摘要:

A feedback method is described, permitting a loudspeaker to be driven automatically so that the sound pressure generated at any one point is constant with frequency, independent of the loudspeaker characteristics. Several applications illustrate the success of the method in the calibration of microphones and in the study of diffraction and reflection effects.

ISSN:0001-4966    

DOI:10.1121/1.1907681

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The properties of horns that are suitable for use in woodwinds are deduced from first principles. The cylindrical pipe and complete cone are shown to be the only shapes which satisfy these requirements exactly. The behavior of nearly perfect cylinders and almost complete cones is described, the influence of closed finger holes on the effective bore of an instrument is discussed, and the effect of the mouthpiece cavity is analyzed. Damping of the normal modes by the walls of the bore is shown to play a dominant role in the playing behavior and tone color of woodwinds, and various consequences are deduced.

ISSN:0001-4966    

DOI:10.1121/1.1907682

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In this study the near noise field of a supersonic jet (Mach 2.87), exhausting into quiescent air, is analyzed with respect to the aerodynamic structure of the jet. The noise field is shown to be shifted away from the jet exit with the most intense sound near the end of the supersonic portion of the exhaust structure. Downstream of this point, the jet radiates noise in the same manner as a subsonic jet.

ISSN:0001-4966    

DOI:10.1121/1.1907683

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In ultrasonic attenuation experiments carried on by the pulse method, it is important to know the part of the measured attenuation contributed by diffraction in the ultrasonic field. In certain cases, particularly at the lower megacycle frequencies, the diffraction loss can be much greater then the attenuation intrinsic to the specimen. The diffraction loss in decibels has been computed elsewhere as a function of the distance the ultrasonic pulse travels back and forth in the sample. Here an expression for the increment to the attenuation is derived taking into consideration which echoes the decibel drop is measured. It is shown that the first echo has suffered a considerable loss at the lower frequencies and that one must consider that loss in computing the increment to the attenuation caused by diffraction if he has used that echo as one at which the decibel loss is measured. If that loss is not considered, the incremental attenuation will be excessive.

ISSN:0001-4966    

DOI:10.1121/1.1907684

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The limiting values of the velocity of sound for high and low frequencies in the halogens in the gaseous state have been calculated. Measurements at ultrasonic frequencies in three gases have confirmed dispersion of the velocity with relaxation times in the vicinity of 10−6sec.

ISSN:0001-4966    

DOI:10.1121/1.1907685

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The speed and attenuation of sound at 11 Mc were measured inN2, O2, and dry air at various pressures between atmospheric and a few mm Hg. The rotational collision numbers were found to be: forN2, 5.26±0.05; forO2, 4.09±0.08; for air, 4.82±0.18.

ISSN:0001-4966    

DOI:10.1121/1.1907686

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

A description is given of modifications to the “sing‐around” and coincidence techniques for velocity measurement. In the case of the “sing‐around” method a gate is incorporated which effectively lengthens the ultrasonic path by allowing retriggering on multiply reflected pulses. This allows the use of short solid specimens having low attenuation. The coincidence technique is modified by using an unrectified rf display and an electronic counter‐timer to measure the pulse recurrence frequency. In both methods, an accuracy of 1 in 104can be achieved in measuring the transit time for 10‐Mc/sec waves through a low‐absorbing specimen before correction is made for the effect of transducer‐specimen bonds, etc.

ISSN:0001-4966    

DOI:10.1121/1.1907687

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The conditions influencing the onset of acoustically‐induced cavitation in tap water have been investigated, with special attention to the effect of air‐filled cavitation nuclei. Cavitation was induced by exciting an acoustic radial mode in the water in a spherical resonator at a frequency near 25 kc/sec. Air‐filled nuclei were detected by observing the reverberant decay of sound in the resonator at frequencies from 150 to 550 kc/sec, the presence of air nuclei causing an increase in the decay rate.Measurements have been made of the sound pressure required for cavitation inception, and of the content of air nuclei, for the following treatments of the water: (1) allowing the water to stand undisturbed after drawing from the tap, (2) partially deaerating the water, and (3) subjecting the water to increased static pressure. Some measurements were also made of the threshold for rectified diffusion into air bubbles.The experimental results have been compared with theoretical predictions based on three alternate forms of air nuclei: (1) free air bubbles, (2) air trapped in cracks on suspended solid particles, and (3) air bubbles surrounded by skins of organic impurities.

ISSN:0001-4966    

DOI:10.1121/1.1907688

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

On the assumption of the additivity of steady and acoustic flow characteristics, an equation was developed for the time variation of a siren port area required to produce a sinusoidal wave. If low efficiencies can be tolerated the port opening may be kept small and the operating pressure made large compared with the acoustic pressure; then the equation reveals the well‐known fact that the proper port area variation is nearly sinusoidal. For high efficiencies the operating pressure must be made to approach the peak acoustic pressure and the port area variation must depart widely from a sinusoid if a sinusoidal pressure wave is to be generated.A siren was designed and built to verify the assumptions. The output signal was found to be sinusoidal at the design operating pressure and to depart from sinusoidal as expected at operating pressures either higher or lower. Efficiency at the design pressure was between 35 and 45% which is between 70 and 90% of the theoretical maximum efficiency for a sinusoidal sound generator of the siren type using a dissipative valving mechanism.The derived equation might be used to determine the port area variation of a siren for generating chosen nonsinusoidal wave form by substituting, within limits, the expression for the desired wave in place of the sine function.

ISSN:0001-4966    

DOI:10.1121/1.1907689

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The absorption of sound in blood occurs primarily on a molecular level and is related to the presence of protein in the cells and plasma. However, a small contribution to the total absorption arises simply from the presence of intact cells in the blood.Analysis based on Epstein's theory of scattering shows that the cellular absorption results from a viscous interaction between the fluid and cells when the latter, because of their greater density, fail to follow the oscillatory motion set up by the sound wave.

ISSN:0001-4966    

DOI:10.1121/1.1907690

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP