Bach 1B vs Kelly 7C-UK
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-UK — 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-UK 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-UK 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.