Among the many occupational hazards to which Army rotary-wing aviators are exposed is intense noise generated from the aircraft. The potential for permanent hearing loss and difficulty communicating in helicopter noise is well known; an appropriate way to evaluate a hearing-impaired pilot's safety risk due to hearing loss is not as well known. Previous research has studied communication ability in helicopter cockpit noise under different headsets, but there are not conclusive data on the combined effects of degraded speech intelligibility due to noise and flight workload under the headset technology currently available to Army helicopter pilots. In particular, there is a scarcity of information on pilots with hearing loss. Currently, Army Aeromedical standards stipulate audiometric threshold criteria for rated helicopter pilots to ensure their safe flying. If the standard is not met, a flight waiver for hearing is generally granted if the pilot demonstrates good (at least 84%) binaural word recognition ability in a quiet environment. A research study was conducted to evaluate Army helicopter pilot performance with regard to flight workload, communication signal quality, headset configuration, and pilot hearing ability. Objectives of the study included the ability to refine current Army audiometric hearing waiver criteria, and to yield data on which to base flight and headset selection recommendations for pilots. In general, it was believed that flight performance and ratings of situation awareness (SA) would decrease as flight workload increased and communication signal quality decreased, and that assistive communication devices coupled with headsets would afford improved flight performance over their passive counterpart. It was also hypothesized that normal-hearing pilots would perform better than hearing-impaired pilots would. Twenty Army helicopter pilots (one group of 10 pilots without a hearing waiver and one group of 10 pilots with a hearing waiver) participated in this study. The pilots flew three flights in a Black Hawk flight simulator, each with a different headset configuration and with varying flight workload levels and varying air traffic control (ATC) communication signal quality. Objective flight performance parameters of heading, altitude, and airspeed deviation and ATC command readbacks were measured. Additionally, measurements were taken on subjective measures of workload, SA, and headset comfort/speech intelligibility. Experimental results partially supported the research hypotheses. Results indicated that flight performance and ratings of SA were negatively affected by increased flight workload and decreased communication signal quality for both groups of pilots. Results also showed that a passive headset/passive earplug combination use by the hearing-impaired group of pilots led to degradation of certain flight performance parameters and lower ratings of SA than the headsets equipped with assistive communication technology; however, the same headset effect was not seen with the group of normal-hearing pilots. This study yielded results that support a conclusion that factors other than hearing thresholds and word recognition ability in a quiet environment should be considered when evaluating Army helicopter pilots flight safety with regard to hearing sensitivity. Rather, the synergistic effects of flight workload and communication signal quality with individual hearing levels should be considered when making continued flight recommendations and headset choice recommendations. Results also support a recommendation requiring hearing-impaired pilots to use assistive communication technology and not be permitted to fly with passive headset devices. Further research should include a functional hearing assessment in which pilot hearing requirements are determined and individual hearing abilities are compared to the requirements. / Ph. D.

Noise levels in modern industrial and military environments are constantly increasing, requiring the improvement of current hearing protection devices. The improvement of passive hearing protection devices lies in examining the performance of major contributors to reduction of noise attenuation. The finite element method can be used to fully explore single hearing protection (SHP) and double hearing protection (DHP) systems, and the major performance mechanisms can be observed numerically as well as visually in modern postprocessing software. This thesis focuses on developing and evaluating double hearing protection finite element models, and exploring the behavior mechanisms responsible for reduced noise attenuation. The double hearing protection model studied consists of an earmuff preloaded to a barrier covered to simulate human flesh, and a foam earplug installed inside a rigid cylinder designed to simulate the human ear canal. Pressure readings are taken at the bottom of the simulated ear canal assembly. Advanced finite element models are used to reconcile differences between the experimental and finite element results, and to investigate the behavior of the modeled system. The foam earplug material properties for the finite element model are required in the same shear state of stress and boundary condition configuration as the experimental DHP setup, therefore a novel material extraction method is used to obtain this data. The effects of radial compression preload on the earplugs are considered, and the resulting foam earplug shear material properties are input into the finite element DHP model where the effects of the updated foam material properties are observed. / Master of Science

Objective assessment for the effect of hearing protectors, background noise levels, and backup alarm acoustic features on listeners' abilities to localize backup alarm signals in the horizontal dimension, as well as on their ability to detect backup alarm signals in the distance dimension, is lacking in the acoustics and safety literature. Accordingly, two research experiments were conducted for this dissertation. In the first experiment, the effect of seven hearing protectors, two background pink noise levels (60 dBA and 90 dBA), and two backup alarm signals (standard and spectrally-modified) on the ability of normal hearing listeners to localize backup alarm signals in the horizontal dimension was investigated. Results indicated that a diotic sound transmission earmuff significantly degraded localization accuracy as compared to all other hearing protectors and the open ear condition. In addition, no significant difference existed between the open ear condition and the other hearing protectors in localization accuracy in most of the conditions tested. However, the E-A-R/3M HiFiTM earplug was advantageous in localization performance since it provided a significantly higher percentage correct localization than the Moldex foam earplug, the diotic earmuff, and the dichotic earmuff in 90 dBA pink noise. As for main effects of the other independent variables, the 90 dBA pink noise significantly degraded localization performance as compared to the quiet condition of 60 dBA, and a spectrally-modified backup alarm significantly improved localization performance as compared to the standard (narrowband) backup alarm. Potential application of these results includes the revision of backup alarm standards. In addition, these results provide clear advice for safety professionals to avoid the application of diotic sound transmission earmuffs for workers if localizing backup alarms is important. In the first experiment, listeners' feeling of comfort for each hearing protector was assessed subjectively by using a comfort rating scale. In addition, a subjective assessment for listeners' confidence in their localization decisions was established. Results indicated no significant difference between the hearing protectors in terms of comfort. However, in terms of listeners' confidence in localization decisions, their confidence was significantly degraded when they were fitted with the diotic earmuff. By contrast, they showed significantly more confidence in their localization decisions when they were fitted with the E-A-R/3M HiFi™ earplug as compared to when they were fitted with the Moldex foam earplug, the E-A-R/3M Ultrafit™ earplug, and the Bilsom passive earmuff. In the second experiment, listeners' performance in detecting a stationary backup alarm signal, including both a standard (narrowband) and broadband (pulsed white noise) alarm, was determined while they were equipped with various passive and electronic hearing protection devices. Listeners' performance was quantified by detection distance, which was defined as the distance between the stationary backup alarm device and the position where the listener detected the backup alarm signal. The resultant data demonstrated that normal hearing listeners detected a standard (narrowband) backup alarm signal at significantly longer distances as compared to the broadband (Brigade™) backup alarm signal, thus indicating the earlier forewarning by the standard alarm. In addition, passive hearing protection devices characterized with high attenuation significantly reduced the detection distance. These results may be applied to assist safety professionals in selecting hearing protectors and backup alarm signals that provide on-foot workers with ample time to react to an approaching backing vehicle, thus improving their safety. / Ph. D.

Exposure to excessive noise during a neonates stay in the neonatal intensive care unit (NICU) can create both immediate and long term health problems such as, hearing loss, neurological deficits, and sleep pattern disturbances. The use of earmuffs or earplugs to decrease the neonate’s exposure to noise can create a more stable environment to facilitate improved growth and development. The purpose of this research was to examine the use of earmuffs or earplugs to reduce the impact of noise on neonates. A systematic review of literature was conducted using online databases including CINAHL, ERIC, Ebsco Host, Medline, and PsychINFO. The search included a combination of the following terms: ‘preterm’, ‘neonate’, ‘NICU’, ‘noise’, ‘earplugs’, and ‘earmuffs’. Peer reviewed, articles published in the English language were examined that tested noise reduction devices in the NICU setting, hearing screening of neonates, and the effect of noise reduction interventions on physiologic changes in the preterm infant receiving care in the NICU. Results yielded 8 articles between the years of 1995 to 2017 which were synthesized for review. The results indicated that the use of earmuffs or earplugs in the NICU may offer a viable solution to reducing the effects of excessive noise on neonate’s growth and development. The use of earmuffs or earplugs has been shown to positively improve vital signs, increase growth, improve physiological and motor development, and improve sleep efficiency. Further research on larger sample sizes is needed in order to validate the findings and offer substantial evidence for its use in the clinical setting.

Identical experiments were conducted between two acoustical-testing laboratories to determine the inter-laboratory differences of using two different hearing protection device (HPD) fitting procedures for testing the real-ear attenuation at threshold (REAT) of a popular vinyl foam earplug and a multi-sized premolded PVC single-flanged earplug. The first fitting procedure tested in the experiment is included in the revision of the American National Standards Institute (ANSI) standard S12.6-1984 by the ANSI Working Group ANSI S12/WG11, <i>Field Effectiveness and Physical Characteristics of Hearing Protectors</i>. This fitting procedure, “subject fit,” is intended to estimate “...the attenuation obtained in the top 10-20% of today’s industrial and military hearing conservation programs, i.e. the attenuation that should be obtained by an informed and motivated work force” (ANSI S12.6-199X, Draft 1.4, p. 4). The subject-fit procedure employs HPD-naive subjects, minimizes experimenter involvement, enforces subject-selection controls, and requires subjects to fit the HPD with reasonable comfort using only the manufacturer’s fitting instructions. The subject-fit method differs from the second procedure tested in this investigation, experimenter fit, in both procedure and objective. In the ANSI S3.19-1974 “experimenter-fit” method, which is the procedure currently required by the Environmental Protection Agency (EPA) for the testing and labeling of HPDs (EPA, 1990), the experimenter fits the HPD to the subject (comfort is not a consideration) to determine the optimum attenuation of the HPD. The development of the subject-fit protocol was motivated by the large discrepancy between the attenuation achieved in the field and that claimed by manufacturers of HPDs using experimenter fit from ANSI S3.19-1974. Some experts have developed schemes to derate manufacturers’ laboratory data to approximate attenuation typically achieved in the field. In addition to investigating the differences between the two fitting protocols, other factors relevant to the revision of ANSI S12.6-1984 were studied: subject and experimenter gender effects, ear canal size effects, inter-laboratory differences, and the number of replications and subjects needed for REAT tests. Results indicated that the subject-fit method provided statistically significantly less attenuation than the experimenter-fit method. Subject-fit tended to overestimate in-field attenuation, but not by as much as experimenter-fit. No consistent subject-gender effects were found in the analysis. Experimenter gender did not have a significant effect on subject-fit foam-earplug attenuation. The lack of significant trial effects indicated that the goodness of fit did not change for either fitting condition or across trials. Ear canal size and attenuation effects were documented with mixed results. / Master of Science

This study examines how a user-centered approach can influence product design to reduce physical discomfort when using in-ear true wireless. The given study is a collaboration with the consumer electronics company Zound Industries. The purpose has been to understand the origins of why physical discomfort can arise when using in-ear true wireless headphones and to what extent the user behaviour plays in it all. Previous studies have shown how physical discomfort in the form of eczema, itching and soreness has been caused by the use of in-ear true wireless. Based on user-centered methods such as expert interviews, cultural probes, user interviews, focus groups, this study has been able to identify not only how, but why physical discomfort can occur when using in-ear true wireless. Furthermore, the study has also been able to identify behavioural patterns among users that reveal how headphones are used for purposes other than what they are intended for. It has been possible to show how users use their headphones like an earplug without music to block out sound in order to be able focus or to communicate they don’t want to be disturbed to avoid social interactions. The conducted knowledge and insights provide a better understanding of how design can be used to enhance the experience of using in-ear true wireless headphones. Applying design strategies within design for behavioural change, an adjustable headphone has been developed that allows the user to use the headphone according to the needs of the user. The study provides a basis for how design can be better utilised in future in-ear true wireless headphones.