in the late 1960s. Early multi-tenors had shells with a flat bottom. These drums sounded a lot like timpani, so they were called timp-toms. As drum sizes got smaller, more drums began to be added to multi-tenor configurations. The largest sets of multi-tenors had 7 drums and were carried by both the 1977 and 1992 Spirit of Atlanta Drum and Bugle Corps tenor lines. Scottish pipe bands use a single tenor drum as part of their drum corps section. Traditional marching bands and drum corps may also use single tenors, which are double-headed drums much like snare drums but without snares, and only use either mallets (one or two, the former used in Spain and Italy and the latter in the UK and Commonwealth, Germany, Belgium, and the Netherlands) or sticks (the latter in marching bands in France). The Scottish form tenors are played with bigger mallets, while regular single tenors have small mallets, all are covered with felt or cotton. Such drums are used either with the sling mount or shoulder mount. Some show bands such as those at historically black colleges and universities use both single tenors and multi-tenors. Bass drums Bass drums used by modern ensembles come in a variety of sizes, with a 14 inch "universal" depth, and diameter measured in 2 inch increments from 14 to 32 inches. The heads of these drums are usually made of a smooth white PET film, which gives a tonality that is midway between clear and coated heads. Unlike tenors and snares, bass drums are mounted so that the cylindrical shell of the drum is mounted on the player's harness and the two drum heads of the drum face out sideways. The player can then play on both heads, one arm for a drum head on either side. Each drummer plays and carries one drum, and a line is created by having several people carry different-sized drums. Such drums are called tonal bass drums. The Cavaliers Drum and Bugle Corps were the first marching unit to use and standardize tonal bass drum tuning. Many groups try to use the largest size bass drum that is comfortable for the physically largest bass drummer to carry as the bottom bass drum, as larger people are generally better able to carry a bigger drum for many hours. In corps-style bands, each bass drummer only plays one segment of the entire bass drum