Bone conduction

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A consumer stereo bone conduction headset. The two transducers fit slightly in front of the ears.

Bone conduction is the conduction of sound to the inner ear through the bones of the skull. Bone conduction transmission can be used with individuals with normal or impaired hearing.

Overview[edit]

Bone conduction is one reason why a person's voice sounds different to him/her when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own voices to be lower and fuller than others do, and a recording of one's own voice frequently sounds higher than one expects it to sound.[1][2]

Hearing aids[edit]

Some hearing aids employ bone conduction, achieving an effect equivalent to hearing directly by means of the ears. A headset is ergonomically positioned on the temple and cheek and the electromechanical transducer, which converts electric signals into mechanical vibrations, sends sound to the internal ear through the cranial bones. Likewise, a microphone can be used to record spoken sounds via bone conduction. The first description, in 1923, of a bone conduction hearing aid was Hugo Gernsback's "Osophone",[3] which he later elaborated on with his "Phonosone".[4]

At the Chalmers University of Technology in December 2012, surgeons performed an inaugural operation as part of a clinical study that involves a new bone-conduction hearing implant. Developed at Chalmers University, in collaboration with Sahlgrenska University Hospital in Gothenburg, Sweden, the invention differs from other bone-conduction implants, as it does not need to be anchored in the skull bone with a titanium screw through the skin and there is no risk of skin infections.[5] The inventors of the device claim that it could help functionally deaf people regain normal hearing. In January 2013, the researchers stated that they were aiming for the initial presentation of results in "early 2013" but, as of June 2013, results are not publicly available from the study.[6]

Products[edit]

Bone conduction products are usually categorized into three groups:

  • Ordinary products, such as hands-free headsets or headphones
  • Hearing aids and assistive listening devices
  • Specialized communication products (e.g. for underwater or high-noise environments)

One example of a specialized communication product is a bone conduction speaker that is used by scuba divers. The device is a rubber over-moulded, piezoelectric flexing disc that is approximately 40 millimetres (1.6 in) across and 6 millimetres (0.24 in) thick. A connecting cable is moulded into the disc, resulting in a tough, waterproof assembly. In use, the speaker is strapped against one of the dome-shaped bone protrusions behind the ear and the sound, which can be surprisingly clear and crisp, seems to come from inside the user's head.[citation needed]

Use in the 21st century[edit]

The Google Glass device employs bone conduction technology for the relay of information to the user through a transducer that sits beside the user's ear. The use of bone conduction means that any vocal content that is received by the Glass user is nearly inaudible to outsiders.[7]

German broadcaster Sky Deutschland and advertising agency BBDO Germany collaborated on an advertising campaign that uses bone conduction that was premiered in Cannes, France at the International Festival of Creativity in June 2013. The "Talking Window" advertising concept uses bone conduction to transmit advertising to public transport passengers who lean their heads against glass train windows. Academics from Australia's Macquarie University suggested that, apart from not touching the window, passengers would need to use a dampening device that is made of material that would not transmit the vibration from the window.[8][9]

Advantages[edit]

Bone conduction products have the following advantages over traditional headphones:

  • Does not block outside sound
  • Maintains sound clarity in very noisy environments
  • Can be used with hearing protection

Disadvantages[edit]

  • Crosstalk between stereo channels (the effect is insignificant for spatial localization of sound sources).[10]
  • Some implementations require more power than headphones
  • Reduced frequency bandwidth

See also[edit]

References[edit]

  1. ^ Zhi Cai; Alan G. Madsen; Douglas G. Richards; Martin L. Lenhardt (2002). "Response of Human Skull to Bone Conducted Sound in the Audiometric to Ultrasonic Range" (PDF). Response of Human Skull to Bone Conducted Sound in the Audiometric to Ultrasonic Range. Virginia Commonwealth University. Retrieved 3 July 2013. 
  2. ^ Brent Zupp (2003–2012). "Why Does Your Voice Sound Different on a Recording?". Wanderings. Brent Zupp. Retrieved 3 July 2013. 
  3. ^ US 1521287, Gernsback, Hugo, "Acoustic Apparatus", published 19 May 1923, issued 30 December 1924 
  4. ^ Kennedy, T. R., Jr. (1958). "From Coherer to Spacistor". Radio-Electronics (Gernsback Publications) 29 (4): 45–59. 
  5. ^ "New implant replaces impaired middle ear" (Press release). Chalmers. Chalmers University of Technology. 14 January 2013. Retrieved 3 July 2013. 
  6. ^ "Bone-conducting implant could help deaf people hear normally". The Engineer. Centaur Communications Ltd. 14 January 2013. Retrieved 3 July 2013. 
  7. ^ Charles Arthur (2 July 2013). "Google Glass – hands-on review". The Guardian. Retrieved 3 July 2013. 
  8. ^ Catherine McMahon; Phillip Nakad (12 July 2013). "Bone conduction: the new front in guerilla advertising". The Conversation Australia. Retrieved 15 July 2013. 
  9. ^ Leo Kelion (3 July 2013). "Talking train window adverts tested by Sky Deutschland". BBC News. Retrieved 15 July 2013. 
  10. ^ MacDonald, J.A.; Henry, P.P.; Letowski, T.R. (2006). "Spatial audio through a bone conduction interface". International Journal of Audiology (Informa Healthcare) 45 (10): 595–599. doi:10.1080/14992020600876519. 

External links[edit]