Traditional Central American marimbas differ from orchestral ones by the use of a 'charleo' or buzzing effect. Tuners place a small hole in the bottom of each wooden resonator and cover it with a thin membrane (historically pig intestine, now wax paper). When the bar is struck, the air in the resonator causes the membrane to vibrate, creating a distinctive buzzing sound. This is considered an essential part of the instrument’s voice, adding a layer of rhythmic complexity to the melody.