If a patient wears earmuffs in combination with custom made earplugs, can you still get hearing loss through bone conduction (through the skull) when shooting a variety of guns? What is the rate of attenuation from external noise to the cochlea through bone conduction?
The limits to the attenuation for a perfectly attenuating hearing protector, that are imposed by the flanking bone-conduction pathways, vary from about 40 - 60 dB across frequency. This means that even if a hearing protector could block all of the sound entering the earcanal, that sound attenuated by 40 to 60 dB would still get though to the cochlea, and like the sound transmitted via the air-conduction pathway, this energy can cause hearing loss. However, in all but the most extreme environments, this will be sufficient protection. For all but the most susceptible ears and all but the most extreme amounts of gunfire, noise reduction that equals the attenuation imposed by the bone-conduction limits should be quite sufficient. The much larger issue is making sure that the shooter is properly wearing the single or double hearing protection devices to get the maximum protection they can provide.
For additional information on the bone-conduction limits see EARLog 5 and 13 which can be found at www.e-a-r.com/hearingconservation/earlog_main.cfm
For a detailed discussion of the limits to attenuation see the article of that name at www.e-a-r.com/hearingconservation/journal_main.cfm
After receiving his M.S. in Acoustical Engineering from North Carolina State University, joined the Aearo Company in 1976. As E A R/Aearo's Senior Scientist, Auditory Research, he conducts hearing protector research and development. He has written over 60 articles on hearing protection/conservation, and was the principal editor for the 4th and 5th editions of the AIHA Noise & Hearing Conservation Manual. Elliott chairs ANSI working group S12/WG11 on real-world hearing protector performance, and is also involved with numerous other standards committees. In 1993 he was the recipient of the National Hearing Conservation Association's Outstanding Hearing Conservationist Award, and in both 1993 and 1998 received their Outstanding Lecture Award. Elliott is Past President of the National Hearing Conservation Association (NHCA), Past-Chair of the American Industrial Hygiene Association's (AIHA) Committee on Noise and a Fellow of the Association, a Board Member of the of the Council for Accreditation in Occupational Hearing Conservation (CAOHC), a Fellow of the Acoustical Society of America (ASA), and a member of the American Speech-Language-Hearing Association (ASHA).