional Fourier transform of the shear velocity field.Under typical conditions, the cross sections for the scattering of a plane wave of frequency ω by a shear flow of given scale and spatial structure are approximately of the form ω4M2, whereMis a characteristic Mach number of the flow. The coupling between the shear and longitudinal velocity fields has a tensor character such the the scattering vanishes at 180 degrees and at 90 degrees. The spectrum of the scattered sound wave is very sharp in the forward direction and becomes broader at larger scattering angles.Explicit expressions for the cross sections are obtained for the case of scattering from a region of isotropic turbulence. When the frequencies of importance in the turbulence are small compared to the frequency of the incident sound wave, the average differential scattering cross section can be expressed directly in terms of the energy spectrum of the turbulence.

ISSN:0001-4966    

DOI:10.1121/1.1907241

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The reflection coefficient for plane waves incident obliquely on a medium in which the velocity decreases exponentially is computed approximately using the WKB method and compared with a computation from the rigorous solution. The approximate reflection coefficient1/[16(ω/g)2 cos6θ+1]where ω is the angular frequency,gis the velocity gradient at the start of the exponential decrease, and θ the angle of incidence is within 0.05 percent of the rigorous value for ω/g⩾ 5 at normal incidence and within 5 percent of the rigorous value for ω/g⩾ 20 for angles of incidence up to about 45°.

ISSN:0001-4966    

DOI:10.1121/1.1907242

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The region of validity of the single‐scattering approximation used in Part I is found by considering the next higher approximation; it is valid fork02arα2≪1, wherek0is the wave number of the incident sound,ris the range from source to observer,ais the mean size of the inhomogeneities, and α is the rms value of the refractive index variations. Some approximate results are given for the case of wavelength large compared with inhomogeneity size. By consideration of the intensity variations, it is found that ray theory is valid for (k0a2/r)≫1, as has been found for plane waves.

ISSN:0001-4966    

DOI:10.1121/1.1907243

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

An apparatus for measuring the absorption of sound in gas mixtures has been developed and tested. The apparatus consists of a sound tube, a movable ribbon‐type speaker, and a fixed condensor microphone. The absorption is determined by recording the sound pressure as the path length between the speaker and the microphone is increased. The measured attenuation coefficient is corrected for the effect of the tube and also for the attenuation due to the viscosity and heat conduction of the gas. Both frequency and pressure are variable and range from 2 to 10 kc and from 3 to 300 mm of Hg, respectively.

ISSN:0001-4966    

DOI:10.1121/1.1907244

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP