TfCD Assignment 2: Bone Conducting Speakers

As part of assignment 2 for the course ‘Technology for Concept Design’, we investigated bone conduction as an 'emerging' technology. Bone conduction itself isn’t a new technology. As early as 1550 it was described by Girolamo Cardano, a physician and mathematician, as a method by which sound was transmitted to the ear by means of a rod or shaft. What's new is that these days bone conduction is being implemented in consumer goods such as hearing aids and headphones.

There are several simple ways that bone conduction can be prototyped to evaluate the sensation of hearing sound via bone conduction. This guide shows the comparison of two of these.

The parts needed for this evaluation are:

• an audio source
• a pair of working earphones (which can be destroyed)
• a DC motor
• a piezoelectric element
• two sets of crocodile cables
• a wire stripper (or cutter)
• a lighter

Say goodbye to your earphones and cut off both the left and right earphone.

Use your wire stripper to strip the isolation cover to expose the copper wires.

Each earphone has two wires connected to it and the wires likely have some coating on them. In this case one earphone had a blue coated wire and a clear copper wire and the other earphone had a green coated wire as well as a clear copper wire.

Run the wires through an open flame from your lighter to burn off the coating in order to ensure proper conduction of electricity. There may also be some thread that can also be burned off since it may be difficult to separate from the fine wires otherwise.

Intertwine the (previously) blue and the green coated wires together. Then do the same for both the clear coated ones.

Attach the two crocodile clips to the intertwined wires. Make sure the metal of the crocodile clip and the wires are touching, in order to ensure conduction.

Attach the two crocodile clips to the wires of the piezoelectric element. It doesn’t matter which cable is connected to which wires, as long as the metal of the crocodile clip and the wires are touching, in order to ensure a connection.

Plug the earphone connector in the audio source to be able to send audio to the piezoelectric element.

Softly bite on the piezoelectric element or hold it your ear to hear the audio.

Detach the two crocodile clips from the piezoelectric element and attach them to the wires of the DC motor. It doesn’t matter which cable is connected to which wires, as long as the metal of the crocodile clip and the wires are touching, in order to ensure a connection.

Softly bite on the shaft of the DC motor or hold it your ear to hear the audio.

The DC motor worked better than the piezoelectric element. Especially when biting the shaft. Both would likely be helped by connecting a small amplifier after the audio source to create stronger vibrations.