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In-Ear Monitoring for Hearing Protection Compliance and Noise Hazard Exposure



OBJECTIVE: Develop and demonstrate a comprehensive solution for in-ear monitoring of noise exposure and auditory function that can be used in lieu of standard hearing protection for Service Members engaged in operational tasks to provide a better understanding of the relationship between noise exposures and hearing injury and better protect warfighter hearing. 

DESCRIPTION: Hazardous noise exposure is a serious problem in the military, and hearing loss and tinnitus are the two most prevalent permanent injuries sustained by our service members. In order to address this problem, we need to improve our understanding of the relationship between noise exposure and hearing injury. Historically, research on the impact of noise exposure on hearing function has relied at least partially on prospective studies that have intentionally exposed listeners to calibrated levels of noise and then used careful laboratory measures to assess the resulting impact on the auditory system. However, recent research suggests that even modest noise exposures that result only in temporary shifts in absolute hearing thresholds may produce permanent degradation in hearing function as a result of auditory synaptopathy (Kujawa and Lieberman, 2009). This means that most future studies of noise exposure will have to rely on data collected from individuals who are unavoidably exposed to noise as a result of occupational requirements. Consequently, there is a need to develop tools that can allow us to monitor the effective levels of noise that Service Members are being exposed to during the course of their assigned duties without in any way modifying the level of exposure that would ordinarily occur and without in any way interfering with the conduct of their duties. Additionally, while Service Members are often required to wear hearing protection, many do not comply. Thus, there is a need to objectively monitor how often Service Members are actually wearing the hearing protection devices that they are issued. No existing technology meets either of these needs. A system that could meet these needs would be able to fit entirely within the form factor of a standard earplug (or possibly a modified earmuff) and could be issued to a service member in lieu of a standard hearing protection device for an extended time period (weeks or months) during their normal course of duty and then downloaded to provide some information about earplug use, exposure, and auditory function over that time period. Service members could also undergo further auditory testing in the clinic before and after this period to determine correlations between the measured noise exposure and any changes in auditory system function. 

PHASE I: Phase I should identify a feasible technological approach (including sensors) for the in-ear monitoring system that can meet the necessary size, weight, and power requirements, develop a strategy for data collection and storage, and, if possible, demonstrate a bench-level prototype of the device. 

PHASE II: In Phase II, the contractor should develop, test, and demonstrate at least four working prototype systems capable of being used in lieu of a standard hearing protector in the ear for a 2+ hour data collection effort. Real-ear attenuation at threshold testing (in accordance with ANSI S12.6) may be required to verify the attenuation performance of the device. At a minimum, the system must: 1) Look and feel like a standard hearing protection device 2) Be compatible with all standard-issue Soldier Personal Protective Equipment 3) Continuously monitor and record timestamped data about: a. Impulse and continuous noise levels both inside and outside the ear plug b. Earplug use (i.e. time history of when it is inserted in the ear) c. Some measure of auditory function (e.g., otoacoustic emissions, middle ear impedance, stapedius reflex activation) 4) Provide ability to download stored data at end of test period 5) Not contain any external wires or devices 6) Have the ability to be combined with a passive earmuff to achieve double hearing protection Other highly desirable system attributes are as follows: 1) Can fit entirely in the ear 2) Have attenuation performance (ANSI S12.6) that a. Can be modified to match an arbitrary hearing protector or, b. Matches the attenuation of a standard passive hearing protector c. Possibly includes the ability to match attenuation of a nonlinear passive protector 3) Potentially provide the ability to conduct behavioral auditory testing (i.e. threshold testing) or psychophysical testing 4) Have an extremely minimal logistical tail (i.e., able be issued to service member for weeks or months of use) 

PHASE III: Both the Army and Navy Public Health Centers have requirements to monitor occupational noise exposure as part of the Defense Occupational and Environmental Health Readiness System Industrial Hygiene (DOEHRS-IH) and have hearing conservation programs that focus on noise hazard identification, hearing protection, and monitoring audiometry. Thus, these systems would be well suited for Government use to monitor the noise exposure, hearing protection usage, and auditory function of Service Members and Civilian Employees who operate in noisy environments, and these centers are examples of potential Government funding sources for acquiring this type of technology. There is also great potential for commercial use in industrial hearing conservation programs. The hearing protection market is estimated to reach $1.9 Billion by 2021, reflecting the large number of individuals with occupational and recreational noise exposure. Furthermore, noise regulations continue to tighten, which will be a catalyst for companies to require increasingly accurate measures of true noise exposure for their workforce in order to avoid building in expensive safety margins to ensure they are in compliance with national and local noise regulations. We anticipate that Phase III has the potential to produce manufacturing demonstration run of useable devices for making in-ear measurements. 


1: MIL-STD-1474D, U.S. Department of Defense Design Criteria Standard, Noise Limits, AMSC A7245, Washington, DC, (1997)

2:  Gallagher, H. L., McKinley, R. L., Theis, M. A., & Bjorn, V. S. (2014). Calibration of an In-Ear Dosimeter for a Single Hearing Protection Device (No. AFRL-RH-WP-TP-2014-0002). USAF RESEARCH LAB WRIGHT-PATTERSON AFB OH HUMAN EFFECTIVENESS DIRECTORATE.

KEYWORDS: Hearing Protection; Noise Dosimetry; Auditory Injury; Otoacoustic Emissions; Middle-Ear Reflex 


Douglas Brungart 

(202) 294-8747 

Ben Sheffield 

(805) 637-0902 

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