Bach 1B vs Kelly 3C
The Kelly 3C has a wider cup diameter, the Kelly 3C features a deeper cup, the Kelly 3C has a larger throat opening.
Cup Diameter
The Kelly 3C has a cup diameter of 17.02 mm / 0.6701 in compared to 17.00 mm / 0.6693 in on the Bach 1B — a difference of 0.02 mm / 0.0008 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 3C has a very deep cup while the Bach 1B has a deep cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Kelly 3C has a wider throat (4.06 mm / 0.1598 in vs 3.66 mm / 0.1441 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Bach 1B is described as unspecified, and the Kelly 3C as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.