Duo, a bronze percussion instrument of the Chinese Bronze Age, similar to a bell but slightly larger.

The cavity of the duo is generally short and wide, with a tile-shaped cross-section, narrow at the top and wide at the bottom, and the mouth is slightly concave. The overall shape is similar to that of bronze musical instruments such as bells, mussels, cymbals, sentences, and zheng, but the difference is that there is a tongue in the cavity. The wooden tongue is called Muduo, and the copper tongue is called Jinduo.

The top of the cavity has two forms: one has a stubby, hollow square bronze handle, which can be inserted with a wooden handle; the other has a long bronze handle. When in use, shake it with the handle, and the tongue hits the cavity to make a sound.
During the Warring States Period, there were mainly Waizu Duo and Ying Liduo. There is a small ring in the cavity for the tongue, and the mouth is very curved like a bell. Ying Suiduo is not attached to the tongue, and the curve of the mouth is shallow.