Bach 3C vs Kelly 5C
The Kelly 5C has a wider cup diameter, the Kelly 5C features a deeper cup, the Kelly 5C has a larger throat opening.
Cup Diameter
The Kelly 5C has a cup diameter of 16.76 mm / 0.6598 in compared to 16.30 mm / 0.6417 in on the Bach 3C — a difference of 0.46 mm / 0.0181 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 5C has a very deep cup while the Bach 3C has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Kelly 5C has a wider throat (3.80 mm / 0.1496 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 3C is described as unspecified, and the Kelly 5C 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.