Most musical instruments include parts that vibrate with and amplify the sound of the instrument. In string instruments this is the body of the instrument.
In many keyboard percussion instruments, below the centre of each note is a tube called the resonator. The length of the tube varies according to the pitch of the note, with higher notes having shorter resonators. The tube is open at the top end and closed at the bottom end, creating a column of air which resonates when the note is struck. This adds depth and volume to the note and lengthens its duration.
In Camille Saint-Saëns' Danse Macabre, a skeleton's dance is depicted by a xylophone. Since the instrument in Saint-Saëns' day did not have resonators, it is often performed with resonators removed (or covered). This makes sound of the instrument more brittle and bone-like.
The vibrato effect of a vibraphone is obtained by a mechanism which opens and shuts the resonators.
