摘要:

An analysis of acoustic wave propagation in a waveguide carrying an incompressible mean flow is presented. The radius of the waveguide is taken to vary slowly as a function of axial location. It is shown that the dynamic behavior of the enclosed fluid can be parametrized by the small parameter ε, where ε is the ratio of the typical duct radiusR0and the wall wavelengthL0. An analytical solution for the pressure field in the duct is given in terms of a regular perturbation expansion in ε. The method of matched asymptotic expansions is used to evaluate the refractive effect of a thin mean‐flow boundary layer on the acoustic pressure field. It is shown that in the case where the duct geometry conforms to that of a circular cosh duct the effect of higher‐order turning points in the wave equation can be effectively handled by a closed‐form solution that approximately solves the governing equations. The results of analysis are compared to those obtained using numerical methods.

ISSN:0001-4966    

DOI:10.1121/1.395380

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Wave extrapolation methods are commonly used to evaluate the farfield radiation pattern of a complex source from nearfield measurements. The nearfield data are usually collected with transducer arrays or matrices. This standard procedure poses problems of signal conditioning, calibration, and recording that may be avoided by performing a synthetic detection of the nearfield. This alternate procedure, which borrows its principle from the field of synthetic aperture radar (SAR), is explored and illustrated in this article. The problem of radial wave extrapolation in a layered configuration is also analyzed. Acoustic wave radiation from a uniform stream to a region at rest is specifically considered. Exact and approximate wave extrapolators are derived. Comparisons between experimental measurements and wave extrapolation results indicate that the combination of synthetic nearfield detection and radial wave extrapolation is reliable and that extrapolation in layered situations may be carried out with little additional effort.

ISSN:0001-4966    

DOI:10.1121/1.395381

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Acoustic analyses were undertaken to explore the durational characteristics of the fricatives [f,θ,s,v,F,z] as cues to initial consonant voicing in English. Based on reports on the perception of voiced–voiceless fricatives, it was expected that there would be clear‐cut duration differences distinguishing voiced and voiceless fricatives. Preliminary results for three speakers indicate that, although differences emerged in the overall mean duration of voiced and voiceless fricatives, contrary to expectations, there was a great deal of overlap in the duration distribution of voiced and voiceless fricative tokens. Further research is needed to examine the role of duration as a cue to syllable‐initial fricative consonant voicing in English.

ISSN:0001-4966    

DOI:10.1121/1.395382

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The threshold for the detection of a brief tone masked by a longer‐duration noise burst is higher when the tone is presented shortly after the onset of the noise than at longer delay times. This finding has been termed the ‘‘overshoot’’ effect [E. Zwicker, J. Acoust. Soc. Am.37, 653–663 (1965)]. The present letter compared the size of the effect in the better and more impaired ear of six subjects with high‐frequency unilateral or asymmetric hearing losses of sensory origin. Thresholds were measured for 5‐ms 4‐kHz tones presented 10, 200, and 390 ms after the onset of a 400‐ms, 2‐ to 8‐kHz noise burst. The better ear of each subject was tested using two noise levels, one equal in sound‐pressure level and one equal in sensation level to that used for the impaired ear. Thresholds for all subjects and all ears decreased monotonically with increasing delay time, with the size of the effect typically 5 dB. Thus a small overshoot effect was observed regardless of hearing impairment.

ISSN:0001-4966    

DOI:10.1121/1.395329

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395330

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395332

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395334

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395336

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395339

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395343

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP