Advancements in Hearing Technology: Bone Conducted Sound

Normally, humans perceive sound by means of air conduction, in which sound waves from the air travel through the pinna and enter the external ear canal, then transmit vibrations through the eardrum to the ossicles and then finally to the cochlea in the inner ear.  However, bone conduction works differently by transmitting vibrations directly to the cochlea through the skull bone.  Air conduction is used to transmit most sounds except for the sound of our own voice, which is transmitted via bone conduction.  Many researchers are investigating the use of bone conduction in new types of hearing technology such as hearing aids and headsets. 

According to the article “Better Than A Hearing Aid? Better Hearing with Bone Conducted Sound,” researchers at Chalmers University of Technology have developed an alternative to hearing aids which involves the detection of vibrations through the skull bone (ScienceDaily, 2009).  The technology requires a Bone Conduction Implant, or BCI, which does not require permanent skin penetration like commonly used Bone-Anchored Hearing Aids (BAHAs) do (ScienceDaily, 2009).   When tested in two-way communication systems, bone conduction has been found to produce better quality of sound especially in loud environments (ScienceDaily, 2009).   When the difference in sensitivity between bone conduction and air conduction sound from the field of surrounding sound was estimated, bone conduction was found to be 40 to 60 dB lower than air conduction (ScienceDaily, 2009).   This shows that a hearing device using bone conduction would cut down on the distraction of external noise.

Likewise, bone conduction headsets, or “bonephones” use a similar concept to transfer sounds to the listener through bone conduction by creating vibrations against the head through the temple and cheekbones.  These types of headsets are small, lightweight, and more comfortable than many standard headphones and they function without covering the ears of the listener.  Since bonephones bypass the eardrum when delivering sound, they are much safer than normal headsets, which are notorious for causing hearing damage.  Bonephones can be extremely useful for people suffering from middle or outer ear disorders, including aural atresia and microtia.  The only major disadvantage of bonephones is the fact that they often require more power than regular headphones.  Although many have suggested that stereo separation is not possible by means of bone conduction, the research team at the Sonification Lab at Georgia Tech has show that it is possible using the Coordinate Response Measure (Walker & Stanley, 2009).  In a study, they asked participants to identify a target speech signal lateralized with interaural time or intensity/level differences. They found that participants performed better when sound was delivered through bonephones rather than normal headphones, meaning that bonephones produce greater sensitivity to interaural time and intensity/level differences.  Researchers at the Georgia Institute of Technology Sonification Lab continue working to develop three-dimensional audio impression with bonephones (Walker & Stanley, 2009).  

Overall, bone conduction hearing devices can be useful in a variety of settings: at home for personal use, in the office, and even underwater.  Although such devices have mainly been used in the past for military purposes, they are now becoming more widely available and popular among the general public.  Perhaps the future of hearing devices lies in bone conduction technology. 

Posted By: Katherine Travis

ScienceDaily. (June 22, 2009). Better than a hearing aid? Better hearing with bone conducted sound. Science Daily. Retrieved November 21, 2011, from http://www.sciencedaily.com/releases/2009/06/090622194227.htm.

Walker, B. N. & Stanley, R.  (2009). Bone conduction headsets (“bonephones”) research.  Georgia Institute of Technology Sonification Lab. Retrieved November 21, 2011, from http://sonify.psych.gatech.edu/research/bonephones/.