摘要:

The problem of steady‐state sound scattering by an infinite elastic circular cylinder is treated by performing a Sommerfeld‐Watson transformation on the normal‐mode series. The complex velocities of the ensuing circumferential waves are found by obtaining zeroes of a 3 × 3 determinant in the complex plane, identical to that used by Goodman and Grace in the theory of free vibrations of an elastic cylinder. We find numerically two kinds of zeroes: (α) Franz‐type zeroes, similar to (and for aluminum cylinders, almost identical with) those appearing in scattering from rigid cylinders; (β) Rayleigh‐type zeroes, as found by Goodman and Grace, which for large cylinders tend to the Rayleigh and Stoneley wave velocities, and which enter the cylinder surface at a certain critical angle. These two types correspond to the “diffracted” and the ordinary surface waves conjectured by Keller and Karal. We also consider the causality relations of sound pulses and show mathematically that they lead to arrival times in accord with the (complex) ray paths of Keller's theory. Finally, the trajectories of the zeroes in the complex plane for variations ofkaand the group velocities of circumferential sound pulses have been obtained.

ISSN:0001-4966    

DOI:10.1121/1.1910757

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Surface‐reflected/bottom‐reflected ray transmissions in a divergent channel are studied when the sound velocity decreases linearly with depth. The sound source and receiving point are located on the bottom. Under certain simplifying assumptions, ray geometry is examined, and conditions are given under which a ray is surface reflected, refracted, or a combination of these. Expressions are developed for travel time and geometrical spreading loss. For an isovelocity medium, initial ray angle, travel time, and spreading loss of individual arrivals are examined as functions of bottom angle. These quantities are shown to be greater for a divergent channel than for a horizontal channel. Assuming a CW source and Rayleigh reflection theory, the total field at a receiving point is determined. It is found that the variation in intensity values decreases with increasing bottom divergence.

ISSN:0001-4966    

DOI:10.1121/1.1910745

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The theories developed by Rayleigh, Marsh, and Kuo are applied to the problem of determining the acoustic field generated by a vibrating boundary. A special case, the noise field generated by a vibrating sonar dome, is formulated and solved. An investigation performed by White is identified as a special case of the general formulation. This general formulation is such that a vast number of varied problems can be solved.

ISSN:0001-4966    

DOI:10.1121/1.1910758

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The directional response of a two‐ or three‐dimensional point array is a function of two independent directions and also a function of frequency. A suitable mapping of these three parameters into a pseudodirection and a pseudofrequency allows the examination of the major and minor lobe structure of the array response with only a two‐parameter computation. This method has been applied during the design of a 32‐element planar array, to permit adjustment of the element positions for a minimum and uniform minor‐lobe structure.

ISSN:0001-4966    

DOI:10.1121/1.1910759

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The mechanisms underlying compressor noise radiation are reviewed in detail with particular emphasis on potential methods for compressor noise reduction. It appears that many independent methods of reducing compressor noise are possible, so that large (20–30 dB) reductions of noise radiation may be practicable. Analyses of the effects of rotor‐stator spacing and duct‐mode directivity are presented. It is concluded that an increase in the number of rotor blades may be desirable from several points of view.

ISSN:0001-4966    

DOI:10.1121/1.1910760

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Subjects compared the apparent repetition rates of trains of dichotically alternating clicks, presented at 1–40/sec, with the apparent rates of monotic trains. All dichotic rates were underestimated, the degree of underestimation varying from a few percent at 1/sec to 35%–40% from about 7.5/sec onward. The latter rate corresponds to the switching rates producing minimal intelligibility of speech presented alternately to the two ears. Unlike the results of switched‐speech experiments, however, the present results appear to be unequivocally interpretable as indicating a difficulty in integrating dichotically alternating inputs into a single percept.

ISSN:0001-4966    

DOI:10.1121/1.1910761

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Four subjects were run in a 2IFC psychophysical study in auditory masking. The signal consisted of a 100‐msec tone burst delivered in phase to the two ears. Signal frequencies between 250 and 4000 Hz were used. The masking noise had spectrum levels of 45, 25, and 15 dB SPL. For each signal frequency, the signal level was found that producedP(c) of 0.54 in wide‐band noise at each spectrum level. The high‐ and low‐frequency cutoffs of the noise were then varied independently (band limited), and changes in detectability were observed. Detectability remained constant until the cutoff of the noise was raised or lowered to a critical value; from that point on, detectability improved. The function traced by improvement in detectability represents the “critical band” for the stimulus conditions used. The width of the critical band was directly related to stimulus intensity for all signal frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1910762

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The validity of a previously introduced psychophysical method of numerical magnitude balance is discussed. The method is applied to loudness scaling at low sound frequencies. The results are shown to agree with loudness‐matching data obtained in several investigations.

ISSN:0001-4966    

DOI:10.1121/1.1910763

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Certain psychophysical procedures assume that successive responses are statistically independent. A method for testing the validity of this assumption using the up‐down procedure is described. Two identical up‐down strategies are run concurrently. Observations for each strategy are interleaved according to a rule designed to produce a large difference between the resulting estimates should a sequential dependency exist. The null hypothesis that no dependency exists is postulated, and the two estimates are compared for differences significantly larger than could have occurred by chance. The experiment reported here was designed to test the possibility that responses of the same type are more likely to follow in sequence than would occur with statistically independent judgments. The masked threshold for a 250‐Hz tone in wide‐band noise was measured for five subjects on three separate occasions. Two of the five subjects showed a small but consistent difference between the two concurrent estimates, indicating a slight tendency for like responses to follow in sequence. The technique of interleaving by rule may also be of value in measuring hysteresis effects and in detection‐theory experiments, where it may be possible to discriminate between sequential effects influencing the subject's sensitivity and those affecting the subject's choice of criterion.

ISSN:0001-4966    

DOI:10.1121/1.1910764

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Marill's expression for the psychometric function generated by pure tones in noise, and based on ideal detection, is shown to be obtainable directly from energy fluctuations of a narrow‐band noise. The formula is then generalized to wide‐band noise. Estimates of effective bandwidth using detection data are reexamined in the light of such findings.

ISSN:0001-4966    

DOI:10.1121/1.1910765

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP