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Scalable Multi-person Hearing Protection Device Fit-testing System


OUSD (R&E) MODERNIZATION PRIORITY: General Warfighting Requirements (GWR)




OBJECTIVE: Develop a system that can simultaneously fit-test multiple people with hearing protection devices (HPDs). The system should be usable in clinical and non-clinical settings to quickly test the fit of HPDs from various manufacturers.


DESCRIPTION: The Hearing Conservation Program is the largest occupational health program in the Department of Defense (DOD), crucial because the majority of military members are exposed to hazardous noise. Civilian personnel are also assigned to the program when subject to noise exposure associated with work such as aircraft, vehicle, or ship maintenance and other activities. One of the methods used to reduce noise exposure and prevent occupational hearing loss is the use of hearing protection devices (HPD). Until recently, the only way to ensure proper fit of hearing protection was to perform a real ear attenuation threshold (REAT) test in an audiometric booth. This type of testing is time- and labor-intensive. In recent years, commercial systems have been developed to enable HPD fit-testing outside of an audiometric booth. The Department of Defense Instruction 6055.12, Hearing Conservation Program, cites fit-testing as a best practice. Recent studies performed at Navy and Marine Corps accession points to determine the viability of large-scale HPD fit-testing on large numbers of recruits determined that testing at 500, 1000, and 2000 Hertz provided good fit-test results. However, these studies also found that on initial fitting, 55% of participants did not receive adequate protection; some (3.75%) new recruits could not achieve an adequate personal attenuation rating (PAR) with their issued HPDs and had to be offered alternative HPDs. Researchers concluded that adequate protection depends upon proper fit of the issued HPD as well as the quality of initial training (Federman & Duhon, 2016). A more recent study showed earplug PARs were highly variable across study participants; compared to participants with normal hearing, those with hearing loss had significantly lower PARs (Ullman et al., 2021). Other studies have shown that low levels of background noise do not affect PARs, which supports the feasibility of performing HPD fit-testing in the field (Gallagher et al., 2016). One study reported good results with fit-testing using modified ear cups for the Benson medical headphones (TDH-39) (Stefanson & Ahroon, 2019).


In 2018, the Acoustical Society of America (ASA) approved a national consensus standard (ANSI/ASA S12.71-2018) for field attenuation estimation systems (FAES) to measure HPD PAR. Various technical approaches can be used to determine attenuation, including non-audiometric booth REAT tests, field microphone in real ear tests, loudness balance tests, and audiometric booth REAT tests designed for multi-person booths. To date, only one FAES meets the ASA standard for individual HPD fit-testing, but the system can only be used to test one manufacturer’s HPDs. The Department of Defense needs an HPD fit-test system that is scalable to allow testing of at least one person, with the ability to simultaneously fit-test multiple people (up to100 or more). The device(s) should be portable to allow for testing in a variety of settings, including clinics, quiet office spaces, in the field, aboard ships, and with mobile audiometric testing platforms. The device(s) must be able to fit-test most commercially available earplugs. PAR should be calculated using 3, 5, or 7 frequencies, with an overall PAR and individual PAR values per octave band.


PHASE I: Phase I awardees will conceptualize and design an innovative system to rapidly fit-test multiple people at once and provide individualized PARs. The system must be usable in clinics, training classrooms, aboard ship, and in field locations such as firing ranges. Solution could include hardwired equipment or be an application (app) which uses existing methods to generate auditory signals. Designs should incorporate commercially available electronic and computer components. Software systems should have capability to store and forward results for upload into occupational health records, safety records and military medical readiness systems. Individual files would include personally identifiable information but no personal health information. Data must be mineable and able to be packaged individually, by commands or bases for the military, and by company and work centers for industry. The system’s power supply should use standard U.S. power and be designed to operate by battery with a minimum battery life of 4 hours and quick recharging capability. Batteries should not require specialized handling. Design should use standard ruggedization comparable to regular safety instruments such as sound level meters. Equipment should be able to operate in normal hot and cold environments, but does not need to be designed for extreme environments. Due to military constraints, wifi and Bluetooth-enabling should not be the only way to connect multiple individuals to the system.


Phase I deliverables: A concept and demonstration that the theoretical concept is valid for fit-testing hearing protection for multiple individuals simultaneously. Concepts will be evaluated on the number of individuals the system can test simultaneously, the speed of testing, and portability of any equipment.


PHASE II: Using results from Phase I, Phase II will develop, fabricate, and validate a prototype of the multi-person fit-testing system. Phase II initial goal will be to develop and fabricate a system capable of fit-testing multiple people at once. The second goal will be to validate the fit-testing system under an IRB-approved research protocol followed by HRPO-approval. Research does not need to be conducted at a DoD facility and can use a civilian IRB. A third goal will be to demonstrate system ability to conduct fit-testing in a variety of settings and with background noise. One fully functional prototype will constitute the fourth deliverable, accompanied by validation test reports and other relevant reports and designs. Factors used to assess the solution will be:

  1. The number of people able to be tested at once where greater numbers are of higher value.
  2. Speed of testing where faster is better.
  3. Fidelity of test results where smaller levels of uncertainty are better.
  4. Sensitivity and specificity where accuracy is valued more than precision.
  5. Level of background noise under which the system can be used.


PHASE III DUAL USE APPLICATIONS: Implement any design changes from phase II. Develop production processes, training software, and manuals for the product system. Final product configuration should minimize footprint and weight for portability and ease of storage. The primary target users for the product are companies with large hearing conservation programs. The ability to test multiple people quickly and at the same time will increase the desirability of the product to industry. System would be further enhanced if it requires minimal training and can be used by non-medical personnel. This system could be marketed to many industrial, transportation, mining, and construction companies to improve their hearing conservation programs and increase compliance with the Occupational Safety and Health Administration and other regulatory requirements. In addition, the work may result in technology transition to an Acquisition Program managed by the Service Product Developers. The contractor can also propose product use to the military Services. Connectivity to DoD safety systems should be able to be accomplished as the system becomes GOTS/COTS. Utility of the product will be enhanced if the device is easily portable and requires minimal supervision to produce repeatable results. The capability to administer HPD fit-testing to large groups of people at once will ensure that personnel exposed to noise can be properly trained and fitted with HPDs in an efficient and effective manner.



  1. ANSI/ASA S12.71-2018 Performance criteria for systems that estimate the attenuation of passive hearing protectors for individual users.
  2. Federman J, Duhon C. The viability of hearing protection device fit-testing at navy and marine corps accession points. Noise Health [serial online] 2016 [cited 2017 Jan 5 ];18:303-311
  3. Gallagher H, Murata TK, McKenna EA, et al. Personal Attenuation Ratings reported using Fit Check Solo: Is background noise a concern? 5th Joint Meeting of the Acoustical Society of American and the Acoustical Society of Japan 2016.
  4. Stefanson EW, Ahroon WA. Computer-controlled audiometer’s application as an earplug fit-testing tool. The Journal of the Acoustical Society of America 140, 3274 (2016).
  5. Ullman ED, Smith LM, McCullagh MC, et al. Hearing loss as a predictor for hearing protection attenuation among miners. Occup Environ Med 2021;78:371–376.


KEYWORDS: hearing, hearing loss, hearing protection, noise, personal protective equipment, hearing protector fit testing, injury prevention, personal attenuation rating

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