sound vessels
Schallgefäse
Sounding vases
Echea
acoustic jar
Antike theater un Maske refers to the theatre (seehttp://wikimapia.org/1136863/Roman-Theater-of-Nora) but there is not much info.
a pot, chamber or vessel that is similar in function to a modern-day bass trap. They were supposedly used in ancient Greek theaters to enhance the voices of performers through resonance,[2][3] though no archaeological evidence has been found. They were typically made of bronze, but were also made of earthenware[4] for economic reasons.
The vessels mentioned by Vitruvius in his De architectura are made of bronze and designed specifically for each unique theatre. They were then placed in niches between the theatre's seats, specifically so that nothing was touching them. They used mathematical calculations to decide where they should be placed.[5] "They should be set upside down, and be supported on the side facing the stage by wedges not less than half a foot high."[6]
5th century BC
An Echea is a bronze sound vessel, installed in ancient theatres to amplify and acoustically improve singing and instrumental music. The vessels, probably bell-shaped, were placed in the auditorium and had sound slits open towards the audience.