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 drums, Ashiko), goblet shaped (djembe), and joined truncated cones (talking drum).
Drums with cylindrical shells can be open at one end (as is the case with timbales), or can have two drum heads. Single-headed drums normally consist of a skin which is stretched over an enclosed space, or over one of the ends of a hollow vessel. Drums with two heads covering both ends of a cylindrical shell often have a small hole somewhat halfway between the two heads; the shell forms a resonating chamber for the resulting sound. Exceptions include the African slit drum, also known as a log drum as it is made from a hollowed-out tree trunk, and the Caribbean steel drum, made from a metal barrel. Drums with two heads can also have a set of wires, called snares, held across the bottom head, top head, or both heads, hence the name snare drum.
On modern band and orchestral drums, the drumhead is placed over the opening of the drum, which in turn is held onto the shell by a "counterhoop" (or "rim), which is then held by means of a number of tuning screws called "tension rods" which screw into lugs placed evenly around the circumference. The head's tension can be adjusted by loosening or tightening the rods. Many such drums have six to ten tension rods. The sound of a drum depends on several variables, including shape, size and thickness of its shell, materials from which the shell was made, counterhoop material, type of drumhead used and tension applied to it, position of the drum, location, and the velocity and angle in which it is struck.
Prior to the invention of tension rods drum skins were attached and tuned by rope systems such as that used on the Djembe or pegs and ropes such as that used on Ewe Drums, a system rarely used today, although sometimes seen on regimental marching band snare drums.
Several factors determine the sound a drum produces, including the type, shape and construction of the drum shell, the type of drum heads it has, and the tension of these drumheads. Different drum sounds have different uses in music. Take, for example, the modern Tom-tom drum. A jazz drummer may want drums that are high pitched, resonant and quiet whereas a rock drummer may prefer drums that are loud, dry and low-pitched. Since these drummers want different sounds, their drums will be constructed a little differently.
The drum head has the most effect on how a drum sounds. Each type of drum head serves its own musical purpose and has its own unique sound. Double-ply drumheads dampen high frequency harmonics since they are heavier and they are suited to heavy playing. Drum heads with a white, textured coating on them muffle the overtones of the drum head slightly, producing a less diverse pitch. Drum heads with central silver or black dots tend to muffle the overtones even more. And drum heads with perimeter sound rings mostly eliminate overtones (Howie 2005). Some jazz drummers avoid using thick drum heads, preferring single ply drum heads or drum heads with no muffling. Rock drummers often prefer the thicker or coated drum heads.
The second biggest factor affecting the sound produced by a drum is the tension at which the drum head is held against the shell of the drum. When the hoop is placed around the drum head and shell and tightened down with tension rods, the tension of the head can be adjusted. When the tension is increased, the amplitude of the sound is reduced and the frequency is increased, making the pitch higher and the volume lower.
The type of shell also affects the sound of a drum. Because the vibrations resonate in the shell of the drum, the shell can be used to increase the volume and to manipulate the type of sound produced. The larger the diameter of the shell, the lower the pitch. The larger the depth of the drum, the louder the volume. Shell thickness also determines the volume of drums. Thicker shells produce louder drums. Mahogany raises the frequency of low pitches and keeps higher frequencies at about the same speed. When choosing a set of shells, a jazz drummer may want smaller maple shells, while a rock drummer may want larger birch shells. For more information about tuning drums or the physics of a drum, visit the external links listed below.
Drums are usually played by the hand, or by one or two sticks. In many traditional cultures drums have a symbolic function and are often used in religious ceremonies. Drums are often used in music therapy, especially hand drums, because of their tactile nature and easy use by a wide variety of people.
Macaque monkeys drum objects in a rhythmic way to show social dominance and this has been shown to be processed in a similar way in their brains to vocalizations suggesting an evolutionary origin to drumming as part of social communication. Other primates make drumming sounds by chest beating or hand clapping, and rodents such as kangaroo rats also make similar sounds using their paws on the ground.
In the past drums have been used not only for their musical qualities, but also as a means of communication, especially through signals. The talking drums of Africa can imitate the inflections and pitch variations of a spoken language and are used for communicating over great distances. Throughout Sri Lankan history drums have been used for communication between the state and the community, and Sri Lankan drums have a history stretching back over 2500 years.
Chinese troops used tàigǔ drums to motivate troops, to help set a marching pace, and to call out orders or announcements. For example, during a war between Qi and Lu in 684 BC, the effect of drum on soldier's morale is employed to change the result of a major battle. Fife-and-drum corps of Swiss mercenary foot soldiers also used drums. They used an early version of the snare drum carried over the player's right shoulder, suspended by a strap (typically played with one hand using traditional grip). It is to this instrument that the English word "drum" was first used. Similarly, during the English Civil War rope-tension drums would be carried by junior officers as a means to relay commands from senior officers over the noise of battle. These were also hung over the shoulder of the drummer and typically played with two drum sticks. Different regiments and companies would have distinctive and unique drum beats which only they would recognize. In the mid-19th century, the Scottish military started incorporating pipe bands into their Highland Regiments.