The Structure of the Marimba
[Experiment1]Tone plate sanding depth and sound pitch experiment
Performing a sound experiment
When the central portion of the underside of the tone plate is sanded down, the note it produces is lowered. How much does the note go down for a given amount sanded off? Try sanding down a little bit at a time.
- Have a piece of hard wood 20 mm thick, 50 mm wide, and 400 mm long.
- Sand down the central portion of the underside, strike the top side with a mallet, and listen to the sound.
- Continue sanding, listening to the sound at intervals.
*Note: As this was an experiment, the recorded pitches differed from the correct notes.
The note can continue to be lowered as long as the wood does not break
Oak wood was used for this experiment. It is a very hard and heavy wood, and so an electric sander is used.
Before sanding, the note sounded like a B, but measurement with a tuner demonstrates that it was actually 20 cents higher than the intended note. One cent is equivalent to one one-hundredth of a semitone. After slightly shaving the bar down, the note was lowered by a semitone to a B♭. Further sanding brought the note down to an A and then a G. The experiment confirmed that simply sanding down a tone plate can change how high a note is, even keeping the size of the bar constant.
To lower the fundamental tone, the parts inside the nodes should be made thinner. As long as enough thickness remains that the wood does not break when hit with a mallet, the note can be lowered even further.