Typical ranges of the orchestral xylophone, marimba, and glockenspiel.
Keyboard percussion instruments include the western xylophone, marimba, vibraphone, glockenspiel, and tubular bells, the log xylophones and marimbas of Africa and Central America, and the barred instruments used in the Indonesian gamelan. They are played either with percussion mallets or hands, and, in the case of the western forms, play chromatic notes arranged in a similar pattern to that of a piano keyboard.
Keyboard instruments such as the celesta and keyboard glockenspiel are not considered keyboard percussion instructions, because of the very different skills needed to play them. These instruments are percussion instruments in most senses but are considered part of the keyboard section rather than the percussion section of an orchestra. Keyboard percussion instruments don't have keyboards as such, but instead follow the arrangement of the keyboard.
The orchestral xylophone, marimba, and glockenspiel have thin wooden or metal rectangular bars laid out like a chromatic piano keyboard. The back row of bars – the sharps and flats – are raised above those in front. The bars of the xylophone and marimba are suspended on string held between pegs. Glockenspiel bars are held in place with rubber pins. Keyboard percussion instruments are played with beaters with cane or plastic shafts and small oval or round heads made of plastic, rubber, wood, or brass, Marimba beaters are commonly overwound with yarn.
The bars of a keyboard percussion instrument are rectangular with a curved underside to ensure that the bar will tune to a true pitch. Tuning the bars is achieved using longer, thinner bars for lower notes, and shorter, thicker bars for higher notes. Fine-tuning is achieved by removing material from the center underside of the bar to flatten the pitch and filling the underside of the ends of the bars to sharpen the pitch. Any damage to the bar will result in a loss of true pitch and an impaired sonority.
To achieve a resonant sound, the bar is struck either at the very end or in the middle – the points of maximum vibration (antinodes) of the sound waves produced by the bar. Holes are drilled for supports for the bar at the nodal points, where the bar does not resonate.
Orchestral xylophones, marimbas, and some glockenspiels have vertical tube resonators with a stopped lower end, which are placed under each bar. Each resonator is tuned to the same fundamental frequency as the bar, and amplifies the sound. However, the combined vibrations of the bar and and the air column in the resonator cause a loud initial attack and a rapid decay. This gives the xylophone and marimba a relatively short sound. The resonators increase in size as the pitch of the bar lowers. On a 4½-octave marimba they range in size from 6.25 centimeters (2.5 inches) for c''' to 71 centimeters (28.5 inches) for A. Concert xylophones and marimbas may have a set of dummy resonators on the side of the instrument that faces the audience. These are usually arranged in an arc, with long resonators at the top and bottom of the instrument. These are still tuned in the normal way, but the resonators at the top end are extended below the stopped end.
Keyboard percussion instruments are played with a matched grip and the player must develop good memory in order to move around the keyboard fluently. There is a considerable distance between the notes, especially at the lower end of the instrument, and the performers must make sure that they hit the correct part of the bar. This is particularly true in fast passages.
Performers often practice playing a single-stroke roll smoothly and evenly – they need to make an instrument that naturally has a short decay sound smooth and seamless when playing legato passages. The marimba and vibraphone can also be played with four beater – two in each hand – to play chords with up to four notes. These can also be rolled as a single-stroke roll, or played as a tremolo with the hands rocking the pair of sticks in each hand to create a shimmering effect. A roll can also be played on a single bar with one hand, by holding the pair of sticks above and below the bar and moving the beaters up and down.