摘要:

Clad rods have been investigated for use as long delay lines because they offer isolation of the signal from the surface and low dispersion. In addition, single‐mode propagation is achieved with a larger (and hence more conveniently transduced) cross section than is possible with a homogeneous rod at the same frequency. This paper describes the modes that have a steady‐state sin(ωt−βz) dependence on (t,z), with emphasis on the modes and ranges of parameters that are of interest for delay lines. Only rods of circular cross section, and isotropic, linear elastic materials are considered. Attention is drawn to correspondences with homogeneous rods and with the hypothetical case of infinite thickness cladding, which is most useful as a model for understanding the behavior of corresponding modes in an actual clad rod. Written for the nonspecialist, the paper includes a tutorial review of the concepts and results needed to understand wave propagation in rods and clad rods. In addition, the following new results are reported: (1) for homogeneous rods, a representation of the lowest flexural mode dispersion curve that is for practical purposes independent of Poisson’s ratio; (2) for homogeneous rods, displacement distributions of the first three high‐frequency shear modes, i.e., the ’’flexural’’ modes that are asymptotic to the shear velocity (it was found that the distribution previously attributed to the lowest such mode actually belongs to the next); (3) for clad rods, the first demonstration of interface modes of the Stoneley type for nonaxially symmetric waves; (4) classification of clad rods according to the nature and ordering of their asymptotic velocities showing that there are eight types of clad rod, rather than four as stated in the previous literature; (5) for infinitely clad rods having the same shear modulus, proof that the dispersion of torsional waves and their penetration into cladding are universal functions off/fc∞. The ratio of the shear velocities of the two materials affects the cutoff frequencyfc∞, but not the universal penetration and dispersion functions. Subjects on which significant tutorial or descriptive material is given include typical waveguide dispersion, characteristic velocities of an isotropic elastic material, the effect of coupling of dilatational and shear waves at a boundary, waves in homogeneous rods, the connection of isolation to total internal reflection (with Love waves and SH waves in a clad plate as an example), Stoneley waves at a plane interface, and previous results on the clad rod.

ISSN:0001-4966    

DOI:10.1121/1.381962

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The theory of a broadband constant beamwidth transducer which is to be used primarily as a projector is presented. The transducer is a spherical cap of arbitrary half angle α shaded so that the normal velocity is equal toU0Pν(cos ϑ), wherePνis the Legendre function whose root of smallest angle occurs at ϑ=α. The required value for ν, the order of the Legendre function (which is not, in general, an integer) can be obtained to within 1% for α?1 radian from the approximation ν?0.5[(4.81/α)−1]. The transducer is shown to have uniform acoustic loading, extremely low sidelobes, and an essentially constant beam pattern for all frequencies above a certain cutoff frequency. Under piezoelectric drive the transducer is shown to have a flat transmitting current response over a broad band.

ISSN:0001-4966    

DOI:10.1121/1.381954

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A series of experiments examined listeners’ ability to detect mispronounced words in a short story. Mispronunciations were produced by changing a single consonant segment in a word to produce a (phonologically permissible) nonsense word. The results of six different experiments showed that prestressed word‐initial stop consonants are more perceptible than other consonants. For example, mispronunciations produced by changing the voicing of a word‐initial stop (e.g., ’’boy’’ to ’’poy’’) were detected about 70% of the time, while changes in voicing of a word‐initial fricative (e.g., ’’voice’’ to ’’foice’’) were detected about 38% of the time. Mispronunciations produced by changing the place of articulation of a prestressed word‐initial stop were most detectable of all (80% to 90% detection) for three different speakers. A change in place of articulation of a word‐initial stop (e.g., ’’baby’’ to ’’daby’’) was detected as often as a change in both place of articulation and voicing (e.g., ’’baby to ’’taby’’). Finally, it was found that a mispronunciation was detected about twice as often in word‐initial than in word‐final position in one syllable words for both stops and nasals. The results suggest that listeners pay special attention to word‐initial stop consonants in natural continuous speech.

ISSN:0001-4966    

DOI:10.1121/1.381955

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This study investigated the effects of lengthened transitions on the perception of stop consonants. In experiment I, three continua representing the phonetic categories [da] and [ga]containing transitions of 45, 95, or 145 ms were presented to 20 subjects for both labeling and discrimination. Results indicated that although there was a significant change in identification performance from 95 to 145 ms, the shape of the functions, and the locus and slope of the phonetic boundary did not significantly vary across transition lengths. In addition, discrimination of within‐category stimulus comparisons was significantly better at the 95‐ms transition length than at 45 or 145 ms. In experiment II, the availability of acoustic information was investigated further with the adaptation paradigm. Eight subjects labeled the 45‐ms series before and after adaptation with 45‐, 95‐, and 145‐ms [da] stimuli. No effect of transition length was found. These results suggest that the slope and duration of formant transitions seem to contribute minimally to the perception of place of articulation in stop consonants.

ISSN:0001-4966    

DOI:10.1121/1.381956

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The contributions of vocal‐fold tension and of subglottal air pressure to changing fundamental frequencyF0are indirectly assessed by comparing human glottal‐source data with synthetic glottal waveforms generated by the Ishizaka–Flanagan two‐mass model of vocal‐fold vibration. In this model, synthetic male and female glottal waves may be generated with known values of subglottal air pressure and vocal‐fold tension. Human glottal waves were recorded with a reflectionless tube into which ten male and female adults phonated. The subjects produced interrogative (risingF0) and declarative (fallingF0) glides and trisyllabic words with primary stress on the initial, medial, or final syllable. Two types of change in the glottal wave over time are possible, depending on whetherF0is changed primarily by vocal‐fold tension or by subglottal air pressure. Comparison of the natural and synthetic glottal waves indicates that (1) the rise of frequency in interrogative words is due principally to increasing vocal‐fold tension, while (2) the fall of frequency in declarative words is due principally to decreasing subglottal air pressure; (3) in the polysyllabic words, the change of frequency within syllables resembles that of the declarative monosyllables and appears due primarily to changes of subglottal air pressure; and (4) the heightenedf0of the stressed syllable is due to an increase in the vocal‐fold tension, typically accompanied by increased subglottal air pressure.

ISSN:0001-4966    

DOI:10.1121/1.381957

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This study investigates and acoustically defines some of the perceptual parameters used to distinguish among normal male and female voices. Twenty normal speaking subjects, ten male and ten female, produced speech segments which were paired, randomized, and presented to ten listener judges. The judges rated the similarity of all combinations of voices on a seven‐point scale, and these similarities were analyzed by a multidimensional analysis technique, INDSCAL. For each speaker, eight acoustical measures were obtained, and psychophysical ratings of four commonly used descriptive terms were made by ten speech pathologists. These measurements and ratings provided the interpretation of the INDSCAL solution and were also submitted to correlational analyses. The results indicate that, when distinguishing among the voices, the judges gave the greatest weight to the male versus female dimension and its acoustical correlates. The results of both the INDSCAL analysis and the correlational analyses suggest that listeners may use different perceptual strategies to classify male voices than they use to classify female ones.

ISSN:0001-4966    

DOI:10.1121/1.381958

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The use of glottal stops in continuous speech in American English has not been well studied, in spite of the common belief that they may serve as boundary markers. This paper reports the result from measurements of five speakers’ readings of four stories, each arranged in both list and story form. Data were analyzed according to the difference in speakers, materials, versions, phonological situations (phoneme sequence and stress situations), grammatical conditions, and frequency of occurrence of words. Results show that higher‐level factors such as speaker’s reading style and difficulty of material have a stronger influence than phonological and grammatical factors.

ISSN:0001-4966    

DOI:10.1121/1.381959

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper is primarily concerned with issues of symmetry–asymmetry in the joint dependence of binaural performance on interaural time delay and interaural amplitude ratio. The predictions of our model based on auditory‐nerve data are shown to be inadequate for available data showing asymmetries in interaural time discrimination. Measured detection thresholds for a 500‐Hz tone burst masked by wide‐band noise are reported for nonunity amplitude ratios and both polarities of delays in order to test for asymmetries analogous to those observed in the time discrimination case. The detection results show only small asymmetries and are not inconsistent with the model. A general discussion of our model and the implications of available empirical results leads to a suggested modification of the model. We show by an example that modifications of the type we are suggesting are capable of describing the detection data and at least the gross trends of the discrimination data.

ISSN:0001-4966    

DOI:10.1121/1.381960

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Subjects made magnitude estimations of the loudness of pure tones (100, 400, and 1000 Hz), which were presented at equal and unequal sound pressure levels to the two ears. The results were consistent with a model of linear binaural loudness summation: The estimates of loudness approximated the linear sum of the loudness estimates of the individual left‐ear and right‐ear components. The relation between loudness and sound pressure, over moderate SPLs, can be described by a power function with an exponent of about 0.6 at 400 and 1000 Hz, 0.75 at 100 Hz.

ISSN:0001-4966    

DOI:10.1121/1.381976

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Chinchillas were trained with shock‐avoidance procedures to discriminate or detect pure‐tone frequency differences. Initial attempts at determining frequency‐difference thresholds utilized a complex discrimination paradigm and a go–no‐go response. Although discriminations of large frequency differences were obtained from chinchillas after considerable training, discriminations of small frequency differences could not be trained. Therefore, determinations of frequency‐difference thresholds could not be made with the complex discrimination paradigm and the go–no‐go response task. A simple detection paradigm, involving the detection of frequency alternation in an ongoing train of tone bursts proved to be a more successful technique. Frequency‐alternation detection was quickly learned by six chinchillas, and frequency‐difference thresholds were obtained with an adaptive sequential procedure. Psychometric functions were reconstructed from the threshold tracking data of chinchillas, and comparisons were made with differential frequency thresholds from cats and humans obtained by previous investigators. Differential frequency thresholds from chinchillas paralleled those from cats and were about twice as large. Differential frequency thresholds from humans were considerably smaller than from chinchillas, especially for low‐frequency tones. When a constant detectability index was used to specify differential frequency sensitivity in chinchillas, chinchilla and human differential sensitivity functions paralleled one another. Human differential sensitivity was about ten times better than that of the chinchilla.

ISSN:0001-4966    

DOI:10.1121/1.381977

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP