The bore

A large-bore mouthpiece makes it possible to produce more volume and it raises the high and low registers. If the bore is too large, however, the notes begin to flutter and become thin. A smaller bore usually produces a purer and more concentrated, but weaker tone; it increases the resistance and shortens the entire register. The result is that high notes get too low and low notes get too high (especially C sharp and D). A mouthpiece with a cylindrical bore about 5 to 10 mm (2"-3.9") long is more likely to maintain the pitch and steadiness of the notes than one with only a taper.

The shank backbore

If the backbore is too small, then the high register is generally too low.

If the backbore is too large, then the mouthpiece does not have sufficient resistance (produce sufficient back-pressure) and this has a negative influence on endurance.

A more steeply tapered backbore makes it easier to produce high notes (typical of jazz trumpets), but smothers tone and volume. The WCS Schmidt Special Backbore, which widens toward the outside, increases volume and range.

Caution: Going too far results in coarse, fluttering notes whose pitch tends to become inaccurate.