Drums vary widely in size, shape, and, more importantly, sound. Drummers sometimes describe their instruments as having, for example, "a warm sound" or "a lot of attack." And while nondrummers may find it difficult to fully appreciate such descriptions, nearly everyone can hear distinct differences between different drum types: Some drums are low-pitched and carry their sound for a long time; others are higher-pitched and "snappier."
Drums, like all other musical instruments, produce sound by vibrating. When the top, or head, of a drum is struck, it moves downward. Tension in the drumhead then causes it to snap back and vibrate up and down, much like a plucked guitar string. These vibrations cause air molecules surrounding the drumhead to be pushed together and pulled apart rhythmically. These air molecules, in turn, cause the air molecules next to them to be pushed together and pulled apart, and so on and so forth, creating waves of high- and low-pressure air that emanate from the drum. In addition, the body of the drum also vibrates when the drum is played and provides a chamber where air molecules inside will continue to be excited by the vibrations. The drum's chamber intensifies and prolongs the sound, or makes the sound resonate.
Many factors influence the type of sound a drum makes. One of the most important of these is the tension of the drumhead, which is determined by its thickness and how tightly it is stretched over the drum body. The greater the tension of the drumhead, the faster it vibrates when struck. The faster the drumhead vibrates, the shorter the wavelength and the higher the frequency of the sound waves produced. The higher the frequency of the sound waves, the higher the pitch. A tight, or high-tension, drumhead, therefore, produces higher-pitched sounds, while a lower-tension head produces lower-pitched sounds.