Mouthpiece (woodwind)

The mouthpiece of a woodwind instrument is that part of the instrument which is placed partly in the player's mouth. Single-reed instruments, capped double-reed instruments, and fipple flutes have mouthpieces while exposed double-reed instruments (apart from those using pirouettes) and open flutes do not.

On single-reed instruments, such as the clarinet and saxophone, the mouthpiece is that part of the instrument to which the reed is attached. Its function is to provide an opening through which air enters the instrument and one end of an air chamber to be set into vibration by the interaction between the air stream and the reed.

Single-reed instrument mouthpieces are basically wedge shaped, with the reed placed against the surface closest to the player's lower lip (the table). The player's breath causes the reed to vibrate, which in turn causes the column of air inside the instrument to vibrate. The top half to three-quarters of the table is open to the inside of the mouthpiece.

As with the brass instruments, the shape of the interior of the mouthpiece can greatly affect the sound of the instrument. Mouthpieces with a large, rounded chamber will produce a quite different sound from one with a small or square chamber.

The distance between the tip of the mouthpiece and the tip of the reed is known as the tip opening. The tip opening has little effect on tone, which is more affected by the design of the mouthpiece's chamber (interior space).

The facing (or lay) is a curved section that leaves the flat table and continues to the tip of the mouthpiece. The length of a facing — defined as the distance from the tip of the mouthpiece to the point where the reed and mouthpiece meet — can vary. Different facing lengths have different response properties.

...
Wikipedia