Bach 14½D vs Kelly 5G-EU
The Kelly 5G-EU has a wider cup diameter, the Kelly 5G-EU features a deeper cup.
Cup Diameter
The Kelly 5G-EU has a cup diameter of 25.40 mm / 1.0000 in compared to 24.50 mm / 0.9646 in on the Bach 14½D — a difference of 0.90 mm / 0.0354 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 5G-EU has a — cup while the Bach 14½D has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Material
The Bach 14½D is described as unspecified, and the Kelly 5G-EU 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.