Portland State University. Department of Speech Communication.
Date of Award
Master of Science (M.S.) in Speech Communication
Speech and Hearing Sciences
1 online resource (2, 55 p.)
Hearing aids, Hearing disorders, Industrial noise
Industrial workers who have sustained hearing losses often wear hearing aids on the job in order to hear their co-worker's speech. However they risk damaging their hearing further by amplifying the high levels of background noise typical of such environments. The Occupational Safety and Health Administration (OSHA) has established guidelines to protect workers' hearing. A maximum allowable level of 90 dBA averaged over a period of eight hours is considered safe. Wearing hearing aids on the job may expose an individual to a considerably higher levels, however no guidelines as to maximum allowable levels of amplified noise exist at this time. This study evaluated the performance of four hearing aids in noise to determine which would provide appropriate amplification without exceeding the OSHA maximum. The instruments were adjusted to provide 14 different frequency responses and placed on the Knowles Mannequin for Acoustic Research (KEMAR). A microphone in the position of KEMAR's eardrum recorded amplified levels of taped industrial noise. A sound level meter integrated the levels to give the OSHA Time Weighted Average (TWA), simulating the acoustic effect of an 8-hour noise exposure on an industrial worker. Amplified noise remained below the OSHA maximum (90 dBA) in 2 of the 14 hearing aid conditions studied. Noise amplified by the Argosy Expander, an experimental noise-reducing hearing aid, remained below the OSHA maximum when the instrument was set to provide minimum gain and maximum noise reduction. The Argosy 3-Channel Clock also maintained amplified noise at a safe level when adjusted to provide gain only in a limited frequency region. Noise amplified by the Danavox Aura X programmed to provide a TILL response remained within one dB of the OSHA maximum. This study demonstrated that it is possible to use amplification in environments with constant background noise without risking additional noise-induced hearing loss. Two hearing aids were proven effective in maintaining amplified industrial noise at safe levels, however determining their effect on speech intelligibility in noise is beyond the scope of this study. Further research is needed to address this issue.
Gilbert, Alison Mary, "Limiting Noise Exposure Associated with Hearing Aid Use" (1995). Dissertations and Theses. Paper 5193.