The treujenn gaol is a clarinet in B flat with thirteen keys, made of ebony, sometimes with two movable rings on this lower body. It is sometimes called a "half-Boehm" clarinet. It is the most widespread type of clarinet in all of upper Cornouaille and the south of Trégor.
Introduced in Brittany in the 19th century, it gradually became popular and became a very popular instrument from the second half of the 19th century, where it was a favorite instrument of "sonneurs" (players) alongside the drum, the accordion and the bagpipe.
At the end of the 19th century, it was called treujenn gaol ("cabbage trunk") in upper Cornouaille, and tronc d'chou in Mené and the countries of Vitré and Fougères. In Central Brittany, it was the preferred instrument for festivities and celebrations until the Second World War, before undergoing a period of relative decline, then a revival from the 1970s-1980s.
Treujenn gaol "sonneurs" most often play in pairs, according to rules similar to those of the kan ha diskan singers of Upper Cornouaille.

Photo Christian Duro and Zon Budès, © Alain Le Nouail, courtesy of Dastum.