摘要:

Transfer functions measured by near‐field acoustical holography (NAH) are used to simulate the sound radiated by a point‐driven, fluid‐loaded, cylindrical shell with spherical end caps in the time domain for a variety of force inputs. This paper represents a continuation of work described in an earlier paper [J. Acoust. Soc. Am.90, 1656–1664 (1991)]. Radiated sound energy from the shell as a function of force time duration and time separation between multiple pulses in a force is studied. A single pulse consists of a single frequency cosine wave that is Gaussian windowed. A multiple pulse consists of several equally time spaced single pulses. As the time duration of force pulses or spacing between force pulses is varied, the fraction of input mechanical energy which is radiated as sound to the far field varies greatly. For example, as the time separation varies between two pulses in a single force time history, the fraction of sound energy radiated to the far field varied from one third to three halves of the sound energy radiated if the force time history were a single pulse. A frequency domain model is used to explain the variation. Since input mechanical energy is either absorbed by the shell or radiated as sound, the results show that it is possible to force more energy to be mechanically damped in the shell by adding a second pulse to the force, reducing the amount radiated as sound. These properties are noticed when results are observed in the time domain while also considering the frequency domain model.

ISSN:0001-4966    

DOI:10.1121/1.410441

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The problem of acoustic harmonic radiation from a fluid‐loaded infinite cylindrical elastic shell subjected to arbitrary loading is addressed using three‐dimensional elasticity theory. The classical integral transform technique is used to derive a formal expression for the radiated pressure in the fluid. This expression is then evaluated for the observation point in the far field using the standard stationary phase method. The general formulation is then applied for a special case of a fluid‐loaded shell excited by a harmonic ring drive. Numerical results over a wide range of parameters are presented for the far‐field directionality patterns for a steel shell immersed in water. The results are presented as a function of the excitation frequency of the ring drive, the relative thickness of the shell, and the circumferential mode number. The characteristics of the directionality patterns are then related to the wave field on the shell–fluid interface.

ISSN:0001-4966    

DOI:10.1121/1.410443

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

This experiment examines the effects on modulation discrimination interference (MDI) of differences in level between the signal and masker carriers. The task was to detect a change in depth of amplitude modulation of a 1‐kHz signal carrier, in the presence of modulated or unmodulated masker carriers that were either reasonably close to the signal carrier frequency (540 and 1380 Hz) or distant from it (230 and 3300 Hz). The relative level of the signal and masker carriers was systematically varied. The results show that modulated maskers can impair the detection of changes in modulation depth even when the maskers are distant in frequency from the signal carrier and 30–40 dB lower in level than the signal carrier. The magnitude of the interference effect changes only slowly with relative level of the signal and masker carriers, suggesting that the interference depends primarily on across‐channel processes.

ISSN:0001-4966    

DOI:10.1121/1.410444

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

As everyday practice as well as laboratory experiments have shown abundantly, the hearing aid falls short in eliminating the difficulties of many subjects with sensorineural hearing losses in understanding speech in noise. The attempt by Lee and Humes to demonstrate the opposite with only 11 spondees as speech material does not alter this situation. As far as their experiment allows any conclusion, it supports the view that the speech‐reception threshold of hearing‐impaired listeners is characterized by a distortion factor as well as an attenuation factor.

ISSN:0001-4966    

DOI:10.1121/1.410445

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

In his commentary on our recent evaluation [L. W. Lee and L. E. Humes, J. Acoust. Soc. Am.93, 2879–2885 (1993)] of Plomp’s speech‐reception threshold (SRT) model, Plomp [J. Acoust. Soc. Am.96, 586–587 (1994)] attempts to make three points: (1) that our results were invalid due to the use of a restricted set of spondaic words as stimuli; (2) that our results, as well as those of Smoorenburg [J. Acoust. Soc. Am.91, 421–437 (1992)] which we cited as supporting our results, were entirely consistent with his SRT model; and (3) that the articulation index (AI) model provided a poorer explanation of these data than his model. Each of these points are discussed in this letter.

ISSN:0001-4966    

DOI:10.1121/1.410446

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Extending the paper ‘‘Nature of the sound sources in low‐speed jet impingement’’ [A. Powell, J. Acoust. Soc. Am.90, 3326–3331 (1991)], it is first pointed out that the directionality of far‐field radiation of the postulated dominant lateral quadrupoles with one pair of the four maxima randomly oriented in the plane of the plate, i.e., about the normal to the plate (the direction of the other maxima), differs somewhat from that of the individual quadrupoles. Further comparison is now made with experiments by Sutherland and Brown [Tech. Rep. AFFDL‐TR‐71‐180, Wright–Patterson Air force Base, OH (1972)]in which flow resonance occurred, in which the deep minima at close to the theoretical angle were observed. Recent correlation measurements by Shen and Meecham [J. Acoust. Soc. Am.94, 1415–1424 (1993)] for turbulent (nonresonant) impingement noise display deeper minima than do simple intensity measurements, at close to the theoretical 48°. The substantial agreement with experiment appears to validate the type of dominant quadrupole postulated in the theory, and therefore use of both the ‘‘reflection argument’’ [A. Powell, J. Acoust. Soc. Am.32, 982–990 (1960)] and the ‘‘three‐sound‐pressures theorem’’ [A. Powell, J. Acoust. Soc. Am.34, 902–906 (1962)], for such a flow. The latter has implications for certain other flows, e.g., free turbulent jets.

ISSN:0001-4966    

DOI:10.1121/1.410447

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

To mathematically model the oscillations of a spherical bubble, either the time‐dependent volumeV(t) or the radiusR(t) can be used as the dependent variable. A recent exchange between the advocates of the volume approach [E. A. Zabolotskaya, J. Acoust. Soc. Am.94, 2448 (1993)] and the radius approach [J. Wu and G. Du, J. Acoust. Soc. Am.94, 2446 (1993)] concerns an apparent discrepancy in the predicted nonlinear acoustic emissions from a bubble subject to a time‐periodic external pressure field. This Letter attempts to resolve the discrepancy via an examination of the arguments offered by both sides. In addition, some general comments on nonlinear harmonic and subharmonic emissions from acoustically forced bubble oscillations are presented.

ISSN:0001-4966    

DOI:10.1121/1.410448

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.410450

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.411332

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.411457

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP