摘要:

A 3700‐seat, general purpose auditorium was included in the convention center for the City of Austin, Texas. The hall is designed with removable, upholstered seats on the main floor, with the hall opening out into the exhibition area so that the auditorium proper can be converted into a dining area for 5000 people. The acoustical problems in this type of all‐purpose design are discussed and measurements presented on the reverberation time, echo structure, and articulation in the building. Since the auditorium is also used as a concert hall, subjective remarks by various musicians using the building also will be presented. Some particular problems in the use of a large auditorium by Broadway theater casts will also be discussed.

ISSN:0001-4966    

DOI:10.1121/1.1936233

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The results of a study on the properties that influence the performance of acoustical materials at high sound levels is reported. Experimental data for nonlinear acoustic resistance of simple structures such as screens and perforated plates agree well with theoretical calculations. Similar data obtained for more complex structures such as fibrous or cellular materials indicate that in general the performance of an acoustical material at high intensities is determined by the conventional parameters such as its dc flow resistanceR0, applicable at low intensities, plus a resistive term that depends on the particle velocityv. The dynamic flow resistance can in general be described asR = R0(1 + v/vcr), wherevcris the velocity at which the resistance becomes twice the low velocity value. Other properties of several acoustical materials, including dynamic, mechanical, and thermal performance at high intensities, are reported. (Supported by the U. S. Navy Bureau of Ships.)

ISSN:0001-4966    

DOI:10.1121/1.1936241

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Ultrasonic attenuation measurements were made in liquid carbon disulfide over a frequency range from 5 to 155 Mc at a temperature of −63°C. Further measurements were made when methyl, propyl, and butyl alcohol were added in concentrations up to 0.06 mole percent. In each case the relaxation frequency is increased linearly with the amount of alcohol added. The relaxation frequency for pureCS2is 27.8 Mc. The shifts of relaxation frequency in liquidCS2with alcohol added are:methyl alcohol 24.7 Mc/mole percentpropyl alcohol 38.7 Mc/mole percentbutyl alcohol 50.7 Mc/mole percent.The collision probabilities (P) of like and unlike molecules in the liquid as compared to the gas are unexpectedly close, (PAB/PAA)liqbeing approximately 0.65 (PAB/PAA)gas. Possible reasons for this will be considered.

ISSN:0001-4966    

DOI:10.1121/1.2142336

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

By adapting F. A. Angona's [J. Acoust. Soc. Am.25, 1111 (1953)] construction to H. Oberst's [Akust. Z.2, 76 (1937)] method—essentially the Kundt's tube—resonance tubes have been constructed that are capable of going to several hundred atmospheres of pressure at 300°C. The tubes are, conveniently, about 2 ft long with a fundamental frequency of 250 to 300 cps, depending on the gas. By casting the basic tube in a lead or die‐casting alloy jacket the annoying mechanical vibrations of the tubes are suppressed or moved to high frequencies above the region of interest—500 to 10 000 cps. The plane modes are used exclusively, from the 2nd to the 20th harmonic, though the 55th and higher can be recognized and measured. The width of the resonances at the 3 db points is proportional to the absorption, after allowance for the tube effect (Kirchhoff). Relative velocity can, of course, be measured accurately also. The work of H. and L. Knötzel [Ann. Physik2, 393 (1948)] with oxygen has been repeated to test the method, and their results are completely confirmed both as to magnitude of the absorption and the value of the relaxation time. It is intended shortly to apply this method to nitrogen at high temperatures. A minimumf/pof perhaps 1 cps‐atm should be attainable. (Work supported by the Office of Naval Research.)

ISSN:0001-4966    

DOI:10.1121/1.1936323

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Although secondary reasons can be found for the influence of shock and vibration on air‐frame design, the primary current reason is the prevention of structural failure. In attaining such a goal, the primary requirement is to keep the material stresses (sometimes strains) within safe limits. This is accomplished by providing additional material, by using damping or detuning, or by isolation of the source from the structure. To apply these measures rationally, the structural designer must be able to recognize those sources of shock and vibration which are potentially critical and have methods available to analyze their seriousness. This paper reviews those sources now known to be significant, as well as the methods available to determine the degree to which each is critical. The sources considered include landing impact, taxi, gusts, turbulent air flow, rotating and reciprocating mechanisms, and acoustically induced vibration.

ISSN:0001-4966    

DOI:10.1121/1.1936325

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An analytical investigation of the effects of boundaries on the damping of plates by constrained viscoelastic layers has been carried out as an extension of earlier work [E. M. Kerwin, Jr., J. Acoust. Soc. Am.31, 952 (1959)]. It is assumed that the plate is in vibration with straight‐crested one‐dimensional flexural waves. Various geometries of plate and constraining layer are considered: infinite, semi‐infinite, and finite plates; and semi‐infinite and finite constraining layers. Boundary conditions considered are: supported, free, and clamped for the plate, and free and clamped for the constraining layer. By calculating the energy dissipation near the boundary relative to what it would be far from the boundary, a measure of the damping efficiency near the boundary may be obtained. Such energy ratios are presented for the various cases. It is found that the local dissipation near the boundary can be either greater or less than the “far‐field” dissipation. These edge effects occur principally within the first half wavelength from the boundary. Numerical calculations were carried out on a high‐speed digital computer. [This work was supported by the U. S. Air Force, Wright Air Development Center (subcontract from the University of Minnesota), and by the U. S. Navy, Bureau of Ships.]

ISSN:0001-4966    

DOI:10.1121/1.1936333

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A great many underwater acoustic propagation measurements have been made using either sinusoidal acoustic signal generators or explosives which generate very wide‐band impulsive type signals. Because of the extremely different characteristics between the two signals and the fact that the shock wave of the explosive signal does not follow the propagation theory developed, considering only infinitesimal displacements, considerable concern has existed as to whether the results obtained by the two methods are comparable. An experimental study was conducted to compare propagation measurements made using explosives with continuous and pulsed sinusoidal signals. By using available source level values for explosive charges, a comparison is made between the various type signals, and the results are shown to be in agreement within about 3 db.

ISSN:0001-4966    

DOI:10.1121/1.1936338

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The current techniques available for predicting interior noise levels are outlined, and the limitations of these techniques, particularly in their application to future high‐speed aircraft, are discussed. The relative importance of each external noise source is discussed, with special emphasis on the boundary layer, the engines, and the wake. Interaction of the noise sources and the effect of this interaction on interior noise predictions are mentioned—for example, the interaction of the engine noise on the boundary layer pressure field. Also, the anticipated exterior noise levels for future aircraft are estimated. Presented curves, obtained from flight test data, laboratory measurements, and analysis, compare transmission loss through the fuselage side wall (skin plus soundproofing) of a modern transport airplane. In the commentary on these results, an attempt is made to explain the discrepancies between the predictions. The relative merit of each prediction method is discussed, together with that of another method, namely, a boundary layer test facility. In conclusion, the paper contains a brief discussion explaining the influence that aircraft interior noise requirements have on the design of fuselage side walls, including skin gage, damping properties, and stringer and frame spacings.

ISSN:0001-4966    

DOI:10.1121/1.1936344

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A segmentation scheme is being developed to operate as a first step in a general speech recognition program. Input to the segmenter is sampled, quantized spectral data (35 frequency channels scanned every 5.5 msec). The output is a sequence of boundary markers together with a rough classification of the enclosed segments. The segments are generally phonemic, or smaller, in size, and the classification corresponds either to type of phoneme (e.g., fricative, nasal, vowel) or to sound characteristic (e.g., silence, aspiration). The segmenter operates by first classifying each 5.5‐msec scan of the spectral data. This classification is obtained by computing a number of measurements of different attributes of the spectral pattern and combining the results with suitable weighting functions. The number of such measurements is made larger than the logical minimum to avoid placing too much dependence on any one measurement. Segments are then built by grouping together scans which have the same individual classifications. Finally these primitive segments are subjected to an editing process which modifies and merges together certain of the primitive segments according to rules based on length, amplitude, the classification of neighboring segments, etc. The effect of the editing process is to insure that the output segment sequence does not violate any simple articulatory rules for the language. (Lincoln Laboratory is operated with support from the U. S. Army, Navy, and Air Force.)

ISSN:0001-4966    

DOI:10.1121/1.1936353

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The important features of sound spectra of nasal consonants have been examined quantitatively with the assistance of a computer. The computer program (1) allows the experimenter to select the frequencies and bandwidths of poles and zeros of an arbitrary transfer function, (2) calculates the corresponding sound spectrum, (3) provides visual comparison between the calculated spectrum and any given stored speech spectrum, and (4) calculates measures of the goodness of fit of the two spectra. The speech samples were drawn from the materials described in a paper on vowel formants presented at this meeting. In order to match spectra of nasal consonants in the frequency range below 3000 cps, one or two pole‐zero pairs attributable to the closed oral cavity must be used, together with three or four poles. The bandwidths of the poles in nasal consonants are always greater than the bandwidths found in nonnasal vowels. The locations of poles and zeros which give the best match for [m] may vary significantly with vowel environment and may change during the period of mouth closure. Theoretical considerations can explain and to some extent predict these pole‐zero characteristics. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research); and in part by the National Science Foundation.]

ISSN:0001-4966    

DOI:10.1121/1.1936358

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP