摘要:

A surface acoustic intensity meter is described for measuring acoustic intensity at a vibrating surface using a fiber optic lever as a displacement transducer and a condenser microphone to measure surface pressure. Digital signal processing using a two‐channel FFT analyzer allows the calculation of surface intensity as a function of frequency. The technique has been tested in an anechoic chamber on a point monopole and a steel plate clamped at the edges. Calculated sound power levels are compared with results obtained by traditional techniques.

ISSN:0001-4966    

DOI:10.1121/1.2021314

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Recently, measurements of pressure‐temperature cross spectra were made in a duct downstream of a combustor to provide additional information beyond that available from pressure spectra and cross spectra measurements so that an appropriate source region model could be selected and to provide information on the physical mechanisms active at the combustion noise source. The model developed to interpret the measurements is presented and compared with the data. The results show good agreement with the data.

ISSN:0001-4966    

DOI:10.1121/1.2021366

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In a series of 24 acute experiments on pentobarbital anesthetized dogs, thermal distributions generated by ultrasonic heating using a 1‐MHz PZT transducer were compared with intensity distributions mapped in a test tank. Relatively flat temperature distributions from 1 to 3 cm have been mapped in normal dog brain using “shaped” intensity distributions generated from ultrasonic emission patterns which are formed by the interaction between compressional, transverse, and flexural modes activated within the crystal. In contrast, these same intensity distributions generated marked variations in three malignant brain tumors presumably due to variations in tumor blood flow. The results of this study suggest that a practical clinical system for uniform heating of large tumor volumes with varying geometries is not an achievable goal. Our laboratory is developing a scanning ultrasonic rapid hyperthermia treatment system which will be able to sequentially heat small volumes of tumor tissue either to temperatures which will sterilize tumor or to a more conventional thermal dose. [Supported by NIH/NCI CA29731.]

ISSN:0001-4966    

DOI:10.1121/1.2021415

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The third lumbar region of the neonatal mouse spinal cord was irradiated with 1‐MHz ultrasound using intensities between 46 and 289 W/cm2at hydrostatic pressures of 1 and 16 atm. It was previously reported that the threshold exposure duration necessary for production of hind limb paralysis of the neonates increased with hydrostatic pressure at 289 W/cm2but not at the lower intensities, although subharmonic and harmonic signals were observed at all intensities [Frizzellet al., J. Acoust. Soc. Am.74, 1062–1065 (1983)], suggesting that acoustic cavitation is involved at 289 W/cm2Examination with electron and light microscopy reveals that permanent paralysis is always accompanied by altered spinal cord morphology and that the minimum tissue damage is altered synaptic morphology similar to that observed in the cat brain [Borrelliet al., J. Acoust. Soc. Am.69, 1514–1516 (1981)]. Tissue damage was greatest at the perimeter of the spinal cord, possibly as a result of higher temperatures resulting from heat conduction from the more highly absorbing spinal column. This suggests that hyperthermia plays a role in development of tissue damage even when another mechanism is involved. [This work was supported in part by grants from the NSF and the NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2021459

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In psychophysical experiments, the reduction in the effect of one stimulus (the masker) due to the addition of a second stimulus (the suppressor) is attributed to the suppression of the masker by the suppressor. Kramer [reported by F. L. Wightman, T. McGee, and M. Kramer, inPsychophysics and Physiology of Hearing, edited by E. F. Evans and J. P. Wilson Academic, London, 1977)] measured “unmasking patterns” (signal threshold as a function of suppressor frequency) in listeners with high‐frequency hearing loss. Although he observed normal suppression effects in a region of normal hearing, he found no evidence of suppression in regions of impaired heating. One factor which might have contributed to this failure was an unlucky selection of the suppressor level. This experiment compares the effect of suppressor level in normal and hearing‐impaired frequency regions. Thresholds for 10‐ms signals (10‐ms, cosine‐squared ramps with no steady state) were obtained for signals at 1 and 4 kHz forward masked by 300‐ms, narrow‐band (50‐Hz‐wide) noise maskers centered at the signal frequencies. Masker levels were 50 and 70 dB (total noise power), respectively. Suppressor levels varied from 30 to 90 dB SPL; suppressor frequencies were 0.7 kHz for the 1‐kHz masker and 2.8 and 5.0 kHz for the 4‐kHz masker. As observed by Kramer, suppression effects appear to be absent in regions of hearing impairment. However, in this experiment, this absence does not appear to be correlated with an absence of a difference between simultaneous and forward masking. [Research supported by grants from NSF and NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2021518

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Moore [J. Acoust. Soc. Am.54, 610–619 (1973)] has suggested that under the assumptions of a place or excitation‐pattern theory of frequency discrimination, frequency DLs should be dependent on auditory excitation‐pattern slopes only for long‐duration tones with spectral slopes that are steeper than those of the excitation pattern. Otherwise, according to this theory, it is the slopes of the stimulus spectrum that limit the frequency DL. In this paper, we extend these ideas to evaluate the prediction that for very short, spectrally broad tones, frequency DLs obtained from hearing‐impaired subjects should not differ systematically from those obtained from normal‐hearing listeners. Frequency DLs were obtained as a function of intensity at 500, 1000, and 2000 Hz for 5‐ and 300‐ms pure tones in normal‐hearing and moderately hearing‐impaired subjects. The DLs obtained from hearing‐impaired subjects were larger than normal for long‐duration but not short‐duration pure tones; these results are consistent with the predictions of the excitation‐pattern theory. However, an unexpected but consistent finding of nonmonotonic frequency DL‐intensity functions in the 5‐ms condition in normal‐hearing subjects complicates interpretations of the results.

ISSN:0001-4966    

DOI:10.1121/1.2021567

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The present study was designed to contribute information on kinematic details of the glottal abduction‐adduction gesture in voiceless consonant production. Transillumination was used to record glottal movements. The linguistic material consisted of multiple repetitions of dental stops and fricatives which differed in stress and were spoken at two different rates. Two native American English speakers served as subjects. As expected, glottal opening was larger for fricatives than for stops. Preliminary kinematic results suggest a stable positive relationship between maximum displacement and peak velocity of glottal movements. That is, peak velocity of both abduction and adduction was positively correlated with peak glottal opening for both fricatives and stops. An increase in glottal opening was also associated with stress, with stressed voiceless consonants having a larger peak glottal opening than their unstressed counter‐parts. In general, peak velocity of glottal abduction was higher than that of glottal adduction. Results from laryngeal articulatory gestures are consistent with reports for other articulators. [Work supported by NINCDS and BRSG.]

ISSN:0001-4966    

DOI:10.1121/1.2021622

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A multiple regression model was developed to account for the variance in phonatory jitter among normal speakers and for predicting an expected jitter value and confidence interval for individual subjects. Jitter was measured with a system resolution capable of measuring a minimum perturbation of 2.15 μs. Measures were made from maximum phonation lengths of 95 adults without laryngeal pathology. Seven factors were examined for contributions to the prediction of jitter: sex, age, smoking history, drinking habits,F0, vocal intensity, and length of phonation. A multiple correlation coefficient of determination of 97.6% was obtained for the normal subject pool with a three‐factor model including: vocal intensity,F0and phonation length. For 20 patients with laryngeal pathology, individual predicted jitter values and 90% confidence intervals were computed using the normal regression model, for determining when patients' actual jitter values were outside of their expected confidence intervals. Only 30% of the patients with confirmed laryngeal pathology had jitter values outside of their predicted intervals, indicating that this measure would not be valid for use in screening for laryngeal pathology.

ISSN:0001-4966    

DOI:10.1121/1.2021673

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Numerous music acoustics and psychomusicology text books claim that it is not possible to hear the individual pitches when two simultaneous tones are separated by a half‐step. Musicians, on the other hand, find that their day‐to‐day experience does not correspond well with this claim. Remarkably little research literature was found which tests this question in a musical situation. Because this task pits the information available in the frequency domain and that available in the time domain in opposition, it is important to determine who is right. The results of a test in which subjects used the method of adjustment to match a tone to either of two, simultaneous tones are presented. These subjects qualified to take the test by demonstrating fine‐tune pitch matching ability to a single tone. In contrast to the previously accepted limit of frequency discrimination, the results indicate that the subjects were able to effectively analyze one of the pitches out of a two‐tone stimulus whose frequencies were as little as one‐quarter step apart.

ISSN:0001-4966    

DOI:10.1121/1.2021697

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In J. Acoust. Soc. Am. Suppl. I69, S103 (1981) a computer program was presented, which works as a musical version of a text‐to‐speech‐conversion program. Thus, the input is the melody in musical notation, and the output is the melody played. The “pronunciation rules” in this program, which serve the purpose of improving the musical quality of the performance, have now been further developed. New rules have been formulated which work with a time window corresponding to one or several bars. In a formal test the musical effect of these rules have been approved by a group of professional musicians. The purpose and means of the rules are discussed. Some rules apparently serve the purpose of emphasizing unexpected notes or marking structural components of the melody such as chord shifts and phrases. The ways in which this is signaled in the performance often show a striking similarity with rules for speech suggesting that the rules refer to the listener's acquaintance with speech. Other rules seem to allude to the listener's previous experience of motion. In this way, the project seems to shed some light on some basic requirements for music communication.

ISSN:0001-4966    

DOI:10.1121/1.2021270

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP