Drum /

The drum is a member of the percussion group of musical instruments, technically classified as the membranous. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a shell and struck, either directly with the player's hands, or with a drumstick, to produce sound. There is usually a "resonance head" on the underside of the drum, these are usually tuned to a slightly lower pitch than the top drumhead. Other techniques have been used to cause drums to make sound, such as the thumb roll. Drums are the world's oldest and most ubiquitous musical instruments, and the basic design has remained virtually unchanged for thousands of years. A few types of drums such as timpani are always tuned to a certain pitch. Often, several drums, other than timpani drums, can be arranged together to create a drum kit. The shell almost invariably has a circular opening over which the drumhead is stretched, but the shape of the remainder of the shell varies widely. In the western musical tradition, the most usual shape is a cylinder, although timpani, for example, use bowl-shaped shells. Other shapes include a frame design (tar, Bodhrán), truncated cones (bongo