The „double-belled euphonium“ or also known as „echo horn“, is a euphonium with two bells! Developed by the American instrument manufacturers „Conn“, the first bell is a „normal“ euphonium bell, whereas the second is a tenor trombone bell. Through the use of a fifth valve the player can change from euphonium to trombone sound during performance.

One of the most prominent virtuosos on the „double-belled euphonium“ was Simone Mantia. He was euphonium soloist with the world famous „John Philip Sousa Band“ and became renowned worldwide for his virtuosic performances.