ISSN:0001-4966    

DOI:10.1121/1.1906857

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906858

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906860

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In a previous paper a method of direct ultrasonography was developed. This paper deals with recent experiments on indirect ultrasonoscopy and ultrasonography mainly using special phosphors. The actual technique involved in the new methods is discussed and their results illustrated by lantern slides.

ISSN:0001-4966    

DOI:10.1121/1.1917410

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

During the course of some experiments on listening by bone conduction, the author noticed an increase in the pitch of a pure tone in the middle audiofrequency region when a pure tone of lower frequency was sounded, and the qualitative results of several ensuing experiments were reported in a letter to the editor. The work to be described here dealt with the rise in pitch of a pure 2000-cps tone in the presence of a broad band of thermal noise and also in the presence of pure tones of lower frequency. All sounds were presented by bone conduction using the air and bone conduction audiotesting assembly developed at U.C.L.A. The results of extensive tests on one observer are presented as well as the results of pitch rise tests on several different listeners. All listeners had normal hearing as indicated by audiograms and otological examinations. It was found that the pitch of the 2000-cps tone rose with increasing level of the disturbing sound and that the greatest pitch rise occurred just before the pure tone was masked. Individual differences were evident among listeners. The effect on the pitch of the 2000-cps tone of clenching the teeth is discussed for one observer. A tentative explanation of the phenomena is given.

ISSN:0001-4966    

DOI:10.1121/1.1917418

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

For some time, engineers making noise measurements have required increasingly versatile equipment. The sound-level meter has been supplemented by accessories to meet this need, but it has frequently been a limiting factor in the over-all performance. To remedy this condition a new sound-level meter has been developed. It not only meets the standard specifications but also has the high fidelity range from 20 c to 20 kc necessary for utilization of modern microphones. The stabilized amplifier with wide dynamic range and separate output system supplies a signal suitable for frequency analyzers, high fidelity tape recorders, or level recorders. Miniaturization has led to a compact, light instrument. Many applications, however, can be handled by a simple noise meter and are economically feasible only if a low cost instrument is available. To meet this need a companion instrument, the sound-survey meter, has been developed, whose performance closely approximates that of standard sound-level meters but with simplified operating features. Its diminutive size and good characteristics make it ideal for many tests and survey measurements. With this low cost instrument available, more people will make acoustic measurements, which result should ultimately lead to more widespread understanding and better handling of acoustic problems.

ISSN:0001-4966    

DOI:10.1121/1.1917423

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Sounds in the low audiofrequency region produced by marine life have been recorded at the U. S. Navy SOFAR Station, Kaneohe Bay. The SOFAR hydrophones are located at a depth of 2100 feet on the eastern underwater slope on the island of Oahu. These sounds have levels of the order of 1 microbar, and many have a rather musical quality. There is a marked seasonal variation in the production of these sounds, with the early spring months being the period of most frequent occurrence. This variation is coincident with the seasonal variation of whales in the area, and this feature, plus the characteristics of the sounds themselves, has led to the belief that they are produced by whales—with possibly an assist or two from porpoises. The sounds are described, and information is presented on their spectrum, sound level, and frequency of occurrence.

ISSN:0001-4966    

DOI:10.1121/1.1917427

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Transmissibility data are presented for steel and copper manganese helical springs. It is shown that for frequencies 10 to 30 times the resonant frequency of the spring-mass system, wave phenomena are important and that due to the low damping of the metals, the isolation mount may amplify the force felt by the foundation at the standing wave resonances rather than reduce it. It is shown that several modes of vibration are possible and that a one degree of freedom treatment of the problem is inadequate. The effect of coupling between the modes is discussed. Improvement of the isolation properties by coating the springs with highly viscous materials is demonstrated. It is further demonstrated that if sufficient damping is added, the value of critical coupling exceeds the actual coupling between the modes and in this case the system resembles a one degree of freedom system.

ISSN:0001-4966    

DOI:10.1121/1.1917433

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The possible modes of vibration of a rod under conditions which are intermediate between a perfectly flexible string and a stiff bar have been calculated from existing general theory. An experimental investigation of the first ten modes yields results in agreement with the theory with in approximately 0.5 percent Deviation from a harmonic series increases with the number of the mode of vibration.

ISSN:0001-4966    

DOI:10.1121/1.1917444

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

This paper considers the propagation of a plane elastic pulse through a nonhomogeneous, elastic, and isotropic medium. The inhomogeneity is represented as a constant velocity gradient (caused by changes in the elastic properties) which is assumed to be parallel to the direction of propagation of the pulse. It is shown that it is impossible to transmit a “clean” pulse through such a medium—the disturbance will have a definite onset, but will be followed by a train of slowly decaying oscillations. The period of these oscillations is related to the existing velocity gradient. The case of a reflection from a free boundary normal to the velocity gradient is considered in detail and it is shown that the motion imparted to the boundary will not be a replica of the motion in the incident pulse.

ISSN:0001-4966    

DOI:10.1121/1.1917449

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP