The instrument consists of a series of reeds, most often today made of iron, frequently of flattened iron wire, though one still sometimes sees those made of bamboo or similar material, for example, in Cameroon. The reeds are attached to a wooden board, often the upper surface of a box made either from slats of wood pegged together or by hollowing a thicker piece of wood. The reeds are bridged up by two rails and strongly tied down, normally by wire, between those rails so that they are under tension. The board or box is held between the hands, and the free ends of the reeds, held toward the player, are plucked by the two thumbs and sometimes also the forefingers.
The arrangement of the reeds differs from people to people, but a common pattern is with the longest and lowest pitched toward the middle of the row with progressively shorter reeds to each side. Some patterns, for example, the kalimba of Zimbabwe, have, as it were, an upper manual—a second series of shorter reeds above the lower, usually only to one side. Many of these instruments have buzzing or rattling elements added, either loose rings of iron around the reed between the ligature and the rail nearer the player, or fragments of seashell (now more often old bottle caps) or other rattles fixed to the board. The instruments of plain board, rather than those hollowed or on boxes, are often held inside a large half-gourd to provide added resonance, or are held against or have a smaller gourd attached for this purpose.
Such instruments are, with one exception, unique to Africa, though their use has been spreading recently to “our” culture, either with imports or with instruments made in Europe and America. The sole exception is in the Caribbean, where they are also used. Much larger instruments—called, for instance, marímbula in Cuba— have been made there by the descendants of slaves, often using segments of old wind-up gramophone springs fixed on a resonator box large enough for the player to sit on.
There is one type of instrument in our culture that is analogous with these: the musical box. Here, instead of separate reeds tied to a frame, there is a steel comb, each tooth a different length, that is placed so that the end of each tooth is within reach of pins fixed in a revolving metal cylinder or barrel. The barrel is turned by a clockwork motor, and the pins are set so that each tooth or reed is plucked at the moment required by the tune set on the barrel.
The reason that the term reed is used throughout this section is that, as Hugh Tracey pointed out, the tongues or lamellae (as they are often called) behave acoustically in exactly the same way as the free reeds of mouth organs, concertinas, reed organs, and similar instruments. The tongues or “feathers” of trumps (or Jew’s harps) behave similarly. All are tuned in the same way, by length and mass, and all can be fine-tuned by adding additional mass to the free end of the reed.