摘要:

Mechanical impedance is now being measured by a number of investigators. Since the equipment and procedures used vary considerably, some differences in measured impedances may be expected. The ASA Shock and Vibration Committee has initiated a program to obtain comparisons of impedances on “representative” structures, including several beams, as measured by various investigators. This paper gives preliminary progress of this program; considerations involved in experimental design and in establishing appropriate structures are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1937250

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

In the course of a program to develop a convenient method for transient calibration of accelerometers, a compact shock exciter of fairly novel design was developed. This unit, built around a modified “captive‐bolt” cartridge‐actuated cattle stunner, is useful for applying shock pulses to accelerometers and other small components. The shape of the acceleration curve is approximately a distorted half‐sine pulse with a duration between one and two milliseconds. By varying the powder charge in the cartridge and the mass load on the moving assembly, the peak acceleration can be varied over about a 10:1 range, peak values ranging from about 400 to 4000 g. The corresponding velocity changes range from about 10 to about 50 ft/sec.

ISSN:0001-4966    

DOI:10.1121/1.1937252

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The mechanics and physiology of the hair cells of the cochlea are very difficult to investigate for obvious technical reasons. The hair cells of the lateral line of fish are embryologically and morphologically very similar to the hair cells of the inner ear. The morphological similarity is so close, in fact, that it seems warranted to investigate the hypothesis that all these different hair cells behave physiologically in a similar way. The ear can be thought of as an invaginated lateral line organ with a middle ear of some kind attached to transform pressure waves into volume displacements. We find, however, differences as well as similarities. Morphologically, the lateral‐line organ of the killifish shows a curious polarization: in an oval patch of supporting cells, a strip of hair cells is embedded along the major axis. Physiologically, the organ is directionally sensitive along this axis, too. One remarkable difference is that, although the cochlear microphonic over a wide intensity range is proportional to the oval window displacement, the lateral line microphonic shows a double frequency which is indicative of some type of rectification.

ISSN:0001-4966    

DOI:10.1121/1.1937262

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The boundary conditions at the traction‐free interface of a semi‐infinite elastic cylinder can, with one exception, be satisfied exactly only if an infinite number of modes of propagation is considered. For the low‐frequency range (diameter

ISSN:0001-4966    

DOI:10.1121/1.1937267

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The hot‐wire anemometer was adapted to the measurement of attenuation and phase velocity of sound waves in long capillary tubes in the presence of laminar mean flow. Two hot wires were placed across the inside of the capillary tube at two different locations. One end of the tube was connected to the sound source (a loudspeaker driver), the other end to an air tank and a pump. The air was driven through the tube at variable speeds. The dimensions of the tubes measured 11 to 15 ft long with an inside diameter of 0.030 in. By comparing the two hot‐wire signals, the velocity of propagation and attenuation were measured. The frequency of the generating signal ranged from 100 to 12000 cps. By changing the distance between the two hot‐wire stations, attenuation and phase shift were obtained in function of distance of propagation. For a comparison with theoretical predictions, a theory was developed by using decomposition into modes [L. S. G. Kovasznay, “Turbulence in supersonic flow,” J. Aeronaut. Sci.20(October 1953)]. [This work was sponsored by Project Squid (Office of Naval Research), Princeton, New Jersey.]

ISSN:0001-4966    

DOI:10.1121/1.1937270

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Further developments in a statistical method for estimating vibrational levels of ribbed panels are presented [R. H. Lyon and G. Maidanik, J. Acoust. Soc. Am.33, 1668A (1961)]. Specifically, the radiation resistance of ribbed panels is analyzed as a function of frequency. It is shown that, below the coincidence frequency of the panel, the stringers and frames usually increase the radiation resistance of the panel and, hence, its coupling to the acoustic field. The results of experiments which were conducted to test the theory are reported. The agreement between theory and experiments appears to be satisfactory. (This work was supported by the National Aeronautics and Space Administration.)

ISSN:0001-4966    

DOI:10.1121/1.1937278

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Several types of commercial microphones and their related equipment have been tested in a nuclear reactor to determine the effect of intense nuclear radiation on their performance. In the past, microphones used to measure the sound field near the exhaust of a nuclear reactor have failed to perform satisfactorily due to high radiation levels. In order to obtain meaningful acoustical data during subsequent tests around a similar engine, an experimental study has been made to determine the performance of microphone assemblies while they were exposed to intense nuclear radiation. The subjects discussed in this paper include: (a) description of the test installation; (b) types of tests conducted; (c) types of failures observed in different kinds of microphones; (d) microphones used for this test are rated in the order of their sensitivity to nuclear radiation.

ISSN:0001-4966    

DOI:10.1121/1.1937284

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An analysis of the intrinsic errors of a class of data‐reduction techniques is presented. To obtain wide dynamic range, the logarithm of an incomplete average of a fluctuating quantity is obtained and then fully averaged. This is the process of reading a meter with a logarithmic scale or of estimating the mean value from a recording of fluctuations of the output of a level recorder. The visual averaging has been replaced in an instrumentation concept implemented by D. N. Keast. We present a mathematical analysis. It is shown that the intrinsic errors are a function of the input bandwidth, internal averaging time (that is, prior to taking the logarithm), and the type of detection used. (This work was supported in part by the George C. Marshall Space Flight Center, National Aeronautics and Space Administration.)

ISSN:0001-4966    

DOI:10.1121/1.1937288

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An experiment was conducted, using tones generated by the computer, to determine the just‐noticeable differences in the rise time of a 1000‐cycle pure tone with a duration of 1 sec, and with a linear (not exponential) attack, a steady‐state portion, and a 100‐msec decay. A forced choice, paired‐comparison test was run with 10 different subjects. Fourteen different rise times were used, ranging from 2 to 50 msec. A clear time‐order effect appeared which, although it is of considerable interest in itself, made the results of the test somewhat inconclusive. Still, a rough estimate of the results indicate that, within the range of rise times from 8 to 50 msec, the jnd approximates a constant proportion of a given rise time. Within this range, the smallest ratio of two rise times that can be judged correctly 75% of the time is roughly 3 : 2. Below this range (i.e., from 2 to 6 msec), the smallest difference that can be discriminated is 3 or 4 msec, so that the constant‐proportionality relation no longer holds.

ISSN:0001-4966    

DOI:10.1121/1.1937296

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The problem of scattering of acoustic waves and pulses by fluid spheres immersed in fluid media is investigated for the case where the two media are very similar acoustically. This situation allows Taylor expansions to be used, and the results obtained for back‐scattered plane waves are found to be much simpler than the exact results. The amplitudes and time dependences for back‐scattered acoustic pulses to first order in the approximation can then be calculated. The result of considering higher‐order terms of the approximation has not been fully investigated at this time. In the proper limit. the results obtained in the first‐order approximation are compatible with Rayleigh scattering. but differ in the algebraic sign of the difference in density of the two media with the results obtained using the Born approximation.

ISSN:0001-4966    

DOI:10.1121/1.1937298

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP