Kelly 31 vs Yamaha HR-35C4
The Yamaha HR-35C4 has a wider cup diameter, the Kelly 31 features a deeper cup, the Yamaha HR-35C4 has a larger throat opening.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Kelly 31
• French Horn
GeneralCup diameter17.53 mm / 0.6902 in
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
French horn deep cup
vs
Mouthpiece B
Yamaha HR-35C4
• French Horn
Cup diameter18.08 mm / 0.7118 in
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Yamaha HR-35C4 has a cup diameter of 18.08 mm / 0.7118 in compared to 17.53 mm / 0.6902 in on the Kelly 31 — a difference of 0.55 mm / 0.0217 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.