Bach 1B vs Kelly 5C
The Bach 1B has a wider cup diameter, the Kelly 5C features a deeper cup, the Kelly 5C has a larger throat opening.
Cup Diameter
The Bach 1B has a cup diameter of 17.00 mm / 0.6693 in compared to 16.76 mm / 0.6598 in on the Kelly 5C — a difference of 0.24 mm / 0.0094 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 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 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 1B 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.