Bach 14½D vs Kelly 51D-EU
The Kelly 51D-EU has a wider cup diameter, the Kelly 51D-EU features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 14½D
• Baritone / Euphonium
Cup diameter24.50 mm / 0.9646 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Kelly 51D-EU
• Baritone / Euphonium
ProfessionalCup diameter25.40 mm / 1.0000 in
Best suited for
Orchestral playing — large cup for full, dark tone
Professional euphonium
Cup Diameter
The Kelly 51D-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.
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.