part, unlike the snares and tenors. This is known as a split part. A unison refers to when all or some bass drummers play together at the same time. Lines can vary in size from as few as 3 players in small high schools to as many as 9 in very large college marching bands. A line of 5 (with individual drum sizes ranging from 18 to 32-inches) is the most common in a drum corps. Some traditional groups, such as some show-style marching bands from historically black colleges and universities continue to use a non-tonal bass drums, where each drum is roughly the same size and each drummer plays the same part. Pipe bands and some traditional groups use a single bass drummer, who typically carries the pulse of the group. The bass drums used by pipe bands have seen an increase in size and more of a focus on tone in recent times. Typical sizes range from 12 to 18-inches deep by 28 inches in diameter. The goal is to produce a subtle deep tone which is usually in tune with the drones of the bagpipe. Various muffling techniques (sometimes referred to as "treatments") can be used on bass drums to achieve a desired sound. The most common of these involve applying foam weatherstripping, either on the head directly or on the shell of the drum. Some drumhead manufacturers make heads that are "pre-muffled." These heads usually have separate pieces of PET film or other material which are set into the head's flesh hoop and touch the head to control overtones. Drumlines most frequently use pitched bass drums as tonal drums split between several percussionists. Marching bass drums, which produce the deepest sound in the battery, are larger drums carried on harnesses or straps with the heads facing to the left and right of the player. The musicians carrying the bass drums typically line up in drum size order, but will also assume various positions for the purpose of a drill. Bass drummers use mallets with rounded or cylindrical heads often made of hard felt. High school, Colleges, and drum corps drumlines typically consist of four to six different bass drum sizes to ensure enough for a melody. Sometimes, in smaller bands, one may see only two or three bass drummers perform. A bass drum can weigh anywhere between 15 pounds and 40 pounds, depending on the model