When looking for a mouthpiece, there are many variables that you will need to consider. This can often get confusing! The dimensions and shape of a mouthpiece have a direct impact on its feel, playability and sound. We hope to give you a brief overview of the various parts and Jargon used when talking about mouthpieces and their effects on the mouthpiece characteristics.
Cup diameter (Internal Rim)
In general, a small cup diameter makes it easier to play high notes and can increase endurance, however volume is limited. A larger cup diameter on the other hand provides plenty of volume and easy low tones, but endurance may be sacrificed.
Since this is the part of the mouthpiece that comes into contact with the lips, it is a critical parameter for playing comfort. Rim contour also has a large effect on attack and clarity. The majority of players prefer a relatively flat contour with the peak closer to the inner edge.
A thick rim provides greater lip contact area for easier high notes and extended endurance, but lip movement is limited, reducing tonal flexibility. A thin rim offers plenty of control over a wide range but can quickly cause fatigue. Most players opt for a medium thick rim.
The bite of the rim (the sharpness of the inner rim edge) has a large influence on attack, clarity and pitch control. Sharp bites generally make it easier to produce accurate, stable pitch and a rich tone, however too sharp lip control can become limited, compromise comfort and reduce endurance. A soft bite on the other hand will be comfortable to play at the expense of a clean attack.
Shallow cups produce a brighter tone and are easier to control in the higher register, at the expense of volume. Deep cups offer a dark tone, easy low notes and plenty of power.
Cup shapes range from ‘U’ to ‘V’ shapes. The more ‘U’ shaped a cup is, the brighter the sound and the easier it is to play in the high register. As the cup approaches the ‘V’ shape, the sound becomes darker and the lower register easier to play.
The throat is the narrowest portion of the mouthpiece bore, and therefore the point of highest sound pressure. The diameter and length of this part of the mouthpiece has a major influence on playing resistance, which contributes to fast response, brilliant tone and enhanced playability in the high register. A wide, short throat is more playable in the low register and is capable of producing great volume – but requires a lot of air and can cause fatigue.
The backbore is the inner section of the mouthpiece that follows the throat. It has a complex flare that can significantly affect high-register pitch. The diameter of the backbore also influences tibre and resistance. A narrow backbore results in increased resistance, brighter tone and easier playing in the higher register. A larger backbore decreases resistance for darker tone and easier playing in the lower range.
The shank is the outside dimensions of the mouthpiece receiver and is of prime importance in determining if a mouthpiece fits into your instrument. In particular small bore trombones and baritones require a small shank mouthpiece, whereas large bore trombones and euphoniums require a large shank mouthpiece.
For further research and consideration, it's well worth reading Vincent Bach's Mouthpiece Guide, which I've attached to this post.