Key design, material properties, and temperature factors in frequency variation of Sisaala <i>jengsi</i> (xylophone) keys

Dimensions, mass, volume, and density are used to describe the complex geometries and concomitant frequencies of keys on a pair of 17-keyed jengsi (from northwestern Ghana). Frequency variations, with keys in free and bound states, are analyzed at equilibrium under selected temperature and relative humidity conditions, and in a diurnal cycle simulated for the West African dry season. Frequency, length, nodal, and central thickness are accurately interrelated with the irregular geometries. It was discovered that key width/length, an important aesthetic factor, is nearly constant. Under climatic change, material properties of the wood are much more critical factors in frequency variation than key geometry. Jengsi keys (missanda wood) showed decreases of about 0.96 cents per 1.0°C increase in temperature in the range 10° to 38°C, with greater decrease at 44°C.