摘要:

Transient cavitation is a discrete phenomenon that relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1‐μm polystyrene spheres, microbubbles in the 1‐ to 10‐μm range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. These experimental measurements of cavitation thresholds elucidate the importance of ultrasound, host fluid, and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate analytical theory for the prediction of the onset of cavitation.

ISSN:0001-4966    

DOI:10.1121/1.400102

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Comparison of the resonance frequencies of modes in conical and cylindrical piccolos showed pronounced differences in the degree to which the octaves are stretched. Measurements for a note on a flute with only two modes showed that second harmonic generation and total radiated power were greatest when the modes were stretched 25 cents from an exact octave, supporting the idea that mode stretching may be beneficial in flutelike instruments.

ISSN:0001-4966    

DOI:10.1121/1.400103

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.400104

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In same–different discrimination tasks employing isolated vowel sounds, subjects often give significantly more ‘‘different’’ responses to one order of two stimuli than to the other order. Cowan and Morse [J. Acoust. Soc. Am.79, 500–507 (1986)] proposed aneutralizationhypothesisto account for such effects: The first vowel in a pair is assumed to change its quality in memory in the direction of the neutral vowel, schwa. Three experiments were conducted using a variety of vowels and some initial support for the hypothesis was obtained, using a large stimulus set, but conflicting evidence with smaller stimulus sets. Rather than becoming more similar to schwa, the first vowel in a pair seems to drift toward the interior of the stimulus range employed in a given test. Several possible explanations are discussed for this tendency and its relation to presentation order effects obtained in other psychophysical paradigms is noted.

ISSN:0001-4966    

DOI:10.1121/1.400105

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Modulation of the acoustic amplitude of a sustained vowel across the cardiac (ECG) cycle was examined by signal‐averaging techniques. Ten normal men prolonged [a] at a comfortableF0maintained within three SPL ranges: 60–68, 70–78, and 80–88 dB. Peak‐to‐peak amplitude variation associated with the heart cycle averaged 8.5% (s.d.=5.4)re: mean, varying from about 14% at low SPLs to approximately 3% at high SPLs. The amplitude modulation was estimated to account for 11.8% of the measured short‐term amplitude perturbation (shimmer), ranging from about 5% to almost 22% for individual samples. The mean deterministic shimmer (Sd) was 0.036 dB (s.d.=0.019), with a trend toward decreasingSdwith increasing SPL. Additionally, fundamental frequency variation across the heart cycle within these phonations was comparable to that observed by Orlikoff and Baken [J. Acoust. Soc. Am.85, 888–893 (1989)], and was shown to be uninfluenced by vocal SPL, although deterministic jitter (Jd) did decrease with vocal intensity. The results are discussed in terms of how the phonovascular relationship may affect the reliability and interpretation of acoustic shimmer measures.

ISSN:0001-4966    

DOI:10.1121/1.400106

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This study investigated some effects of postlingual deafness on speech by exploring selected properties of consonants, vowels, and suprasegmentals in the speech of seven totally, postlingually deafened individuals. The observed speech properties included parameters that function as phonological contrasts in English, as well as parameters that constitute primarily phonetic distinctions. The results demonstrated that postlingual deafness affects the production of all classes of speech sounds, suggesting that auditory feedback is implicated in regulating the phonetic precision of consonants, vowels, and suprasegmentals over the long term. In addition, the results are discussed in relation to factors that may influence the degree of impairment, such as age at onset of deafness.

ISSN:0001-4966    

DOI:10.1121/1.400107

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The effects of masker bandwidth on the detection of narrow‐ and wideband signals have been investigated. For both kinds of signals, plots of threshold as a function of masker bandwidth yielded by both narrow‐ and wideband signals are reasonably described with two intersecting lines. Thresholds initially increase with masker bandwidth and then become independent of further increases. The rate of increase depends on the signal spectrum. The bandwidth at which the lines intersect varies with signal bandwidth and also mode of masker presentation (i.e., whether the masker is gated with the signal or is present continuously). Internal filtering is most accurate when the masker is present continuously. A model is proposed in which a listener’s decisions about the presence of narrow‐band signals are based upon estimates of stimulus energy within a critical band. These estimates are degraded by bandwidth‐dependent processing errors. When the signal to be detected spans several critical bands (i.e., is wideband), the model forms a test statistic by summing the outputs of the relevant critical bands. The model permits the contribution of each band to the sum to vary with masker bandwidth because it incorporates a form of lateral suppression. Thresholds of narrow‐band signals in gated maskers and wideband signals in gated and continuous maskers are predicted by the model. However, the model fails to account for the detectability of narrow‐band signals in continuous maskers.

ISSN:0001-4966    

DOI:10.1121/1.400108

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

For normal‐hearing adult listeners, two simultaneous pure tones with a frequency ratio close to 2/1 may perceptually fuse into a single sound, which shows that such listeners are sensitive to ‘‘octave harmony.’’ Many adult listeners are also able to consistently adjust two successive pure tones ‘‘one octave apart,’’ which shows that they possess melodic octave templates. According to Terhardt [J. Acoust. Soc. Am.55, 1061–1069 (1974)], melodic octave templates and the perception of octave harmony originate from a common learning process taking place in early life. In the two experiments reported here, subjects performed repeated octave adjustments for pairs of simultaneous and successive tone bursts. Both tones were presented monaurally, at 45 or 65 dB SPL. The frequency of the lower tone (fref) was an independent variable, while the frequency of the higher tone was adjustable within a 500‐cent range. In some conditions, when the two tones were presented simultaneously, they were sinusoidally frequency modulated in a coherent manner, at a rate of 2 or 4 Hz; the aim of this frequency modulation was to force the subjects to adopt a synthetic listening strategy, i.e., to base their adjustments on perceived harmony. Forfrefvalues ranging from 270–2000 Hz, subjects performed consistent adjustments when the tones were presented successively:frefhad little effect on the adjustments’ variability. However, in the same frequency range, the variability of the harmonic adjustments markedly increased withfref; for the highestfrefvalues, it was much greater than the variability of the melodic adjustments. The results suggest that, in adult listeners, the perception of octave harmony disappears at frequencies for which melodic octaves are still accurately perceived.

ISSN:0001-4966    

DOI:10.1121/1.400109

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A sound at a low level is heard as much softer after having decreased continuously from higher levels than if presented after a period of silence at that same low level. Canévet [Acustica61, 256–264 (1986)] demonstrated this phenomenon for a tone that (1) decreased from 65 to 20 dB in 180 s; he also presented a tone that (2) increased from 20 dB, or (3) was presented as pairs of bursts at various levels in random order. Below about 40 dB, loudness changed most rapidly in the decreasing condition so that, at 20 dB, the tone was judged ten times softer than in conditions (2) and (3). In the present experiments, magnitude estimation was used to examine the possible role of judgmental biases and adaptation in this rapid loudness decline, which we calldecruitment. Results show that decruitment did not come about because subjects made many successive loudness judgments; loudness declined as much when a tone was judged only twice, at the beginning and end of its 180‐s decrease. In contrast, interrupting the decreasing tone so that it was heard only at 70 dB and 160 s later at 30 dB greatly diminshed the decruitment. Similarly, pairs of 500‐ms tone bursts presented at successively lower levels instead of continously decreasing did not show decruitment, suggesting that sequential biases are irrelevant. The likely cause of decruitment is sensory adaptation.

ISSN:0001-4966    

DOI:10.1121/1.400110

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Forward‐masked psychophysical tuning curves were obtained from normal‐hearing listeners at different probe levels in quiet and in a broadband background noise. In quiet, tuning‐curve shape changed with probe level. For six listeners, tuning curves became broader with increasing probe level, primarily due to a decrease in the low‐frequency slopes. For one listener, tuning curves became narrower with increasing probe level. The addition of a background noise, which was presented continuously at a level 10 dB below the noise level required to mask the probe tone, reduced the masker levels required to mask the probe tone. The reduction was greater near the tip of the tuning curve than on the tail, so that tuning curves in background noise were narrower than those obtained in quiet. Tuning curves with comparable masker levels near the tip of the tuning curve (Lmtip) were similar in shape, regardless of probe level or whether tuning curves were obtained in quiet or noise. Comparisons of tuning‐curve characteristics derived by fitting tuning curves with least‐squares procedures, indicated that low‐frequency slopes decreased withLmtip. As a consequence,Q10 dBvalues decreased withLmtip. These results are consistent with the interpretation that tuning‐curve shapes are determined by the intensities of the maskers required to mask the probe tone. The addition of a background noise restricted (partially masked) the excitation pattern of the probe so that lower masker intensities were required to ‘‘forward mask’’ the probe tone, and narrower tuning curves resulted from less intense maskers. The results are well described by a two‐process model of auditory excitation patterns.

ISSN:0001-4966    

DOI:10.1121/1.400111

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP