A slit drum is a hollow percussion instrument. In spite of the name, it is not a true drum but an idiophone, usually carved or constructed from bamboo or wood into a box with one or more slits in the top. Most slit drums have one slit, though two and three slits (cut into the shape of an "H") occur. If the resultant tongues are different width or thicknesses, the drum will produce two different pitches. It is used throughout Africa, Southeast Asia, and Oceania. In Africa such drums, strategically situated for optimal acoustic transmission (e.g., along a river or valley), have been used for long-distance communication.The ends of a slit drum are closed so that the shell becomes the resonating chamber for the sound vibrations created when the tongues are struck, usually with a mallet. The resonating chamber increases the volume of the sound produced by the tongue and presents the sound through an open port. If the resonating chamber is the correct size for the pitch being produced by the tongue, which means it has the correct volume of airspace to complete one full sound wave for that particular pitch, the instrument will be more efficient and louder.
Here is one purchased for $9 at an antique store.