An echea or sounding vase (literally echoer) is a pot, chamber or vessel that is similar in function to a modern-day bass trap. They were originally used in ancient Greek theaters to enhance the voices of performers by resonance. They were usually made of bronze, but could also be earthenware if necessary for economic reasons.
Echea were placed with a "due regard to the laws and harmony of physics" according to the Roman writer Vitruvius. The number of echea used and their positioning depended on the size and shape of the theatre. The vases operated by resonance, enhancing key frequencies of the performers' voices and absorbing those of the audience, thereby changing the sound in the theatre to make voices clearer and more lush.
Both their use in Roman times and usefulness at any point have been debated, as by Thomas Noble Howe who wrote in his commentary on Virtuvius' Ten Books on Architecture: "These vessels, bronze or clay, may be another example of Vitruvius singling out a highly technical feature of Greek architecture that was uncommon, but between eight and sixteen potential sites with evidence of echea have been identified. It is debatable whether such vessels amplified or deadened sound."
Similar devices have been used in early churches, and some were discovered in the vaulted ceiling of the choir of Strasbourg Cathedral, and in mosques dating back to the 11th century.