摘要:

A program for segmentation of an acoustical continuum of speech sounds into discrete parts suitable for further analyses is described. The speech wave is read into the computer using an A‐D converter. Analysis is performed directly on the acoustic waveform, using an IBM‐7090. The pattern‐recognition techniques used to segment the acoustic waveform into sustained and transitional parts are discussed. Some results obtained by the computer program are given.

ISSN:0001-4966    

DOI:10.1121/1.1910071

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Ultrasonic absorption measurements have been made in benzene over the frequency range from 7 to 570 Mc/sec at 6° and 25° C. Velocity measurements at both ultrasonic and hypersonic frequencies also were made in the temperature range 6°–60°C. The observed relaxation effects may be interpreted in terms of double relaxation of the vibrational specific heat. Analysis of the absorption data indicates that the vibrational specific heat associated with all but the lowest vibrational mode relaxes in the ultrasonic range, with the measured relaxation frequency varying from 510 Mc/sec at 6°C to 560 Mc/sec at 25°C. Correlation of the ultrasonic and hypersonic data also indicates a second relaxation frequency (associated with the lowest vibrational mode) of the order of 10 Gc/sec.

ISSN:0001-4966    

DOI:10.1121/1.1910072

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The temperature and velocity of a particle suspended in an acoustic field are subject to fluctuations that may lag behind those of the surrounding fluid. A theory for acoustic attenuation and dispersion in an aerosol based on these particulate‐relaxation processes is given. The close relationship between particulate relaxation and relaxation mechanisms due to lagging molecular or atomic internal degrees of freedom is displayed. The particulate‐relaxation theory predicts attenuation and dispersion by small, heavy particles, in close agreement with existing, more‐detailed theories, for values of ωτd, (ω is the circular acoustic frequency, τdis the dynamic relaxation time of the particle) smaller than and including order unity. Comparison with existing experimental data of attenuation and dispersion [J. W. Zink and L. P. Delsasso, J. Acoust. Soc. Am.30, 765–771 (1958)] shows good agreement. However, the existence of a maximum attenuation per wavelength, when ωτd≈ 1, that is predicted by the theory is not tested by the above experiments, which were conducted with ωτd>1. Similarly, the maximum dispersion that occurs at the low‐frequency limit was not tested in the previous experiments.

ISSN:0001-4966    

DOI:10.1121/1.1910073

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The exact series solution for the scattering of a plane wave by hard spheroids is used to obtain explicit long‐wavelength approximations in powers ofk= 2π/λ, where λ is the wavelength. The far field scattering amplitude is given to the sixth power ofkand the nearfield is given to the second power. The results are valid for prolate and oblate spheroids and arbitrary angles of incidence and observation.

ISSN:0001-4966    

DOI:10.1121/1.1910074

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The response of a fluid‐filled waveguide with perfectly rigid or pressure‐release boundaries and uniform cross section to acoustic transients propagated down the axis of the guide is studied. Exact solutions are obtained for step‐function and gated sine‐wave excitations of the source. The particle velocity resulting from the latter input can be written as the sum of the familiar steady‐state solution and a transient signal composed of two Lommel functions. An approximate expression is obtained that allows quantitative estimation of the behavior of the first portion of the transient as a function of the dimensionless parameterzλ/a2, whereais the radius of the waveguide,zis the distance that the transient has traveled, and λ is the free‐field wavelength associated with the carrier frequency of the gated sine wave. Some experimental confirmations of the predicted waveforms are presented. The relevence of these propagation effects on the accuracy of velocimeters is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910075

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The basic equations for axisymmetric, nontorsional vibration of a spherical shell in an acoustic medium are obtained by the use of Lagrange's equations. Dynamic displacements and the pressure in the fluid were obtained for the case of forced motion of the shell under a harmonic, concentrated force.

ISSN:0001-4966    

DOI:10.1121/1.1910076

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The sound field of a circular piston in an infinite rigid plane baffle is calculated when the motion of the piston consists of the conventional uniform velocity normal to the plane of the piston plus a wobbling motion about a diameter of the circle: as an axis. There is a net resultant moment owing to the wobble; this moment is proportional to an integral of the square of the farfield pattern function over real and imaginary angles. A wobble impedance is defined as the moment divided by the angular velocity of the wobble. The real part of the wobble impedance is obtained from the integral of the square of the farfield pressure over real angles, and the imaginary part is obtained from the real part by the use of the Kramers‐Kronig, or dispersion relations. Numerical results for the wobble impedance are presented. It is shown that for small pistons a merely wobbling piston is less efficient as a generator of sound than the customary uniform‐velocity piston.

ISSN:0001-4966    

DOI:10.1121/1.1910077

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The acoustic system studied is that of a plane, rigid wall having a circular window in it, across which is stretched a membrane under tension, in contact with an acoustic medium on both sides. A plane wave of frequency ω/2π is directed at one side of the wall plus membrane, at an angle of incidence θ. The integral equations relating the motion of the membrane and the pressure difference across the membrane are obtained. Fairly accurate solutions to these two equations are then obtained by a variational procedure. Values of the functions involved are plotted and tabulated. Formulas are derived for the total power transmitted through the membrane and for the distribution in angle of the transmitted wave; typical plots are given of the results. These are discussed to demonstrate the contribution of the membrane resonances and anti‐resonances to the transmitted wave. It is known that an unbounded membrane is transparent to an incident plane wave when the wavenumber of the transverse wave in the membrane is equal to the component of the incident wavenumber parallel to the membrane. The solution for the transmission through a membrane of finite size, obtained in this paper, shows how the resonances and antiresonances, typical of the finite membrane, radically modify the transparency effect.

ISSN:0001-4966    

DOI:10.1121/1.1910078

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

In this paper, a convenient method is presented for obtaining a closed‐form (not series) solution for solving the problem of free vibrations of a partially fixed beam, with unequal end fixities, and carrying an arbitrary number of concentrated masses in an arbitrary way. The method utilizes finite Fourier sine transforms. By this method, the simplified frequency equations to a general case and two special cases are given. The eigenfrequencies of a partially fixed beam (equal end fixities) with a mass in the middle and at quarter‐span are evaluated numerically; and the results of the former are compared with those of an earlier publication, where the classical method is utilized.

ISSN:0001-4966    

DOI:10.1121/1.1910079

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The partial‐differential equations derived by Reissner, Uflyand, and Mindlin governing the motions of plates are solved for a plate bounded by circular contours and radial lines. Two cases have to be considered. They are:Case I:a plate bounded by circular contours and radial lines (r=r1,r=r2,r2>r1; θ = θ1, θ = θ2);Case II:a plate bounded by two concentric circles (r=r1,r=r2,r2>r1… circular ring). The solution for each partial‐differential equation is an infinite series of product solutions. Case I cannot be solved by product solutions because of the impossibility of satisfying boundary conditions along the radial lines θ = θ1and θ = θ2. Case II is solved for each of the eight different boundary conditions entering into this theory for each eigenvaluem= 0, 1, 2, … Hence, after the elimination of the arbritrary constants form= 0, 1, 2, …, the frequency equation for each problem is obtained by solving a determinant of sixth order equated to zero. A comparison between the classical theory and the present theory, which includes coupling between flexural and shear motions, for the case of the clamped circular ring is included.

ISSN:0001-4966    

DOI:10.1121/1.1910080

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP