An acoustic jar, also known by the Greek name echea, or sounding vases, are ceramic vessels found set into the walls, ceilings, and sometimes floors, of medieval churches. They are believed to have been intended to improve the sound of singing, and to have been inspired by the theories of Vitruvius. They were supposedly used in ancient Greek theaters to enhance the voices of performers, though no archaeological evidence has been found.

Vitruvius was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled De architectura. As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissance as the first book on architectural theory, as well as a major source on the canon of classical architecture. It is not clear to what extent his contemporaries regarded his book as original or important.