摘要:

A progressive wave apparatus featuring an automated data processor is described. The apparatus accurately determines the propagation constants of an extensional acoustic wave by exciting one end of a strip of material while the other end is suspended under constant tension. The apparatus is capable of making measurements in the frequency range of 100 Hz to 40 kHz, depending on the extensional wave velocity and attenuation in the material. As illustrations of the technique, measurements were made on three rubber compounds: a polyurethane, a neoprene, and a nitrile rubber. Extensional sound speed, attenuation, modulus, and loss factor were determined over a frequency range of 1–10 kHz and a temperature range of 4 °–47 °C. Applying the time–temperature superposition principle to the data, master curves were constructed and WLF shift constants were determined. The apparatus was found to be a fast and reliable method to determine the dynamic viscoelastic constants.

ISSN:0001-4966    

DOI:10.1121/1.383672

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The basic auditory physiology of crickets, and particularly ofTeleogrylluscommodus(Walker) is examined and its behavior simulated by electrical analog networks, beginning from the simplest possible model and progressing by stages to the full system found in the real insect. It is found that the attenuation of sound in the auditory trachea plays a crucial role in the mechanism for directional hearing in even the simplest model and that the tracheal diameter is in fact appropriate to produce the desired attenuation. In a more complex model in which it is recognized that the auditory system probably responds to pressure changes in the tracheal sacs underlying the tympana rather than simply to tympanic motion, it is found that the phase shift produced by the combined effects of the central septum and the adjoining cavities leading to the spiracles is also important to hearing directionality. The final model which includes both tympana and spiracles is able to simulate both the hearing directionality and, in part, the frequency selectivity of the system. It appears, however, that a large measure of the observed frequency selectivity is due to some form of selectivity in the neural transducers themselves rather than in the simple acoustic components of the system.

ISSN:0001-4966    

DOI:10.1121/1.383668

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

There is extensive evidence that in the same phonetic environment the voice fundamental frequency (F0) of vowels varies directly with vowel ’’height.’’ ThisF0difference between vowels could be caused by acoustic interaction between the first vowel formant and the vibrating vocal folds. Since higher vowels have lower first formants than low vowels the acoustic interaction should be greatest for high vowels whose first formant frequencies are closer in frequency toF0. Ten speakers were used to see if acoustic interaction could cause theF0differences. The consonant [m] was recorded in the utterances [umu]and [ama]. Although the formant structure of [m]in [umu] and [ama]should not differ significantly, theF0of each [m] allophone was significantly different. However, theF0of each [m] allophone did not differ significantly from theF0of the following vowel. These results did not support acoustic interaction. However, it is quite reasonable to conclude that theF0variation of [m] was caused by coarticulatory anticipation of the tongue and jaw for the following vowel. Another experiment is offered in order to help explain the physical causes of intrinsic vowelF0. In this experimentF0lowering was found at the beginning of vowels following Arabic pharyngeal approximants. This finding indicates that theF0of pharyngeal constricting vowels, e.g., [] and [a], might be lowered as a result of similar articulatory movements, viz. tongue compression and active pharyngeal constriction.

ISSN:0001-4966    

DOI:10.1121/1.383669

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A series of experiments was carried out to investigate how fundamental frequency declination is perceived by speakers of English. Using linear predictor coded speech, nonsense sentences were constructed in which fundamental frequency on the last stressed syllable had been systematically varied. Listeners were asked to judge which stressed syllable was higher in pitch. Their judgments were found to reflect normalization for expected declination; in general, when two stressed syllables sounded equal in pitch, the second was actually lower. The pattern of normalization reflected certain major features of production patterns: A greater correction for declination was made for wide pitch range stimuli than for narrow pitch range stimuli. The slope of expected declination was less for longer stimuli than for shorter ones. Lastly, amplitude was found to have a significant effect on judgments, suggesting that the amplitude downdrift which normally accompanies fundamental frequency declination may have an important role in the perception of phrasing.

ISSN:0001-4966    

DOI:10.1121/1.383670

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Chinchillas were treated with kanamycin sulfate (150–200 mg/kg/day) to produce high‐frequency hearing loss extending to about 4.0 kHz. Thresholds and psychophysical tuning curves (PTCs) were obtained before and after treatment, utilizing a shuttlebox avoidance procedure, and cochlear hair cells were evaluated under phase contrast microscopy. Hair cell loss resulting from kanamycin treatment varied from restricted lesions of the outer hair cells (OHCs) in the cochlear base, with no loss of inner hair cells (IHCs), to more extensive lesions involving both OHCs and IHCs. Threshold shift of at least 40 dB was always associated with OHC loss. PTCs obtained from frequency regions exhibiting 40–50 dB of threshold shift were normal in shape. With threshold shift in excess of 50 dB, PTCs were progressively distorted, with truncation of the tip segment and in some cases increased sensitivity of the tail segment. The results suggest that the threshold of optimally functional IHCs after kanamycin‐induced OHC loss is about 40 dB higher than normal. Threshold shift in excess of 40 dB may represent IHC damage. IHCs are capable of transducing the fine‐frequency information necessary for generating normally sharp PTCs in the absence of OHCs. However, with threshold shift in excess of approximately 50 dB, this frequency resolution is increasingly compromised.

ISSN:0001-4966    

DOI:10.1121/1.383194

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

This experiment investigated some interactions between combination tones (CT) and unmasking. Data were obtained from nine normal‐hearing listeners in a forward‐masking paradigm in which a 2000‐Hz, 35‐dB SPL masker preceded a 2000‐Hz test signal. An adaptive, three‐interval forced‐choice procedure was employed to estimate the threshold for the test signal. This measurement provided a baseline. When a second sinusoid, the suppressor, of variable frequency and 55 dB SPL was presented concurrently with the masker, the amount of masking could be less than in the baseline condition. This two‐tone unmasking was observed when the suppressor was approximately 2300 Hz. In the cubic difference tone (CDT) condition, two higher‐frequency sinusoids of 80 dB SPL (with the lower frequency fixed at 2800 Hz) were added to the masker. In the difference tone (DT) condition, two higher‐frequency sinusoids of 100 dB SPL (with the lower frequency fixed at 3500 Hz) were added to the masker. None of these sinusoids produced unmasking when presented individually, but when the CDT and DT were approximately 2300 Hz, unmasking was observed. The unmasking produced by the CTs was similar in its frequency characteristics to that of the single, suppressor tone. These results indicate that unmasking can be produced by CTs, just as if CTs were present in the stimulus. These data indirectly support the notion that CTs may be present in the form of traveling waves propagated along the basilar membrane.

ISSN:0001-4966    

DOI:10.1121/1.383671

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Intensive and temporal characteristics of forward masking were assessed using a pure‐tone masker and a 1‐kHz probe. For a given interval between masker and probe, the slope of the masking function tends to decrease with increasing masker frequency, but is always less than unity. When the masker frequency equals that of the probe, increasing the masker‐probe interval decreases the slope of the masking function. Implications of these data for forward‐masked psychophysical tuning curves are discussed. A model, based on a linear combination of exponential decays and an initial logarithmic transform of stimulus intensity, predicts the general form of the masking function for varying interval between masker and probe, and suggests time constants which decrease with increasing masker level.

ISSN:0001-4966    

DOI:10.1121/1.383673

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Measurements of the masking function with different masker envelopes suggest that short‐term spectral broadening at offset affects the frequency extent of forward masking, at least for masker frequencies above the probe frequency.

ISSN:0001-4966    

DOI:10.1121/1.383674

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A model based on a peripheral weighting function rather than on critical bands is used to provide predictions for the repetition pitch and pitch strength associated with ripple noise. The peripheral weighting function along with a bandpass filter representing the middle and outer ears produces a transformation of the ripple noise spectrum. The Fourier transform (autocorrelation) of this spectrum produces predictions consistent with the data obtained on repetition pitches. This approach is discussed in relation to other recent models of the pitch of complex stimuli. In particular, the predictions of the pattern‐transformation model for the pitch of complex stimuli were compared to data from ripple noise experiments. The pattern‐transformation model does not appear capable of accounting for many of the pitches associated with ripple noise.

ISSN:0001-4966    

DOI:10.1121/1.382942

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In chinchillas, the length of the organ of Corti was found to vary by as much as 26% of the mean (18.31 mm). In specimens of different lengths, areas in which the basilar membrane and organ of Corti have the same physical dimensions were found to be located at the same percentage distance along the cochlear partition. Average densities of the inner and outer hair cells were noted to decrease with increasing cochlear length. However, the rate of decrease in density was less than the rate of increase in length. These findings indicate that long cochleas have a greater amount of the organ of Corti (and hence more sensory cells) in a given frequency region.

ISSN:0001-4966    

DOI:10.1121/1.383092

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP