摘要:

Jet aircraft and engine test facilities are being designed to operate using air cooling only in the exhaust system. Many of these facilities are experiencing low‐frequency noise due to aerodynamic instability. The presentation will include a discussion of low‐frequency noise generation in jet engine test facilities and measured data. Data are measured down to 2 Hz since much of the noise energy is in the infrasonic frequency range.

ISSN:0001-4966    

DOI:10.1121/1.2023103

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The A‐weighted sound‐pressure levels for 75 different industrial noise spectra were determined. Previously published sound‐pressure level transformations by Kuhn and Guernsey [J. Acoust. Soc. Am.73, 95–105 (1983)] from the field, either progressive or diffuse, to the body or head surface were applied to these noise spectra and the resulting A‐weighted sound‐pressure levels were calculated. For the most part, a microphone at the torso or head measures a larger A‐weighted sound‐pressure level than a microphone in the unobstructed sound field. The range of the resulting measurement error, due to the presence of the body or the head, is approximately − 1 dB(A) to + 5 dB(A). The magnitude of the error is sensitive to the type of sound field, the subject's orientation relative to the angle of incidence of the sound, the noise spectrum, and the microphone location. Other factors, for example, the microphone size and directivity, the distance between the microphone and the body, and the absorption of the sound by different types of clothing will also affect the measurement errors. Although these factors are implicit in some of the reported transformations, their individual, explicit effect on the measurement errors remains to be determined.

ISSN:0001-4966    

DOI:10.1121/1.2023156

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The velocity of sound and the nonlinearity parameters of HY80 3.25% NiCrMoV steel samples which were heat treated at 538 °C for periods ranging from 0–100 h were measured. Elastic constants (c11andc111) associated with these measurements were reported, and they were compared with values obtained from other steels. It was found that the difference between measured values among the samples is larger than one would expect. Possible reasons for the discrepancies are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2023217

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The acoustic radiation force was measured for a dual‐temperature resonant chamber. This rectangular chamber has its long dimension approximately 8.5 times the square cross‐sectional dimension and the opposite ends are at widely different temperatures. Force profiles were obtained for two hot‐end temperatures of 500 °C and 750 °C, while the cool end remained at approximately room temperature. The lateral force was measured as a function of the long dimension of the chamber along the temperature gradient, and as a function of the drive voltage. The highest force per unit mass measured at 500 °C was 103.8 dyn/g for a frequency of 4450 Hz, and at 750 °C the highest force was 82.8 dyn/g for a frequency of 5500 Hz. Qualitatively, the measured force profiles correspond well with the theoretical curves; however, correlation of absolute magnitude is yet to be determined. [Work supported by NASA.]

ISSN:0001-4966    

DOI:10.1121/1.2023258

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Last spring we reported to this meeting findings from a series of auditory‐evoked response (AER) tests designed for studying individual differences in AER's by comparing between‐subject (BS) variability with within‐subject (WS) variability. The series involved a repeated‐measures design, where seven young adult subjects were tested weekly for eight sessions; in each session, AER's were collected for right monaural, left monaural, and binaural click stimulation. Continuing analysis of the brain stem data, focusing on comparisons of binaural versus monaural responses, shows further examples of: (1) clear differences between the two types of variability; (2) distinct patterns, or “profiles,” of individual performance that are articulated both in terms of differences according to ear of stimulation and peak of the response; (3) striking degree of replicability of individual patterns of performance; (4) deviations from replicability that most often take one of two forms—(a) increases in stability with continued testing, and/or (b) “emergence” of response patterns that may result in the response profile of one subject coming to resemble that shown by other individuals. [Work supported, in part, by AFOSR 84‐0335 and 85‐0379.]

ISSN:0001-4966    

DOI:10.1121/1.2023306

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Cortical auditory‐evoked potentials (AEP's) were recorded simultaneously with the collection of behavioral responses to consonant‐vowel stimuli presented both dichotically and diotically in a group of 16 right‐handed normal females. During dichotic listening, the mean N1‐P2 component of the AEP's recorded over the temporal region of the left hemisphere was found to be significantly larger in amplitude than the mean recorded over the homologous area of the right hemisphere. No significant amplitude differences were found for any AEP component during diotic listening. The latencies of AEP components revealed no systematic trend across hemispheres during either dichotic or diotic listening. The mean amplitude of N1, and the mean peak‐to‐peak amplitudes of P1 and N1 and N1‐P2 were significantly larger over the right hemisphere during dichotic listening than during diotic listening, a result opposite to that expected if suppression of right hemisphere activity had occurred during dichotic testing. Correlation analyses revealed no significant relationships between hemispheric differences in AEP's, a measure of strength of handedness, and a measure of right‐ear advantage during dichotic listening.

ISSN:0001-4966    

DOI:10.1121/1.2023357

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Attempts were made to learn how well timing alone could be used to differentiate words from each other when speakers and tempo vary. In addition, we wanted to determine if this information is being missed by some commercial speech recognizers. A set of 12 phrases and words was selected describable in terms of the same sequence of acoustic intervals but differing in stress, consonant voicing, vowel tensity, etc.:accuse, Otis, advise, it froze, outhouse, appease, abbeys, etc.). The lists were recorded at two tempos by four speakers and prominent intervals were measured. First, discriminant analysis was employed on the measurements to identify the words. Second, the recordings were used with a commercial isolated‐word speaker‐dependent recognizer for training and testing. Many simple experiments were conducted with these two systems comparing their performance with training on (1) one tempo, testing on the other, (2) one speaker, testing another, and (3) one versus several speakers. The results show that (1) a temporal description for each wordcanbe reliably made that is invariant across speakers and speaking tempo, and (2) for these words, timing performs about as well as the commercial system but made different errors, thus suggesting that such timing information might improve recognizer performance.

ISSN:0001-4966    

DOI:10.1121/1.2023402

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In a previous study [R. Sturm and J. Jakimik, J. Acoust. Soc. Am. Suppl. 176, S29 (1984)], positive and negative effects of linguistic context on identification of whispered words were found. Relative to neutral contexts, appropriately biased contexts improved identification, whereas inappropriately biased contexts reduced correct identifications, and led to misperceptions, even for words accurately perceived in neutral contexts. The present study follows up on these results using more carefully controlled stimulus materials, and more sensitive response measures. Acoustically identical whispered words were presented in various contexts, and listeners rated their confidence in the words they identified. The accuracy and confidence results are examined to establish the scope of the effects of context. The implications of the findings for models of the integration of acoustic‐phonetic and higher‐level information in speech perception are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2023450

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

From its consistent presence in sweep‐frequency measurements and in natural speech data, the spectral antiformant in the 2700‐Hz region might be thought to be a candidate perceptual feature involved in distinguishing laterals from vowels. However, in isolated synthetic steady‐state stimuli, the presence versus absence of an antiformant is barely detectable. This finding can be interepreted (consistent with other experiments using fricatives) as indicating that the auditory filter “smoothes over” the spectral notch. The width of the notch was exaggerated experimentally, as a probe for the width of the auditory filter in speech. A value in excess of 1 bark, and consistent with the assumption of a 3‐ to 3.5‐bark‐wide filter, was found. This property of auditory analysis seems to underlie a rather large range of speech effects. A second question which arises is whether the antiformant might be detected by temporal auditory mechanisms, such as enhanced onset/offset of discharge in the appropriate channel. But, when stimuli with and without the antiformant were embedded in an intervocalic context, hardly any evidence of perceptual enhancement was found: Differences were again barely detectable. Instead, apparently, the contrast lateral versus vowel relies on grosser auditory characteristics such as transition duration, steady‐state duration, and the amplitude envelope.

ISSN:0001-4966    

DOI:10.1121/1.2023493

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Reaction time measurements to tokens composed by means of categorial phonetic mismatches have indicated that information which is distributed throughout a syllable is used in making segment identification judgments [Whalen, Percept. Psychophys.35, 49–64 (1984)]. This raises the possibility that speech perception proceeds from syllable perception “backwards” to segment identification. The mismatches created using tokens similar to those of Whalen's experiment 1 are not identical in their demands on the listener. Thus the mismatched fricative may be closer or further from the expected fricative depending on the degree of coarticulatory rounding. For instance, if the formant transitions lead the subject to expect a palatal fricative, the fricative noise of [us]will be closer to the expected fricative than that of [is]. It is proposed in this paper that the perception by syllables approach would predict that subjects would recover from the mismatch more quickly when the actual fricative noise is close to the expected fricative while the perception by segments would predict the opposite. The results of an experiment testing these hypotheses support the perception by segments approach. The interaction (in an ANOVA) between actual fricative and original vocalic context of the fricative was significant [F(3,42) = 3.52,p<0.05] in the appropriate direction.

ISSN:0001-4966    

DOI:10.1121/1.2023060

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP