December 11, 2012

listening to bone conduction

Bone conduction isn't pretty, especially when isolated and amplified. How do I know this? From a happy accident. I was at the Listening Centre in Toronto having my ears tuned up, wearing earphones that gave me air and bone conducted sound—the latter stimulating my cochlea through a electromechanical transducer embedded in the earphone. I had just started my session for the day which consisted of repeating poetry that was spoken by a woman. The sound of my voice was filtered at a high level, that is, the lower frequencies were attenuated, as was the woman's voice. But when I started repeating what I heard, I became aware that something was wrong. I didn't feel right. After a minute or so, I figured out that I didn't have my headphones on correctly: the transducer wasn't touching my skull, so I wasn't getting bone-conducted sound. So I adjusted my headphones—and bam! The difference between having it, and not having it, was very clear. You can't hear what I experienced on this page, but in visual terms, it was like going from two dimensions to three. The tickle of tone in my ear had a distinct feeling to it. Without it—without the transducer touching my head—there was no depth of tone, no ring, no center of the tone. Just a hollowness. Being deprived of bone conduction stimulation left me feeling cut off, both auditorially and psychologically (the latter  deserves a separate post). 

So I proceeded to do what any curious guy in my situation would do. I experimented with shifting the headphones, removing the transducer from my head and then putting it back in place—all the while watching my face with hand mirror and listening to the difference between having and not having bone conduction. What did I learn in the process?  

  1. Bone conduction is the feeling of the sound. It leads the voice. 
  2. Without heightened bone conduction, the face will not 'open.'  
  3. Bone conduction is buzzy and associated with the vowel /i/. 
  4. Bone conduction is hum-like. 
  5. Bone conduction makes the bones sing. 
  6. The phonemes 'm', 'n' and 'ng' aid it. 
  7. When highly developed, bone conduction is 'heard' in the center of the head, towards the front of the face,  as well as downward through the throat to the sternum and pelvis.  
  8. Bone conduction 'meets' with air conduction at the front of the mouth. 
  9. Highly concentrated bone conduction results in clarity of vowel.
  10. The voice is heard 'stereophonically' when bone conduction is highly concentrated and the vowels are clear.

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