摘要:

Biot and Tolstoy [J. Acoust. Soc. Am.29,381–391 (19571] have used the normal coordinate method to obtain a simple exact expression for the impulse response of a rigid wedge. This solution is appropriate to arbitrary wedge angle as well as arbitrary point receiver and explosive point source locations. Trorey [Geophysics35,762–784 (1970)] has developed a simple expression for the back‐scattered impulse response of a half plane in the Kirchhoff approximation. The Biot‐Tolstoy solution has been used by Medwin and Novarini [J. Acoust. Soc. Am.67,S67(A)(1980)] to model back‐scatter from the ocean surface. In doing so, they evaluated the accuracy of a similar but earlier model [J. Acoust. Soc. Am.64,260–268 (1978)] that used the Trorey Helmholtz‐Kirchhoff solution. Because of the nature of the Kirchhoff approximation, the Trorey solution ignores field effects associated with shadow zones. The Biot‐Tolstoy solution, on the other hand, does not. Here, an explicit comparison between the two solutions for simplified geometries (e.g., a single half‐plane wedge) is discussed. [Work supported by NORDA.]

ISSN:0001-4966    

DOI:10.1121/1.2004619

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A generalized and simple Lagrangian formulation of the acoustic properties of a microscopically homogeneous and isotropic medium consisting of two or more interpenetrating solid or fluid constituents is presented in terms of a set of phenomenological bulk parameters. The isotropy severely limits the kinds of terms (the number of parameters) that can appear. Biot's theory for the fluid‐solid system and Tiersten and Jahanmir's theory for the solid‐solid system are shown to be special cases. The approach is extended to interfacial properties of two such systems where boundary conditions are derived in terms of phenomenological surface parameters; again, isotropy and positive definiteness of the strain energy severely limit the number of different parameters. The model dependent boundary conditions of Rosenbaum, Tiersten and Jahanmir, Geerstsma and Smit, and others are shown to be special cases of the general formulation.

ISSN:0001-4966    

DOI:10.1121/1.2004659

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In multidimensional echo imaging of the heart, the anatomy and motion of the heart structures can be observed by placing the transducer over the intercostal window. The ultrasonic beam may be scattered, reflected or refracted from its path by the ribs and soft tissues between them. Since beam distortion is directly related to the loss of resolution in pulse‐echo imaging systems, an investigation of the effects of these intervening tissues on the ultrasonic beam characteristics may be useful for establishing criteria for selecting suitable transducers in clinical scanning procedures. In order to address this problem, an automated system for rapid mapping of transducer field based on a microcomputer has been developed in our laboratory. In this paper, we will present the initital results on our investigation of the beam distortions produced by the rib cage in terms of 3‐dimensional display of the intensity contours at various distances from the transducer. Also to be discussed is the effect of transducer angulation in relation to the breast plate on the transmitted ultrasonic beam.

ISSN:0001-4966    

DOI:10.1121/1.2004714

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A point source in a 6‐ft cubed anechoic space was designed to provide predictable audio sound fields at 1 m without near‐field effects. The chamber was acoustically isolated to permit measurement down to 25 dB SPL in an812 × 9 × 11foot o.d.enclosure. A control microphone 20 cm from the source maintained a constant SPL at 1 m over the entire frequency range. The presence of a full size human manikin did not affect the sound field at the control microphone. SPL followed inverse square law (± 1 dB) from 10 cm to 1 m from the source over a 200 Hz to l0 kHz frequency range. Eight loudspeakers, mounted behind the upper edge wedges could develop 70 dB SPL quasi‐diffuse noise at the working location.

ISSN:0001-4966    

DOI:10.1121/1.2004769

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A computer program designed for predicting the acoustical limitation of discrimination of speech sounds by hearing impaired children is described. In this program, the kind of identifiable phones and the probable confusion among the phones are estimated based on the aided frequency characteristic of each individual hearing impaired child. The program is currently being used to find the most appropriate methods of prescribing hearing aids and evaluating use of the aided characteristics, especially in the courses of extending the highest limit of the frequency range or depressing the low frequency components and of utilizing directional microphones and telephone pickup coils mounted in the hearing aids.

ISSN:0001-4966    

DOI:10.1121/1.2004826

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In this paper we propose that full use is not made of available noise‐exposed threshold data. Specifically, data from noise‐exposed populations can be analyzed to assess impact of exposure in two ways: (1) to provide estimates of the number of cases of hearing loss attributable to noise in the population or, (2) to provide estimates of increased risk of hearing loss in an exposed individual relative to the unexposed person. Previous studies have neglected prediction of risk to the individual, emphasizing instead the impact on the population. To more fully understand the effect of noise exposure, the approaches must be combined. We will present two statistics which may be calculated from population threshold data:Percent riskis the statistic commonly computed from hearing conservation data. Percent risk is an estimate of the number or of the proportion of cases of hearing loss attributable to noise exposure.Rate ratiois the second statistic we will discuss. The rate ratio estimates the increased risk of hearing loss to an individual as a consequence of exposure. It is adjusted for the background rate and is, therefore, comparable across studies. Each statistic complements the information provided by the other. We will also discuss how potential risk factors for hearing loss may be evaluated and combined to yield a composite risk estimate.

ISSN:0001-4966    

DOI:10.1121/1.2004875

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Ultrasonic energy interacts very strongly with biological tissue because the inhomogeneties in the intrinsic properties (density, compressibility, attentuation) have spatial dimensions ranging from much less than a wave length to much greater than a wave length at medical ultrasound frequencies. The magnitude of variations in the intrinsic properties varies from less than 10% to greater than 200%. Thus, the interaction of biological tissue with ultrasonic energy must be considered to include both refractive terms and diffractive terms. Wave equations that characterize tissue/ultrasound interactions can be developed which give insight into various imaging modes currently used in diagnostic instruments. Restraints on transducer and scan geometries created by biological barriers to ultrasonic energy, such as gas and bone, provide specific constraints on methods of solving the wave equations for the intrinsic tissue properties. Computerized ultrasonic tomographic methods useful in diagnosis of breast cancer will be described. Future development of methods for diffraction limited quantitative imaging of tissues will require numerical if not analytical inverse scattering solutions to the appropriate wave equations.

ISSN:0001-4966    

DOI:10.1121/1.2004934

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Success in deconvolution of signals by homomorphic techniques depends on accurate reconstruction of the continuous phase spectrum. The usual algorithms for this process—integration of the phase derivative, adaptive integration, and iterative phase ramp removal—all have subtle but serious flaws of which the user must be aware. Recent processing of high signal‐to‐noise ratio, broadband geoacoustic data uncovered these problems and led to the development of an alternative procedure incorporating an error monitor. This paper summarizes the evaluation of phase reconstruction processes and illustrates their pitfalls when applied to measurement signals. Also, the error monitoring procedure is described along with applications to ocean geoacoustic measurements.

ISSN:0001-4966    

DOI:10.1121/1.2004989

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Recent studies have shown that phonetic and phonological context influences vowel identification. For instance, vowels are better identified when presented in a syllabic environment than when presented in isolation [Strange, Verbrugge, Shankweiler, and Edman, J. Acoust. Soc. Am.60,213–224 (1976)], and when the syllabic environment is represented by natural speech formant transitions rather than “flipped formants” [Fowler and Shankweiler, J. Acoust. Soc. Am. Suppl. 163,S4 (1978)]. The identification of steady‐state vowels presented in concatenated sequences is also influenced by context factors [Alfonso and Kerivan, J. Acoust. Soc. Am. Suppl. 166,S86 (1979)]. Finally, familiarity of contextual language‐specific factors affect vowel identification [Gottfried, J. Acoust. Soc. Am. Suppl. 165,S6 (1979); Rudnicky, .I. Acoust. Soc. Am. Suppl. 165,S110 (1979)]. The study reported here demonstrates that vowel discrimination is also context dependent. Two groups of subjects, native American‐English and native Hebrew speakers, discriminated among six vowels, three that are familiar to both groups, and three that are represented in English but not Hebrew. AX discrimination CVC pairs consisted of the following: two vowels familiar to the Hebrew group, designated (FF), two unfamiliar vowels (UU), or combinations of unfamiliar and familiar vowels (UF). The Hebrew group demonstrated significantly poorer discrimination than the English group on the (UF) pairs. The results and the possible use of unfamiliar speech stimuli in the clinical management of the hearing impaired will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2005039

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

How is the information specifying place of articulation and vowel color encoded in a stop‐vowel syllable? Are place cues located in just the burst, or the first 20 ms of a CV waveform as some investigators have suggested? Alternatively, are place cues encoded simultaneously (i.e., in parallel) with vowel information in the formant transitions? To answer these questions, an identification experiment was conducted using the consonants /b, d, g/ paired with the vowels /i, e, a, o, u/ produced by two male talkers. Using computer techniques, five truncated stops were edited from each original syllable. Cuts were made after the release burst, and then the burst plus 1, 3, 5, or 7 pitch pulses. On different days, naive subjects identified either the consonant or the vowel. Identification functions for /b/ and /d/ reached 95% correct within the first 20 ms. Vowels, except for /i/, were identified near chance for the shortest stimuli. The consonant /g/ needed a longer duration, 40 to 50 ms, for correct place identification, although /gi/ was never identified accurately even at the longest durations. We conclude that sufficient acoustic information for identifying the stops /b/ and /d/ can be found within the first 20 ms of a CV syllable, although information for the /g/ extends over somewhat longer durations. Formant transitions appear to carry information about the vowel although somewhat less information about the consonant, except for /g/ before front vowels. [Supported by NINCDS Grant NS‐12179.]

ISSN:0001-4966    

DOI:10.1121/1.2004541

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP