摘要:

In the analysis of the absorption characteristics of a porous layer with perforated facing, it is usually assumed that the facing contributes only a mass reactance to the total impedance. In the present paper it is shown that the facing also causes an additional acoustic resistance which is often larger than the acoustic resistance of the porous layer itself. This resistance obtained only when the porous material is in close contact with the facing and becomes practically zero when the air space between facing and material exceeds approximately one perforation diameter. The effect is due to the near field (higher mode) losses in the porous material around the perforations. The resulting effect on the absorption characteristics considerable, as demonstrated in some examples, and may at least partly explain reported disagreement between measurements and previous calculations.

ISSN:0001-4966    

DOI:10.1121/1.1907299

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The information transmission associated with elementary auditory displays consisting of a large number of independent stimulus aspects, e.g., the frequency or the sound level of a tone, was examined. In general, multiple stimulus encoding is a satisfactory procedure for increasing the information transmission associated with elementary auditory displays. Further, extreme subdivision of each stimulus aspect fails to produce substantial improvement in the information transmission.

ISSN:0001-4966    

DOI:10.1121/1.1907300

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Calculations based on the usual one‐dimensional theory of piezoelectric crystal systems have been carried out for several particular variable resonant frequency crystal systems radiating into water. Curves are presented showing the (1) power output as a function of frequency for operation both on and off resonance, (2) resonant frequency shift as a function of backing length, and (3) relative band width as a function of frequency. The validity of certain approximations is checked so that the operating characteristics of systems made up of different materials can be quickly estimated. The curves indicate that a variable resonant frequency system of crystals all of equal free‐free resonant frequency operating with an allowable power variation for fixed applied field strength of 2:1 can have a continuous variation of resonant frequency of about 2.3:1. A system half the crystals of which have twice the free‐free resonant frequency of the others for the same allowable field strength variation can operate over a frequency range of about 5.3:1.

ISSN:0001-4966    

DOI:10.1121/1.1907301

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The resonant frequency for the lowest mode of a circular plate is calculated for the conditions of concentrated mass loading at the center, water loading on one side, simply supported and clamped at the edge. These results are compared with those of Lamb and others.

ISSN:0001-4966    

DOI:10.1121/1.1907302

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Most investigations of the sound field of a moving source deal only with point sources. We have examined the sound field of finite sources, moving with constant velocity. The simplest possible vibrators have been chosen,viz., a pulsating circular cylinder and a pulsating sphere. The solution is an infinite series in terms of Mathieu functions in the two‐dimensional case, and in terms of prolate ellipsoidal functions in the three‐dimensional case. Besides the rigorous solutions, asymptotic formulas valid for large distances away from the source are given.

ISSN:0001-4966    

DOI:10.1121/1.1907303

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A theory is presented for the self‐maintained transverse oscillations which arise in a low‐velocity jet as it plays upon an obstacle, thus generating edge tones. It is assumed that transverse forces act on each particle of the jet as it travels toward an obstacle, and that this force is due to “sources” of hydrodynamic origin localized near the obstacle. The law of motion is set up in the form of an integral equation involving unknown functions for the force field. It is shown that a number of important properties of jet‐edge systems, and of the edge tones they produce, can be deduced from the equation, even for highly simplifying trial assumptions about the unknown functions.

ISSN:0001-4966    

DOI:10.1121/1.1907304

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The limitations imposed upon the usual elastic and viscoelastic constants are reinvestigated. Defining viscoelastic properties of a higher order, it is found that methods which have been used for the first‐order quantities are insufficient to determine relationships between the higher‐order constants. Necessary but non‐sufficient criteria are arrived at by means of arguments involving energies in dissipative processes.

ISSN:0001-4966    

DOI:10.1121/1.1907305

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The coefficient of variation for a series of sound pulses and the correlation function for successively received sound pulses are evaluated for arbitrary pulse length, using the assumption that the correlation function of the refractive index inhomogeneities is expressible as the product of time‐ and space‐dependent functions. For the case of pulse length much less than the time constant of refractive index correlation function, the coefficient of variation is found to be independent of the pulse length, and the pulse‐correlation function is found to be identical with the time‐dependent part of the refractive index correlation function. Comparison is made with data obtained from Sheehy. An approximate calculation shows that the motion of source and receiver will distort the pulse‐correlation function so that little information can be obtained from the data concerning the time dependance of the refractive index.

ISSN:0001-4966    

DOI:10.1121/1.1907306

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The reflection of a plane wave at a rough interface separating two fluid media is examined in the approximation of “small roughness,” such that second‐order terms in the magnitude of the roughness may be neglected. Exact solutions are obtained when the roughness is harmonic, while asymptotic results are obtained for arbitrary distributions. The analysis deals principally with an incident wave that is harmonic in time, but the problem of the reflection of a pulse from a perfectly reflecting, sinusoidal boundary is solved. It is found that such a boundary acts as a band‐pass filter of the nonspecular components of the reflected wave. Outisde of this pass band the reflection is not only specular but distortionless. Rather less generality is possible when the boundary is not perfectly reflecting, but the pass band is found to be independent of the properties of the reflecting medium.

ISSN:0001-4966    

DOI:10.1121/1.1907307

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The propagation of dominant mode plane sound waves within a cylindrical tube having arbitrary cross section and extending indefinitely from an open end is studied theoretically. A quantity of special interest is the end correction, which characterizes the reflection coefficient at wave lengths large compared to the transverse tube dimensions. The reflection coefficient and end correction fit naturally into a boundary value formulation of the wave propagation problem, whose solution hinges on that of one or more integral equations. Since the integral equations do not in general admit of exact solution, practical techniques for approximately determining the physical quantities are important. Among these are the stationary or variational principles, which can be cast into a variety of independent forms, corresponding to the different nature of boundary distributions. Another technique is based on initial modification of an integral equation so as to utilize the possibility of explicit and rigorous solution. Approximate forms of the reflection coefficient and end correction are obtained in this manner, with the distinction of yielding exact results when the tube cross section is circular. A brief comparison of the different procedures is included.

ISSN:0001-4966    

DOI:10.1121/1.1907308

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP