Bone Conduction Transducer

This post about bone conduction transducers will help you to design and fabricate bone conduction speakers and headphones yourself.

Alright! The general idea was to get a sound signal input, amplify it, put it out through a bone conduction transducer.

Would it be really possible to listen sounds not through your ears but through your skull? Let us see...

A bone conduction transducer can generate sound through direct vibration of the bones in the head.

Also, it is capable of converting surfaces into speakers via vibration when placed on materials such as desks, walls, doors, and many other solid materials.

A quick example is the DAYTONE AUDIO's BCT-3 44 x 32mm Bone Conducting Transducer!

Such a bone conduction transducer can be pressed up against the jaw or ear bone to turn the skull into a speaker cavity.

The outcome then is a great quality audio that is coming from within your head that nobody else can hear. You can also press it against your elbow bone and stick a finger in your ear to hear the audio transmitted through your arm.

Note that this odd loudspeaker does not have a moving cone like traditional loudspeakers, instead, a small metal rod is wrapped with the voice coil.

So, when current is pulsed through the coil, the magnetic field causes a piece of metal to expand and contract (if pressed against a flat surface or cavity it turns it into a loudspeaker).

As Wikipedia says, Bone conduction is the conduction of sound to the inner ear primarily through the bones of the skull, allowing the hearer to perceive audio content even if the ear canal is blocked.

Bone conduction transmission occurs constantly as sound waves vibrate bone, specifically the bones in the skull, although it is hard for the average individual to distinguish sound being conveyed through the bone as opposed to the sound being conveyed through the air via the ear canal.

Intentional transmission of sound through bone can be used with individuals with normal hearing - as with bone-conduction headphones - or as a treatment option for certain types of hearing impairment.

Bones are generally more effective at transmitting lower-frequency sounds compared to higher-frequency sounds...

Well, you can simply connect a bone conduction transducer as you would any other loudspeaker, because it works great with most audio amplifier circuits.

However, note at this point that the sound pressure level (SPL) and frequency response of a bone conduction transducer will vary with what you use as the transducer surface.

Frankly, this intro post contains only a scratch of the details We are about to demo a practical bone conduction audio project a later writeup.

Spoiler »

Now we are doing a little project to make a bone conduction transducer to use as a 'privacy' earphone.

First we started with an existing LM386 audio amplifier circuit design.

The LM386 is a venerable power amplifier IC designed for use in low voltage consumer applications.

But after achieving to create the bone conduction effect successfully, we have decided to design our own monoaural earphone audio amplifier circuit (still in progress).

Keep the questions coming...