Bach 1B vs Kelly 7C
The Bach 1B has a wider cup diameter, the Bach 1B features a deeper cup.
Cup Diameter
The Bach 1B has a cup diameter of 17.00 mm / 0.6693 in compared to 16.51 mm / 0.6500 in on the Kelly 7C — a difference of 0.49 mm / 0.0193 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Bach 1B has a deep cup while the Kelly 7C has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 3.66 mm / 0.1441 in, so resistance feel will be comparable.
Material
The Bach 1B is described as unspecified, and the Kelly 7C 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.