摘要:

The diffraction of transient waves by a curvilinear boundary using the theory of generalized rays is developed. The generalized ray integrals, which represent the Fourier transform of diffracted waves, involve a double integration with respect to two wave slownesses. The inverse Fourier transform of these double integrals are computed by applying the simultaneous transformation of variables and the Cagniard method. The phase functions of the integrand provide the ray paths of incident, reflected, and diffracted waves. Since the pulses arrive at a point of observation in successive order, the theory furnishes an exact solution up to the time of arrival of the next ray and enables one to analyze, in detail, the signals recorded by the receiver.

ISSN:0001-4966    

DOI:10.1121/1.2023522

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Sound penetration into large enclosures can be modeled approximately by ray methods. When these enclosures are elongated so as to admit simulation by a waveguide, the interplay between rays and guided modes becomes important. To clarify the relevant phenomenology, we examine the prototype problem of a rigid semi‐infinite baffled or unbaffled circular waveguide. Using the methodology of the geometrical theory of diffraction (GTD) and its modification to account for a guiding environment [L. B. Felsen and H. Y. Yee, J. Acoust. Soc. Am.44, 1028–1039 (1968)], the interior field for arbitrary plane wave incidence is constructed by edge diffracted‐multiple reflected ray tracing, by modal expansion, and by physical optics (PO) applied to the aperture field. Stationary phase evaluation of the PO modal excitation coefficients establishes the connection with GTD, especially the mechanism of coupling from GTD into the modal fields. By reciprocity, the radiation problem can be handled in a similar way. Some conclusions are drawn for guides with noncircular cross section. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2023528

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

If a pulsed, radially symmetric planar source imbedded in a rigid baffle of infinite extent is described by a normal surface acceleration history of the forman = δ(t + r/vs), whereris radial surface distance from the source center,v, is the speed of uniform radial contraction, and the motion proceeds fromr=ator= 0, then convergent and intersecting wave fronts can be produced in the nearfield of this source. Fields from this source have been calculated using techniques described previously [S. I. Warshaw, J. Acoust. Soc. Am. Suppl. 177, S60 (1985); and79, S90 (1986); Proc. 12th ICA, Toronto, 1986] in the time domain. The calculation technique will be reviewed briefly and compared for contracting and expanding ring sources. Details of the time‐evolving two‐dimensional wave field will be presented in the form of contours of constant acoustic amplitude calculated at different times from source onset to propagation past the convergence zone. The various dynamically changing wave front patterns will be indicated and discussed. [Work supported by U.S. Department of Energy.]

ISSN:0001-4966    

DOI:10.1121/1.2023529

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Using free field acoustic stimulation conditions, the spatial response areas of single neurons and auditory space representation in the inferior colliculus (IC) of the big brown batEptesicus fuscus, was studied under different ear positions. A best frequency stimulus was delivered from the loudspeaker which was moved manually across the frontal auditory space of the bat to determine the response center of the neuron. At the response center, the neuron had its maximal directional sensitivity. The spatial response area of each neuron was determined for acoustic stimuli set at several intensity levels above the minimum threshold of the neuron. The spatial response areas of each IC neuron expanded unsymmetrically with the stimulus intensity. The size of the spatial response area was not correlated with the minimum threshold, best frequency, or recording depth of each neuron. Although each neuron had a point of maximal directional sensitivity, the point‐to‐point representation of the auditory space was not systematically organized. This representation was not correlated with the recording site of each neuron in the mediolateral, posteroanterior and dorsoventral axes of the IC. Both the response centers and spatial response areas of individual neurons varied with ear position but individual variations were complementary. It is likely that a mobile auditory space representation may provide the bat with versatility in maximizing the directional sensitivity of its echolocation system for accurate prey capture. [Work of Philip Jen supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2023539

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

This paper presents results from a general study of nasal airflow for a speaker of English. Nasal flow was recorded for approximately 1000 tokens in a carrier phrase, along with the audio output. The results support a hierarchical arrangement of vowels according to manifestation of nasal flow (in nasal environments) which parallels their oral impedance. This is consistent with acoustical studies of the effects of nasal coupling, as well as some perceptual studies, but differs in crucial ways from previous articulatory work. Other contextual segmental effects are observed, including a striking attenuation of the flow curve in final voiceless clusters. A revised definition of nasality, based on aerodynamic criteria, is advanced. Based on this definition, the circumstances under which nasality “spreads” was investigated, along with the flow characteristics of different segments. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2023540

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In recent years, glottographic techniques have been used more frequently to study vocal fold vibratory motion in clinical populations with voice abnormalities. However, some types of laryngeal pathology can result in deviant vocal fold movement, making interpretation of glottographic signals difficult. In the absence of other evidence, glottal events must be assigned to corresponding glottographic signals by inference usually from the study of normal phonation. This study was designed to confirm the relationship of simultaneously recorded photoglottographic (PGG) and electroglottgraphic (EGG) signals to vibratory movements of the vocal folds in the living human larynx. Photographs of the vocal folds were made using an 80‐μs flash. The flash was recorded as an impulse on the PGG trace, indicating the location on the glottographic signals of the corresponding single‐frame photograph displaying the glottal configuration. The instants at which the upper vocal fold margins first begin to open, separate completely, reach maximal lateral excursion, the lower margins first make contact, and close completely were documented. It appears that the timing of these events can be accurately identified in glottographic signals from normal and pathologic voices. [Work supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2023544

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

When listeners' identifications of speech sounds are influenced by adjacent sounds, do they operate only on the physical phonetic characteristics of there sounds or could they also use just their linguistic identity? We tested this by leading subjects to restore or induce the noise‐obliterated medial consonant in VCV utterances by first presenting them with several prior utterances where this medial consonant was consistently the same, either a /b/ or /d/. Included as V1 were synthetic vowels from the /i‐u/ continuum. As expected, more /u/s were identified out of this continuum in the environment of physically present /d/s than /b/s [Ohalaet al., J. Acoust. Soc. Am. Suppl. 164, S18 (1978)]. But restored /d/s and /b/s had thesameeffect (though with slightly less intensity) thus indicating that the influence of context need not operate only via physical phonetic features. We discuss the implications of this finding for “direct realist” theories of speech perception and for claims of the existence of invariant phonetic elements. [Supported by the Cognitive Science Program, UCB.]

ISSN:0001-4966    

DOI:10.1121/1.2023558

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The phonetic quality of front vowels along a synthetic /I/‐/e/ FI continuum can be influenced by passing the vowels through a filter that has a sloping characteristic in the FI region. The shift in phoneme boundary that occurs for different filter slopes was measured and whether the influence of various conditions listeners can compensate for the characteristics of the transmission channel was examined. These conditions include placing the vowel in a consonantal context and preceding the vowel with a carrier phrase that has been subjected to the same filtering as the vowel. Experiments have also been performed on the preception of natural vowels in isolation and in a consonantal context. [Work supported by SERC.]

ISSN:0001-4966    

DOI:10.1121/1.2023561

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Scattering or time‐varying mechanisms in the oceanic medium can affect the performance of a passive broadband cross‐correlation system. These mechanisms include internal waves, sea‐surface motion, and angular spreading caused by rough boundaries. The system involves three horizontal, collinear sensors and source location parameters are determined from time‐delay estimates obtained by cross‐correlation techniques. Tests for measuring the amount of spread or wander in correlograms with sufficiently high signal‐to‐noise ratios are presented. These tests are useful for determining the magnitued of the combination of scattering and time‐varying effects in correlogram data. Spread is measured by comparing the average main‐lobe width of stabilized correlograms over a period of time to the width of an ideal, “frozen‐ocean” correlogram. Wander is estimated by a comparison of the standard deviation of correlogram peak location values over a period of time to the average main‐lobe width of these correlograms. Examples of the application of the tests to simulated data are discussed. Finally, there is an identification of several correlogram types that can be associated with large amounts of spread and wander.

ISSN:0001-4966    

DOI:10.1121/1.2023565

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Propagation of sound in shallow water is commonly analyzed in terms of trapped normal modes. The process of normal‐mode detection by adjustment of the response of individual hydrophones in a vertical array to match the pattern of a particular normal mode is normal‐mode filtering. Despite the nonorthogonality of the normal modes in the water column, normal‐mode filtering is based on the assumption that the modes are orthogonal. The error induced by this assumption is known as leakage. It has been estimated to range from 3% to 10% of a measured mode. In this paper, the error involved in treating the modes as orthogonal for a variety of bottom types, water depths, and source frequencies is analyzed, and a method for avoiding the error is demonstrated. Density and sound‐speed ratios are selected from models fitted to experimentally measured values. To render the results indicative of a broad range of water depths and frequencies, use is made of dimensionless variables. Leakages as large as 19% are calculated.

ISSN:0001-4966    

DOI:10.1121/1.2023576

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP