摘要:

On the basis of the impulse diagrams of various weapons and many audiometric tests, the CHABA impulse‐noise damage‐risk criteria (DRC) are compared with those of the Federal Republic of Germany. Both DRC indicate maximum permissible exposures in terms of peak‐pressure level and of effective duration. Both DRC aim to protect 95% of the exposed population from permanent auditory damage. The computation of the effective duration differs between the CHABA DRC and the German DRC, and it generally results in a longer effective duration for CHABA. The current study is based on the results for more than 10 000 soldiers, who were audiometrically tested in a mobile monitoring station before firing practice and beginning 2 min after exposure until complete recovery. In a special study, it was possible to compare the results for 478 German soldiers and to evaluate the relative value of the CHABA DRC and the German DRC. This comparison showed that the CHABA DRC are too restrictive, permitting unnecessary ’’less maximum permissible load’’ than the German DRC. Moreover, owing to the large variability in TTS2, measurement of the whole recovery time beginning 2 min after exposure has a greater predictive value. Therefore, recovery time should be used in the evaluation of the DRC.

ISSN:0001-4966    

DOI:10.1121/1.383886

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

This article describes some results on the effect of the preceding stimulus on performance in an intensity‐identification experiment with feedback. Based on previous research and our own subjective experiences as listeners, we had expected that sensitivity would increase when the intensities of the preceding and current stimuli were close together. The results of our experiments show, however, that this is not the case: sensitivity is independent of the preceding stimulus. The fact that the response variance tends to decrease when the intensities of the preceding and current stimuli are close together is found to be caused solely by sequential effects in response bias. These findings create an interesting puzzle concerning the mechanism by which feedback improves sensitivity in identification. Apparently, the most obvious hypothesis—namely, that the feedback enables the previous stimulus to be used as a standard for judging the current stimulus—is false.

ISSN:0001-4966    

DOI:10.1121/1.383887

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Four subjects with low‐frequency hearing loss were evaluated to determine whether their responses to low‐frequency stimulation might be the result of stimulation of nerve fibers with higher characteristic frequencies. Two masking paradigms were employed to indirectly investigate the contribution of high‐frequency nerve fibers to the detection of low‐frequency stimuli: (1) masking of a low‐level, fixed‐frequency probe by a variable‐frequency pure‐tone masker (psychophysical tuning curve) and (2) masking of pure‐tones by a high‐level, fixed‐frequency pure‐tone masker. Low‐frequency remote masking by tones and displacements in the tips of tuning curves to higher frequencies were interpreted as evidence that low‐frequency signals near threshold were being detected by high‐frequency fibers in three of the subjects. Three subjects were also tested with high‐pass, low‐pass, and unfiltered speech both in quiet and in the presence of a high‐pass noise masker. Results were interpreted as showing a relatively small contribution of high‐frequency fibers to the perception of low‐frequency speech.

ISSN:0001-4966    

DOI:10.1121/1.383888

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Two cats were trained to discriminate between rising and falling pitch sequences generated by complex tones. The finding of Heffner and Whitfield [J. Acoust. Soc. Am. 59, 915–919 (1976)], that the intact animals respond to the fundamental pitch rather than to the harmonic content, was confirmed. After bilateral ablation of auditory cortex this was no longer the case. The animals lost their initial training, but could be retrained to respond to the complex tone sequences; however, they now required to be separately trained to each complex tone and did not exhibit transfer between tone pairs that had similar pitch shift but different harmonic composition. The results suggest that cats without auditory cortex respond only to the individual frequencies of the complex and are unable to detect the overall pitch to which those complexes normally give rise.

ISSN:0001-4966    

DOI:10.1121/1.383889

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A series of listening tests with brief synthetic consonant–vowel syllables was carried out to determine whether the initial part of a syllable can provide cues to place of articulation for voiced stop consonants independent of the remainder of the syllable. The data show that stimuli as short as 10–20 ms sampled from the onset of a consonant–vowel syllable, can be reliably identified for consonantal place of articulation, whether the second and higher formants contain moving or straight transitions and whether or not an initial burst is present. In most instances, these brief stimuli also contain sufficient information for vowel indentification. Stimulus continua in which formant transitions ranged from values appropriate to [b], [d], [g] in various vowel environments, and in which stimulus durations were 20 and 46 ms, yielded categorical labeling functions with a few exceptions. These results are consistent with a theory of speech perception in which consonant place of articulation is cued by invariant properties derived from the spectrum sampled in a 10–20 ms time window adjacent to consonantal onset or offset.

ISSN:0001-4966    

DOI:10.1121/1.383890

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Error propagation equations are derived for four different sound‐power measurement techniques: hemispherical freefield, reference source, reverberation time, and two surface. The analysis shows the hemispherical freefield and two‐surface methods to be governed by the same error equation. Of the four methods examined, the reference‐source method is shown to exhibit the strongest dependence on errors in measuring the space averaged sound pressure. The results obtained can be used in planning and executing more accurate sound‐power measurements.

ISSN:0001-4966    

DOI:10.1121/1.383891

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A technique for estimating the diffuse‐field response of piezoelectric transducers on a solid is developed. The procedure is based on a reciprocity principle and is analogous to the technique used for calibrating transducers in a fluid medium. Both ultrasonic and acoustic emission transducers have been calibrated and the results compared to the diffuse‐field response calculated from transducer face‐to‐face response characteristics.

ISSN:0001-4966    

DOI:10.1121/1.383892

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

We postulate that measurement precision and the magnitude of acoustic emission signals will be affected by the type and thickness of the couplant used to couple the transducer to a structure. A theoretical solution is provided to determine the transmission coefficient of a multilayer system ofnlayers. A longitudinal wave is assumed to be normally incident on the system. Theoretical transmission coefficients are obtained for waves transmitted through three, four, and five layers. Specific calculations are carried out for a particular five‐layer system which is applicable to an acoustic emission transducer. Conclusions are drawn concerning the measurement precision likely to be obtained from this type of transducer used in this configuration.

ISSN:0001-4966    

DOI:10.1121/1.383893

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The equivalent circuit in the mobility analogy of a magnetostrictive transducer in the presence of eddy currents is derived. This equivalent circuit is used to predict the effect of eddy currents on the efficiency, the electrical impedance, the transmitting responses, and the receiving sensitivity of a magnetostrictive transducer. Lumped‐parameter equivalent circuits are also presented which use approximations to the exact theory to simply and accurately predict the efficiency and electrical impedance of a transducer with eddy currents within a frequency range of practical interest near the clamped characteristic frequency. It was found that the eddy current theory predicted a sharp drop in the eddy current loss in a narrow frequency range just past resonance. This effect was experimentally observed by Savage and Abbundi [IEEE Trans. Magn. 14, 545 (1978)].

ISSN:0001-4966    

DOI:10.1121/1.383894

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A new one‐piece earphone cushion, model 51, that should afford more reliable hearing measurement data than the conventional two‐piece MX‐41/AR earphone cushion, has been developed by Telephonics Corporation. In particular, the material used for the one‐piece cushion should be more stable over a long period of time than the sponge material used in the two‐piece MX‐41/AR cushion. In addition, the single material of the one‐piece cushion is more easily compounded and thus easier to control than those materials used in the two‐piece cushion, and the cementing operation required for the two‐piece cushion is avoided. The acoustical performances of the one‐ and two‐piece cushions mounted on a TDH‐39 earphone were compared by threshold‐loudness‐balance and coupler measurements. The comparison with threshold‐loudness‐balance measurements on ten subjects showed no significant differences with a confidence of 95% and coupler measurements showed differences less than 0.8 standard deviations in all cases (i.e., no significant differences with α=0.05). In summary, the one‐piece earphone cushion does not differ significantly in acoustical performance from the two‐piece MX‐41/AR cushion. In addition, there is a strong indication that the one‐piece cushion will afford more consistent performances between units, more long‐term stability, and better wearer comfort than the conventional MX‐41/AR cushion.

ISSN:0001-4966    

DOI:10.1121/1.383895

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP