Based on the instruments, the northern ensembles are relatively similar. Both include a pair of gendang barrel-shaped drums of two sizes, the larger of the pair is referred as the 'mother' drum ("pengibu" or just "ibu") and the smaller one as the 'child' ("penganak" or "anak"). Included in the ensemble is a hanging knobbed gong that may vary in size, shape and material construction. The gendang play loud rhythms in interlocking style, accenting specific beats. On every other beat, the knobbed gong is struck with a padded beater. Melodies are played using a reef aerophone called "serunai". It is generally blown using a circular or continuous breathing technique, and provides a lively melodic line in eighth- and sixteenth- note movement throughout the silat performance. The music is polyphonic and features a melodic line, percussive rhythmic patterns and a periodic gong unit played on the single gong. It begins in a slow tempo and accelerates until the performance climaxes.