摘要:

A procedure has been developed for recognition of spoken digits by means of digital computer simulation. Using power spectra computed at 10‐msec intervals, the words are segmented into vowels and consonants. Vowels are then classified into one of 11 categories by a multivariate statistical decision method operating on approximations of the measurements. Consonants are classified into one of three categories by means of an empirically derived decision tree. Recognition is then performed by means of a dictionary search. When tested on a sample of 493 words spoken by 50 speakers, and with the internal dictionary adjusted for optimum results, 97% of the words were identified correctly. It appears that this procedure is more tolerant of interspeaker variations than those previously reported.

ISSN:0001-4966    

DOI:10.1121/1.1909006

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An experimental study was made of the mechanism by which the ultrasonic vibration of liquid surfaces causes atomization.At exciting frequencies in the range of 10 to 800 kc, uniform patterns of crossed capillary waves were found on the liquid surface when atomization occurred. The number‐median diameter of the particles produced was found to be a constant fraction, 0.34, of the capillary wavelength; the capillary wavelength is calculable by Kelvin's equation using the exciting frequency and properties of the fluid being atomized.The evidence is strong that the mechanism of ultrasonic atomization involves the rupture of capillary surface waves and the subsequent ejection of the wave peaks from the surface as particles.

ISSN:0001-4966    

DOI:10.1121/1.1909020

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An extensive theoretical treatment is presented of the problem of plane progressive sound waves (simple waves) produced by continuous, high‐amplitude motion of a piston in a lossless, semi‐infinite tube. The fluid in the tube is assumed to be nondissipative; liquids as well as perfect gases are considered. The analysis is given in both Eulerian and Lagrangian coordinates. Earnshaw's exact solution in parametric form is first given for arbitrary piston motion. Special attention is then given to the case of sinusoidal piston motion. Approximate but explicit power‐ and Fourier‐series solutions for this case are derived from the exact solution. Alow‐amplitude nonlinear theory of simple wavesis proposed. In this theory nonlinear effects are considered in a simple yet general manner.A brief analysis of shock formation is also given. It is shown that the generally accepted formula for the distance at which the shock forms when the piston motion is sinusoidal is rigorously correct only under very special circumstances.

ISSN:0001-4966    

DOI:10.1121/1.1909033

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An rf pulse system is described for investigating progressive distortion of finite amplitude waves propagating in liquids. The system employs pulses short enough to avoid reflections but long enough to approach continuous wave conditions. A 25‐Mc quartz crystal backed by fused quartz serves as a nonresonant receiver for the first few harmonics of the 2.58‐Mc working frequency. Harmonic content is determined by Fourier analysis of waveform photographs, or by use of a heterodyne analyzer having bandwidth adequate to pass the pulse envelope. For an initially sinusoidal wave of 3.0 or 6.0 atm pressure amplitude in water, curves are shown tracing the decay of the fundamental and the growth and decay of harmonics through the fourth, to a propagation distance of 40 cm. Results are in good agreement with published theory within the region of convergence of the latter.

ISSN:0001-4966    

DOI:10.1121/1.1909008

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Pochhammer's method of analysis for waves in circular cylinders is extended to Biot's theory for an elastic porous solid saturated with a compressible viscous fluid. Attention is given mainly to slender rods vibrating at low frequencies. The boundary condition of zero stresses on the curved cylindrical surface is used to derive the frequency equation from which phase velocity and attenuation may be obtained. In general, two types of extensional waves exist, just as there are two types of dilatational waves. The attenuation per unit length of the first kind of wave is proportional to the square of the frequency at low frequencies except when the wavelength of dilatational waves of the second kind is about half the perimeter of the cylinder. In the neighborhood of this frequency the attenuation may show a maximum. Waves of the second kind behave like a diffusion phenomenon, except in the same neighborhood.

ISSN:0001-4966    

DOI:10.1121/1.1909010

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The classical Euler beam equation is modified by introducing a hysteresis damping term which is proportional to the strain but which is in phase with the strain velocity. General solutions are obtained for the cantilever, clamped, and pin‐supported beams whose supports are moved by a prescribed function of time. For sinusoidal vibration of the support, the analysis of a cantilever beam is compared with experiment and with the corresponding solution in which the damping is proportional to the rate of strain as formulated by Sezawa. The hysteresis type damping gives results closer to the experimental values than Sezawa's method. The shear stress and displacement in a cantilever beam whose support falls on an elastic platform are investigated. The analysis is applicable to clamped and pin‐supported beams by substituting the appropriate resonant frequencies and eigenfunctions. Simple formulas for dynamic load factors at the resonant frequencies are found by comparing the maximum displacement or shear stress of the beam under sinusoidal vibration of its supports with the corresponding displacement or shear stress for a static loading under a centrifugal acceleration of the same amplitude as the sinusoidal acceleration. Rice's theory of random noise is applied to the response of the beam on a support vibrating in a random manner.

ISSN:0001-4966    

DOI:10.1121/1.1909012

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The dynamic mechanical properties of rubberlike materials have been briefly reviewed. The value of a mounting composed of a low‐ and a high‐damping rubber in parallel is in this way made apparent. Expressions have been derived from which the ability of the so‐called parallel mounting to isolate vibration from any nonrigid foundation may be determined, if the mechanical impedance of the foundation is known.One‐ and two‐stage mounting systems have been considered. To compare their performance, the mechanical impedance of a damped beam has been employed to simulate the behavior of a nonrigid foundation. It is shown that the parallel mounting suppresses resonant motion at the natural frequencies of the foundation and the mounting systems with similar effectiveness to the high‐damping rubber, yet provides the greater isolation at other frequencies. The isolation afforded by the mounting is, in fact, often comparable to that which the low‐damping rubber affords.

ISSN:0001-4966    

DOI:10.1121/1.1909014

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A theory is presented which enables the computation to be made of 200‐ to 3000‐cps bottom reverberation returning from very great ranges in shallow water. Typical computed curves are presented for reverberation level vs range/water depth. Computed curves are presented for scattering strength vs range/water depth. These later curves are presented for both the isospeed and negative sound‐speed gradient cases.

ISSN:0001-4966    

DOI:10.1121/1.1909016

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The fluctuation of the received sound for frequencies of 350, 700, 1200, and 2400 cps was studied for transmission over flat 60‐fathom sand and 50‐fathom sandstone bottoms out to ranges of 15 miles. The received sound fluctuated over a range of 50 db. In general, the amplitude distribution was neither Gaussian nor Rayleigh. No significant correlation was found between the outputs of the receiving hydrophones which were separated vertically by 90 or more feet. The frequency was spread due to transmission and the relative powerPis related to the half‐width of the spectra|f − f0|from 350 to 2400 cps byP = bf0|f − 0|−3, whereb = (7.7±0.8)×10−6 (cps)2for the sand bottom and(3.9±2.7)×10−6 (cps)2for the sandstone bottom. Special measurements indicated no significant asymmetry between the spectra abovef0from that belowf0.

ISSN:0001-4966    

DOI:10.1121/1.1909018

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The average frequency spacing 〈Δfmax〉 between adjacent maxima of the frequency response curve between two points in a room is determined by experiment, theory, and Monte Carlo computation. In earlier papers it had been shown that, above a certain critical frequency, 〈Δfmax〉 is reciprocally related to reverberation time and not dependent on other room characteristics—disproving a belief that 〈Δfmax〉 is a useful measure of the acoustical quality of rooms. Theory predicts〈Δfmax〉 = 3.91/T60, whereT60is the reverberation time. Monte Carlo computation gives 3.90/T60. Measurements in two very different rooms using a vacuum tube voltmeter for reading the sound pressure are in good agreement with these predictions. Measurements with a logarithmic level recorder give, as in earlier investigations, much larger values. The discrepancy cannot be explained by the level recorder's 0.5‐db quantization. This paper shows that: (1) The Monte Carlo method is a useful tool for solving complex problems in room acoustics. (2) Level recorder measurements of frequency (or space) irregularities of rooms must be taken with several grains of salt.

ISSN:0001-4966    

DOI:10.1121/1.1909022

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP