摘要:

The feedback mechanism of classical low‐speed edgetones in which the action at the edge is interpreted as an acoustical source is developed in detail. A theoretical development indicating that the acoustic field is primarily due to the dipole associated with the fluctuating fluid force on the edge has been verified. It is the hydrodynamic field of the dipole which disturbs the jet, whose instability characteristics are shown to depend acutely on the Reynolds and Strouhal numbers, and the orifice‐edge distance. The gain criterion is developed in detail, it being shown how the eigenfrequencies (which can form no algebraic sequence) arise; the lower limit to the orifice‐edge distance is discussed, yielding an estimate of the “linear” instability of the stream. The amplitude of the established edgetone depends on the nonlinear behavior of large‐amplitude stream disturbances and the corresponding upper limit to the edge force proves to be in satisfactory agreement with measurements, thus yielding acceptable expressions for the sound pressure. Multiple tones and the circumstances of the hysteretic frequency jumps are discussed. The basic action depends only on Reynolds number for geometrically similar systems, while the sound power depends on the cube of the Mach number also.

ISSN:0001-4966    

DOI:10.1121/1.1908677

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The correlation properties of turbulent wall pressure fluctuations are investigated experimentally with a view toward developing an adequate phenomenological model of the pressure correlation function for use in engineering calculations. It was found that both mean eddy sizes and mean eddy lifetimes determined by averaging over broad frequency bands did not contain sufficient information to accurately describe the high frequency end of the turbulent power spectrum. Thus, such gross quantities are of somewhat limited utility in detailed analysis, for instance, in predicting response of multimodal mechanical systems driven by flowing turbulence. However, by measuring eddy sizes and lifetimes over narrow frequency bands it appears possible to construct mathematical models for the turbulent pressure correlations which are successful in predicting the turbulent power spectrum over the frequency band of interest which could include the entire spectrum. In addition, measurements of rms pressure and space‐time correlations are presented which supplement the data obtained by W. W. Willmarth [NASA Memo. 3‐17‐59 W (1959)] [or a somewhat higher reach range.

ISSN:0001-4966    

DOI:10.1121/1.1908679

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This paper considers some basic problems inherent in the instrumental analysis of intonation. The problems are illustrated by a detailed analysis of one intonation contour in American English. The material studied consisted of two sets of data. The first set involved 1263 sentences recorded by one speaker with determined stress and pitch patterns. The sentences consisted of 1263 CNC words produced in an identical frame, with primary stress and the peak of the intonation contour occurring on the CNC word in the frame. The second set of frame sentences involved a subset of 70 minimally different words, uttered by five different speakers of the same general dialect. The fundamental frequency values for the various levels of the intonation contour were measured from narrow‐band sound spectrograms and the measurements were correlated with the segmental phonetic structure of the sentences in which the intonation contour was produced. The intrinsic fundamental frequencies of the various syllable nuclei and the influence of preceding and following consonants are described. The relationships among successive intonation levels are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908681

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This paper describes two IBM 704 EDPM programs which were written to aid in the development of mechanical speech recognition devices. Both are based upon multivariate statistical techniques. It further describes the application of the two programs to the problem of vowel recognition using fundamental frequency and formant information.

ISSN:0001-4966    

DOI:10.1121/1.1908683

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The propagation of elastic pulses in wires of circular cross section has been studied for conditions in which pulses having carrier frequencies ranging from 0.5 to 4.0 Mc were transmitted in wires having diameters between 0.1 and 0.2 cm. The pulses used in the experiments were shaped to have relatively narrow frequency spectra. At certain frequencies, herein called critical frequencies, pulses propagating in certain modes were observed to undergo pronounced distortion in which the peak amplitude of an affected pulse was reduced and the duration of the pulse was increased many times its original length. This pulse distortion associated with the presence of critical frequencies is shown to be caused by coupling between two modes of propagation. In agreement with predictions of the general theory of mode coupling, the critical frequencies are frequencies at which two modes of propagation have the same phase velocity.

ISSN:0001-4966    

DOI:10.1121/1.1908685

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A cylindrical wave reciprocity parameterJc = (2/ρc) (Rλ)12Lfor use in a standard reciprocity calibration when the waves between the source and receiving transducers are cylindrical is derived from both four‐terminal network theory and wave propagation theory. Experimental data from calibration measurements on underwater sound line transducers are presented to prove the validity of the parameter.

ISSN:0001-4966    

DOI:10.1121/1.1908687

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The effects of a strongly refracting summer thermocline on the initial pressure pulse from an underwater explosion were accurately measured in a flooded quarry. The familiar exponentially decaying pulse shape was observed to be drastically altered in highly divergent regions of the field. Closely spaced measurements permitted these shape changes, as well as the increased amplitude and decreased time constant in a caustic region, to be followed continuously from the source. It is presently impossible to compute the observed pulse shapes although measured shock pressures agreed well with ray‐theory predictions except near the caustic. Measured travel time differences between initial arrivals and both second direct arrivals and surface reflections agreed quite exactly with predictions.

ISSN:0001-4966    

DOI:10.1121/1.1908689

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The high intensity and low distortion of underwater acoustic signals propagated to convergence zones justifies a comprehensive description and an effort toward better organization of pertinent and related information. Convergence zones are the result of SOFAR Channel propagation from shallow sources to shallow receivers. The acoustic paths are analogous to those of skip‐wave radio transmission. Although only illusive references exist in the open literature, there have been experiments showing as many as thirteen well‐formed zones spaced over a 400 mile range interval. The propagation is quantitatively predictable, and quite stable. Convergence of acoustic energy along caustics results in losses smaller by about 20 db than those encountered in a free field.

ISSN:0001-4966    

DOI:10.1121/1.1908691

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This paper demonstrates by theoretical and numerical examples that in the calculation of ray‐theory intensities in an underwater sound field the use of constant gradient layers can introduce spurious caustics and in some cases can omit real caustics. The theoretical intensity is discontinuous and becomes zero for a ray which is horizontal at any layer interface where the slope of the velocity‐depth function is discontinuous, not only for constant gradient layers but for any function which might be used to approximate the profile. If the slopes as well as velocities are continuous at a layer interface, the intensity will generally be continuous. The use of curved line segments preserving both velocity and slope continuity in the profile approximation is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1908693

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The Tanglewood Music Shed, a large fan‐shaped hall seating 6000 people indoors (approximately 6000 more can be accommodated outdoors on the lawn) was modified in 1959 to improve the acoustics. The acoustical qualities that were to be improved included sectional balance for large orchestra, balance between orchestra and soloist, clarity of music inside the hall, and loudness of music on the lawn. The architectural solution was the design of an orchestra enclosure and a canopy over the orchestra and the front part of the audience. Also, a 14‐ft high chamber music orchestra enclosure was installed in 1960. This paper discusses the details of the construction and presents comments by musicians and listeners following its completion.

ISSN:0001-4966    

DOI:10.1121/1.1908695

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP