This one is rather tricky. A clavier is a very heavy object made of a steel or wood frame and filled with metal cable. It can be either used as a siege weapon to tear down walls and battlements due to its weight or as a weapon of mass desruction cutting soldiers in slices with the metal wires. When hitting an obstacle the clavier brings forth a series of melodious sounds. You can produce the sounds by hitting the clavier in different places with a hard object, but you can easily wound yourself or others around you with it.
A well-tempered clavier is a more balanced variation of heavier weight. You have to concentrate very hard to use it correctly, be of even mind (well-tempered). The masters using this siege weapon were often calles "Maestro". When several Maestros used their weapons at the same time, it was called "in concerto".