摘要:

The attenuation and speed of sound at 11 Mc were measured in pureN2over the pressure range 760 to 1 mm Hg using apparatus previously described. The excess attenuation in the nondispersive (low‐frequency/pressure) region as obtained from 70 measurements made between 80 and 760 mm Hg is(35.88 ± 0.04%)corresponding to a relaxation number of 5.26 collisions. The results will be compared with those of other investigators.

ISSN:0001-4966    

DOI:10.1121/1.1929952

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Amplitude variations in commercial audio oscillators have been found to be of the order of 50 to 60 db below the amplitude of the oscillator fundamental output. In a companion paper these variations are considered with respect to their effect on psychophysical experiments, as in audition. This paper presents a summary of the sources of variation in amplitude and discusses their relative magnitudes and differences in spectra. The quantityN0, noise power per unit band width of white noise, is related to the amplitude spectra of the variations in oscillator output, and the spectral value at the oscillator average frequency is shown to be important as an equivalent noise power per unit band width in psychophysical experiments. Results of typical approximate measurement of this quantity are given. (This work was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center.)

ISSN:0001-4966    

DOI:10.1121/1.1929956

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A procedure for transmitting the letters of the alphabet by tone‐coded signals was examined in quiet and against a noise background. The procedure employed successive selections, each from among a small number of alternatives, in order to transmit a target‐vocabulary of 25 letters. Four stimulus variables: tonal frequency, sound level, location, and duration were examined, one at a time. Successive selections were made among two, three, and five alternatives per variable. With less than 1 min of practice at slow rates of presentation with the two‐alternative frequency code, naive listeners were able to receive the entire vocabulary with insignificant error. The highest transmission rate was obtained with a three‐alternative, frequency‐coded display, at only about 1.5 bits per sec. Transmission of tone‐coded signals in noise was nearly equivalent to that in the quiet, when the tonal signals were about 3 db above masked threshold.

ISSN:0001-4966    

DOI:10.1121/1.1929962

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

It has been found, on the basis of a recent, anticipatedly exact theory of homogeneous turbulence, that the acoustic power radiated at high Reynolds numbers and low Mach numbers is dominated by the high‐frequency contributions from the inertial wave‐number range. The inertial range pressure wave‐number spectrum in the isotropic case has been found to beP(k) = aρ2εv0k−2, where ρ is density, ε is the dissipation rate by viscosity, per unit mass, andv0is the rms turbulent velocity in any direction. The universal numberais determined by the theory. The power spectrum of the inertial range radiation per unit mass has been found to beW(ω) = AM5εω−1, whereMis the Mach numberv0/cand the universal numberAis determined by the theory. The total inertial range radiation power is of orderAM5εlnR02/3, whereR0is the Reynolds numberv04/εν(ν = kinematic viscosity) which characterizes the turbulent macrostructure. In the present paper, an attempt will be made to give an elementary physical interpretation of these results in terms of the dynamical interaction of the sharply defined shear fronts and vortex filaments which make up high Reynolds number turbulence. Some implications for radiation from jets, wakes, and boundary layers will be discussed briefly. (The research described was supported by the Mechanics Branch, Office of Naval Research.)

ISSN:0001-4966    

DOI:10.1121/1.1929970

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The spatial distribution of noise source strength along a jet is investigated theoretically. It is found, in particular, that a “slice” of jet (section between two adjacent planes normal to the axis) in the region of similar profiles downstream of the potential core contributes asx−7, wherexis measured from a virtual origin near the nozzle. Because of this striking attenuation of strength with distance, the “fat” part of the jet may contribute much less to the total noise power than is commonly supposed on the basis of near‐field measurements.

ISSN:0001-4966    

DOI:10.1121/1.1929972

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A new hand instrument, having numerous ultrasonic uses, and operated in the 25 kc/sec range, will be described and shown. This device is entirely portable and features a light weight hand‐piece, which permits quick change of the transducer insert elements, without conventional mechanical attachments. The small electronic generator is of a new type and is semi‐automatic insofar as frequency selection and control are concerned. The operating characteristics of this instrument will be described. Special emphasis will be given to the vibratory properties of the transducer which is utilized to produce simultaneously controlled longitudinal and flexural vibrations. This results in a variety of motions at the instrument's operating end. Practical design considerations led also to a new transmission line for connecting the magnetostrictive transducer to the operative output elements. An elementary coupling theory for the flexual and longitudinal vibrations will be presented in order to account for the elliptical mechanical motions achieved in practice.

ISSN:0001-4966    

DOI:10.1121/1.1929980

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

An investigation has been carried out in connection with fine material of the order of a few microns suspended in water. It was desired to treat approximately 1 200 000 gal per day and to substitute ultrasonic methods for poacher house pits. A bibliography and study of work done to date indicate that no systematic study has been made in this field. Tests were made at cavitation and below‐cavitation levels at several different frequencies ranging from 20 kc to 1 Mc. Breakdown of the fine material into small uniform particles was observed at cavitation levels and agglomeration at levels under those necessary for cavitation. All tests were made on laboratory samples. Every test was repeated a number of times to determine reliability. Results indicate that the method has promise for accomplishing the results desired. [The work was sponsored by Hercules Powder Company and the Radford Arsenal.]

ISSN:0001-4966    

DOI:10.1121/1.1929983

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The methods used in solving the problems related to the interpretation of frequency response curves of large rooms [M. R. Schroeder, J. Acoust. Soc. Am.29, 1258 (1957)] are employed for the computation of the principal parameters of spatial response curves in large rooms at fixed frequencies. The results for the rms response fluctuations and the mean level difference between maxima and minima are the same as for frequency response curves, namely 11 and 10 db, respectively. The mean spacing of adjacent maxima depends upon the dimensionality of the space, the wavelength, λ, and the isotropy of the sound field. The mean spacings are 0.50λ, 0.67λ, and 0.79λ for complete isotropy in one, two, and three dimensions, respectively.

ISSN:0001-4966    

DOI:10.1121/1.1929990

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A discussion on noise caused by the excitation of panels by turbulent boundary layers, commenting upon approaches based on infinite and finite walls, and illustrating the role of cross‐correlation of the pressures at the surface.

ISSN:0001-4966    

DOI:10.1121/1.1929994

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

From the information theory viewpoint, the combined neural and motor mechanisms of speech production serve as the primary information source in oral communication. While extensive studies of motor mechanisms in human physiology have been made during the past decade, there has been little advance in understanding the physiological processes of speech and in the development of instrumental techniques for the study of the physiology of speech. There is at present much opportunity for the development of basic physical theory of speech sound formation and for experimental research with modern electro‐acoustical instrumentation on speech generation. The research opportunities apply to all aspects of speech production, including respiration, phonation, articulation, and nasalization. In such studies, fundamental consideration must be given to the interactions of the mechanical and the acoustical aspects of speech sound production.

ISSN:0001-4966    

DOI:10.1121/1.1930000

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP