Density, sound velocity, modulus and damping explained

Density: mass per volume

Density ρ is mass divided by volume, expressed in kg/m³. In ToneWood it depends on your mass and geometry inputs. Check those measurements before interpreting an unusually high or low density.

For workshop decisions, compare the material in its intended part and geometry. A low-density soundboard blank and a back blank serve different purposes; one common target cannot describe every part.

Sound velocity and dynamic modulus

In a longitudinal material model, c = √(E/ρ), so E = ρc². Use c in m/s and ρ in kg/m³ to obtain E in pascals; divide by 10⁹ for GPa. Wood is direction-dependent, so label the measurement direction.

In the app, these values share measured inputs and model assumptions. They are not independent confirmations of one another. A dynamic estimate should not be presented as a static load-test result.

Damping: read the mode and method

Damping describes energy loss. For a lightly damped, isolated resonance, the loss factor is approximately η = 1/Q: higher Q indicates slower decay. This interpretation assumes a suitable single-mode signal.

Inspect the retained decay evidence and measurement method before comparing two Q values. Keep the material direction and recording setup in the comparison; a larger number by itself is not a finished-instrument listening assessment.

Radiation ratio and impedance

The radiation ratio R = c/ρ has units m⁴/(kg·s). Characteristic acoustic impedance Z = ρc has units kg/(m²·s). Both combine density and velocity into material descriptors.

Use these descriptors to organize comparable records. They do not specify a violin’s radiated sound level, bridge mobility or recorded frequency response. Those describe the assembled instrument and require different measurements.

Use measurements alongside making experience

First compare materials with similar use, direction, geometry and test conditions. Then inspect the original evidence and consider the planned thickness, arching and construction. ToneWood’s Acoustic Score is a project-defined screening model, not a universal grade or a prediction of finished tone.