摘要:

The Zwislocki theory of temporal summation was tested for vibrotactile sensitivity. Vibrotactile thresholds were determined as a function of pulse repetition rate and pulse number for short pulses. Thresholds for various burst durations of sinusoidal signals were also determined. The results indicate that the theory is sufficient to predict vibrotactile thresholds for the temporal patterns used. An earlier finding, which suggested that glabrous skin contains at least two populations of mechanoreceptors, was confirmed by using contactors of varying size.

ISSN:0001-4966    

DOI:10.1121/1.1909458

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Utilizing a simplified equivalent circuit for an electroacoustic transducer with a single resonance, it is shown that the mean‐square thermally generated noise voltage for the entire frequency range is justkT kc2/C0, wherekis the Boltzman constant,Tis the Kelvin temperature,kcis the effective electromechanical coupling coefficient, andC0is the clamped capacitance. This voltage is generated by the mean total thermal energykTin the circuit, which results from the circuit's two degrees of freedom. From impedance measurements on a transducer with two pronounced resonances, it has been shown that this relationship, with some modifications, approximates the conditions existing in a transducer with multiple resonances. Expressions for the equivalent noise pressure of a transducer and applications to the measurement of low‐level signals with a resonant transducer are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909460

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The elements that are important in the identification of the violin, viola, 'cello, and bass‐viol tones were analyzed. These elements were found to be the harmonic structure of the middle portion of the tone; the harmonic structure of the ending portion of the tone (certain partials decayed rapidly leaving an afterring); the attack and decay of the tones; the vibrato (when present) of the tones; and the noises inherent in the mechanics of producing the tones. With the exception of vibrato, the important elements were determined and successful synthesis was accomplished. By the use of a jury of observers, identification tests were made. A successful description was arrived at when and only when synthetic tones could not be identified from real tones. It was found that there is a vibrato both in frequency and relative intensity.

ISSN:0001-4966    

DOI:10.1121/1.1909462

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A number of methods are described for increasing the sensitivity of a measuring technique that has proven to be particularly useful for determining 3rd‐order moduli and other quantities from measured changes in ultrasonic delay times [J. Acoust. Soc. Am.33, 12 16(1961)]. Pulse cancellation, phase comparison, and methods involving either pulse position or frequency modulation have been examined. Two of the circuits developed are amenable to automatic frequency control, with precisions better than one part in 106.

ISSN:0001-4966    

DOI:10.1121/1.1909464

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The problem called “high‐frequency combustion instability in rocket motors” has been considered to be one in which the acoustics of the combustion chamber, nozzle, and flame front are significant for determining whether or not a motor will experience pressure oscillations of an acoustic type. To date, no theory has been developed for demonstrating the effects of the location and width of the flame front in the combustion chamber upon the occurrence of pressure oscillations of the longitudinal mode. In this paper, the rocket motor is treated as a constant‐diameter duct with a finite width of combustion zone located between two uniform regions. It also is considered to have finite wave‐transmission coefficients at the nozzle and the injector ends. For these conditions, stability criteria are established for the longitudinal mode of pressure oscillations. It is shown that, while the energy release rate per unit width of the combustion zone is significant in determining whether the motor will be stable, the location of the combustion zone in the motor, the over‐all length of the motor, and the total amount of energy released also influence the stability of the motor in the longitudinal mode.

ISSN:0001-4966    

DOI:10.1121/1.1909466

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An experimental investigation was made to determine the mechanical radiation impedance of a rigid piston on the surface of clay soil. The force on and the velocity of the piston were measured to determine both the real and imaginary parts of the radiation impedance as a function of excitation frequency of the piston. Measurements were made for six different combinations of moisture and density of the soil, and results of these measurements are presented in graphical form. In the frequency range 50–200 cps, the load presented to the piston by the soil is essentially the same as would be presented by a mechanical compliance, the value of which varies with both moisture and density of the soil. The value of this compliance was computed for six different combinations of moisture and density. Second‐order dependence of compliance on moisture and density was assumed, and coefficients in a second‐order equation relating compliance to moisture and density were computed. The three‐dimensional surface that represents this equation is presented in graphical form. Errors in the results are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909468

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This paper complements an earlier study of refracted/bottom‐reflected rays by the author and considers surface‐reflected/bottom‐reflected transmissions in a model ocean having a horizontal surface and bottom and sound velocity that decreases linearly with depth. The case of increasing velocity is implicit since transmissions in media with velocity gradients +gand −gare geometrically equivalent. The paper is concerned primarily with an analysis of spreading loss. General expressions are derived for spreading loss, range, and travel time, and the problem of multiple arrivals at a fixed receiving point is examined. The spreading loss along a ray is considered in detail after the ray has experienced many reflections. Detailed results are presented for the case of a bottomed source and receiving point, and these are compared with the corresponding results for refracted/bottom‐reflected transmissions.

ISSN:0001-4966    

DOI:10.1121/1.1909470

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A recent theory for the prediction of the pressure field produced by an impulsive sound source in a fluid overlying an elastic solid layer that rests on a solid half‐space is extended to include the effects of an air‐fluid boundary above. Experimental‐model data are presented to support the theoretical results. It is felt that this extension will aid in the application of the theory to problems of sound propagation in shallow water.

ISSN:0001-4966    

DOI:10.1121/1.1909472

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The wave solution for sound transmission through an air‐water interface is given. Numerical computations are presented for a point directly below the source and compared with the ray‐theory solution. The general wave solution for shallow water, treating the bottom as a semiinfinite fluid layer, is also presented.

ISSN:0001-4966    

DOI:10.1121/1.1909474

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Discrete‐frequency tones can be generated when objects obstruct the path of an axially symmetric jet. An experimental study of this phenomenon was conducted when the objects were (1) a flat plate perpendicular to the jet axis, there being a hole in the plate of the same diameter as the jet orifice and concentric with the jet, and (2) a ring whose plane was perpendicular to the jet axis and whose diameter was equal to that of the jet orifice. The tone from the former geometry is the hole tone and that from the latter, not previously observed, is the ring tone. The mechanism of tone generation appears to be very similar to that of the edge tone, although presently only qualitative explanations can be offered for certain aspects of the phenomena. The axially symmetric jet systems are sensitive to very weak acoustic reflections.

ISSN:0001-4966    

DOI:10.1121/1.1909476

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP