An experiment was conducted to study earmuff wearers’ signal detection in noise performance and perceptions of comfort and acceptability with two amplitude-sensitive earmuffs as compared to their conventional counterparts. Passive and electronic amplitude-sensitive earmuffs were tested, represented by the EAR Ultra 9000 and the Peltor T7-SR, respectively. Directly comparable earmuffs, the EAR 2000 and Peltor H7A, were used as conventional controls. The effect of the Peltor T7-SR’s gain on noise exposure and the attenuation of all earmuffs was also assessed. Signal detection performance was assessed via masked threshold determination in three levels of pink noise (75, 85, and 95 dBA), using a digitized back-up alarm as the detection stimulus. A modified Hughson-Westlake procedure was used to obtain 10 trials for each earmuff under each noise level. Comfort and acceptability were investigated via questionnaire. Real-ear-at-threshold (REAT) attenuation measures were recorded at 500 and 1000 Hz to ensure consistent earmuff fitting and measurements were made of the effect of subjects’ Peltor T7-SR gain settings in each noise level using a KEMAR manikin. Results indicated that only the noise level significantly influenced subjects mean masked thresholds; masked threshold increased linearly with noise level. The lack of a significant earmuff main effect or interaction could have resulted from the step size used to present the stimulus, the noise type or levels used, or the number of experimental conditions/sessions. No earmuffs were judged significantly different in comfort or acceptability. Noise level and gain status (on vs. off) were found to influence the measures taken on the noise level under the Peltor T7-SR, but the increase in noise dose with the gain control on was small. The estimates of attenuation obtained were reasonable for the devices tested. / Master of Science

An experiment was conducted to determine the effects of different acoustic characteristics of the testing environment on the measured attenuation of hearing protection devices (HPDs) when using a standard real-ear attenuation at threshold (REAT) protocol. In the experiment, three earmuffs and three earplugs were tested in two diffuse sound fields implemented in two different sound environments with different loudspeaker configurations. In the first case, the testing environment was reverberant, with frequency-specific reverberation time characteristics as specified in ANSI $3.19- 1974, "Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs" and with three loudspeakers, one in each principal plane of the room. In the other case, a diffuse sound field was established within an anechoic chamber (free-field), as permitted by ANSI S12.6-1984 "Method for the Measurement of the Real-Ear Attenuation of Hearing Protectors" using four loudspeakers, one at each vertex of a tetrahedron with the subject's head center position at the centroid. Each of the environments met the requirements of the applicable ANSI standard as well as the requirements of standards adopted by several foreign countries. The experimental design allowed a direct comparison of the testing environments (reverberant vs. free-field) permitted by the two aforementioned ANSI standards. Results indicate that for both earmuffs and earplugs, the environment in which a REAT evaluation is performed has a statistically significant impact on the results of the evaluation. These results have implications for ongoing standards development efforts not only in the United States but also abroad since the testing environments investigated in this research are either required or allowed by several international standards. These international standards include: International Standard ISO 4869-1981, Canadian Standard CSA Z94.2-M1984, British Standard BSI 5108:1983, and Swedish Standard SS 882151 (1981). The impact of outlier dismissal on the results of REAT tests of HPDs was also investigated and found to have minimal impact on the results obtained in this experiment. However, this result is most likely case-specific and it is doubted that any generalizations can be made concerning outlier tests and their impact on HPD evaluations. As a side issue, it was also determined that ear canal size is highly correlated with attenuation achieved using premolded earplugs with attenuation decreasing with increasing ear canal size. No consistent gender effects were found in the analysis, indicating that gender alone may not be an important factor in determining how much attenuation can be obtained with a given HPD. Finally, the lack of a significant trial effect points to the absence of a strong practice effect over the three trials of a REAT evaluation, at least for subjects who are highly practiced in the REAT procedures. / Master of Science

Call number: LD2668 .T4 1985 S99 / Master of Arts

A field research study was conducted to determine the actual noise attenuation and perceived comfort achieved by 40 noise-exposed industrial workers in 5 industrial workplaces wearing 4 different industrial hearing protection devices (HPDs) while on the job. Over 2 consecutive 3-week periods of HPD use, the study investigated the effects of 2 different HPD fitting procedures (subject-fit versus trained-fit) on the spectral field attenuation and user-rated comfort achieved with a user-molded foam earplug, a premolded, triple-flanged polymer earplug, a popular foam cushion earmuff, and an ear canal cap with compliant rubber earpods. Workers were pulled from their workplaces without prior knowledge of when they were to be tested and without re-adjusting the fit of their HPDs. Attenuation data were collected using psychophysical real-ear-attenuation-at-threshold measurement procedures as per the ANSI S12.6-1984 standard. Subjective comfort data were also obtained based on multi-dimensional bipolar rating scales. The results of statistical analyses indicated that when training for proper fitting was used, the earplugs significantly improved in noise protection (from 7.2 to 14.6 dB, depending on the frequency and the earplug) at frequencies of 125 - 1000, 6300, and 8000 Hz, whereas the earmuff and the ear canal cap were relatively resistant to the fitting effect. The training was most effective for the slow-recovery foam earplug over the 3-week period. For the comfort rating data, the foam earplug was again sensitive to the fitting effect, but the other HPDs were not. Among the 4 HPDs evaluated in the study, the canal cap protector was judged as the least comfortable HPD, while the other 3 HPDs yielded about the same perceived comfort. This research also showed that the overall field HPD protection afforded can be accurately predicted from single test band (i.e., centered at 500 or 1000 Hz) attenuation measurements. In addition, the field study demonstrated that laboratory simulation protocols designed to simulate field influences on HPD performance (used in the precursor laboratory study) may not be relied upon to yield accurate estimates of field performance of all HPDs. However, the estimates of field attenuation performance were more accurate for the earmuff than for the earplugs tested. Finally, this study demonstrated that the labeled manufacturers' single-number noise reduction ratings (NRRs) and frequency-specific data substantially overestimate the actual HPD attenuation performance achieved in the field. Consequently, on the basis of the results of this study, it appears that an appropriate, device-specific derating scheme to correct unrealistic labeled attenuation data is needed. / Ph. D.

Laboratory-obtained, manufacturer-supplied hearing protector attenuation ratings typically overestimate the workers' protection level In the workplace. In addition, several work-related in-field factors often degrade protection performance of the hearing protection devices (HPDs), posing the threat of underprotection for industrial workers. This research investigated the effects of HPD wearing time, subject activity movement, and HPD fitting procedure on the frequency-specific attenuation and user-rated comfort achieved with a popular foam cushion earmuff, two types of earplugs (user-molded foam and pre-molded, triple-flanged polymer), and an earmuff over foam earplug combination. Both attenuation and comfort data were collected from 40 naive but audiometrically normal subjects. Using a psychophysical real-ear-attenuation-at-threshoId-measurement procedure, attenuation data were obtained before, during, and after the activity movement tasks, which induced typical worker movements, so that the influence of wearing time and activity movement could be determined. Bipolar comfort rating data were also collected before and after the activity movement tasks, The results of statistical analyses indicated that achieved attenuation and user comfort significantly decreased over a two-hour wearing period and that training to achieve better fitting markedly improved protection, although these changes were device- and frequency-specific. Loss in frequency-specific attenuation over the wearing period was up to 6.3 dB for all HPDs except the foam plug, and attenuation Improvement due to training ranged from 4 to 14 dB for all HPDs except the earmuff at 1000 Hz and below. Almost no difference In achieved attenuation or comfort was found between the two activity (head/torso and temporomandibular) movements, but the earmuff tended to slip during highly kinematic head/torso movement. In general, out of the four different HPD configurations used in the study, the foam plug was very resilient to either type of activity movement but did benefit more than the other devices from the training for proper tilting; it was also perceived as the most acceptable and stable HPD by the subjects. In summary, the research illuminated the strong influence of in-field factors on HPD effectiveness. / Master of Science

Thesis (Ph.D.)--James Madison University, 2010. / Includes bibliographical references.

Thesis (Au.D.)--James Madison University, 2010. / Includes bibliographical references.

Thesis (Ph.D.)--James Madison University, 2010. / Includes bibliographical references.

Thesis (Au.D.)--James Madison University, 2010. / Includes bibliographical references.