Computer-Controlled Audiometer's Application as an

Computer-Controlled Audiometer's Application as an Earplug Fit-Testing Tool JR W. Stefanson1 and William A. Ahroon, Ph.D.2 2U.S.

Introduction The aim of this evaluation was to determine if the computer-controlled audiometer (Benson Medical Instruments CCA-200mini) used in the Army Hearing Program could be used as a Hearing Protection Device (HPD) fit-testing tool. The Benson Medical headphones (TDH-39) have shallow supra-aural ear cups which press upon the pinna and may contact the stem of an earplug if the earplug protrudes from the ear canal. To prevent this interference, an earlier study used large circumaural ear cups (pictured below) instead of the TDH-39s.However, we observed high unoccluded thresholds when using these headphones. This was problematical since the occluded thresholds of a listener with a hearing loss might (i.e., did) exceed the maximum output of the audiometer. The current study solved this complication by substituting the TDH-39 ear cushions with cushions fabricated using 3D printing technologies with additional ear cup depth. This allowed for earplugs to be inserted and the headphones to be donned without contacting the earplug.

1zCore Business Solutions Inc. Round Rock, TX Army Aeromedical Research Laboratory, Fort Rucker, AL

Methods

Results Cont.

Deeper ear cup cushions were printed using a Stratasys Connnex 350 3D printer and coupled with the Benson Medical Instruments CCA200mini’s TDH-39 headphones. The TDH-39 headphones were calibrated to the audiometer with the deeper ear cup cushions. No calibration adjustments were required. Twenty volunteers accustomed to the hearing test procedures were given otoscopic exams to rule out infections and conditions that would preclude the use of insert earplugs used in this study. Half of the subjects were given an unoccluded audiogram at seven test frequencies from 500Hz to 8KHz, followed by an occluded audiogram at the same frequencies. Subjects’ inserted their own earplugs and were inspected by the tester for adequate depth and appearance of correct fit. The other half of subjects were given an occluded audiogram followed by an unoccluded audiogram. Attenuation results and personal attenuation ratings were computed.

Results

Average Personal Attenuation Ratings for the Howard-Leight AirSoft earplug using the Michael & Associates FitCheck system and the Benson CCA-200mini with large circumaural headphones and standard TDH-39s with 3D printed ear cushions.

Discussion

Average unoccluded and occluded thresholds using the Benson Medical CCA-200mini with large-volume circumaural headphones (from the Michael & Associates FitCheck system). UNCLASSIFIED

Average unoccluded and occluded thresholds using the Benson Medical CCA-200mini with 3D printed ear cushions.

Earplug fit-testing with computer-controlled audiometers is feasible with modified ear cups. The advantage of this procedure is that, without the acquisition of a dedicated fit-test system, individual earplug evaluations may be conducted quickly following annual audiometric testing. After the audiogram has been completed, the individual being tested may insert his/her earplugs, wait for an appropriate time (for expandable-foam earplugs), and run the audiogram again. During the next iteration of the acquisition of computer-controlled audiometers, a requirement could include ear cup depths that would not interfere with a an earplug. This may be in the form of deeper ear cup cushions as demonstrated in this study or circumaural headphones designed for use with audiometers used in the Army Hearing Program.

The views, opinions, and/or findings contained in this report/presentation are those of the author(s) and should not be construed as an official Department of the Army (DA) position, policy, or decision. Citation of trade names in this presentation does not constitute an official DA endorsement or approval of the use of such commercial items.

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