摘要:

The acoustics in space, apart from the obvious function of communication has branched out into many other areas of applications. The acoustical positioning device developed at JPL for manipulating and controlling liquid systems in a 0‐genvironment has the potential of becoming one of the most versatile tools for space research and applications. For example, in order to study the liquid drop systems originated from the Newton—Cassini controversy experimentally, we need a free suspended liquid drop without any dense medium surrounding it. Hence, both the 0‐genvironment and the acoustic manipulation chamber appear to be necessary. In order to carry out many of the processes for Material Science Laboratory in Space the melt is to be positioned and formed within a container but without making contact with the container walls. Electromagnetic methods of positioning and forming are limited to melts which are electrically conducting. The acoustical method is useful in the control of any moltem material including material that is electrically nonconducting. In this presentation, I will describe the principle of operation of this apparatus and the results of tests both in our laboratory and in the 0‐genvironment provided by the Johnson Space Center aircraft flights.

ISSN:0001-4966    

DOI:10.1121/1.2003223

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Experiments performed summer 1976 in an anechoic chamber at NASA Langley Research Center consisted of (1) diffraction around screen from point source not necessarily far from edge, (2) such diffraction when air is blowing parallel to screen sides with diffracting edge as trailing edge, (3) diffraction of noise from a jet of air exiting on one side of a thin screen, and (4) diffraction of sound around a barrier with curved top with radius of curvature larger or comparable to an acoustic wave‐wavelength. These experiments were prompted by problems of assessing effects on aircraft noise when engines are mounted above wings. Accompanying theoretical work consisted of (1) generation of a convenient rapidly convergent numerical integration method for computation of Green's function given arbitrary sources and listener locations near a rigid wedge and (2) extension of Candell's solution of plane wave diffraction by screen in presence of ambient air flow to the point source case. [Work supported by NASA Langley Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.2003226

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The Standard Light Rail Vehicle (SLRV), currently being produced in quantity for Boston and San Francisco, has been designed to stringent interior and wayside noise criteria. The articulated joint in the carbody required an unusual design to reduce acoustic flanking paths. The average carbody transmission loss exceeded 30 dBAfor the roof and sidewalls and was 35 dBAfor the floor. The carbody design resulted in an interior noise level of 75 dBAat 40 mph, whether operating at grade or underground. Equipment noise levels were generally below 65 dBAat a distance of 15 ft from the track centerline. Acoustically damped wheels eliminated squeal on curves and resulted in 40‐mph pass‐by noise levels of 70 dBAat a distance of 50 ft from track centerline. Considerable appeal is expected by transit patrons, when the cars are introduced into revenue service.

ISSN:0001-4966    

DOI:10.1121/1.2003233

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Aerial noise measurement methods may be well suited to the determination of spatially averaged traffic noise exposure levels, and could possibly be used as a means of assessing the long‐term effectiveness of motor vehicle noise regulations. In this study two theoretical models are developed for some specific aerial measurement situations. Several characteristics of the models are examined. Limited experimental measurements agree well with theoretically predicted results; elevated measured noise levels are nearly proportional to the density of the traffic (in vehicles per unit area) on the city streets.

ISSN:0001-4966    

DOI:10.1121/1.2003236

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A “curvilinear wedge” finite‐element has been developed which is broadly applicable to the family of transducers variously classified as “flextionsional” [G. A. Brigham and L. H. Royster, J. Acoust. Soc. Am.46, 92(A) (1969)]. The essential aspects of the direct development of the finite element in cylindrical coordinates are presented, with emphasis on advantages over elements employing polynomial mappings. The resolution of the problem of infinite energy density at the coordinate singularity is effected under conditions sufficiently general for the solution of problems arising in the mathematical modeling of flextensional transducers. Results for the short‐circuited normal modes are presented for Class II, Class IV, and Class V configurations and compared to experimental and other analytical results for these transducers. Good agreement of the predicted spectra with reported experimental data is found. It is demonstrated that constraints in interface compatibility specifications in multicomponent models may produce large errors and involve generally untenable assumptions.

ISSN:0001-4966    

DOI:10.1121/1.2003238

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Comparisons of the temporal patterns of pairs of syllables differing only as to presence versus absence of a particular consonant suggests that the temporal effect of the consonantal articulation is not necessarily either additive or simply related to the duration of the acoustic segment conventionally associated with the consonant. In a study of such temporal effects, various monosyllables were embedded in turn in a short carrier sentence, and each version of the sentence was read 30 times at a carefully controlled tempo by one speaker. Durations of segments, syllables and breath‐groups were measured from oscillograms, and least pairs, e.g.,sayversusslay, compared. It appears that final stop or final nasal lengthens both syllable and breath group by an amount roughly equal to the durations of the corresponding acoustic segment; an initial stop, liquid or aspirate induces no appreciable lengthening, other segments in the syllable being sharply reduced; and initial /s/ lengthens the syllable breath group by an amount approaching the duration of the fricative segment the durations of the other acoustic segments being slightly reduced. It is hoped that these results will contribute to more adequate synthesis by rule. [Work supported by NIH and VA.]

ISSN:0001-4966    

DOI:10.1121/1.2003246

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Text consists of structured content. Do readers reflect that structure in their production? A system is under design to map the content pattern of a given text, sentence by sentence, thus locating major and lesser topic boundaries. The system depends on word frequency and distribution in that text, and on the recognition of synonyms and other forms of reference, which establish links betwen text segments. Acoustic tools help to identify significant variations in reading performance, and these can then be interpreted in terms of the text structure. Material for the present paper consists primarily of four passages, each read by three speakers; about an hours' reading in all. The passages are structurally independent excerpts from much larger works. All of the sentences were randomized together and read as one list, and then each passage was read in original form. A study based on duration measurements, indicates clear agreement among speakers as to the locations where reading speed changes occur: e.g., in sentences of transition between major topics, and at points of salient semantic shift. However, the nature of the change increase or decrease in speed is highly speaker dependent.

ISSN:0001-4966    

DOI:10.1121/1.2003250

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Ninety‐six normally hearing children (24 each at ages 11, 13, 15, and 17 years) were individually administered the Speech Perception in Noise (SPIN) Test (see preceding paper by Kalikow, Stevens, and Elliott) at signal‐to‐noise (SIN) levels of 5, 0, and −5 dB in counterbalanced order and in quiet. Their task was to repeat the last word of each sentence. Average performance of the 17‐year old Ss was very similar to performance of adults on all conditions. An age effect appeared in the results for the high‐predictability sentences at 0‐dB S/N level, with younger Ss showing poorer performance. This age effect was specific to the listening‐in‐noise condition, since the 11‐year‐old Ss demonstrated perfect or near perfect scores when later tested in quiet. Implications of these findings will be discussed and the results of testing some children with learning disabilities will also be presented. [Supported by a grant from B.E.H.]

ISSN:0001-4966    

DOI:10.1121/1.2003255

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Diagnosing the condition of a machine by its vibration signature has a great deal of appeal. The problems that have been encountered in its widespread use involve the availability of analysis equipment and the skill of the data analyst. Combining a real time analyzer with a computer can process a great amount of data quickly and reduce the drudgery of analysis. Single‐frequency Fourier component calculation may easily be made in the computer and can take the place of tracking filters and phase meters. This ability to process, store, and recall data quickly, coupled with the ability to program a computer to recognize basic problem symptoms, is making automated signature analysis for machine diagnostics possible, Hardware and software examples demonstrating this capability are presented to support the conclusions.

ISSN:0001-4966    

DOI:10.1121/1.2003261

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Vibration response signals containing periodic components such as obtained from rotating equipment, gears, etc., can be effectively analyzed in the frequency domain. The averaging of spectra wherein the Fourier transform operation is synchronized with a particular periodic component, will reinforce that frequency component and all of its harmonics, while all nonsynchronous data will tend to be nonreinforced, thereby enhancing the synchronous spectral components. Features such as gear teeth and turbine blade passing frequencies, etc., and their related sidebands, can be extracted as signatures for baseline comparison and fault evaluation. This paper will discuss signatures obtained from averaged spectra and the related set of synchronous spectra; i.e., a synchronous average spectrum for each periodic component of interest.

ISSN:0001-4966    

DOI:10.1121/1.2003269

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP