摘要:

In some studies of the reflection of sound from submerged models, the sound intensity has been displayed graphically as a function of both frequency and angle. With the frequency swept repeatedly over a chosen range while the angle is swept only once through its range, the intensity is mapped on anXYplotter as a raster of lines varying in width, much as a picture is produced on a TV screen. Many of the patterns obtained in this way exhibit ripples that bear no obvious relation to the expected patterns. The particularly striking ripples observed for reflection from a plate with a corrugated surface led to a study of the reflection from arrays of parallel rods. The ripples are shown to be related to the moiré patterns familiar in optics but have some features that are usually absent from optical demonstrations. Like their optical counterparts, the acoustic moiré patterns may be useful in measuring strains or certain types of displacements.

ISSN:0001-4966    

DOI:10.1121/1.3437247

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A series of photographs displaying sound wave space patterns, made with a sound field scanner at Bell Laboratories, was first shown publicly to the Acoustical Society of America at its 40th Meeting, November 1950, by Kock and Harvey [J. Acoust. Soc. Am.23, 149(A) (1951); Bell Syst. Tech. J.30, 564–587 (1951)]. Because of renewed interest, the scanning techniques are recalled with regard to the mechanics of motion, the registration of the photographic image, the calibration of the gray scale and the electronics needed to delineate the amplitude and phase patterns. The initial pictorial results are presented from examples on file, including some not previously given. (More displays from later experiments are described by W. E. Kock in a following paper.) In addition, a 16‐mm film loop portraying a progressive wave in transit through a focal area is shown.

ISSN:0001-4966    

DOI:10.1121/1.3437256

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The scanning technique of the previous paper permits the visual observation, by photographic recording, of the two basic phenomena of holography, namely, wave interference and wave diffraction. Examples are presented and discussed to explain both the hologram concept and the recent medical development in acoustic holography which provides a real‐time, x‐ray‐like visual presentation of bone structures and tumors in the human body. [References: the author's books,Seeing Sound(Wiley, New York, 1971);Lasers and Holography(Doubleday, New York, 1969); andAcoustic Holography, in the forthcoming Vol. 10 ofPhysical Acoustics(Academic, New York).]

ISSN:0001-4966    

DOI:10.1121/1.3437257

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The author has previously derived an effective‐stiffness velocity‐corrected theory of laminated composite plates based upon a microstructure plate theory developed by C. T. Sun. The velocity‐corrected effectivestiffness plate theory is now used to study the flexural and extensional vibrations of simply supported rectangular plates; comparisons are made to similar results obtained from a reduced effective modulus or transversely isotropic plate theory. In each instance, free vibrations are assumed and a corresponding set of dimensionless differential equations and boundary conditions is found. Frequency equations for simply supported edges are developed by passing solutions harmonic in both length and width through the differential equations while at the same time automatically‐satisfying the boundary conditions for simple supports. The variation of dimensionless frequency for such dimensionless variables as number of layer pairs, width‐to‐thickness ratio, elastic ratio, width‐to‐length ratio, thickness ratio, and density ratio is presented graphically and discussed in detail. Also, comparisons of the effective stiffness and effective modulus frequencies are made for each of the varied dimensionless parameters.

ISSN:0001-4966    

DOI:10.1121/1.3437265

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

This talk describes the present state of performance of the HEARSAY system. [For more complete descriptions of the system see D. R. Reddy, L. D. Erman, and R. D. Neely, “A Model and a System for Machine Recognition of Speech,” IEEE Trans. Audio Electroacoust. AU‐21, 229–238 (1973) and D. R. Reddy, L. D. Erman, R. D. Fennell, and R. B. Neely, “The HEARSAY Speech Understanding System : An Example of the Recognition Process,” Proc. 3rd Int. Joint Conf. on Artificial Intelligence (Aug. 1973)]. The system uses task and context‐dependent information to help in the recognition of the utterance; this system consists of a set of cooperating parallel processes, each representing a different source of knowledge (e.g., acoustic‐phonetic, syntactic, semantic). The knowledge is used either to predict what may appear in a given context or to verify an hypothesis resulting from a previous prediction. Performance data of the system on several tasks (e.g., medical diagnosis, news retrieval, chess, and programming) will be presented. For example: The voice‐chess task contains a 31‐word vocabulary with about 5 000 000 possible sentences. One particular set of data contains 19 utterances of three to nine (mean =4.5) words each. Seventy‐nine percent of the utterances are correctly recognized (at about four times real time on a PDP10 computer); removing the semantic source of knowledge (but leaving the syntactic and acoustic‐phonetic) reduces recognition to 42%.

ISSN:0001-4966    

DOI:10.1121/1.3437267

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An automatic algorithm is described for locating the endpoints of an utterance which has been digitized using adaptive, differential coding techniques (ADPCM) [P. Cummiskey, N. S. Jayant, and J. L. Flanagan, Proc. IEEE Int. Coram. Conf., Seattle (June 1973)]. The ADPCM coder operates at a 6‐kHz sampling rate, and adaptively quantizes the speech using four‐bit samples (the code words). Since the ADPCM coder effectively has an automatic gain compression and expansion or companding feature, it is possible to distinguish between silence and speech by simple measurements on the code words. In the actual implementation of the endpoint location algorithm, a threshold is set on the energy in the code words. The beginning of an utterance is defined as the time at which the code word energy exceeds the threshold for a fixed duration. The end of an utterance is defined as the time at which the code word energy falls below the threshold for another fixed duration. Extensive testing of the algorithm on single words and phrases, spoken in isolation, gave essentially perfect results as determined by both auditory and visual examination of the speech data. For the same corpus of data, other standard measures of the beginning and end of an utterance, such as speech energy, differentiated speech energy, and energy in the quantizer step size, gave far worse results.

ISSN:0001-4966    

DOI:10.1121/1.3437272

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Comparison of actual pronunciations of words with dictionary entries is used to study possible occurrences of phonological rules in continuous speech. We have been concerned with the collection of phonological rules and with rule testing techniques to ascertain the statistical counts for the number of times a rule has or has not occurred in recordings of natural speech. The preliminary investigations at this time indicate some of the complex relations that need to be studied in dictionary processing and the application of phonological rules for automatic speech recognition. [The research is supported by the Office of Naval Research, Contract N00014‐73‐C‐022L]

ISSN:0001-4966    

DOI:10.1121/1.3437277

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Studies of dichotic fusion suggest that “language‐bound” (LB) subjects perceive speech sounds through the abstract linguistic structure of their language, while “stimulus‐bound” (SB) subjects can set aside linguistic rules and make accurate judgments about nonlinguistic events. In the present experiment, subjects of both types were asked to scan a matrix of letters in all directions in order to find words that exemplify a particular theme, e.g., musical instruments. SBs consistently found more words. Perhaps SBs simply have better spatial abilities, since the task requires scanning in eight directions. An alternative view is that the groups have comparable spatial abilities, but that LBs are preoccupied with linguistic operations: given a string of letters, they translate it into “phonetic sense” no matter what direction they happen to scan. For example, the highly pronounceable string TENIPS may obscure the fact that SPINET is spelled out in the reverse direction. Hence the two groups may differ in the relative amount of work performed by the two cerebral hemispheres: SBs are free to rely on right‐hemisphere (spatial) operations to conduct an efficient scan, while LBs are more restricted to left‐hemisphere (linguistic) operations and hence spend less time in effective scanning.

ISSN:0001-4966    

DOI:10.1121/1.3437285

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A free‐field measuring technique for determining the absorption characteristics of an absorbent material at oblique incidence has been investigated. This method, developed by Ingard and Bolt, compares the pressure and phase of an approximately plane wave measured as a function of incident angle at a point on the surface of the absorbent material to a similar measurement with a reflecting surface. From these results, the impedance and absorption coefficient can be determined as a function of incident angle. Measurements were made with the sample mounted on a 6‐ft2panel and with a smaller panel. The results indicated a low‐frequency limit for measurements that was inversely proportional to sample size and a problem of possible diffraction from the edges that made phase measurements difficult. The characteristics of several fibrous absorbents of the Owens Corning 700 fiberglass series were measured and compared with impedance tube measurements. These results were compared with calculations based on derivations by Pyett and Monna for porous layers of absorbent materials. Several recommendations are made on the measuring technique of Ingard and Bolt and factors to be improved upon are also listed. [This work is supported under NSF Grant No. GK‐32584.]

ISSN:0001-4966    

DOI:10.1121/1.3437289

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Self‐generated noise due to flow over acoustic treatment diminishes its effectiveness. A formulation of noise generated by flow over the treatment and its effect on linear performance based in part on J. E. Ffwocs‐Williams's analysis [“The Acoustics of Turbulence Near Sound Absorbent Liners,” J. Fluid Mech.51, Part 4 (Feb. 1972)] are presented and compared with measurements.

ISSN:0001-4966    

DOI:10.1121/1.3437291

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP