摘要:

This paper describes a method of generating both line and point sources of acoustic emission (AE) signals by a powerful, transient Joule heating of a thin, conductive film deposited on an insulating plate or a small diameter metal wire buried inside it. Point‐and line‐source AE signals are generated by heating a short or a long section of thin film, respectively. The versatility of this method is demonstated by the diversity of AE signals that can be produced by simply changing the rise time, magnitude, and duration of the current pulse that provides the heating. An analysis shows that both the line and the point AE sources are of dipolar type for the case of the heated thin film. The line source resulting from an imbedded long, thin wire appears to be a two‐dimensional center of dilatation. Short‐duration current pulses generate a step source whose rise time is approximately equal to that of the input electrical power pulse while long‐current pulses produce a linear ramp source that resembles the temperature rise of the heated conducting film or wire.

ISSN:0001-4966    

DOI:10.1121/1.398721

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The perturbing effect of an ultrasonic transducer on determination of sound velocity by continuous‐wave methods is reanalyzed. The Bolef–Menes (1+δ) formula is found usually to apply only within a very narrow frequency range around the transducer’s resonant frequencies. Thus it should be regarded as a ‘‘near‐transducer’’ rather than a ‘‘thin‐transducer’’ correction. Outside the applicable frequency range, it is more appropriate to multiply δ by the square of the ratio of the specimen’s mechanical impedance to that of the transducer. The effect of the bond between specimen and transducer is assessed.

ISSN:0001-4966    

DOI:10.1121/1.398722

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The method of laser Doppler anemometry is applied to the measurement of particle velocity in a hydroacoustic field. The field is created in an Underwater Sound Reference Detachment‐type G19 calibrator. The anemometer is operated in the forward‐scattering mode. Seeding particles of varying material and size are dispersed in the acoustic medium (water). The laser Doppler anemometry results are compared with the values for the velocity obtained from the pressure gradient measured by a hydrophone.

ISSN:0001-4966    

DOI:10.1121/1.398723

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

This paper reports on a continued investigation of violin plate properties. The plates were thinned in steps, and the shifts of the resonance frequencies were measured with different boundary conditions: free, glued to rigid ribs, and glued to the flexible ribs of a simplified violin model. It was found that, in spite of large frequency shifts for the free plates, the corresponding shifts for the glued plates were small. The experimental results imply that the boundary conditions have a major effect on the resonance frequencies and that the fundamental plate mode of the violin model is related to that of the free plate mode 5; i.e., the frequencies of both modes were most sensitive to thinning off‐center and less sensitive to thinning in the center. The investigation is empirical; the information is collected under controlled conditions to serve as a base for future refined theoretical and experimental work.

ISSN:0001-4966    

DOI:10.1121/1.398724

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A real‐time peak‐picking fundamental period estimation device is described which is used in advanced hearing prostheses for the totally and profoundly deafened. The operation of the peak picker is compared with three well‐established fundamental frequency estimation techniques: the electrolaryngograph, which is used as a ‘‘standard,’’ hardware implementations of the cepstral technique, and the Gold/Rabiner parallel processing algorithm. These comparisons illustrate and highlight some of the important advantages and disadvantages that characterize the operation of these techniques. The special requirements of the hearing prostheses are discussed with respect to the operation of each device, and the choice of the peak picker is found to be felicitous in this application.

ISSN:0001-4966    

DOI:10.1121/1.398725

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Within‐subject variation of three vocal frequency perturbation indices was compared across multiple sessions. The magnitude of jitter factor (JF), pitch perturbation quotient (PPQ), and directional perturbation quotient (DPF) was measured every other day for 33 consecutive days for ten female and five male normal young adult speakers. Perturbation measures were calculated using a zero‐crossing analysis of taped [i] and [u]productions. Pearson product‐moment correlations among the three perturbation indices were calculated to examine their relation over time. Coefficients of variation for JF, PPQ, and DPF were considered indicative of the temporal stability of the three measures. JF and PPQ provided redundant information about laryngeal behaviors in steady‐state productions. DPF, however, appeared to measure different laryngeal behaviors. Also, JF and PPQ varied considerably within individuals across sessions while DPF was the more temporally stable measure. Multiple sampling sessions and measurement of both the magnitude and direction of period differences are advised for future investigations of vocal frequency perturbation.

ISSN:0001-4966    

DOI:10.1121/1.398778

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Individuals with congenital velopharyngeal impairment generally maintain adequate levels of intraoral pressures during consonant production by increasing respiratory effort. The purpose of the present study was to determine if normal individuals respond to a decrease in velopharyngeal resistance in a similar way. The velar mechanism was perturbed by having subjects voluntarily lower the soft palate during a series of words involving plosive consonants. The pressure‐flow technique was used to measure oral pressures, calculate velopharyngeal orifice resistance, and estimate velopharyngeal orifice area. Inductive plethysmography was used to measure breathing volumes associated with the words. The data indicate that, in most instances, intraoral pressure remained at appropriate levels (>3.0 cm H2O) after velar lowering. Speech breathing volume did not change during inspiration, but increased during speech expiration when the velopharyngeal port was open. The difference was statistically significant (p<0.01). Duration of the utterance did not change across conditions. A mechanical model was then used to determine how intraoral pressure would be affected by simulating the same conditions in a passive system. The modeling data revealed that pressure would drop threefold. It was concluded that increased respiratory volumes tend to stabilize intraoral pressure when vocal tract resistance is experimentally reduced.

ISSN:0001-4966    

DOI:10.1121/1.398726

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The temporal evolution of masking and frequency selectivity was studied in the goldfish using classical respiratory conditioning and a tracking psychophysical procedure. The temporal position of a brief tonal signal within a longer duration, tonal masker has little or no effect on signal detectability when the frequency of the masker is less than or equal to that of the signal. For masker frequencies above that of the signal, signal detectability improves as the signal onset is delayed relative to that of the masker. These patterns of tone‐on‐tone masking are quite similar to those observed for humans. These temporal masking patterns are qualitatively similar in shape to the peristimulus‐time histogram profiles of the low‐frequency saccular fibers thought to be used in this task. Frequency‐ and time‐dependent changes in signal detectability result in specific changes in the sharpness of psychophysical tuning curves (PTC). In general, PTCs determined for signals occurring at masker onset are the most broadly tuned, and PTCs determined in forward masking are the most sharply tuned. The PTCs for signals temporally centered in the masker are intermediate. These results suggest that temporal tone‐on‐tone masking patterns and the temporal evolution of psychophysical tuning curves result from the response properties of peripheral auditory‐nerve fibers.

ISSN:0001-4966    

DOI:10.1121/1.398727

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

This paper reports on some initial experiments using the sample discrimination paradigm to investigate normal‐hearing listeners’ ability to process information in complex, nonspeech sounds. An important feature of the sample discrimination experiment is that the value of thedifferenceto be discriminated randomly varies from trial to trial. It is this variation that yields potential information. In the present study, listeners heard a pair of multitone complexes (or sequences) on each trial. The individual levels of the tones were drawn from two normal distributions differing only in mean. The listener’s task was to identify the sound having the higher mean tone level. For an ideal observer in these experiments, performance ind’grows as the square rootn, wherenis the number of tones. Obtainedd’grew more nearly as the cube root ofnregardless of whether the tones were played sequentially or simultaneously or whether they were increased in number from high frequencies to low or from low frequencies to high. A preliminary model is proposed in which discrimination performance depends predominantly on the information content of the sounds and is largely independent of the physical dimensions along which the sounds vary. Information content is defined in terms of the variance of the underlying stimulus distributions and a stimulus equivocation factor that is derived from the data. Based on this model, transmitted information is estimated to be between 1.0 and 2.6 bits.

ISSN:0001-4966    

DOI:10.1121/1.398728

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Two experiments evaluated discrimination of simulated single‐formant frequency transitions. In the first experiment, listeners received practice with trial‐by‐trial feedback in discriminating either rising or falling frequency transitions of three different durations (30, 60, and 120 ms). Transitions either occurred in isolation or were followed by a steady‐state sound matched in frequency to the transition end point. Some improvement in discrimination over practice runs occurred for the shortest transitions. Whether performance was evaluated at the beginning or end of practice, there were no differences attributable to transition direction or to whether transitions were followed by steady‐state sound. Discrimination, however, was significantly better for the longest transitions. Just noticeable differences (jnd’s) for the longest transitions, measured in Hz at transition onsets, were of approximately the same magnitude as jnd’s for steady‐state sounds that were equal in frequency to the midpoints of the transitions. Subjects of the second experiment discriminated the longer rising and falling transitions, but did not receive extensive practice. Results of experiment 2 replicated results of experiment 1 in showing similar jnd’s. Experiment 2 also showed no differences attributable to transition direction or to the presence of the steady‐state sound following transitions.

ISSN:0001-4966    

DOI:10.1121/1.398729

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP