摘要:

Several theoretical studies of the acoustic properties of homogeneous isotropic porous material have been presented in the past, and the results have been shown to be in good agreement with experiments. However, no corresponding satisfactory theoretical analysis of the commonly used perforated porous tile seems to have been given. In this paper this problem is treated in some detail, and from the resulting formulas and equivalent circuits the acoustic properties of the tile can be calculated in terms of the geometry and the properties of the porous material. As an example, the acoustic impedance and absorption coefficient have been calculated as a function of perforation depth for a typical tile, and the results are shown to be in good agreement with measurements.

ISSN:0001-4966    

DOI:10.1121/1.1907331

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A detailed theoretical analysis of the operation of thermocouple probes used to determine absolute sound levels or acoustic absorption coefficients is presented.The probe consists of a thermocouple imbedded in a sound absorbing medium which closely matches in density and sound velocity the medium in which the sound level is to be determined. In use the transducer which generates the acoustic field is excited to generate sound pulses with a rectangular envelope. The initial time rate of change of the temperature at the thermocouple junction is determined. In addition to the measurement of the temperature change, the calculation of the absolute sound intensity requires only a knowledge of the absorption coefficient of the imbedding material and its heat capacity per unit volume at the temperature at which the measurements are made.The theoretical discussion includes an analysis of the relation between the temperature rise at the junction resulting from absorption in the body of the imbedding medium and the sound level. In addition, the effects of (a) viscous forces arising from relative motion between the thermocouple and the imbedding fluid and (b) heat conduction between the thermocouple and the fluid, in contributing to the temperature change at the thermocouple junction are analyzed.Based on the analysis, a set of design formulas is obtained which are summarized and illustrated for the convenience of other investigators who may wish to design and use such probes.

ISSN:0001-4966    

DOI:10.1121/1.1907332

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A stable, readily constructable thermocouple probe has been developed for determining absolute sound levels in ultrasonic fields in liquid media. This paper includes criteria for design of such probes and a discussion of experimental measurements made with such a device.It is a consequence of the method that if the sound intensity at an appropriate size thermocouple junction imbedded in an absorbing medium is known the acoustic absorption coefficient of the material can be determined. The method thus makes possible the determination of absorption coefficients of minute quantities of material.The probe consists of a thermocouple imbedded in a sound absorbing medium which closely matches in density and sound velocity the medium in which the sound level is to be determined. In use the transducer which generates the acoustic field is exctied to generate sound pulses with a rectangular envelope. The initial time rate of change of the temperature at the thermocouple junction is determined. In addition to the measurement of the temperature change, the calculation of the absolute sound intensity requires only a knowledge of the absorption coefficient of the imbedding material and its heat capacity per unit volume at the temperature at which the measurements are made.The experimental results include a comparison of the sound level determined by a thermocouple probe and a determination by radiation pressure methods. The values obtained by the two methods agree within the uncertainty of the experimental measurements.

ISSN:0001-4966    

DOI:10.1121/1.1907333

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Acoustically treated, doorless telephone booths can increase the effectiveness of telephone communication in noisy environments even though practical size and open area requirements limit the amount of noise reduction which can be achieved. The principal factors determining the noise reduction of an acoustically treated booth (where the noise reduction is considered as the decibel difference in octave band noise levels measured outside and inside the booth) have been investigated by use of full size and13model booths.The principal parameters affecting the reduction of an acoustically treated telephone booth were found to be (1) the sound absorption coefficients of the wall surfaces as function of frequency; (2) the ratio of open area to the wall area of the phone booth; (3) the transmission loss of the walls of the phone booth; and (4) the size and shape of the booth.The investigation resulted in a new triangular design of booth which is fully as effective acoustically as the rectangular booths, yet has added practical advantages.

ISSN:0001-4966    

DOI:10.1121/1.1907334

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A theoretical analysis of the propagation of pressure waves through liquid filled flexible tubes is presented. Expressions are derived which show the dependence of phase velocity and damping factor on the viscosity of the liquid, and on internal damping in the tube wall. The analysis is restricted to tubes with thin walls and to waves whose amplitude is infinitesimal and whose wavelength is large compared to the radius of the tube.

ISSN:0001-4966    

DOI:10.1121/1.1907335

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The speed of a plane compression wave in a gross mixture (a suspension or a porous medium) which obeys a simple density mixture law is derived. The results agree with a relation proposed by Wood and others. The derivation of these investigators requires an addition to a density mixture law an assumption concerning the compressibility of the mixture in terms of the constituent compressibilities. It is shown that the latter assumption is a direct consequence of the density mixture law, and is hence not required. It is indicated that the derivation is applicable to waves of arbitrary amplitude.

ISSN:0001-4966    

DOI:10.1121/1.1907336

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A radially symmetric progressive acoustic beam has been set up in a closed, gas‐filled tube to cause streams driven by the Eckart, volume, source of verticity. A careful determination of the acoustic pressure at all points of a cross section of the beam has been used successfully to predict the stream velocities at this cross section, for argon. The work with argon and the results of further experiments with dry nitrogen and moist air indicate that: (1) the Navier‐Stokes equation, the equation of continuity, and the acoustic “equation of state”p1 = ρ1c02+Rρ̇1, provide a valid basis for second‐order studies of streaming; (2) thermal conduction effects may be introduced into the Eckart streaming equations in the same manner as they appear in the attenuation formulas; (3) the macroscopic quantity, bulk viscosity, is made up of contributions from the intramolecular processes of vibrational and rotational relaxation.

ISSN:0001-4966    

DOI:10.1121/1.1907337

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The method described in Part III has been applied to another normal mode of a particular disk by combining the motions corresponding to the one imaginary and two real values of α. The residual stresses at the cylindrical surface of the disk are small, and the displacement distribution of the plane surfaces agrees reasonably well with that obtained experimentally.

ISSN:0001-4966    

DOI:10.1121/1.1907338

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Experimental observations of peak pressure, decay constant, and energy flux for TNT and pentolite are presented to ranges (in feet) defined byR≅2000W12, whereWis charge weight in pounds. Previously published results extended only toR≅30W12.

ISSN:0001-4966    

DOI:10.1121/1.1907339

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Previous analysis of the equivalent circuit for the ultrasonic delay line was applied to quartz crystal transducers and a vitreous silica delay medium. The analysis has been extended to evaluate the use of other materials such as magnesium, aluminum, and steel, and to includeBaTiO3ceramic transducers. Calculations show the decrease in loss to be expected as the impedance of the delay medium is decreased and conversely the increase in band width to be expected as the impedance of the delay medium is increased. The increase in band width resulting from symmetrical loading of the transducers is also evaluated. Modifications to the equivalent circuits for the case ofBaTiO3ceramic transducers are considered. Theoretically losses can be reduced to 10 db or less using the ceramic transducers with a vitreous silica medium. The band width is slightly less than for quartz crystal transducers. However, by utilizing higher impedance materials, band widths approaching 100 percent should be achieved.

ISSN:0001-4966    

DOI:10.1121/1.1907340

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP