The bell of a wind instrument is the round, flared opening opposite the mouthpiece. It is found on clarinets, saxophones, oboes, horns, trumpets and many other kinds of instruments. On brass instruments, the acoustical coupling from the bore to the outside air occurs at the bell for all notes, and the shape of the bell optimizes this coupling. It also plays a major role in transforming the resonances of the instrument. On woodwinds, most notes vent at the uppermost open tone holes; only the lowest notes of each register vent fully or partly at the bell, and the bell's function in this case is to improve the consistency in tone between these notes and the others.
