On the acoustics of bone

The question

When you tap a human skull with your fingernail, it rings. Not like a bell — more like a ceramic bowl with a crack in it. A dull, truncated note that dies before you can identify the pitch. The question was whether that resonance could be amplified and sustained by coupling it with a secondary material.

Method

Three materials were tested as coupling bodies: maple, cherry, and MDF. Each was CNC-milled to the skull's surface topology using the same 3D scan. A single spring steel tine was mounted identically on each assembly. The tine was plucked. The sound was recorded.

Maple produced a bright, almost metallic sustain — clean but thin. MDF absorbed the vibration entirely, producing a sound best described as a polite cough. Cherry sat in the middle: warm, present, with enough harmonic complexity to suggest the bone was contributing something the wood could not generate alone.

Finding

The bone does not amplify sound. It modulates it. The calvaria introduces micro-irregularities into the waveform — tiny imperfections in the resonance curve that give the tone its character. A perfect resonance body would be boring. Bone is not perfect. This is its advantage.

The same principle applies to concert halls. The best ones are not acoustically flawless. They have quirks — odd reflections, uneven absorption — that musicians describe as 'warmth' or 'presence.' Bone has warmth. It has presence. It also used to have a face.