Bone conduction is the conduction of sound to the inner ear through the bones of the skull.

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.

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.

APPLICATIONS

1) Bone conduction is one reason why a person's voice sounds different to them 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.

2) Musicians may use bone conduction while tuning stringed instruments to a tuning fork. After the fork starts vibrating placing it in the mouth with the stem between the back teeth ensures that one continues to hear the note via bone conduction, and both hands are free to do the tuning.

3) 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.

4) The use of a wireless microphone placed next to the speaker helps to reduce the effects of reverberation from poor room acoustics, bypasses the sounds between the speaker and the listener, eliminates the background noise by the listener, and by using a directional microphone reduces the background noise by the speaker.

5) One example of a specialized communication product is a bone conduction speaker that is used by divers. An underwater scuba diver communication system is disclosed which is comprised of an oral bone conduction mouthpiece based sound transmission and conduction device, an oral--mouthpiece based microphone, an ultrasonic sound transmission device, an ultrasonic receiving device and the electronic circuitry required to facilitate the transmission or reception of ultrasound transmitted signals through a water medium.

You will need an amplifier to hear the sound clearly, you can either make one or just use a ready made one.

the piezoelectric sensors are used as a prototype but the actually we need a bone conduction transducer. But since it is way more costly and unavailable in my country, I decided to work with the piezoelectric sensors.

Step 1: Materials Required

1. Bone conduction transducer ( here a piezoelectric sensor is used )

2. Female Aux pin and Aux cable

3. Amplifier

4. Electric wires

5. Card board

6. An audio source (computer/mobile phone/audio players etc.)

Step 2: Tools Required

1. Soldering kit

2. Glue (hot glue gun)

3. Heat sink tube

4. Tape (cello tape, insulation tape)

5. Cutting tools

Step 3: Procedure

1.

Take a pair of piezoelectric sensors.

2. Solder the two wires each to the piezoelectric sensors as shown in the circuit diagram ( polarity doesn’t matter )

3. Solder the other ends to the Female Aux as shown in the circuit diagram.

4. Place the whole set in a convenient setup (using a spectacle/hair bow ) and cardboard and glue

5. Observe and record the working of headphone.

Step 4: Conclusion

You will need an amplifier to hear the sound clearly, you can either make one or just use a ready made one.

the piezoelectric sensors are used as a prototype but the actually we need a bone conduction transducer. But since it is way more costly and unavailable in my country, I decided to work with the piezoelectric sensors.

If you want the transducers, here is the link

https://www.adafruit.com/product/1674