Kelly 5G-EU vs Schilke 51D
The Schilke 51D has a wider cup diameter, the Kelly 5G-EU features a deeper cup.
Cup Diameter
The Schilke 51D has a cup diameter of 25.55 mm / 1.0059 in compared to 25.40 mm / 1.0000 in on the Kelly 5G-EU — a difference of 0.15 mm / 0.0059 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 Schilke 51D has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Material
The Kelly 5G-EU is described as Lexan polycarbonate, and the Schilke 51D as unspecified. 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.