The ō-tsuzumi, or 'large tsuzumi' is the larger of the hand drums played in the nō ensemble. It has hourglass-shaped body carved from wood and usually painted with lacquer. Two horse hide skins are affixed to iron rings with larger circumferences than the ends of the drum body. Before each performance, the skins are dried over a brazier, then set at either end of the drum body, and lashed to each other with hemp ropes. The taught skins produce two sounds, softer and louder. The seated drummer rests the drum on the left thigh and strikes it with the open right hand so the palm hits the rim and the fingers strike the drum heads. Since this can be painful, the drummer generally wears a leather padding covering his right palm and sometimes uses papier-mâché pockets on one or two fingers. The result is a sharp clacking sound.
The ō-tsuzumi and ko-tsuzumi function as a pair, playing together to construct the rhythmic patterns. Broadly speaking, the ō-tsuzumi takes charge of the odd number beats that form the rhythmic framework and the first half of the musical phrase, while the ko-tsuzumi governs the even number beats and the last half of the phrase. While the ō-tsuzumi creates the foundation of the rhythm, the ko-tsuzumi plays ornamentation between the ō-tsuzumi beats using variations in timbre and rhythm.