摘要:

Acoustics and noise control has received considerable attention in the various segments of the power industry. In fact, the power industry has contributed significantly to the development of noise control technology. However, as in other industries, the challenge is to bring the right knowledge to bear on the problem at the right time. This communication challenge and the role of the acoustical consultant serving the power industry is discussed.

ISSN:0001-4966    

DOI:10.1121/1.2016911

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In order to apply engineering controls to a noise source it must first be identified. This can be a problem in the power plant environment where a source may dominate in one band and not in others. The problem is complicated by the directivity of the various sources such as fans, ducts, and machinery. A technique of generating sound level contours using relatively large numbers of measurement locations has been developed and aids in source identification. Using a high speed computer to display the sound levels in each frequency band allows the engineer to pinpoint the dominant sources and their frequency. The method is suitable for octave, third‐octave or narrower bands; several examples are given. Extensions including automation using computer controlled graphics are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.2016914

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The single element unidirectional microphone exhibiting the Limaçon directional patternm+ (1 −m) cos θ was an accidental discovery during an effort to develop a bidirectional piezoelectric microphone, affirming the research director's lament that the best inventions are those leading into unexpected directions. Refined through equivalent circuit analysis and embodied in many configurations this principle over the years has been employed in many important and interesting microphone applications in Public Address, Broadcasting, Recording, and others. The theory and some of the most important configurations and applications of this principle are described.

ISSN:0001-4966    

DOI:10.1121/1.2016917

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Acoustical holography is being considered for quantitative studies of acoustic source distributions. We examine the quantitative significance of images reconstructed using the holographic technique described by R. L. Cohen in Pennsylvania State University Applied Research Laboratory Tech. Memo. 76‐05, Jan 1976, for sources distributed over a plane surface. The image is formed by measuring the magnitude and phase of the sound pressure due to the sources on a parallel hologram plane and then calculating values of a Helmholtz integral of these pressures for field points located on the original source plane. Values of this integral form the reconstructed image. If the source and hologram planes are many wavelengths apart, this image represents a pressure distribution over the source plane which is nearly identical to the radiating, low wavenumber portion of the original pressure distribution on the source plane. The original pressure distribution may contain nonradiating high wavenumber components which are attenuated in the reconstructed image. To provide insight for understanding reconstructed images, the radiating portion of the pressure distribution is exhibited for point sources and for a finite circular membrane vibrating in an infinite rigid baffle. The radiating portions of these distributions differ considerably from the total pressure distribution for these sources.

ISSN:0001-4966    

DOI:10.1121/1.2016920

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The third‐order elastic constants of 26 cubic crystals and two mixed crystals belonging to octahedral class have been evaluated from the available literature data on the hydrostatic pressure variation of the corresponding second‐order constants using the method elaborated [O. H. Prasad and M. Suryanarayana Acustica38, 192–193 (1977)] wherein the third‐order constants can be evaluated without any reference to uniaxial stress measurements. The evaluated third‐order constants for each of the crystals are used in the well‐known equations [W. P. Mason and T. B. Bateman, J. Acoust. Soc. Am.36, 644–652 (1964)] to obtain the 39 mode gammas all of which add up to give the Gruneisen parameter γ of the crystal in question. The correctness of the evaluated parameters is verified by evaluating the thermal expansivity α of each crystal using the familiar equation connecting α with γ The crystals studied are NaCl, NaBr, NaF, LiF, KCl, KBr, KI, KF, RbCl, RbBr, RbI, AgCl, AgBr, MgO, CsBr, Nb, Fe‐α, Ag, Cu, Au, Al, Ge, Si, ZnSe, ZnTe, RbAg4I5, and mixed crystals AgCl‐AgBr and KCl‐KBr near room temperature and in a few cases at different temperatures and pressures.

ISSN:0001-4966    

DOI:10.1121/1.2016924

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Measurements were made of the cavitation threshold for polypropylene glycol and for castor oil in a cylindrical resonator at approximately 16.5 kHz. The threshold for degassed castor oil was ∼233 dB//iμPa peak, in agreement with the measurements of Briggs, Johnson, and Mason [J. Acoust. Soc. Am.19, 661–664 (1947)]. Degassed polypropylene glycol exhibited wide variability in threshold, with an initial value ∼240 dB//1μPa peak, dropping quickly to values ∼225–228 dB//1μPa peak. Partial restoration to higher values could be attained after a five‐hour rest period. [Work supported by Naval Sea Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.2016929

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Constrained layer damping treatments, consisting of alternate layers of viscoelastic and elastic materials, are being widely used in industry for vibration and noise control. Many efforts have been made over the past two decades to apply diverse mathematical techniques to the analysis of the dynamic response of various structures with such treatments added, either on the surface, or incorporated into the fabrication of the structure. It remains true, however, that the now classical equations of Ross, Kerwin, and Ungar (RKU) are the simplest, most readily used, and often the most reliable approach toward making such predictions, even in spite of the fact that the equations apply only to beams or plates with pinned edges. While these equations are strictly limited to this type of boundary conditions other classical boundary conditions have commonly been accounted for simply by defining an appropriate modal semiwavelength in terms of the eigenvalue and the actual length. This seems to work quite well in most cases, but breaks down quite badly for the fundamental mode of a cantilever beam. This is particularly unfortunate, since cantilever beams are becoming very widely used for measuring the damping properties of viscoelastic materials. The aim of this paper will be to (i) discuss the derivation of equivalent modal wavelengths for nonpinned boundary conditions; (ii) describe the reduction of data from tests on cantilever and clamped‐clamped beams with multiple layer damping treatments added in order to determine equivalent free layer properties; (iii) use the equivalent free‐layer approach and the RKU approach to predict modal damping of some particular structures, making use of given complex modulus properties of the materials selected for the viscoelastic layers, and compare the two analyses with measured results; and (iv) discuss a computer program to optimize the geometry of constrained layer treatments for beams of various cross sections and for plates.

ISSN:0001-4966    

DOI:10.1121/1.2016941

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Velocity‐sensitive phonograph cartridges can be very useful for vibration measurements on light structures where accelerometers present too much mass loading. This paper describes how stereo phonocartridges may be calibrated and used to measure in‐plane (horizontal) and also transverse (vertical) motion. Topics of discussion include frequency response, dynamic range, proper mounting methods, and calculation of the effect of the stylus impedance on vibration of beams and plates. Data from measurements on several different structures is included.

ISSN:0001-4966    

DOI:10.1121/1.2016944

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

There were 48 “sentences” (e.g., “LAS a BAS a LAS, a GAS a LAS a PAS” or “KAS a LAS a PAS, a LAS a BAS a LAS”) each pronounced with a slight phraselike boundary after the fifth syllable. Four groups of practiced subjects pressed a reaction‐time (RT) button to their assigned segmental target /b, d, g, or k/ which occurred equally often in syllables one, three, five (first phrase), seven, nine or eleven (second phrase). The decrease in target RT as a function of time into the sentence was not monotonic. Instead, target RT decreased successively within the first phrase, but increased after the boundary before decreasing again within the second phrase. This “scallop” effect suggests a relative discontinuity across boundaries in both production and perception. Phrases are units in the sense that articulatory‐acoustic sequential redundancy (correlation) is higher within that between phrases. In perception, such redundancy facilitates increased ease in “tracking” the successive syllables in a phrase until the boundary is reached. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2016948

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Various task constraints were imposed on subjects making same/different, AX discriminations within and between phonetic categories. The experiments employed four 50‐ms, synthetic vowels from an/i/‐/I/continuum and five interstimulus delays (0‐2000 ms). In the first experiment, stimuli were presented with all trial types randomized together or with between‐ and within‐category shifts in separate trialblocks. Between‐category performance was superior with separate blocks, whereas within‐category performance did not differ in the two procedures. A second experiment involved AX presentations to subjects who were or were not initially informed of the intended category labels. Surprisingly, category knowledge improvedwithin‐categorydiscriminations. In a third experiment, subjects were required to identify both vowels in an AX pair. Between‐category discrimination was higher, and within‐category discrimination lower, with AX identification as compared to a same/different response. The results of these experiments suggest that a stable phonetic and an unstable auditory short‐term memorybothcontribute to within‐andbetween‐category discrimination, with some labeling occurring on a comparative basis. Furthermore, task demands alter the relative contributions of auditory and phonetic memory.

ISSN:0001-4966    

DOI:10.1121/1.2016956

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP