The origins of TPC
Bringing tonewood damping measurement into the luthier’s workshop
I developed the original Tonewood Parameters Characterisation system in 2022 right after the production of my book Mastering the sound of the acoustic guitar, to make quantitative wood assessment practical for luthiers, with particular attention to a parameter often judged by ear: damping.
When we tap a piece of wood, we hear both its resonances and how quickly they decay. TPC brought the measurement of that decay into a dedicated workflow for tonewood selection, alongside density, stiffness, and radiation coefficient.
The original system combined Windows software, a microphone, and a sample-support rig. The current TPC continues this work as a free browser-based tool.
The TPC, from listening to measurements
I designed the Tonewood Parameters Characterization software specifically for luthiers. This innovative tool analyzes the audio impulses from a tap test to calculate key mechanical properties of the wood, including:
- Q (quality) factor
- Young’s modulus
- Density
- Radiation coefficient
The parameters are calculated with the method of the free beam, with the sample usually excited on its first longitudinal bending mode, along the grains of the wood.
The software allows to
- Save the complete measurement files.
- Export the data for postprocessing or easy access on the supplied excel sheet.
- Record the tap tone of tone wood samples to constitute a virtual audio database of the wood stash.
- Measure frequency response of complete instruments and evaluate damping factor of single resonances.
A dedicated support rig should be used to handle the sample and excite the resonance without interfering on its oscillations; the quality of the excitation stimulus and the support rig have a strong influence on the consistency and precision of the results.
System requirements
The software runs on Windows based 64 bits PC. The USB measurement microphone MiniDSP Umik-1 is suggested, available as main audio input of the system. A wireless mouse and keyboard system should be used, to keep the working space cable free and maximize the simplicity of the setup. A Laptop computer is also a good choice.
Where to perform the measurements?
TPC system should be installed in a quiet room, with smooth acoustic characteristics; the measurement must be performed in the close field (microphone at around 5cm from the plate), to avoid reflections from the wall to interfere with the acquisition.
TPC software interface
Signal processing
Once acquired the audio sample the three signal windows allow to postprocess it in both the time and frequency domain.
The main purpose of the software is to calculate the tone wood parameters and the Q factor.
Nevertheless, it is possible also to measure:
- Frequency response of complete instruments
- Q factor of specific resonances.
- Decay time of different spectrum portion of the instrument’s bandwidth.
The TPC software, thanks to its specific versatility, is a powerful tool to also investigate the Q factor of specific guitar resonance, to investigate the influence of different materials, finishes, or soundport geometry.
The software package comprises:
- TPC installer (windows only)
- Excel data import spreadsheet
- Tonewood audio sample, with TPCA file, jpeg export, txt export
- Acoustic guitar measurement with audio sample and TPCA file.
- 3D drawing of marble ramp
- 2D drawing of suggested measurement Jig.
The TPC comprises:
- Tonewood parameters characterization software
- xls import spreadsheet
- marble ramp 3D drawing
- measurement jig 2D drawings
- audio and Tpca samples
TPC today
The current TPC focuses on tonewood characterisation and soundboard thickness planning, and is available free of charge. Instrument analysis and the related educational tools are being brought together in the Acoustic Guitar Analyser.
This page documents the original Windows system and its role in the development of these tools.