Source: http://en.wikipedia.org/wiki/File:Lenke_djembe_from_Mali.jpeg
Perhaps in the earliest times humans beat on calabashes or other hollow objects. At some time in the ancient past, skin was stretched over some hollow object, and the drum was born.
The drum vellum is a membrane stretched over a vessel, which functions like a pipe. When the membrane is struck, it moves the air column within the pipe, which acts as resonator increasing the volume. The larger the diameter of the pipe, the lower the resulting frequency. Pitch can be varied by the degree of tension of the membrane, and also slightly by varying the point of impact. Closer to the center the frequency is lower, while towards the rim the harmonics are higher.
Source: http://en.wikipedia.org/wiki/File:Lenke_djembe_from_Mali.jpeg
Source: http://www.wikipedia.org/wiki/Drum.htm
Source: http://www.wikipedia.org/wiki/Drum.htm
http://www.youtube.com/watch?v=2mQ1JOOs6LE
http://www.beginband.com/sndclips.shtml