A kempul is a type of hanging gong used in Indonesian gamelan music. It is a set of tuned, hanging gongs with knobs, often made of bronze, wood, and cords. The kempul has a flat surface with a knob in the center and is struck with the soft part of a mallet. The mallet has a round head covered with thick padding attached to a short wooden handle. The size of a kempul ranges from 19 to 25.4 cm (7.5 to 10.0 in) in diameter. The number of kempul gongs in a gamelan ensemble can vary. Although there may be two to ten kempul on one rack, it is common to have five kempul hanging on the same rack as the Gong ageng and gong siyem (two larger gongs).

Kempul in music

Gamelan orchestra instruments are usually grouped into three main categories:

• Instruments that help show the structure of the music;
• Instruments that help control the timing of the music;
• Instruments that play melodies, both simple and complex.

Instruments in the first group include large and medium hanging gongs (Gong ageng and gong suwukan), small hanging gongs (kempul), large standing gongs (kenong), and a pair of small standing gongs (kethuk-kempyang). The kempul helps separate the nongans, which are the parts of the music between strikes of the kenong.

In the center of the gamelan, a basic melody called the balungan is played on bronze metallophones. The balungan is supported by larger gongs (gong and kempul) and horizontally-mounted gongs (kenong, kethuk, and kempyang) at the back of the gamelan. The kempul, a middle voice gong, marks halfway points in the metric cycle, which is played by the kenong (the kettle gongs). In all central Javanese traditions, pieces like Ayak-ayakan, Srepegan, and Sampak share a common relationship between kempul and kenong: one kempul beat occurs every second kenong beat.

Tuning

A gamelan orchestra has two sets of gongs because there are two musical scales, called laras. These scales are named slendro and pelog, which means the full gamelan ensemble is made up of two separate sets. The slendro set is usually placed in the front, and the pelog set is placed on the side. The two sets are never played at the same time. The slendro scale has five notes in each octave, with intervals that include both small and medium steps. The pelog scale has seven pitches in each octave.

In older ensembles from East Java, there is typically one kempul, tuned to pitch 6 or pitch 5, and one Gong ageng, with no siyem or gong suwukan. However, in Central Java, ensembles have grown larger over the past century. As a result, many East Javanese ensembles now include one or two siyem and three or four kempul for each tuning system.