The surdo is a large bass drum used in many kinds of Brazilian music, such as Axé/Samba-reggae and samba, where it plays the lower parts from a percussion section. Surdo sizes normally vary between 16" and 26" diameter, with some as large as 29". In Rio de Janeiro, surdos are generally 60cm deep. Surdos used in the northeast of Brazil are commonly more shallow (50cm deep). Surdos may have shells of wood, galvanized steel, or aluminum. Heads may be goatskin or plastic.