There are typical 3 or 4 surdo (bass drum) parts in samba-reggae. The surdos are 50 cm deep, shorter drum than the classic Rio size of 60 cm. Surdos in samba-reggae are usually worn quite low on the body with a waist strap; in Rio they are more likely to be worn higher and with a shoulder strap. In samba-reggae, the first (largest-diameter) and second (next largest) surdos keep the beat, typically with the lowest drum hitting beat 2 and the higher drum hitting beat 1. Together, the first and second surdos of samba-reggae are known as the "fundos", the back, presumably because they always stand in the back row of the samba-reggae band. The third surdo plays the classic third-surdo part of samba. The fourth surdo is tuned very tightly and plays rapid 16th-note rolls with two mallets, which gives samba-reggae its unmistakable rumbling sound. Some modern afro blocos are eliminating the third-surdo part or combining it with the fourth-surdo part.