ToneWood · Measurement guide
How to estimate wood sound velocity with a phone
Prepare a wood blank, record repeatable tap tones and understand how dimensions and resonance become an estimated sound velocity.
What the phone measures
ToneWood records the sound of a tapped wood blank with the iPhone or iPad microphone. A resonance peak is a frequency in hertz. Sound velocity is a calculated result that also depends on the dimensions, geometry and vibration model; the microphone does not directly measure a wave travelling through the wood.
This guide follows the current app’s wood-blank flexural measurement workflow. A carved violin plate, a joined plate or another geometry needs its own mode interpretation. Do not apply a carved-plate Mode 5 instruction to a blank.
Prepare the sample and tools
Have the app, a scale and suitable dimension-measuring tools ready. Identify the length direction and the geometry requested by the app. Measure mass and dimensions yourself, check the input units and record the available environmental conditions. Do not enter zero for an unknown moisture value.
Choose a quiet area, clear the microphone and keep the sample away from hard contact with the bench. Use the same setup when repeating a measurement.
Record a set of taps
Open the app’s How to Tap guide for the material geometry you are measuring. For the illustrated blank, it shows the length axis vertical and a light grip on the thick edge near 0.224 times the length from the end. This is a model-based starting position, not a universal node for every piece of wood.
- Hold the blank lightly as shown in the in-app guide so it can vibrate without pressing against your palm or the bench.
- Use a gentle, short rubber-mallet strike at the indicated back-face position, with the microphone facing the opposite face. Keep the distance and strike direction consistent.
- Allow the vibration to decay before tapping again. Follow the app’s multi-tap recording flow and inspect the recording-quality feedback.
- Repeat the session after repositioning. If the chosen resonance changes substantially, inspect the setup and mode selection before keeping the result.
Read the result with its evidence
Check the selected frequency, the spectrum, decay evidence and entered geometry together. A strong peak alone does not identify the intended mode. Keep the app’s calculation version and measurement history with the material record so a later comparison uses the same assumptions.
An estimate that repeats well is useful for comparing similar blanks under similar conditions. Repeatability does not establish absolute accuracy. Establishing accuracy requires a suitable reference measurement and a controlled validation experiment.