摘要:

A model is presented for predicting the behavior of tall, thin piezoelectric transducer elements, typical of those encountered in phased or linear array assemblies. Based on a block diagram, systems feedback approach, the model is amenable to computer implementation as well as satisfying intuitive and physical constraints. The method permits a ready understanding of electrical, piezoelectric, and mechanical coupling that occurs when two, loosely coupled vibrational modes are present within a transducer structure. A range of experimental and theoretical results, including impedance and pulse‐echo characteristics, is presented for different transducer configuration ratios. Provided that the constraint of twin, compressional modes of vibration is satisfied, the model is shown to predict the principal resonance features with an accuracy ranging from 1%–5.2%.

ISSN:0001-4966    

DOI:10.1121/1.398594

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A new type of probe was developed to evaluate the distribution of kinetic, thermal, and acoustic energy in an ultrasonically induced cavitation field. The probe is based on an electrochemical mass transfer technique for direct measurement of the flux of reactants to a surface. Cavitation was generated in a focused ultrasonic field at 1.58 MHz over a large range of focal intensities. Electrochemical measurements of the reduction of ferricyanide to ferrocyanide in a NaOH solution show that the focal area dimensions (as characterized by the cavitation activity) increased almost an order of magnitude in the presence of intense cavitation. The cavitation activity is attributed to fluid motion generated by cavitation‐induced jets and microstreaming. A mathematical model is proposed to predict the mass transfer rate at the surface under cavitation conditions and to relate the mass transfer coefficient to the acoustic focal intensity. The concept of the mass transfer probe resulted from the author’s previous work in the study of the electrochemistry of metals in the presence of ultrasound [S. Perusich, Ph.D. thesis, University of Illinois at Urbana, Urbana, IL (1985)].

ISSN:0001-4966    

DOI:10.1121/1.398595

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A variety of dolphin sonar discrimination experiments have been conducted, yet little is known about the cues utilized by dolphins in making fine target discriminations. In order to gain insights on cues available to echolocating dolphins, sonar discrimination experiments were conducted with human subjects using the same targets employed in dolphin experiments. When digital recordings of echoes from targets ensonified with a dolphinlike signal were played back at a slower rate to human subjects, they could also make fine target discriminations under controlled laboratory conditions about as well as dolphins under less controlled conditions. Subjects reported that time‐separation‐pitch and duration cues were important. They also reported that low‐amplitude echo components 32 dB below the maximum echo component were usable. The signal‐to‐noise ratio had to be greater than 10 dB above the detection threshold for simple discrimination and 30 dB for difficult discrimination. Except for two cases in which spectral cues in the form of ‘‘click pitch’’ were important, subjects indicated that time‐domain rather than frequency‐domain processing seemed to be more relevant in analyzing the echoes.

ISSN:0001-4966    

DOI:10.1121/1.398596

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

All note durations were measured in an Estonian runic song where one and the same melodic pattern is repeated 32 times in succession. It was found that the durations acoustically tend to form two categories that could be called the short and the long note. This result was confirmed by the multidimensional scaling of the measured durations. Other dimensions that seem to influence the relative duration of a particular note in the performance are related to the metrical position of the note and to whether a vowel or a diphthong corresponds to the note in the sung text. The results of this study suggest also that the opposition of the short and long notes may determine the rhythmic structure of the runic song rather than the properties of the verbal text.

ISSN:0001-4966    

DOI:10.1121/1.398597

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Whispering is a common, natural way of reducing speech perceptibility, but whether and how whispering affects consonant identification and the acoustic features presumed important for it in normal speech perception are unknown. In this experiment, untrained listeners identified 18 different whispered initial consonants significantly better than chance in nonsense syllables. The phonetic features of place and manner of articulation and, to a lesser extent, voicing, were correctly identified. Confusion matrix and acoustic analyses indicated preservation of resonance characteristics for place and manner of articulation and suggested the use of burst, aspiration, or frication duration and intensity, and/or first‐formant cutback for voicing decisions.

ISSN:0001-4966    

DOI:10.1121/1.398598

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Chinese words may begin with /t/ and /d/, but a /t/–/d/ contrast does not exist in word‐final position. The question addressed by experiment 1 was whether Chinese speakers of English could identify the final stop in words likebeatandbead. The Chinese subjects examined approached the near‐perfect identification rates of native English adults and children for words that were unedited, but performed poorly for words from which final release bursts had been removed. Removing closure voicing had a small effect on the Chinese but not the English listeners’ sensitivity. A regression analysis indicated that the Chinese subjects’ native language (Mandarin, Taiwanese, Shanghainese) and their scores on an English comprehension test accounted for a significant amount of variance in sensitivity to the (burstless) /t/–/d/ contrast. In experiment 2, a small amount of feedback training administered to Chinese subjects led to a small, nonsignificant increase in sensitivity to the English /t/–/d/ contrast. In experiment 3, more training trials were presented for a smaller number of words. A slightly larger and significant effect of training was obtained. The Chinese subjects who were native speakers of a language that permits obstruents in word‐final position seemed to benefit more from the training than those whose native language (L1) has no word‐final obstruents. This was interpreted to mean that syllable‐processing strategies established during L1 acquisition may influence later L2 learning.

ISSN:0001-4966    

DOI:10.1121/1.398599

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

An examination of the effect of phrase‐final lengthening on the temporal correlates of voicing in syllable‐final /s/ and /z/ was conducted. Discriminant analyses revealed that a combination of vowel duration, frication duration, and the duration of simultaneous voicing and frication was quite successful in determining voicing independently of phrase‐final lengthening. Two perceptual experiments revealed that human listeners’ recognition of the segments does benefit from hearing the syllables in sentential context as opposed to when they are excised from context and presented in isolation. The benefit was greatest for /s/ in phrase‐final position and /z/ in phrase‐internal position. This suggests that the presence of sentential context allows listeners to factor out the influence of phrase‐final lengthening on vowel duration and to more accurately interpret this cue to voicing of the final fricative. These findings extend previous results on rate‐dependent processing of overall speaking rate to the processing of local speaking rate. By doing so, they provide further evidence of the importance of extended phonetic context in speech recognition.

ISSN:0001-4966    

DOI:10.1121/1.398600

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

An approximate but realistic model of the human larynx was constructed to gain better knowledge of the complex glottal impedance and its dependence on glottal width, flow, and frequency. The glottal width was adjustable from 0 to 3 mm, the flow from 0 to 500 cm3/s. The model was fitted into a system of tubes, through which compressed air could be conducted. Supraglottally, a broadband signal was fed into the tube, and, with a two‐microphone directional coupler, the complex glottal impedance at a given reference plane was directly determined as a function of frequency. Since the calculated impedance is sensitively dependent on the definition of the position of the reference plane, it is difficult to obtain quantitative statements about the frequency dependence. Nevertheless, in the presence of flow, it is possible to achieve reliable results by analysis of the relative position of the measured curves. On the one hand, the glottal inductance decreases linearly with increasing flow velocity; on the other hand, it diminishes nonlinearly with decreasing frequency. Finally, some difficulties in the definition of glottal impedance are pointed out.

ISSN:0001-4966    

DOI:10.1121/1.398601

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The authors respond to Fitch’s comments [H. Fitch, J. Acoust. Soc. Am.86, 2017–2019 (1989)] on an earlier paper. New analyses are presented to address the question of whetherF1 differences observed in the original report are an artifact of linear predictive coding (LPC) analysis techniques. Contrary to Fitch’s claims, the results suggest that theF1 differences originally reported are, in fact, due to changes in vocal tract resonance characteristics. It is concluded that there are important acoustic‐phonetic differences in speech when talkers speak in noise. These differences reflect changes in both glottal and supraglottal events that are designed to maintain speech intelligibility under adverse conditions.

ISSN:0001-4966    

DOI:10.1121/1.398602

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

This paper describes two experiments intended to test excitation‐pattern models of frequency discrimination. In experiment I, frequency DLs (DLFs) for pulsed sinusoids were measured in four conditions: (1) in quiet with the level fixed at 70 dB SPL; (2) in quiet with the level of each tone varied randomly over a 6‐dB range around 70 dB SPL; (3) in the presence of a bandpass noise designed to mask the upper side of the excitation pattern, with the level fixed; and (4) with bandpass noise and with the level of the signal randomized over a 6‐dB range. Center frequencies of 0.5, 1.0, 2.0, 4.0, and 6.5 kHz were used. DLFs for conditions 3 and 4 were somewhat larger than DLFs for conditions 1 and 2, indicating that frequency discrimination is not based solely on information from the low‐frequency side of the excitation pattern. DLFs for condition 4 were, on average, 1.65 times as large as those for condition 1 but, except at 6.5 kHz, were considerably smaller than the values predicted on the assumption that the DLFs were based on the detection of changes in excitation level on the low‐frequency side of the excitation pattern. It is suggested that phase‐locking information plays a role in determining DLFs at 4.0 kHz and below. Experiment II was similar to experiment I, except that thresholds (FMDLs) for detecting frequency modulation (FM) at a 4‐Hz rate were measured, and, in conditions 2 and 4, a 4‐Hz amplitude modulation (AM) with a peak‐to‐valley ratio of 6 dB was imposed on all signals; the phase of the AM relative to the FM was random. The FMDLs were affected more by the noise and by the variation in level than were the DLFs; FMDLs for condition 4 were, on average, 2.36 times as large as those for condition 1. Furthermore, the data for condition 4 were not inconsistent with the assumption that the FMDLs were based on the detection of changes in excitation level on the low‐frequency side of the excitation pattern. However, neither a single‐band nor a multiple‐band excitation‐pattern model was able to account for the effect of the bandpass noise on the FMDLs.

ISSN:0001-4966    

DOI:10.1121/1.398603

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP