Female voice communications in high levels of aircraft cockpit noises--Part I: spectra, levels, and microphones.

HYPOTHESIS: Female produced speech, although more intelligible than male speech in some noise spectra, may be more vulnerable to degradation by high levels of some military aircraft cockpit noises. The acoustic features of female speech are higher in frequency, lower in power, and appear more susceptible than male speech to masking by some of these military noises. Current military aircraft voice communication systems were optimized for the male voice and may not adequately accommodate the female voice in these high level noises. METHODS: This applied study investigated the intelligibility of female and male speech produced in the noise spectra of four military aircraft cockpits at levels ranging from 95 dB to 115 dB. The experimental subjects used standard flight helmets and headsets, noise-canceling microphones, and military aircraft voice communications systems during the measurements. RESULTS: The intelligibility of female speech was lower than that of male speech for all experimental conditions; however, differences were small and insignificant except at the highest levels of the cockpit noises. Intelligibility for both genders varied with aircraft noise spectrum and level. Speech intelligibility of both genders was acceptable during normal cruise noises of all four aircraft, but improvements are required in the higher levels of noise created during aircraft maximum operating conditions. CONCLUSIONS: The intelligibility of female speech was unacceptable at the highest measured noise level of 115 dB and may constitute a problem for other military aviators. The intelligibility degradation due to the noise can be neutralized by use of an available, improved noise-canceling microphone, by the application of current active noise reduction technology to the personal communication equipment, and by the development of a voice communications system to accommodate the speech produced by both female and male aviators.

Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data.

The mandate of ASA Working Group S12/WG11 has been to develop "laboratory and/or field procedure(s) that yield useful estimates of field performance" of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et at., "Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise," J. Acoust. Soc. Am. 99, 1506-1526 (1996); ANSI S12.6-1997, "American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors" (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-à-vis attenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.

Increase in jammed word intelligibility due to training of listeners.

Data are presented on the effect of training on naive subjects' ability to listen to voice communications under conditions of simulated cockpit noise and active jamming. The results indicate that training improved the performance of listeners under all conditions tested. Suggestions are made for further research to quantify increases in performance of communicators in jammed environments due to training.

Identification of the minimum noise level capable of producing an asymptotic temporary threshold shift.

The present study was designed to identify the minimum noise level capable of producing an asymptotic temporary threshold shift (ATTS). It was estimated that at some level below 85 dBA, probably 70-80 dBA, there existed an exposure level at which no ATTS would occur. It is assumed that if a long-duration noise does not produce temporary changes in hearing levels, then it would not produce permanent changes either. This level would then define an exposure condition below which personnel could be exposed for indefinite periods of time without adverse auditory effects. Subjects were exposed to continuous pink noise for 24 h at levels of 65, 70, 75, 80, and 85 dBA. TTS growth and recovery was measured at specific intervals throughout each condition. Results demonstrate that at the most sensitive frequency (4000 Hz), at ATTS threshold level would be predicted in the region of 75-80 dBA.

Pinto--a new coat patterning factor in Syrian hamsters.

A new patterning factor is described for the Syrian golden hamster. It is called pinto (symbol pi), and it causes large random white areas to be present on the sides and dorsum, interrupting the ground color of the animal. Belly fur is white instead of grayish and there is an overall color lightening effect on self-colored areas. Pinto acts as an autosomal recessive factor. The relationship of pinto to other white patterning factors in hamsters is discussed. It is concluded that pinto is non-allelic with and not linked to any of the other autosomal white patterning factors: piebald (s), white band (Ba), anophthalmic white (Wh), and dominant spot (Ds). The remaining white patterning factor, mottled white (Mo), is sex linked and is assumed to be genetically unrelated to pinto.

Asymptotic behavior of temporary threshold shift and recovery from 24- and 48-hour noise exposures.

Temporary hearing loss (TTS) from long-duration noise exposure reaches an asymptote between 8 and 16 h and does not increase further during continued exposure for durations of at least 48 h. Potential auditory hazards of long-duration exposures are examined in terms of growth and recovery patterns of TTS. TTS growth and recovery patterns were compared during 24- and 48-h exposures of humans to continuous pink noise at a level of 85 dB A-weighted. Results indicate similar patterns of acquisition and relatively equal amounts of TTS for the two exposure durations. However, recovery of preexposure hearing at 4000 Hz following termination of the 48-h noise exposure differed somewhat from that which followed the 24-h exposure. The implications of these findings for long missions in noisy environments are discussed.

Long-duration exposure to intermittent noises.

The effects were examined of various patterns of interruption--of continuous noise by periods of quiet--on the growth and recovery of temporary threshold shift of hearing over an exposure period of 24 h. Monaural thresholds of hearing were measured prior to, during, and following exposure to a pink noise at a level of 85 dBA and to four conditions in which the pink noise was interrupted with various on-off ratios. The interrupted exposure patterns and levels were adjusted to make their average levels equivalent to 85 dBA. Among the results: 1) the growth of TTS clear.ly reached an asymptote for all interrupted exposure conditions, even when the TTS was as small as 5 dB, 2) the interrupted exposures produced lower asymptotic levels than the continuous exposure with the same amount of energy, and 3) the TTS recovery patterns were essentially the same at 1 h and beyond, for all conditions. These data support the concept that, following a long exposure, one should be provided at least as much time for recovery as the duration of the exposure.