Staab (2012) indicates that knowledge of bone conduction hearing has been around since the time of Girolamo Cardano (1501-1576), a physician, mathematician and philosopher as well as an early deaf educator in the early 1550s. In one of Cardano’s 230 books, entitled “De Subtilitate,” (1550), he described a method by which sound was transmitted to the ear by means of a rod, or the shaft of a spear held between one’s teeth.
Bone conduction is among the first concepts mastered by young audiologists in the assessment of their patients, as it is part of the information necessary to arrive at a diagnosis for a hearing difficulty. When initially discovered, it was primarily of academic interest until Cabrei in 1846 and then Bulwer in 1848, who capitalized on the use of a rod invented by Itard in 1821.
Bone conduction has had some intermittent use in the education of the deaf and some success with hearing aids for the deaf, particularly for those disorders that involved the middle ear, but its use was rather cumbersome as it could cause frequent headaches, and other issues to the person that was the recipient of its use.
While known to professionals such as otolaryngologists, audiologists and others for some time it has only been in the past 20 years or so that bone conduction it has been seen as a possible method for implantation of amplification. Implants that capitalize on bone conduction hearing, such as the Bone Anchored Hearing Aid ( BAHA), the Sophono, Bonebridge, Soundbite and others now offer an alternative to cochlear implants, traditional hearing aids and other treatment.
Bone Conduction Headsets: A Safer Alternative to Earbuds?
Although bone conduction has been around for a long time in audiology, otolaryngology and other hearing circles, it has only recently appeared in the electronics market as a concept for military communication gear and consumer electronic products. Unlike Ear buds or other types of air conduction headphones, bone conduction headphones do not block out ambient noises. Since they do not plug the ear canal, users can hear what is going on in the environment while listening to their favorite music, running, or other activities. Navy SEAL teams and other military, SWAT teams and other police applications can communicate during missions yet stay in tune with what is happening around them. These devices are light-weight and well-vented, yet robust and adjustable. Worn around the back of the head, they offer volume controls and other features that make them full-featured headsets.
Because the bone conduction headset does not cut the user off from the environment, it is considered safer than air conduction alternatives. Additionally, there is no damage from stimulus intensity and/or the constant ear insertion ear buds and other types of insert headphones.
There seems to be two general types of these products:
- those used for the tactical military operations such as combat or police purposes, selling from $225-850 US$
- the more affordable type for the rest of us, consisting of consumer electronic versions available from $20 – 150 US$
The latter type are used for leisure, business, sports, study and probably could be used by some hearing impaired individuals (those with conductive or mixed hearing losses). The devices have the capability to pair to most any cellphone or other device that has Bluetooth connection capability. The packaging for some of these headsets even include earplugs to block out the outside noises and enjoy a better (probably higher intensity) sound from the headset.
When access to ambient sound is important, leaving the ear canals open could be beneficial. For this reason, bone conduction headsets are popular among cyclists. Additionally, in recent years, as smart glasses have begun to again rise in popularity, we’ve begun to see bone conduction audio features appear in sunglasses from popular brands like Bose, Ray Ban and a number of other startups.
How Do Bone Conduction Headphones Work?
Bone conduction occurs when sound travels through the bones of the skull to the inner ear. Bone conduction actually occurs every time you speak and explains why your voice sounds somewhat higher pitched when you listen to yourself on a tape recorder.Bone conduction by itself offers a deeper fuller sound and your voice sounds deeper when not mixed with the sound that comes to the ear from the ear canal.
Audiologists know that sound travels in waves and when it hits the eardrum it is translated into a series of mechanical vibrations. When sound first enters the ear, the pinna focuses it into the auditory canal and then on to the ear drum, which vibrates sympathetically to the sound. These vibrations are passed on by the three auditory ossicles that vibrate into the cochlea. The cochlea is a fluid filled labyrinthine chamber that translates vibrations into the electrical signals that the brain perceives as sounds This is called air conduction hearing.
Bone conduction hearing bypasses everything and transmits these vibrations through the bone directly to the cochlea, effectively leaving ear canal and eardrums free to listen to other things. Virtually all of the bone conduction headphone manufacturers use a jaw bone placement for the stimulus rather than the traditional mastoid stimulus commonly used for audiometry, as it appears to provide a clearer, more consistent signal.
Brandy (2013). What is bone conduction? A look at headphones of the future. High Tech society. Retrieved July 12, 2016.
Henry, P. & Letowski, T. (2007). Bone Conduction: Anatomy, Physiology, and Communication. Human Research and Engineering Directorate, ARL. ARL-TR-4138. Retrieved June 20, 2016.
Staab, W. (2012). The origins of bone conduction hearing. Hearing Health and Technology Matters, LLC. Retrieved June 20, 2016.