摘要:

The electrical and acoustical performance of a number of commercially available audiometers has been examined in the light of requirements for pure tone diagnostic audiometers recently issued by the American Medical Association and now under consideration by the American Standards Association, Inc. Performance has been judged to be satisfactory except for discrepancies at 8000 c.p.s. in the case of several audiometers. Likewise, it is concluded that the specifications themselves are reasonable.

ISSN:0001-4966    

DOI:10.1121/1.1906700

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

An audiofrequency electromechanical filter using a tuning fork as the resonant element is described.Q's ranging from 1000 to 20,000 were attained. Typical response curves have been plotted and the factors that affect theQ, insertion loss and stability are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1906701

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The boundary layer attenuation caused by viscous and thermal losses of all higher order modes of propagation in rigid walled rectangular and circular tubes has been calculated using the concept of boundary layer admittance introduced by Cremer. In the case of the rectangular tube Cremer's admittance formula for obliquely incident waves is applied directly in conjunction with Morse's duct formulas to obtain the attenuation of (ny, 0) and (ny,n2) modes. The boundary layer admittance of higher order modes in circular tubes is obtained from an extension of Cremer's method for plane waves. An electromagnetic wave‐guide technique for calculating “skin” losses is applied to determine the attenuation of the asymmetric (m, n) circular tube modes. It is shown that the symmetric (0,n) circular tube modes are the least attenuated of all higher order modes in both rectangular and circular tubes; above a certain frequency the attenuation is less than the plane wave attenuation.

ISSN:0001-4966    

DOI:10.1121/1.1906702

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The problem of the diffraction of a plane wave by the convex surface of a paraboloid of revolution is solved. An infinite set of equations is obtained for the coefficients of the pressure fields inside of and outside of the paraboloid. For the particular case of a rigid paraboloid the coefficients of the series for the scattered field can be obtained explicitly. The ratio of the total pressure at the nose of the paraboloid to the pressure of the incident wave is shown as a function of the shape of the paraboloid for a plane wave whose wave front is perpendicular to the axis of revolution. The same quantity is plotted for the case of a sphere whose radius of curvature is equal to that of the paraboloid at the nose.

ISSN:0001-4966    

DOI:10.1121/1.1906703

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Consideration is given to the direct sound which is observed to penetrate the so‐called “shadow zone” of ocean acoustics. It is shown by ray theory that the assumption that the sound velocity gradient approaches zero in the top few feet of the oceans predicts sound levels in the “shadow” which are of the same order of magnitude as those which are measured at a frequency of 24 kc/sec.

ISSN:0001-4966    

DOI:10.1121/1.1906704

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The absorption coefficient for moist air has been measured at 1.46 Mc for relative humidities varying from zero to 84 percent. Maximum absorption at this frequency (α = 0.52 cm−1) is found to occur at 46 percent relative humidity.

ISSN:0001-4966    

DOI:10.1121/1.1906705

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The velocity of sound through various animal organ tissues and through living human tissues is measured, using an ultrasonic pulse method, at 1.25 and 2.5 Mc. The effect of anisotropy (fiber direction) on velocity is determined with beef muscle. Values obtained with the beam traversing the tissue perpendicularly to the long axis of the muscle bundles do not differ significantly from those found with the energy directed parallel with the muscle fibers.Velocity through living human tissues, consisting mostly of muscle, is measured by transmitting the ultrasound through various thicknesses of the arm, leg, and thigh.Specific gravities of the tissues are measured. The characteristic acoustic impedances (ρcvalues), calculated from the density and velocity data, vary between 1.5×105and 1.7×105g/cm2/sec. The imaginary component of tissue impedance is calculated and found to be negligible at the frequencies at which these measurements are made.

ISSN:0001-4966    

DOI:10.1121/1.1906706

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The results of the first step in a systematic investigation of the mechanism of the action of ultrasound on tissue are reported. The temperature changes resulting from absorption of acoustic energy were determined while irradiation was in progress.Experimental evidence is presented which demonstrates the existence of non‐temperature effects in various nerve tissue preparations.

ISSN:0001-4966    

DOI:10.1121/1.1906707

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A conically shaped piezoelectric probe of ammonium dihydrogen phosphate is described. Its sensitivity over a frequency range from 1235 to 1280 kc was obtained by means of a reciprocity calibration. The average value is about 0.12 microvolt per dyne per square centimeter. Since the measured pattern of the probe as a receiver was the same at various points in the acoustic field, it may be concluded that the probe is a “point source.”

ISSN:0001-4966    

DOI:10.1121/1.1906708

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906709

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP