All percussion instruments rely on the vibration of a whole instrument or some part of an instrument to produce sound. They are usually categorized by the specific methods used to produce that vibration. A further dividing line between different sorts of instruments separates those that produce a regular musical pitch and those that do not.
Percussion instruments come in a wide variety of shapes and forms. Drums, cymbals, bells, and chimes are among the most common sorts of percussion. All of these produce a noise when they are struck or agitated. Occasionally other very specialized instruments, such as certain types of whistles, might be classified as percussion instruments, but this is more a matter of convenience than good musical theory.
Some percussion instruments produce sound when the whole of the instrument vibrates. Bells and cymbals, for example, operate in such a fashion. This type of percussion instrument is generally made of a material that produces a specific and distinctive sound when struck, such as glass. These percussion instruments are known as idiophones. Instruments such as the xylophone, although they contain parts that do not vibrate, fall into this category because the whole of each bar on the instrument vibrates.
A second category of instruments produce sound as a result of the vibration of a stretched membrane. Drums typically fall into this category, and make up the majority of such instruments. This variety of instrument is known as a membranophone because of the central role played by a vibrating membrane.
In addition to categorization by the method of sound production, percussion instruments can also be divided into groups of tuned and untuned instruments. Tuned instruments produce notes with a specific pitch. The xylophone is a good example of this sort of instrument because the pitch produced by each bar of the instrument is distinct.
Percussion instruments, however, do not always produce sound at a specific pitch. Cymbals, for instance, produce sound waves on a number of frequencies, and cannot easily be classified as producing a single note. Other instruments can be tuned, in theory, but are rarely tuned in practice. The darbuka, a type of goblet drum, can be tuned to produce a specific note with a reasonable degree of accuracy, so long as it is struck consistently. This is not the normal method of playing this type of drum, however.
Cultures tend to build traditions around collections of musical instruments that work well together when producing a particular style of music. The western drum kit, with snare drums, bass drum and cymbals is one such combination. The Indonesian gamelan ensemble is another, very different, combination. These cultural ensembles provide another method of classifying percussion instruments.