Percussion instruments are those which are struck to make a sound. They may be hit, shaken, and scraped, or made to vibrate by friction. They are struck with the hands or with beaters, or struck against one another like a pair of cymbals. Percussion beaters or sticks come in a huge variety of shapes and sizes. Sometimes the beater may be part of the instrument, like the clapper of a bell, or hidden inside the instrument, like the hammers of a celesta.
Drums, or membranophones, are struck on a membrane or skin. This is stretched over a hollow body that acts as a resonator and amplifier. Drums are classified according to the shape of their body. All other percussion instruments are idiophones – literally, instruments that sound of themselves. These include instruments like the triangle, which is made of a sonorous material that vibrates when struck. Idiophones also have resonators to project their sound.
The percussion family incorporates some of the very largest and smallest instruments, from the Japanese o-daiko or fat drum, which is a huge 240 centimeters (96 inches) diameter and 240 centimeters long, down to tiny ankle bells worn by dancers. Percussion instruments can be very simple to make, such as a dried bean-pod shaker, or they can require complex engineering processes like western church bells,
Tuned and untuned percussion
Unlike other instruments, both drums and idiophones can be tuned or untuned. The acoustic construction of the instrument determines whether or not it can play a specific pitch. Like all instruments, the sound of a percussion instrument is a combination of the fundamental frequency and a series of overtones or harmonics that the ear hears as a homogenous sound. If the overtones are in a harmonic relationship with the fundamental tone, then the ear hears this as a pitched note, as in a tuned percussion instrument like the steel pan or the xylophone. In an untuned percussion instrument, like the tambourine, the overtones are not in a harmonic relationship and the ear hears this as a noise. Untuned instruments of different sizes may be constructed to make higher or lower sounds, like the tom toms on a drum kit, but they can't be tuned to a pitched note.
Timbre (tone color) of percussion instruments
The way a percussion instrument is constructed and the material from which it is made will emphasize certain overtones, and this contributes to its timbre or tone color. In drums, the shape of the body, the type of skin that the drumhead is made from, how the drumhead is attached to the body of the drum, and what kind of beaters are used are all significant. An African djembe is made from goat or calf skin, which is shaved to be very thin on the playing surface. The animal's hair is left around the rim of the drum to muffle the lower frequencies, and both factors contribute to give the drum a bright and ringing sound, clearly distinguishable from the other drums in the ensemble.
Where on the playing surface a percussion instrument is struck will also result in different qualities of sound. When an instrument is struck it produces sound waves that have nodal and antinodal points. There is no displacement of the sound wave at nodal points, so the instrument will make a limited resonant sound when struck at that spot. The instrument will make a resonant sound when struck at an antinodal point, where there is a maximum displacement of the sound wave.
Different musical cultures favor different sounds from percussion instruments. For example, the nodal point on a drum with a bowl-shaped body, like a timpani or kettledrum, is at the center of the skin. Hitting the drum directly in the middle produces a dull sound. Its antipodes are found at about one-sixth of its diameter in from the rim, and this is the point to hit for maximum resonance. An orchestral timpanist will play the drum only at this point to produce a rich, ringing sound. Indian tabla are also kettledrums and the tabla player will strike the drum on both nodal and antinodal points on the skin in order to get different sonorities and pitches from the instrument.
The global map of percussion shows links between instruments in different locations. African concepts of barrel and waisted or goblet drums, shakers, scrapers, bells, and log xylophones traveled to the New World with African slaves and are commonly used in Latin-American music. The orchestral xylophone and marimba also descend from the traditional African instrument. Bells and gongs originated in the Far East and India, and traveled into Western Europe with return Christian missionaries. Western military drums like the snare drum and timpani, as well as frame drums, derive from Middle Eastern drums. The Turkish cymbal has also been widely used in western music, and is played in the orchestra, and in the drum kit. Percussion instruments have also been developed through local ingenuity – one good example being the Caribbean steel pans.