Noun
sound post (plural sound posts)
(lutherie) A wooden rod located inside the body of a violin-family instrument, close to the treble-side bridge foot.
This can be accomplished by modifying the cello front plate, attaching a wolf eliminator, or moving the sound post. Source: Internet
Like the bridge, the sound post is not glued, but is kept in place by the tensions of the bridge and strings. Source: Internet
The latter are more heavily constructed and are fitted with a bass bar and sound post, like modern stringed instruments. Source: Internet