The xylophone is a tuned idiophone, common throughout west and central Africa. In Nigeria, they are most common in the southern part of the country, and are of the central African model. Several people sometimes simultaneously play a single xylophone. The instruments are usually made of loose wood placed across banana logs. Pit- and box-resonated xylophones are also found. Ensembles of clay pots beaten with a soft pad are common; they are sometimes filled with water. Although normally tuned, untuned examples are sometimes used to produce a bass rhythm. Hollow logs are also used, split lengthways, with resonator holes at the end of the slit. They were traditionally used to communicate over great distances.